CN113506861B

CN113506861B - Silicon-based composite negative electrode material of lithium ion battery and preparation method thereof

Info

Publication number: CN113506861B
Application number: CN202111035322.6A
Authority: CN
Inventors: 贺翔; 许迪新; 李阁; 程晓彦; 岳风树
Original assignee: Shanxi Fuji New Energy Material Technology Co ltd; Beijing One Gold Amperex Technology Ltd
Current assignee: Shanxi Fuji New Energy Material Technology Co ltd; Beijing One Gold Amperex Technology Ltd
Priority date: 2021-09-06
Filing date: 2021-09-06
Publication date: 2022-05-17
Anticipated expiration: 2041-09-06
Also published as: CN113506861A

Abstract

The invention provides a silicon-based composite negative electrode material of a lithium ion battery and a preparation method thereof, wherein the silicon-based composite negative electrode material is composed of silicon, silicon oxide, doped metal and a carbon material, wherein the silicon and the doped metal are dispersed in a substrate formed by the silicon oxide, the carbon material is uniformly coated on the surface of material particles, and the negative electrode material is in-situ nano-scale bulk phase doped metal; the doping metal is selected from one or more of fourth and fifth period transition metal elements and/or fourth and fifth main group metal elements; the total mass of the silicon-based composite negative electrode material is 100%, the mass of the doped metal accounts for 3-12%, and the mass of the carbon material accounts for 1-10%. Metal is doped in the silicon monoxide, a part of lithium in the buffer layer is released through a reversion reaction, agglomeration and growth of a silicon crystal region in a circulation process are inhibited, and the first coulombic efficiency, the multiplying power and the circulation performance of the cathode material are improved.

Description

Silicon-based composite negative electrode material of lithium ion battery and preparation method thereof

Technical Field

The invention belongs to the technical field of batteries, and particularly relates to a silicon-based composite negative electrode material of a lithium ion battery and a preparation method thereof.

Background

With the continuous development of human society and the continuous consumption of non-renewable resources such as coal and petroleum, the future development of human society faces the risk of energy shortage. The use of fossil energy also poses serious environmental pollution problems. The development of green, safe and sustainable new energy technology is one of the methods for solving the problems of energy and environment. Among various new energy technologies, lithium ion batteries have an important position in energy storage technologies due to the characteristics of high energy density, long service life, high charging and discharging speed, good safety and the like.

One of the development directions of lithium ion batteries is higher energy density, and the development of novel electrode materials is an effective means for improving the energy density. As for the negative electrode material, the actual capacity of graphite, which is currently widely commercially used, has approached its theoretical capacity, and therefore, it is necessary to develop a new high-capacity negative electrode material to further increase the energy density of the battery.

Among all novel anode materials, pure silicon anode material has very high theoretical specific capacity (4200 mAh g)^-1With Li₂₂Si₅Meter), lower redox potential, abundant reserves and environmental friendliness are considered to be the most promising next generation anode materials. However, the large volume change (over 300%) and low electronic and ionic conductivity in the charge and discharge process caused by the high capacity lead to the problems of low cycle life of repeated SEI cracking, irreversible Li consumption, low capacity exertion in practical application, and the like, which seriously hinders the application of pure silicon negative electrode materials in full batteries. Excessive theoretical capacity is not of great value in a full cell, and a silica material with moderate specific capacity, less volume expansion, and longer cycle life is the most commercially promising negative electrode material.

Patent CN 109494360A discloses a hard carbon and elastic polymer material co-coated silica/C composite material, the method firstly mixes silica with carbon source, the carbon source is carbonized into hard carbon to be coated on the silica outer layer after two-stage high temperature treatment, then a chain conductive agent and the hard carbon coated silica are mixed in Py (pyrrole) solution, then oxidant is added to polymerize pyrrole monomer into polypyrrole (PPy) and coated on the surface of hard carbon, the chain conductive agent is coated in the polypyrrole in the polymerization process, and finally the conductive agent is obtainedThe composite material is a silica/C-PPy composite material which is doubly coated by hard carbon and elastic high polymer material PPy and is used as a bridge. The double-layer coating structure can effectively inhibit the relative volume change in the lithium intercalation/deintercalation process, and the conductive agent is used as a bridge to further improve the conductivity of the silicon monoxide and ensure that Li⁺The rapid embedding and releasing can improve the cycle and rate capability of the lithium ion battery. However, hard carbon as a conductive coating layer generates more "dead lithium", consuming the Li source in the battery leads to reduced battery efficiency and capacity fade.

Patent CN 111261838A discloses a method for prelithiation of a silicon oxide electrode sheet using a prelithiation reagent containing aromatic organic substances. Dissolving an aromatic compound in a certain amount of organic solvent, adding a certain amount of lithium sheets, oscillating until the lithium sheets are dissolved to obtain a pre-lithiation reagent, dropwise adding the obtained pre-lithiation reagent to the prepared silicon oxide negative electrode sheet, and drying to realize the pre-lithiation of the electrode sheet. The method can only realize the improvement of the coulombic efficiency for the first time to a small extent, the utilization rate of lithium in the prelithiation reagent is not high, and although the operation method seems to be simple, the large-scale application still faces a great problem after considering the toxicity and the cost of aromatic compounds and organic solvents.

CN112209390A discloses a core-shell structure negative electrode material, which is prepared by depositing silica on the surface of a core negative electrode material (metal or metal oxide) by a high-temperature heating deposition method to form a core-shell nano coating layer. The core anode material (non-silicon-based composite anode material) is mainly used for providing capacity in the structure, and the silicon oxide just serves as a nano coating layer to coat the surface. However, the process needs to strictly regulate and control the heating deposition conditions of the silicon oxide, otherwise, the deposition is not uniform, a core-shell structure cannot be formed, the energy density improvement range of the silicon oxide nano coating is limited, various defects of poor cycle and rate performance of the silicon oxide are introduced, the silicon oxide nano coating is not a very effective coating means, the generation of phenomena such as self agglomeration, volume expansion, internal cracks and the like of the silicon negative electrode material cannot be solved, and particularly, the cycle stability performance of the negative electrode material cannot be ensured after long-term operation.

The existing metal element doping is to directly obtain a composite material by ball milling, or to obtain the composite material by hydrothermal reaction, or to obtain a precursor by liquid phase reaction and then to calcine the composite material by non-in-situ doping method, which has the disadvantages that the doped metal is not uniformly distributed in the material, the doping can not go deep into the material, the doped metal is too large in size (dozens to hundreds of nanometers) in the material, and the content is not easy to control, thus being not beneficial to industrial popularization. Moreover, intrinsic defects such as silicon monoxide agglomeration, significant increase in silicon grain size and the like cannot be solved.

In order to improve the cycle life of the silica, a porous or hollow structure is constructed in various ways and compounded with a carbon material, the volume expansion is buffered, and the material interface is stabilized to improve the cycle performance, but some intrinsic defects of the silica are not improved. Compounding with carbon materials can improve the conductivity between particles, but the conductivity of the silica phase is not improved. The first coulombic efficiency is low due to irreversible lithium oxide and lithium silicate phases generated during the first charge and discharge process. In addition, during charging and discharging of the silicon monoxide, the silicon crystal areas inside the silicon monoxide can be continuously agglomerated and grown, so that the silicon crystal areas are larger and larger, cracks are more easily generated, and the cycling stability of the battery is reduced. The agglomeration also makes the distribution of Si in the interior of the silicon monoxide more uneven, so that the volume change and stress distribution during charging and discharging become uneven, the structural integrity is more easily damaged, and the buffering effect of the surrounding buffer layer is greatly weakened due to the uneven distribution of Si. Therefore, it is necessary to develop a new method capable of improving the intrinsic defects of the silicon monoxide, thereby further improving the overall performance of the silicon-based composite anode material.

Disclosure of Invention

The invention aims to solve the problems of poor rate capability, low first coulombic efficiency and short cycle life of the existing silicon-based material caused by low bulk phase conductivity, irreversible phase generated by first charging and discharging, and silicon crystal region agglomeration in the circulating process, and provides a silicon-based composite negative electrode material of a lithium ion battery and a preparation method thereof, so that the circulating and rate capability of the current negative electrode material of the lithium ion battery is improved.

In order to achieve the purpose, the invention provides a silicon-based composite negative electrode material which is composed of silicon, silicon oxide, doped metal and a carbon material, wherein the silicon and the doped metal are dispersed in a substrate formed by the silicon oxide, the carbon material is uniformly coated on the surface of material particles, and the negative electrode material is in an in-situ nano bulk phase doped structure.

Specifically, through metal in-situ doping, the composite negative electrode material has metal elements existing from inside to outside and is uniformly distributed, uniform bulk phase doping is formed, and the metal exists in the form of grains with the size of a few nanometers in the material.

The doped metal in the composite negative electrode material is selected from one or more of fourth and fifth period transition metal elements and fourth and fifth main group metal elements.

The fourth and fifth periodic transition metal elements are selected from one or more of scandium, titanium, manganese, iron, cobalt, nickel, zinc, zirconium and niobium, preferably one or more of titanium, cobalt or zirconium.

The fourth and fifth main group metal elements (IV, V) are one or more of germanium, tin, lead, antimony and bismuth, preferably one or more of tin, antimony and bismuth.

More preferably, the doping metal is a compound of one of fourth and fifth period transition metal elements and one of fourth and fifth main group metal elements, the fourth and fifth period transition metal elements are preferably cobalt, and the fourth and fifth main group metal elements are preferably tin.

The existence form of the doping metal comprises one or more of simple metal, alloy and metal compound oxide.

The metal compound is selected from one or more of oxide, nitride, carbide, sulfide, hydroxide, carbonate, oxalate, silicate, halide, preferably the metal compound is selected from one or more of metal oxide, nitride, carbide or sulfide.

More preferably, the metal compound is a metal nitride or sulfide.

The total mass of the silicon-based composite negative electrode material is 100%, the mass of the doped metal accounts for 3-12%, preferably 4-9%, and the mass of the carbon material accounts for 1-10%.

The silicon in the composite cathode material is generated in situ in the preparation process of the silicon monoxide or obtained by reaction in the subsequent process of forming the composite cathode material, and is in an amorphous state or a crystalline state.

Wherein the composition of the silicon oxide can be SiO_xExpressed, wherein the stoichiometric number x of oxygen elements is in the range of 0.1 ‹ x.ltoreq.2.0, more preferably 0.9 ‹ x.ltoreq.1.1.

Preferably, the surface-coated carbon material may be one or a combination of amorphous carbon, graphitized carbon, graphene, carbon nanotubes, and conductive polymers. The thickness of the coating is 5-30 nm, preferably 10-20 nm.

Preferably, the electronic conductivity of the silicon-based composite anode material is 0.1-4S/cm, preferably 0.6-2.5S/cm.

Before the silicon-based composite negative electrode material is circulated, the size of silicon crystal grains inside the silicon-based composite negative electrode material is 1-10 nm. The size of the doped metal (simple substance, alloy or compound) cluster in the silicon-based composite negative electrode material is 1-20 nm.

After 500 cycles, the size of silicon crystal grains in the silicon-based composite negative electrode material is 50-150 nm, and the size of the more preferable silicon crystal grains is 50-100 nm. The cluster size of the doped metal (simple substance, alloy or compound) is 50-100 nm. Therefore, the silicon-based composite negative electrode material can effectively inhibit the expansion of the silicon-based material and has excellent cycle stability.

Preferably, the median particle size of the silicon-based composite negative electrode material is 0.1-20 mu m, preferably 1-10 mu m, and the tap density of the composite negative electrode material is 1.7-2.5 g/cm³Preferably 1.9 to 2.2 g/cm³。

According to the invention, through doping metal (simple substance, alloy or compound), agglomeration of silicon crystal grains in the charging and discharging process can be inhibited, the cycle performance is improved, and through the reversion reaction of the metal compound and lithium oxide in the buffer layer, the first coulombic efficiency of the material is improved.

In addition, the invention also provides a preparation method of the silicon-based composite anode material, which comprises the following steps:

(1) pretreatment:

drying a raw material A capable of generating silicon monoxide (0.1 ‹ x is less than or equal to 2.0) under the high-temperature high-vacuum condition and a raw material B containing doping elements in a non-oxidizing atmosphere to obtain pretreated raw materials A and B;

(2) metal compound doped silicon-based composite material:

heating the pretreated raw material A and the raw material B in a heating device, reacting the raw material A and the raw material B to generate steam containing silicon monoxide and doped metal, diffusing the steam to a collecting device for condensation and deposition to obtain a metal-doped silicon-based composite anode material, and transferring the metal-doped silicon-based composite anode material to a sintering furnace through a transition bin for high-temperature sintering to further stabilize the structure of the material so as to better improve the electrochemical performance;

(3) carbon coating:

and (3) crushing the composite material obtained in the step (2) to obtain a powder material with a proper granularity, and then carrying out carbon coating to obtain the silicon-based composite anode material.

According to the invention, the metal-doped raw material and the silicon-containing raw material are synchronously steamed out and deposited together in the vacuum sintering process to form metal in-situ doping, and the deposited material has metal element doping from inside to outside and is uniformly distributed to form uniform bulk phase doping. The doping metal (simple substance, alloy or compound) exists in the form of several nano-sized grains inside the material.

Wherein the raw material A in the step (1) is a silicon-containing raw material, and is selected from one or a combination of two or more of silicon oxide powder, silicon powder and silicon dioxide powder.

The raw material B is one or a combination of more of simple substances, alloys, oxides, nitrides, carbides, hydroxides, carbonates, oxalates, silicates and halides of doped metals. One or more of simple metal, oxide, nitride, carbide and sulfide is preferred.

Research shows that the electrochemical activity of the silicon monoxide comes from the random combination of Si and O, so that the polarization of Si-O bonds is caused, and the polarization enhances the SiO_xWith Li⁺Thereby producing electrochemical activity. In SiO_xThe metal compound of nitride, carbide or sulfide is doped in the material, and the polarity of Si-O bond can be further enhanced through the combination of nitrogen and sulfur hetero atoms and silicon, so that the SiO is enhanced_xThe barrier to diffusion and reaction of lithium ions within the material, especially for batteries, is reduced.

After the fourth and fifth period transition metal elements and the fourth and fifth main group metal elements are doped into the silicon protoxide material, local structural distortion can be caused because the atomic radius of the metal elements is different from that of Si, the metal elements play the role of atomic scale barriers, the structural distortion increases the dislocation forming energy and the dislocation movement resistance, the dislocation slippage is difficult to carry out, and the generation and the growth of cracks of the silicon protoxide particles in the circulating process are inhibited. In the actual circulation process, after volume expansion is generated, valence electrons in the metal element doped material tend to migrate from a compression region to a tension region in a stress field, a local dipole is generated at a stressed part at the moment, the interaction of the dipoles can increase the dislocation forming energy of the material at the part, the dislocation forming is more difficult, the generation of cracks is prevented, and the circulation performance of the material is improved.

In addition, after the transition metal elements such as titanium, cobalt, zirconium and the like are doped into the silicon monoxide, the vacant 3d orbit of the transition metal elements and lone pair electrons on oxygen in the silicon monoxide generate coordination, the lone pair electrons tend to enter the vacant 3d orbit, electron clouds of oxygen are polarized, the capability of oxygen for binding bonding electrons in Si-O bonds is enhanced, and the polarity of the Si-O bonds is enhanced by the synergistic effect of the transition metal elements such as nitrogen, sulfur and the like, so that the transition metal elements are easier to be coated by Li⁺Destroy and strengthen SiO_xThe reactivity of the material is improved, the first coulombic efficiency of the material is improved, and the rate capability of the material is improved.

The mass ratio of the raw material A to the raw material B is 10-25: 1, the mass range of doped metal (simple substance, alloy or compound) in the anode material is about 3-12%, and the mass ratio of the raw material A to the raw material B is preferably 10-25: 1. specifically, if the mass ratio is higher than 25: 1, the doping amount is too small to play a role in improving the conductivity and blocking silicon agglomeration, and if the doping amount is less than 10:1, the doping elements can form agglomerates and cannot be uniformly dispersed in the silicon monoxide, and the effects of buffering volume expansion, improving conductivity and inhibiting silicon crystal grain growth are greatly reduced.

The raw material A and the raw material B are both powder, and the particle size range is 50-150 mu m.

The drying treatment in the non-oxidizing atmosphere in the step (1) is preferably performed under the conditions of argon, nitrogen, helium, neon and vacuum, and more preferably under the vacuum condition. The drying temperature is 60-110 ℃, and the drying time is 6-12 h.

In the step (2), the heating device used in the present invention is a vacuum furnace with a collecting device, which generally has one or more heating chambers, and the collecting device and each heating chamber can independently control the temperature therein, wherein the heating temperature is 1000-.

If the vacuum furnace has only one heating chamber, the raw material A and the raw material B are mixed into uniform powder by the method, then the uniform powder is loaded into the heating chamber, and the reaction is carried out under the condition of vacuum high temperature: the raw materials A and B are uniformly mixed and placed together, the raw materials A and B can react in the heating process, and the reaction product leaves the reaction system in a steam phase state.

Preferably, the vacuum furnace of the present invention has two heating chambers, the raw material a and the raw material B are charged into the different heating chambers, respectively, and the temperatures of the heating chambers are controlled so that the silicon monoxide and the doping element can be uniformly deposited. In a vacuum furnace with double heating cavities, raw material A reacts to generate silicon monoxide and form steam, raw material B forms steam, and the steam of the raw material A and the steam of the raw material B meet and react to form in-situ doping.

Wherein the heating temperature of the raw material A is 1200-1600 ℃, and the heating temperature of the raw material B meets the condition that the ratio of the evaporation rates of the raw materials A and B is basically the same as the mass ratio of the raw materials A and B. The ratio of the evaporation rates of the raw materials A and B and the mass ratio of the raw materials A and B are basically the same, and the difference between the ratios is not more than 10%.

In one embodiment of the present invention, the heating temperature of the raw material B is 1083 ℃, and the specific value can be calculated according to the ratio of saturated vapor pressure, and can also be obtained by testing in an actual reaction system.

Specifically, the ratio of the reaction products of the raw materials A and B is different depending on the feed ratio, and the vapor pressures of the reaction products are different at the same temperature, so that the evaporation rates are different. In order to realize uniform deposition of the doping metal (simple substance, alloy or compound), the temperature in different reaction chambers needs to be controlled, so that the ratio of the evaporation rates of the two reaction products is basically the same as the ratio of the mass of the products, thereby ensuring that the concentration of the doping metal of the deposited silicon monoxide from the bottom layer to the top layer is basically consistent, i.e. the concentration of the doping metal is uniform and stable. Therefore, the reaction temperature and the reaction pressure of the two are required to satisfy the condition that the ratio of the evaporation rate is consistent with the ratio of the products.

The ratio of the evaporation rates of the raw materials in the two heating chambers of the double-temperature chamber is consistent with the ratio of the mass of the raw materials in the two heating chambers, specifically, the temperature of the double-temperature chamber is set to enable the evaporation rate to be approximately equal to the ratio of the amount of the raw materials in the two temperature chambers, and the temperature and the pressure of the heating chamber for doping elements or compounds can be calculated according to the ratio of the temperature and the pressure of the heating chamber for silicon-containing raw materials and the amount of the added raw materials.

Wherein, the ratio of the evaporation rate can be calculated by the ratio of the saturated vapor pressure, and the theoretical formula is Clausius-Clapeyron equation:

wherein L is the latent heat of vaporization,

is the change in the molar volume of the gas and liquid phases。

Most of the data of the metal compounds at a certain temperature are found according to the Law chemical handbook, and part of the substances need to be calculated and simulated according to a thermodynamic formula. Specifically, the saturated vapor pressure of the pure substance can be calculated according to the density functional theory by using cosmo-rs software.

Since the saturated vapor pressures of the raw material A and the raw material B are different at the same temperature, the evaporation rates are different. Therefore, in order to achieve uniform deposition of the doped metal, it is necessary to control the temperature so that the ratio of the evaporation rates of the reactant materials a and B is substantially the same as the mass ratio of the reactants a and B.

For example, the vapor pressure of raw material A to form silica at 1400 ℃ in a heating chamber is about 10 Pa, the vapor pressure of Sn is controlled to 1 Pa according to the ratio of the added raw material A to the raw material B of 10:1, and the vapor pressure of Sn at 1083 ℃ is known by referring to the data (Law's handbook of chemistry), so that the ratio of the evaporation rate to the mass of the raw material is maintained to be substantially the same by controlling the temperature of the heating chamber 1 to 1400 ℃ and the temperature of the heating chamber 2 to 1083 ℃.

As another example, the raw material B is Co₃N₂In this case, the vapor pressure of the raw material A to form silica in the heating chamber at 1400 ℃ is about 10 Pa, and the ratio of the amount of the added raw material A: the proportion of the raw material B is calculated by cosmo-rs software according to the density functional theory, and the temperature of the heating chamber 2 is 1440 ℃ to ensure that the proportion of the evaporation rate and the proportion of the raw material mass are basically the same.

The heating time of the step (2) is 8-20 h; the vacuum pressure range in the heating chamber of the silicon-containing raw material (raw material A) is 10-50 Pa.

The condensation deposition is carried out at the temperature of 200-600 ℃, and particularly, the vapor containing the silicon monoxide and the doping metal is diffused into the collecting device.

If the condensation deposition temperature in the collecting device is higher than 600 ℃, the doped metal can be agglomerated in the silicon monoxide, and a uniform doped material cannot be formed, whereas if the deposition temperature is lower than 200 ℃, the silicon monoxide can be deposited in the form of island crystals, and the electrochemical performance of the amorphous silicon monoxide is inferior to that of the amorphous silicon monoxide which is uniformly deposited in a layered mode;

the sintering process after condensation and deposition in the step (2) comprises the following steps: specifically, the discharge end of the vacuum furnace is connected with a double-wire winding sintering furnace through a transition bin, and the interior of the vacuum furnace is in an inert gas atmosphere, preferably nitrogen or argon. After the deposition of the silicon oxide is finished, the collecting device is transferred into the sintering furnace through the transition bin to be sintered, and the combination of the doped metal and the silicon oxide substrate is promoted to further stabilize the structure of the material.

The sintering temperature is 400-900 ℃, and the sintering time is 0.5-1.5 h. The double-winding wire can enable the temperature field in the sintering furnace to be distributed more uniformly, so that a better sintering effect is realized.

And (3) the crushing method comprises the steps of using a ball mill, a sand mill, a jet mill, a pair of rollers, a jaw crusher, a hammer crusher and a rotary impact crusher. The particle size of the powder material is 0.1-20 mu m, and the preferred particle size range is 0.5-10 mu m; the specific surface area of the powder material is 1-50 m²A preferred specific surface area is 2 to 30 m²(ii) in terms of/g. Specifically, the particle size of the powder is less than 0.1 μm, a carbon layer is difficult to uniformly coat the surface of the powder subsequently, the specific surface area is increased when the particle size is too small, uniform slurry is difficult to form when battery slurry is prepared, the contact area between the material and electrolyte is too high when the specific surface area of the material in the battery is too large, and the generated side reaction and the generated SEI film exceed the requirements of normal use. The particle size of the powder is larger than 20 mu m, which indicates that the material is too large in particle size and difficult to scrape into a pole piece with uniform thickness, and the large particle size can cause the deterioration of the dynamic property of the material, and the overpotential increase can generate additional side reactions, which are not beneficial to the exertion of the battery capacity and the maintenance of even the safety hazards of short circuit, gas expansion and the like;

the preparation method of the silicon-based composite anode material is characterized by comprising the following steps of: and (3) the carbon coating method is solid phase coating, liquid phase coating or gas phase coating.

As a preferred technical scheme of the invention, the carrier gas for carbon-coated high-temperature treatment is one or more of nitrogen, argon, helium, neon and krypton, the type of the coating layer is one or more of amorphous carbon, graphitized carbon, graphene and carbon nano tubes, and the thickness of the coating layer is 5-30 nm, preferably 10-20 nm.

The application provided by the invention is the application of the silicon-based composite negative electrode material or the silicon-based composite negative electrode material prepared by the preparation method as a negative electrode material of a lithium ion battery, and the lithium ion battery contains the silicon-based composite negative electrode material provided by the invention or the silicon-based composite negative electrode material prepared by the preparation method provided by the invention.

Compared with the prior art, the silicon-based composite anode material for the lithium ion battery and the preparation method thereof provided by the invention have the following advantages:

the silicon-based composite negative electrode material obtained by the method has uniformly doped metal elements inside, the electronic conductivity of the material body phase can be improved, chemical bonds formed by silicon and oxygen atoms around the silicon-based composite negative electrode material are distorted due to the introduction of N, S and other non-oxygen atoms, a channel beneficial to Li + diffusion is generated, the ionic conductivity of the material is improved, and the rate capability is improved.

During the charging process, the nano-sized doped metal uniformly dispersed in the silicon monoxide has high reactivity and can perform a reversion reaction with lithium oxide in the buffer layer generated during discharging:

metal oxide is generated and a portion of the lithium in the buffer layer is reversibly released, thereby increasing the first coulombic efficiency. The metal elements dispersed in the silicon monoxide can not interact with the simple substance silicon, so that the metal elements can serve as an isolation layer between silicon crystal regions, prevent the silicon crystal regions from agglomerating and growing in the charging and discharging process, limit the silicon crystal regions to a small size, and inhibit the generation of cracks in the long-circulating process. The buffer layer can better play the role of buffering volume expansion by avoiding the aggregation of the silicon crystal region, so that the volume change and stress distribution of the silicon oxide particles are more uniform, thereby reducing the cracking of the particles, the pulverization and the stripping of the pole piece, better maintaining the structural integrity of the particles and the pole piece and prolonging the cycle life of the silicon oxide material.

The carbon coating on the surface further improves the conductivity of the particles, and meanwhile, even if the particles crack, the carbon coating on the surface can still maintain integrity, so that broken particles in the carbon layer can not lose electric contact, the exposure of a fresh surface and the repeated generation of an SEI (solid electrolyte interphase) film are reduced, and the cycle performance of the silicon protoxide material is improved.

According to the invention, by controlling the proportion, mixing mode, heating temperature, vacuum degree, deposition temperature and sintering process after condensation of the silicon-containing raw material and the doped metal raw material, in-situ doping of metal elements is realized in the evaporation deposition process of the silicon monoxide; after deposition is finished, a sintering step is added to enable the doped metal to be better combined with a network structure of the silicon oxide, and the stability of the material is enhanced, so that the cycle performance is improved; the even distribution of the doped metal on the nanometer scale leads the activity of the doped metal to be enhanced, and the doped metal can be mixed with Li in an inert buffer layer in the charging process₂O reacts to reversibly convert a part of irreversible lithium, thereby having an advantage of high initial efficiency.

Besides the advantages, the preparation method provided by the invention also has the advantages of simple process flow, no involvement of toxic and harmful substances, environmental friendliness, low-cost and easily-obtained raw materials, easiness in realization of industrial production and the like.

Drawings

FIG. 1 is an X-ray diffraction spectrum of a silicon-based composite anode material prepared in example 1;

FIG. 2 is a scanning electron microscope photograph of the silicon-based composite anode material prepared in example 1;

FIG. 3 is a TEM photograph of the Si-based composite anode material prepared in example 1;

FIG. 4 is a transmission electron micrograph of a silica negative electrode material of comparative example 1;

FIG. 5 is a charge-discharge curve at 0.2C when the silicon-based composite anode material prepared in example 1 is used as an anode of a lithium ion battery;

FIG. 6 is a cross-sectional view of the particle after 500 cycles of the negative electrode material of comparative example 1;

FIG. 7 is a cross-sectional view of a particle of a silicon-based composite anode material prepared in example 1 after 500 cycles;

fig. 8 is an EDS diagram of a silicon-based composite anode material prepared in example 1.

Detailed Description

The present invention will be further described with reference to the following examples, but the present invention is not limited to the following examples.

The experimental methods described in the following examples are all conventional methods unless otherwise specified; the reagents and materials are commercially available, unless otherwise specified.

Characterization of silicon-based composite negative electrode material

The X-ray diffraction peaks of the composite material were analyzed using an X-ray diffraction analyzer (XRD, Rigaku D/max 2500, Cu K α), fig. 1 is an X-ray diffraction pattern of the silicon-based composite anode material prepared in example 1, and fig. 2 is an X-ray diffraction pattern of the silicon-based composite anode material prepared in comparative example 1. As can be seen in fig. 1, the diffraction peaks for the crystal planes of silicon (111), (220) and (311) appear at 28.4 °, 47.3 ° and 56.1 °, and the diffraction peaks for the crystal planes of tin (200), (101), (220), (211), (112) and (321) appear at 30.6 °, 32.0 °, 43.9 °, 44.9 °, 62.5 ° and 64.6 °. The silicon-based composite anode material containing tin can be obtained by an evaporation deposition method. In fig. 2, only the silicon (111), (220) and (311) crystal plane diffraction peaks at 28.4 °, 47.3 ° and 56.1 ° are present.

The change of silicon crystal grains and the condition of metal clusters can be characterized by a high-resolution transmission electron microscope. Fig. 3 and 4 are transmission electron micrographs of example 1 and comparative example 1, respectively. As can be seen from FIG. 3, the composite material obtained in example 1 has two distinct crystal lattice fringes inside, the lattice fringes with a spacing of 0.31 nm corresponding to the (111) plane of Si and 0.29 nm corresponding to the (200) plane of Sn. The grain sizes of silicon and tin are 3-5nm and 4-6 nm, respectively. As can be seen from FIG. 4, the composite material prepared in comparative example 1 had lattice fringes of only silicon (111) planes with a spacing of 0.31 nm, which had a size of 4 to 6 nm. The transmission electron micrograph shows that tin is incorporated inside the silica particles, and silicon and tin are uniformly dispersed in the particles in a size of several nanometers, while comparative example 1, which is not doped with a metal, has only crystal grains of silicon. Tin can inhibit the agglomeration of silicon in the charging and discharging processes, and can be used as a buffer layer to buffer volume expansion, so that the tin has more excellent cycle stability compared with undoped materials. The grain size is an important index, less increase indicates that the agglomeration degree of silicon grains is less, the silicon is more uniformly dispersed, the cycle performance is favorably improved, and after 500 cycles, the grain size of tin in the cathode material is still below 100 nanometers (about 70 nm) and no obvious agglomeration occurs.

The morphology of the composite material was analyzed by a scanning electron microscope (SEM, Japanese Electron scanning Electron microscope JEOL-6701F), and FIG. 2 is a scanning electron microscope picture of the material prepared in example 1. As can be seen from the figure, the particles showed irregular morphology, had substantially no fine powder on the surface and had a uniform particle size distribution of 3 to 8 μm. The particle size of the composite material described in example 1 was measured with a Malvern laser particle sizer (Malvern, Mastersizer 3000) with a median particle size of 5.6 μm.

The tap density of the composite anode material prepared in example 1 was measured to be 2.1 g/cm by a tap density meter (micromeritics, ACCUPYC II 1345)³。

And testing the content of the metal or the compound in the prepared composite negative electrode material by using an ion inductively coupled atomic emission spectrometry (ICP-AES, Agilent 5110 VDV).

It can be seen from the EDS (fig. 8) that the composite anode material particles prepared in example 1 have signals of Sn metal from inside to outside and are uniformly distributed, and uniform bulk phase doping is formed.

Electrochemical performance test

The electrochemical properties of the silicon-based composite anode materials prepared in the following examples and comparative examples were tested according to the following methods: mixing the prepared silicon-based composite negative electrode material, carbon black, carboxymethyl cellulose (CMC) and Styrene Butadiene Rubber (SBR) composite binder in a mass ratio of 80:10:10 to prepare slurry (wherein the mass ratio of the CMC to the SBR is 1: 4), uniformly coating the slurry on a copper foil current collector, and performing vacuum drying for 12 hours to prepare the silicon-based composite negative electrode materialA working electrode; lithium foil as counter electrode, glass fibre membrane (from Whatman, UK) as separator, 1 mol/L LiPF₆(the solvent is a mixed solution of ethylene carbonate and diethyl carbonate with the volume ratio of 1: 1) is used as an electrolyte, VC with the volume fraction of 1% and FEC with the volume fraction of 5% are added into the electrolyte, and the button cell is assembled in a German Braun inert gas glove box in an argon atmosphere.

And (3) carrying out charge and discharge tests on the assembled battery on a LAND charge and discharge tester. Cycling tests were conducted at a charge and discharge rate of 0.2C (1C =1600 mA/g) over a voltage range of 0.005-1.5V. The first-cycle discharge capacity is 1543.0 mAh/g, the first coulombic efficiency is 84.3%, and the discharge capacity retention rate after 500 cycles is 84.0%. Rate tests are carried out on the charge and discharge rates of 0.2C, 0.5C, 1C, 2C and 5C, under the current density of 5C, the battery discharge capacity is 1197.2 mAh/g, the capacity retention rate of 5C is 77.6%, the discharge capacity is 1503.9 mAh/g after the battery returns to 0.2C, the difference between the discharge capacity and the capacity before the rate tests is small, and the material has better cycle and rate performance.

The electron conductivity of the material prepared in example 1 was measured to be 1.24S/cm using a powder conductivity tester (ROOKO, FT-8100), indicating that the material has a good conductivity property.

According to the same method, the silicon-based composite negative electrode materials obtained in the examples and the comparative examples are used as negative electrode materials to be assembled into button lithium batteries, and the electrochemical test results are shown in Table 2.

Example 1

(1) Pretreatment: 0.8 kg of silicon powder with the particle size of 100 mu m and 1.2 kg of silicon dioxide powder with the particle size of 100 mu m are taken and added into a mixer, the silicon powder and the silicon dioxide powder are mixed for 15 min at the rotating speed of 600 r/min under the condition of circulating water cooling, so that uniformly mixed raw material A is obtained, and 200 g of Sn powder with the particle size of 70 mu m is taken as raw material B. And respectively drying the raw material A and the raw material B for 6 hours at the temperature of 80 ℃ in an argon atmosphere to remove water, thereby obtaining the pretreated raw material.

(2) Sn element doped silicon-based composite material: and (2) putting the raw material obtained in the step (1) into a vacuum furnace with a collecting device and two heating chambers, putting the raw material A into a heating chamber 1, putting the raw material B into a heating chamber 2, pumping the pressure to below 10 Pa, then starting to heat, heating the heating chamber 1 to 1400 ℃ at the speed of 6 ℃/min, then preserving the temperature for 10 h, heating the heating chamber 2 to 1083 ℃ at the same temperature-rising time, then preserving the temperature for 10 h, controlling the temperature of the collecting device to be 400 ℃, transferring the deposited material into a sintering furnace in a nitrogen atmosphere after finishing preserving the temperature, rising the temperature to 800 ℃ at the temperature-rising speed of 5 ℃/min, sintering for 1 h, and naturally cooling to room temperature to obtain the blocky Sn-doped silicon-based composite material.

(3) The carbon-coated Sn-doped silicon-based composite negative electrode material comprises the following components in percentage by weight: and (3) airflow crushing the block material obtained in the step (2) to particles with the particle size of 10 mu m, putting the particles into an intermittent coating furnace, introducing acetylene at the flow rate of 800 sccm, preserving heat at 800 ℃ for 3.5 h, placing the coated material in a nitrogen atmosphere, heating to 900 ℃ at the speed of 5 ℃/min, preserving heat for 1 h, naturally cooling to room temperature to obtain the carbon-coated Sn-doped silicon-based composite negative electrode material with the outer layer uniformly coated with carbon and the inner layer uniformly doped with Sn, wherein the thickness of the carbon coating layer is 8 nm, and the carbon material accounts for 5 wt% of the silicon-based composite negative electrode material. The doping element Sn accounts for 8.3 percent of the silicon-based composite negative electrode material.

Example 2

And (3) operating according to the same method as the embodiment 1, wherein the difference is that the vacuum furnace in the step (2) is not sintered after heat preservation is finished, and is naturally cooled to room temperature to obtain a blocky Sn doped silicon-based composite negative electrode material, and finally the carbon-coated Sn doped silicon-based composite negative electrode material is obtained. The doping element Sn accounts for about 8 percent of the silicon-based composite cathode material.

Example 3

The operation was carried out in the same manner as in example 1 except that the temperature of the collecting apparatus was controlled at 200 ℃ in step (2).

Example 4

The operation was carried out in the same manner as in example 1 except that the temperature of the collecting device was controlled at 600 ℃ in step (2).

Example 5

Heating by adopting a single temperature cavity: (2) putting the pretreated raw materials obtained in the step (1) into a heating chamber of a vacuum furnace with a collecting device, pumping the pressure to be below 10 Pa, starting heating, raising the temperature to 1400 ℃ at the speed of 6 ℃/min, preserving the temperature for 10 h, and controlling the temperature of the collecting device to be 400 ℃ all the time. After the heat preservation is finished, transferring the deposited material into a sintering furnace in nitrogen atmosphere through a transition cabin, heating to 800 ℃ at the heating rate of 5 ℃/min, preserving the heat for 1 h, and naturally cooling to room temperature to obtain a blocky Sn-doped silicon-based composite material; the other steps were the same as in example 1.

Example 6

The operation was carried out in the same manner as in example 1 except that the heating was started in step (2) when the pressure in the vacuum furnace was evacuated to 50 Pa.

Example 7

The operation was carried out according to the single-temperature chamber heating method of example 5, except that in the step (1), 2 kg of the silicon oxide powder with the particle size of 100 μm was taken as the raw material A, and 200 g of CoO powder with the particle size of 70 μm was taken as the raw material B.

Example 8

(1) Pretreatment: taking 2 kg of silicon monoxide powder with the particle size of 100 mu m as a raw material A, taking 200 g of CoO powder with the particle size of 70 mu m as a raw material B, and drying the raw material A and the raw material B at the temperature of 80 ℃ for 6 h under the argon atmosphere to remove water, thereby obtaining a pretreated raw material.

(2) CoO-doped silicon-based composite material: and (2) putting the raw material obtained in the step (1) into a vacuum furnace with a collecting device and two heating chambers, putting the raw material A into a heating chamber 1, putting the raw material B into a heating chamber 2, pumping the pressure to below 10 Pa, starting to heat, heating the heating chamber 1 to 1400 ℃ at the speed of 6 ℃/min, then preserving the temperature for 10 h, heating the heating chamber 2 to 1550 ℃ at the same temperature-rise time, then preserving the temperature for 10 h, controlling the temperature of the collecting device to be 400 ℃, transferring the deposited material to a sintering furnace in a nitrogen atmosphere through a transition cabin after the heat preservation is finished, sintering the material for 1 h after the temperature is increased to 800 ℃ at the temperature-rise speed of 5 ℃/min, and naturally cooling the material to room temperature to obtain the CoO-doped silicon-based composite material.

(3) Carbon-coated CoO doped silicon-based composite negative electrode material: and (3) airflow crushing the composite material obtained in the step (2) to particles with the particle size of 10 mu m, putting the particles into an intermittent coating furnace, introducing acetylene at the flow rate of 800 sccm, preserving heat for 3.5 hours at 800 ℃, placing the coated material in a nitrogen atmosphere, heating to 900 ℃ at the speed of 5 ℃/min, preserving heat for 1 hour, and naturally cooling to room temperature to obtain the carbon-coated CoO-doped silicon-based composite anode material with the outer uniform carbon-coated inner CoO layer uniformly doped, wherein the thickness of the carbon coating layer is 8 nm, the carbon material accounts for 5 wt% of the silicon-based composite anode material, and the CoO accounts for 7.6% of the silicon-based composite anode material.

To further examine the amount of the metal raw material added, examples 9 to 12 were carried out.

Example 9

(1) Pretreatment: taking 2 kg of silicon monoxide (SiO) powder with the granularity of 100 mu m as a raw material A, taking 200 g of Sn powder with the granularity of 70 mu m as a raw material B, and drying the raw material A and the raw material B at the temperature of 80 ℃ for 6 h respectively in an argon atmosphere to remove water, thereby obtaining a pretreated raw material.

(2) Sn element doped silicon-based composite material: and (2) putting the raw material obtained in the step (1) into a vacuum furnace with a collecting device and two heating chambers, putting the raw material A into a heating chamber 1, putting the raw material B into a heating chamber 2, pumping the pressure to below 10 Pa, then starting to heat, heating the heating chamber 1 to 1400 ℃ at the speed of 6 ℃/min, then preserving the temperature for 10 h, heating the heating chamber 2 to 1083 ℃ at the same temperature-rising time, then preserving the temperature for 10 h, controlling the temperature of the collecting device to be 400 ℃, transferring the deposited material into a sintering furnace in a nitrogen atmosphere after finishing preserving the temperature, rising the temperature to 800 ℃ at the temperature-rising speed of 5 ℃/min, preserving the temperature for 1 h, and naturally cooling to room temperature to obtain the blocky Sn-doped silicon-based composite negative electrode material.

(3) The carbon-coated Sn-doped silicon-based composite negative electrode material comprises the following components in percentage by weight: and (3) airflow crushing the block material obtained in the step (2) to particles with the particle size of 10 mu m, putting the particles into an intermittent coating furnace, introducing acetylene at the flow rate of 800 sccm, preserving heat for 3.5 hours at 800 ℃, placing the coated material in a nitrogen atmosphere, heating to 900 ℃ at the speed of 5 ℃/min, preserving heat for 1 hour, and naturally cooling to room temperature to obtain the carbon-coated Sn-doped silicon-based composite negative electrode material with the outer uniform carbon-coated inner layer Sn element uniformly doped, wherein the thickness of the carbon-coated layer is 8 nm, the carbon material accounts for 5 wt% of the silicon-based composite negative electrode material, and the doped element Sn accounts for 9.0% of the silicon-based composite negative electrode material.

Example 10

In the step (1), 1.9 kg of raw material A, namely, the silicon monoxide powder, and 220 g of raw material B, namely, Sn powder, are mixed according to the proportion of 8.3: 1, the temperature of the heating chamber 2 was 1380 ℃, and the other steps were the same as in example 11. The doping element Sn accounts for 12 percent of the silicon-based composite cathode material.

Example 11

In the step (1), 2.06 kg of raw material A, namely the silicon monoxide powder, and 140 g of raw material B, namely Sn powder, are mixed according to a proportion of 14.7: 1, the temperature of the heating chamber 2 was 1150 ℃, and the other steps were the same as in example 11. The doping element Sn accounts for 5.9 percent of the silicon-based composite negative electrode material.

Example 12

In the original step (1), 2.09 kg of the material A, namely the silicon monoxide powder, and 87 g of the material B, namely the Sn powder are mixed according to the proportion of 24: 1, the temperature in the heating chamber 2 was 1060 ℃, and the other steps were the same as in example 11. The doping element Sn accounts for 3.5 percent of the silicon-based composite anode material.

To further examine the effect of different metal starting materials on the formation of doped metals on the negative electrode material, examples 13-18 were conducted.

Example 13

(1) Pretreatment: taking 2 kg of silicon monoxide powder with the particle size of 100 mu m as a raw material A, and taking ZrO with the particle size of 70 mu m₂100 g of powder is used as a raw material B, and the powder is mixed for 15 min at the rotating speed of 600 r/min under the condition of circulating water cooling to obtain a mixed raw material B. And respectively drying the raw material A and the mixed raw material B at the temperature of 80 ℃ for 6 hours under the argon atmosphere to remove water, thereby obtaining the pretreated raw material.

（2）ZrO₂Doping the silicon-based composite material: putting the raw material obtained in the step (1) into a vacuum furnace with a collecting device and two heating chambers, putting the raw material A into a heating chamber 1, putting the raw material B into a heating chamber 2, pumping the pressure to below 10 Pa, starting to heat, heating the heating chamber 1 to 1400 ℃ at the speed of 6 ℃/min, then preserving the temperature for 10 h, heating the heating chamber 2 to 1730 ℃ at the same temperature rise time, preserving the temperature for 10 h, controlling the temperature of the collecting device to be 400 ℃, transferring the deposited material into a sintering furnace in a nitrogen atmosphere through a transition cabin after the heat preservation is finished, increasing the temperature to 800 ℃ at the temperature rise speed of 5 ℃/min, preserving the heat for 1 h, and naturally cooling to room temperature to obtain the productTo bulk ZrO₂The silicon-based composite anode material is doped, and other steps are the same as those of the embodiment 1. Detected, ZrO₂Accounting for 4.1 percent of the silicon-based composite anode material.

Example 14

The other steps are the same as the example 13, and the difference is only that the raw material B in the step (1) is Sb with the particle size of 70 mu m₂O₃100 g, and the temperature of the heating chamber 2 in the step (2) is 1120 ℃. Detected, Sb₂O₃Accounting for 4.6 percent of the silicon-based composite anode material.

Example 15

The other steps are the same as the example 13, and the difference is only that the raw material B in the step (1) is Co with the particle size of 70 mu m₃N₂And (3) in the step (2), the temperature of the heating chamber 2 is 1440 ℃. By detection, Co₃N₂5.9 percent of the silicon-based composite anode material.

Example 16

The other steps are the same as the example 13, and the difference is only that the raw material B in the step (1) is SnS with the granularity of 70 mu m₂In the step (2), the temperature of the heating chamber 2 is 1130 ℃. Detected, SnS₂7.8 percent of the silicon-based composite anode material.

Example 17

The other steps are the same as the example 13, and the difference is only that the raw material B in the step (1) is SnO with the particle size of 70 mu m₂100 g, and the temperature of the heating chamber 2 in the step (2) is 1500 ℃. Detected, SnO₂5.0 percent of the silicon-based composite anode material.

Example 18

The other steps are the same as the example 13, and the difference is only that the raw material B in the step (1) is 100 g of CoO powder with the particle size of 70 mu m, and the temperature of the heating chamber 2 in the step (2) is 1550 ℃. Detection shows that CoO accounts for 5.2% of the silicon-based composite anode material.

Comparative example 1

The operation was carried out in the same manner as in example 1 except that the raw material A in step (1) was 2 kg of the silicon oxide powder having a particle size of 100 μm, and the raw material B was not added.

The first coulombic efficiency and cycle performance test in the table was at 0.2C (1C =1600 mA g)^-1) At a current density of (a).

Before the cycle test of the negative electrode material, the silicon crystal grains cannot be changed greatly due to the limitation of the critical nucleation size of the silicon crystal grains, namely the sizes of the silicon crystal grains are different, and the grain diameter ranges from about 3 nm to about 5 nm. For the convenience of calculating the coefficient of expansion of silicon crystal grains, the silicon crystal grains before the cycle of the negative electrode materials of examples and comparative examples were 5nm, and the size of the silicon crystal grains in the materials after the cycle was measured, thereby calculating the suppression expansion rate of the silicon crystal grains.

The method for inhibiting expansion rate of silicon crystal grains is to calculate the size (216 nm) of the silicon crystal grains of the negative electrode material of comparative example 1 (without metal doping) after 500 cycles, and the inhibition expansion rate is (216-80)/216 × 100% =63.0% when the expansion rate of the negative electrode material of example 1 after 500 cycles is 80nm based on the expansion rate of 5nm before the cycle to 216nm after the cycle being 100%, and the data of other examples and comparative examples are calculated according to the calculation mode. The larger the suppression expansion ratio, the more stable the suppression of the obtained anode material in the battery operation.

The embodiment data show that the cathode material prepared by the invention has higher inhibition silicon crystal grain expansion rate, can effectively inhibit the agglomeration of silicon crystal grains in the material through metal doping, ensures that the agglomerated silicon crystal grains are re-dispersed in circulation, and can inhibit the silicon crystal grain expansion rate by more than 30 percent, more preferably more than 60 percent, thereby improving the circulation efficiency of the cathode material and still maintaining excellent circulation efficiency after 500 cycles.

As can be seen from examples 1 and 2, after 500 charge and discharge cycles, the silicon-based composite anode material without sintering has large silicon grains, and the first specific capacity, the first library efficiency and the cycle retention rate are all reduced, because the deposition temperature of the material in the collecting device is low, the doped metal is only deposited in the silicon protoxide and does not completely react with the silicon protoxide, so that the doped metal is not bonded with the silicon grains in the silicon protoxide and cannot inhibit the growth of the silicon grains, and therefore, the silicon grains of the material in example 3 continuously grow up during the cycle process, which causes the deterioration of the cycle and rate performance. The sintering process can enable the metal (simple substance, alloy or compound) which is deposited in the silicon oxide and does not completely react to further react with the silicon oxide substrate, thereby better playing the role of doping the metal to inhibit the agglomeration growth of silicon crystal grains and improving the electrochemical performance of the material.

As can be seen from examples 1, 3, 4, and 6, the deposition temperature and pressure (i.e., the temperature in the collection device) have a certain influence on the cycle stability of the negative electrode material and the size of silicon crystal grains after the cycle.

From examples 1 and 5 and examples 7 and 8, it can be seen that the use of the dual-temperature chamber, the control of the difference of the heating temperature of the raw materials, the higher first coulombic efficiency, and the improvement of the cycle and rate capability. The evaporation rate of the reaction product can be controlled by controlling the temperature of the double-temperature cavity, so that the concentration of the doped metal of the deposited silicon monoxide from the bottom layer to the top layer is more uniform, the effects of better improving the conductivity and inhibiting the silicon agglomeration are obtained, and the material has more excellent comprehensive performance.

From examples 9 to 13, starting material A: the proportion of the raw material B is 10-25: 1, the doped metal content is ensured to be appropriate, the conductivity can be improved, the silicon agglomeration is blocked, and the silicon grain growth is inhibited, wherein the content is preferably 10-20: 1, the metal content is 4-9%, and the electrochemical effect is better.

It can be seen from examples 13 to 18 that the doping effect of the metal simple substance and the compound is good, especially the doping effect of the nitride and the sulfide of the metal cobalt and tin is better, the first coulombic efficiency and the cycle performance of the negative electrode material are improved, and especially the first coulombic efficiency and the rate capacity are obviously improved.

Even under the conditions that silicon raw materials are more and silicon crystal grains are easy to agglomerate, the anode material with the uniformly doped metal in the bulk phase prepared by the invention still has higher first coulombic efficiency and cycling stability. Therefore, the use amount of the metal raw materials can be reduced by adjusting the types of the metal raw materials, the utilization rate of each raw material is improved, the cost is reduced, the expansion of silicon crystal grains can be inhibited, and the electrical properties of the negative electrode material, such as the first coulombic efficiency, the cyclicity and the like, can be ensured.

Through the data of the examples and the comparative examples, as can be clearly seen in fig. 6-8, the metal-doped silicon-based composite anode material can inhibit crack generation and silicon agglomeration, reduce internal expansion of the silicon-based material, and inhibit higher expansion rate, so that better and excellent electrical property and cycle stability (high cycle stability of 500 cycles) are improved.

In conclusion, the preparation method disclosed by the invention is simple in process, environment-friendly, rich in raw materials and has industrial potential. Compared with undoped materials, the prepared silicon-based composite negative electrode material has higher conductivity and better structural stability, realizes the improvement of the first coulombic efficiency, rate capability and cycle performance, and has more excellent comprehensive performance.

The applicant states that the present invention is illustrated by the above examples to describe the detailed preparation method of the present invention, but the present invention is not limited to the above detailed preparation method, i.e. it does not mean that the present invention must rely on the above detailed preparation method to be carried out. It should be understood by those skilled in the art that any modification of the present invention, equivalent substitutions of the raw materials of the product of the present invention, addition of auxiliary components, selection of specific modes, etc., are within the scope and disclosure of the present invention.

Claims

1. A preparation method of a silicon-based composite anode material of a lithium ion battery is characterized by comprising the following steps:

(1) pretreatment: taking 2 kg of silicon monoxide powder with the granularity of 100 mu m as a raw material A, and SnS with the granularity of 70 mu m₂100 g of powder is taken as a raw material B, and the raw material A and the mixed raw material B are respectively dried for 6 hours at the temperature of 80 ℃ under the argon atmosphere to remove moisture, so as to obtain a pretreated raw material;

（2）SnS₂doping the silicon-based composite material: charging the raw materials obtained in the step (1) into a container with a collecting device and twoIn a vacuum furnace with a heating chamber, a raw material A is filled into the heating chamber 1, a raw material B is filled into the heating chamber 2, the heating is started after the pressure is pumped to below 10 Pa, the heating chamber 1 is heated to 1400 ℃ at the speed of 6 ℃/min and then is insulated for 10 h, the heating chamber 2 is heated to 1130 ℃ for 10 h at the same heating time, the temperature of a collecting device is controlled to be 400 ℃, the deposited material is transferred into a sintering furnace in the nitrogen atmosphere through a transition cabin after the insulation is finished, the temperature is increased to 800 ℃ at the heating speed of 5 ℃/min and is insulated for 1 h, and the material is naturally cooled to room temperature to obtain blocky SnS₂Doping a silicon-based composite negative electrode material;

(3) carbon-coated SnS₂Doping a silicon-based composite anode material: airflow crushing the block material obtained in the step (2) to particles with the particle size of 10 mu m, putting the particles into an intermittent coating furnace, introducing acetylene at the flow rate of 800 sccm, preserving heat at 800 ℃ for 3.5 h, placing the coated material in a nitrogen atmosphere, heating to 900 ℃ at the speed of 5 ℃/min, preserving heat for 1 h, naturally cooling to room temperature to obtain an inner SnS layer with an outer layer and a uniform carbon coating₂Uniformly doped carbon-coated SnS₂The silicon-based composite negative electrode material comprises a carbon coating layer with the thickness of 8 nm, a carbon material accounting for 5 wt% of the silicon-based composite negative electrode material, and SnS₂7.8 percent of the silicon-based composite anode material.