CN116470055A - Composite positive electrode material, preparation method thereof and lithium ion battery - Google Patents

Composite positive electrode material, preparation method thereof and lithium ion battery Download PDF

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CN116470055A
CN116470055A CN202310436036.3A CN202310436036A CN116470055A CN 116470055 A CN116470055 A CN 116470055A CN 202310436036 A CN202310436036 A CN 202310436036A CN 116470055 A CN116470055 A CN 116470055A
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positive electrode
electrode material
ball milling
composite positive
source
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苏丽云
何海平
张凯
敬登伟
张兄文
王进仕
丁坤鹏
栾琳
夏晓倩
吴瑞华
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Gree Altairnano New Energy Inc
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Gree Altairnano New Energy Inc
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/50—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese
    • H01M4/505—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of manganese of mixed oxides or hydroxides containing manganese for inserting or intercalating light metals, e.g. LiMn2O4 or LiMn2OxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/48—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides
    • H01M4/52—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron
    • H01M4/525—Selection of substances as active materials, active masses, active liquids of inorganic oxides or hydroxides of nickel, cobalt or iron of mixed oxides or hydroxides containing iron, cobalt or nickel for inserting or intercalating light metals, e.g. LiNiO2, LiCoO2 or LiCoOxFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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Abstract

The invention provides a composite positive electrode material, a preparation method thereof and a lithium ion battery. The composite positive electrode material sequentially comprises a positive electrode material core, a lithium phosphate coating layer and a carbon coating layer from inside to outside, wherein the material of the positive electrode material core is an oxide of M element, the M element is Co, ni or Mn, and the molar ratio of P element to M element in the lithium phosphate coating layer is 1 (1-3). Compared with the surface-coated lithium fluoride coating, the lithium phosphate coating can effectively reduce the overpotential of the first charge and improve the first discharge capacity, thereby improving the electrochemical specific capacity of the composite positive electrode material. The carbon coating layer is favorable for exerting the conductivity of the carbon material on one hand, so that the electrochemical performance of the composite positive electrode material is improved, and is favorable for inhibiting the volume effect of the composite positive electrode material during charge and discharge on the other hand, so that the structural stability of the composite positive electrode material is improved, and the cycle stability of the lithium ion battery is improved.

Description

Composite positive electrode material, preparation method thereof and lithium ion battery
Technical Field
The invention relates to the technical field of lithium ion battery materials, in particular to a composite positive electrode material, a preparation method thereof and a lithium ion battery.
Background
Currently, lithium ion battery technology has been dominant in the secondary battery market, and is widely used in the fields of portable electronic products and electric automobiles. The positive electrode material is used as a key component of the lithium ion battery, the structural stability of the positive electrode material directly influences the safety performance of the battery, and the specific capacity of the positive electrode material directly determines the energy density of the battery. Therefore, the development of positive electrode materials with high energy density and good safety performance is a hot spot of current global research.
Currently, the most commonly used cathode materials are lithium-containing transition metal compounds having one-, two-or three-dimensional open structures, such as olivine (LiMPO) 4 M=transition metal), lamellar (LiMO 2 M=transition metal) or spinel material. However, these materials constitute only a very small portion of the redox active transition metal compounds present in nature, and in addition there are many materials such as transition metal oxides, sulfides, phosphates and nitrides, some of which may exhibit suitable electrochemical potentials with respect to lithium, but are often ignored because they do not contain lithium or do not contain lithium conduction pathways。
It has been found that a surface modification of a lithium-free transition metal oxide (e.g., mnO, feO, coO, etc.) that does not contain a lithium conduction path with nanoscale lithium fluoride can be converted into a positive electrode material for a high-capacity lithium ion battery, but there are several problems with this material: firstly, a large overpotential exists after the first charge; secondly, the volume change of the transition metal oxide is large in the charge and discharge process, so that the active particles and the current collector are in electrical contact, and the circulation stability is reduced; finally, the conductivity of the excessive metal oxide is poor, and the conductivity of the electrode is affected.
On the basis, research and development of a positive electrode material for lithium ion batteries prepared by using a lithium-free transition metal oxide as a raw material are of great significance for improving the resource utilization rate.
Disclosure of Invention
The invention mainly aims to provide a composite positive electrode material, a preparation method thereof and a lithium ion battery, and aims to solve the problems of low energy efficiency and poor cycle stability of the lithium ion battery caused by poor structural stability of the positive electrode material prepared by taking a lithium-free transition metal oxide as a raw material in the prior art.
In order to achieve the above purpose, the invention provides a composite positive electrode material, which comprises a positive electrode material core, a lithium phosphate coating layer and a carbon coating layer from inside to outside, wherein the material of the positive electrode material core is an oxide of M element, the M element is Co, ni or Mn, and the molar ratio of P element in the lithium phosphate coating layer to M element in the positive electrode material core is 1 (1-3).
Further, the thickness of the carbon coating layer is 3-20 nm.
In order to achieve the above object, another aspect of the present invention further provides a method for preparing the above composite positive electrode material, where the method for preparing the composite positive electrode material includes: step S1, performing first ball milling on an M source, a lithium source and a phosphorus source to obtain a first ball milling system; wherein the M source is cobalt acetate, nickel acetate or manganese acetate; the molar ratio of the M source to the lithium source to the phosphorus source is 1 (3-9): 1-3; s2, performing second ball milling on the first ball milling system and the conductive carbon material to obtain a second ball milling system; and S3, calcining the second ball milling system to obtain the composite anode material.
Further, the weight of the conductive carbon material is 5-20wt% of the M source.
Further, the lithium source is lithium acetate and/or lithium citrate; preferred phosphorus sources are NH 4 H 2 PO 4 The method comprises the steps of carrying out a first treatment on the surface of the Preferably the conductive carbon material is superconductive carbon black.
Further, step S1 includes: performing first ball milling on the M source, the lithium source, the phosphorus source, the first solvent and the ball milling medium to obtain a first ball milling system; the step S2 comprises the following steps: performing second ball milling on the first ball milling system, the conductive carbon material and the first ball milling system to obtain a second ball milling system; preferably, the temperature of the first ball milling process is 20-25 ℃ and the time is 4-6 h; the temperature of the second ball milling process is 20-25 ℃ and the time is 4-6 h; preferably, the weight ratio of the solid materials in the first ball milling system to the ball milling media is 1 (20-30).
Further, the temperature of the calcination treatment is 400-700 ℃, the time is 2-6 h, and the temperature rising rate is 3-5 ℃/min.
Further, when the M source is cobalt acetate, the calcination treatment temperature is 500-550 ℃ and the calcination treatment time is 4-5 h; and/or when the M source is nickel acetate, the calcination treatment temperature is 550-600 ℃ and the calcination treatment time is 2-4 h; and/or when the M source is manganese acetate, the calcination treatment temperature is 480-530 ℃ and the calcination treatment time is 2-2.5 h.
Further, a drying treatment step is further included between the calcination treatment and the second ball milling process, and the temperature of the drying treatment process is preferably 80-100 ℃ and the time is preferably 12-24 hours.
In another aspect, the invention provides a lithium ion battery, which comprises a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode comprises the composite positive electrode material provided by the application or the composite positive electrode material prepared by the preparation method of the composite positive electrode material provided by the application.
By applying the technical scheme of the invention, the lithium phosphate coating layer is arranged on the surface of the inner core (oxide of M element) of the positive electrode material, compared with the surface coated with the lithium fluoride coating layer, the lithium fluoride coating layer has the bond energy of 341kJ/mol which is far lower than the bond energy of Li-F (577 kJ/mol), so that the overpotential of primary charging can be effectively reduced, the primary discharge capacity is improved, and the electrochemical specific capacity of the composite positive electrode material can be improved. The composite positive electrode material further comprises a carbon coating layer arranged on the surface of the lithium phosphate coating layer at one side far away from the inner core of the positive electrode material. The method is favorable for exerting the conductivity of the carbon material, so that the electrochemical performance of the composite positive electrode material is improved, and the volume effect of the composite positive electrode material during charge and discharge is restrained, so that the structural stability of the composite positive electrode material is improved, and the cycle stability of the lithium ion battery is improved.
Compared with other ranges, the molar ratio of the P element in the lithium phosphate coating layer and the M element in the positive electrode material core is limited in a specific range, so that the overpotential of primary charging is reduced, and the electrochemical specific capacity of the composite positive electrode material can be improved.
The composite positive electrode material provided by the application is applied to a lithium ion battery, so that the lithium ion battery has excellent electrochemical specific capacity, cycle performance and safety performance.
Drawings
The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the invention. In the drawings:
fig. 1 shows the results of 0 to 200 cycles of rate performance test of the lithium ion batteries manufactured in examples 1 to 4 and comparative example 1;
fig. 2 shows the 0-200-turn capacity retention test results of the lithium ion batteries manufactured in examples 1 to 4 and comparative example 1.
Detailed Description
It should be noted that, in the case of no conflict, the embodiments and features in the embodiments may be combined with each other. The present invention will be described in detail with reference to examples.
As described in the background art, the existing positive electrode material prepared by using the lithium-free transition metal oxide as a raw material has the problems of low energy efficiency and poor cycle stability due to poor structural stability of the positive electrode material. In order to solve the technical problems, the application provides a composite positive electrode material, which sequentially comprises a positive electrode material core, a lithium phosphate coating layer and a carbon coating layer from inside to outside, wherein the material of the positive electrode material core is an oxide of M element, the M element is Co, ni or Mn, and the molar ratio of P element to M element in the lithium phosphate coating layer is 1 (1-3).
It should be noted that, the lithium storage mechanism of the composite positive electrode material provided in the present application is different from the conventional lithium storage mechanism of the positive electrode material for a lithium ion battery, in this application, the positive electrode material core (oxide of M element) can generate a multi-electron reversible oxidation-reduction reaction with lithium ions, namely a "conversion reaction", and the electrochemical conversion reaction based on the lithium ion battery can be represented as follows:
wherein M has the same definition as the previous, and X may represent an oxygen element, a fluorine element, or the like. In this conversion lithium storage mechanism, the number of lithium ions participating in the redox reaction is no longer limited by the structure of the intercalation host material, but rather by the lithium compound Li n The lithium content in X.
The lithium phosphate coating layer is arranged on the surface of the inner core (oxide of M element) of the positive electrode material, compared with the lithium fluoride coating layer coated on the surface, the lithium phosphate coating layer is far lower than the bond energy (577 kJ/mol) of Li-F because the bond energy of Li-O is 341kJ/mol, so that the overpotential of primary charging can be effectively reduced, the primary discharge capacity is improved, and the electrochemical specific capacity of the composite positive electrode material can be improved. The composite positive electrode material further comprises a carbon coating layer arranged on the surface of the lithium phosphate coating layer at one side far away from the inner core of the positive electrode material. The method is favorable for exerting the conductivity of the carbon material, so that the electrochemical performance of the composite positive electrode material is improved, and the volume effect of the composite positive electrode material during charge and discharge is restrained, so that the structural stability of the composite positive electrode material is improved, and the cycle stability of the lithium ion battery is improved.
Compared with other ranges, the molar ratio of the P element in the lithium phosphate coating layer and the M element in the positive electrode material core is limited in a specific range, so that the overpotential of primary charging is reduced, and the electrochemical specific capacity of the composite positive electrode material can be improved.
The composite positive electrode material provided by the application is applied to a lithium ion battery, so that the lithium ion battery has excellent electrochemical specific capacity, cycle performance and safety performance.
In order to further improve the conductivity of the composite positive electrode material and thus further improve the electrochemical performance of the composite positive electrode material, the carbon coating layer preferably has a thickness of 3 to 20nm.
The second aspect of the present application also provides a method for preparing the above composite positive electrode material, where the method for preparing the composite positive electrode material includes: step S1, performing first ball milling on an M source, a lithium source and a phosphorus source to obtain a first ball milling system; wherein the M source is cobalt acetate, nickel acetate or manganese acetate; the molar ratio of the M source to the lithium source to the phosphorus source is 1 (3-9): 1-3; s2, performing second ball milling on the first ball milling system and the conductive carbon material to obtain a second ball milling system; and S3, calcining the second ball milling system to obtain the composite anode material.
Compared with other types of M sources, the M source of the preferred type can provide sources of Co, ni and Mn elements on one hand, has a wider electrochemical window on the other hand, and can improve the electrochemical performance of the composite positive electrode material. The M source, the lithium source and the phosphorus source are subjected to first ball milling, so that a precursor material is formed, and a layer of deposition layer containing phosphorus element is formed on the surface of the precursor material at the same time, so that a first coating layer containing lithium phosphate is formed through calcination. And (3) calcining the second ball milling system, wherein acetic acid groups in the precursor material are carbonized in the calcining process, and finally carbon dioxide is formed to escape, so that a positive electrode material core is formed, and meanwhile, a phosphorus element-containing deposition layer is coated on the surface of the positive electrode material core in the calcining process to form a first coating layer.
The molar ratio of the M source, the lithium source and the phosphorus source includes but is not limited to the above range, and limiting the molar ratio to the above specific range is beneficial to reducing the overpotential of the first charge, thereby being beneficial to improving the electrochemical specific capacity of the composite positive electrode material.
In a preferred embodiment, the conductive carbon material is present in an amount of 5 to 20wt% based on the weight of the M source. The amount of the conductive carbon material includes, but is not limited to, the above-mentioned range, and the above-mentioned range is advantageous for further improving the conductivity of the composite positive electrode material, thereby further improving the electrochemical performance of the composite positive electrode material, and for further suppressing the volume effect of the composite positive electrode material during charge and discharge, thereby further improving the structural stability of the composite positive electrode material, thereby further improving the cycling stability of the lithium ion battery.
In order to further improve the conductivity of the composite positive electrode material and to further suppress the volume effect of the composite positive electrode material during charge and discharge, preferably, the conductive carbon material accounts for 15wt% of the M source.
In a preferred embodiment, the lithium source is lithium acetate and/or lithium citrate. Compared with other types of lithium sources, the lithium source with the specific type is favorable for exerting the advantage of wide electrochemical window, so that the subsequently prepared composite positive electrode material has better electrochemical performance.
In a preferred embodiment, the phosphorus source is NH 4 H 2 PO 4 . Compared with other types of phosphorus sources, the adoption of the specific type of phosphorus source is beneficial to reducing the introduction of impurities, thereby being beneficial to the improvement of the electrochemical performance of the composite positive electrode material.
In order to further improve the conductivity of the composite positive electrode material and thus further improve the rate capability of the lithium ion battery, the conductive carbon material is preferably superconducting carbon black.
In a preferred embodiment, step S1 comprises: performing first ball milling on the M source, the lithium source, the phosphorus source, the first solvent and the ball milling medium to obtain a first ball milling system; the step S2 comprises the following steps: and performing second ball milling on the first ball milling system, the conductive carbon material and the first ball milling system to obtain a second ball milling system.
Performing first ball milling on an M source, a lithium source, a phosphorus source, a first solvent and a ball milling medium, and forming a layer of phosphorus-containing deposition layer on the surface of a precursor material while forming the precursor for preparing a core of the anode material, so that a lithium phosphate coating layer can be formed through calcination in the follow-up process; and performing second ball milling on the first ball milling system, the conductive carbon material and the first ball milling system to form a carbon coating layer on the surface of the lithium phosphate coating layer.
In a preferred embodiment, the temperature of the first ball milling process is 20 to 25℃for 4 to 6 hours. The temperature and time of the first ball milling process include, but are not limited to, the above ranges, and the above ranges are limited to facilitate the improvement of the ball milling effect of the first ball milling, the improvement of the deposition effect or the coating effect of the phosphorus-containing deposition layer, the formation of the positive electrode material core with stable structure, and the improvement of the structural stability of the subsequently prepared composite positive electrode material, thereby facilitating the improvement of the electrochemical performance of the lithium ion battery containing the composite positive electrode material.
In a preferred embodiment, the second ball milling process is carried out at a temperature of 20 to 25℃for a period of 4 to 6 hours. The temperature and time of the second ball milling process include, but are not limited to, the above ranges, and the second ball milling process is limited to the above ranges, so that on one hand, the conductive performance of the carbon material is further facilitated to be further exerted, and further, the electrochemical performance of the composite positive electrode material is further facilitated to be improved, and on the other hand, the volume effect of the composite positive electrode material during charge and discharge is further facilitated to be further restrained, and therefore, the structural stability of the composite positive electrode material is further facilitated to be improved, and the cycling stability of the lithium ion battery is further facilitated to be improved.
In order to further improve the ball milling effect of the first ball milling, preferably, the weight ratio of the solid materials in the first ball milling system to the ball milling medium is 1 (20-30).
In a preferred embodiment, the calcination treatment is carried out at a temperature of 400 to 700℃for a period of 2 to 6 hours and at a rate of 3 to 5℃per minute. The temperature, time and heating rate of the calcination treatment include, but are not limited to, the above ranges, and the limitation of the above ranges is beneficial to improving the purity of the composite positive electrode material crystal form, and the structural stability, thereby being beneficial to improving the cycle performance of the lithium ion battery.
In order to pertinently improve the structural stability of the composite positive electrode material and further improve the cycle performance of the lithium ion battery, preferably, when the M source is cobalt acetate, the calcination treatment temperature is 500-550 ℃ and the time is 4-5 h; and/or when the M source is nickel acetate, the calcination treatment temperature is 550-600 ℃ and the calcination treatment time is 2-4 h; and/or when the M source is manganese acetate, the calcination treatment temperature is 480-530 ℃ and the calcination treatment time is 2-2.5 h.
In a preferred embodiment, a drying process step is further included between the calcination process and the second ball milling process. The adoption of the drying treatment step is beneficial to volatilizing and removing most of the solvent in the system before the calcination treatment, and is convenient for the subsequent calcination treatment.
In order to further improve the solvent removal effect and provide better conditions for the subsequent calcination treatment, the drying treatment process is preferably carried out at a temperature of 80-100 ℃ for 12-24 hours.
The third aspect of the application also provides a lithium ion battery, which comprises a positive electrode, a negative electrode, a diaphragm arranged between the positive electrode and the negative electrode and electrolyte, wherein the positive electrode comprises the composite positive electrode material provided by the application or a composite positive electrode material prepared by the preparation method of the composite positive electrode material provided by the application.
The composite positive electrode material provided by the application is applied to a lithium ion battery, so that the lithium ion battery has excellent electrochemical specific capacity, cycle performance and safety performance.
The present application is described in further detail below in conjunction with specific embodiments, which should not be construed as limiting the scope of the claims.
Example 1
NiO@Li 3 PO 4 The preparation method of the @ C composite positive electrode material comprises the following steps:
(1) 2.49g of Ni (CH) was weighed out separately 3 COO) 2 ·4H 2 O (Nickel acetate tetrahydrate), 3.06g CH 3 COOLi·2H 2 O (lithium acetate dihydrate) with 1.15g NH 4 H 2 PO 4 For standby, and Ni (CH) 3 COO) 2 ·4H 2 O、CH 3 COOLi·2H 2 O and NH 4 H 2 PO 4 The molar ratio of (2) is 1:3:1; mixing the weighed M source and lithium source with absolute ethyl alcohol, adding the mixture into a planetary ball mill (Japanese Xinji AR-100), and placing 166.5g of ball milling medium into the ball milling device for first ball milling to obtain a first ball milling system; wherein the temperature of the first ball milling is 25 ℃ and the time is 6 hours; the weight ratio of the solid materials to the ball milling media in the first ball milling system is 1:30; the solid materials refer to an M source, a lithium source and a phosphorus source;
(2) Weighing 0.37g of superconducting carbon black (KB, D50 is 40 nm) for standby; mixing the obtained first ball milling system with weighed superconductive carbon black and 212g of ball milling medium, adding the mixture into the planetary ball milling instrument (Japanese Xinji AR-100), and performing second ball milling to obtain a second ball milling system; wherein, the weight ratio of the M source to the lithium source to the phosphorus source to the conductive carbon material is 2.49:3.06:1.15:0.37, and the superconductive carbon black accounts for 15wt% of the nickel acetate tetrahydrate (M source); the temperature of the second ball milling is 25 ℃ and the time is 6 hours;
(3) Transferring the second ball milling system into a vacuum drying oven, and drying at 80 ℃ for 12 hours;
(4) Transferring the dried material obtained in the step (3) into a tube furnace, introducing argon, heating to 550 ℃ at a heating rate of 4 ℃/min, and calcining for 4 hours to obtain NiO@Li 3 PO 4 And @ C composite positive electrode material.
The composite positive electrode material prepared in the embodiment 1 is assembled into a button cell for rate performance test and cycle stability test, and the test results are shown in fig. 1 and fig. 2 respectively.
The assembly process of the button cell is as follows: the prepared composite positive electrode material is taken as a positive electrode, a lithium sheet is taken as a negative electrode, a 6 mu mPP base film is taken as a diaphragm, electrolyte is Xuecheng 1901, and the prepared composite positive electrode material is assembled into a button cell, and the prepared button cell is expressed as: positive electrode case positive electrode sheet electrolyte diaphragm electrolyte lithium sheet collector leaf negative electrode case.
Example 2
The difference from example 1 is that: in the second ball milling process, the weight of the superconducting carbon black was 0.50g. The superconductive carbon black accounts for 20wt% of the tetrahydrated nickel acetate.
Example 3
The difference from example 1 is that: in the second ball milling process, the weight of the superconducting carbon black was 0.25g. The superconductive carbon black accounts for 10 weight percent of the tetrahydrated nickel acetate.
Example 4
The difference from example 1 is that: in the second ball milling process, the weight of the superconducting carbon black was 0.12g. The superconductive carbon black accounts for 5wt% of the tetrahydrated nickel acetate.
Example 5
The difference from example 1 is that: the temperature of the first ball milling process is 20 ℃ and the time is 4 hours; the temperature of the second ball milling process was 20℃for 4 hours.
Example 6
The difference from example 1 is that: the temperature of the first ball milling process is 50 ℃ and the time is 8 hours; the temperature of the second ball milling process was 50℃for 8 hours.
Example 7
The difference from example 1 is that: the calcination treatment was carried out at 400℃for 6 hours.
Example 8
The difference from example 1 is that: the calcination treatment temperature was 700℃and the time was 4 hours.
Example 9
The difference from example 1 is that: the temperature of the calcination treatment was 350 ℃.
Example 10
The difference from example 1 is that: the calcination treatment was carried out at 600℃for 2 hours.
Comparative example 1
The difference from example 1 is that: in the second ball milling process, the weight of the superconducting carbon black was 0g. The superconductive carbon black accounts for 0 weight percent of the tetrahydrated nickel acetate. The composite positive electrode material prepared in the comparative example 1 is assembled into a button cell for rate performance test and cycle stability test, and the test results are shown in fig. 1 and fig. 2 respectively.
The composite positive electrode materials prepared in the above examples and comparative examples were assembled to form a coin cell (the assembly method was the same as in example 1), and a cycle performance test and constant current charge and discharge tests at different rates (0.05C, 0.5C) were performed. Wherein the cycle performance test is carried out within 2.0-4.5V.
TABLE 1
From the above description, it can be seen that the above embodiments of the present invention achieve the following technical effects:
as can be seen from comparing example 1 with comparative example 1, limiting the molar ratio of the P element in the lithium phosphate coating layer to the M element in the core of the positive electrode material within a specific range is advantageous in reducing the overpotential for the first charge, as compared with other ranges, and thus in being able to improve the electrochemical specific capacity of the composite positive electrode material.
As is clear from comparative examples 1 to 4 and comparative example 1, the specific discharge capacity of the composite positive electrode material decreases with an increase in discharge rate. When the magnification is returned from 0.5C to 0.05C, the specific discharge capacity is again increased. From test data, when the weight percentage of the superconducting carbon black in the lithium-free transition metal source is 15wt%, the rate performance of the lithium ion battery prepared from the superconducting carbon black is superior to that of composite positive electrode materials prepared from the superconducting carbon black with other contents.
As can be seen from comparing examples 1, 5 and 6, the temperature and time of the first ball milling process include, but are not limited to, the preferred ranges of the present application, and the limitation of the temperature and time in the preferred ranges of the present application is beneficial to improving the ball milling effect of the first ball milling, the deposition effect or the coating effect of the deposition layer containing the phosphorus element, the formation of the core of the cathode material with stable structure, and the structural stability of the subsequently prepared composite cathode material, thereby improving the electrochemical performance of the lithium ion battery containing the composite cathode material. The temperature and time of the second ball milling process include, but are not limited to, the preferred ranges of the application, and the second ball milling process is limited to the preferred ranges of the application, so that on one hand, the conductive performance of the carbon material is better to be further exerted, and the electrochemical performance of the composite positive electrode material is better to be further improved, and on the other hand, the volume effect of the composite positive electrode material during charge and discharge is better to be further restrained, and the structural stability of the composite positive electrode material is better to be further improved, and the cycling stability of the lithium ion battery is better to be improved.
As can be seen from comparing examples 1, 7 to 9, the temperature, time and heating rate of the calcination treatment include, but are not limited to, the preferred ranges of the present application, and limiting the same to the preferred ranges of the present application is advantageous for improving the purity of the composite positive electrode material crystal form, and for improving the structural stability thereof, thereby being advantageous for improving the cycle performance of the lithium ion battery.
As can be seen from comparing examples 1 and 10, in the case where the M source is nickel acetate, the preferred calcination conditions adopted in the present application purposefully improve the structural stability of the composite positive electrode material, and further improve the cycle performance of the lithium ion battery.
It should be noted that the terms "first," "second," and the like in the description and in the claims of the present application are used for distinguishing between similar objects and not necessarily for describing a particular sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances such that the embodiments of the application described herein are, for example, capable of operation in sequences other than those described herein.
The above description is only of the preferred embodiments of the present invention and is not intended to limit the present invention, but various modifications and variations can be made to the present invention by those skilled in the art. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (10)

1. The composite positive electrode material is characterized by sequentially comprising a positive electrode material core, a lithium phosphate coating layer and a carbon coating layer from inside to outside, wherein the material of the positive electrode material core is an oxide of an M element, the M element is Co, ni or Mn, and the molar ratio of a P element in the lithium phosphate coating layer to the M element in the positive electrode material core is 1 (1-3).
2. The composite positive electrode material according to claim 1, wherein the carbon coating layer has a thickness of 3 to 20nm.
3. A method for preparing the composite positive electrode material according to claim 1 or 2, characterized in that the method for preparing the composite positive electrode material comprises the steps of:
step S1, performing first ball milling on an M source, a lithium source and a phosphorus source to obtain a first ball milling system; wherein the M source is cobalt acetate, nickel acetate or manganese acetate; the molar ratio of the M source to the lithium source to the phosphorus source is 1 (3-9):
(1～3)；
s2, performing second ball milling on the first ball milling system and the conductive carbon material to obtain a second ball milling system;
and step S3, calcining the second ball milling system to obtain the composite anode material.
4. The method of preparing a composite positive electrode material according to claim 3, wherein the conductive carbon material is 5 to 20wt% based on the weight of the M source.
5. The method for preparing a composite positive electrode material according to claim 4, wherein the lithium source is lithium acetate and/or lithium citrate; preferably, the phosphorus source is NH 4 H 2 PO 4 The method comprises the steps of carrying out a first treatment on the surface of the Preferably, the conductive carbon material is superconducting carbon black.
6. The method for preparing a composite positive electrode material according to claim 4 or 5, wherein the step S1 comprises: performing the first ball milling on the M source, the lithium source, the phosphorus source, the first solvent and a ball milling medium to obtain the first ball milling system;
the step S2 includes: performing the second ball milling on the first ball milling system, the conductive carbon material and the first ball milling system to obtain a second ball milling system;
preferably, the temperature of the first ball milling process is 20-25 ℃ and the time is 4-6 h; the temperature of the second ball milling process is 20-25 ℃ and the time is 4-6 h;
preferably, the weight ratio of the solid materials in the first ball milling system to the ball milling media is 1 (20-30).
7. The method for preparing a composite positive electrode material according to claim 3, wherein the calcination treatment is carried out at a temperature of 400 to 700 ℃ for 2 to 6 hours at a heating rate of 3 to 5 ℃/min.
8. The method for preparing a composite positive electrode material according to claim 7, wherein when the M source is cobalt acetate, the calcination treatment is performed at a temperature of 500-550 ℃ for 4-5 hours; and/or the number of the groups of groups,
when the M source is nickel acetate, the temperature of the calcination treatment is 550-600 ℃ and the time is 2-4 h; and/or the number of the groups of groups,
when the M source is manganese acetate, the temperature of the calcination treatment is 480-530 ℃ and the time is 2-2.5 h.
9. The method for preparing a composite positive electrode material according to claim 3, further comprising a drying step between the calcination treatment and the second ball milling process, wherein the drying step is preferably performed at a temperature of 80 to 100 ℃ for a time of 12 to 24 hours.
10. A lithium ion battery comprising a positive electrode, a negative electrode, a separator between the positive electrode and the negative electrode, and an electrolyte, wherein the positive electrode comprises the composite positive electrode material according to claim 1 or 2, or the composite positive electrode material produced by the production method of the composite positive electrode material according to any one of claims 3 to 9.
CN202310436036.3A 2023-04-20 2023-04-20 Composite positive electrode material, preparation method thereof and lithium ion battery Pending CN116470055A (en)

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