Lithium-ion battery positive electrode material and preparation method

Abstract

The present invention discloses a lithium-ion battery cathode material and preparation method. The surface of the cathode material substrate is coated with a coating material composed of one or both of amorphous SnO2 and ZnO. By coating with an oxide and etching a portion of the oxide to form a porous structure, the present invention significantly improves the crystal structure stability of the cathode material while optimizing conductivity, thereby extending the service life and safety performance of the lithium-ion battery under high voltage, high current, and rapid charge and discharge conditions.

Description

Technical Field

[0001] The present invention relates to the field of special inorganic non-metallic materials, and in particular to a lithium ion battery positive electrode material and a preparation method thereof. Background Art

[0002] The widespread adoption of lithium-ion batteries in electric vehicles, handheld electronic devices, and other fields has led to higher demands on the safety, energy density, rate capability, and stability of their core cathode materials. Common cathode materials for lithium-ion batteries include lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and ternary materials. While ternary materials for lithium-ion batteries have evolved from the original low-nickel NCM333 to the high-nickel NCM811, increased internal resistance and decreased capacity and cycle performance remain unavoidable challenges in battery manufacturing.

[0003] Therefore, more and more researchers tend to locally dope and modify existing materials, partially optimize their crystal structure, and improve electrochemical performance. A common method to improve its safety is surface coating modification; through surface coating, it is possible to prevent direct contact between the positive electrode material and the electrolyte, inhibit the phase change of the positive electrode material, improve its structural stability, reduce the disorder of the cations in the lattice, and thus reduce the heat generated by side reactions. Improving the capacity, cycle, and safety performance of electrodes through surface coating has received widespread attention and is considered to be one of the most direct, economical, and efficient methods to improve the performance of NCM electrodes. However, due to the differences in the materials and technical methods used for modification, the effects vary greatly.

[0004] The existing high-nickel ternary positive electrode materials, especially during high-temperature cycles and long cycle life, will undergo a phase transition on the particle surface, from the original layered structure to the spinel structure, and then to the inactive rock phase, causing the capacity and cycle performance to decay; moreover, during the cycle process, due to the shrinkage and expansion of the crystals, some cracks will appear. These cracks will cause electronic short circuits on the one hand, and the appearance of cracks will also cause these fresh surfaces to produce more negative reactions with the electrolyte, affecting the cycle performance and safety of the entire battery. Summary of the Invention

[0005] In view of this, the technical problem solved by the present invention is to provide a lithium-ion battery positive electrode material and a preparation method, which improves safety, battery capacity and cycle stability, and further increases service life.

[0006] The technical solution of the present invention is implemented as follows: on the one hand, the present invention provides a lithium-ion battery positive electrode material, which includes a positive electrode material matrix and a coating layer on the surface of the positive electrode material matrix, and the coating layer includes one or both of amorphous SnO2 and ZnO.

[0007] Preferably, the positive electrode material matrix includes lithium manganese oxide, lithium cobalt oxide, lithium iron phosphate and a ternary material. More preferably, the ternary material includes NCM333, NCM523, NCM622 and NCM811.

[0008] Preferably, in terms of weight percentage, the weight of the coating layer accounts for 0.5% to 3.0% of the weight of the positive electrode material, and the content of ZnO in the coating layer is not less than 20%.

[0009] Preferably, the lithium-ion battery cathode material has a porous structure, and the surface pore size is controlled to be 10 to 40 nm.

[0010] On the other hand, the present invention also provides a method for preparing the lithium ion battery positive electrode material according to the first aspect of the present invention, comprising the following steps:

[0011] Take a positive electrode material matrix, and coat the surface of the positive electrode material matrix with an amorphous SnO2 or ZnO coating layer to obtain a lithium-ion battery positive electrode material.

[0012] Preferably, the method for preparing the lithium-ion battery positive electrode material further comprises the following steps:

[0013] S1, preparation of surface coating layer precursor: preparing sol containing tin ions or zinc ions,

[0014] S2, preparation of coating layer: take the positive electrode material matrix, disperse it in an organic solvent, add the sol containing tin ions or zinc ions prepared in step S1, adjust the pH value to form an organic mixed sol containing tin or zinc, heat treat until SnO2 or ZnO is precipitated, and coat it on the surface of the positive electrode material matrix, heat treat and dry it to obtain the positive electrode material for lithium ion batteries.

[0015] Preferably, the preparation process of the sol containing tin ions or zinc ions in step S1 comprises the following steps:

[0016] S1-1, take 99.0-99.5% by mass of citric acid, add deionized water and stir for 0.5-1h to obtain a citric acid aqueous solution, set aside;

[0017] S1-2, weigh tin tetrachloride pentahydrate SnCl4·5H2O and dissolve it in deionized water, stir, then add the citric acid aqueous solution obtained in step A1, and add triethanolamine dropwise until the solution is clear to prepare a tin ion-containing sol;

[0018] S1-3, weigh zinc acetate dihydrate Zn(CH3COO)2·2H2O, add anhydrous ethanol, stir at 70-75°C for 0.5-1h, add triethanolamine, stir for 0.5-1h, cool to 20-25°C, and prepare a sol containing zinc ions.

[0019] Preferably, in step S2, amorphous SnO2 or ZnO is formed by low-temperature heat treatment, and the heat treatment temperature is controlled at 220-350°C, and the heat treatment time is 10-72h.

[0020] More preferably, step S2 comprises the following steps:

[0021] S2-1, weighing a positive electrode material matrix, adding anhydrous ethanol and acetic acid for surface activation, wherein the mass ratio of the positive electrode material matrix to anhydrous ethanol and acetic acid is 1:(0.78-0.80):(0.1-0.12), stirring at 40-45° C. for 1.5-2 hours to prepare a mixture;

[0022] S2-2, according to the content of the coating layer, measure the sol containing tin ions or zinc ions in step S1, add it to the mixture in step S2-1, and stir for 1.5-2 hours to mix evenly;

[0023] S2-3, slowly dripping ammonia water to adjust the pH value to 9-10 at a dripping rate of 3-10 ml / min, stirring for 20-24 hours, the oxide slowly precipitates and coats the surface of the particles, and the obtained mixture is dried to obtain the lithium-ion battery positive electrode material.

[0024] Preferably, the lithium-ion battery positive electrode material obtained in step S2 is subjected to acid washing and etching treatment.

[0025] More preferably, the pickling and etching steps include:

[0026] S3, performing strong acid pickling on the lithium-ion battery positive electrode material obtained in step S2, wherein the strong acid solution includes hydrochloric acid or nitric acid, and the concentration of the etching solution is 0.2-0.6 mol / L, and the etching time is controlled within 5-15 minutes.

[0027] As a control, it was determined that the prepared surface modification material was an amorphous structure. The SnO2 and ZnO solutions prepared by the above-mentioned sol-gel method were coated on the surface of a glass substrate and achieved by slow heat treatment using a low-temperature method. X-ray diffraction structure testing showed that there were no significant diffraction peaks of ZnO and SnO2, indicating that these two materials did not form effective crystals and were in an amorphous state.

[0028] The lithium-ion battery positive electrode material and preparation method of the present invention have the following beneficial effects compared with the prior art:

[0029] (1) The oxide coated on the surface of the positive electrode material of the present invention has an amorphous structure, which is achieved by a low-temperature slow heat treatment method, wherein the slow heat treatment ensures that the organic matter is slowly and completely oxidized, and the low-temperature environment causes the inorganic material of the coating layer to become amorphous, maintain weak conductivity, and reduce the internal resistance of the battery.

[0030] (2) Strong acid etching technology is used to form a porous structure on the surface of the positive electrode material through acid etching, and the porosity is precisely controlled by the acid concentration.

[0031] (3) The existing process will cause damage to the material structure after material modification. However, due to the low temperature of the heat treatment in the present invention, weak oxidation is achieved during the low-temperature preparation process, and the amorphous state of the coating layer is achieved. This process technology will not affect the existing structure of the positive electrode material and maintain the high performance characteristics of the raw material.

[0032] (4) The collective surface modification of the cathode material of the present invention is achieved by the sol-gel method. The organic matter present in the coating layer precursor is slowly burned off under low-temperature weak oxidation conditions to form an ultra-thin surface modification layer, thereby increasing the proportion of the active cathode material matrix. DETAILED DESCRIPTION

[0033] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0034] Example 1

[0035] A lithium-ion battery positive electrode material, wherein the coating layer comprises 0.3% SnO2 and 0.2% ZnO by weight of the oxides, and the preparation method comprises the following steps:

[0036] S1, prepare the surface coating layer precursor; citric acid aqueous solution A preparation: take 99.0% citric acid 5.0g, dissolve in 25ml deionized water, stir for 0.5h, and obtain citric acid aqueous solution A; tin tetrachloride precursor sol B preparation: 35.1g tin tetrachloride pentahydrate SnCl4·5H2O is dissolved in deionized water, stirred for 0.5h, and then add 80ml of citric acid solution A obtained in step S1, and add triethanolamine dropwise with a dropper until the solution is clear to prepare a 0.4mol / L sol, in The mixture was allowed to stand at 20°C for 40 h. Preparation of zinc acetate dihydrate sol C: 41.31 g of zinc acetate dihydrate Zn(CH3COO)2·2H2O was weighed and placed in a beaker. 150 ml of anhydrous ethanol was added and stirred at 70°C for 0.5 h. 25 ml of triethanolamine was added and stirred for 0.5 h. The mixture was cooled to 20°C to prepare 0.75 mol / L sol C. The mixture was allowed to stand for 40 h. Preparation of acid etching solution D: 22.5 ml of hydrochloric acid was placed in a volumetric flask and water was added to prepare 0.2 mol / L acid etching solution D.

[0037] S2, preparation of coating layer, weighing 1000g of positive electrode material matrix NCM811 into a reactor, adding 780g of anhydrous ethanol and 100g of acetic acid, and stirring at 40°C for 1.5h to prepare a mixture; using a burette to measure 50ml of sol B and 32.5ml of sol C, adding them to the mixture obtained in step S2-1, and stirring for 1.5h; slowly adding ammonia water to the mixture obtained in step S2-2 through a micro dropper at a rate of 3ml / min to adjust the pH value to 9, stirring for 20h, and the oxide slowly precipitates and coats the surface of the particles. The obtained mixture is dried in an oven to form a powder; the obtained powder is placed in a muffle furnace, and the heat treatment temperature is controlled at 350°C for 10h to obtain a coating layer;

[0038] S3, placing the coating layer obtained in step S2 into 1000 ml of acid etching solution D, stirring, controlling the etching time to 5 minutes, filtering, and drying to obtain the finished product, and the surface pore size is controlled to be 10-40 nm.

[0039] Example 2

[0040] A lithium-ion battery positive electrode material, wherein the coating layer comprises 0.8% ZnO by weight of the oxide, and the preparation method comprises the following steps:

[0041] S1, prepare the surface coating layer precursor; citric acid aqueous solution A preparation: take 6.0g of citric acid with a mass fraction of 99.5%, dissolve it in 30ml of deionized water, and stir for 1h to obtain citric acid aqueous solution A; tin tetrachloride precursor sol B preparation: dissolve 70.2g of tin tetrachloride pentahydrate SnCl4·5H2O in deionized water, stir for 1h, then add 100ml of citric acid solution A obtained in step S1, and add triethanolamine dropwise with a dropper until the solution is clear to prepare a 0.5mol / L sol, The mixture was allowed to stand at 25°C for 48 hours. Preparation of zinc acetate dihydrate sol C: 43.90 g of zinc acetate dihydrate Zn(CH3COO)2·2H2O was weighed and placed in a beaker. 200 ml of anhydrous ethanol was added and stirred at 75°C for 1 hour. 30 ml of triethanolamine was added and stirred for 1 hour. The mixture was cooled to 25°C to prepare 0.8 mol / L sol C. The mixture was allowed to stand for 48 hours. Preparation of acid etching solution D: 67.5 ml of nitric acid was placed in a volumetric flask and water was added to prepare 0.6 mol / L acid etching solution D.

[0042] S2, coating layer preparation: weigh 1000g of the positive electrode material matrix NCM333 into a reactor, add 800g of anhydrous ethanol and 120g of acetic acid, and stir at 45°C for 2h to prepare a mixture; use a burette to measure 130ml of sol C and add it to the mixture obtained in step S2-1, and keep stirring for 2h; slowly add ammonia water to the mixture obtained in step S2-2 using a micro dropper at a rate of 10ml / min to adjust the pH value to 10, and stir for 24h. The oxide slowly precipitates and coats the surface of the particles. The obtained mixture is dried in an oven to form a powder; the obtained powder is placed in a muffle furnace, and the heat treatment temperature is controlled at 220°C for 72h to obtain a coating layer;

[0043] S3, placing the coating layer obtained in step S2 into 1000 ml of acid etching solution D, stirring, controlling the etching time to 6 minutes, filtering, and drying to obtain the finished product, and the surface pore size is controlled to be 10-40 nm.

[0044] Example 3

[0045] A method for preparing a positive electrode material for a lithium-ion battery, wherein the coating layer comprises 0.8% SnO2 and 1.2% ZnO by weight of the oxides, and the preparation comprises the following steps:

[0046] S1, prepare the surface coating layer precursor; citric acid aqueous solution A preparation: take 99.4% by mass of citric acid 5.5g, dissolve in 28ml deionized water, stir for 0.8h, to obtain citric acid aqueous solution A; tin tetrachloride precursor sol B preparation: 60.2g of tin tetrachloride pentahydrate SnCl4·5H2O is dissolved in deionized water, stirred for 0.8h, and then add 90ml of the citric acid solution A obtained in step S1, and add triethanolamine dropwise with a dropper until the solution is clear to prepare a 0.45mol / L sol, The mixture was allowed to stand at 22°C for 44 hours. Preparation of zinc acetate dihydrate sol C: 42.90 g of zinc acetate dihydrate Zn(CH3COO)2·2H2O was weighed and placed in a beaker. 180 ml of anhydrous ethanol was added and stirred at 72°C for 0.8 hours. 28 ml of triethanolamine was added and stirred for 0.8 hours. The mixture was cooled to 22°C to prepare 0.78 mol / L sol C. The mixture was allowed to stand for 44 hours. Preparation of acid etching solution D: 42.5 ml of hydrochloric acid was placed in a volumetric flask and water was added to prepare 0.4 mol / L acid etching solution D.

[0047] S2, coating layer preparation, weighing 1000g of the positive electrode material matrix NCM811 into a reactor, adding 790g of anhydrous ethanol and 110g of acetic acid, and stirring at 42°C for 1.8h to prepare a mixture; using a burette to measure 132ml of sol B and 195ml of sol C respectively, adding them to the mixture obtained in step S2-1, and keeping stirring for 1.8h; slowly adding ammonia water to the mixture obtained in step S2-2 through a micro dropper at a rate of 6ml / min to adjust the pH value to 9.5, stirring for 22h, and the oxide slowly precipitates and coats the surface of the particles. The obtained mixture is dried in an oven to form a powder; the obtained powder is placed in a muffle furnace, and the heat treatment temperature is controlled at 260°C for 36h to obtain a coating layer;

[0048] S3, placing the coating layer obtained in step S2 into 1000 ml of acid etching solution D, stirring, controlling the etching time to 8 minutes, filtering, and drying to obtain the finished product, and the surface pore size is controlled to be 10 to 40 nm.

[0049] Example 4

[0050] A lithium-ion battery positive electrode material, wherein the coating layer comprises 0.3% SnO2 and 0.7% ZnO by weight of the oxides, and the preparation method comprises the following steps:

[0051] S1, prepare the surface coating layer precursor; citric acid aqueous solution A preparation: take 99.0% citric acid 5.0g, dissolve in 25ml deionized water, stir for 1h, and obtain citric acid aqueous solution A; tin tetrachloride precursor sol B preparation: 35.1g tin tetrachloride pentahydrate SnCl4·5H2O is dissolved in deionized water, stirred for 0.5h, and then add 80ml of citric acid solution A obtained in step S1, add triethanolamine dropwise with a dropper until the solution is clear, and prepare a 0.4mol / L sol, and at 2 The mixture was allowed to stand at 0°C for 40 h. Preparation of zinc acetate dihydrate sol C: 41.31 g of zinc acetate dihydrate Zn(CH3COO)2·2H2O was weighed and placed in a beaker. 150 ml of anhydrous ethanol was added and stirred at 70°C for 0.5 h. 25 ml of triethanolamine was added and stirred for 0.5 h. The mixture was cooled to 20°C to prepare 0.75 mol / L sol C. The mixture was allowed to stand for 40 h. Preparation of acid etching solution D: 22.5 ml of strong acid was placed in a volumetric flask and water was added to prepare 0.2 mol / L acid etching solution D.

[0052] S2, coating layer preparation, weighing 1000g of the positive electrode material matrix NCM523 into a reactor, adding 780g of anhydrous ethanol and 100g of acetic acid, and stirring at 40°C for 2h to prepare a mixture; using a burette to measure 50ml of sol B and 114ml of sol C respectively, adding them to the mixture obtained in step S2-1, and keeping stirring for 2h; slowly adding ammonia water to the mixture obtained in step S2-2 through a micro dropper at a rate of 8ml / min to adjust the pH value to 10, stirring for 24h, and the oxide slowly precipitates and coats the surface of the particles. The obtained mixture is dried in an oven to form a powder; the obtained powder is placed in a muffle furnace, and the heat treatment temperature is controlled at 330°C for 10h to obtain a coating layer;

[0053] S3, placing the coating layer obtained in step S2 into 1000 ml of acid etching solution D, stirring, controlling the etching time to 5 minutes, filtering, and drying to obtain the finished product, and the surface pore size is controlled to be 10 to 40 nm.

[0054] Example 5

[0055] A lithium-ion battery positive electrode material, wherein the coating layer comprises 2.4% SnO2 and 0.6% ZnO by weight of the oxides, and a preparation method comprises the following steps:

[0056] S1, prepare the surface coating layer precursor; citric acid aqueous solution A preparation: take 99.0% citric acid 5.0g, dissolve in 25ml deionized water, stir for 1h, and obtain citric acid aqueous solution A; tin tetrachloride precursor sol B preparation: 35.1g tin tetrachloride pentahydrate SnCl4·5H2O is dissolved in deionized water, stirred for 0.5h, and then add 80ml of citric acid solution A obtained in step S1, add triethanolamine dropwise with a dropper until the solution is clear, and prepare a 0.4mol / L sol, and at 2 The mixture was allowed to stand at 0°C for 40 h. Preparation of zinc acetate dihydrate sol C: 41.31 g of zinc acetate dihydrate Zn(CH3COO)2·2H2O was weighed and placed in a beaker. 150 ml of anhydrous ethanol was added and stirred at 70°C for 0.5 h. 25 ml of triethanolamine was added and stirred for 0.5 h. The mixture was cooled to 20°C to prepare 0.75 mol / L sol C. The mixture was allowed to stand for 40 h. Preparation of acid etching solution D: 22.5 ml of strong acid was placed in a volumetric flask and water was added to prepare 0.2 mol / L acid etching solution D.

[0057] S2, coating layer preparation, weighing 1000g of the positive electrode material matrix NCM811 into a reactor, adding 780g of anhydrous ethanol and 100g of acetic acid, and stirring at 40°C for 2h to prepare a mixture; using a burette to measure 396ml of sol B and 97.5ml of sol C respectively, adding them to the mixture obtained in step S2-1, and keeping stirring for 2h; slowly adding ammonia water to the mixture obtained in step S2-2 through a micro dropper at a rate of 10ml / min to adjust the pH value to 10, stirring for 24h, and the oxide slowly precipitates and coats the surface of the particles. The obtained mixture is dried in an oven to form a powder; the obtained powder is placed in a muffle furnace, and the heat treatment temperature is controlled at 350°C for 12h to obtain a coating layer;

[0058] S3, placing the coating layer obtained in step S2 into 1000 ml of acid etching solution D, stirring, controlling the etching time to 15 minutes, filtering, and drying to obtain the finished product, and the surface pore size is controlled to be 10 to 40 nm.

[0059] Comparative Example 1

[0060] A lithium ion battery positive electrode material, which differs from Example 1 in that the material used is a carbon coating layer and has not been surface modified.

[0061] Comparative Example 2

[0062] A lithium-ion battery positive electrode material, which differs from Example 3 in that the material has not been etched with an acid solution and does not have a porous structure.

[0063] Comparative Example 3

[0064] A lithium-ion battery positive electrode material, which differs from Example 3 in that the material has not been etched with an acid solution and does not have a porous structure; and in step S2, the heat treatment temperature is increased to 600°C and the heat treatment time is 36 hours to obtain a crystalline powder.

[0065] Performance testing:

[0066] Compared with 5Ah cells made of untreated positive electrode materials, the capacity retention rate after 1000 cycles, the capacity retention rate after 28 days of storage at 45°C and the capacity recovery rate of 95.6%, the upper limit voltage without fire or explosion during 1C overcharge, and the needle penetration test were systematically compared. The test data are shown in the following table:

[0067] Table 1 Comparison of test results of lithium-ion battery positive electrode materials

[0068]

[0069]

[0070] It can be seen that the lithium-ion battery positive electrode material of the present invention effectively improves the battery capacity, safety and cycle stability.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for preparing a positive electrode material for a lithium ion battery, characterized in that: The following steps are involved: S1, preparation of surface coating layer precursors: preparing a sol containing tin ions and a sol containing zinc ions respectively; S2, preparation of coating layer: taking the positive electrode material matrix, dispersing it in an organic solvent, adding the tin ion sol and the zinc ion sol prepared in step S1, adjusting the pH value to form an organic mixed sol containing tin and zinc, and heat treating it at 220-260°C for 10-72 hours until SnO2 and ZnO are precipitated and coated on the surface of the positive electrode material matrix, and drying; S3, performing strong acid pickling and etching on the lithium-ion battery positive electrode material obtained in step S2, wherein the strong acid etching solution includes hydrochloric acid or nitric acid, and the concentration of the strong acid etching solution is 0.2-0.6 mol / L, and the etching time is controlled at 5-15 min, thereby obtaining the lithium-ion battery positive electrode material; in, The coating layer components include amorphous SnO2 and amorphous ZnO, and the weight content of ZnO in the coating layer is not less than 20%; The lithium-ion battery positive electrode material has a porous structure, and the surface pore size is controlled to be 10-40 nm; The process of preparing the sol containing tin ions and the sol containing zinc ions in step S1 includes the following steps: S1-1, take 99.0-99.5% by mass of citric acid, add deionized water and stir for 0.5-1h to obtain a citric acid aqueous solution, set aside; S1-2, weighing tin tetrachloride pentahydrate SnCl4·5H2O and dissolving it in deionized water, stirring, then adding the citric acid aqueous solution obtained in step S1-1, and adding triethanolamine dropwise until the solution is clear to prepare a tin ion-containing sol; S1-3, weigh zinc acetate dihydrate Zn(CH3COO)2·2H2O, add anhydrous ethanol, stir at 70-75°C for 0.5-1h, add triethanolamine, stir for 0.5-1h, cool to 20-25°C, and prepare a sol containing zinc ions.

2. The method for preparing a positive electrode material for a lithium ion battery according to claim 1, wherein: Calculated by weight percentage, the coating layer accounts for 0.2% to 3.0% of the lithium-ion battery positive electrode material.

3. The method for preparing a positive electrode material for a lithium ion battery according to claim 1, wherein: The process for preparing the coating layer in step S2 comprises the following steps: S2-1, weighing a cathode material matrix, adding anhydrous ethanol and acetic acid for surface activation, wherein the mass ratio of the cathode material matrix to anhydrous ethanol and acetic acid is 1:(0.78-0.80):(0.1-0.12), stirring at 40-45°C for 1.5-2h to prepare a mixture; S2-2, weighing the sol containing tin ions and zinc ions in step S1 according to the content of the coating layer, adding it to the mixture obtained in step S2-1, stirring for 1.5-2 hours, and mixing evenly; S2-3, slowly dripping ammonia water to adjust the pH value to 9-10 at a dripping rate of 3-10 ml / min, stirring for 20-24 hours, the oxide slowly precipitates and coats the surface of the particles, and drying the obtained mixture to obtain the lithium-ion battery positive electrode material.

4. A lithium ion battery positive electrode material obtained by the preparation method according to any one of claims 1 to 3.

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