Core-shell structure carbon-coated chromium oxide-based positive electrode material and preparation method thereof

Abstract

The invention relates to the technical field of lithium batteries, and discloses a positive electrode material based on core-shell structure carbon-coated chromic oxide and a preparation method of the positive electrode material. Comprising the following steps: S1, uniformly mixing chromium oxide, conductive carbon and a binder; granulating at the temperature of 150 to 160 DEG C by a spraying method; sintering at the temperature of 190-450 DEG C for 12-24 hours to obtain a chromic oxide active material; and S2, sequentially adding the chromic oxide active material, the modified conductive material and the composite binding material into a solvent, grinding and uniformly mixing to obtain the positive electrode material. The chromium oxide active material comprises the following raw materials in parts by mass: 90-99 parts of chromium oxide, 0.1-5 parts of conductive carbon and 1-3 parts of a binder, the D50 of the chromic oxide is CrO3 with the particle size of 5-6 microns; the conductive carbon comprises one or more of carbon nanotubes, graphene, carbon fibers and conductive carbon black; the binder comprises polyacrylic acid.

Description

Technical Field

[0001] The invention relates to the technical field of lithium batteries and discloses a positive electrode material based on core-shell structure carbon-coated chromium oxide and a preparation method thereof. Background Art

[0002] Lithium batteries have high energy density and are widely used in various fields. Introducing chromium oxide into the positive electrode material of new lithium batteries can produce high-performance lithium batteries with a high discharge voltage platform and no voltage hysteresis at medium and low rates.

[0003] In the prior art, new lithium battery positive electrode materials based on chromium oxide have the problem of difficult electron transfer, and it is necessary to further improve the electrical properties of such positive electrode materials, so as to develop chromium oxide-based lithium batteries with high discharge capacity, high rate performance and high stability. First, it is necessary to effectively improve the conductive path when chromium oxide is used as an active material to promote the capacity of chromium oxide active materials. Second, positive electrode materials are generally obtained by mixing active materials, conductive materials, and binding materials. It is necessary to further improve the interaction between chromium oxide active materials and other substances, and use the cross-linked network formed by conductive materials and binding materials to promote electron transfer, thereby improving electrical performance; in addition, the binding materials in positive electrode materials generally have the disadvantage of poor stability, which leads to a decrease in adhesion, an increase in electron transfer resistance, a decrease in electrical performance, and a deterioration in battery performance.

[0004] In summary, it is of great significance to solve the above problems and study a high energy density and high stability positive electrode material based on core-shell structure carbon-coated chromium oxide and its preparation method. Summary of the invention

[0005] The object of the present invention is to provide a positive electrode material based on core-shell structure carbon-coated chromium oxide and a preparation method thereof, so as to solve the problems raised in the above background technology.

[0006] In order to solve the above technical problems, the present invention provides the following technical solution: a method for preparing a positive electrode material based on core-shell structure carbon-coated chromium oxide, comprising the following steps: S1: uniformly mix chromium oxide, conductive carbon and binder; granulate by spraying at 150-160°C; sinter at 190-450°C for 12-24h to obtain chromium oxide active material; S2: Add the chromium oxide active material, modified conductive material and composite binding material to the solvent (water solvent) in sequence, grind and mix them evenly to obtain the positive electrode material.

[0007] More optimally, the chromium oxide active material comprises the following raw materials, by weight: 90-99 parts of chromium oxide, 0.1-5 parts of conductive carbon, and 1-3 parts of a binder; the D50 of the chromium oxide is 5-6 μm CrO 3; The conductive carbon includes one or more of carbon nanotubes, graphene, carbon fibers, and conductive carbon black; and the binder includes polyacrylic acid.

[0008] More optimally, the positive electrode material includes the following raw materials, calculated by mass: 95-97 parts of chromium oxide active material, 2-3 parts of modified conductive material, and 1-3 parts of composite binding material; the composite binding material includes polyacrylic acid and a cross-linking toughening agent in a mass ratio of 1:(0.5-1).

[0009] Preferably, the preparation of the modified conductive material comprises the following steps: Step 1: Mix vinyl boric acid pinacol ester, methyl acrylate and N-phenylmaleimide to prepare an oily monomer; Step 2: Mix acrylic acid and hydroxyethyl acrylate to obtain a water-based monomer; Step 3: Take water, 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid sodium salt, aqueous monomer, and oily monomer, mix and stir, heat to 80-85°C, add initiator, add double-bonded conductive carbon, polymerize for 4-6 hours, adjust pH to neutral, keep warm for 20-30 minutes, remove solvent, and obtain modified conductive material.

[0010] More optimally, the modified conductive material includes the following raw materials, calculated by mass: 150-200 parts of water, 0.2-0.3 parts of 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid sodium salt, 13-21 parts of aqueous monomers, 8-15 parts of oily monomers, 0.1-0.2 parts of initiators, and 400-500 parts of double-bonded conductive carbon.

[0011] More optimally, the aqueous monomer comprises acrylic acid and hydroxyethyl acrylate in a mass ratio of (10-15):(3-6); the oily monomer comprises methyl acrylate, vinyl boric acid pinacol ester and N-phenylmaleimide in a mass ratio of (3-6):(2-3):(3-6).

[0012] More optimally, the preparation of the double-bonded conductive carbon includes the following steps: adding vinyltrimethoxysilane to ethanol and water, stirring at 40-50°C for 1-2 hours, adding conductive carbon, stirring at 40-50°C for 4-6 hours, filtering the solid, and drying to obtain the double-bonded conductive carbon; the double-bonded conductive carbon includes vinyltrimethoxysilane and conductive carbon in a mass ratio of (1-2): (10-15).

[0013] More optimally, the preparation of the cross-linked toughening agent includes the following steps: (1) adding pyromellitic anhydride, stearyl alcohol, and lutidine to tetrahydrofuran, mixing evenly, heating to reflux for 4 to 6 hours, removing the solvent, and purifying to obtain the toughening agent; (2) taking the toughening agent, N,N-dimethylformamide, and butyltriphenylphosphonium bromide, heating to 100 to 110° C., adding epichlorohydrin to react for 5 to 8 hours, and post-treating to remove the solvent and unreacted epichlorohydrin to obtain the cross-linked toughening agent.

[0014] More optimally, the toughening agent includes the following raw materials, calculated by weight: 2-3 parts of pyromellitic anhydride, 5-8 parts of stearyl alcohol, 0.1-0.2 parts of lutidine, and 60-80 parts of tetrahydrofuran; The cross-linking toughening agent comprises the following raw materials, calculated by weight: 35-40 parts of toughening agent, 0.5-1 parts of butyl triphenylphosphonium bromide, and 12-15 parts of epichlorohydrin.

[0015] More optimally, the preparation of the double-bonded conductive carbon includes the following steps: adding 1.5 parts of vinyltrimethoxysilane to 60 parts of ethanol and 40 parts of water, stirring at 50°C for 1 hour, adding 10 parts of conductive carbon, stirring at 50°C for 5 hours, filtering the solid, and drying to obtain the double-bonded conductive carbon.

[0016] Optimally, the positive electrode material is coated on the surface of the current collector so that the loading amount (chromium oxide active material, modified conductive material, composite bonding material) is 1.5~2 mg / cm 2 , treated at 120-140° C. for 4-6 hours to obtain a lithium battery positive electrode sheet; the lithium battery positive electrode sheet can be used to prepare a lithium battery.

[0017] Compared with the prior art, the beneficial effects achieved by the present invention are: (1) preparing a chromium oxide active material; in view of the defect of poor electron transport of chromium oxide itself, a layer of conductive carbon layer with vertical growth is constructed on the surface of chromium oxide particles to increase the conductivity of the particles and form an electronic conductive path; the coating layer on the surface of chromium oxide includes a binder, conductive carbon, and chromium oxide. After sintering, the electrical contact between the chromium oxide particles can be uniform, the chromium oxide specific capacity can be promoted, the electronic conductivity of the battery electrode can be improved, and the high-rate discharge of the chromium oxide battery can be achieved; and the chromium oxide and the conductive carbon have good bonding strength.

[0018] (2) The chromium oxide active material is combined with a modified conductive material and a composite binder material to form a positive electrode material; by modifying the conductive material and further limiting and optimizing the modified composite binder material, the electrical properties and stability of the positive electrode material are effectively and synergistically promoted, thereby enhancing the applicability of the new lithium battery positive electrode material based on chromium oxide.

[0019] Among them, the modified conductive material is to first modify the conductive carbon into double bonds, then introduce double bond-containing monomers, copolymerize under the action of an initiator, introduce similar structures, and enhance the bonding strength between the conductive carbon and the composite adhesive material; a certain proportion of aqueous monomers and oily monomers are introduced during the modification, among which methyl acrylate can improve the flexibility of the polymer, vinyl boric acid pinacol ester and N-phenylmaleimide can improve high temperature resistance, thereby improving the stability and durability of the positive electrode sheet. The proportion of oily monomer added needs to be controlled. Too little addition will result in no obvious improvement in high temperature resistance, while too much addition will result in a decrease in adhesion.

[0020] Among them, in order to further improve the stability and durability of the positive electrode material, the present invention also introduces a cross-linking toughening agent in the composite bonding material, in addition to the common polyacrylic acid as a binder, with heat-resistant pyromellitic anhydride as the matrix, grafted with stearyl alcohol, to improve the overall heat resistance and flexibility, improve the problem that polyacrylic acid is easy to fall off when used alone, and introduce an epoxy group through epichlorohydrin, which can react with the composite bonding material and the modified conductive material in the subsequent steps to form a three-dimensional network, has good flexibility, and effectively improves the life of the battery; the amount of the cross-linking toughening agent added should not be too much, and too much addition will lead to excessive cross-linking and increased brittleness, which will affect the performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Specific capacity-voltage test curves of samples in Examples 1 to 5. DETAILED DESCRIPTION

[0022] 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.

[0023] It should be noted that there is no special restriction on the purchase manufacturers of all raw materials involved in the present invention, and illustratively include: carbon nanotubes (AM-C6-067-1, Zhejiang Yamei Nano Technology Co., Ltd.), conductive carbon black (AM-C1-064-1, Zhejiang Yamei Nano Technology Co., Ltd.), polyacrylic acid (Article No. 181285, average Mv~450000, Sigma-Aldrich), pyromellitic anhydride (CAS: 89-32-7), stearyl alcohol (CAS: 112-92-5), lutidine (CAS: 108-48-5), tetrahydrofuran (CAS: 109-99-9), N,N-dimethylformamide (CAS: 68-12-2), butyltriphenylphosphonium bromide (CAS: 1779-51-7), epichlorohydrin (CAS: 106-89-8), vinyltrimethoxysilane (CAS: 2768-02-7 ), ethanol (CAS: 64-17-5), 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid sodium salt (CAS: 5165-97-9), acrylic acid (CAS: 79-10-7), hydroxyethyl acrylate (CAS: 818-61-1), methyl acrylate (CAS: 96-33-3), vinylboronic acid pinacol ester (CAS: 75927-49-0), N-phenylmaleimide (CAS: 941-69-5), initiator (sodium persulfate CAS: 7775-27-1); Unless otherwise specified, the following are parts by mass and mass ratios; Example 1: Chromium oxide, carbon nanotubes and polyacrylic acid are mixed in a mass ratio of 97:2:1 to obtain a mixture; the mixture is dried at 150° C. and granulated, and kept at 400° C. for 18 hours to obtain a chromium oxide active material.

[0024] Example 2: Chromium oxide, carbon nanotubes and polyacrylic acid are mixed in a mass ratio of 96:2:2 to obtain a mixture; the mixture is dried at 150° C. and granulated, and kept at 400° C. for 18 hours to obtain a chromium oxide active material.

[0025] Example 3: Chromium oxide, conductive carbon black and polyacrylic acid are mixed in a mass ratio of 97:2:1 to obtain a mixture; the mixture is dried at 150° C. and granulated, and kept at 400° C. for 18 hours to obtain a chromium oxide active material.

[0026] Example 4 (comparative example without adding conductive carbon): chromium oxide and polyacrylic acid are mixed in a mass ratio of 99:1 to obtain a mixture; the mixture is dried at 150° C. and granulated, and kept at 400° C. for 18 hours to obtain a chromium oxide active material.

[0027] Example 5 (comparative example without adding conductive carbon): chromium oxide and polyacrylic acid are mixed in a mass ratio of 98:2 to obtain a mixture; the mixture is dried at 150° C. and granulated, and kept at 400° C. for 18 hours to obtain a chromium oxide active material.

[0028] Performance test: Take the active materials prepared in Examples 1 to 5, mix the chromium oxide active material, carbon nanotubes, and polyacrylic acid in a mass ratio of 96:2:2 to obtain a positive electrode material; apply the positive electrode material to the surface of the current collector to make the loading amount 1.6 mg / cm 2 , 130℃ for 5h, to obtain a positive electrode sheet for lithium battery, and assemble a lithium battery according to the conventional method, and use this as a sample to test its performance; see Figure 1 with Table 1; Table 1:

[0029] Based on the chromium oxide active material prepared according to the formula of Example 1, Examples 6 to 8 are provided: Example 6: S1: Add 1.5 parts of vinyltrimethoxysilane to 60 parts of ethanol and 40 parts of water, stir at 50°C for 1 hour, add 10 parts of carbon nanotubes, stir at 50°C for 5 hours, filter out the solid, and dry to obtain double-bonded conductive carbon; S2: Take 160 parts of water, 0.3 parts of 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid sodium salt, 12 parts of acrylic acid, 3 parts of hydroxyethyl acrylate, 5 parts of methyl acrylate, 2 parts of vinyl boric acid pinacol ester, 5 parts of N-phenylmaleimide, stir and heat to 82°C, add 0.1 parts of initiator sodium persulfate, add 480 parts of double-bonded conductive carbon, polymerize for 5 hours, adjust the pH to neutral, keep warm for 30 minutes, remove the solvent, and obtain a modified conductive material; S3: Add 3 parts of pyromellitic anhydride, 8 parts of stearyl alcohol, and 0.1 parts of 4-lutidine to 60 parts of tetrahydrofuran, mix well, heat under reflux for 5 hours, remove the solvent, and obtain a toughening agent after post-treatment and purification; Take 38 parts of toughening agent, 50 parts of N,N-dimethylformamide, and 0.5 parts of butyl triphenylphosphonium bromide, heat to 100°C, add 15 parts of epichlorohydrin and react for 6 hours, and remove the solvent and unreacted epichlorohydrin by post-treatment to obtain a crosslinking toughening agent; S4: 97 parts of active material, 2 parts of modified conductive material, 1 part of polyacrylic acid, and 0.6 parts of cross-linking toughening agent are added into the solvent, and the mixture is ground and mixed evenly to obtain a positive electrode material.

[0030] Example 7: S1: Add 1.5 parts of vinyltrimethoxysilane to 60 parts of ethanol and 40 parts of water, stir at 50°C for 1 hour, add 10 parts of carbon nanotubes, stir at 50°C for 5 hours, filter out the solid, and dry to obtain double-bonded conductive carbon; S2: Take 160 parts of water, 0.3 parts of 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid sodium salt, 10 parts of acrylic acid, 5 parts of hydroxyethyl acrylate, 3 parts of methyl acrylate, 2 parts of vinylboronic acid pinacol ester, 4 parts of N-phenylmaleimide, stir and heat to 82°C, add 0.1 parts of initiator sodium persulfate, add 480 parts of double-bonded conductive carbon, polymerize for 5 hours, adjust the pH to neutral, keep warm for 30 minutes, remove the solvent, and obtain a modified conductive material; S3: Add 3 parts of pyromellitic anhydride, 8 parts of stearyl alcohol, and 0.1 parts of 4-lutidine to 60 parts of tetrahydrofuran, mix well, heat under reflux for 5 hours, remove the solvent, and obtain a toughening agent after post-treatment and purification; Take 38 parts of toughening agent, 50 parts of N,N-dimethylformamide, and 0.5 parts of butyl triphenylphosphonium bromide, heat to 100°C, add 15 parts of epichlorohydrin and react for 6 hours, and remove the solvent and unreacted epichlorohydrin by post-treatment to obtain a crosslinking toughening agent; S4: 97 parts of active material, 2 parts of modified conductive material, 1 part of polyacrylic acid, and 0.6 parts of cross-linking toughening agent are added into a solvent, ground and mixed to obtain a positive electrode material.

[0031] Example 8: S1: Add 1.5 parts of vinyltrimethoxysilane to 60 parts of ethanol and 40 parts of water, stir at 50°C for 1 hour, add 10 parts of carbon nanotubes, stir at 50°C for 5 hours, filter out the solid, and dry to obtain double-bonded conductive carbon; S2: Take 160 parts of water, 0.3 parts of 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid sodium salt, 10 parts of acrylic acid, 5 parts of hydroxyethyl acrylate, 3 parts of methyl acrylate, 2 parts of vinylboronic acid pinacol ester, 4 parts of N-phenylmaleimide, stir and heat to 82°C, add 0.1 parts of initiator sodium persulfate, add 480 parts of double-bonded conductive carbon, polymerize for 5 hours, adjust the pH to neutral, keep warm for 30 minutes, remove the solvent, and obtain a modified conductive material; S3: Add 3 parts of pyromellitic anhydride, 8 parts of stearyl alcohol, and 0.1 parts of 4-lutidine to 60 parts of tetrahydrofuran, mix well, heat under reflux for 5 hours, remove the solvent, and obtain a toughening agent after post-treatment and purification; Take 38 parts of toughening agent, 50 parts of N,N-dimethylformamide, and 0.5 parts of butyl triphenylphosphonium bromide, heat to 100°C, add 15 parts of epichlorohydrin and react for 6 hours, and remove the solvent and unreacted epichlorohydrin by post-treatment to obtain a crosslinking toughening agent; S4: 97 parts of active material, 2 parts of modified conductive material, 1 part of polyacrylic acid, and 0.5 parts of cross-linking toughening agent are added into a solvent, ground and mixed to obtain a positive electrode material.

[0032] Example 9 (Comparative example of changing the preparation method of modified conductive material, the remaining method steps are consistent with Example 6): S1: Add 1.5 parts of vinyltrimethoxysilane to 60 parts of ethanol and 40 parts of water, stir at 50°C for 1 hour, add 10 parts of carbon nanotubes, stir at 50°C for 5 hours, filter out the solid, and dry to obtain double-bonded conductive carbon; S2: Take 160 parts of water, 0.3 parts of 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid sodium salt, 6 parts of acrylic acid, 1 part of hydroxyethyl acrylate, 8 parts of methyl acrylate, 4 parts of vinylboronic acid pinacol ester, 5 parts of N-phenylmaleimide, stir and heat to 82°C, add 0.1 parts of initiator sodium persulfate, add 480 parts of double-bonded conductive carbon, polymerize for 5 hours, adjust the pH to neutral, keep warm for 30 minutes, remove the solvent, and obtain a modified conductive material; S3: Add 3 parts of pyromellitic anhydride, 8 parts of stearyl alcohol, and 0.1 parts of 4-lutidine to 60 parts of tetrahydrofuran, mix well, heat under reflux for 5 hours, remove the solvent, and obtain a toughening agent after post-treatment and purification; Take 38 parts of toughening agent, 50 parts of N,N-dimethylformamide, and 0.5 parts of butyl triphenylphosphonium bromide, heat to 100°C, add 15 parts of epichlorohydrin and react for 6 hours, and remove the solvent and unreacted epichlorohydrin by post-treatment to obtain a crosslinking toughening agent; S4: 97 parts of active material, 2 parts of modified conductive material, 1 part of polyacrylic acid, and 0.5 parts of cross-linking toughening agent are added into a solvent, ground and mixed to obtain a positive electrode material.

[0033] Example 10 (Comparative example with a different amount of cross-linking toughening agent added, the remaining steps are the same as those of Example 6): S1: Add 1.5 parts of vinyltrimethoxysilane to 60 parts of ethanol and 40 parts of water, stir at 50°C for 1 hour, add 10 parts of carbon nanotubes, stir at 50°C for 5 hours, filter out the solid, and dry to obtain double-bonded conductive carbon; S2: Take 160 parts of water, 0.3 parts of 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid sodium salt, 12 parts of acrylic acid, 3 parts of hydroxyethyl acrylate, 5 parts of methyl acrylate, 2 parts of vinyl boric acid pinacol ester, 5 parts of N-phenylmaleimide, stir and heat to 82°C, add 0.1 parts of initiator sodium persulfate, add 480 parts of double-bonded conductive carbon, polymerize for 5 hours, adjust the pH to neutral, keep warm for 30 minutes, remove the solvent, and obtain a modified conductive material; S3: Add 3 parts of pyromellitic anhydride, 8 parts of stearyl alcohol, and 0.1 parts of 4-lutidine to 60 parts of tetrahydrofuran, mix well, heat under reflux for 5 hours, remove the solvent, and obtain a toughening agent after post-treatment and purification; Take 38 parts of toughening agent, 50 parts of N,N-dimethylformamide, and 0.5 parts of butyl triphenylphosphonium bromide, heat to 100°C, add 15 parts of epichlorohydrin and react for 6 hours, and remove the solvent and unreacted epichlorohydrin by post-treatment to obtain a crosslinking toughening agent; S4: 97 parts of active material, 2 parts of modified conductive material, 1 part of polyacrylic acid, and 1.2 parts of cross-linking toughening agent are added into a solvent, ground and mixed to obtain a positive electrode material.

[0034] Example 11 (comparative example with a changed amount of cross-linking toughening agent added, the remaining steps are consistent with Example 6): S1: Add 1.5 parts of vinyltrimethoxysilane to 60 parts of ethanol and 40 parts of water, stir at 50°C for 1 hour, add 10 parts of carbon nanotubes, stir at 50°C for 5 hours, filter out the solid, and dry to obtain double-bonded conductive carbon; S2: Take 160 parts of water, 0.3 parts of 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid sodium salt, 12 parts of acrylic acid, 3 parts of hydroxyethyl acrylate, 5 parts of methyl acrylate, 2 parts of vinyl boric acid pinacol ester, 5 parts of N-phenylmaleimide, stir and heat to 82°C, add 0.1 parts of initiator sodium persulfate, add 480 parts of double-bonded conductive carbon, polymerize for 5 hours, adjust the pH to neutral, keep warm for 30 minutes, remove the solvent, and obtain a modified conductive material; S3: Add 3 parts of pyromellitic anhydride, 8 parts of stearyl alcohol, and 0.1 parts of 4-lutidine to 60 parts of tetrahydrofuran, mix well, heat under reflux for 5 hours, remove the solvent, and obtain a toughening agent after post-treatment and purification; Take 38 parts of toughening agent, 50 parts of N,N-dimethylformamide, and 0.5 parts of butyl triphenylphosphonium bromide, heat to 100°C, add 15 parts of epichlorohydrin and react for 6 hours, and remove the solvent and unreacted epichlorohydrin by post-treatment to obtain a crosslinking toughening agent; S4: 97 parts of active material, 2 parts of modified conductive material, 1 part of polyacrylic acid, and 0.3 parts of cross-linking toughening agent are added into a solvent, ground and mixed to obtain a positive electrode material.

[0035] Performance test: Take the positive electrode materials prepared in Examples 6 to 11 and coat the positive electrode materials on the surface of the current collector to make the loading amount 1.6 mg / cm 2 , treated at 130℃ for 5h to obtain a lithium battery positive electrode sheet, and assembled a lithium battery according to a conventional method, and used this as a sample to test its performance; see Table 2 for details; Table 2:

[0036] It can be seen from Table 2 that the use of modified conductive materials and the introduction of cross-linking toughening agents in the positive electrode materials can further improve the discharge capacity and stability of the lithium battery; Example 9 changes the preparation method of the modified conductive material, that is, changes the addition ratio of the oily monomer and the aqueous monomer, which affects the performance; Example 10 and Example 11 change the addition amount of the cross-linking toughening agent, and the performance is not as good as Examples 6 to 8; It can be seen that the lithium battery prepared by the positive electrode material based on the core-shell structure carbon-coated chromium oxide prepared by the scheme of the present invention has good energy density, high discharge capacity, good stability and long service life.

[0037] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for preparing a positive electrode material based on core-shell carbon-coated chromium oxide, characterized in that: The following steps are involved: S1: uniformly mix chromium oxide, conductive carbon and binder; granulate by spraying at 150-160°C; sinter at 190-450°C for 12-24h to obtain chromium oxide active material; S2: Add the chromium oxide active material, the modified conductive material and the composite binding material to the solvent in sequence, grind and mix them evenly to obtain the positive electrode material.

2. The method for preparing a positive electrode material based on core-shell carbon-coated chromium oxide according to claim 1, characterized in that: The chromium oxide active material includes the following raw materials, calculated by weight: 90-99 parts of chromium oxide, 0.1-5 parts of conductive carbon, and 1-3 parts of a binder; the D50 of the chromium oxide is 5-6 μm CrO3; the conductive carbon includes one or more of carbon nanotubes, graphene, carbon fibers, and conductive carbon black; and the binder includes polyacrylic acid.

3. The method for preparing a positive electrode material based on core-shell carbon-coated chromium oxide according to claim 1, characterized in that: The positive electrode material comprises the following raw materials, calculated by weight: 95-97 parts of chromium oxide active material, 2-3 parts of modified conductive material, and 1-3 parts of composite binding material; The composite bonding material comprises polyacrylic acid and a cross-linking toughening agent in a mass ratio of 1: (0.5-1).

4. The method for preparing a positive electrode material based on core-shell carbon-coated chromium oxide according to claim 3, characterized in that: The preparation of the modified conductive material comprises the following steps: Step 1: Mix vinyl boric acid pinacol ester, methyl acrylate and N-phenylmaleimide to prepare an oily monomer; Step 2: Mix acrylic acid and hydroxyethyl acrylate to obtain a water-based monomer; Step 3: Take water, 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid sodium salt, aqueous monomer, and oily monomer, mix and stir, heat to 80-85°C, add initiator, add double-bonded conductive carbon, polymerize for 4-6 hours, adjust pH to neutral, keep warm for 20-30 minutes, remove solvent, and obtain modified conductive material.

5. The method for preparing a positive electrode material based on core-shell carbon-coated chromium oxide according to claim 4, characterized in that: The modified conductive material includes the following raw materials, calculated by mass: 150-200 parts of water, 0.2-0.3 parts of 2-methyl-2-[(1-oxo-2-propenyl)amino]-1-propanesulfonic acid sodium salt, 13-21 parts of aqueous monomers, 8-15 parts of oily monomers, 0.1-0.2 parts of initiators, and 400-500 parts of double-bonded conductive carbon.

6. The method for preparing a positive electrode material based on core-shell carbon-coated chromium oxide according to claim 5, characterized in that: The water-based monomers include acrylic acid and hydroxyethyl acrylate in a mass ratio of (10-15):(3-6); the oily monomers include methyl acrylate, vinyl boric acid pinacol ester and N-phenylmaleimide in a mass ratio of (3-6):(2-3):(3-6).

7. The method for preparing a positive electrode material based on core-shell carbon-coated chromium oxide according to claim 4, characterized in that: The preparation of the double-bonded conductive carbon comprises the following steps: adding vinyltrimethoxysilane to ethanol and water, stirring at 40-50° C. for 1-2 hours, adding conductive carbon, stirring at 40-50° C. for 4-6 hours, filtering out solids, and drying to obtain double-bonded conductive carbon; the double-bonded conductive carbon comprises vinyltrimethoxysilane and conductive carbon in a mass ratio of (1-2):(10-15).

8. The method for preparing a positive electrode material based on core-shell carbon-coated chromium oxide according to claim 3, characterized in that: The preparation of the cross-linking toughening agent comprises the following steps: (1) adding pyromellitic anhydride, stearyl alcohol and dimethyl pyridine to tetrahydrofuran, mixing evenly, heating under reflux for 4-6 hours, removing the solvent and purifying to obtain the toughening agent; (2) taking the toughening agent, N,N-dimethylformamide and butyltriphenylphosphonium bromide, heating to 100-110° C., adding epichlorohydrin to react for 5-8 hours, and post-treating to remove the solvent and unreacted epichlorohydrin to obtain the cross-linking toughening agent.

9. The method for preparing a positive electrode material based on core-shell carbon-coated chromium oxide according to claim 8, characterized in that: The toughening agent comprises the following raw materials, calculated by weight: 2-3 parts of pyromellitic anhydride, 5-8 parts of stearyl alcohol, 0.1-0.2 parts of lutidine, and 60-80 parts of tetrahydrofuran; The cross-linking toughening agent comprises the following raw materials, calculated by weight: 35-40 parts of toughening agent, 0.5-1 parts of butyl triphenylphosphonium bromide, and 12-15 parts of epichlorohydrin.

10. A positive electrode material prepared according to the method for preparing a positive electrode material based on core-shell carbon-coated chromium oxide according to any one of claims 1 to 9.

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