A positive electrode material and a preparation method thereof

Abstract

This invention provides a cathode material and its preparation method, relating to the field of lithium-ion battery cathode material technology. A method for preparing a cathode material includes the following steps: S1, uniformly dispersing cellulose in a polyimide precursor solution and heating to react, obtaining a mixed solution A; S2, weighing raw materials according to the chemical composition of the cathode active material to obtain a cathode active material precursor, adding an acid anhydride compound to obtain a mixture, mixing the mixture with a solvent, and heating to react, obtaining a mixed solution B; S3, adding mixed solution B to mixed solution A, adding a precipitant, a complexing agent, and an esterification catalyst, heating to react once, then adding manganese barium ore, heating to react a second time, and drying to obtain an intermediate; S4, mixing the intermediate with a lithium source and calcining to obtain the cathode material. The cathode material prepared by this invention exhibits high capacity, excellent cycle performance, and stable electrochemical performance under high voltage conditions.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery cathode materials technology, and in particular to a cathode material and its preparation method. Background Technology

[0002] With the widespread application of lithium-ion batteries in power, consumer, and energy storage fields, the requirements for battery performance are becoming increasingly stringent, especially for cathode materials. Ternary cathode materials, with their characteristics of low toxicity, low cost, and high rate capability, have become one of the most widely used cathode materials.

[0003] Currently, the most common method to improve the driving range of power batteries is to increase the battery's cutoff voltage. However, at high cutoff voltages, the side reactions on the electrode surface also increase accordingly, leading to a significant decrease in the discharge capacity and cycle performance of nickel-cobalt-manganese cathode materials, thus failing to achieve the goal of high-range lithium-ion batteries for vehicles. Although there are many coated and modified ternary cathode materials in existing technologies, general coated materials do not have electrochemical activity. Although coating modification can improve the material's performance, it also leads to increased polarization and reduced capacity and rate performance. In addition, polycrystalline ternary cathode materials will have their structure destroyed by the electrolyte, generating new interfaces. These new interfaces increase the occurrence of side reactions between the cathode material and the electrolyte, resulting in a decrease in battery capacity, cycle performance, and safety performance. Therefore, there is an urgent need to develop a single-crystal ternary cathode material with long cycle life and high discharge capacity at high voltage. Summary of the Invention

[0004] Based on the technical problems existing in the background technology, the present invention proposes a positive electrode material and its preparation method.

[0005] The present invention proposes a cathode material comprising, from the inside out, a cathode active material, a porous carbon layer, and a manganese barium ore layer; wherein the cathode active material is LiNi. x Co y Mn 1-x-y O2, 0.5≤x≤0.9, 0.1≤y≤0.3.

[0006] The cathode material provided by this invention uses single-crystal active materials. Coating the surface of these single-crystal particles with a porous carbon layer and a manganese barium oxide layer helps improve the material's interfacial stability. The cathode material provided by this invention exhibits high capacity, excellent cycle performance, and stable electrochemical performance under high voltage conditions.

[0007] Preferably, the particle size D50 of the positive electrode active material is 0.5–3 μm.

[0008] This invention also proposes a method for preparing a cathode material, comprising the following steps:

[0009] S1. Cellulose is uniformly dispersed in a polyimide precursor solution and heated to react, resulting in a mixed solution A;

[0010] S2. Weigh the raw materials according to the chemical composition of the positive electrode active material to obtain the positive electrode active material precursor, add acid anhydride compounds to obtain a mixture, mix the mixture with a solvent, heat and react to obtain mixed solution B;

[0011] S3. Add mixed solution B to mixed solution A, add precipitant, complexing agent and esterification catalyst, heat to react once, add manganese barium ore, heat to react a second time, dry to obtain intermediate;

[0012] S4. The intermediate is mixed with the lithium source and then calcined to obtain the cathode material.

[0013] The preparation method provided by this invention utilizes the anchoring effect of the three-dimensional network porous structure of polyimide / cellulose, the ester bond and hydrogen bond to stabilize the interface and encapsulate the positive electrode active material, then coats it with manganese barium ore, and performs gradient calcination to prepare a small and uniform porous carbon and manganese barium ore coated positive electrode material.

[0014] Preferably, in S1, the polyimide precursor solution comprises a diamine monomer, a dianhydride monomer, and a solvent; the diamine monomer is selected from one or more of 4,4'-diaminodiphenyl ether (ODA), p-phenylenediamine (PDA), and m-phenylenediamine (MPDA); the dianhydride monomer is selected from one or more of pyromellitic dianhydride (PMDA), 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA), and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA); and the solvent is selected from one or more of N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0015] Preferably, in S1, the preparation of the polyimide precursor solution includes mixing a diamine monomer, a dianhydride monomer, and a solvent, and reacting them to obtain the product.

[0016] The preparation of precursor solutions for polyimide facilitates the subsequent formation of polyimide.

[0017] More preferably, the reaction temperature is 20-30°C.

[0018] Preferably, in S1, the molar ratio of cellulose to polyimide is (1-4):1.

[0019] Within a certain range, the molar ratio of cellulose to polyimide facilitates in-situ polymerization on or inside the cellulose surface, forming a "cellulose-polyimide interpenetrating network" during subsequent calcination.

[0020] Preferably, in S1, the heating reaction temperature is 60–80°C.

[0021] This invention involves fully condensing diamine and dianhydride to form a polyamic acid (PAA) solution, which is the precursor solution of the polyimide described in this invention. By controlling the temperature of the heating reaction, this invention partially imidizes the polyimide precursor solution and promotes the full swelling and uniform dispersion of cellulose in the solution, resulting in mixed solution A.

[0022] Preferably, in S2, the raw material is selected from one or more of nickel source, cobalt source, and manganese source; the nickel source is selected from one or more of nickel chloride, nickel sulfate, and nickel acetate; the cobalt source is selected from one or more of cobalt chloride, cobalt sulfate, and cobalt acetate; and the manganese source is selected from one or more of manganese chloride, manganese sulfate, and manganese acetate.

[0023] The selection of raw materials helps to synthesize single-crystal positive electrode active materials. The single-crystal structure has excellent structural stability and reduces the occurrence of side reactions with the electrolyte.

[0024] Preferably, in S2, the anhydride compound is selected from one or more of maleic anhydride, itaconic anhydride, and nadic anhydride.

[0025] Anhydride compounds are used to perform surface grafting modification on the precursor of positive electrode active material. The anhydride of the anhydride compound reacts with the hydroxyl groups on the surface of the positive electrode active material precursor to achieve carboxylation modification, which improves dispersibility, inhibits particle agglomeration, and enhances interfacial bonding.

[0026] Preferably, in S2, the solvent is selected from one or more of water, N-methylpyrrolidone (NMP), and N,N-dimethylacetamide (DMAc).

[0027] Preferably, in S2, the mass ratio of the positive electrode active material precursor to the acid anhydride compound is (50-100):1.

[0028] Maintaining a certain mass ratio of the positive electrode active material precursor to anhydride compounds helps to regulate the degree of carboxylation on the surface of the positive electrode active material precursor, ensuring an appropriate number of active sites while avoiding excessive coating of the organic layer. This optimizes particle dispersibility, inhibits agglomeration, strengthens the interfacial bonding with the coating layer, and improves the structural stability and electrochemical performance of the positive electrode material.

[0029] Preferably, in S2, the heating reaction temperature is 80–100°C.

[0030] Within a certain temperature range, heating the reaction helps promote the grafting reaction between acid anhydride compounds and the surface of the cathode active material precursor, thereby increasing the degree of surface functionalization. At the same time, it avoids precursor structure deterioration, particle agglomeration, or acid anhydride side reactions, ensuring uniform and controllable surface modification, enhancing the interfacial bonding force between the subsequent coating layer and the matrix, and improving the cycle stability and rate performance of the cathode material.

[0031] Preferably, in S2, the mixed solution B is the carboxylated positive electrode active material precursor.

[0032] Preferably, in S3, the precipitant is selected from one or more of sodium hydroxide solution and potassium hydroxide solution; the complexing agent is selected from one or more of ammonia water, citric acid solution, and ethylenediamine; and the esterification catalyst is selected from one or more of dicyclohexylcarbodiimide solution and thionyl chloride.

[0033] The role of the precipitant is to provide an alkaline environment, enabling metal ions to undergo a co-precipitation reaction and form a uniformly morphologically and structurally complete cathode active material precursor. The role of the complexing agent is to form stable, soluble complexes with the metal ions, regulating the release and precipitation rates of the metal ions, ensuring uniform growth and concentrated particle size distribution of the precursor particles, and preventing localized rapid agglomeration. The role of the esterification catalyst is to promote the esterification grafting reaction between acid anhydride compounds and the hydroxyl groups on the surface of the cathode active material precursor, lowering the activation energy, improving the surface carboxylation efficiency, and making the functionalization modification more complete and uniform.

[0034] More preferably, the mass concentration of the ammonia water is 5% to 28%.

[0035] Preferably, in S3, the temperature of the first heating reaction is 40-60°C; and the temperature of the second heating reaction is 70-90°C.

[0036] Controlling the temperature of the primary heating reaction within the range of 40–60°C helps to gently promote the simultaneous occurrence of metal ion co-precipitation, complexation coordination, and surface esterification grafting reactions, resulting in a precursor with regular morphology and uniform particle size. This also avoids excessively high temperatures that could lead to particle agglomeration or decomposition of acid anhydrides, and prevents incomplete reactions and insufficient interfacial bonding caused by excessively low temperatures. Controlling the temperature of the secondary heating reaction within the range of 70–90°C further promotes the uniform loading and interfacial bonding of manganese barium ore on the precursor surface, improving the structural stability of the intermediate. Simultaneously, it allows for the slow removal of residual solvent, preventing particle cracking or morphological damage caused by excessively rapid heating.

[0037] Preferably, in step S3, the drying temperature is 80–100°C.

[0038] Preferably, in S3, the volume ratio of mixed solution A, mixed solution B, precipitant, complexing agent, and esterification catalyst is (10-30):(5-15):1:(0.1-0.6):(0.2-0.8).

[0039] Controlling the volume ratio of mixed solution A, mixed solution B, precipitant, complexing agent, and esterification catalyst within a certain range helps ensure a suitable ratio between the cellulose-polyimide dispersed phase and the cathode active material precursor solution. This ensures a stable and orderly co-precipitation process, appropriate complexation control, and moderate esterification grafting efficiency. It also avoids abnormal system viscosity, particle agglomeration, uneven morphology, or incomplete reaction caused by imbalance in the ratio. Consequently, a uniformly structured intermediate with tight interfacial bonding is obtained, which is beneficial for obtaining cathode materials with stable electrochemical performance and excellent cycle life after calcination.

[0040] Preferably, in S3, the manganese barium ore is an oxide material containing Ba, Mn, and O, and may be further doped with one or more metal elements selected from Ni, Co, Al, Mg, Zr, and Ti; the particle size D50 of the manganese barium ore is 100 nm to 5 μm.

[0041] Preferably, in S3, the molecular formula of barium manganese ore is BaMn8O. 16 .

[0042] Preferably, in S3, the molar ratio of manganese barium ore to the total metal ions in mixed solution B is (0.01-0.25):1.

[0043] The total number of metal ions in mixed solution B is the same as the total number of metal ions in the positive electrode active material.

[0044] This invention uses manganese barium ore as a coating material for the positive electrode active material, thereby improving the structural stability of the material. Manganese barium ore forms a channel structure along the c-axis, and the presence of one-dimensional channels in the crystal structure achieves low tortuosity in the electrode fabrication, accelerating ion transport.

[0045] Preferably, in S4, the molar ratio of the total metal ions of the positive electrode active material in the intermediate to the lithium ions in the lithium source is 1:(1~1.1).

[0046] Within a certain range, the molar ratio of the total metal ions in the intermediate cathode active material to the lithium ions in the lithium source helps to ensure that lithium and transition metals fully react in the solid phase during calcination, forming a cathode material with accurate stoichiometry and complete crystal structure. This avoids abnormal grain growth and impurity phase formation due to excessive lithium, or lattice defects and low capacity due to insufficient lithium, thereby improving the specific capacity, cycle stability and rate performance of the material.

[0047] Preferably, in S4, the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, and lithium acetate.

[0048] Preferably, in S4, the calcination treatment includes first pre-calcining at 300-500°C with a temperature increase of 1-5°C / min for 3-5 hours, and then calcining at 700-900°C with a temperature increase of 1-5°C / min for 1-3 hours.

[0049] The segmented calcination process serves several purposes. The low-temperature pre-calcination stage allows for the slow removal of moisture, organic components (cellulose, polyimide carbon residue, etc.), and residual solvents from the intermediates, preventing material cracking, particle breakage, or agglomeration caused by rapid heating. Simultaneously, it initially forms an oxide precursor framework, resulting in uniform grain nucleation and a dense structure. During calcination, a three-dimensional porous network of polyimide / cellulose is formed, encapsulating the positive electrode active material. The high-temperature calcination stage promotes a full solid-state reaction between lithium ions and transition metals, completing lattice reconstruction and phase growth to obtain a positive electrode material with high crystallinity and a complete layered structure. This segmented calcination synergistically achieves morphology control, impurity removal, and phase optimization, ultimately improving the structural stability, cycle performance, and rate performance of the positive electrode material.

[0050] Preferably, in S4, the calcination atmosphere for the calcination treatment is selected from one or more of nitrogen and argon.

[0051] Preferably, in S4, the calcination method for the calcination treatment is selected from one or more of the following: muffle furnace calcination, roller kiln calcination, pusher kiln calcination, and tube furnace calcination.

[0052] Application of the above-described cathode material or the cathode material prepared by the above-described method in lithium-ion batteries.

[0053] The cathode material provided by this invention is applied to lithium-ion batteries, providing a continuous transport channel for lithium ions, reducing diffusion resistance, improving material conductivity, and exhibiting excellent battery cycle performance even under high voltage conditions.

[0054] The beneficial effects of this invention are as follows:

[0055] This invention utilizes an ingenious preparation method to obtain a cathode material with a single-crystal active material core, coated sequentially with a porous carbon layer and a manganese barium ore layer. This reduces side reactions with the electrolyte and results in excellent electrochemical performance under high voltage conditions. The invention employs polyimide / cellulose to embed the active material within its three-dimensional porous network structure, increasing particle dispersion. Simultaneously, the hydroxyl groups within the polyimide / cellulose undergo esterification with the carboxyl groups on the surface of the treated precursor particles, forming a stable interfacial bond through ester and hydrogen bonds. This effectively prevents precursor particle aggregation, allowing the size of the active material to be controlled to the nanoscale and uniformly dispersed, thus obtaining a single-crystal active material. The polyimide / cellulose, acting as a carbon source, forms porous carbon after sintering, further stabilizing the structure of the single-crystal active material. The porous carbon structure enhances the material's conductivity, providing continuous transport channels for lithium ions, reducing diffusion resistance, improving conductivity, and enhancing battery cycle performance. This invention enhances the structural stability of a cathode active material by further coating it with manganese barium ore as a coating material. The manganese barium ore forms a channel structure along the c-axis, and the presence of one-dimensional channels in the crystal structure achieves low tortuosity in the electrode fabrication, accelerating ion transport. The cathode material provided by this invention exhibits high capacity, excellent cycle performance, and stable electrochemical performance under high voltage conditions. Attached Figure Description

[0056] Figure 1 This is a SEM image of the cathode material prepared in Example 1 of the present invention. Detailed Implementation

[0057] The technical solution of the present invention will be described in detail through specific embodiments.

[0058] In the following examples and comparative examples, the specific information regarding the raw materials used is as follows:

[0059] Maleic anhydride: Manufacturer: Qixiang Tengda; Grade: Industrial Superior (99.5%).

[0060] Manganese barium ore: Manufacturer: Chongqing Jintai Electrometallurgy; Grade: Lithium battery grade (synthetic);

[0061] The chemical structural formula of barium manganese ore is BaMn. 2+ Mn7 4+ O 16 The molecular formula is BaMn8O 16 Its theoretical molecular weight is 832.85 g / mol; its theoretical mineral mass composition is: BaO 18.42%, MnO 8.51%, MnO2 73.07%.

[0062] Unless otherwise specified, all materials and reagents used in the following examples and comparative examples are commercially available.

[0063] Example 1

[0064] A method for preparing a positive electrode material includes the following steps:

[0065] S1. Under nitrogen protection, the diamine monomer 4,4'-diaminodiphenyl ether and N-methylpyrrolidone (NMP) were mixed and stirred until completely dissolved. Then, the dianhydride monomer pyromellitic dianhydride was added in batches under stirring, with the molar ratio of diamine monomer to dianhydride monomer controlled at 1:1.05. The system temperature was controlled at 20℃ and stirred for 8 hours to allow the diamine and dianhydride to fully undergo a polycondensation reaction, forming a polyimide precursor solution. Cellulose was uniformly dispersed in the polyimide precursor solution, and the temperature was increased to 70℃ at a rate of 1℃ / min, and stirred for 3 hours to perform partial imidization and dispersion stabilization treatment, allowing the cellulose to fully swell and uniformly disperse in the polyimide solution, resulting in mixed solution A. The molecular weights of cellulose and polyimide were 162.14 g / mol and 476.4 g / mol, respectively; the molar ratio of cellulose to polyimide was 2:1.

[0066] S2. Weigh nickel acetate, cobalt acetate, and manganese acetate in a molar ratio of 8:1:1 to obtain a positive electrode active material precursor. Add maleic anhydride to the positive electrode active material precursor to obtain a mixture. Mix the mixture with deionized water, stir, and heat in a water bath at 80°C to obtain mixed solution B. The mass ratio of the positive electrode active material precursor to maleic anhydride is 80:1.

[0067] S3. Slowly add mixed solution B to mixed solution A, with a volume ratio of mixed solution A to mixed solution B of 10:8. Then add 2 mol / L sodium hydroxide aqueous solution, 2.5 mol / L ammonia water (mass concentration 12%), and 4 mol / L dicyclohexylcarbodiimide solution (solvent N-methylpyrrolidone) at a volume ratio of 1:0.2:0.5. Control the heating temperature at 50℃ and stir to ensure complete reaction. Then add manganese barium ore, stir, heat in an 80℃ water bath, and dry at 90℃ to obtain the intermediate. The molar ratio of manganese barium ore to the total metal ions in mixed solution B is 0.05:1.

[0068] S4. The intermediate is mixed with lithium carbonate and then calcined: pre-calcined at 500℃ for 4 hours at a rate of 2℃ / min, and then calcined at 900℃ for 2 hours at a rate of 3℃ / min to obtain the cathode material; wherein, the molar ratio of the total metal ions of the cathode active material precursor in the intermediate to the lithium ions in the lithium carbonate is 1:1.05.

[0069] Figure 1The image shown is a SEM image of the cathode material prepared in Example 1 of this invention, which shows that the cathode material prepared in this invention has a single-crystal particle structure.

[0070] Example 2

[0071] A method for preparing a positive electrode material includes the following steps:

[0072] S1. Under nitrogen protection, 4,4'-diaminodiphenyl ether and N-methylpyrrolidone (NMP) were mixed and stirred until completely dissolved. Then, the dianhydride monomer, pyromellitic dianhydride, was added in batches under stirring. The molar ratio of the diamine monomer to the dianhydride monomer was controlled at 1:1.05. The system temperature was controlled at 20℃ and stirred for 8 hours to allow the diamine and dianhydride to fully undergo a polycondensation reaction, forming a polyimide precursor solution. Cellulose was uniformly dispersed in the polyimide precursor solution, and the temperature was increased to 70℃ at a rate of 1℃ / min, and stirred for 3 hours to obtain mixed solution A; wherein the molar ratio of cellulose to polyimide was 1:1.

[0073] S2. Weigh nickel chloride, cobalt chloride, and manganese chloride in a molar ratio of 8:1:1 to obtain a positive electrode active material precursor. Add maleic anhydride to the positive electrode active material precursor to obtain a mixture. Mix the mixture with deionized water, stir, and heat in a water bath at 90°C to obtain mixed solution B. The mass ratio of the positive electrode active material precursor to maleic anhydride is 50:1.

[0074] S3. Slowly add mixed solution B to mixed solution A, with a volume ratio of mixed solution A to mixed solution B of 10:12. Then add 2 mol / L potassium hydroxide aqueous solution, 2.5 mol / L ammonia water (mass concentration 12%), and 4 mol / L dicyclohexylcarbodiimide (solvent N-methylpyrrolidone) at a volume ratio of 1:0.1:0.2. Control the heating temperature at 55℃ and stir to ensure complete reaction. Then add manganese barium ore, stir, heat in an 80℃ water bath, and dry at 100℃ to obtain the intermediate. The molar ratio of manganese barium ore to the total metal ions in mixed solution B is 0.01:1.

[0075] S4. The intermediate is mixed with lithium carbonate and then calcined: pre-calcined at 450℃ for 4 hours at a rate of 2℃ / min, and then calcined at 850℃ for 2 hours at a rate of 3℃ / min to obtain the cathode material; wherein, the molar ratio of the total metal ions of the cathode active material precursor in the intermediate to the lithium ions in the lithium carbonate is 1:1.05.

[0076] Example 3

[0077] A method for preparing a positive electrode material includes the following steps:

[0078] S1. Under nitrogen protection, the diamine monomer p-phenylenediamine and N-methylpyrrolidone (NMP) are mixed and stirred until completely dissolved. Then, the dianhydride monomer pyromellitic dianhydride is added in batches under stirring, with the molar ratio of diamine monomer to dianhydride monomer controlled at 1:1.05. The system temperature is controlled at 20℃ and stirred for 8 hours to allow the diamine and dianhydride to fully undergo a polycondensation reaction, forming a polyimide precursor solution. Cellulose is uniformly dispersed in the polyimide precursor solution, and the temperature is increased to 70℃ at a rate of 1℃ / min, and stirred for 3 hours to obtain mixed solution A; wherein the molar ratio of cellulose to polyimide is 4:1.

[0079] S2. Weigh nickel sulfate, cobalt sulfate, and manganese sulfate in a molar ratio of 8:1:1 to obtain a positive electrode active material precursor. Add maleic anhydride to the positive electrode active material precursor to obtain a mixture. Mix the mixture with deionized water, stir, and heat in a water bath at 95°C to obtain mixed solution B. The mass ratio of the positive electrode active material precursor to maleic anhydride is 100:1.

[0080] S3. Slowly add mixed solution B to mixed solution A, with a volume ratio of mixed solution A to mixed solution B of 10:8. Then add 2 mol / L sodium hydroxide aqueous solution, 2.5 mol / L ammonia solution (mass concentration 12%), and 4 mol / L thionyl chloride at a volume ratio of 1:0.6:0.8. Control the heating temperature at 50℃ and stir to ensure complete reaction. Then add manganese barium ore, stir, heat in an 80℃ water bath, and dry at 90℃ to obtain an intermediate. The molar ratio of manganese barium ore to the total metal ions in mixed solution B is 0.2:1.

[0081] S4. The intermediate is mixed with lithium carbonate and then calcined: pre-calcined at 500℃ for 4 hours at a rate of 2℃ / min, and then calcined at 900℃ for 2 hours at a rate of 3℃ / min to obtain the cathode material; wherein, the molar ratio of the total metal ions of the cathode active material precursor in the intermediate to the lithium ions in the lithium carbonate is 1:1.05.

[0082] Comparative Example 1

[0083] A method for preparing a positive electrode material includes the following steps:

[0084] S1. Weigh out nickel acetate, cobalt acetate, and manganese acetate in a molar ratio of 8:1:1 and dissolve them completely in deionized water. Stir and heat in an 80°C water bath. Adjust the pH to 10 with 2.5 mol / L ammonia water. Wash and dry to obtain the precursor.

[0085] S2. The precursor and lithium carbonate are mixed at a molar ratio of 1:1.05 and then calcined: the temperature is increased to 500℃ at 2℃ / min for 4 hours for pre-calcination, and then increased to 800℃ at 3℃ / min for 2 hours for high-temperature calcination to obtain the cathode material.

[0086] Comparative Example 2

[0087] The only difference between Comparative Example 2 and Example 1 is that step S1 was not performed; otherwise, they are the same as Example 1, that is, a positive electrode active material coated with manganese barium ore is obtained as the positive electrode material.

[0088] Comparative Example 3

[0089] The only difference between Comparative Example 3 and Example 1 is that manganese barium ore was not added in step S3. The rest is the same as Example 1, that is, a porous carbon-coated positive electrode active material is obtained as the positive electrode material.

[0090] Specifically: Steps S1 and S2 are the same as in Example 1. In S3, mixed solution B is slowly added to mixed solution A, with a volume ratio of mixed solution A to mixed solution B of 10:8. Then, 2 mol / L sodium hydroxide aqueous solution, 2.5 mol / L ammonia (mass concentration 12%), and 4 mol / L dicyclohexylcarbodiimide solution (solvent N-methylpyrrolidone) are added at a volume ratio of 1:0.2:0.5. The heating temperature is controlled at 50°C, and the mixture is stirred and heated to ensure complete reaction. The mixture is then dried at 90°C to obtain an intermediate. Step S4 is the same as in Example 1, yielding the positive electrode material.

[0091] Electrochemical performance testing of materials:

[0092] The positive electrode materials prepared in the examples and comparative examples were used to fabricate 3Ah wound pouch batteries. The specific methods are as follows: Positive electrode material, PVDF, carbon black, and carbon nanotube slurry were mixed in a mass ratio of 97.8:1.5:0.56:0.14 to form a slurry. This slurry was then coated, rolled, baked, cut, and had tabs welded to form the positive electrode sheet. Graphite, SP, CMC, and SBR were mixed in a mass ratio of 96.5:0.5:1.2:1.8 to form a slurry. This slurry was then coated, rolled, baked, cut, and had tabs welded to form the negative electrode sheet. The battery was then wound, encased, top-side sealed, injected with electrolyte, sealed again, formed, aged, sealed again, and capacity tested to obtain the 3Ah wound pouch battery. The battery was tested at 1C initial discharge and initial efficiency, room temperature cycling, and 4C rate discharge at voltages ranging from 2.8 to 4.35V. The test results are shown in Table 1.

[0093] Table 1

[0094]

[0095] As can be seen from the test results in Table 1, the battery assembled from the cathode material prepared in this invention has high initial discharge capacity and efficiency under high voltage conditions, as well as excellent 1C cycle retention rate and 4C discharge capacity retention rate. From the comparative example and the embodiment, it can be seen that the initial efficiency of the embodiment is greatly improved and the specific capacity is higher; at 1C rate, after 500 cycles, the capacity retention rate of the embodiment is significantly better than that of the comparative example; at 4C rate discharge capacity retention rate, the capacity retention rate of the embodiment is also significantly better than that of the comparative example. Analysis shows that: (1) In this invention, the cathode active material particles are embedded in the three-dimensional network porous structure of polyimide / cellulose to increase the dispersion of the particles. At the same time, the hydroxyl groups inside the polyimide / cellulose undergo esterification reaction with the carboxyl groups on the surface of the precursor particles of the treated cathode active material. Through the interaction of ester bonds and hydrogen bonds, a stable interface bond is formed, which can effectively prevent the aggregation of precursor particles, so that the size of the cathode active material can be controlled to the nanoscale and the dispersion is uniform, thus obtaining a single crystal cathode active material. (2) Polyimide / cellulose, as a carbon source, forms porous carbon after sintering to coat the single-crystal positive electrode active material, further stabilizing its structure. The porous carbon structure improves the conductivity of the material, provides a continuous transport channel for lithium ions, reduces diffusion resistance, improves the conductivity of the material, and enhances the battery cycle performance. (3) This invention improves the structural stability of the positive electrode active material by using manganese barium ore as a coating material on the surface of the porous carbon layer. The manganese barium ore forms a channel structure along the c-axis, and the crystal structure contains one-dimensional channels, achieving low tortuosity in the electrode preparation and accelerating ion transport. Therefore, this invention effectively improves the specific capacity, initial efficiency, cycle life, and rate performance of the material by coating the surface of the positive electrode active material with a porous carbon layer and a manganese barium ore layer.

[0096] In summary, the cathode material prepared by this invention exhibits excellent cycle performance and rate performance when applied in the field of lithium-ion batteries. The cathode material provided by this invention possesses high capacity, excellent cycle performance, and stable electrochemical performance under high voltage conditions.

[0097] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A positive electrode material, characterized in that, From the inside out, it includes a positive electrode active material, a porous carbon layer, and a manganese barium ore layer; the positive electrode active material is LiNi. x Co y Mn 1-x-y O2, 0.5≤x≤0.9, 0.1≤y≤0.

3.

2. A method for preparing the cathode material according to claim 1, characterized in that, Includes the following steps: S1. Cellulose is uniformly dispersed in a polyimide precursor solution and heated to react, resulting in a mixed solution A; S2. Weigh the raw materials according to the chemical composition of the positive electrode active material to obtain the positive electrode active material precursor, add acid anhydride compounds to obtain a mixture, mix the mixture with a solvent, heat and react to obtain mixed solution B; S3. Add mixed solution B to mixed solution A, add precipitant, complexing agent and esterification catalyst, heat to react once, add manganese barium ore, heat to react a second time, dry to obtain intermediate; S4. The intermediate is mixed with the lithium source and then calcined to obtain the cathode material.

3. The preparation method according to claim 2, characterized in that, In S1, the polyimide precursor solution includes a diamine monomer, a dianhydride monomer, and a solvent; the diamine monomer is selected from one or more of 4,4'-diaminodiphenyl ether, p-phenylenediamine, and m-phenylenediamine; the dianhydride monomer is selected from one or more of pyromellitic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 3,3',4,4'-biphenyltetracarboxylic dianhydride; and the solvent is selected from one or more of N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide.

4. The preparation method according to claim 2, characterized in that, In S1, the molar ratio of cellulose to polyimide is (1-4):

1.

5. The preparation method according to claim 2, characterized in that, In S2, the raw materials are selected from one or more of nickel source, cobalt source, and manganese source; the nickel source is selected from one or more of nickel chloride, nickel sulfate, and nickel acetate; the cobalt source is selected from one or more of cobalt chloride, cobalt sulfate, and cobalt acetate; the manganese source is selected from one or more of manganese chloride, manganese sulfate, and manganese acetate; the mass ratio of the positive electrode active material precursor to the acid anhydride compound is (50-100):1; the heating reaction temperature is 80-100℃; and the acid anhydride compound is selected from one or more of maleic anhydride, itaconic anhydride, and nadic anhydride.

6. The preparation method according to claim 2, characterized in that, In S3, the precipitant is selected from one or more of sodium hydroxide solution and potassium hydroxide solution; the complexing agent is selected from one or more of ammonia water, citric acid solution, and ethylenediamine; and the esterification catalyst is selected from one or more of dicyclohexylcarbodiimide solution and thionyl chloride.

7. The preparation method according to claim 2, characterized in that, In S3, the temperature of the first heating reaction is 40-60℃; the temperature of the second heating reaction is 70-90℃; the volume ratio of mixed solution A, mixed solution B, precipitant, complexing agent, and esterification catalyst is (10-30):(5-15):1:(0.1-0.6):(0.2-0.8); and the molar ratio of manganese barium ore to the total metal ions in mixed solution B is (0.01-0.25):

1.

8. The preparation method according to claim 2, characterized in that, In S4, the molar ratio of the total metal ions of the positive electrode active material in the intermediate to the lithium ions in the lithium source is 1:(1~1.1); the lithium source is selected from one or more of lithium carbonate, lithium hydroxide, and lithium acetate.

9. The preparation method according to claim 2, characterized in that, In S4, the calcination treatment includes first pre-calcining at 300-500℃ for 3-5 hours by raising the temperature at 1-5℃ / min, and then calcining at 700-900℃ for 1-3 hours by raising the temperature at 1-5℃ / min; the calcination atmosphere for the calcination treatment is selected from one or more of nitrogen and argon.

10. The application of the cathode material according to claim 1 or the cathode material prepared by any one of claims 2 to 9 in a lithium-ion battery.

Images