Preparation method and application of ternary positive electrode material

Abstract

The present invention discloses a preparation method and application of a ternary positive electrode material. The preparation method of the ternary positive electrode material provided by the present invention comprises the following steps: activating a nano-metal ion sol; adding a silane coupling agent, a solvent, and a ternary positive electrode active substance to the obtained activation solution, subjecting the activated solution to a hydroxyl condensation reaction, and calcining to obtain a positive electrode material coated with a nanocomposite formed by metal oxide and silicon oxide. The present invention solves the problem of poor stability of ternary positive electrode materials in the prior art by double coating without affecting the electrical properties of the material itself, and effectively removes residual lithium on the surface of the positive electrode material, thereby ensuring that the prepared lithium-ion battery has good stability and high-temperature cyclability.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a preparation method and application of a ternary positive electrode material. Background Art

[0002] Lithium-ion batteries have advantages such as high energy density, long cycle life, and a wide operating range. Therefore, they are in huge demand and attract much attention in fields such as portable electronic devices, electric vehicles, and space technology. As the market demand for the driving range of electric vehicles increases, lithium-ion batteries are required to have higher energy density, safety performance, and rate performance. However, the energy density of the current commercial cathode materials is relatively low, which limits their promotion in some fields. Therefore, improving the specific capacity and rate performance of ternary cathode materials for lithium-ion batteries has become a hot research topic. In response to market demand, the performance of lithium-ion battery cathode materials is mainly improved by doping, coating, and optimizing the synthesis process. Coating technology is one of the most widely used and most effective methods. That is, by coating a layer of oxide or other salt substances on the surface of the cathode material, its specific capacity, cycle performance, and rate performance are improved.

[0003] Ternary cathode materials have become the most promising materials for lithium-ion battery cathode materials used in new energy vehicles due to their high platform, high specific capacity and low price. However, ternary cathode materials are easily reacted with moisture in the air, which deteriorates the battery cycle stability; and the materials are easily reacted with the electrolyte to cause battery bulging. At the same time, the Ni generated by high nickel ternary cathode materials during the electrochemical cycle is 4+ It is easy to react with the electrolyte, produce irreversible phase change, reduce the battery discharge capacity, and deteriorate the battery cycle performance.

[0004] To solve the above problems, researchers coated a layer of inert oxide on the surface of the ternary positive electrode material to reduce the material's sensitivity to air, reduce the reaction between the material and the electrolyte, and improve the battery's cycle stability.

[0005] For example, patent ZL201610443127.X discloses a single-crystal lithium nickel cobalt manganese oxide positive electrode material obtained by high-temperature sintering doping and high-temperature sintering coating. Although this material has better cycle performance than the undoped and coated ternary substrate, the doping and coating are both achieved through solid-phase high-temperature sintering, and the uniformity of the doping and coating is poor. In addition, the material is relatively hard, and the surface of the material is easily damaged during the crushing process, which aggravates the degree of side reactions on the surface of the material and shortens the cycle life of the material.

[0006] For example, patent CN108878799A discloses a mesoporous lithium aluminum silicate-coated doped single-crystal ternary positive electrode material and its preparation method. Although the surface coating layer of this material has a high-speed electron channel, it has not yet solved the problem of poor stability of the ternary positive electrode material.

[0007] For example, patent CN115117318A discloses a process for preparing a mesoporous hydroxyalumina silicon-coated lithium battery positive electrode material, which includes the following steps: S1, preparing a hydroxyalumina silicon-coated material to obtain a mixed colloid A2, which contains a hydroxyalumina silicon precursor; S2, spheroidizing and coating to obtain a mixed system B1, which contains a mesoporous hydroxyalumina silicon-coated lithium battery ternary positive electrode material precursor; and S3: filtering, washing, drying, and calcining to obtain a lithium battery ternary positive electrode material B3 uniformly coated with mesoporous hydroxyalumina silicon. The present invention uses 99.9% aluminum alkoxide, which is co-hydrolyzed with a silicon source and a lithium source; adding the ternary positive electrode material, refluxing and stirring to uniformly mix, spheroidizing the particles, and coating; and finally calcining to obtain the mesoporous hydroxyalumina silicon-coated lithium battery positive electrode material. The product has high purity, good sphericity, and a high powder specific gravity. Its energy density is 10-20% higher than that of ordinary nano-alumina-coated products. The material has high surface activity and good chemical and thermal stability, but the preparation process of this material is too complicated.

[0008] In view of this, the present invention is proposed. Summary of the Invention

[0009] The purpose of the present invention is to provide a method for preparing a ternary positive electrode material.

[0010] Another object of the present invention is to provide a ternary positive electrode material obtained by the above preparation method.

[0011] Another object of the present invention is to provide a lithium-ion battery containing the above-mentioned ternary positive electrode material.

[0012] In order to achieve the above object, the present invention adopts the following technical solutions:

[0013] In a first aspect, the present invention provides a method for preparing a ternary positive electrode material, comprising the following steps:

[0014] S1, activating the nano metal ion sol;

[0015] S2. Add a silane coupling agent, a solvent and a ternary positive electrode active material to the activation solution obtained in step S1, perform a hydroxyl condensation reaction and then calcine to obtain a positive electrode material coated with a nanocomposite formed by metal oxide and silicon oxide.

[0016] The present invention selects nano-metal ion sol as raw material, activates it and allows metal cations and nano-silicon ions therein to form a nano-composite under hydroxyl condensation reaction conditions. The activation can make it easier for hydroxyl groups to be generated on the surface of the nano-metal ion sol, so that the silane coupling agent reaction can be better carried out after hydrolysis to form metal-O-Si-R; and then further forms a fine and uniform coating layer under wet conditions to firmly coat the surface of the ternary positive electrode material matrix, thereby improving the unevenness problem of traditional solid-phase mixing (ball milling mixing and high-mixer mixing) and effectively removing residual lithium on the surface of the positive electrode material. At the same time, the outstanding stability and excellent electrochemical activity of the metal cations and silicon ions are utilized to improve the stability and high-temperature cyclability of the ternary positive electrode material.

[0017] In the above preparation method, in step S1, the nano metal ions are selected from one or more of aluminum, zirconium, cerium and tungsten.

[0018] In the above preparation method, in step S1, the mass fraction of the nano metal ion sol is 10-30wt%, 4≤pH≤7, preferably pH4-5, and the particle size is 10-15nm.

[0019] In the above preparation method, in step S1, the total mass of metal ions in the nano-metal ion sol is 0.03-0.3% of the mass of the positive electrode active material, preferably 0.15-0.3%.

[0020] In the above preparation method, in step S1, the surfactant used in the activation treatment is selected from one or more of sodium oleate, sodium laurate, cetyltrimethylammonium bromide, octadecyltrimethylammonium chloride, sodium dodecylbenzenesulfonate, sodium cetylsulfonate, potassium stearate, sodium stearate, stearic acid, sodium dodecylaminopropionate, and sodium hexametaphosphate. Preferably, the surfactant is one or more of sodium dodecylbenzenesulfonate, sodium cetylsulfonate, and sodium hexametaphosphate.

[0021] In the above preparation method, in step S1, the amount of the surfactant used is 1-5% of the mass of the nano-metal ion sol, preferably 1-2%.

[0022] In the above preparation method, in step S2, the silane coupling agent is selected from one or more of methyltrimethoxysilane, vinyltrimethoxysilane, dodecyltrimethoxysilane and hexadecyltrimethoxysilane, preferably one or more of methyltrimethoxysilane and vinyltrimethoxysilane.

[0023] In the above preparation method, in step S2, the mass ratio of the silane coupling agent to the total mass of metal ions in the nano-metal ion sol is 1:(1-2).

[0024] In the above preparation method, in step S2, the solvent is ethanol.

[0025] In the above preparation method, in step S2, the mass ratio of the silane coupling agent to the solvent is 1:(1-4).

[0026] In the above preparation method, in step S2, the hydroxyl condensation reaction is carried out according to the following operation: a silane coupling agent and a solvent are added to the solution obtained in step S1, reacting at 20-40° C. for 15-30 minutes, and then adding a positive electrode active material to react for 2-4 hours.

[0027] In the above preparation method, in step S2, the calcination conditions are: in an oxygen or air atmosphere, a temperature of 300-650° C., and a time of 2-8 hours.

[0028] In the above preparation method, in step S2, the chemical formula of the ternary positive electrode active material is LiNi x Co y Mn 1-x- y O2, 0.60≤x≤1, 0<y≤0.2.

[0029] According to a specific embodiment of the present invention, the chemical formula of the positive electrode active material is LiNi 0.88 Co 0.08 Mn 0.04 O2.

[0030] In a second aspect, the present invention also provides a ternary positive electrode material obtained by the above preparation method.

[0031] The ternary positive electrode material comprises positive electrode active material particles and a coating layer on the surface thereof; the coating layer is composed of a nano-composite formed by nano-metal ions and silicon ions.

[0032] In a third aspect, the present invention provides a lithium-ion battery comprising a positive electrode; the material of the positive electrode is the above-mentioned ternary positive electrode material.

[0033] Compared with the prior art, the present invention has the following beneficial effects:

[0034] In the present invention, metal cations and nano-silicon ions form a nano-composite under hydroxyl condensation reaction conditions, and form a fine and uniform coating layer under wet conditions, which is firmly coated on the surface of the ternary positive electrode material matrix, thereby improving the unevenness problem of traditional solid-phase mixing (ball milling mixing and high-mixer mixing) and effectively removing residual lithium on the surface of the positive electrode material. At the same time, the outstanding stability and excellent electrochemical activity of metal cations and silicon ions are utilized to improve the stability and high-temperature cyclability of the ternary positive electrode material. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 1 and 2 are SEM images of the ternary positive electrode materials prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2.

[0036] Figure 2 This is a comparison of room temperature cycle tests of the ternary positive electrode materials prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2.

[0037] Figure 3 This is a comparison of high temperature cycle tests of the ternary positive electrode materials prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2.

[0038] Figure 4 This is a comparison of low-temperature DCR tests of the ternary positive electrode materials prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2.

[0039] Figure 5 The capacity retention rate and capacity recovery rate of the ternary positive electrode materials prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 after being stored at high temperature are shown.

[0040] Figure 6 The internal resistance growth rate and thickness change rate (expansion rate) of the ternary positive electrode materials prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 after being stored at high temperature are shown. DETAILED DESCRIPTION

[0041] The present invention will be further described below with reference to specific examples, but the present invention is not limited to the following examples.

[0042] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0043] Unless otherwise specified, the reagents, materials, instruments, etc. used in the following examples can be obtained from commercial sources.

[0044] Nano-aluminum sol: The particle size of the sol is 10-15nm, and it is a commercially available product.

[0045] Nano-tungsten sol: The particle size of the sol is 10-15nm, and it is a commercially available product.

[0046] Example 1

[0047] Sodium hexametaphosphate was added to 25% wt nano-aluminum sol and nano-zirconium sol respectively for activation treatment, and then a sol mixed activation solution was prepared with an aluminum-zirconium mass ratio of 1:2;

[0048] The sol mixed activation solution was added to a mixture of methyltrimethoxysilane (silane coupling agent) and ethanol, wherein the mass ratio of silane coupling agent to ethanol was 1:4, and the mass ratio of silane coupling agent to aluminum ion was 1:2. The mixture was heated to 40°C and stirred for 5 minutes. The ternary positive electrode material LiNi was further added at a mass ratio of aluminum ion to ternary positive electrode material of 0.1:100. 0.88 Co 0.08 Mn 0.04 O2, react at 40℃ for 2h; after filter pressing, washing and drying, place it in a Zhongpeng furnace and calcine at 350℃ for 5h to obtain a ternary positive electrode material double-coated with cationic aluminum & zirconium and silicon ions.

[0049] Example 2

[0050] Add 1% hexadecyltrimethylammonium bromide to the 15%wt nano-tungsten sol for activation to obtain a sol activation solution;

[0051] The sol activation solution was added to a mixture of hexadecyltrimethoxysilane and ethanol, wherein the mass ratio of the silane coupling agent to the ethanol was 1:2, and the mass ratio of the silane coupling agent to the aluminum was 1:1. The mixture was stirred at room temperature at 25°C for 30 minutes, and the ternary positive electrode material LiNi was added at a mass ratio of tungsten ions to ternary positive electrode material of 0.15:100. 0.88 Co 0.08 Mn 0.04 O2, react at 25℃ for 4h; after filter pressing, washing and drying, place it in a Zhongpeng furnace and calcine at 650℃ for 2h to obtain a ternary positive electrode material double-coated with tungsten ions and silicon ions.

[0052] Comparative Example 1

[0053] Prepare a mixture of methyltrimethoxysilane and ethanol, wherein the mass ratio of silane coupling agent to ethanol is 1:4, heat to 40℃ and stir for 5min; add ternary cathode material LiNi according to the mass ratio of silicon ions in silane coupling agent to ternary cathode material of 0.05:100. 0.88 Co 0.08 Mn 0.04 O2, react at 40℃ for 2h; after filter pressing, washing and drying, place it in a Zhongpeng furnace and calcine at 350℃ for 5h to obtain nano-silicon ion-coated ternary positive electrode material.

[0054] Comparative Example 2

[0055] According to the mass of aluminum ions in nano-aluminum sol and the ternary cathode material LiNi 0.88 Co 0.08 Mn 0.04 The mass ratio of O2 is 0.1:100 and the mixture is evenly mixed. After mixing, it is placed in a Zhongpeng furnace and calcined at 350°C for 5 hours to obtain an aluminum ion-coated ternary positive electrode material.

[0056] Test results

[0057] The performance indicators of the ternary cathode materials obtained in Example 1 (Example 1 in the figure), Example 2 (Example 2 in the figure), Comparative Example 1, and Comparative Example 2 were tested according to the requirements of the lithium-ion battery industry standards. The results are as follows:

[0058] Depend on Figure 1 It can be seen that compared with Comparative Example 1, the surface coating of the materials obtained in Examples 1 and 2 and Comparative Example 2 is more uniform.

[0059] Depend on Figure 2-4 It can be seen that compared with Comparative Example 2, the impedance of the materials obtained after coating the surface of the ternary positive electrode material with nano-silicon in Example 1 and Example 2 increased significantly, and the room temperature cycle, high temperature cycle and capacity were all improved.

[0060] Depend on Figure 5 、 6 It can be seen that the inert metal oxide coating can effectively reduce the contact between the material and the air and electrolyte, improve the battery's gas production problem and the battery's thickness expansion problem when the battery is stored at high temperature, and significantly reduce the battery's internal resistance growth rate.

[0061] Although the present invention has been described in detail above using general descriptions and specific embodiments, it will be apparent to those skilled in the art that modifications and improvements may be made based on the present invention. Therefore, such modifications and improvements, which do not depart from the spirit of the present invention, are intended to be within the scope of protection claimed herein.

Claims

1. A method for preparing a ternary cathode material, comprising the following steps: S1, activating the nano metal ion sol; S2, adding a silane coupling agent, a solvent, and a ternary positive electrode active material to the activation solution obtained in step S1, and calcining after a hydroxyl condensation reaction to obtain a positive electrode material coated with a nanocomposite formed by metal oxide and silicon oxide; The nano metal ions are selected from one or more of aluminum, zirconium, cerium and tungsten; The pH of the nano metal ion sol is: 4≤pH≤7; The surfactant used in the activation treatment is selected from one or more of sodium oleate, sodium laurate, cetyltrimethylammonium bromide, octadecyltrimethylammonium chloride, sodium dodecylbenzenesulfonate, sodium cetylsulfonate, potassium stearate, sodium stearate, stearic acid, sodium laurylaminopropionate and sodium hexametaphosphate.

2. The preparation method according to claim 1, characterized in that In step S1, the mass fraction of the nano metal ion sol is 10-30wt%, and the particle size is 10-15nm; The total mass of the metal ions in the nano-metal ion sol is 0.03-0.3% of the mass of the ternary positive electrode active material.

3. The preparation method according to claim 2, characterized in that In step S1, the amount of the surfactant used is 1-5% of the mass of the nano-metal ion sol.

4. The preparation method according to claim 3, characterized in that In step S2, the silane coupling agent is selected from one or more of methyltrimethoxysilane, vinyltrimethoxysilane, dodecyltrimethoxysilane and hexadecyltrimethoxysilane; The mass ratio of the silane coupling agent to the total mass of the metal ions in the nano-metal ion sol is 1:(1-2); The solvent is ethanol; The mass ratio of the silane coupling agent to the solvent is 1:(1-4).

5. The preparation method according to claim 4, characterized in that In step S2, the hydroxyl condensation reaction is carried out according to the following operation: a silane coupling agent and a solvent are added to the activation solution obtained in step S1, and the mixture is reacted at 20-40°C for 15-30 minutes, and then a positive electrode active material is added and the mixture is reacted for 2-4 hours.

6. The preparation method according to claim 5, characterized in that In step S2, the calcination conditions are: in an oxygen or air atmosphere, at a temperature of 300-650° C., and for 2-8 hours.

7. The preparation method according to claim 6, characterized in that In step S2, the chemical formula of the ternary positive electrode active material is LiNixCoyMn1-x-yO2, 0.60≤x≤1, 0<y≤0.

2.

8. The ternary positive electrode material obtained by the preparation method according to any one of claims 1 to 7.

9. A lithium-ion battery comprising a positive electrode; the material of the positive electrode is the ternary positive electrode material according to claim 8.

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