Preparation method and application of modified lithium cobalt oxide positive electrode material

Abstract

The invention relates to the technical field of positive electrode materials, and particularly discloses a preparation method and application of a modified lithium cobalt oxide positive electrode material. The preparation method comprises the following steps: S1, preparing modified graphene by taking polyvinyl alcohol modified porous graphene, phosphatic acid, 5-boracolinic acid, zinc sulfate and carboxymethyl chitosan as raw materials; s2, adding carboxymethyl chitosan into water, stirring and dissolving, adding the modified graphene, and uniformly mixing to obtain a modified solution; spraying the modified liquid on the surface of lithium cobalt oxide, and drying to obtain a modified lithium cobalt oxide positive electrode material; the modified graphene is prepared from the following raw materials in parts by mass: 10 to 12 parts of polyvinyl alcohol modified porous graphene, 2.5 to 4 parts of phosphatic acid, 2 to 3 parts of 5-boron pyridine carboxylic acid and 3 to 4 parts of carboxymethyl chitosan; the modified liquid is prepared from the following raw materials in parts by mass: 3 to 5 parts of carboxymethyl chitosan, 120 to 150 parts of water and 0.6 to 1 part of modified graphene.

Description

Technical Field

[0001] The invention relates to the technical field of positive electrode materials, and specifically discloses a preparation method and application of a modified lithium cobalt oxide positive electrode material. Background Art

[0002] Lithium batteries have high operating voltage, high energy density, and good cycle performance, and are widely used in various fields. The performance of lithium-ion batteries is mainly determined by the positive electrode material. Lithium cobalt oxide positive electrode materials are easy to synthesize, have high specific energy, and have mature production processes. They are the most commonly used positive electrode materials for lithium-ion batteries.

[0003] In order to further improve the cycle stability of lithium cobalt oxide positive electrode materials, the existing technology often coats the surface of lithium cobalt oxide positive electrode materials. However, the existing coating materials have problems such as low lithium ion diffusion coefficient, low conductivity, and poor bonding with the lithium cobalt oxide material matrix, which limits the application of lithium cobalt oxide positive electrode materials. Therefore, it is of great significance to study a preparation method for a modified lithium cobalt oxide positive electrode material with a large discharge rate and good cycle stability. Summary of the invention

[0004] The purpose of the present invention is to provide a preparation method and application of a modified lithium cobalt oxide positive electrode material to solve the problems raised in the prior art.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for preparing a modified lithium cobalt oxide positive electrode material, comprising the following steps:

[0006] S1: Add polyvinyl alcohol-modified porous graphene, phosphatidyl salicylic acid, and 5-boropyridine carboxylic acid into water, mix well, add zinc sulfate, heat and pressurize, react at 110-120°C for 8-10 hours, add carboxymethyl chitosan and zinc sulfate, continue to react for 3-4 hours, remove the solvent, and obtain modified graphene;

[0007] S2: adding carboxymethyl chitosan into water and stirring to dissolve, adding modified graphene, mixing evenly to obtain a modified liquid; spraying the modified liquid onto the surface of lithium cobalt oxide, drying, and obtaining a modified lithium cobalt oxide positive electrode material having a modified layer on the surface.

[0008] More optimally, the modified graphene includes the following raw materials, calculated by weight: 10 to 12 parts of polyvinyl alcohol modified porous graphene, 2.5 to 4 parts of phosphatidylcholine, 2 to 3 parts of 5-boropyridinecarboxylic acid, and 3 to 4 parts of carboxymethyl chitosan.

[0009] More optimally, the specific preparation method of the modified graphene is: add 10-12 parts of polyvinyl alcohol modified porous graphene, 2.5-4 parts of phosphatidylcholine, and 2-3 parts of 5-boropyridinecarboxylic acid to 150-200 parts of water, mix evenly, add 1-2 parts of zinc sulfate, heat and pressurize, react at 110-120°C for 8-10 hours, add 3-4 parts of carboxymethyl chitosan and 0.5-1 part of zinc sulfate, react at 110-120°C for 3-4 hours, remove the solvent, and obtain modified graphene.

[0010] More optimally, the modified liquid includes the following raw materials, calculated by weight: 3-5 parts of carboxymethyl chitosan, 120-150 parts of water, and 0.6-1 part of modified graphene.

[0011] More optimally, the preparation method of the modified lithium cobalt oxide positive electrode material comprises the following steps: spraying the modification liquid on the surface of the modified lithium cobalt oxide at a mass ratio of (1-1.1):1, and drying to obtain the modified lithium cobalt oxide positive electrode material.

[0012] More optimally, the preparation of the polyvinyl alcohol-modified porous graphene includes the following steps: dispersing porous graphene oxide in water to obtain a dispersion; adding polyvinyl alcohol, stirring evenly, adding an ammonia solution and a hydrazine hydrate solution, stirring evenly, stirring at 85-90° C. for 4-5 hours, washing, and centrifuging to obtain polyvinyl alcohol-modified porous graphene.

[0013] More optimally, the concentration of the dispersion is 4-5 mg / mL; the polyvinyl alcohol-modified porous graphene includes the following raw materials, calculated by mass: 150-200 parts of dispersion, 6-7 parts of polyvinyl alcohol, 20-30 parts of 25% ammonia solution, and 1-2 parts of 80% hydrazine hydrate solution.

[0014] More optimally, the lithium cobalt oxide is modified to obtain modified lithium cobalt oxide before use, which specifically includes the following steps: mixing porous graphene and lithium cobalt oxide, heating at 550-650° C. for 5-6 hours, and cooling to obtain modified lithium cobalt oxide.

[0015] More optimally, the modified lithium cobalt oxide includes the following raw materials, calculated by weight: 0.6-1 parts of porous graphene and 10-15 parts of lithium cobalt oxide.

[0016] Compared with the prior art, the beneficial effects achieved by the present invention are: porous graphene is doped with lithium cobalt oxide and compounded by heat treatment, the graphene has good conductivity, its porous structure increases the specific surface area of ​​the material, provides a channel for the transmission of lithium ions, and can improve the bonding force with the modified layer; the amount of porous graphene added should not be too much, and too much porous structure may lead to a decrease in structural stability;

[0017] The modified liquid includes carboxymethyl chitosan and modified graphene. The preparation of the modified graphene includes the following steps: firstly, porous graphene oxide is modified with polyvinyl alcohol. Polyvinyl alcohol has the functions of improving dispersibility, viscosity and stability, and its chain segment is relatively long, which is helpful to improve film-forming property; at the same time, polyvinyl alcohol contains multiple hydroxyl groups, which can provide reaction sites for subsequent reactions; the subsequent reaction obviously introduces phosphatidylcholine and 5-boropyridine carboxylic acid; PO in phosphatidylcholine has a stabilizing effect on O atoms and has the function of stabilizing the surface structure of lithium cobalt oxide, and at the same time, phosphatidylcholine has a corrosion inhibition effect and can inhibit the dissolution of Co atoms; 5-boropyridine carboxylic acid contains nitrogen and boron, and the co-doping of nitrogen and boron can increase the defect sites of carbon and improve the discharge rate of positive electrode materials; the above two substances are added in a certain proportion, on the one hand, the surface stability of lithium cobalt oxide is improved, and on the other hand, the lithium ion channel is increased, which plays a synergistic role in improving the cycle stability and discharge rate.

[0018] After introducing phosphatidylcholine and 5-boropyridine carboxylic acid, carboxymethyl chitosan is added to react, so as to improve the compatibility with carboxymethyl chitosan in the modified solution. Carboxymethyl chitosan contains a large number of carboxyl groups, which improves the binding force with the modified lithium cobalt oxide matrix. Carboxymethyl chitosan has a large steric hindrance. If it is added simultaneously with phosphatidylcholine and 5-boropyridine carboxylic acid for reaction, it may affect the grafting rate and lead to a decrease in performance.

[0019] Porous graphene is added to both the modified liquid and the modified lithium cobalt oxide, which improves the migration and diffusion ability of lithium ions and is beneficial to improving the discharge rate and cycle performance. DETAILED DESCRIPTION

[0020] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] The following parts are by mass unless otherwise specified;

[0022] Example 1: S1: disperse porous graphene oxide in water to obtain a 4 mg / mL dispersion; take 160 parts of the dispersion, add 6.5 parts of polyvinyl alcohol, stir evenly, add 25 parts of 25% ammonia solution and 1 part of 80% hydrazine hydrate solution, stir evenly, stir at 90° C. for 4 h, wash, and centrifuge to obtain polyvinyl alcohol-modified porous graphene;

[0023] S2: 0.8 parts of porous graphene and 12 parts of lithium cobalt oxide are mixed, heated at 600° C. for 6 h, and cooled to obtain modified lithium cobalt oxide;

[0024] S3: Add 12 parts of polyvinyl alcohol modified porous graphene, 3 parts of phosphatidylcholine, and 2.5 parts of 5-boronic pyridine carboxylic acid to 200 parts of water, mix well, add 2 parts of zinc sulfate, heat and pressurize, react at 115°C for 8h, add 3 parts of carboxymethyl chitosan and 1 part of zinc sulfate, react at 120°C for 4h, remove the solvent, and obtain modified graphene;

[0025] S4: Add 5 parts of carboxymethyl chitosan to 120 parts of water, stir and dissolve, add 0.8 parts of modified graphene, mix evenly, and obtain a modified liquid; spray the modified liquid on the surface of the modified lithium cobalt oxide at a mass ratio of 1:1, dry, and obtain a modified lithium cobalt oxide positive electrode material.

[0026] Example 2: S1: disperse porous graphene oxide in water to obtain a 4 mg / mL dispersion; take 160 parts of the dispersion, add 6 parts of polyvinyl alcohol, stir evenly, add 25 parts of 25% ammonia solution and 1 part of 80% hydrazine hydrate solution, stir evenly, stir at 90° C. for 5 h, wash, and centrifuge to obtain polyvinyl alcohol-modified porous graphene;

[0027] S2: 0.6 parts of porous graphene and 10 parts of lithium cobalt oxide are mixed, heated at 550° C. for 6 h, and cooled to obtain modified lithium cobalt oxide;

[0028] S3: Add 10 parts of polyvinyl alcohol modified porous graphene, 2.5 parts of phosphatidylcholine, and 2 parts of 5-boropyridine carboxylic acid to 200 parts of water, mix well, add 1 part of zinc sulfate, heat and pressurize, react at 115°C for 8h, add 3 parts of carboxymethyl chitosan and 0.5 parts of zinc sulfate, react at 120°C for 4h, remove the solvent, and obtain modified graphene;

[0029] S4: Add 4 parts of carboxymethyl chitosan to 120 parts of water, stir and dissolve, add 1 part of modified graphene, mix evenly, and obtain a modified liquid; spray the modified liquid on the surface of the modified lithium cobalt oxide at a mass ratio of 1:1, dry, and obtain a modified lithium cobalt oxide positive electrode material.

[0030] Example 3: S1: disperse porous graphene oxide in water to obtain a 4 mg / mL dispersion; take 160 parts of the dispersion, add 7 parts of polyvinyl alcohol, stir evenly, add 25 parts of 25% ammonia solution and 1 part of 80% hydrazine hydrate solution, stir evenly, stir at 90° C. for 4-5 hours, wash, and centrifuge to obtain polyvinyl alcohol-modified porous graphene;

[0031] S2: Mix 1 part of porous graphene and 15 parts of lithium cobalt oxide, heat at 650° C. for 5 h, and cool to obtain modified lithium cobalt oxide;

[0032] S3: Add 12 parts of polyvinyl alcohol modified porous graphene, 4 parts of phosphatidylcholine, and 2 parts of 5-boropyridine carboxylic acid to 200 parts of water, mix well, add 2 parts of zinc sulfate, heat and pressurize, react at 115°C for 8h, add 4 parts of carboxymethyl chitosan and 1 part of zinc sulfate, react at 120°C for 4h, remove the solvent, and obtain modified graphene;

[0033] S4: Add 5 parts of carboxymethyl chitosan to 120 parts of water, stir and dissolve, add 0.6 parts of modified graphene, mix evenly, and obtain a modified liquid; spray the modified liquid on the surface of the modified lithium cobalt oxide at a mass ratio of 1:1, dry, and obtain a modified lithium cobalt oxide positive electrode material.

[0034] Example 4: S1: porous graphene oxide is dispersed in water to obtain a 4 mg / mL dispersion; 160 parts of the dispersion are added with 7 parts of polyvinyl alcohol, stirred evenly, 25 parts of 25% ammonia solution and 1 part of 80% hydrazine hydrate solution are added, stirred evenly, stirred at 90° C. for 5 h, washed, and centrifuged to obtain polyvinyl alcohol-modified porous graphene;

[0035] S2: Mix 1 part of porous graphene and 10 parts of lithium cobalt oxide, heat at 650° C. for 5 h, and cool to obtain modified lithium cobalt oxide;

[0036] S3: Add 12 parts of polyvinyl alcohol modified porous graphene, 4 parts of phosphatidylcholine, and 2 parts of 5-boropyridine carboxylic acid to 200 parts of water, mix well, add 2 parts of zinc sulfate, heat and pressurize, react at 115°C for 8h, add 4 parts of carboxymethyl chitosan and 1 part of zinc sulfate, react at 120°C for 4h, remove the solvent, and obtain modified graphene;

[0037] S4: Add 3 parts of carboxymethyl chitosan to 120 parts of water, stir and dissolve, add 1 part of modified graphene, mix evenly, and obtain a modified liquid; spray the modified liquid on the surface of the modified lithium cobalt oxide at a mass ratio of 1:1, dry, and obtain a modified lithium cobalt oxide positive electrode material.

[0038] Example 5: S1: disperse porous graphene oxide in water to obtain a 4 mg / mL dispersion; take 160 parts of the dispersion, add 7 parts of polyvinyl alcohol, stir evenly, add 25 parts of 25% ammonia solution and 1 part of 80% hydrazine hydrate solution, stir evenly, stir at 90° C. for 5 h, wash, and centrifuge to obtain polyvinyl alcohol-modified porous graphene;

[0039] S2: 0.6 parts of porous graphene and 15 parts of lithium cobalt oxide are mixed, heated at 650° C. for 6 h, and cooled to obtain modified lithium cobalt oxide;

[0040] S3: Add 12 parts of polyvinyl alcohol modified porous graphene, 2.5 parts of phosphatidylcholine, and 3 parts of 5-boropyridine carboxylic acid to 200 parts of water, mix well, add 1-2 parts of zinc sulfate, heat and pressurize, react at 115°C for 8h, add 4 parts of carboxymethyl chitosan and 0.5 parts of zinc sulfate, react at 120°C for 4h, remove the solvent, and obtain modified graphene;

[0041] S4: Add 5 parts of carboxymethyl chitosan to 120 parts of water, stir and dissolve, add 0.6 parts of modified graphene, mix evenly, and obtain a modified liquid; spray the modified liquid on the surface of the modified lithium cobalt oxide at a mass ratio of 1:1, dry, and obtain a modified lithium cobalt oxide positive electrode material.

[0042] Comparative Example 1 (increasing the amount of porous graphene added in the modified lithium cobalt oxide, and the remaining method steps are consistent with Example 1): S1: Dispersing porous graphene oxide in water to obtain a 4 mg / mL dispersion; taking 160 parts of the dispersion, adding 6.5 parts of polyvinyl alcohol, stirring evenly, adding 25 parts of 25% ammonia solution and 1 part of 80% hydrazine hydrate solution, stirring evenly, stirring at 90° C. for 4 hours, washing, and centrifuging to obtain polyvinyl alcohol-modified porous graphene;

[0043] S2: 1.8 parts of porous graphene and 12 parts of lithium cobalt oxide are mixed, heated at 600° C. for 6 h, and cooled to obtain modified lithium cobalt oxide;

[0044] S3: Add 12 parts of polyvinyl alcohol modified porous graphene, 3 parts of phosphatidylcholine, and 2.5 parts of 5-boronic pyridine carboxylic acid to 200 parts of water, mix well, add 2 parts of zinc sulfate, heat and pressurize, react at 115°C for 8h, add 3 parts of carboxymethyl chitosan and 1 part of zinc sulfate, react at 120°C for 4h, remove the solvent, and obtain modified graphene;

[0045] S4: Add 5 parts of carboxymethyl chitosan to 120 parts of water, stir and dissolve, add 0.8 parts of modified graphene, mix evenly, and obtain a modified liquid; spray the modified liquid on the surface of the modified lithium cobalt oxide at a mass ratio of 1:1, dry, and obtain a modified lithium cobalt oxide positive electrode material.

[0046] Comparative Example 2 (using graphene instead of porous graphene, using graphene oxide instead of porous graphene oxide, and the remaining method steps are consistent with Example 1): S1: dispersing graphene oxide in water to obtain a 4 mg / mL dispersion; taking 160 parts of the dispersion, adding 6.5 parts of polyvinyl alcohol, stirring evenly, adding 25 parts of 25% ammonia solution and 1 part of 80% hydrazine hydrate solution, stirring evenly, stirring at 90° C. for 4 h, washing, and centrifuging to obtain polyvinyl alcohol-modified graphene;

[0047] S2: 0.8 parts of graphene and 12 parts of lithium cobalt oxide are mixed, heated at 600° C. for 6 h, and cooled to obtain modified lithium cobalt oxide;

[0048] S3: Add 12 parts of polyvinyl alcohol modified graphene, 3 parts of phosphatidylcholine, and 2.5 parts of 5-boronic pyridine carboxylic acid to 200 parts of water, mix well, add 2 parts of zinc sulfate, heat and pressurize, react at 115°C for 8h, add 3 parts of carboxymethyl chitosan and 1 part of zinc sulfate, react at 120°C for 4h, remove the solvent, and obtain modified graphene;

[0049] S4: Add 5 parts of carboxymethyl chitosan to 120 parts of water, stir and dissolve, add 0.8 parts of modified graphene, mix evenly, and obtain a modified liquid; spray the modified liquid on the surface of the modified lithium cobalt oxide at a mass ratio of 1:1, dry, and obtain a modified lithium cobalt oxide positive electrode material.

[0050] Comparative Example 3 (increasing the amount of modified graphene added in the modified solution, and the remaining method steps are consistent with Example 1): S1: Dispersing porous graphene oxide in water to obtain a 4 mg / mL dispersion; taking 160 parts of the dispersion, adding 6.5 parts of polyvinyl alcohol, stirring evenly, adding 25 parts of 25% ammonia solution and 1 part of 80% hydrazine hydrate solution, stirring evenly, stirring at 90° C. for 4 hours, washing, and centrifuging to obtain polyvinyl alcohol-modified porous graphene;

[0051] S2: 0.8 parts of porous graphene and 12 parts of lithium cobalt oxide are mixed, heated at 600° C. for 6 h, and cooled to obtain modified lithium cobalt oxide;

[0052] S3: Add 12 parts of polyvinyl alcohol modified porous graphene, 3 parts of phosphatidylcholine, and 2.5 parts of 5-boronic pyridine carboxylic acid to 200 parts of water, mix well, add 2 parts of zinc sulfate, heat and pressurize, react at 115°C for 8h, add 3 parts of carboxymethyl chitosan and 1 part of zinc sulfate, react at 120°C for 4h, remove the solvent, and obtain modified graphene;

[0053] S4: Add 5 parts of carboxymethyl chitosan to 120 parts of water, stir and dissolve, add 1.8 parts of modified graphene, mix evenly, and obtain a modified liquid; spray the modified liquid on the surface of the modified lithium cobalt oxide at a mass ratio of 1:1, dry, and obtain a modified lithium cobalt oxide positive electrode material.

[0054] Comparative Example 4 (the preparation process of modified graphene is changed, and the remaining method steps are consistent with Example 1): S1: porous graphene oxide is dispersed in water to obtain a 4 mg / mL dispersion; 160 parts of the dispersion are taken, 6.5 parts of polyvinyl alcohol are added, and stirred evenly, 25 parts of 25% ammonia solution and 1 part of 80% hydrazine hydrate solution are added, and stirred evenly, stirred at 90° C. for 4 h, washed, and centrifuged to obtain polyvinyl alcohol-modified porous graphene;

[0055] S2: 0.8 parts of porous graphene and 12 parts of lithium cobalt oxide are mixed, heated at 600° C. for 6 h, and cooled to obtain modified lithium cobalt oxide;

[0056] S3: Add 12 parts of polyvinyl alcohol modified porous graphene, 3 parts of phosphatidyl salicylic acid, 2.5 parts of 5-boropyridine carboxylic acid, and 3 parts of carboxymethyl chitosan to 200 parts of water, mix well, add 3 parts of zinc sulfate, heat and pressurize, react at 115°C for 12 hours, remove the solvent, and obtain modified graphene;

[0057] S4: Add 5 parts of carboxymethyl chitosan to 120 parts of water, stir and dissolve, add 0.8 parts of modified graphene, mix evenly, and obtain a modified liquid; spray the modified liquid on the surface of the modified lithium cobalt oxide at a mass ratio of 1:1, dry, and obtain a modified lithium cobalt oxide positive electrode material.

[0058] Comparative Example 5 (changing the amount of raw materials added in the modified graphene, and the other method steps are consistent with Example 1): S1: Dispersing porous graphene oxide in water to obtain a 4 mg / mL dispersion; taking 160 parts of the dispersion, adding 6.5 parts of polyvinyl alcohol, stirring evenly, adding 25 parts of 25% ammonia solution and 1 part of 80% hydrazine hydrate solution, stirring evenly, stirring at 90° C. for 4 hours, washing, and centrifuging to obtain polyvinyl alcohol-modified porous graphene;

[0059] S2: 0.8 parts of porous graphene and 12 parts of lithium cobalt oxide are mixed, heated at 600° C. for 6 h, and cooled to obtain modified lithium cobalt oxide;

[0060] S3: Add 12 parts of polyvinyl alcohol modified porous graphene, 5 parts of phosphatidylcholine, and 0.5 parts of 5-boropyridine carboxylic acid to 200 parts of water, mix well, add 2 parts of zinc sulfate, heat and pressurize, react at 115°C for 8h, add 3 parts of carboxymethyl chitosan and 1 part of zinc sulfate, react at 120°C for 4h, remove the solvent, and obtain modified graphene;

[0061] S4: Add 5 parts of carboxymethyl chitosan to 120 parts of water, stir and dissolve, add 0.8 parts of modified graphene, mix evenly, and obtain a modified liquid; spray the modified liquid on the surface of the modified lithium cobalt oxide at a mass ratio of 1:1, dry, and obtain a modified lithium cobalt oxide positive electrode material.

[0062] Comparative Example 6 (changing the amount of raw materials added in the modified graphene, and the other method steps are consistent with Example 1): S1: Dispersing porous graphene oxide in water to obtain a 4 mg / mL dispersion; taking 160 parts of the dispersion, adding 6.5 parts of polyvinyl alcohol, stirring evenly, adding 25 parts of 25% ammonia solution and 1 part of 80% hydrazine hydrate solution, stirring evenly, stirring at 90° C. for 4 hours, washing, and centrifuging to obtain polyvinyl alcohol-modified porous graphene;

[0063] S2: 0.8 parts of porous graphene and 12 parts of lithium cobalt oxide are mixed, heated at 600° C. for 6 h, and cooled to obtain modified lithium cobalt oxide;

[0064] S3: Add 12 parts of polyvinyl alcohol modified porous graphene, 1 part of phosphatidylcholine, and 4.5 parts of 5-boronic pyridine carboxylic acid to 200 parts of water, mix well, add 2 parts of zinc sulfate, heat and pressurize, react at 115°C for 8h, add 3 parts of carboxymethyl chitosan and 1 part of zinc sulfate, react at 120°C for 4h, remove the solvent, and obtain modified graphene;

[0065] S4: Add 5 parts of carboxymethyl chitosan to 120 parts of water, stir and dissolve, add 0.8 parts of modified graphene, mix evenly, and obtain a modified liquid; spray the modified liquid on the surface of the modified lithium cobalt oxide at a mass ratio of 1:1, dry, and obtain a modified lithium cobalt oxide positive electrode material.

[0066] In the above embodiments, the test methods used are conventional methods unless otherwise specified; the raw materials used are commercially available unless otherwise specified, and the sources of the raw materials are as follows: porous graphene oxide (Article No.: 532523, pore size 5 nm, Xi'an Qiyue Biotechnology Co., Ltd.); polyvinyl alcohol (S30196, Shanghai Yuanye); porous graphene (YM-NM-039, Changsha Yimo Biotechnology Co., Ltd.); lithium cobalt oxide (S41544, Shanghai Yuanye); phosphatidylcholine (CAS: 6064-83-1); 5-boropyridinecarboxylic acid (CAS: 913836-11-0); zinc sulfate (CAS: 7733-02-0); carboxymethyl chitosan (S30948, Shanghai Yuanye).

[0067] Experiment: The modified lithium cobalt oxide positive electrode materials prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were assembled into experimental button-type lithium-ion batteries under the protection of an argon atmosphere; (1) the electrochemical performance was tested; the test voltage range was 3.0 to 4.55 V, and the rate was 0.5C; (2) after 60 cycles, the capacity retention rate was tested; the specific data are shown in the table below;

[0068]

[0069] Conclusion: In comparative example 1, the amount of porous graphene added in the modified lithium cobalt oxide is increased, resulting in changes in structural stability and reduced performance; in comparative example 2, porous graphene is replaced by graphene, and porous graphene oxide is replaced by graphene oxide, and the performance is obviously not as good as that of the embodiment; in comparative example 3, the amount of modified graphene added in the modified liquid is increased, and the performance is reduced; in comparative example 4, the preparation process of the modified graphene is changed, and phosphatidylcholine, 5-boropyridinecarboxylic acid, and carboxymethyl chitosan are added simultaneously for reaction, which leads to a decrease in performance due to the influence of steric hindrance, grafting rate, etc.; in comparative examples 5 and 6, the addition ratio of phosphatidylcholine and 5-boropyridinecarboxylic acid in the modified graphene is changed, and the performance is not as good as that of the embodiment, which shows that the amount of raw materials added is also of great significance; in summary, the modified lithium cobalt oxide positive electrode material prepared by the present invention has a large discharge rate and good cycle performance.

[0070] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be considered exemplary and non-restrictive in all respects, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims be included in the present invention.

Claims

1. A method for preparing a modified lithium cobalt oxide positive electrode material, characterized in that: The following steps are involved: S1: Add polyvinyl alcohol-modified porous graphene, phosphatidyl salicylic acid, and 5-boropyridine carboxylic acid into water, mix well, add zinc sulfate, heat and pressurize, react at 110-120°C for 8-10 hours, add carboxymethyl chitosan and zinc sulfate, continue to react for 3-4 hours, remove the solvent, and obtain modified graphene; S2: adding carboxymethyl chitosan into water and stirring to dissolve, adding modified graphene, and mixing evenly to obtain a modified solution; The modified liquid is sprayed on the surface of lithium cobalt oxide and dried to obtain a modified lithium cobalt oxide positive electrode material.

2. The method for preparing a modified lithium cobalt oxide positive electrode material according to claim 1, characterized in that: The modified graphene comprises the following raw materials, calculated by weight: 10-12 parts of polyvinyl alcohol modified porous graphene, 2.5-4 parts of phosphatidylcholine, 2-3 parts of 5-boronic acid, and 3-4 parts of carboxymethyl chitosan.

3. The method for preparing a modified lithium cobalt oxide positive electrode material according to claim 1, characterized in that: The modified liquid comprises the following raw materials, calculated by weight: 3-5 parts of carboxymethyl chitosan, 120-150 parts of water, and 0.6-1 part of modified graphene.

4. The method for preparing a modified lithium cobalt oxide positive electrode material according to claim 1, characterized in that: The preparation method of the modified lithium cobalt oxide positive electrode material comprises the following steps: spraying a modification liquid on the surface of the modified lithium cobalt oxide at a mass ratio of (1-1.1):1, and drying to obtain the modified lithium cobalt oxide positive electrode material.

5. The method for preparing a modified lithium cobalt oxide positive electrode material according to claim 1, characterized in that: The preparation of the polyvinyl alcohol modified porous graphene comprises the following steps: The porous graphene oxide is dispersed in water to obtain a dispersion; polyvinyl alcohol is added and stirred evenly; an ammonia solution and a hydrazine hydrate solution are added and stirred evenly; the mixture is stirred at 85-90° C. for 4-5 hours; the mixture is washed and centrifuged to obtain polyvinyl alcohol-modified porous graphene.

6. The method for preparing a modified lithium cobalt oxide positive electrode material according to claim 5, characterized in that: The concentration of the dispersion is 4-5 mg / mL; the polyvinyl alcohol-modified porous graphene includes the following raw materials, calculated by weight: 150-200 parts of dispersion, 6-7 parts of polyvinyl alcohol, 20-30 parts of 25% ammonia solution, and 1-2 parts of 80% hydrazine hydrate solution.

7. The method for preparing a modified lithium cobalt oxide positive electrode material according to claim 1, characterized in that: The lithium cobalt oxide is modified to obtain modified lithium cobalt oxide and then used, which specifically includes the following steps: mixing porous graphene and lithium cobalt oxide, heating at 550-650° C. for 5-6 hours, and cooling to obtain modified lithium cobalt oxide.

8. The method for preparing a modified lithium cobalt oxide positive electrode material according to claim 7, characterized in that: The modified lithium cobalt oxide comprises the following raw materials, calculated by weight: 0.6-1 parts of porous graphene and 10-15 parts of lithium cobalt oxide.

9. Use of a modified lithium cobalt oxide positive electrode material prepared by the method for preparing a modified lithium cobalt oxide positive electrode material according to any one of claims 1 to 8 in a battery.

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