CN109888201B

CN109888201B - Positive electrode active material, positive electrode containing the same, and lithium secondary battery

Info

Publication number: CN109888201B
Application number: CN201910004332.XA
Authority: CN
Inventors: 雷敏; 莱东圣; 郑小建; 杨新河; 周恒辉
Original assignee: Pulead Technology Industry Co ltd; Beijing Taifeng Xianxing New Energy Technology Co ltd
Current assignee: Pulead Technology Industry Co ltd; Beijing Taifeng Xianxing New Energy Technology Co ltd
Priority date: 2019-01-03
Filing date: 2019-01-03
Publication date: 2021-02-26
Anticipated expiration: 2039-01-03
Also published as: CN109888201A

Abstract

The present invention relates to a positive electrode active material, a positive electrode containing the positive electrode active material, and a lithium secondary battery. The positive active material is a carbon-deposited alkali metal oxyanion, and the preparation method comprises the following steps: (a) dry or wet milling a precursor of the alkali metal oxyanion, the milled precursor being dried to obtain a solid compound when wet milled; then heat-treating the ground precursor in a protective atmosphere to obtain a heat-treated material; (b) carrying out microbead nano-grinding on the material obtained in the step (a) in at least one alcohol-based system to obtain a nano-suspension; (c) drying the nanosuspension obtained in step (b) to obtain a solid compound; (d) placing the solid compound obtained in step (c) in at least one vapor phase carbon source vapor to obtain a carbon-deposited alkali metal oxyanion using a vapor phase carbon source deposition process. The present invention can be easily used to manufacture various grades of high performance and low cost positive electrode materials.

Description

Positive electrode active material, positive electrode containing the same, and lithium secondary battery

Technical Field

The invention relates to a carbon-deposited alkali metal oxyanion, to a multistep preparation process thereof, and to the use of said carbon-deposited alkali metal oxyanion as a positive electrode material for lithium secondary batteries.

Background

Olivine-type LiFePO₄Has excellent capacity retention rate, thermal stability, nontoxicity and safety, and becomes an important anode material of the lithium ion battery. But olivine type LiFePO₄There are significant drawbacks such as low intrinsic electronic and ionic conductivity. The electronic conductivity can be improved by carbon coating and the diffusion of lithium ions can be addressed by synthesizing small particles.

Under the specific condition of carbon deposition of lithium iron phosphate, C-LiFePO is abbreviated as₄Several processes for making such materials have been proposed, either by carbon precursors in LiFePO₄By thermal decomposition of lithium, iron, PO₄The source and the carbon precursor are simultaneously reacted. For example, EP1049182A3 and US2002/0195591A1 describe the synthesis of LiFePO by a solid-state thermal process₄The reaction formula is as follows:

Fe(III)PO₄+ Li-Source + carbon precursor → C-LiFe (II) PO₄

Wherein the carbon precursor is an organic substance which forms a carbon deposit by thermal decomposition while the produced gas effectively reduces fe (iii).

US2007/0054187A1 discloses a lithium metal phosphate LiMPO₄By a source of Li, at least one source of M (M may be Fe, Mn, Co, Ni) and at least one PO₄The source is obtained by hydrothermal reaction at the temperature of 100-250 ℃ and the pressure of 1-40 bar. The disclosed method comprises mixing LiMPO₄Mixing with a carbon precursor, drying and calcining the mixture to synthesize C-LiMPO₄。

This approach presents challenges in industrial implementation because it involves many simultaneous chemical, electrochemical, gas phase, gas-solid reactions, sintering reactions, and carbon deposition processes. Thus, the electrochemical properties of the alkali metal oxyanion cathode material with carbon deposition depend on many parameters, such as surface characteristics, wetting characteristics, surface area, porosity, particle size distribution, moisture content, crystal structure, conductivity of the carbon deposition, and the chemical nature of the raw materials, reaction feed rate, gas flow rate, and the like. All these properties are difficult to control in a very precise manner during the reaction, which can lead to non-stoichiometric products, incomplete reactions or residual impurities in the product.

Therefore, the problem remains to find a simple, optimized process to produce higher quality positive electrode materials for battery applications.

Disclosure of Invention

The object of the present invention is to provide a novel method for producing a carbon-deposited alkali metal oxyanion positive electrode material, which performs similarly, even if not better than the electrochemical performance exhibited by the materials obtained by the prior art, when the carbon-deposited alkali metal oxyanion obtained by the present invention is used as an active electrode material for a lithium secondary battery. It is also an object of the present invention to provide a general method for producing carbon-deposited alkali metal oxyanions, which includes only a few steps and can be easily used to produce various grades of high performance and low cost positive electrode materials. Moreover, the process allows for effective control and optimization of the precursors, impurities detrimental to cell operation, particle morphology, and quality of carbon deposition at each step.

The object of the present invention is achieved by a process for the preparation of carbon-deposited alkali metal oxyanions by a multi-step process. Under the specific condition of carbon deposition of lithium iron phosphate, C-LiFePO is abbreviated as₄The process preferably comprises the following steps:

(a) a starting material compound comprising at least one lithium source, at least one ferric orthophosphate source, and at least one organic carbon source is mixed, preferably milled, and the starting material is heated to provide a carbon-deposited lithium iron phosphate, preferably comprising a ferrous phosphate or pyrophosphate phase.

(b) Nano-ball milling the material obtained in step (a) in at least one alcohol group;

(c) drying the nanomilled suspension obtained in step (b) to obtain a solid compound;

(d) heating the solid compound obtained in step (c) in the presence of a gaseous organic carbon source to obtain carbon-deposited lithium iron phosphate.

The invention also provides a method for carbon deposition of alkali metal oxyanions by a chemical vapor deposition process in the presence of a vapor phase organic carbon source. According to the invention, the deposited carbon content is less than 2.5 wt.%, preferably less than 2.0 wt.%, more preferably less than 1.6 wt.%, even more preferably less than 1.2 wt.%.

The present invention also provides a carbon-deposited alkali metal oxyanion obtained by the process of the present invention, having a deposited carbon content of less than 2.5 wt% and a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, still more preferably less than 20 ppm.

The present invention also provides a graphene-like carbon-deposited alkali metal oxyanion obtained by the process of the present invention, which has 1 to 8 graphene-like carbon layers.

The present invention also provides a graphene-like carbon deposit alkali metal oxyanion obtained by the process of the invention, which has from 1 to 8 graphene-like carbon layers with a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, even more preferably less than 20 ppm.

The present invention also provides a carbon-deposited alkali metal oxyanion obtained by the process of the present invention, which has a deposited carbon content of less than 2.5 wt%, and an average primary particle size of the alkali metal oxyanion of less than 500nm, in preferred embodiments less than 250nm, and in more preferred embodiments less than 150 nm. In another preferred embodiment, the primary particles have an average particle size of between 25 and 250nm, preferably between 50 and 150nm, more preferably between 70 and 130 nm.

The invention also provides a carbon deposition alkali metal oxyanion obtained by the process, wherein the carbon deposition content of the carbon deposition alkali metal oxyanion is less than 2.5 wt%, and the carbon deposition alkali metal oxyanion is aggregated into secondary spherical aggregates by primary particles with the average particle size of 50-250 nm, and the BET value of the secondary spherical aggregates is 3-11 m²/gPreferably 3 to 9m²A ratio of 3 to 7 m/g²A more preferable range is 3 to 5 m/g²(ii) in terms of/g. In another preferred embodiment, the BET value is ≦ 11m²A/g, preferably ≤ 9m²A/g, more preferably 7m or less²A ratio of 5m or less per gram²/g。

The present invention also provides a carbon-deposited alkali metal oxyanion obtained by the process of the present invention, having a deposited carbon content of less than 2.5 wt% and a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, still more preferably less than 20 ppm. And the carbon-deposited alkali metal oxyanion is agglomerated into secondary spherical agglomerates by primary particles with an average particle size of 50-250 nm, and the BET value of the secondary spherical agglomerates is 3-11 m²Between/g, preferably 3 to 9m²A ratio of 3 to 7 m/g²A more preferable range is 3 to 5 m/g²(ii) in terms of/g. In another preferred embodiment, the BET value is ≦ 11m²A/g, preferably ≤ 9m²A/g, more preferably 7m or less²A ratio of 5m or less per gram²/g。

The present invention also provides a graphene-like carbon deposit alkali metal oxyanion obtained by the process of the invention, which has from 1 to 8 graphene-like carbon layers with a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, even more preferably less than 20 ppm. And the carbon-deposited alkali metal oxyanion is agglomerated into secondary spherical agglomerates by primary particles with an average particle size of 50-250 nm, and the BET value of the secondary spherical agglomerates is 3-11 m²Between/g, preferably 3 to 9m²A ratio of 3 to 7 m/g²A more preferable range is 3 to 5 m/g²(ii) in terms of/g. In another preferred embodiment, the BET value is ≦ 11m²A/g, preferably ≤ 9m²A/g, more preferably 7m or less²A ratio of 5m or less per gram²/g。

The invention also provides the use of the carbon-deposited alkali metal oxyanion prepared by the process of the invention for preparing a positive electrode for a lithium secondary battery.

The invention also provides the use of a carbon-deposited alkali metal oxyanion, prepared by the process of the invention, having a deposited carbon content of less than 2.5 wt%, a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, still more preferably less than 20ppm, for the preparation of a lithium secondary battery positive electrode having excellent high temperature electrochemical performance.

The invention also provides the use of the graphene-like carbon-deposited alkali metal oxyanion prepared by the process of the invention, which has 1-8 layers of graphene-like deposited carbon and has a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, even more preferably less than 20ppm, for preparing a lithium secondary battery positive electrode having excellent high-temperature electrochemical properties.

The present invention also provides a lithium secondary battery composed of a negative electrode, a positive electrode and an electrolyte, wherein the positive electrode is a carbon-deposited alkali metal oxyanion produced by the process of the present invention.

These and other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.

Drawings

FIG. 1 is a graph of cycle performance of C-LiFePO prepared according to comparative examples 1 and 2 with carbon as the negative electrode₄Two liquid electrolyte cells as positive electrodes were subjected to static cycle testing at 60 ℃ under a C/4 current. The Y-axis represents the battery capacity (mAh/g), the X-axis represents the number of cycles, and the initial capacity is determined using a C/5 current test at 25 ℃ for a lithium metal battery. The cell 1 is composed of C-LiFePO synthesized by the ball milling nano-step in water₄Preparation (curve B), cell 2 was made of C-LiFePO synthesized by a ball milling nanocrystallization step in isopropanol₄Preparation (curve a).

FIG. 2 is a graph of the cycling performance of C-LiFePO prepared according to example 1 with metallic lithium as the negative electrode₄Two liquid electrolyte cells as positive electrodes were subjected to static cycle testing at 60 ℃ under a C/4 current. The Y-axis represents the battery capacity (mAh/g), the X-axis represents the number of cycles, and the initial capacity is determined using a C/5 current test at 25 ℃ for a lithium metal battery. Battery with a battery cell3C-LiFePO synthesized by a ball-milling nanocrystallization step in water₄Preparation (curve B), cell 4 was made of C-LiFePO synthesized by a ball-milling nanocrystallization step in isopropanol₄Preparation (curve a).

Fig. 3 is an SEM image of primary particles after ball milling and nanocrystallization using isopropanol as a carrier liquid prepared in example 2.

Fig. 4 is an SEM image of carbon deposit secondary agglomerates composed of primary particles prepared in example 2.

FIG. 5 is a C-LiFePO obtained by the vapor phase carbon source thermal CVD process in example 2₄TEM of the carbon deposition layer.

FIG. 6 is a graph of cycle performance with carbon as the negative electrode, C-LiFePO₄The 5-piece liquid electrolyte cell as the positive electrode was subjected to static cycle test at 60 ℃ under a current of 1C. The Y-axis is the cell capacity (mAh/g), the X-axis is the number of cycles, and the initial capacity is determined by testing at 25 ℃ under C/5 current. According to example 2, the cell 5b is made of C-LiFePO with a sulphur content of 745ppm₄Preparation (curve E), cell 6b from C-LiFePO with a sulfur content of 339ppm₄Preparation (curve D), cell 7b from C-LiFePO with a sulfur content of 71ppm₄Preparation (curve C), cell 8b from C-LiFePO with a sulfur content of 34ppm₄Preparation (curve B) of the cell 9B from C-LiFePO with a sulfur content of 13ppm₄Preparation (curve a).

FIG. 7 is a positive electrode capacity diagram with carbon as the negative electrode, C-LiFePO₄The liquid electrolyte cell as the positive electrode was tested at 25 ℃ C/5 discharge rate. The Y-axis is the cell voltage (relative to Li)⁺Per Li), the X-axis is the capacity (mAh/g). The cell 10 was made of C-LiFePO obtained in example 3₄Sample D1.

Fig. 8 is a graph of cycle performance for 3 liquid electrolyte cells with carbon as the negative electrode, or LCO mixed with C-LiFePO4 as the positive electrode material, or pure LCO as the positive electrode material, tested in static cycle at 60℃ and 1C discharge rate. The Y-axis is the battery capacity (mAh/g) and the X-axis is the number of cycles. The initial capacity is determined by testing at 25 ℃ under C/5 current. According to the method of example 4, curve A is the cycling performance of a pure LCO anode and curve B is C-LiFePO₄(sulfur content 33ppm) and LCO as the cycle performance of the cathode materialC is C-LiFePO₄(the sulfur content is 386ppm) and LCO are mixed to be used as the cycle performance of the anode material.

Figure 9 is a test of 3 block liquid electrolyte cells with mixed pulse power performance (HPPC), carbon as the negative electrode, or a mixture of NMC532 and C-LiFePO4, or pure NMC532 as the positive electrode material, at 10s 3C pulse charge rate at 25 ℃. The Y-axis is the cell voltage (relative to Li)⁺Li), the X-axis is the area resistivity (Ω. cm)²). According to the method of example 4, curve A is C-LiFePO₄(sulfur content 38ppm) and NMC532 as input data of the mixed electrode of the positive electrode material, curve C is the HPPC input data of the same mixed electrode after static circulation at 60 ℃ and 1C for 200 weeks, and curve D is C-LiFePO₄(Sulfur content 251ppm) and NMC532 as the anode material HPPC input data after 1C static cycling for 200 weeks at 60 ℃.

Detailed Description

Despite low energy density of oxide positive electrode materials such as NMC, NCA, etc., the demand for advanced batteries with excellent safety performance, high tolerance to electrochemical abuse, unique efficiency over a wide operating temperature range, extremely long cycle life, low life cycle cost (price/kWh/cycle number), extremely high power/energy ratio, outstanding high temperature performance, without the use of a critical raw material cobalt, means carbon deposition LiFePO₄Will be a key, low cost electrode material in the future, with a rapidly growing market of applications such as direct replacement of lead acid batteries, micro-hybrid 48V automotive batteries, large scale energy storage, electric buses, electric trucks, autonomous cars, forklifts, hybrid and pure electric trains, or hybrid and pure electric marine battery systems (ferries equipped with large marine megawatt batteries).

The inventors have discovered that synthesis of carbon-deposited alkali metal oxyanions, such as C-LiPOPO, by a multi-step process of precursor sintering, alcohol-based nanomilling, and chemical vapor carbon deposition₄In order to ensure excellent performance under the most severe conditions (high temperature cycling and storage), it is highly desirable to control impurities and side reactions to unexpectedly low levels at each step.

In a non-limiting senseIn the illustrative embodiment, the alkali metal oxyanion is one corresponding to the general nominal formula A_aM_m(XO₄)_xThe compound of (1), wherein: a represents Li alone or partially substituted by Na and/or K atoms by up to 20%; m comprises at least 95 atomic% Fe (II) or Mn (II) or mixtures thereof; XO₄Represents singly or partially selected from SO₄And SiO₄At least one group of (a) is substituted for up to 30% of PO₄(ii) a a. m, x are such that: 0 < a.ltoreq.8, 1. ltoreq. m.ltoreq.3, 0 < x.ltoreq.3, and wherein M, X, a, M and X are selected so as to maintain the electroneutrality of the compound.

In another non-limiting embodiment, the alkali metal oxyanion is one that corresponds to the general nominal formula A_aM_m(XO₄)_xThe compound of (1), wherein: a represents Li alone or partially substituted by Na and/or K atoms by up to 20%; m is selected from the group consisting of Fe (II), Mn (II), or mixtures thereof, alone or partially substituted with up to 5 atomic percent of one or more metals selected from the group consisting of Ni, or Co, or equivalent or dissimilar valence combinations of metals selected from the group consisting of Mg, Mo, Nb, Ti, Al, Ta, Ge, La, In, Y, Yb, Cu, Sm, Sn, Pb, Ag, V, Ce, Hf, Cr, Zr, Bi, Zn, Ca, Cd, Ru, Ga, Sr, Ba, B, W. XO₄Represents singly or partially selected from SO₄And SiO₄At least one group of (a) is substituted for up to 30% of PO₄(ii) a a. m, x are such that: 0 < a.ltoreq.8, 1. ltoreq. m.ltoreq.3, 0 < x.ltoreq.3, and wherein M, X, a, M and X are selected so as to maintain the electroneutrality of the compound.

In another non-limiting embodiment, the alkali metal oxyanion is a compound having an olivine structure, corresponding to the general nominal formula LiMPO₄Wherein M comprises at least 95 atomic%, preferably at least 97 atomic%, more preferably at least 99 atomic% of Fe (II) or Mn (II), or mixtures thereof. One or more other metals selected from Ni, or Co, or from the group consisting of equivalent or aliovalent Mg, Mo, Nb, Ti, Al, Ta, Ge, La, In, Y, Yb, Cu, Sm, Sn, Pb, Ag, V, Ce, Hf, Cr, Zr, Bi, Z, may be selected for metal balancen, Ca, Cd, Ru, Ga, Sr, Ba, B, W metal.

In another non-limiting embodiment, the alkali metal oxyanion is a compound having an olivine structure, corresponding to the general nominal formula LiMPO₄Wherein M comprises at least 65 atomic% Mn (II) and at least 25 atomic% Fe (II), alone or partially substituted by up to 5% of one or more other atoms selected from Ni, or Co, or from combinations of equivalent or aliovalent metals of Mg, Mo, Nb, Ti, Al, Ta, Ge, La, In, Y, Yb, Cu, Sm, Sn, Pb, Ag, V, Ce, Hf, Cr, Zr, Bi, Zn, Ca, Cd, Ru, Ga, Sr, Ba, B, W.

In another non-limiting embodiment, the alkali metal oxyanion is a compound having an olivine structure, corresponding to the general nominal formula LiMPO₄Wherein M comprises at least 97% atomic, preferably at least 98% atomic, more preferably at least 99% atomic Fe (II), one or more other metals may be selected to be In metal balance, selected from Ni, or Co, or from combinations of equivalent or aliovalent Mg, Mo, Nb, Ti, Al, Ta, Ge, La, In, Y, Yb, Cu, Sm, Sn, Pb, Ag, V, Ce, Hf, Cr, Zr, Bi, Zn, Ca, Cd, Ru, Ga, Sr, Ba, B, W metals.

In another non-limiting embodiment, the alkali metal oxyanion is a compound having an olivine structure, corresponding to the general nominal formula LiFePO₄。

The "general nominal formula" indicates that the stoichiometry of the materials of the present invention can vary by a few percent from the stoichiometry due to the presence of substitutional or other defects in the structure, including inversion structural defects, such as, but not limited to, LiFePO₄The disorder of cations between iron and lithium sites in the crystal structure is described in Maier et al [ Defect Chemistry of LiFePO ]₄,Journal of the Electrochemical Society,155,4,A339-A344,2008]And Nazar et al [ Proof of Supervalent dosing in Olivine LiFePO₄,Chemistry of Materials,2008,20(20),6313-6315]Examples in the paper.

a) Sintering step of precursor

Preferably, the synthetic olivine-structured alkali metal oxyanion is LiMPO₄Wherein M comprises at least 95 atomic%, preferably at least 97 atomic%, more preferably at least 99 atomic% of Fe (II) or Mn (II), or mixtures thereof. One or more other metals may be selected to perform a metal balance (hereinafter "added metal") selected from Ni, or Co, or from a combination of equivalent or aliovalent metals of Mg, Mo, Nb, Ti, Al, Ta, Ge, La, In, Y, Yb, Cu, Sm, Sn, Pb, Ag, V, Ce, Hf, Cr, Zr, Bi, Zn, Ca, Cd, Ru, Ga, Sr, Ba, B, W.

For the synthesis of LiMPO₄Comprises at least one lithium source, at least one metallic iron source and/or metallic manganese source, optionally at least one additional metal source, at least one phosphorus source and at least one organic carbon source. These starting materials are subjected to at least one mixing, preferably dry or wet grinding step. The source may be in the form of a compound having more than one source element.

Wet grinding is carried out in the presence of a carrier fluid. Such as water or organic solvents and mixtures thereof. Preferably the carrier fluid is selected from water or alcohols and mixtures thereof.

In one non-limiting embodiment, the water is preferably demineralized water, and the degassing of the fluid carrier can be carried out prior to the wet milling step by any method known to those of ordinary skill in the art.

During the development of the present process, the inventors realized that some detrimental side reactions are induced when using water as carrier liquid, depending on the different precursors. For example, with Li₂CO₃And FePO₄Synthesis of LiFePO₄In time, grinding in water may produce some undesirable iron-containing impurities, such as, but not limited to, Fe (OH)₃FeO (OH), or Fe (OH)₂Potentially negatively affecting the electrochemical performance of the carbon-deposited cathode material of the present invention. Also, when dry milling is performed without a carrier fluid, the milling efficiency in some embodiments may be relatively low, particularly at large scale milling. Moreover, in some instancesDry milling in the example may lead to local overheating of the precursor, forming potentially undesirable impurities. Conversely, wet grinding the carrier fluid therein can help remove heat.

This is why in a preferred embodiment the grinding is wet grinding in the presence of an alcohol carrier liquid. The alcohol is preferably selected from aliphatic alcohols having 1 to 10 carbon atoms, such as methanol, ethanol, propanol, such as n-propanol or isopropanol, butanol, such as n-butanol or isobutanol, and mixtures thereof.

Any known dry or wet milling technique may be used, such as, but not limited to, ball or bead milling, planetary ball milling, colloid milling, vibratory milling, agitator milling, rotor-stator milling, shaker ball milling, disc milling, sand milling, pebble milling, jar milling, ultrasonic and ultrasonic assisted grinding, submerged basket milling, basket sand milling, high kinetic rotor ball milling, agitated bead milling, agitated milling, and equivalent milling equipment. The dry or wet milling is preferably ball or bead milling, more preferably high energy ball or bead milling.

Available industrial equipment may be used to perform at least one dry and/or wet high energy ball or bead milling step. Suitable high energy milling equipment may be from Union Process (Akron, 44313, Ohio), Zoz GmbH (Viden, Germany), Navy-Feinmahltechnik GmbH (Seulb, Germany), Retsch GmbH (Haen, Germany), Fritsch GmbH (Italy Obertain, Germany), Buhler AG (Utzville, Switzerland), SPEX SamplePrep (N.J. Mettachi, 08840), Shandong Longxing chemical industry mechanical group, Inc. (Shandong tobacco bench), among other possible suppliers. Examples of such suitable high energy milling equipment include, but are not limited to, 7.6L process volumes

1-S, 200L processing capacity

SD-30, 300L processing volume

SD-50(Union Process), Simoloyer CM08(Zoz), MasterMill 30 ball mill with submerged basket ball mill (resistant to speed), Centex^TMT3 Agitator Mill (Buhler), LMJ-37 basket Mill (Shandong Longxing), SPEX8000D Mixer/Mill (SPEX samplePrep). Those skilled in the art will be able to select suitable equipment for wet grinding and/or dry grinding without departing from the spirit of the present invention.

In one non-limiting embodiment, the duration of the milling step of the present invention is between 5 minutes and 4 hours, preferably between 10 minutes and 2 hours, more preferably between 15 minutes and 1 hour. In another non-limiting embodiment, the milling step is performed for less than 2 hours, preferably less than 1 hour, more preferably less than 30 minutes, and even more preferably less than 15 minutes.

After grinding, and optionally a drying step if wet ground, the ground material is subjected to at least one heat treatment.

Optionally, at least one compaction step may be added, which may be done mechanically, for example with a roller or sheet press, or by rolling, stacking or pelletizing, or by any other method suitable to the skilled person.

In a broad, non-limiting embodiment, the milled material is heated in a chemical reactor to control the atmosphere and/or heat treatment temperature.

In one non-limiting embodiment, the temperature of the ground material is between 300 and 800 ℃, in a preferred embodiment between 500 and 700 ℃, in another preferred embodiment between 550 and 650 ℃, and in a further preferred embodiment between 575 and 625 ℃.

In a non-limiting example on a laboratory scale, the process of the invention is conveniently carried out in a tube furnace or in a closed metal vessel placed in a heating furnace. Both have air inlets and air outlets to control the atmosphere contacting the ground material.

In non-limiting examples on an industrial scale, the process of the invention is preferably carried out continuously in a reactor which facilitates the equilibration of the ground feed with the gas phase. Reactors which can control the gas composition and circulation, for example from these: rotary kiln, pushed slab kiln, roller kiln, mesh belt kiln, belt-driven kiln, fluidized bed, etc.

In one non-limiting embodiment, the milled material is heated in a protective atmosphere, preferably in a non-oxidizing or inert atmosphere, such as, but not limited to, nitrogen, argon, carbon dioxide, helium, other inert gases, and mixtures thereof. In addition to the reducing atmosphere resulting from the thermal decomposition of the organic carbon source, the additional reducing atmosphere may be optionally selected to participate in the reduction or to prevent the continued oxidation of ferrous and/or manganese and to prevent complete reduction to the elemental state, if desired. The external reducing atmosphere includes gases such as, but not limited to, CO, H₂、NH₃HC, wherein HC means any hydrocarbon and its derivatives or carbonaceous products in gaseous or vaporous form; the atmosphere also includes inert gases such as, but not limited to, nitrogen, argon, carbon dioxide, helium, other inert gases, and mixtures thereof.

In another non-limiting embodiment, the heating step of the present invention lasts between 10 minutes and 4 hours, preferably between 20 minutes and 2 hours, more preferably between 30 minutes and 1 hour.

In a further non-limiting embodiment, the total time of the grinding, optional drying, and heating steps of the present invention is less than 180 minutes, preferably less than 150 minutes, more preferably less than 120 minutes, and even more preferably less than 90 minutes.

In a broad non-limiting embodiment, the duration of the milling step, the temperature and duration of the heating step of the present invention are selected as a function of the precursor properties and other parameters, such as reasonable time limits. Those skilled in the art will be able to identify suitable alternative parameters without undue effort without departing from the invention.

The iron and/or manganese metal sources are generally in their fully or partially oxidized form Fe (III) and/or Mn (III), and in order to ensure the quality of the final cathode material, the total iron and/or manganese is reduced to the Fe (II) and/or Mn (II) oxidation state during the heat treatment. However, the original sourceThe material compounds are preferably not completely converted to olivine structured lithium metal phosphates, thereby facilitating fine-tuning of the grain size and optimizing the energy efficiency of the heat treatment. At the same time, the partial conversion prevents unwanted impurities from remaining in the material even after the subsequent thermal CVD step. For example in LiFePO₄It is well known that higher heat treatment temperatures and/or longer reaction times under reducing conditions lead to phosphide impurities (FeP, Fe)₂P、Fe₃P) formation, which has a potentially detrimental effect on the anode material, in particular its high temperature cycling performance. In the subsequent thermal CVD step, the appropriate stoichiometric ratio of the remaining phase will be converted to the desired olivine structured lithium metal phosphate. Because the materials in the reaction are pre-nanocrystallized, the reaction kinetics are enhanced. For example in LiFePO₄The residual phase contains ferrous phosphate Fe₃(PO₄)₂And Li₃PO₄(1: 1 molar ratio) or at a lower heating temperature comprises ferrous pyrophosphate Fe₂P₂O₇And Li₂CO₃(1: 1 molar ratio) and conversion to LiFePO of olivine structure in a subsequent thermal CVD step₄。

That is why another object of the present invention is to change the starting raw material compound into an olivine-structured LiMPO after grinding in the heat treatment step₄Is between 30 and 99 mol%, preferably between 40 and 90 mol%, more preferably between 50 and 80 mol%, wherein all iron and/or manganese atoms in the heat-treated material are in the Fe (II) and/or Mn (II) oxidation state.

The organic carbon source is used to provide a reducing atmosphere and to control the grain size by avoiding or limiting sintering of the precursor, while leaving residual carbon in the material. In the subsequent nanomilling step, residual carbon will be abraded from the surface of the material to be present as a low-quality carbon component, and therefore it is preferable to limit the amount of such carbon residue.

This is why it is a further object of the invention that the initial starting compound after heat treatment contains less than 1 wt% residual carbon, preferably less than 0.7 wt%, more preferably less than 0.4 wt%, even more preferably less than 0.1 wt%. In other preferred models of the present invention, the residual carbon is preferably in the range of 0.01 to 1 wt%, more preferably in the range of 0.05 to 0.75 wt%, and still more preferably in the range of 0.1 to 0.5 wt%.

In one non-limiting embodiment, the lithium source compound is selected from, for example, lithium oxide, lithium hydroxide, lithium carbonate, neutral lithium phosphate Li₃PO₄、LiPO₃Lithium hydrogen phosphate LiH₂PO₄、Li₂HPO₄One of lithium oxalate, lithium acetate, lithium polyacrylate, lithium stearate, and mixtures thereof. A person skilled in the art will be able to select any alternative suitable compound or to select any of the above source compounds without departing from the spirit of the invention. Preferably, the lithium source is selected among lithium hydroxide and lithium carbonate, more preferably the lithium source is lithium carbonate.

In one non-limiting embodiment, the lithium source is present in the form of particles, or in the form of agglomerates or blocks of particles, D₉₀Preferably less than 40 μm, more preferably less than 20 μm, even more preferably less than 10 μm, and even more preferably less than 5 μm.

In another non-limiting embodiment, the metal source and the phosphorus source are preferably provided from the same source and are selected from compounds such as aqueous or dehydrated FePO₄、MnPO₄、(Fe,Mn)PO₄、FeHPO₄、MnHPO₄、(Fe,Mn)HPO₄、Fe₃(PO₄)₂、Mn₃(PO₄)₂、(Fe,Mn)₃(PO₄)₂、Fe₂P₂O₇、Mn₂P₂O₇、(Fe,Mn)P₂O₇、NH₄FePO₄、NH₄MnPO₄、NH₄(Fe,Mn)PO₄And a mixture thereof. A person skilled in the art will be able to select any alternative suitable compound or to select any of the above source compounds without departing from the spirit of the invention. The metal phosphate source is preferably aqueous or dehydrated FePO₄、MnPO₄、(Fe,Mn)PO₄And mixtures thereof. When LiMPO₄Is LiFePO₄When the source is Fe (III) PO, the iron phosphate is preferably Fe (III) PO₄And hydrated iron phosphate Fe (III) PO₄·xH₂O (x.ltoreq.4, preferably x.2). The metal phosphate source may be amorphous, amorphized, or crystallized (including but not limited to stringite, metastrengite I, metastrengite II, or orthorhombic crystal structure).

In one non-limiting embodiment, the metal phosphate source is a particle, agglomerate or aggregate of particles, or platelet morphology, D₉₀Preferably less than 40 μm, more preferably less than 20 μm, even more preferably less than 10 μm, and even more preferably less than 5 μm. In another non-limiting embodiment, the metal phosphate is derived from an agglomerate or aggregate of primary particles having an average particle size of less than 500nm, preferably the average particle size of the primary particles is less than 200nm, more preferably less than 100nm, even more preferably less than 50 nm.

In a further non-limiting embodiment, the added metal source is a compound without any limitation that adds a carbonate, oxalate, acetate, stearate, nitrate, phosphate, hydroxide, oxide, organometallic, even non-preferred halide or sulfate salt of a metal, and mixtures thereof. The addition of metal does not preclude the introduction as part of another source, e.g., (Fe, Mg) PO with 2% Mg in place of Fe₄Those skilled in the art will be able to select any alternative suitable combination without departing from the spirit of the invention.

One skilled in the art will be able to produce other alkali metal oxyanions by selecting the appropriate base, metal, oxyanion source compound without departing from the spirit of the present invention.

In further non-limiting embodiments, the organic carbon source may be selected from any liquid phase containing carbon atoms, semi-solid phase, waxy, or solid organic matter, such as may be selected from polycyclic aromatics (e.g., tars and pitches), polyols (e.g., sugars and carbohydrates), lactose, glycerol, fatty acids, aminopolycarboxylic acids (e.g., ethylenediaminetetraacetic acid), glycols, oligomers, polymers, copolymers, block copolymers, cellulose, starch and its esters and ethers, and any derivatives of the foregoing organic carbon sources, and mixtures thereof, without limitation. As examples of the polymer or oligomer, there may be mentioned polymers or oligomers including polyolefins, polybutadienes, polyethylene glycols, polyvinyl alcohols, polyvinyl pyrrolidones, polyvinyl butyrals, polyethylene glycols, polyethylene, polypropylene, polyacrylates, etc., phenol condensates (including condensates obtained by reaction with aldehydes), polymers or oligomers derived from furfuryl alcohol, ethylene oxide and/or propylene oxide, maleic anhydride, styrene, divinylbenzene, naphthalene, pentadiene, acrylonitrile, acrylates, acrylamides, vinyl ether, ethylene, propylene, butylene, butadiene, vinyl acetate, and any derivatives of the above polymers or oligomers, and mixtures thereof. The replacement of all or part of the liquid, semi-solid or solid organic carbon source by an external gas phase organic carbon source is not excluded.

b) Nano grinding step

The material obtained in step a) (referred to as "material a") is subjected to at least one liquid-phase bead milling nanocrystallization process step in the presence of a carrier liquid. During the development of this process, the inventors have realized that when water is used as the carrier liquid, in some embodiments, the carrier liquid may contain metallic impurities (on the order of 100ppm or more) of iron and/or manganese, which negatively affects the electrochemical performance of the carbon-deposited cathode material. Without being bound by any theory, the inventors believe that the formation of impurities may be due to partial dissolution of material a during the high energy water-based bead milling nanocrystallization process step. This is why nanomilling uses alcohol groups as the carrier liquid.

The material obtained in step a) (referred to as "material a") is subjected to at least one alcohol-based nanomilling process step.

As used herein, "nanomilling" refers to the step of grinding a compound from top to bottom to obtain an average primary particle size (corresponding to D)₅₀) Particles of the compound of less than 500nm, in preferred embodiments less than 250nm, and in more preferred embodiments less than 150 nm. In another embodiment, the nano-milled primary particles have an average particle size between 25 and 250nm, preferably between 50 and 150nmBetween nm, more preferably between 70 and 130 nm.

In one non-limiting embodiment, the particle size distribution of the nano-abrasive material a of the present invention is characterized by a span (defined as (D)₉₀-D₁₀)/D₅₀) Less than 2.5, preferably less than 1.5, more preferably less than 1, and still more preferably less than 0.75.

As used herein, "alcohol-based nanomilling" refers to wet grinding in the presence of an alcohol carrier fluid. The alcohol is preferably selected from aliphatic alcohols having 1 to 10 carbon atoms, such as methanol, ethanol, propanol, such as n-propanol or isopropanol, butanol, such as n-butanol or isobutanol, and mixtures thereof. Methanol, ethanol, and isopropanol are preferred carrier fluids.

In one non-limiting embodiment, the nanomilling is operated in an inert atmosphere, such as, but not limited to, one of nitrogen, argon, carbon dioxide, helium, other inert gases, and mixtures thereof. The term "inert atmosphere" generally refers to a gas mixture that contains little or no oxygen.

In another non-limiting embodiment, degassing of the alcohol-based carrier fluid is performed prior to the nanomilling step using any method known to one of ordinary skill in the art, such as depressurization, removal of the solvent, membrane degassing, and inert gas substitution.

In another non-limiting example, the wet bead milling device may be selected from the group of stirred bead mills known to those skilled in the art, which are capable of reducing particle size to the nanometer range. Specifically, there may be mentioned an Ultra APEX mill of Japan Shentong Industrial Co., Ltd, a high-speed Titana and Neos stirred bead mill of Germany Nashin Co., Ltd, a Hosokawa Alpine AHM mill of Japan Kagaku Co., Ltd, a horizontal type nano mill PHN series of Brazil China, a nano mill ZBW/5L of China Shandong Longxing Co., Ltd, and a Brazil Co., Switzerland

L&

X series mill.

In a further non-limiting embodiment, the grinding chamber and the grinding unit are made of a layer of protective material and/or of a wear-resistant and corrosion-resistant material to avoid contamination of the formulation, in particular metallic contamination. Preferably, the material from which the metal-free grinding apparatus parts are made is or contains a polymer, such as polyurethane or polyethylene; or ceramic containing, such as zirconia, tungsten carbide, silicon nitride or silicon carbide.

In another non-limiting embodiment, the grinding energy consumption of the input suspension is preferably set to 200-2500 kWh/t, wherein the reference mass (t) refers to the mass of the material a in the suspension. The input energy generates heat, so the suspension must be cooled with suitable cooling equipment.

The grinding beads may be made, for example, of alumina, zirconia, yttrium or cerium stabilized zirconia or carbide. The zirconia may also comprise hafnium oxide HfO₂(ZrO₂+HfO₂). In a preferred embodiment, the grinding beads are made of yttrium or cerium stabilized zirconia, optionally containing the hafnium oxide HfO₂。

In one non-limiting embodiment, the alcohol-based bead milling nanocrystallization process step according to the present invention uses milling beads having an average diameter of 50 to 800 μm. In a preferred embodiment, the average diameter of the grinding beads is from 100 to 400 μm. In another preferred embodiment, the grinding beads have an average diameter of 100 to 200. mu.m. Since the agitated media milling is an energy intensive process, energy efficiency should be optimized, the use of smaller milling beads allows for a more efficient milling process, lower milling energy consumption (kwh/t), shorter milling time, and a reduced particle size distribution range. Reducing the grinding energy consumption and/or shortening the grinding time helps to improve the quality of the cathode material of the present invention, and can limit potentially harmful side reactions that accompany harsh high-energy grinding processes.

The filling ratio of the grinding medium in the grinding chamber has an important influence on the grinding effect. As the filling rate increases, the number of contacts between media increases and the distance between individual grinding media decreases, thereby improving the grinding effect. However, a filling rate of the grinding media exceeding a certain ratio can have a negative grinding effect, since too small a distance between the grinding media limits the freedom of movement. Optimization of the packing of the grinding beads can optimize processing efficiency and also reduce particle size distribution.

This is why another object of the invention is that in a preferred embodiment the filling rate of the grinding chamber and the grinding beads is between 50 and 90 vol%; in another preferred embodiment, the filling rate is 60-85 vol%; in another preferred embodiment, the filling rate is 70-85 vol%.

Without any limitation, nanomilling may be operated in one of four modes, namely a single pass mode, a multiple pass mode (in which the suspension passes through the same mill multiple times), a cascade mode (in which the suspension passes through two connected mills), and a circulation mode (in which the suspension may be pumped through the mill multiple times in succession). The cascade mode allows the use of two mills with different sized grinding media, the first mill with large sized grinding media milling the coarse feed to a particle size that allows it to enter the small sized grinding media mill, thereby ultimately achieving the desired particle size. In addition to optimizing the process (grinding energy consumption, grinding time, particle size distribution), the cascade mode can reduce the wear of the expensive fine grinding beads. In a preferred embodiment, the first mill uses beads having an average diameter of 300 to 800 μm, and the second mill uses beads having an average diameter of 100 to 300 μm.

The flexibility of the process according to the invention allows the production of various grades of nano-sized material a and fine cathode material. For example, it is possible to produce suspensions of different particle size distributions and/or with different chemical compositions, which are stored in a production tank, and to mix them before the drying step c) in order to modify the properties of the positive electrode material. In one non-limiting embodiment, in order to optimize the compaction density of the positive electrode material, a first suspension of a first nano-sized material a having an average particle size of 50 to 200nm (10 to 90 wt% based on the total weight) and a second suspension of a second nano-sized material a having an average particle size of 250 to 500nm are mixed. In a further non-limiting embodiment, at least two nanometerized materials having different chemical compositions are mixeda. Optionally, for example, a nanosized LiFe0.25Mn0.73Mg0.01PO4 having an average particle diameter of 78nm (87 wt% of the total amount) and a nanosized LiFePO having an average particle diameter of 134nm₄The positive electrode materials are mixed to optimize the energy density of the positive electrode materials. Mixing with other positive electrode materials, such as lithium metal oxides, is not excluded. Any other combination is also part of the invention, such as products of core-shell structure, including combinations obtained by coating in a subsequent drying step, such as LiFePO₄Coating of manganese-rich LiMPO₄Or an inverted core-shell structure.

The alcohol-based nanomilling may optionally be carried out in the presence of at least one reducing agent to avoid eventual partial oxidation of material a. In one non-limiting embodiment, the optional reducing agent is selected from the group consisting of hydrazine or derivatives thereof, hydroxylamine or derivatives thereof, ascorbic acid, citric acid, oxalic acid, formic acid, thiols, dithiophosphates, thiosulfates, phosphites, hypophosphites, phosphorous acid, alcohols, pyrroles, polyphenols, hydroquinones, compounds containing readily oxidizable double bonds and mixtures thereof.

In one non-limiting embodiment, the amount of optional reducing agent used in the nanomilling is less than 10000ppm, in one preferred embodiment less than 5000ppm, in another preferred embodiment less than 2500ppm, and in a more preferred embodiment less than 1000ppm, relative to the material a being milled. The reducing agent may be added before the nanomilling process or continuously during the process.

In the nano-milling process, it is preferable to add at least one stabilizer to lubricate the suspension by increasing particle dispersion to improve milling efficiency, while reducing particle agglomeration by mainly counteracting van der waals forces through particle surface charge modification and increasing repulsive force between particles. Therefore, it is possible to grind a suspension of higher concentration, increase the unit yield, reduce the grinding energy consumption, and reduce the nanoparticle size distribution by stably dispersing and controlling the nano-agglomeration.

In further non-limiting embodiments, the at least one stabilizer is an organic compound, which may be selected from the group consisting of organic electrostatic or electrical steric stabilizers, surfactants, dispersants, and sealants, many of which are commercially available. The amount of the at least one stabilizer is usually 0.05 to 2 wt%, preferably 0.1 to 1 wt%, more preferably 0.1 to 0.5 wt%, and still more preferably 0.1 to 0.25 wt% based on the weight of the material a in the suspension.

In further non-limiting embodiments, the at least one stabilizer, for example, may be selected from fatty acid salts (e.g., oleic acid, stearic acid, and lithium salts thereof), fatty acid esters, fatty alcohol esters, alkoxy alcohols, alkoxy amines, fatty alcohol sulfates or phosphates, imidazoles, and quaternary ammonium salts, ethylene oxide/propylene oxide copolymers, ethylene oxide/butylene oxide copolymers, and reactive surfactants.

Some derivatives of fatty acids are also of particular interest. First, the sugar ester compounds are composed of hydrophilic sugar moieties (particularly sucrose, sorbitol and sorbitol), hydrophobic fatty acid moieties and optionally polyoxyethylene segments. For example, mention may be made of the tweens produced by the company Croda, in particular tween 20 (polyoxyethylene sorbitol monolaurate), tween 80 (polyoxyethylene sorbitol monooleate) and tween 85 (polyoxyethylene sorbitol trioleate).

The alcohol acid alcohol may be selected from alcohols obtained from ethylene oxide and/or propylene oxide. The most common alcoholic precursors are fatty alcohols and alkylphenols (for example octyl or nonyl phenol), in particular the alkoxyalcohols sold under the tradenames Igepal (Solvay) and Brij (Croda). The alkoxyamines are available from Huntsman under the trade names Jeffamine and surfamine. Fatty alcohol sulfates or phosphates, including their four-dimensional electronic form, are available, for example, from Stepan corporation.

Ethylene oxide/propylene oxide copolymer surfactants are primarily Pruron, produced by basf. The EO/PO ratio and the molecular weight are changed, and a large number of low-cost and high-efficiency choices are provided for obtaining the surfactants with different adjustable characteristics such as solubility, surface tension, wettability and the like. Polyvinyl butyral, polyvinyl alcohol, polyvinyl pyrrolidone, polyethylene glycol, carboxylic, sulfonic or phosphonic acids and salts thereof, tartaric acid and salts thereof, glycolic acid and salts thereof, polyacrylic acid and salts thereof, ethylene diamine tetraacetic acid and salts thereof can also be used as surfactants, such as any of their derivatives and mixtures thereof. When salts are used, their lithium salts are preferred.

In one non-limiting embodiment, the at least one stabilizer may be selected from silicone surfactants (e.g., from Evonik or dow corning) that lower the surface tension of polar liquids below the typical level achieved with organic surfactants.

In further non-limiting embodiments, the disclosed stabilizers may also be used partially or wholly as an organic carbon source for the precursor sintering step a).

In one non-limiting embodiment, the suspension has a solids content of between 20 and 70 wt%, in a preferred embodiment between 30 and 65 wt%, in a more preferred embodiment between 40 and 60 wt%, and in a further preferred embodiment between 45 and 55 wt%.

In one non-limiting embodiment, the nanomilling step operating time described herein is selected from the following time ranges: about 5 minutes to about 4 hours, about 10 minutes to about 4 hours, about 30 minutes to about 4 hours, about 60 minutes to about 4 hours, about 90 minutes to about 4 hours, about 120 minutes to about 4 hours, about 150 minutes to about 4 hours, about 180 minutes to about 4 hours, about 210 minutes to about 4 hours, about 230 minutes to about 4 hours. Those skilled in the art will be able to select any suitable time period or employ any time period within the above range without departing from the spirit of the invention.

In another non-limiting embodiment, the nanomilling step is performed for a time period of less than 4 hours, preferably less than 2 hours, more preferably less than 1 hour, and even more preferably less than 30 minutes.

The nano-milling equipment is expensive and also requires periodic replacement of expensive fine milling beads to maintain high efficiency. During the development of the present invention, the inventors have found that in some cases, material a is subjected to inexpensive and efficient wet or dry micro bead pre-milling, which is beneficial to the nano milling process. The pre-grinding reduces the abrasion of the nano grinding beads, can increase the output, reduce the grinding time, improve the quality of nano particles, particularly obtain narrower particle size distribution, and reduce the time of the material exposed to severe high-energy ball milling process. Moreover, since a large amount of input energy is consumed as heat in the nano-milling process, the pre-milling significantly improves the energy efficiency of the entire process. The application of pre-grinding can also reduce the requirement of the process on the measurement of the granularity of the synthetic material a, particularly the granularity distribution after the nano-grinding step under the same operation condition.

In one non-limiting embodiment, the pre-milling described herein is an alcohol-based high energy milling, preferably operating in a batch, single pass, multiple pass, cyclic, or continuous manner in a stirred ball mill. The blender may use inexpensive, efficient pre-milling equipment, specific examples of which include, but are not limited to, the Attritor SL series, Attritor Q or OL series cyclic mills, Attritor C, H or CLS series continuous mills from 34-2200L processing chambers of Union Process, Inc., and equivalents thereof. Preferably, the agitator mill is partially lined or made of wear and corrosion resistant materials to avoid contamination by impurities, particularly metals, such as alumina, carbides, zirconia and polyurethane. The grinding beads are made of, for example, alumina, talc, zirconium silicate, zirconia, yttrium or cerium stabilized zirconia or carbide. In a preferred embodiment, the grinding beads are made of cerium or yttrium stabilized zirconia, preferably with a bead diameter of 2-20 mm. As used herein, "micromilling" refers to the step of milling the compound to obtain D in the particle size distribution₉₀A compound having a particle size of 1 to 5 μm, preferably 1 to 3 μm, more preferably 1 to 2 μm. In another non-limiting embodiment, the pre-milling step is less than 1 hour, preferably less than 30 minutes, and more preferably less than 15 minutes. The pre-milling may optionally be carried out in the presence of at least one reducing agent and/or at least one stabilizer. In one non-limiting embodiment, the nanomilling is conducted in an inert atmosphere, such as nitrogen, argon, carbon dioxide, helium. In yet another non-limiting embodiment, the alcohol-based liquid is degassed prior to nanomilling. In one non-limiting embodiment, the grinding energy input to the agitator mill is preferably set in the range of from 30kWh/t to 300kWh/t, more preferably in the range of from 50kWh/t to 200kWh/t, and even more preferably in the range of from 50kWh/t to 150kWh/t, wherein reference mass (t) refers to the mass of material a in the agitator mill. The input energy generates heat, thus canA suitable cooling device can be required to cool the agitator mill.

In yet another non-limiting embodiment, the pre-micron milling is performed in a circulation mode in a stirred mill with attached reservoir. After the pre-milling is completed, the reservoir is connected to the nanodevice.

In one non-limiting embodiment, functional additives may also be added to the nanomilled formulation to improve the quality of the positive electrode material in accordance with the present invention. Specific examples include, but are not limited to, conductive additives and surface treatment agents. Additives may be added to the formulation before, during or after nanomilling, and without any limitation, before or during nanomilling.

The conductive additive may be selected from the group consisting of carbon particles, carbon fibers, carbon nanofibers, carbon nanotubes, graphene oxide, and mixtures thereof. In one non-limiting embodiment, the conductive additive is in the form of an easily dispersible pigment having stabilizing groups attached to its surface. Preferably, the ionic species is, for example, a carboxylic acid (-CO)₂M) and sulfonic acid (-SO)₃M) salts, wherein M is preferably selected from H, Li, Na or K, more preferably from among H or Li. Readily dispersible carbon particles are commonly used in inks or graphic paints and are an economically efficient solution. The average particle size of the disclosed carbon particles is less than 200nm, preferably less than 100nm, more preferably less than 50nm, and even more preferably less than 25 nm. For example, LITX 200 and LITX 300 manufactured by Cabot, pigment Carbon black FW200 manufactured by Orion engineering Carbon Co., Ltd, Tokabess #8500/F manufactured by Tokai Carbon Co., Ltd, High Color Furnace #2650 manufactured by Mitsubishi chemical Co., Ltd can be mentioned. According to the present invention, such carbon particles can increase the compacted density of the positive electrode material, in addition to potentially improving the electrochemical performance of the positive electrode material, particularly at high current density and low temperature operation. In one non-limiting example, the conductive additive is preferably readily dispersible carbon particles in an amount less than 4 wt%, preferably less than 2 wt%, more preferably less than 1 wt%, and even more preferably less than 0.5 wt% relative to the total mass of the nanomilled material a.

The surface treatment agent may be selected from organometallic compounds such as metal alkoxides including titanium, zirconium, aluminum, organosilanes including silicon alkoxides, and mixtures thereof. According to the invention, the surface treatment agent can be used as a passivating agent to act on a fresh and high-reactivity surface generated in the nano-grinding process, so that the electrochemical performance of the cathode material is improved. In one non-limiting embodiment, the amount of surface treatment agent is less than 2 wt%, preferably less than 1 wt%, more preferably less than 0.5 wt%, and even more preferably less than 0.25 wt% relative to the total mass of the nanomilled material a.

In one non-limiting example, the high energy nanomilling step may be performed in the presence of chemical additives that are effective to react with impurities that are unexpectedly present in material a, such as iron particles, iron oxides, lithium, transition metals, and phosphorous-containing impurities. For example, the iron particles or iron oxide may be in LiH₂PO₄The reaction takes place by mechanosynthesis in the presence of a catalyst which gives a catalyst having the appropriate Li: fe: p balance ratio of compounds. In one embodiment, a batch of C-LiFePO₄Unexpectedly containing high magnetic impurities, which is comparable to FePO₄·2H₂Presence of Fe in O₂O₃Impurities are involved. Thus, in preliminary experiments, LiH at stoichiometric ratio₂PO₄In the presence of the magnetic impurities, the C-LiFePO containing about 300ppb of magnetic impurities instead of 4000ppm can be obtained by nanomilling the same batch of material a₄。

c) Drying step

After the nanomilling, the carrier liquid is removed from the suspension to obtain a solid compound of the nanometerized material a. Essentially any process may be used. For example, filter pressing, freeze drying, evaporation, flash evaporation, tray drying, paddle drying, fluidized bed drying, conical screw drying, media agitation drying, spray drying all can remove the flux.

Spray drying is a widely used method for producing dry powder by rapidly drying a suspension with hot gas, and is the preferred drying equipment in the present invention. The suspension is first atomized to produce droplets, which are subsequently contacted with hot gas in a spray-drying chamber, after leaving the drying chamber, the moisture content being further reduced in a second stage drying process, for example in a fluidized-bed or vibrating-bed dryer. The suspension is atomized by using a rotary atomizer, a hydraulic nozzle, a pneumatic nozzle, a combined type hydraulic pneumatic nozzle for pressurizing suspension and gas spraying medium, or an ultrasonic atomizer. The nozzles may be selected from, for example, single fluid nozzles, two fluid nozzles, four fluid nozzles, in-line mixing nozzles, inkjet nozzles, dual jet pneumatic nozzles, combination nozzles, and ultrasonic nozzles. The spray drying chamber can be designed for co-current, mixed-current or counter-current atomization. The atomizing gas medium is an inert gas, such as nitrogen.

The additional cost of using an inert gas as the spray medium, unlike the use of air for water-based carrier fluids, is partially offset by the superior evaporation rate of the alcohol solvent under equivalent operating conditions. The evaporation rate of methanol, ethanol or isopropanol is generally 2-3 times that of water. Furthermore, spray drying of the alcohol-based suspension with an inert gas facilitates purification of the dried material.

Numerous spray dryer designs are available to meet a variety of product specifications and can control particle morphology from slightly agglomerated primary particles to secondary agglomerates of primary particles, preferably in the form of secondary spherical agglomerates of primary particles.

The nano-suspension obtained in step b) may be subjected to a dispersion treatment before the spray drying step. This treatment can be carried out using any commercially available dispersing equipment, such as a rotor/stator disperser or a colloid mill. Before spray drying, the suspension may be re-agglomerated in order to prevent clogging of the atomizer and to reduce the viscosity of the suspension before atomization. Any suitable additives may also optionally be added during the dispersion treatment prior to spray drying, such as the previously defined surface treatment agents and conductive additives.

In one non-limiting embodiment, the drying operation of the suspension is carried out at a temperature of 120-500 ℃ in the air inlet device of the spray dryer, and the temperature is usually 200-370 ℃. The outlet temperature is usually in the range of 60 to 150 ℃, preferably 80 to 120 ℃. The solid product can be separated from the gas by any commercially available gas-solid separation system, such as a cyclone, electrostatic precipitator or filter, preferably a bag filter with a pulsed jet dust removal system.

Optionally, at least one classification process step, such as screening, screening or sifting, may be added after spray drying. In particular, the sieving and/or sieving step may use a nominal 30 to 40 μm sieve.

Optionally, at least one compaction process step may be added after spray drying, which may be mechanical compaction, e.g. by a roller or tablet press, but may also be roller compaction, stacking, granulation, or by any other suitable technical method known to the person skilled in the art.

During the development of the process, the inventors have also found that in some implementations, even if the moisture content of the nanometerized material a is low after drying, it may have a detrimental effect on the electrochemical performance of the positive electrode material. Thus, in one non-limiting embodiment, the moisture content of the material after drying and before chemical vapor carbon deposition is less than 4000ppm, preferably less than 2000ppm, more preferably less than 1000ppm, and even more preferably less than 500 ppm.

d) Chemical vapor carbon deposition

Chemical Vapor Deposition (CVD) is a chemical process for producing deposited carbon on various substrates that are exposed to one or more gaseous carbon sources, such as carbonaceous gases or thermal decomposition products of organic matter. In the present invention, the thermal CVD process is used to produce a continuous uniform adsorption, high crystallinity, low resistance carbon deposit, preferably a graphene-like carbon deposit, on the nanosized particles obtained in step c).

"graphene-like carbon deposition" as used herein refers to I_D/I_GCarbon deposition in a ratio of less than 0.9, preferably less than 0.8, more preferably less than 0.7, and even more preferably less than 0.6. I is_D/I_GThe ratio is typically 1360cm in Raman analysis^-1Peak (I)_DAssociated with amorphous carbon) and 1580cm^-1Peak (I)_GAssociated with crystalline carbon).

In one non-limiting embodiment, the deposited carbon obtained by the thermal CVD process of the present invention consists of at least 99.5 wt% carbon, preferably at least 99.7 wt%, more preferably at least 99.9 wt%, and even more preferably at least 99.95 wt%.

In another non-limiting embodiment, to ensure that all of the particle surfaces are exposed to the gas phase carbon source, the powder is preferably stirred and rotated in a rotary kiln, or passed through a gas phase suspension in a fluidized bed, optionally with the assistance of pulsation assisted techniques to effectively fluidize the nanoparticles (of particular interest is the generation of uniform carbon deposited primary particles.

Raman spectrum analysis of the lithium metal phosphate shows that the lithium metal phosphate is multimodal, such as 900-1200 cm^-1Corresponds to LiFePO₄Spectrogram (called I)_v). The quality of the deposited carbon can be represented by I_v/(I_D+I_G) The specific monitoring is carried out because the surface is 900-1200 cm when the surface is completely coated by the deposited carbon^-1The range has no peaks.

This is why another object of the present invention is to obtain a carbon-deposited cathode material by a chemical vapor deposition process in the presence of a vapor-phase carbon source, wherein I_v/(I_D+I_G) The ratio is in the range of 0 to 0.05, preferably 0 to 0.03, more preferably 0 to 0.01.

Without any limitation, as a carbon source for the thermal CVD process, a gas such as methane, ethane, propane, butane, ethylene, propylene, butene, natural gas, Liquefied Petroleum Gas (LPG), or acetylene; vaporized liquids such as alkane compounds, e.g., pentane, hexane or cyclohexane, aromatic compounds, e.g., benzene, toluene, xylene or ethylbenzene; or an alcohol such as methanol, ethanol, propanol or butanol; a vaporized solid such as phenol, quinone, hydroxyquinone, naphthalene, anthracene, biphenyl, or biphenyl; and combinations of the above. The carbon source may also be a gas stream of complex decomposition products produced by the cracking of organic matter, and any carbon-containing organic matter such as polypropylene, polyethylene, polystyrene, polyvinyl alcohol, polyolefin, polybutadiene, tar, starch, carbohydrate, or cellulose and its derivatives may be used without any limitation. In one non-limiting embodiment, the carbon source is comprised of carbon and hydrogen. Preferred carbon sources are benzene, propylene or acetylene. Optionally, the addition of a derivative of nitrogen (such as urea, ammonia, aliphatic amine or nitrile) or boron (such as borane or boric acid) allows the synthesis of nitrogen or boron doped carbon deposits. Optionally, the carbon deposition process may be plasma enhanced CVD or laser activated CVD.

In the course of the development of the present invention, the inventors have also found that gas phase catalytic reforming with increased concentration of aromatic compounds contributes to improved carbon deposition characteristics, particularly I, when using carbon sources derived from the cracking of organic matter_D+I_GRatio reduction and conductivity improvement. The gas stream may be upgraded, without limitation, for example with a zeolite catalyst (such as a Y zeolite or zeolite ZSM-5 catalyst) at a temperature between 400 ℃ and 700 ℃. This is why another object of the invention is to provide a thermal CVD carbon source obtained by cracking of organic matter, which is subjected to a further reforming step with at least one catalyst to increase the concentration of aromatic compounds. It is not excluded to apply a catalytic reforming step to other carbon sources to increase the aromatic content.

The carbon deposition thermal CVD process may be performed in one or more thermal processes, for example, in one non-limiting example, CVD may be performed in a first rotary furnace and heat treatment may be performed in a second continuous furnace (e.g., in an inert atmosphere) using the same or different carbon sources; or the first CVD can be carried out in a first rotary furnace and the second CVD in a second continuous furnace. The total reaction time is usually 10 minutes to 4 hours, preferably 10 minutes to 2 hours, more preferably 10 minutes to 1 hour, still more preferably 20 to 40 minutes.

In a non-limiting embodiment, the reaction temperature is preferably between 600 ℃ and 750 ℃ in a one-step or at least one-step multi-step process, in a preferred embodiment between 625 ℃ and 725 ℃, in another preferred embodiment between 625 ℃ and 700 ℃, and in a more preferred embodiment between 625 ℃ and 675 ℃.

In one non-limiting embodiment, the first CVD step temperature is between 200 deg.C and 600 deg.C, preferably between 300 deg.C and 500 deg.C, and more preferably between 300 deg.C and 400 deg.C. The use of a first low temperature step may have several benefits, such as limiting sintering of the nanosized particles and also limiting the formation of impurities that can adversely affect electrochemical performance. In the course of the development of the present invention, the inventors have also found that when a compound having a short dehydrogenation time (less than 1 minute at 400 ℃) such as benzene is used as a carbon source, the first low-temperature thermal CVD process is advantageous for obtaining ordered graphene-like deposited carbon having a lower defect density. The second heat treatment is then carried out at a temperature of between 600 ℃ and 750 ℃, in a preferred embodiment between 625 ℃ and 725 ℃, in a more preferred embodiment between 625 ℃ and 700 ℃, and in a still more preferred embodiment between 625 ℃ and 675 ℃.

In one non-limiting embodiment, the method of the present invention optionally includes a subsequent flash heat treatment on the final product to improve the degree of graphitization of the carbon deposit while avoiding partial decomposition of the material. The flash heat treatment temperature is between 750 ℃ and 950 ℃, preferably between 800 ℃ and 900 ℃. The flash heat treatment duration is preferably between 10 seconds and 10 minutes, more preferably between 1 minute and 5 minutes.

The thickness and content of the deposited carbon can be controlled by the exposure time of the nanoparticles to the gaseous carbon source, and/or by adjusting the flow rate of the gaseous carbon source in the furnace, and/or by adjusting the concentration of the gaseous organic carbon source. To control the concentration of the carbon source in the gas stream, the organic material may be mixed with an inert carrier gas, such as nitrogen, argon, CO₂Helium or reducing gases, e.g. CO or H₂Or any combination of the above.

Suitable gas phase carbon source flow rates for the thermal CVD step generally depend on the particular circumstances (reactor type, load, residence time, and type of starting materials), which can be determined by one skilled in the art using the information contained herein. In some embodiments, good results are obtained with flow rates of about 0.1 to about 5L/min, or about 0.1 to about 3L/min, or about 0.1 to about 2L/min, optionally in combination with an inert carrier gas, and flow rates of about 0.5 to about 10L/min, about 0.5 to about 8L/min, about 1 to about 5L/min, or about 1 to about 3L/min, although the exact flow rate depends on the type of reactor, material to be treated, and other process parameters. In other embodiments, a pre-prepared mixture of a gaseous carbon source and a nitrogen or argon carrier gas may be used for the thermal CVD step. For example, the coating can be carried out in a fluidized bed reactor at a higher flow rate, such as a flow rate of about 1 to 50L/min, 10 to 25L/min, or 20 to 25L/min. In some embodiments, the ratio of the gaseous carbon source to the inert carrier gas in the mixture is 1: 20 to 1: 5.

the thermal CVD step is typically performed under a slight positive pressure. Therefore, in a specific embodiment, the pressure of the thermal CVD step is 0-80 mbar, 0-60 mbar, 0-50 mbar, 10-60 mbar, 10-50 mbar, or 0-40 mbar above the atmospheric pressure.

In one non-limiting embodiment, the carbon-deposited cathode material according to the present invention has a deposited carbon content from thermal CVD of less than 2.5 wt%, preferably less than 2.0 wt%, more preferably less than 1.6 wt%, and even more preferably less than 1.2 wt% of the total weight. In other preferred embodiments of the present invention, the content of the deposited carbon from thermal CVD in the carbon-deposited positive electrode material according to the present invention is preferably in the range of 0.2 to 1.2 wt%, more preferably 0.5 to 1 wt%, and further more preferably 0.6 to 0.95 wt%.

In another non-limiting embodiment, the carbon deposit has a thickness of about 0.3 to about 3.7nm, preferably about 0.8 to about 2.2 nm.

In another non-limiting embodiment, the carbon deposit is in the form of a graphene-like carbon deposit having 1 to 8 layers, preferably 2 to 5 layers of the graphene-like carbon deposit.

In a further non-limiting embodiment, the carbon deposition cathode material obtained by the method of the invention is formed by secondary spherical agglomerates of primary particles, and the deposited carbon content is less than 2.5 wt%, and the BET value is 3-11 m²A ratio of 3 to 9 m/g²A ratio of 3 to 7 m/g²A more preferable range is 3 to 5 m/g²Between/g. In another preferred embodiment, the BET value is ≦ 11m²A/g, preferably ≤ 9m²A/g, more preferably 7m or less²A ratio of 5m or less per gram²/g。

In one non-limiting embodiment, the carbon-deposited positive electrode material having a deposited carbon content of less than 2.5 wt% obtained by the method of the present invention is in the form of secondary spherical agglomerates of primary particles having an average particle size of 50 to 250nm, and a BET value of 3 to 11m²Between/g, preferably 3 to 9m²A ratio of 3 to 7 m/g²A more preferable range is 3 to 5 m/g²(ii) in terms of/g. In another preferred embodiment, the BET value is ≦ 11m²A/g, preferably ≤ 9m²A/g, more preferably 7m or less²A ratio of 5m or less per gram²/g。

The positive electrode material in the form of primary particles agglomerated into secondary spherical agglomerates preferably has a minimum porosity to allow solvated lithium ions in the secondary battery electrolyte to penetrate the agglomerates and reach the primary particles, particularly to support large charge and discharge batteries, but too much porosity is detrimental to electrode density. This is why the porosity is preferably 5 to 40%, more preferably 10 to 35%, and further preferably 15 to 30%. The pore size distribution can be obtained by mercury intrusion porosimetry, and in one non-limiting embodiment, the cathode material preferably has an average pore size of 50 to 500 nm.

In one non-limiting embodiment, the present invention deposits D of the positive electrode material as secondary spherical agglomerates of primary particles₅₀The particle size is 2 to 30 μm, preferably 3 to 20 μm, more preferably 3 to 10 μm, and further preferably 3 to 7 μm.

In another non-limiting embodiment, the particle size distribution of the carbon-deposited cathode material present in the present invention in the form of secondary spherical agglomerates of primary particles is characterized by its span (defined as (D)₉₀-D₁₀)/D₅₀) Less than 3, preferably less than 2.5, more preferably less than 2, and still more preferably less than 1.5.

In a further non-limiting embodiment, the particle size distribution of the carbon-deposited positive electrode material present in the invention in the form of secondary spherical agglomerates of primary particles is characterized by D₃₀/D₇₀The ratio is greater than 0.45, preferably greater than 0.6, more preferably greater than 0.75。

The bulk density of the positive electrode material of the invention can be optimized by controlling the particle size distribution characteristics, and higher compacted density can be obtained.

As already discussed, the carbon deposit, preferably a graphene-like carbon deposit, has a low resistivity, and therefore the powder resistivity of the carbon-deposited positive electrode material obtained according to the method of the present invention is less than about 20 Ω · cm, preferably less than 10 Ω · cm, more preferably less than 7 Ω · cm, and still more preferably less than 4 Ω · cm. The lower limit of the powder resistivity is more than 0.05. omega. cm, preferably more than 0.5. omega. cm, and more preferably more than 1. omega. cm. The material disclosed by the invention is low in powder resistivity, and is beneficial to being applied to batteries with excellent high power/energy ratio performance.

The material compaction density is more or less related to the density of the electrode or the density of the so-called active substance, which ultimately also relates to the battery capacity. The higher the compaction density, the higher the cell capacity. In one non-limiting embodiment, the compacted density of the carbon-deposited cathode material obtained by the process of the present invention exceeds 2g/cm³Preferably more than 2.2g/cm³More preferably more than 2.4g/cm³。

In one non-limiting embodiment, the carbon-deposited cathode material of the present invention, in the form of secondary spherical agglomerates of primary particles, has a powder compaction density of 2.4 to 3g/cm³Preferably 2.5 to 2.9g/cm³More preferably 2.6 to 2.8g/cm³In the meantime.

In one non-limiting embodiment, the carbon-deposited cathode material present in the present invention in the form of secondary spherical agglomerates of primary particles is preferably spherical and has an aspect ratio (L/D) of 0.7 to 1.5, preferably 0.8 to 1.3, more preferably 0.9 to 1.1, and even more preferably 0.95 to 1.05. The compacted density of the cathode material decreases with increasing aspect ratio, particularly when the aspect ratio exceeds 1.5.

The carbon-deposited cathode materials according to the present invention exhibit excellent volume and tap density to improve the processability of these materials during electrode fabrication. This is because the machine for manufacturing the electrodes can be filled to a greater extent with the material to be processed, so that a higher yield can be obtainedAnd (4) output. The bulk density of the material is 1-1.4 g/cm³Within the range. The tap density of the material is 1.4-2 g/cm³Within the range.

During the development of the present invention, the inventors have also found that surprisingly, even very low sulfur impurity levels can have a detrimental effect on the electrochemical performance at high temperatures (60 ℃ cycle and 85 ℃ cycle) of carbon deposited cathode materials on which carbon deposits from the thermal CVD process, particularly graphene-like deposited carbon, are present. Therefore, a carbon-deposited positive electrode material excellent in performance, which has a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, and still more preferably less than 20ppm, is produced at a high temperature.

Without being bound by any theory, the inventors believe that surprisingly even carbon deposits obtained from thermal CVD processes, in particular trace amounts of sulphur in graphene-like carbon deposits, can cause electrocatalytic reactions of the carbon deposit cathode material surface with the battery electrolyte. Trace amounts of sulfur may also cause an increase in BET values, possibly due to more disordered carbon deposition.

This is why another object of the present invention is a low sulfur carbon deposition cathode material obtained by a chemical vapor deposition process in the presence of a vapor phase organic carbon source, wherein the carbon deposition content is less than 2.5 wt% and the sulfur content is less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, still more preferably less than 20 ppm.

This is why another object of the present invention is a low sulfur carbon deposition cathode material wherein the carbon deposition is a 1-8 layer graphene-like carbon deposition wherein the sulfur content is less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, still more preferably less than 20 ppm.

This is why another object of the present invention is a low sulfur carbon deposition positive electrode material, preferably graphene-like deposited carbon, in which the carbon deposition content is less than 1.2 wt%, and the ratio of the sulfur content to the carbon deposition content (referred to as "S/C") is less than 0.8%, preferably less than 0.6%, more preferably less than 0.4%, still more preferably less than 0.2%.

This is why another object of the invention is toThe carbon deposition anode material is obtained by the method, and the carbon deposition content is lower than 2.5 wt%; its sulfur content is less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, still more preferably less than 20 ppm; the particle is in the form of a secondary spherical aggregate of primary particles, and the average particle size of the primary particles is 50-250 nm; the BET value is 3 to 11m²Between/g, preferably 3 to 9m²A ratio of 3 to 7 m/g²A more preferable range is 3 to 5 m/g²(ii) in terms of/g. In another preferred embodiment, the BET value is ≦ 11m²A/g, preferably ≤ 9m²A/g, more preferably 7m or less²(ii)/g, more preferably 5m or less²/g。

This is why another object of the present invention is to obtain a graphene-like carbon deposit positive electrode material having 1 to 8 layers of the graphene-like carbon deposit by the method of the present invention; a sulphur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, more preferably less than 20 ppm; the particle is in the form of a secondary spherical aggregate of primary particles, and the average particle size of the primary particles is 50-250 nm; the BET value is 3 to 11m²Between/g, preferably 3 to 9m²A ratio of 3 to 7 m/g²A more preferable range is 3 to 5 m/g²(ii) in terms of/g. In another preferred embodiment, the BET value is ≦ 11m²A/g, preferably ≤ 9m²A/g, more preferably 7m or less²(ii)/g, more preferably 5m or less²/g。

This is why another object of the present invention is to use a carbon-deposited cathode material obtained by the method of the present invention, which has a carbon deposition content of less than 2.5 wt% in the preparation of a cathode material for a lithium secondary battery excellent in high-temperature electrochemical properties; and has a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, and even more preferably less than 20 ppm.

The other purpose of the invention is to apply the graphene-shaped carbon deposition cathode material obtained by the method in the preparation of a cathode material of a lithium secondary battery with excellent high-temperature electrochemical performance, wherein the cathode material comprises 1-8 layers of graphene-shaped carbon deposition; and has a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, and even more preferably less than 20 ppm.

Optionally, at least one particle classification process step may be added to remove the coarse or fine powder fraction of the carbon-deposited positive electrode material of the present invention. This may be done by any commercially available particle sorting apparatus, such as cyclones, air classifiers, screens, sieves, or combinations thereof. In one embodiment of the invention, the part of the secondary spherical aggregate carbon deposition cathode material with the particle size less than 2 μm, preferably less than 1 μm, is removed by a grading process. In another embodiment of the invention, the carbon deposited positive electrode material is sieved on a sieve screen with a nominal mesh size of 30-40 μm, preferably 40 μm, cleaned by a combination of ultrasound and air brushes. The fine powder remains as the product and the coarse powder cannot. Coarse and/or fine powders that cannot be used as products can be recycled as raw materials in the process.

Jet mills equipped with integrated classifiers are often a convenient tool for reducing the particle size distribution of carbon-deposited cathode materials. However, when the positive electrode material is in the form of secondary spherical agglomerates, it is preferable not to use a jet mill in order not to destroy such agglomerates.

In a preferred mode of operation, after the thermal CVD step, the carbon-deposited positive electrode material, preferably graphene-like carbon deposit, has a water content of less than 200ppm, preferably less than 100ppm, more preferably less than 50ppm, even more preferably less than 25 ppm.

However, optionally, the moisture content of the obtained material may be reduced by a subsequent drying step, which is useful. Without being limited in any way, a vacuum drying apparatus, a cyclone vacuum dryer, a rotary vacuum dryer, a conical paddle dryer, a fluidized bed dryer, a vibrating bed dryer, or a conical screw dryer may be used. Those skilled in the art will be able to identify suitable alternative drying apparatus without undue effort without departing from the invention.

In a further non-limiting embodiment, the total duration from steps a) to d) is less than 8 hours, preferably less than 6 hours, more preferably less than 4 hours.

Any step after the thermal CVD process, such as classification, compaction, jet milling, drying, mixing, handling or storage, is operated under a dry atmosphere, preferably an inert atmosphere, to maintain the product quality until packaged in a suitable closed container, especially in an aluminum plastic foil packaging bag.

The process of the invention allows the synthesis of carbon-deposited positive electrode materials with little metallic or magnetic impurities, the achievement of which is facilitated by the very low sulphur and moisture content. In some embodiments, one or more demagnetizers are optionally used during any step to further remove potential residual magnetic impurities.

This is why another object of the present invention is to use a carbon-deposited positive electrode material obtained by the method of the present invention. The carbon content of the cathode material is lower than 2.5 wt%; a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, even more preferably less than 20 ppm; the water content is less than 100 ppm; the magnetic impurity content is less than 300ppb, preferably less than 200ppb, more preferably less than 100ppb, still more preferably less than 50 ppb.

This is why another object of the present invention is to use a graphene-like carbon-deposited cathode material obtained by the method of the present invention. The positive electrode material has 1-8 layers of the graphene-like carbon deposit, and the sulfur content of the carbon deposit is less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, and even more preferably less than 20 ppm; the water content is less than 100 ppm; the magnetic impurity content is less than 300ppb, preferably less than 200ppb, more preferably less than 100ppb, still more preferably less than 50 ppb.

The ferromagnetic impurities in the carbon-deposited cathode material according to the invention are related to their specific magnetization level, and the very low sulfur impurity content and moisture contribute to achieving low specific magnetization characteristics.

This is why another object of the present invention is to use a carbon-deposited positive electrode material obtained by the method of the present invention. Its carbon content is less than 2.5 wt%; a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, even more preferably less than 20 ppm; the water content is less than 100 ppm; the specific magnetization is less than 0.1emu/g, preferably less than 0.01emu/g, more preferably less than 0.001emu/g, and still more preferably less than 0.0001 emu/g.

This is why another object of the present invention is to use a graphene-like carbon-deposited cathode material obtained by the method of the present invention. The positive electrode material has 1-8 layers of the graphene-like carbon deposit, and the sulfur content of the carbon deposit is less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, and even more preferably less than 20 ppm; the water content is less than 100 ppm; the specific magnetization is less than 0.1emu/g, preferably less than 0.01emu/g, more preferably less than 0.001emu/g, and still more preferably less than 0.0001 emu/g.

Sulfur impurities in the carbon deposit produce hygroscopic species, so a very low sulfur content is beneficial in limiting water absorption. This is why another object of the present invention is to use a graphene-like carbon-deposited cathode material obtained by the method of the present invention. The positive electrode material comprises 1-8 layers of graphene-like carbon deposition, and the moisture content of the graphene-like carbon deposition is lower than 100 ppm; the sulfur content is less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, and even more preferably less than 20 ppm.

Sulfur impurities in the carbon deposit can generate ions that can form detrimental effects on the surface of the carbon deposit on pH sensitive materials, such as non-optimal electrode porosity, tortuosity, density, resistivity, or cycling performance. This can be determined by the Zeta potential method (measuring the surface charge of the material). Without being bound by any theory, the inventors believe that when particles of the carbon-deposited, preferably graphene-like, carbon-deposited cathode material are dispersed in water and/or organic solution, repulsion phenomena occur between the particles, which are related to the surface charge of the particles in water and/or organic solution when the particles are in close proximity to each other. In fact, when the particles of carbon-deposited cathode material become very close to each other, their surface charge begins to act by repelling adjacent particles, thereby preventing close packing of the particles, thereby limiting maximum compaction of the electrode. The very low sulfur content allows the carbon-deposited cathode material, preferably in the form of secondary spherical agglomerates, to be less sensitive to ambient pH and therefore more suitable for processing by solvent-based slurry coating, including aqueous slurry coating.

This is why another object of the present invention is to use a carbon-deposited positive electrode material obtained by the method of the present invention. Its carbon content is less than 2.5 wt%; preferably in the form of secondary spherical agglomerates; a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, even more preferably less than 20 ppm; and has a Zeta potential of less than 20mV, preferably less than 15mV, more preferably less than 10mV, and still more preferably less than 5mV in absolute value in a neutral pH aqueous solution.

This is why another object of the present invention is to use a graphene-like carbon-deposited cathode material obtained by the method of the present invention. The positive electrode material has 1-8 layers of graphene-like carbon deposition; preferably in the form of secondary spherical agglomerates; a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, even more preferably less than 20 ppm; and has a Zeta potential of less than 20mV, preferably less than 15mV, more preferably less than 10mV, and still more preferably less than 5mV in absolute value in a neutral pH aqueous solution.

Lithium-containing metal composite oxide positive electrode materials (referred to as "oxide positive electrodes"), such as layered-structured or spinel-structured oxides, have been reported to have surface modifications and coatings that improve their properties, such as limiting capacity fade, impedance increase, transition metal dissolution, surface amorphization and passivation. The coating of the oxide anodes with lithium metal phosphate (preferably carbon-deposited) improves their thermal stability and electrochemical properties, and it should be mentioned in particular that the coating material is carbon-deposited LiFePO₄In (1).

During the development of the present invention, the inventors have also found that the carbon-deposited positive electrode material of the present invention, coating the oxide positive electrode and having a very low sulfur impurity content, is particularly advantageous for maintaining excellent high temperature performance, including cycle performance and optimal Area Specific Impedance (ASI).

This is why another object of the present invention is a positive electrode for a lithium secondary battery comprising at least one oxide positive electrode and at least one carbon-deposited positive electrode material obtained by the process of the present invention, having a carbon content of less than 2.5 wt% and a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, still more preferably less than 20 ppm. The method is used for preparing the anode of the lithium secondary battery with excellent high-temperature electrochemical performance and improved thermal stability, and the anode contains an oxide anode.

This is why a further object of the present invention is a positive electrode for a lithium secondary battery comprising at least one oxide positive electrode and at least one graphene-like carbon deposit positive electrode material obtained by the present invention, which contains 1 to 8 layers of said graphene-like carbon deposit, and which has a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, still more preferably less than 20 ppm; the method is used for preparing the anode of the lithium secondary battery with excellent high-temperature electrochemical performance and improved thermal stability, and the anode contains an oxide anode.

In one non-limiting embodiment, the carbon-deposited positive electrode material of the present invention has a proportion of 0.5 to 30 wt%, preferably 2 to 20 wt%, more preferably 4 to 10 wt% with respect to the mass of the oxide.

In a further non-limiting embodiment, D of the oxide positive electrode₅₀The carbon deposition cathode material consists of primary particles, optionally in the form of secondary spherical aggregates, the average particle diameter of the primary particles being between 25 and 250nm, preferably between 50 and 150nm, more preferably between 70 and 130nm, and is between 5 and 20 mu m. The specific surface area of the oxide positive electrode is 0.01 to 1m²A concentration of 0.05 to 0.7 m/g²A concentration of 0.1 to 0.4 m/g²/g。

In addition to low sulfur impurity levels, the present inventors have also discovered that the high conductivity of carbon deposits, particularly graphene-like carbon deposits, is beneficial for preparing a positive electrode for a lithium secondary battery comprising at least one positive electrode coated with the carbon deposit positive electrode material of the present invention and at least one oxide positive electrode. Without being bound by any theory, the inventors believe that the high conductivity of the carbon deposit allows the current to pass more uniformly, thereby avoiding the formation of excessive interfacial reaction impedance; the inventors also believe that the high conductivity of the carbon deposit allows for optimal Area Specific Impedance (ASI) and thus may allow forThe beneficial effects on its thermal safety are maintained by the intrinsically safe phosphate cathode material. Oxide positive electrodes, such as LiCoO2, LiNi1/3Mn1/3Co1/3O2 or LiNi0.8Co0.15Al0.05, have conductivities of 10^-4To 10^-2S/cm, conductivity of more than 5.10 in the carbon-deposited positive electrode material of the present invention^-2S/cm, preferably more than 10^-1S/cm。

This is why a further object of the invention is a positive electrode for a lithium secondary battery comprising at least one oxide (powder conductivity σ ox) and at least one carbon-deposited positive electrode material (powder conductivity σ carbon) obtained by the process of the invention, having a powder conductivity ratio (σ _ carbon/σ _ ox) in the range of 1 to 10⁴Preferably in the range of 10 to 10³。

In non-limiting examples of oxide positive electrodes, oxide positive electrodes that can be used include LiCoO₂、NMC111(LiNi_1/3Mn_1/3Co_1/3O₂)、NMC433、NMC532、NMC622、NMC811、NCA(LiNi_0.8Co_0.15Al_0.05)、LiNi_0.5Co_0.5O₂、LiNi_0.5Mn_1.5O₄、LiMn₂O₄、LiMn_1.9Al_0.1O₄、LiNi_0.43Mn_1.57O₄Lithium-and manganese-rich layered oxides xLi₂MnO₃·(1-x)Li(Ni,Mn,Co)O₂(x is more than or equal to 0 and less than or equal to 0.15) and Li lacking lithium_1-x(Ni,Mn,Co)O₂、LiNiO₂Stable LiNiO₂Base cathode material (e.g., AM-7platform developed by CAMX Power LLCC Co., Ltd.), Li_xMg_yNiO₂(0.9<x<1.3，0.01<y<0.1，0.91<x+y<1.3) grain boundary Co-rich Li_1.01Mg_0.024Ni_0.88Co_0.12O_2.03Or Li_1.01Mg_0.023Ni_0.93Co_0.07O_2.03Ni-rich layered composite oxide Li (Ni)_1-y-zCo_yMn_z)O₂(1-y-z ≧ 0.8), and also a core-shell structure or a core-shell structure having a concentration gradient distribution, for example, the core is Li_xMg_yNiO₂(0.9<x<1.3,0.01<y<0.1，0.91<x+y<1.3) and the shell is Li_aCo_bO₂(0.7<a<1.3,and 0.9<b<1.2) core-shell Structure, the core being nickel-rich Li (Ni)_0.89Co_0.01Mn_0.1)O₂And the shell is Ni-deficient Mn-rich Li (Ni)_0.61Co_0.09Mn_0.3)O₂Full concentration gradient distribution (FCG) Li (Ni)_0.65Co_0.08Mn_0.27)O₂Or Li (Ni) of FCG_0.77Co_0.12Mn_0.11)O₂. The oxide positive electrode may also have a coating layer, such as a ceramic coating, e.g. Al₂O₃、AlF₃、LiAlF₄、ZrO₂And TiO₂(ii) a Such as a functionalized organic coating, e.g., silicone. Coating can be achieved by, for example, liquid phase, sol gel, mechanical processes, sputtering, and atomic layer deposition.

The carbon-deposited positive electrode material-coated oxide positive electrode can be obtained during pre-mixing with a suitable mixing technique, or during preparation of the electrode coating.

The carbon-deposited positive electrode material may also be mixed with any other positive electrode active material, preferably with a lithium-containing metal composite oxide, in any proportion, with the aim of obtaining a performance that may be more balanced than any of the compounds alone. The low-sulfur high-conductivity carbon-deposited cathode material of the present invention is particularly useful for lithium secondary batteries using such cathode materials, as well as preferred embodiments.

For example, the C-LiFePO of the present invention₄Can be blended with NMC811 (50 wt% of the total positive electrode material content) for the development of SLI (pneumatic-lighting-ignition) lithium secondary batteries with high energy density, high power, improved cycle life, good low temperature performance and safety. The C-LiFePO of the invention₄It can also be blended with NMC622 (20 wt% of total positive electrode material content) for the development of a lithium secondary battery with improved high temperature cycle performance with improved charge-discharge pulse power performance (measured at lower ASI value) at high energy density, low state of charge (SOC), which is applied to PHEVs. Meanwhile, the C-LiFe of the invention_0.3Mn_0.7PO₄Can react with Li (Ni)_0.45Co_0.1Mn_1.45)O₄(50 wt% of the total positive electrode material) for the manganese oxide dissolution stability and higher discharge rate (more than 1C, relatively pure C-LiFe)_0.3Mn_0.7PO₄) Development of a lithium secondary battery having improved lower energy density, power density, tap density, and high-temperature cycle performance, which is applied to the 3C market.

Another object of the present invention is a lithium secondary battery composed of at least two electrodes and at least one electrolyte, characterized in that at least one of the electrodes, preferably the positive electrode, contains at least one carbon-deposited alkali metal polyoxoanion according to the invention.

Non-limiting examples of the lithium secondary battery include a lithium metal secondary battery, a lithium ion secondary battery, a lithium metal polymer secondary battery, and a lithium ion polymer secondary battery.

The method of manufacturing the positive electrode according to the present invention is not particularly limited, and may be performed using any conventional method known in the art. In one embodiment, the positive electrode of the present invention is manufactured by applying a positive electrode slurry comprising at least one carbon-deposited alkali metal oxyanion on a current collector, and then drying the applied slurry. In this case, a small amount of a conductive agent and/or a binder may be added. The positive electrode can also be prepared by drying the mixed and/or coated components, including extrusion, compaction, machining, lamination, spraying, and electrospray techniques.

In one non-limiting embodiment, the conductive agent is a carbon material such as, but not limited to, carbon particles, carbon fibers and carbon nanofibers, vapor grown carbon fibers, carbon nanotubes, graphene oxide, or any of their derivatives, including organic functional grafts (e.g., carboxylate, sulfonic acid, phosphonate ionic groups) to aid in dispersion, and mixtures of any of the above.

According to an advantageous method, the electrolyte is a polar liquid which is immobilized in a microporous separator and contains one or more metal salts in solution. Preferably, at least one of these metal salts is a lithium salt. In another embodiment, the electrolyte is a polymer that is solvated or insolubilized, and optionally plasticized or gelled in solution by a polar liquid containing one or more metal salts.

Polymers for bonding electrodes or as electrolytes, advantageously polyethers, polyolefins, polyesters, polymers based on acrylic esters, styrene, ethylene oxide, propylene oxide, vinyl or vinyl ether units, polymers based on acrylonitrile, polymers containing vinylidene fluoride (CF)₂＝CH₂) Hexafluoropropene (CF)₂＝CF-CF₃) Or trifluoroethylene (CF)₂CHF) monomers, and any derivatives thereof.

According to another advantageous method, at least one negative electrode is metallic lithium, a lithium alloy, in particular of aluminum, antimony, zinc, tin, possibly a mixture of lithium oxide and a nano-molecule, or a carbon-based intercalation compound, in particular synthetic or natural graphite, or a dinitrogen compound of lithium and iron, cobalt or manganese, or a silicon-based intercalation compound, optionally intercalated in a carbon matrix, or a lithium titanate (Li)₄Ti₅O₁₂) And any derivatives thereof.

The electrolyte of a lithium secondary battery contains a solvent comprising ethylene carbonate or propylene carbonate, vinyl fluoride carbonate, vinylidene fluoride carbonate, bis (2,2, 2-trifluoroethyl) carbonate,

methyl

2,2,3,4,4, 4-hexafluorobutyl carbonate, vinyl meta carbonate, and also alkyl carbonates having 1 to 4 carbon atoms, dimethyl carbonate, γ -butyrolactone, methyl propionate, methyl acetate, methyl butyrate, ethyl difluoroacetate, ethylene sulfite, vinyl sulfate, tris (trimethylsilyl) phosphite, tetraalkylsulfonamides, and also α - ω dialkyl ethers of mono-, di-, tri-, tetra-or oligo-ethylene glycols having a molecular weight of less than or equal to 5000, and also sultones, such as propane sultone, and mixtures of any of the above solvents.

The electrolyte typically also contains LiPF₆Which is wholly or partially substituted with an anionic salt, preferably a lithium salt, thereby improving the performance of the lithium secondary battery, particularly safety, low-temperature performance, high-temperature cycle performance, suppressing increase in internal resistance, and promoting formation of a negative electrode passivation layer. The lithium salt is preferably selected from boron bisoxalateLithium salt, LiPO₂F₂、LiN(SO₂F)₂LiN (SO2F) (SO2CnF2n +1) (n is 1-4, preferably 1 and 2), LiN (SO₂CnF_2n+1)(SO₂C_mF_2m+1) (n and m are each 1 to 4), a reactive anion and a polymer containing the same, for example, without any limitation, styrene-SO₂N(Li)SO₂C_nF_2n+1(n is 0 to 4, preferably 0 to 2). LiPF is not used except for lithium metal polymer batteries₆May be substituted with 1 to 30 mol% of those salts, preferably 5 to 25 mol%, more preferably 10 to 20 mol%.

Preferably, LiPF₆The substitution being selected from LiPO₂F₂、LiN(SO₂F)₂、LiN(SO₂F)(SO₂CF₃)、LiN(SO₂CF₃)₂、LiN(SO₂C₂F₅)₂More preferably from LiPO₂F₂And LiN (SO)₂F)₂More preferably LiN (SO)₂F)₂。

In the high temperature test of the lithium ion secondary battery in which the carbon-deposited positive electrode material of the present invention is mixed with the high voltage lithium-containing metal composite oxide, which contains at least 95 at% of one metal selected from the group consisting of nickel, cobalt, manganese and mixtures thereof, the inventors have realized that excessive sulfur impurities may change the properties of the electrolyte in some cases, negatively affecting the gassing and impedance of the electrode. The electrolyte contains at least one Fe₂PO₂Or FSO₂LiPF substituted by delocalized anionic portion of radical₆In particular LiPO₂F₂And LiN (SO)₂F)₂。

This is why another object of the present invention is a lithium ion secondary battery comprising at least one lithium-containing metal composite oxide, and at least one carbon-deposited positive electrode material obtained by the method of the present invention, which is used for producing a lithium ion secondary battery with improved high-temperature electrochemical properties. Comprising at least 95 at% of a metal selected from the group consisting of nickel, cobalt, manganese and mixtures thereof, wherein the electrolyte comprises up to 30% of at least one metal selected from the group consisting of LiPO₂F₂And LiN (SO)₂F)₂Lithium salt substituted LiPF of₆(ii) a Meanwhile, at least one carbon-deposited cathode material obtained by the method of the present invention has a carbon content of less than 2.5 wt% and a sulfur content of less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, and still more preferably less than 20 ppm.

This is why a further object of the present invention is a lithium ion secondary battery comprising at least one lithium-containing metal composite oxide, and a graphene-like carbon-deposited positive electrode material obtained by the method of the present invention, which is used for producing a lithium ion secondary battery with improved high-temperature electrochemical properties. Comprising at least 95 at% of a metal selected from the group consisting of nickel, cobalt, manganese and mixtures thereof, wherein the electrolyte comprises up to 30% of at least one metal selected from the group consisting of LiPO₂F₂And LiN (SO)₂F)₂Lithium salt substituted LiPF of₆(ii) a Meanwhile, the graphene-like carbon deposition cathode material obtained by the method has 1-8 layers of graphene-like carbon deposition, and the sulfur content of the graphene-like carbon deposition cathode material is less than 80ppm, preferably less than 60ppm, more preferably less than 40ppm, and further preferably less than 20 ppm.

Further, although the outer shape of the secondary battery obtained according to the above-described method is not limited to any particular shape, it may be a cylindrical shape, a polygonal shape, a soft pack, or an advantageous shape.

All compositions and/or methods of the present disclosure and claims can be made and executed without undue experimentation in light of the present disclosure. While the compositions and methods of this invention have been described in terms of preferred embodiments, it will be apparent to those of skill in the art that variations may be applied to the compositions and/or methods and in the steps or in the subsequent steps of the method described herein without departing from the concept, spirit and scope of the invention. All such similar substitutes and modifications apparent to those skilled in the art are deemed to be within the spirit, scope and concept of the invention as defined by the appended claims.

All references made before and after this document are incorporated by reference.

Suitable methods for determining various properties and parameters of the products described herein are set forth in more detail below.

The measuring method comprises the following steps:

the BET area is determined in accordance with DIN ISO 9277.

The particle size distribution is determined here by laser diffraction using a laser particle sizer of the marvin type Mastersizer S. To determine the PSD, a small sample of carbonaceous material is mixed with a few drops of humectant and a small amount of water. The sample thus prepared was added to the sample holder of the instrument (Mastersizer S), and after 5 minutes of sonication at 100% intensity, the pump speed and stirring speed were set at 40% and the measurement was started. Reference: ISO 13320(2009)/ISO 14887

The carbon content can be measured by the so-called LECO method using an LECO CR12 carbon analyser from LECO (St. Joseph, Mich.) or by ELTRA measurements using a C/S analyser model ELTRA CS 2000.

The sulphur content was determined using a C/S analyser, model ELTRA CS 2000.

The water content is determined by Arizona instruments under the model number

Vapor

Instrumental determination of XL.

Raman analysis was performed by 632.8nm HeNe laser using a micro-Raman spectrometer from LabRAM-ARAMIS, HORIBA. I is_D/I_GThe ratio is based on the ratio of the so-called D and G peak intensities. These peaks are characteristic peaks of the carbon material and are respectively 1350cm^-1And 1580cm^-1Location.

The magnetic impurity content test consisted of charging 150g of carbon-deposited positive electrode material into a clean 1 liter plastic bottle, adding 400g of isopropanol, and then adding a thoroughly cleaned Fe-Nd-B bar magnet of about 1.5cm diameter and about 5cm length coated with Teflon over 5000 gauss strength. The plastic bottle was then sealed and placed on a roller and rolled at 100rpm for 30 minutes. Thereafter, the magnetic rod was removed from the bottle without contact with contaminating substances, and transferred to a sealable, clean 50ml PP or PE tube after a simple wash with isopropanol. The bar magnets were further rinsed with isopropanol in the test tubes, finally filled and sealed with isopropanol and then placed in an ultrasonic bath and treated for 20min at an ultrasonic frequency of at least 50kHz and at a specific ultrasonic power of 20W to 40W per liter of water, so as to clean the surface of the bar gently and thoroughly without breaking the teflon coating. After rinsing the bar magnet with isopropanol in the tube, the tube was again treated in an ultrasonic bath for 20min for final rinsing, and then the isopropanol was decanted. The purpose of this treatment is to remove all paramagnetic lithium transition metal phosphate particles attached to the magnetic rods or particles by surface action, but not to remove diamagnetic contaminant particles that are tightly attached to the magnetic rods, while not exposing the magnetic rods to avoid contamination of the magnetic particles from the environment. The tube with the magnetic rod therein was then heated to reflux with 4.5ml of a mixture of 35% hydrochloric acid and 1.5ml of 65% nitric acid at 80-90 ℃ for 2 hours. After cooling, the magnetic rod was removed from the extract and rinsed into the tube with demineralized water and finally filled to the 50ml mark with demineralized water. The iron content of the extract was then determined by ICP-OES by adding an appropriate diluent and expressed in ppm or ppb with respect to 150g of the starting sample.

The compacted density and the powder resistivity were determined simultaneously on a tablet press of Mitsubishi MCP-PD51 type. The instrument was equipped with a Loresta-GP, MCP-T610 impedance meter mounted in a nitrogen glove box to avoid potential interference with oxygen and humidity. The hydraulic operation of the tablet press was carried out with a hand operated hydraulic press Enerpac PN80-APJ (maximum 10000psi/700 bar).

4g of the sample of the invention was measured under the set-up conditions recommended by the manufacturer of the above-described apparatus.

The powder resistivity was calculated according to the following formula:

powder resistivity [ Ω · cm ] ═ resistance [ Ω ] × thickness [ cm ] × RCF

Where the RCF value is the value determined by the instrument, each sample has been tested according to the manufacturer's recommendations.

The compacted density is calculated according to the following formula:

r is the diameter of the sample piece

The HPPC (Hybrid pulse Power Capacity) Test is an internationalized standard method, which is specified by the United states department of energy (DOE) (FreedomCAR Battery Test Manual for Power-Assist Hybrid Electric Vehicles, DOE/ID-11069,2003).

The invention will be further illustrated by the following non-limiting examples.

Examples

Comparative example 1

In a relaxation-resistant MiniCer model stirring mill connected with a circulating tank and filled with 400 mu m yttrium-stabilized zirconia balls, deionized deoxygenated water is used as a carrier fluid, and nano-grinding carbon is used for depositing LiFePO₄(BeiDainishui Technischen industries, Ltd., product No. P600A, carbon content 1.37 wt%; D₉₀4.9 μm). In order to avoid metal contamination, the agitator mill is equipped with a ceramic grinding chamber. The water contained 0.5 wt% of a surfactant of tween 20 (polyoxyethylene sorbitan monolaurate, a product of Croda) in relation to P600A. After 120 minutes of milling at a milling energy of 0.46kWh per kg P600A (heat removed by cooling water from the outer wall of the milling assembly), samples of the slurry (AC-1) were measured with a PSD analyzer to give a LiFePO having an average particle size of 184nm₄The particles, which were initially carbon-deposited during the nano-milling process as evidenced by TEM analysis, were abraded from the surface of LiFePO4 and were present in the material as carbon residue. Nanocrystallized LiFePO₄After evaporation of the water under vacuum rotation, it was dried in a vacuum oven at 100 ℃ overnight and then deagglomerated in a laboratory rotary mill (Fritsch Pulverisette 14 fitted with an "iron-free" conversion fitting).

A liquid electrolyte battery having a lithium metal negative electrode fabricated as disclosed in example 5, the positive electrode comprising LiFePO₄the/binder/Ketjen black EC-300J content was 70/10/20 wt%, in order to ensure that it contained nano-sized low conductivity LiFePO₄The permeability of the conductive network of (a) necessitates the addition of more high surface area carbon. The loading of the positive electrode of the cell was 2.77mg/cm²Per cm, in²Is expressed as mg of active material on the positive electrode area. At 25 ℃ C/25When electrochemical measurement is carried out, the reversible specific capacity of 122mAh/g is realized.

30g of nano LiFePO₄The mixture was treated as disclosed in US2002/0195591a1 (example 2) by placing in a rotatable tube furnace (zhenzhou CY scientific equipment corporation, model CY-R1200X-100IC), passing dry argon through the tube, heating to 200 ℃ at a rate of 10 ℃/min, maintaining the temperature for 30min, and then passing a mixed gas of 94% argon and 6% propylene through the tube to perform a thermal CVD process. Heating to 675 ℃ at the speed of 10 ℃/min, and then preserving the heat for 1 hour to obtain carbon deposition LiFePO₄Carbon content was 2.65 wt.% as measured by LECO method.

A liquid electrolyte battery having a lithium metal negative electrode fabricated as disclosed in example 5, the positive electrode composition being C-LiFePO₄88/6/6 wt% binder/carbon, load 4.6mg/cm². When electrochemical measurement is carried out at 25 ℃ and C/5, the initial specific discharge capacity of 158mAh/g is realized. A liquid electrolyte lithium ion battery (cell 1) was also assembled with a carbon negative electrode and the same positive electrode in the manner as disclosed in example 5.

Comparative example 2

The P600A nanomilling procedure was repeated as described in comparative example 1, but using isopropanol instead of liquid water as the carrier liquid, to obtain a slurry AC-2 in which LiFePO was present₄D of the particles₅₀Is 186 nm. Followed by a thermal CVD process with propylene gas to form carbon deposited LiFePO₄Wherein the carbon content is 2.73 wt%.

Liquid electrolyte battery with lithium metal as negative electrode assembled according to the method disclosed in example 5, with C-LiFePO when the positive electrode is composed₄88/6/6 wt% binder/carbon, load 4.6mg/cm². When electrochemical measurement is carried out at 25 ℃ and C/5, the initial specific discharge capacity of 157mAh/g is realized. A liquid electrolyte lithium ion battery (cell 2) was also assembled with a carbon negative electrode and the same positive electrode in the manner as disclosed in example 5.

Then, the batteries 1 and 2 are tested in a static cycle mode at the temperature of C/4 and 60 ℃ and between 2 and 3.6V, and the cycle curve is shown in figure 1. The results show that C-LiFePO containing a nano-milling step of isopropanol (curve A) instead of water (curve B)₄Capacity fade at 60 ℃ is reduced。

Example 1

Weighing FePO₄·2H₂O (200g, from Changshahikang chemical Co., Ltd., Battery grade, D)₉₀2.92 μm), Li₂CO₃(molar ratio 2: 1, from Chengdu chemical Co., Ltd., Battery grade, D)₉₀2.84 μm), Brij 35 (in FePO)₄·2H₂3.5 wt% of O from Croda), and deoxyisopropanol (in FePO)₄·2H₂50 wt% of O) was added to a cylindrical zirconia container containing 5mm zirconia balls, wherein the weight ratio of balls/powder was 2: 1. the ball milling was carried out in a Retsch model PM100 planetary ball mill at 400rpm under argon atmosphere for 30 minutes. After milling, the slurry was evaporated to dryness at 80 ℃. The mixture was then heated to 600 ℃ at a heating rate of 10 ℃/min in a tube furnace (zheng zhou CY scientific instruments) charged with a dry oxygen-depleted nitrogen gas stream and held at that temperature for 60min, as disclosed in US2002/0195591a 1.

A carbon-deposited material having a carbon content of 0.38 wt% (measured by LECO) and a composition comprising 75.2 wt% LiFePO as determined by XRD analysis was obtained₄The residual molar ratio is 1: 1 Li₃PO₄And Fe₃(PO₄)₂To phase use

The spectrum was analyzed without Fe (III). LiFePO₄Can be expressed in terms of conversion, i.e. the LiFePO obtained₄The conversion in this case is 75.2% divided by the theoretical amount. This material is referred to as material-a 1.

The synthesis process is repeated, and the precursor is ground in a planetary ball mill of Retsch model PM100 for 60min in a dry method under the nitrogen atmosphere and the rotating speed of 300 rmp. The ball mill is filled with a material with a ball material ratio of 3: 1, 10mm tungsten carbide ball. Then, after a similar heat treatment process, a carbon deposited material was obtained, the carbon content of which was measured by LECO to be 0.33 wt%, and LiFePO thereof was measured by XRD analysis₄Was 75.2 wt%, and a molar ratio of 1: li3PO4 and Fe of 1₃(PO₄)₂And (4) phase(s). The material is calledMaterial-a 1-1.

A liquid electrolyte battery was assembled with a lithium metal negative electrode as disclosed in example 5, the positive electrode consisting of material-a 1/binder/carbon 88/6/6 wt% with a loading of 4.5mg/cm². When measured electrochemically at 25 ℃ C/5 (assuming a capacity equal to LiFePO)₄Theoretical capacity of (d), an initial specific discharge capacity of 67mAh/g is achieved, and the median discharge voltage is 2.85V. The results indicate that the material-al has poor electrochemical properties.

Material-a 1 was nanometerized in water with water as the carrier liquid, as in comparative example 1, using 300 μm yttrium-stabilized zirconia balls (tween 20 as surfactant, nanomilling for 90 minutes, milling energy 0.48kWh per kg material-a 1, resulting in non-carbon-deposited nanometerized particles with average primary particle size of 186nm, slurry a), material-a 1 was also nanometerized in isopropanol with isopropanol as the carrier liquid, as in comparative example 2, using 300 μm yttrium-stabilized zirconia balls (tween 20 as surfactant, nanomilling for 90 minutes, milling energy 0.44kWh per kg material-a 1, resulting in non-carbon-deposited nanometerized particles with average primary particle size of 192nm, slurry B). In both cases, from LiFePO₄The abraded carbon on the surface remains in the component in the form of carbon residue.

Slurry a and slurry B were spray dried with compressed nitrogen through a two fluid nozzle (shanghai yachen instrument, YC-015A model spray dryer fitted with an inert ring) at a gas inlet temperature of 200 ℃ and a gas outlet temperature of 96 ℃ during the spray drying process. Then, vapor phase carbon deposition was performed on the nanoparticles of the spray-dried slurries a and B to obtain samples C-a and C-B as described in comparative example 1, but here a mixture of 97% nitrogen and 3% acetylene gas was used instead of a propylene/argon mixture. Finally, carbon-deposited olivine LiFePO having the carbon deposition amounts (measured by LECO) shown in Table 1 was obtained₄(determined by XRD). The amount of carbon deposition can be obtained by performing LECO measurement before and after thermal CVD, and thus the amount of residual carbon in the material-a 1 can be easily corrected.

TABLE 1

Sample (I)	C-A	C-B
			C-deposition wt%	1.25	1.15
I_D/I_GRatio of	0.84	0.78

Sample B (spray dried material nano-sized in isopropanol as carrier liquid-a 1) was repeatedly subjected to a thermal CVD process in nitrogen containing different concentrations of ethylene, propylene, vaporized benzene at different gas flow rates. LECO measurement shows that C-LiFePO with carbon deposition of 0.21-2.49 wt% is obtained₄。

A liquid electrolyte battery was assembled with a lithium metal negative electrode as disclosed in example 5, the positive electrode having a material-a 1/binder/carbon of 88/6/6 wt%. The electrode capacity and initial specific discharge capacity (first discharge) obtained by the C/5 electrochemical measurement are shown in Table 2. A liquid lithium ion battery (cell 3 of sample C-a, cell 4 of sample C-B) with carbon as the negative electrode and the same positive electrode was also assembled as disclosed in example 5. Then, the batteries 3 and 4 are tested in a static cycle mode at the temperature of C/4 and 60 ℃ and between 2 and 3.6V, and the cycle curve is shown in figure 2. The results show that C-LiFePO containing a nano-milling step of isopropanol (curve A) instead of water (curve B)₄The capacity fade at 60 ℃ is reduced.

The same procedure for the synthesis of material-a 1 was repeated with the appropriate precursors and stoichiometric ratios, by subsequent nanomilling anda thermal CVD step to obtain C-LiFe_0.97Mg_0.03PO₄(FePO₄·2H₂O、Li₂CO₃And MgHPO₄Conversion of 74%, carbon content 0.35 wt.%), C-LiFe_0.3Mn_0.7PO₄(Fe_0.3Mn_0.7PO₄·2H₂O、Li₂CO₃Conversion 75%, carbon content 0.38 wt.%), C-LiMnPO₄(Mn₃(PO₄)₂、Li₃PO₄Conversion 69%, carbon 0.27 wt.%.)

TABLE 2

Sample (I)	C-A	C-B
			Battery with a battery cell	3	4
Load (mg/cm)²)	4.8	4.7
			1^stDischarge capacity (mAh/g)	162	163

Material-a 1-1, obtained by dry grinding of the precursor, was processed as material C-B (nanomilling in isopropanol carrier liquid, spray drying, followed by thermal CVD in an acetylene carbon source), so as to obtainTo obtain a material with similar characteristics, and further used for a liquid electrolyte lithium ion battery with a carbon cathode (the loading of the anode is 4.8 mg/cm)²，1^stDischarge capacity of 164 mAh/g). The battery is statically circulated under the conditions of C/4, 60 ℃ and 2-3.6V. After 400 weeks of cycling, the precursor was subjected to a dry milling step to obtain a positive electrode material having a capacity 7% lower than the initial discharge capacity than that of the wet milled material.

Example 2

The procedure for the synthesis of material-a 1 was repeated as in example 1, with different batches of FePO₄·2H₂O (500 g FePO for each synthesis)₄·2H₂O), then nanomilled with 200 μm yttrium-stabilized zirconia balls in an alcohol group for 90min, followed by spray drying of the suspension.

For each batch, 300g of nano-material was placed in a furnace tube of a rotary kiln (Zhengzhou CY scientific instruments, model CY-R200X-100IC), dry nitrogen gas was introduced into the furnace tube, the temperature was raised to 200 ℃ at a heating rate of 10 ℃/min, the temperature was maintained for 60min, and then a mixed gas of vaporized benzene and argon gas (containing 3% by volume of benzene) was continuously introduced. Heating to 640 ℃ at the speed of 20 ℃/min, and then preserving the heat for 1 hour to obtain carbon deposition LiFePO₄. The sulfur content and carbon content of each batch were measured by combustion analysis using a carbon/sulfur analyzer (LECO corporation), and the results are shown in table 3.

Liquid electrolyte batteries (batteries 5a to 9a and batteries 5b to 9b) with carbon as a negative electrode were assembled in the manner disclosed in example 5, wherein C-LiFePO of Table 3 was used₄The sample is used as a positive electrode material, and the positive electrode is composed of C-LiFePO₄The binder/carbon ratio was 88/6/6 wt%. The batteries 5a to 9a are subjected to a high-temperature storage test, and can accelerate the aging of the battery assembly and perform the influence evaluation of the key parameters.

The specific initial discharge capacity before storage was determined by electrochemical measurement at C/5, 25 ℃ as shown in Table 3. Then, after charging to 3.6V at 25 ℃ C/10, the cell was stored at 85 ℃ for 3 days, and after storage, the discharge capacity was recovered at 25 ℃ C/5 rate, and the results are shown in Table 3.

TABLE 3

Sample (I)	C1	C2	C3	C4	C5
						Nano average primary particle diameter	140	142	141	139	142
C-LiFePO₄D₅₀(μm)	7.2	7.4	7.6	7.3	7.5
						C-LiFePO₄Sulfur content (ppm)	745	339	71	34	13
C-deposition wt. -%)	1.26	1.11	1.02	1.03	1.04
						S/C ratio (%)	5.91	3.05	0.70	0.33	0.12
BET	7.8	6.8	6.2	6.1	6.1
						Battery with a battery cell	5a/b	6a/b	7a/b	8a/b	9a/b
Load (mg/cm)²)	4.7	4.6	4.6	4.6	4.7
						Specific capacity (mAh/g) before storage	162	162	163	163	164
Recovery capacity after storage (mAh/g)	93	102	142	144	146

The results show that the C-LiFePO of the invention₄A very low level of sulfur impurities is ensured for C-LiFePO₄The key point of excellent electrochemical performance.

For sample C5, the SEM image of the nanosized primary particles is shown in FIG. 3, the secondary agglomerates of primary particles C-LiFePO₄Is shown in fig. 4, and a TEM image of the carbon deposition is shown in fig. 5.

The carbon deposition purity of sample C5 was over 99.9% by raman analysis.

The cells 5B-9B are statically cycled at C/1, 60 ℃ and 2-3.6V, and the cycling curve is shown in FIG. 6 (curve A is sample C5, B is C4, C is C3, D is C2, and E is C1). This result demonstrates that in order to obtain the carbon-deposited cathode material of the present invention with excellent high-temperature performance, the sulfur impurity content in the material must be extremely low.

All samples obtained in this example had a moisture content of less than 100ppm and were further dried under vacuum at 300 ℃ for 48 hours to a moisture content of less than 10ppm and then exposed to an atmosphere of 10% relative humidity in a humidifier (Owlstone, USA) while monitoring the sample weight. The results of moisture content after exposure to a humid atmosphere for 120s are shown in table 4.

TABLE 4

Sample (I)	C1	C2	C3	C4	C5
						Moisture content (ppm)	411	256	81	63	43

The results show that the C-LiFePO of the invention₄Very low levels of sulfur impurities are beneficial to limit the water absorption of the material. Without being bound by any theory, the inventors believe that the hygroscopic substance associated with the presence of the sulfur impurity increases the hydrophilicity of the surface.

150g C-LiFePO was added to 400ml of isopropanol in the presence of a Teflon coated Fe-Nb-B bar magnet₄Stirring the sample, pre-mineralizing the magnetic rod aspirate in an acidic medium, analyzing the magnetic substance content in the aspirate by ICP-OES, thereby determining C-LiFePO₄Magnetic impurities of the sample. Selected C-LiFePO₄The magnetization of the sample is determined from the M-H curve. The magnetic impurities are expressed in the form of iron in ppb of the total amount of the sample, and the spontaneous magnetization is shown in Table 5.

TABLE 5

Sample (I)	C1	C2	C3	C4	C5
						Magnetic impurities (ppb)	732	509	133	68	42
Magnetization (emu/g)	0.019	/	0.0013	/	0.0006

The results show that the C-LiFePO of the invention₄Very low levels of sulfur impurities are beneficial to limit the magnetic impurity content.

Containing 5 wt.% solid C-LiFePO₄The Zeta potential measurements of the aqueous suspensions of the samples at neutral pH were carried out using Zeta Probe (Colloidal dynamics, USA) and the results are given in Table 6.

TABLE 6

Sample (I)	C1	C2	C3	C4	C5
						Zeta potential (mV)	-32	-29	-14	-9	-5

The results show that the C-LiFePO of the invention₄The very low and medium levels of sulfur impurities are beneficial in reducing the absolute value of the Zeta potential of the carbon deposition materials of the present invention.

The synthesis process of the carbon deposition material with different sulfur impurity contents is repeated by using a proper precursor and a stoichiometric ratio to obtain the C-LiFe_0.97Ca_0.03PO₄(FePO₄·2H₂O、Li₂CO₃And CaHPO₄Carbon deposition amount is 0.86-1.01 wt.%, sulfur content is 10-686 ppm), C-LiFe_0.29Mn_0.68Zn_0.03PO₄(Fe_0.29Mn_0.68Zn_0.03PO₄·2H₂O、Li₂CO₃Carbon deposition of 0.91-0.96 wt.%, sulfur content of 9-734 ppm), C-LiMnPO₄(Mn₃(PO₄)₂、Li₃PO₄Carbon deposition amount of 0.89-0.96 wt.%, and 12-603 ppm sulfur content). High temperature storage and cycling, water absorption measurements, magnetic impurity levels, spontaneous magnetization, and Zeta potential results also conclude that sulfur impurity levels less than 80ppm and preferably an S/C ratio less than 0.8% are all beneficial to the performance of the carbon deposition materials of the present invention.

As a comparative experiment, ten batches of LiFePO were prepared₄0.3M aqueous LiOH & H2O solution was added to a solution of 0.1MFeSO4 & 7H2O and 0.1M H3PO4 in 50 vol% water and 50 vol% DMSO at 25 ℃ with stirring. Then raising the temperature of the solution to the boiling point of the solution, 108 to 110 ℃, and LiFePO₄Precipitation was initiated. After one hour, the precipitate was filtered and washed with water. Finally, heat treatment is carried out, and the dried precipitate is subjected to weak reduction N₂/H₂(95/5) treating the mixture at 500 ℃ for 3 hours in a gas stream. The ten resulting samples were then subjected to a thermal CVD step in a rotary kiln (Zhengzhou CY scientific Equipment, model CY-R200X-100 IC). Dry nitrogen is introduced into a furnace tube, the furnace tube is heated to 200 ℃ at the speed of 10 ℃/min, the temperature is kept for 60min, and then mixed gas of vaporized benzene and argon (containing 3 percent of benzene by volume) is continuously introduced. Heating to 640 ℃ at the speed of 20 ℃/min, and then preserving heat for 1 hour to obtain carbon-deposited LiFePO₄. The sulfur content and carbon content of each batch were determined by combustion analysis using a carbon/sulfur analyzer (LECO). The obtained C-LiFePO has carbon deposition of 0.92-1.08 wt.% and sulfur impurity content of 24-682 ppm₄Sample batches. The results of the high-temperature storage and cycling tests also conclude that a sulphur impurity content of less than 80ppm and preferably an S/C ratio of less than 0.8% are applied to carbon deposits LiFePO obtained by a thermal CVD process using a gaseous carbon source₄The performance of (2) is advantageous.

Example 3

As in example 1, with high purity FePO₄·2H₂O (100kg), Battery grade Li₂CO₃(molar ratio 1: 2), Pluronic P-123 (relative to FePO)₄·2H₂O2 wt.%; polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer, manufactured by BASF) the procedure for synthesizing the material-a 1 was repeated. The precursors were milled in 200L degassed methanol using a MasterMill model 18 basket mill (purge tolerant). After the solvent is evaporated, theThe material (called material-a 3) was placed in a ceramic crucible, placed in a roller kiln charged with dry oxygen-free nitrogen, treated at 600 ℃ for 60 minutes, then cooled in nitrogen and stored.

A carbon-deposited material having a carbon content of 0.35% by weight (measured by LECO) and a composition containing 73.7% by weight of LiFePO as determined by XRD analysis was obtained₄The residual molar ratio is 1: li3PO4 and Fe of 1₃(PO₄)₂To phase use

The spectrum was analyzed without Fe (III).

A2 Kg batch of material-a 3 was further nanomilled in degassed isopropanol carrier liquid using a purge resistant Alpha 8Neos agitator mill with attached recycle tank. To avoid metal contamination, the agitator mill was equipped with a ceramic milling chamber filled with 100 μm yttrium-stabilized zirconia balls. The isopropyl alcohol contained 1 wt.% Carbowax polyethylene glycol 4000 surfactant (product of dow chemical) relative to the total amount of P600A. The nano-milling was carried out for 60 minutes at a milling energy of 0.34kWh per kg of material-a 3, and the heat was removed by cooling water attached to the outer wall of the milling assembly.

The slurry was spray dried using compressed nitrogen in a closed loop MOBILE MINOR dryer (product of GEA Niro) equipped with COMBI-NOZZLE NOZZLEs. During the spray drying process, the gas inlet temperature was 275 ℃ and the gas outlet temperature was 105 ℃. The spray dried material was then dried under vacuum at 100 ℃ for 24 hours and stored under nitrogen. The vapor phase carbon deposition operation was continuously carried out in a rotary kiln. The rotary kiln is equipped with a carbon furnace tube, mixed gas of propylene and nitrogen (containing 10% by volume of propylene) is continuously introduced, the temperature of a heating zone is 640 ℃, spray-dried materials are input through a controllable screw feeder, and then the materials are accumulated at the outlet of a kiln protected by nitrogen, so that carbon deposition LiFePO with the characteristics shown in Table 7 is obtained₄。

TABLE 7

Sample (I)	D1
		Average primary particle size of nano-milled	92
Nano-milled particle PSD span	1.42
		C-LiFePO₄D₅₀(μm)	7.2
C-LiFePO₄Porosity (%)	26
		C-LiFePO₄Sulfur content (ppm)	29
C-deposition wt. -%)	0.95
		I_D/I_GRatio of	0.75
S/C ratio (%)	0.31
		L/D	1.05
BET(m²/g)	7.6
		Electrical conductivity (S.cm)^-1)	0.12
Water content (ppm)	82
		Magnetic impurities (ppb)	86
Tap density (g/cm)³)	1.67
		Compacted density (g/cm)³)	2.65
Initial specific capacity (mAh/g) (a)	165.6

(a) Determined by the lithium metal battery as disclosed in example 1

The spray drying experiment was repeated using a spray dryer model NL-5 (Ohkawara Kakohki Co.) equipped with RJ-5 double nozzles, and the air inlet temperature was 200 to 250 ℃ to produce secondary agglomerate particles D consisting of primary particles₅₀Between about 2 and 20 μm, and an L/D sphericity of between about 0.95 and 1.05.

Cell 10 was charged at 25C at C/5 rate and subjected to the Ragone test with static discharge at C/5, C, 5C and 10C rates, with the results shown in table 8.

TABLE 8

C-magnification	C/5	C	5C	10C
					Specific capacity of positive electrode (mAh/g)	164.8	147.9	139.2	113.6

The discharge curve at C/5 discharge rate is shown in FIG. 7.

At the temperature of minus 20 ℃, the battery is charged at the rate of C/5 and statically discharged at the rate of C/5, and the specific capacity of the positive electrode of the battery 11 is 112.1 mAh/g.

The synthesis of sample D1 was repeated, but the nanomilling process of material-a 3 was carried out in a carrier liquid of methanol and ethanol instead of isopropanol, resulting in a carbon-deposited positive electrode material with equivalent performance.

The nano-milling, spray-drying, thermal CVD process was repeated on a large amount of 2kg of the material-a 3, but process parameters such as nano-milling bead size, time, chemical composition of alcohol, effective energy, surfactant, spray-drying inlet/outlet temperature, nozzle, thermal CVD carbon source, etc. were changed to prepare C-LiFePO po with different characteristics₄。

All these experiments show that it is possible to achieve without any limitation: primary particles having an average particle diameter of 25 to 250nm, a particle diameter distribution span of less than 2.5 to 0.5, and C-LiFePO₄Carbon deposition amount of 0.2 to 2.5 wt.%, and carbon deposition I_D/I_GLess than 0.9 to 0.6, having 1 to 8 graphene-like carbon deposits, a powder conductivity of more than 5.10^-2～5.10^-1S.cm^-1Sulfur impurity content less than 80-20 ppm, magnetic impurity less than 300-50 ppb, water content less than 200-20 ppm, andthe secondary aggregate of the secondary particles has a BET of less than 11 to 5m2/g, a porosity of 5 to 40%, and D₅₀The powder compaction is more than 2.4-2.8 g/cm at the range of 2-30 mu m and the span is less than 3-1³。

Different batches of C-LiFePO used in the invention₄The battery quality as the anode material shows that 159-169 mAh/g of C/5 rate discharge capacity, 145-155 mAh/g of 1C rate discharge capacity and 130-145 mAh/g of 5C rate discharge capacity can be realized at 25 ℃; at-20 ℃, the discharge capacity at C/5 rate is 100-140 mAh/g.

The synthesis of sample D1 was repeated, but propylene as a carbon source for thermal CVD was replaced by a gas stream generated by Polyethylene (PE) cracking. The polyethylene block was cracked in a pyrolysis reactor at 600 ℃ under a stream of nitrogen. Further experiments conducted an additional reforming step in the catalytic reactor, in which the cracked polyethylene gas stream was further passed through a Y-zeolite catalyst bed at 600 c, increasing the total aromatics content from about 0.5 wt.% to about 39 wt.%. The results are shown in Table 9.

TABLE 9

Thermal CVD carbon source	PE cracking	PE cracking + reforming
			Aromatic content (wt.%) in the carbon source	0.42	39.3
C-deposit content (wt.%)	1.11	1.14
			C-Deposition I_D/I_GRatio of	0.82	0.70
C-deposit conductivity (S.cm)^-1)	0.073	0.134

The synthesis of sample D1 was repeated, and pigment carbon black FW200(Orion engineering carbon ltd) was additionally added at 32 wt% relative to the material-a before the nano-milling step. After spray drying and thermal CVD steps, the C-LiFePO obtained₄The compacted density of the powder is improved by 8.7 percent, and the lithium ion battery similar to the battery 11 shows that the specific capacity of the positive electrode is improved by 6.8 percent when the lithium ion battery discharges at the static multiplying power of C/5 at the temperature of minus 20 ℃.

The synthesis of sample D1 was repeated, with additional addition of phenyltrimethoxysilane of-30.25wt.% relative to the material-a, prior to the nanomilling step. After the spray drying and thermal CVD steps, the lithium ion battery similar to battery 10 using this material showed a 9.3% decrease in capacity fade after 2000 cycles at 2-3.6V, 60 ℃, 1C static cycling, based on the lithium ion battery using sample D1 as the positive electrode material. Repeated experiments with the additional addition of 1 wt.% Tyzor NPZ (n-propyl zirconate in n-propanol, manufactured by Dorf Ketal chemicals) showed that the capacity fade was also effectively reduced after 2000 cycles at 60 ℃.

The synthesis of sample D1 was repeated, but prior to the nanomilling step, material-a 3 was premilled for 15 minutes in a Q-03 metal-free cyclic stirred mill (manufactured by Union Process) filled with 6mm yttrium-stabilized zirconia balls. D90 was reduced from the initial 22 μm to 1.1 μm, followed by nano-milling of the slurry in a sag resistant Alpha 8Neos agitator mill for 40 minutes. Similar nanosized particles with an average particle size of 94nm were obtained, but the particle distribution span was reduced to 1.03. Furthermore, the total specific grinding energy is reduced by 28% by the pre-grinding step, while the wear of the expensive fine nano-grinding beads (determined by measuring the zirconium content in the nano-ground slurry by ICP-OES analysis) is reduced by 36%, with a good impact on the process cost. After a synthesis procedure similar to sample D1 (spray drying and thermal CVD), a Ragone test was performed with a lithium ion battery similar to cell 10 and the results showed that the nanosized particles reduced the particle size distribution span and improved the material power performance, e.g., about a 17% increase in positive electrode capacity at 10C rate discharge.

By optimizing the nanomilling process parameters (such as milling ball size, loading, material-a loading, performing multistep nanomilling, pre-milling stage, surfactant selection, nanometerized material average particle size, or milling energy), the inventors have demonstrated that it is possible to synthesize nanometerized material-a over a span of 0.3 to 3.

The synthesis of sample D1 was repeated, but the nanosized material-a 3 (effective milling energy 0.49kWh per kg of material-a 3) was recovered in a filter press, and the filter cake was dried under vacuum at 100 ℃ for 24 hours and stored under a nitrogen atmosphere. To obtain weakly agglomerated nano-sized particles having an average primary particle diameter of 81nm, and further performing a thermal CVD step at 650 ℃ in a mixed gas using benzene vapor/nitrogen as a carbon source. The obtained C-LiFePO₄Designated sample D2, with a carbon deposition content of 1.4 wt.% and a BET of 13.3m²G, sulfur content 33ppm, I_D/I_GThe ratio was 0.68 and the conductivity was 0.14S.cm^-1The compacted density is 2.44g/cm³The water content was 34ppm, and the magnetic impurity content was 96 ppb.

The synthesis process of the material-a 3 was repeated with the same precursors and the same stoichiometric ratio, and the related experiments were performed, and the subsequent nano-milling and thermal CVD processes yielded C-life0.97zn0.03po4, C-life0.3mn0.7po4, C-life0.33mn0.64mg0.03po4, C-life0.08mn0.88co0.04po4, and C-LiMnPO4, thus confirming the benefits of the carbon deposition material of the present invention.

Example 4

A hybrid electrode coating (designated coating 4.1) was prepared as disclosed in example 5. The C-LiFePO of example 3 was used₄Sample D2 and LiCoO2(LCO983HA, produced in North America, D)₅₀14.3 μm, based on95 wt.% of total positive electrode material) mixture as positive electrode active material. Positive electrode composition (LCO: C-LiFePO)₄) Binder/carbon 88/6/6 wt.%. A similar reference electrode coating (referred to as coating 4.2) was also prepared using LCO983HA only as the positive electrode active material. A mixed electrode coating (referred to as coating 4.3) having the same positive electrode composition was further prepared except that the positive electrode active material was C-LiFePO similar to sample D2 except that the sulfur content was varied to 386ppm₄(referred to as coating D3).

A liquid electrolyte lithium ion battery was assembled with carbon as the negative electrode as disclosed in example 5. The battery is tested in a static cycle at the temperature of C/1, 60 ℃ and 2.6-4.35V. The cycle curves for coatings 4.1 (curve B), 4.2 (curve a) and 4.3 (curve C) are shown in fig. 8.

The results show that the carbon deposited cathode material of the present invention is useful as an oxide cathode coating where the very low sulfur impurity levels are beneficial for maintaining excellent performance at high temperatures.

Similar cells (3) containing coating 4.1 (hybrid positive electrode) and coating 4.2 (pure LCO positive electrode) were subjected to a needle test (1m/min) at 60 ℃ after charging to 4.3V (C/10 rate), the cells with the hybrid electrode passed the test (0/3 failure), those with the pure LCO quickly ignited, and failed the test (3/3 failure).

Replacement of LCO983HA with LiCoO₂Core-shell Li1.05Mg0.025NiO2 of the coating layer (called core-shell replacement LNO, prepared according to the method of US 7381496 in example 7, 5 mol% LiCoO)₂Sample D2 and D3, 92 wt.% of the total cathode material), similar electrode coatings and their corresponding lithium ion batteries were prepared. Containing C-LiFePO₄The hybrid electrodes of samples D2 and D3 exhibited better cycling performance (static cycling test between C/1, 60 ℃, 2.8-4.3V), and the capacity fade of the hybrid cell after 300 cycles was reduced by 88% (sample D2) and 72% (sample D3) compared to the electrode using only the core-shell instead of the LNO positive electrode material.

The synthesis of sample D2 in example 3 was repeated, but the nanosized material-a 3 obtained after pressure filtration was mixed with 6 wt.% lactose in water, instead of being subjected to a thermal CVD step. After drying, byCarbon deposition is carried out in the heat treatment process of 700 ℃ for 1 hour under the nitrogen gas flow to obtain C-LiFePO₄(referred to as sample Dref) with a carbon deposition content of 1.32 wt.% and an electrical conductivity of about 10^-3And S.cm, the material is used for preparing the same mixed electrode coating and lithium ion battery.

Use of C-LiFePO, respectively₄Sample D2 and sample Dref assembled to be similar (LCO: C-LiFePO)₄) A lithium ion battery with mixed electrode coating is used for carrying out alternating current impedance test. The test shows that the discharge current multiplying power is increased under the voltage of 3.7V and the temperature of 25 ℃. The results are shown in table 10 relative to the DC impedance of a similar li-ion battery of pure LCO983HA at 3.7V, along with the conductivity ratios (σ _ carbon/σ _ ox) of sample D2 and sample Dref relative to LCO983HA in table 1.

Watch 10

C-magnification

1C

5C

10C

20C

30C

σ_carbon/σ_ox

Relative DC impedance D2 (%)

＜2

＜3

-4

-6

-22

＞10

Relative DC impedance Dref (%)

6

18

34

98

234

＜10^-1

The results show that the carbon deposition anode material of the invention is used as an oxide anode coating, is beneficial to improving the conductivity and is beneficial to improving the power characteristics of a battery using the mixed electrode.

Similar electrode coatings and their corresponding lithium ion batteries were prepared by replacing LCO983HA with NMC811 oxide positive electrode material (produced by Posco, 92 wt.% of the total positive electrode material of the hybrid electrode containing sample D2) in full concentration gradient distribution (FCG). These cells were subjected to storage tests at 85 ℃ for 3 days following the procedure disclosed in example 2 (after C/10 charging to 4.35V at 25 ℃). Compared with the electrode using pure FCGNMC811 cathode material, the mixed electrode has better storage performance, and the capacity loss of the mixed electrode after storage is reduced by 71%. With C-LiFePO₄The same storage test was conducted with sample D3 (356 ppm sulfur) in place of the mixed electrode of sample D2 (33 ppm sulfur), and the results confirmed that low sulfur impurities were beneficial. The use of FCG NMC811 after surface treatment can improve the performance of lithium ion batteries, for example by obtaining an alumina coating by atomic layer deposition (obtaining Al about 15nm thick from precursor trimethylaluminum in an intermittent fluidized bed reactor₂O₃Deposition) while also maintaining the advantages of hybrid electrodes with the very low sulfur-carbon deposition materials of the present invention in high temperature storage.

A hybrid electrode for PHEV cells was prepared as in example 5. The anode material uses C-LiFePO₄And NMC 532. Wherein C-LiFePO₄Is C-LiFePO dried with a NL-5 spray dryer (Ohkawara Kakohki Co.) as disclosed in example 3₄Sample (D)₅₀3.7um, 38ppm sulfur content), NMC532 (Ecopro) accounted for 88 wt.% of the total positive electrode material. Positive electrode composition (NMC 532: C-LiFePO)₄) Binder/carbon 88/6/6 wt.%. Meanwhile, the same reference electrode coating with pure NMC532 as the positive electrode material is prepared. Further, a mixed electrode coating having the same composition as the positive electrode except that it contains C-LiFePO in which the content of sulfur is similar except that it is 251ppm₄Sample (D)₅₀Is 3.6 μm)

HPPC pulse power characterization experiments (25 ℃, 3C, 10s charge pulses) were performed on the lithium ion batteries as disclosed in example 5. HPPC results (in. omega. cm)²Area specific impedance ASI, vs cell voltage) as shown in fig. 9, the results of the mixed electrode (low sulfur positive electrode material) and pure NMC532 electrode tests are shown on curve a and curve B, respectively, with the results for the mixed electrode of the high sulfur positive electrode material being similar to those for low sulfur. After cycling at 60 ℃ for 200 weeks (static cycling at C/1 ratio between 2.8-4.4V), HPPC tests were repeated and the results are shown on curves C (low sulfur) and D (high sulfur) for the mixed electrode in FIG. 9. The results show that very low sulfur impurity levels are beneficial for the carbon deposition cathode material of the present invention to maintain excellent performance at high temperatures, while the high conductivity of the carbon deposition improves the charge-discharge pulse power characteristics at low state of charge (SOC) due to the lower ASI values measured.

Example 5

Preparation of liquid lithium metal electrolyte battery

A lithium metal liquid electrolyte battery was prepared according to the following procedure. At least one positive electrode material of the invention, HFP-VF₂The copolymer (Kynar's HSV900, manufactured by Atochem Co.) and EBN-1010 graphite powder (manufactured by Superior graphite Co.) were ball-milled in N-methylpyrrolidone (NMP) for 10 hours with a jar mill containing zirconia balls to prepare a slurry, which was obtained from positive electrode/HFP-VF₂Graphite composition 80/10/10 weight ratio. The resulting mixture was then coated on carbon-coated aluminum foil (Exopack Ad) using Gardner equipmentManufactured by advanced Coating corporation), the coated pole pieces were vacuum dried at 80 ℃ for 24 hours and then stored in a glove box. A "button" type cell was assembled and packaged in a glove box consisting of a carbon-coated aluminum foil containing a coating of the positive electrode material of the present invention as the cell positive electrode, a lithium sheet as the negative electrode, and a separator (Celgard) 25 μ M thick soaked in a 1M LiPF6 mixed solution of EC/DEC.

Preparation of lithium ion liquid electrolyte battery

A liquid electrolyte lithium ion battery was prepared according to the following procedure. At least one positive electrode material of the invention, HFP-VF₂The copolymer (Kynar's HSV900, manufactured by Atochem Co.) and EBN-1010 graphite powder (manufactured by Superior graphite Co.) were ball-milled in N-methylpyrrolidone (NMP) for 10 hours with a jar mill containing zirconia balls to prepare a slurry, which was obtained from positive electrode/HFP-VF₂Graphite composition 80/10/10 weight ratio. The resulting mixture was then coated on a carbon-coated aluminum foil (produced by Exopack Advanced Coating Co.) using a Gardner apparatus, and the coated sheet was vacuum-dried at 80 ℃ for 24 hours and then stored in a glove box. A "button" type cell was assembled and packaged in a glove box consisting of a carbon-coated aluminum foil containing a coating of the positive electrode material of the present invention as the cell positive electrode, a lithium sheet as the negative electrode, and a separator (Celgard) 25 μ M thick soaked in a 1M LiPF6 mixed solution of EC/DEC.

The above embodiments are only intended to illustrate the technical solution of the present invention and not to limit the same, and a person skilled in the art can modify the technical solution of the present invention or substitute the same without departing from the spirit and scope of the present invention, and the scope of the present invention should be determined by the claims.

Claims

1. A method of preparing carbon-deposited alkali metal oxyanions, comprising the steps of:

(a) dry or wet grinding a precursor of the starting material compound, i.e. the alkali metal oxyanion, and, when wet grinding, drying the ground precursor to obtain a solid compound; then heat-treating the milled precursor in a protective atmosphere to obtain a heat-treated precursorThe material of (a); wherein the grinding time is 5 minutes to 4 hours, the heat treatment temperature is 300-850 ℃, and the heat treatment time is 10 minutes to 4 hours; during the heat treatment, the total iron and/or manganese is reduced to the Fe (II) and/or Mn (II) oxidation state; the initial starting compound is converted into an olivine-structured LiMPO after the heat treatment₄The conversion rate of (a) is between 30 and 99 mol%;

(b) carrying out microbead nano-grinding on the material obtained in the step (a) in at least one alcohol-based system to obtain a nano-suspension;

(c) drying the nanosuspension obtained in step (b) to obtain a solid compound;

(d) placing the solid compound obtained in step (c) in at least one vapor phase carbon source vapor to obtain a carbon-deposited alkali metal oxyanion using a vapor phase carbon source deposition process.

2. The method of claim 1, wherein the time for grinding, drying, and heat treating of step (a) does not exceed 180 minutes.

3. The method of claim 1, wherein the nanomilling in step (b) uses an alcohol as the fluid carrier, the alcohol being selected from the group consisting of aliphatic alcohols containing from 1 to 10 carbon atoms; step (b) adding a reducing agent in an amount of not more than 10000ppm relative to the mass of the heat-treated material in step (a); the reducing agent is selected from the group consisting of hydrazine, hydroquinone, formic acid, ascorbic acid, and mixtures thereof.

4. The process of claim 1, wherein the drying of step (c) is by spray drying using nitrogen as the gas phase atomizing medium, the moisture content of the dried material after spray drying being no more than 4000 ppm.

5. The method of claim 1, wherein the gaseous carbon source in step (d) is selected from the group consisting of benzene, propylene, acetylene, and mixtures thereof, and wherein the thermal CVD step is performed at a temperature of 600 to 750 ℃ for a time period of 10 minutes to 4 hours; the total time of steps (a) to (d) does not exceed 8 hours.

6. The method of claim 1, wherein the carbon deposit is deposited in an amount of no more than 2.5 wt% based on the total weight of the alkali metal oxyanion and the carbon deposit is between 0.3 and 3.7nm thick, the carbon deposit being in the form of a continuous, adherent, uniform deposit; the sulfur impurity content is less than 80ppm based on the total weight of alkali metal oxyanions deposited on the carbon; a moisture content of less than 200ppm based on the total weight of the carbon depositing alkali metal oxyanion; the proportion of the magnetic impurities in the total weight of the carbon-deposited alkali metal oxyanion is less than 300 ppb.

7. The method of claim 1, wherein the carbon deposit is in the form of a graphene-like carbon deposit having 1 to 8 layers.

8. The method of claim 1, wherein the alkali metal oxyanion has an average primary particle size of less than 500 nm; the median primary particle size of the alkali metal oxyanion is between 25 and 250 nanometers; the carbon-deposited alkali metal oxyanion is in the form of spherical secondary agglomerates of carbon-deposited spherical alkali metal oxyanion primary particles; the porosity of the spherical secondary aggregate is 5-40%; the BET area of the spherical secondary aggregate is 3-11 m²Between/g; d of spherical secondary agglomerates₅₀2-30 μm; the compacted density of the spherical secondary agglomerates is between 2.4 and 3g/cm³In the meantime.

9. The process according to any one of claims 1 to 8, characterized in that the carbon-depositing alkali metal oxyanion is a compound having an olivine structure corresponding to the general nominal formula LiMPO₄Wherein M comprises at least 95 atomic% Fe (II), or Mn (II), or mixtures thereof, M being partially substituted by one or more other elements selected from Ni, or Co, or from the group consisting of equivalent or aliovalent Mg, Mo, Nb, Ti, Al, Ta, Ge, La, In, Y, Yb, Cu, Sm, Sn, Pb, Al,Ag. V, Ce, Hf, Cr, Zr, Bi, Zn, Ca, Cd, Ru, Ga, Sr, Ba, B, W metal.

10. A positive electrode material for a lithium secondary battery, comprising the carbon-deposited alkali metal oxyanion prepared according to any of claims 1 to 9.

11. The positive electrode material for a lithium secondary battery according to claim 10, further comprising a lithium metal oxide.

12. A lithium secondary battery comprising a positive electrode, a negative electrode and an electrolyte, characterized in that the positive electrode uses the positive electrode material for a lithium secondary battery according to claim 10 or 11.