Preparation method of boron sol for coating ternary positive electrode material of lithium battery

Abstract

This invention discloses a method for preparing boron sol for coating ternary cathode materials of lithium batteries, comprising the following steps: (1) mixing and stirring tributyl borate with an organic acid, and then adding it to a mixture of organic solvent and water; (2) adding a yellow sulfonated phenolphthalein solution, wherein the sulfonated phenolphthalein / boron molar ratio is 0.001:1 to 1:1, heating and stirring while maintaining a certain temperature, then adding additives, and refluxing in a reflux device for a certain time to obtain a stable transparent sol; (3) mixing the obtained stable boron sol with a water-soluble resin and ball milling in a ball mill for a period of time to obtain a ternary cathode coating material for lithium batteries. The boron sol obtained by the above preparation method is suitable for aluminum coating of ternary cathode materials for lithium batteries, and can effectively prevent the transformation of the lithium compound layered structure on the surface of the ternary cathode material to a rock salt structure and an disordered spinel structure. At the same time, the formation of an inactive coating layer with a certain mechanical strength can also slow down the collapse of the electrode material structure during long-term cycling, resulting in better cycle performance and safety performance, thereby improving the performance of lithium-ion batteries.

Description

Technical Field

[0001] This invention relates to a method for preparing boron sol and to the field of ternary cathode coating materials for lithium batteries. Background Technology

[0002] With the increasing severity of environmental pollution and the gradual depletion of fossil fuels, the search for new green and environmentally friendly energy sources has become a major issue facing all countries. Compared with traditional lead-acid, nickel-cadmium, and nickel-metal hydride batteries, lithium-ion batteries have advantages such as high energy density, long cycle life, high charge and discharge voltage, environmental friendliness, and no memory effect. Since its invention in the 1980s, it has developed rapidly. Currently, lithium-ion batteries are not only widely used in electronic products, but have also become the preferred power battery for new energy vehicles, making them a key research focus for various countries.

[0003] Lithium-ion batteries mainly consist of several components, including positive electrode materials, negative electrode materials, separators, and electrolytes. Among these, the positive electrode material accounts for more than 30% of the battery cost and determines its performance, making it a key focus of lithium-ion battery research. Currently, the most popular positive electrode materials on the market are LiCoO2, LiFePO4, and Li[Ni,Co,Mn]O2.

[0004] Surface modification is a widely used and effective method to improve the electrochemical performance of cathode materials in lithium-ion batteries. It involves coating the material surface with a stable thin film, which can improve the material's reversible specific capacity, cycle performance, rate performance, and especially thermal stability. Studies have found that the charge / discharge rate significantly affects the structural stability of ternary materials. At high charge / discharge rates, lithium ions on the surface are more easily intercalated and deintercalated, while those located inside the material need to diffuse to the surface first, then through the electrolyte and separator to reach the negative electrode. This diffusion lag results in a higher degree of lithium intercalation and deintercalation on the surface layer and a lower degree inside, creating stress between the particle surface and core, leading to the breakage of spherical ternary material particles. Furthermore, the different degrees of delithiation on the surface and inside the material, along with the varying solubility of transition metals, make the electrolyte more effective at dissolving surface transition metals. This makes the surface structure highly susceptible to damage, potentially transforming it from a layered structure to a rock-salt structure and an disordered spinel structure. Therefore, the cycle performance of ternary materials is closely related to the material-electrolyte interface.

[0005] Common surface modification materials generally possess the following characteristics: First, they must have good chemical compatibility, not reacting chemically with active materials or electrolytes during charging and discharging; second, they must have good thermal stability, not decomposing during charging and discharging; and finally, they must have a certain degree of electronic conductivity, allowing lithium ions to pass through. The main function of coating is to add a protective layer to the material surface. On the one hand, this reduces side reactions between the material and the electrolyte, inhibits the dissolution of transition metal ions, reduces the collapse of the material structure during repeated charging and discharging, and optimizes the material's cycle performance; on the other hand, it appropriately improves the lithium-ion diffusion coefficient and ionic conductivity, reducing lithium-ion diffusion resistance and charge resistance. Simultaneously, surface coating is relatively effective in reducing the residual alkali content on the surface of high-nickel ternary materials. Therefore, inventing a method to effectively improve cycle performance and safety performance, thereby enhancing the performance of lithium-ion batteries, is urgently needed. Summary of the Invention

[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a coating material that can effectively prevent the transformation of the layered lithium compound structure on the surface of ternary cathode materials into a rock salt structure and an disordered spinel structure. Simultaneously, the formation of a non-active coating layer with a certain mechanical strength can also slow down the collapse of the electrode material structure during long-term cycling.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for preparing boron sol for coating ternary cathode materials in lithium batteries includes the following steps:

[0009] (1) Mix tributyl borate with organic acid and stir, then add it to a mixture of organic solvent and water;

[0010] (2) Add yellow sulfonated phenolphthalein solution, with a sulfonated phenolphthalein / boron molar ratio of 0.001:1 to 1:1. Adjust the pH of the solution to a certain range, heat and stir while maintaining a certain temperature until the precipitate is completely dispersed. Then add the additive dropwise, continue to maintain a certain temperature, and reflux in a reflux device for a certain time to obtain a stable boron sol.

[0011] The organic acid solution mentioned in step (1) is formic acid, acetic acid, oxalic acid, citric acid, tartaric acid, etc., including one or more of them.

[0012] The organic solvent mentioned in step (1) is ethanol, methanol, propanol, diethyl ether, methyl acetate, etc., including one or more of them.

[0013] The volume ratio of reagents added in step (1) is: tributyl borate: organic acid: organic solvent: water = (5-10):(2-3):(6-20):(4-5).

[0014] The sulfonated phenolphthalein / boron molar ratio in step (2) is 0.001:1 to 1:1.

[0015] The pH adjustment range in step (2) is 2.0-5.0.

[0016] The sulfonated phenolphthalein solution mentioned in step (2) is one or more of phenol red, cresol red, and bromophenol blue.

[0017] The heat preservation temperature in step (2) is 80-95℃, and the heat preservation time is 6-24h. The additive in step (2) is sodium carboxymethyl cellulose, including sodium alginate, polyacrylamide, and polyethylene glycol, one or more of which are added at a mass of 0.001-0.05 times the mass of the boron sol.

[0018] A method for preparing a ternary cathode coating material for lithium batteries involves mixing a water-soluble resin with a obtained stable boron sol and ball milling the mixture in a ball mill for a period of time to obtain the ternary cathode coating material for lithium batteries.

[0019] The ratio of boron sol to water-soluble resin is 1:2 to 1:3.

[0020] The ball milling time is 10-24 hours.

[0021] The water-soluble resin is one or more of the following: water-based polyurethane resin, water-based polyacrylic acid resin, water-based epoxy resin, and water-based silicone resin.

[0022] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0023] (1) The boron sol prepared in this invention can effectively prevent the transformation of the lithium compound layered structure on the surface of the ternary cathode material into a rock salt structure and an disordered spinel structure. At the same time, the formation of an inactive coating layer with a certain mechanical strength can also slow down the collapse of the electrode material structure during long-term cycling, and the surface coating can reduce the residual alkali content on the surface of the high-nickel ternary material.

[0024] (2) The additive described in this invention is a sol stabilizer. During the sol aging process, it plays a role in structure guidance and space filling, thereby forming a stable framework structure. It can effectively increase the stability of the sol and also improve the adhesion between the sol and the contact material.

[0025] (3) The lithium battery ternary cathode material coating material prepared by the present invention can improve the diffusion coefficient and ionic conductivity of lithium ions, and reduce the diffusion impedance and charge impedance of lithium ions.

[0026] (4) The method of the present invention synthesizes a boron sol with high activity and high stability. The resulting sol is particularly suitable for coating lithium battery ternary cathode materials. The method is simple and effective, and the final material surface is uniformly coated. Lithium-ion batteries containing this material have better cycle performance and safety performance.

[0027] (5) The preparation method of the present invention is simple and low in cost. It has low requirements for equipment and process conditions. The coating layer has fine particles, large specific surface area, better coating effect, and is easier to form a uniform and dense protective film on the surface of ternary materials. Attached Figure Description

[0028] Figure 1 This is an electron microscope image of the coating material of the ternary cathode material for lithium batteries prepared according to the present invention. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to embodiments:

[0030] Example 1: 20 mL of tributyl borate and 10 mL of oxalic acid were mixed and stirred thoroughly for 1 hour. Then, 40 mL of a mixture of tributyl borate and 20 mL of deionized water was added, and stirring continued for 1 hour. A 1% cresol red solution (yellow) was then added and mixed to adjust the pH to 3.6. The mixture was heated and stirred with a magnetic stirrer and kept at a constant temperature of 80°C in a water bath to maintain uniformity. 0.1 g of sodium carboxymethyl cellulose was added to the solution, and the mixture was refluxed in a reflux apparatus for 20 hours to obtain a stable boron sol. 20 g of the boron sol and 40 g of water-soluble polyacrylate were ball-milled for 12 hours to obtain a ternary cathode material coating for lithium batteries.

[0031] Example 2: 20 mL of tributyl borate and 10 mL of oxalic acid were mixed and stirred thoroughly for 1 hour. Then, a mixture of 40 mL and 30 mL of deionized water was added, and stirring continued for 1 hour. A 1% cresol red solution (yellow) was then added and mixed to adjust the pH to 3. The mixture was heated and stirred with a magnetic stirrer and kept at a constant temperature of 80°C in a water bath to maintain uniformity. 0.1 g of polyacrylamide was added to the solution, and the mixture was refluxed in a reflux apparatus for 24 hours to obtain a stable boron sol. 20 g of the boron sol and 60 g of water-soluble epoxy resin were ball-milled for 12 hours to obtain a ternary cathode material coating for lithium batteries.

[0032] Example 3: Aluminum Sol Activity Test

[0033] The high activity of the aluminum sol prepared by the method of this invention is manifested in the significant improvement of the initial charge, initial discharge, and efficiency of the material after ternary material coating. The results are shown in Table 2.

[0034] Table 2 shows the electrical performance test data of the ternary materials after aluminum sol coating. The comparison shows that the electrical performance is significantly improved after coating.

[0035] Table 2 Electrical performance parameters of ternary materials before and after coating.

[0036]

[0037] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be considered equivalent substitutions and shall be included within the protection scope of the present invention.

Claims

1. A method for preparing boron sol for coating ternary cathode materials in lithium batteries, comprising the following steps: (1) Mix tributyl borate with organic acid and stir, then add it to a mixture of organic solvent and water; (2) Add yellow sulfonated phenolphthalein solution, with a sulfonated phenolphthalein / boron molar ratio of 0.001:1 to 1:

1. Adjust the pH of the solution to 3-3.6, heat and stir while maintaining 80°C, then add the additive dropwise, continue to maintain 80°C, and reflux in a reflux apparatus for 20-24 hours to obtain a stable boron sol. The organic acid in step (1) is one or more of formic acid, acetic acid, oxalic acid, citric acid, and tartaric acid; the organic solvent in step (1) is one or more of ethanol, methanol, propanol, diethyl ether, and methyl acetate; the volume ratio of addition in step (1) is: tributyl borate: organic acid: organic solvent: water = (4-10):(1-3):(6-20):(4-5); The sulfonated phenolphthalein solution mentioned in step (2) is one or more of phenol red, cresol red, and bromophenol blue; The additive mentioned in step (2) is one or more of sodium carboxymethyl cellulose, sodium alginate, polyacrylamide, and polyethylene glycol, and the mass added is 0.001-0.05 of the boron sol mass.

2. A method for preparing a ternary cathode coating material for lithium batteries, characterized in that: The stable boron sol obtained according to claim 1 is then mixed with a water-soluble resin and ball-milled in a ball mill for a period of time to obtain a ternary cathode coating material for lithium batteries.

3. The method for preparing the ternary cathode coating material for lithium batteries according to claim 2, characterized in that... The mass ratio of boron sol to water-soluble resin is 1:2 to 1:

3.

4. The method for preparing the ternary cathode coating material for lithium batteries according to claim 2, characterized in that... The ball milling time is 12 hours.

5. The method for preparing the ternary cathode coating material for lithium batteries according to claim 2, characterized in that... The water-soluble resin is one or more of the following: water-based polyurethane resin, water-soluble polyacrylic acid resin, water-soluble epoxy resin, and water-soluble organosilicon resin.

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