A coated lithium cobalt oxide positive electrode material and a positive electrode sheet prepared therefrom

Abstract

The application relates to the technical field of lithium ion battery materials, in particular to a coated lithium cobaltate positive electrode material and a positive electrode sheet prepared from the same. A binder with dynamic reversible bonds such as hydrogen bonds and disulfide bonds is synthesized through free radical polymerization among acrylamide, acrylic acid and double bond end-capped disulfide bond-containing compounds; Mg is used to dope lithium cobaltate first, then a conductive polymer polypyrrole is coated on the surface of the lithium cobaltate, then an organic porous polymer prepared from a quaternary linker 5,10,15,20-tetra(4-aminophenyl)porphyrin and pyromellitic anhydride is coated on the surface of the polypyrrole by using the large pi bond of the polypyrrole; a conductive agent is modified and treated, the conductive agent is mercaptoized by using (3-mercaptopropyl)trimethoxysilane first, then a double bond end-capped disulfide bond-containing compound with reversible bonds is grafted by using mercapto-double bond photo-clicking, so that the stability and safety of the battery performance are improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery materials technology, specifically to a coated lithium cobalt oxide cathode material and the cathode sheet prepared therefrom. Background Technology

[0002] With the booming development of new energy sources, environmentally friendly, high-cycle-stability, and high-specific-capacity lithium-ion batteries have attracted much attention. The positive electrode, as a key component of lithium-ion batteries, directly affects their capacity and cycle performance. Positive electrodes are generally prepared by coating a positive electrode slurry onto the surface of a metal foil layer. This slurry typically consists of positive electrode active materials, modified conductive agents, binders, and solvents. Lithium cobalt oxide is currently one of the mainstream positive electrode active materials on the market. As the market demands increasingly higher energy density from lithium-ion batteries, the need to increase the upper charging voltage limit of lithium cobalt oxide has become urgent.

[0003] Existing lithium cobalt oxide materials exhibit poor structural stability under high voltage, which fails to meet market demands. Summary of the Invention

[0004] The purpose of this invention is to provide a lithium cobalt oxide coated cathode material and the cathode sheet prepared therefrom, so as to solve the problems in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0006] A method for preparing a lithium cobalt oxide coated cathode material includes the following steps:

[0007] S1: Add the self-healing adhesive to deionized water, stir, and then vacuum defoam to obtain the self-healing adhesive solution. Divide it into two parts, denoted as self-healing adhesive solution a and self-healing adhesive solution b.

[0008] S2: Mix self-healing adhesive a and composite lithium cobalt oxide, stir ultrasonically, add modified conductive agent and self-healing adhesive b in sequence, stir ultrasonically to obtain a lithium cobalt oxide coated cathode material.

[0009] Furthermore, the mass ratio of self-healing adhesive a to self-healing adhesive b is 3:1.

[0010] Furthermore, by weight, the contents of each component in the cathode material are as follows: 77-87 parts of composite lithium cobalt oxide, 6-9 parts of modified conductive agent, 4-8 parts of self-healing binder, and 21-26 parts of deionized water.

[0011] Furthermore, the preparation of composite lithium cobalt oxide includes the following steps:

[0012] (1) Mix cobalt tetroxide powder, lithium carbonate powder and magnesium oxide, grind them, and keep them at 1000℃ for 10h in air atmosphere to obtain magnesium-doped lithium cobalt oxide;

[0013] (2) Pyrrole, magnesium-doped lithium cobalt oxide and anhydrous ethanol are mixed, sodium persulfate is added, and the mixture is stirred in an ice-water bath for 5-6 hours. After filtration, washing and drying, pyrrole-coated magnesium-doped lithium cobalt oxide is obtained.

[0014] (3) Mix 5,10,15,20-tetra(4-aminophenyl)porphyrin, pyromellitic anhydride, N-methylpyrrolidone, and 1,3,5-trimethylbenzene, add isoquinoline, sonicate for 10-20 min, transfer to a reaction tube, degas and cycle 3-5 times, keep warm at 150℃ for 5 days, cool, centrifuge, wash with N,N-dimethylformamide and methanol 3-5 times in sequence, add tetrahydrofuran and pyrrole-coated magnesium-doped lithium cobalt oxide, sonicate for 1-2 h, centrifuge, wash and dry to obtain composite lithium cobalt oxide.

[0015] Furthermore, the preparation of the self-healing adhesive includes the following steps:

[0016] Under a nitrogen atmosphere, acrylamide, acrylic acid, a compound with disulfide bonds at double bond ends, and deionized water are mixed, and ammonium persulfate is added. The mixture is kept in an oil bath at 48-52℃ for 7-8 hours, washed with ethanol 3-5 times, and freeze-dried to obtain a self-healing adhesive.

[0017] Furthermore, the preparation of the modified conductive agent includes the following steps:

[0018] 1) Mix the conductive agent, isopropanol, and deionized water, sonicate for 30-40 min, add (3-mercaptopropyl)trimethoxysilane, adjust the pH to 2.9-3.1, keep warm in a water bath at 58-62℃ for 5-6 h, filter, wash, and dry to obtain the mercapto-based conductive agent.

[0019] 2) Mix the mercapto-conductive agent and n-hexane, keep warm in a 60°C water bath for 3-4 hours, add a mixture of double-bond-terminated disulfide compounds and n-hexane, stir for 5-6 hours, add benzoin dimethyl ether, treat with ultraviolet light, wash and dry to obtain the modified conductive agent.

[0020] Furthermore, the conductive agent is obtained by compounding carbon black and silica in a mass ratio of 2:1.

[0021] Furthermore, the working conditions for ultraviolet light treatment are: irradiation with a 365nm ultraviolet lamp for 1 hour.

[0022] Furthermore, the preparation of disulfide-terminated compounds with double bonds includes the following steps:

[0023] Under a nitrogen atmosphere, 4,4-diaminodiphenyl disulfide and acetone were mixed, and ethyl 2-isocyanate methacrylate was added. The mixture was stirred at 18-25°C for 20-21 h, washed, and dried to obtain a compound with double-bond-terminated disulfide bonds.

[0024] Furthermore, a method for preparing a lithium cobalt oxide-coated positive electrode includes the following steps: coating the lithium cobalt oxide-coated positive electrode material on both sides of a metal foil and drying it to obtain a lithium cobalt oxide-coated positive electrode.

[0025] Compared with the prior art, the beneficial effects of the present invention are:

[0026] This invention provides a lithium cobalt oxide coated cathode material and the cathode sheet prepared therefrom. By limiting the process and composition, the cathode sheet of the lithium battery is endowed with excellent cycle stability, thereby improving the durability and safety of the lithium battery.

[0027] Traditional lithium-ion batteries often use polyvinylidene fluoride (PVDF) as a binder for both the positive and negative electrodes. This results in problems such as easy powder shedding and inability to withstand the significant deformation during long-term cycling. Furthermore, the manufacturing process often uses N-methylpyrrolidone, an expensive and harmful organic solvent. This invention, aiming to reduce costs and increase efficiency, uses a more economical aqueous binder for the positive electrode, meeting green production requirements and facilitating market promotion. Through free radical polymerization of acrylamide, acrylic acid, and a double-bond-terminated disulfide compound, a binder with dynamic reversible bonds such as hydrogen bonds and disulfide bonds is synthesized. The double-bond-terminated disulfide compound is prepared from 4,4-diaminodiphenyl disulfide and ethyl 2-isocyanate methacrylate. This effectively improves the mechanical and rheological properties of the positive electrode material, enhancing electrode stability. Simultaneously, the abundant polar groups on the binder form a covalent-non-covalent cross-linked network between conductive particles and copolymer chains, effectively buffering the volume expansion of silica and ensuring the structural integrity of the electrode remains unchanged after cycling.

[0028] To improve the stability of lithium cobalt oxide, this invention first uses Mg doping to stabilize its crystal structure and suppress its irreversible phase transition under high voltage. Then, it coats its surface with the conductive polymer polypyrrole. Next, it utilizes the large π bonds of polypyrrole to coat its surface with an organic porous polymer prepared by the quaternary linker 5,10,15,20-tetra(4-aminophenyl)porphyrin and pyromellitic anhydride, thereby improving its performance in cycle life and rate capability.

[0029] By modifying the conductive agent, firstly by mercaptoizing it with (3-mercaptopropyl)trimethoxysilane, and then by using mercapto-double bond photoclicking, a compound containing disulfide bonds with reversible double bonds is grafted onto it, thereby improving the stability and safety of battery performance. Detailed Implementation

[0030] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0031] It should be noted that if the embodiments of the present invention involve directional indicators such as up, down, left, right, front, and back, these directional indicators are only used to explain the relative positional relationship and movement of components in a specific posture. If the specific posture changes, the directional indicators will also change accordingly. Furthermore, the technical solutions of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0032] The technical solution of the present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0033] Example 1: A method for preparing a positive electrode sheet coated with lithium cobalt oxide, comprising the following steps:

[0034] A lithium cobalt oxide cathode material is coated on both sides of a metal foil and dried to obtain a lithium cobalt oxide cathode sheet.

[0035] A method for preparing a lithium cobalt oxide coated cathode material includes the following steps:

[0036] S1: Add the self-healing adhesive to deionized water, stir, and then vacuum defoam to obtain the self-healing adhesive solution. Divide it into two parts, denoted as self-healing adhesive solution a and self-healing adhesive solution b.

[0037] The mass ratio of the self-healing adhesive a to the self-healing adhesive b is 3:1;

[0038] The preparation of the self-healing adhesive includes the following steps:

[0039] Under a nitrogen atmosphere, 3.2g acrylamide, 3.2g acrylic acid, 1.4g double bond-terminated disulfide compound, and 115mL deionized water were mixed, 39mg ammonium persulfate was added, and the mixture was kept in an oil bath at 48℃ for 8 hours. The mixture was then washed three times with ethanol and freeze-dried to obtain a self-healing adhesive.

[0040] The preparation of the double-bond-terminated disulfide compound includes the following steps:

[0041] Under a nitrogen atmosphere, 2.5 g of 4,4-diaminodiphenyl disulfide and 50 mL of acetone were mixed, and 2.9 mL of 2-isocyanate ethyl methacrylate was added. The mixture was stirred at 18 °C for 21 h, washed, and dried to obtain a compound with double-bond-terminated disulfide bonds.

[0042] S2: Mix self-healing adhesive a and composite lithium cobalt oxide, stir ultrasonically, add modified conductive agent and self-healing adhesive b in sequence, stir ultrasonically to obtain a lithium cobalt oxide coated cathode material;

[0043] The components in the cathode material are as follows, by weight: 77 parts of composite lithium cobalt oxide, 6 parts of modified conductive agent, 4 parts of self-healing binder, and 21 parts of deionized water.

[0044] The preparation of the composite lithium cobalt oxide includes the following steps:

[0045] (1) Mix 2.5g of cobalt tetroxide powder, 1.2g of lithium carbonate powder and 0.4g of magnesium oxide, grind them, and keep them at 1000℃ for 10h in air atmosphere to obtain magnesium-doped lithium cobalt oxide;

[0046] (2) Mix 0.1g pyrrole, 10g magnesium-doped lithium cobalt oxide and 20mL anhydrous ethanol, add 0.4mg sodium persulfate, stir in an ice-water bath for 5h, filter, wash and dry to obtain pyrrole-coated magnesium-doped lithium cobalt oxide;

[0047] (3) Mix 0.2 mmol 5,10,15,20-tetra(4-aminophenyl)porphyrin, 0.4 mmol pyromellitic anhydride, 3 mL N-methylpyrrolidone, and 3 mL 1,3,5-trimethylbenzene, add 0.5 mL isoquinoline, sonicate for 10 min, transfer to a reaction tube, freeze-degas and cycle 3 times, keep warm at 150℃ for 5 days, cool, centrifuge, wash 3 times with N,N-dimethylformamide and methanol respectively, add 10 mL tetrahydrofuran and 100 mg pyrrole-coated magnesium-doped lithium cobalt oxide, sonicate for 1 h, centrifuge, wash, and dry to obtain composite lithium cobalt oxide;

[0048] The preparation of the modified conductive agent includes the following steps:

[0049] 1) Mix 25g of conductive agent, 0.4L of isopropanol and 100mL of deionized water, sonicate for 30min, add 5g of (3-mercaptopropyl)trimethoxysilane, adjust the pH to 2.9, keep warm in a 58℃ water bath for 6h, filter, wash and dry to obtain mercapto-based conductive agent.

[0050] 2) Mix 4.2g of mercapto-conductive agent with 20mL of n-hexane, keep warm in a 60℃ water bath for 3h, add 3.6g of double bond-terminated disulfide compound and 20mL of n-hexane, stir for 5h, add 15.6mg of benzoin dimethyl ether, treat with ultraviolet light, wash and dry to obtain modified conductive agent;

[0051] The conductive agent is obtained by compounding carbon black and silica in a mass ratio of 2:1.

[0052] The working conditions for ultraviolet light treatment are: irradiation with a 365nm ultraviolet lamp for 1 hour.

[0053] Example 2: A method for preparing a positive electrode sheet coated with lithium cobalt oxide, comprising the following steps:

[0054] A lithium cobalt oxide cathode material is coated on both sides of a metal foil and dried to obtain a lithium cobalt oxide cathode sheet.

[0055] A method for preparing a lithium cobalt oxide coated cathode material includes the following steps:

[0056] S1: Add the self-healing adhesive to deionized water, stir, and then vacuum defoam to obtain the self-healing adhesive solution. Divide it into two parts, denoted as self-healing adhesive solution a and self-healing adhesive solution b.

[0057] The mass ratio of the self-healing adhesive a to the self-healing adhesive b is 3:1;

[0058] The preparation of the self-healing adhesive includes the following steps:

[0059] Under a nitrogen atmosphere, 3.2g acrylamide, 3.2g acrylic acid, 1.4g double bond-terminated disulfide compound, and 115mL deionized water were mixed, 39mg ammonium persulfate was added, and the mixture was kept in an oil bath at 50℃ for 7.5h. After washing with ethanol four times, the mixture was freeze-dried to obtain a self-healing adhesive.

[0060] The preparation of the double-bond-terminated disulfide compound includes the following steps:

[0061] Under a nitrogen atmosphere, 2.5 g of 4,4-diaminodiphenyl disulfide and 50 mL of acetone were mixed, and 2.9 mL of ethyl 2-isocyanate methacrylate was added. The mixture was stirred at 20 °C for 20.5 h, washed, and dried to obtain a compound with double-bond-terminated disulfide bonds.

[0062] S2: Mix self-healing adhesive a and composite lithium cobalt oxide, stir ultrasonically, add modified conductive agent and self-healing adhesive b in sequence, stir ultrasonically to obtain a lithium cobalt oxide coated cathode material;

[0063] The components in the cathode material are as follows, by weight: 83 parts of composite lithium cobalt oxide, 7 parts of modified conductive agent, 6 parts of self-healing binder, and 23 parts of deionized water.

[0064] The preparation of the composite lithium cobalt oxide includes the following steps:

[0065] (1) Mix 2.5g of cobalt tetroxide powder, 1.2g of lithium carbonate powder and 0.4g of magnesium oxide, grind them, and keep them at 1000℃ for 10h in air atmosphere to obtain magnesium-doped lithium cobalt oxide;

[0066] (2) Mix 0.1g pyrrole, 10g magnesium-doped lithium cobalt oxide and 20mL anhydrous ethanol, add 0.4mg sodium persulfate, stir in an ice-water bath for 5.5h, filter, wash and dry to obtain pyrrole-coated magnesium-doped lithium cobalt oxide;

[0067] (3) Mix 0.2 mmol 5,10,15,20-tetra(4-aminophenyl)porphyrin, 0.4 mmol pyromellitic anhydride, 3 mL N-methylpyrrolidone, and 3 mL 1,3,5-trimethylbenzene, add 0.5 mL isoquinoline, sonicate for 15 min, transfer to a reaction tube, freeze-degas and cycle 4 times, keep warm at 150℃ for 5 days, cool, centrifuge, wash 4 times with N,N-dimethylformamide and methanol, add 10 mL tetrahydrofuran and 100 mg pyrrole-coated magnesium-doped lithium cobalt oxide, sonicate for 1.5 h, centrifuge, wash, and dry to obtain composite lithium cobalt oxide;

[0068] The preparation of the modified conductive agent includes the following steps:

[0069] 1) Mix 25g of conductive agent, 0.4L of isopropanol and 100mL of deionized water, sonicate for 35min, add 5g of (3-mercaptopropyl)trimethoxysilane, adjust the pH to 3, keep warm in a 60℃ water bath for 5.5h, filter, wash and dry to obtain mercapto-based conductive agent.

[0070] 2) Mix 4.2g of mercapto-conductive agent with 20mL of n-hexane, keep warm in a 60℃ water bath for 3.5h, add 3.6g of a compound with double bond-terminated disulfide bonds and 20mL of n-hexane, stir for 5.5h, add 15.6mg of benzoin dimethyl ether, treat with ultraviolet light, wash and dry to obtain the modified conductive agent;

[0071] The conductive agent is obtained by compounding carbon black and silica in a mass ratio of 2:1.

[0072] The working conditions for ultraviolet light treatment are: irradiation with a 365nm ultraviolet lamp for 1 hour.

[0073] Example 3: A method for preparing a positive electrode sheet coated with lithium cobalt oxide, comprising the following steps:

[0074] A lithium cobalt oxide cathode material is coated on both sides of a metal foil and dried to obtain a lithium cobalt oxide cathode sheet.

[0075] A method for preparing a lithium cobalt oxide coated cathode material includes the following steps:

[0076] S1: Add the self-healing adhesive to deionized water, stir, and then vacuum defoam to obtain the self-healing adhesive solution. Divide it into two parts, denoted as self-healing adhesive solution a and self-healing adhesive solution b.

[0077] The mass ratio of the self-healing adhesive a to the self-healing adhesive b is 3:1;

[0078] The preparation of the self-healing adhesive includes the following steps:

[0079] Under a nitrogen atmosphere, 3.2g acrylamide, 3.2g acrylic acid, 1.4g double bond-terminated disulfide compound, and 115mL deionized water were mixed, 39mg ammonium persulfate was added, and the mixture was kept in an oil bath at 52℃ for 7h. The mixture was then washed 5 times with ethanol and freeze-dried to obtain a self-healing adhesive.

[0080] The preparation of the double-bond-terminated disulfide compound includes the following steps:

[0081] Under a nitrogen atmosphere, 2.5 g of 4,4-diaminodiphenyl disulfide and 50 mL of acetone were mixed, and 2.9 mL of 2-isocyanate ethyl methacrylate was added. The mixture was stirred at 25 °C for 20 h, washed, and dried to obtain a compound with double-bond-terminated disulfide bonds.

[0082] S2: Mix self-healing adhesive a and composite lithium cobalt oxide, stir ultrasonically, add modified conductive agent and self-healing adhesive b in sequence, stir ultrasonically to obtain a lithium cobalt oxide coated cathode material;

[0083] The contents of each component in the cathode material by weight are as follows: 87 parts of composite lithium cobalt oxide, 9 parts of modified conductive agent, 8 parts of self-healing binder, and 26 parts of deionized water.

[0084] The preparation of the composite lithium cobalt oxide includes the following steps:

[0085] (1) Mix 2.5g of cobalt tetroxide powder, 1.2g of lithium carbonate powder and 0.4g of magnesium oxide, grind them, and keep them at 1000℃ for 10h in air atmosphere to obtain magnesium-doped lithium cobalt oxide;

[0086] (2) Mix 0.1g pyrrole, 10g magnesium-doped lithium cobalt oxide and 20mL anhydrous ethanol, add 0.4mg sodium persulfate, stir in an ice-water bath for 6h, filter, wash and dry to obtain pyrrole-coated magnesium-doped lithium cobalt oxide;

[0087] (3) Mix 0.2 mmol 5,10,15,20-tetra(4-aminophenyl)porphyrin, 0.4 mmol pyromellitic anhydride, 3 mL N-methylpyrrolidone, and 3 mL 1,3,5-trimethylbenzene, add 0.5 mL isoquinoline, sonicate for 20 min, transfer to a reaction tube, freeze-degas and cycle 5 times, keep warm at 150℃ for 5 days, cool, centrifuge, wash 5 times with N,N-dimethylformamide and methanol respectively, add 10 mL tetrahydrofuran and 100 mg pyrrole-coated magnesium-doped lithium cobalt oxide, sonicate for 2 h, centrifuge, wash, and dry to obtain composite lithium cobalt oxide;

[0088] The preparation of the modified conductive agent includes the following steps:

[0089] 1) Mix 25g of conductive agent, 0.4L of isopropanol and 100mL of deionized water, sonicate for 40min, add 5g of (3-mercaptopropyl)trimethoxysilane, adjust the pH to 3.1, keep warm in a 62℃ water bath for 5h, filter, wash and dry to obtain thiolized conductive agent.

[0090] 2) Mix 4.2g of mercapto-conductive agent with 20mL of n-hexane, keep warm in a 60℃ water bath for 4h, add 3.6g of double bond-terminated disulfide compound and 20mL of n-hexane, stir for 6h, add benzoin dimethyl ether, treat with ultraviolet light, wash and dry to obtain modified conductive agent;

[0091] The conductive agent is obtained by compounding carbon black and silica in a mass ratio of 2:1.

[0092] The working conditions for ultraviolet light treatment are: irradiation with a 365nm ultraviolet lamp for 1 hour.

[0093] Comparative Example 1: Using Example 3 as the control group, the self-healing adhesive was replaced with polyacrylic acid (P104272: Aladdin reagent), and other processes were normal.

[0094] Comparative Example 2: Using Example 3 as the control group, magnesium-doped lithium cobalt oxide was used to replace the composite lithium cobalt oxide, while other processes were normal.

[0095] Comparative Example 3: Using Example 3 as the control group, carbon black was used to replace the modified conductive agent, while other processes were normal.

[0096] The thickness of the cathode material after curing on the surface of the metal foil (aluminum foil) is 100µm.

[0097] Sources of raw materials used (for illustrative purposes only):

[0098] 5,10,15,20-Tetra(4-aminophenyl)porphyrin S44659: Shanghai Yuanye Biotechnology Co., Ltd.; Acrylamide A108465, Acrylic acid A103526, 4,4-Diaminodiphenyl disulfide A101817, ethyl methacrylate 2-isocyanate I121957, Cobalt tetroxide powder C111617, Lithium carbonate powder L101679, Magnesium oxide M103940, Pyrrole P104878, Pyromellitic anhydride P109616, N-methyl Pyrrolidone M103246, 1,3,5-trimethylbenzene T105015, isoquinoline I105573, N,N-dimethylformamide D111999, tetrahydrofuran T103263, (3-mercaptopropyl)trimethoxysilane M100619, benzoin dimethyl ether B104003, carbon black C742510, fumed silica S104599: Aladdin Reagent; Ammonium persulfate, ethanol, acetone, sodium persulfate, methanol, isopropanol, n-hexane, analytical grade: Sinopharm Group Reagent.

[0099] Performance testing: The positive electrode sheets prepared in the examples and comparative examples were tested:

[0100] Using lithium metal sheets as the counter electrode and the prepared electrode sheets as the working electrode, the battery was assembled for testing. The separator was made of polypropylene Celgard 2400 (industrial grade), and the electrolyte was a 1 mol / L LiPF6 carbonate solution (the solvent was carbonate with a volume ratio of EC, DEC, and DMC of 1:1:1).

[0101] Cyclic performance: At 45℃, charge at 1.5C constant current and constant voltage to 4.5V and hold for 5min, then discharge at 0.7C constant current to 3V and hold for 5min, cycle 500 times, and test capacity retention.

[0102] Heating test: Heat the charged battery to 90°C and keep it at that temperature for 2 hours. Observe whether the battery leaks. If it does not leak, heat it to 149°C and keep it at that temperature for 2 hours. Take 10 batteries from each of the examples and comparative examples. If none of them catch fire or explode, they are considered qualified.

[0103] Overcharge test: Charged at 4.6V for 7 hours, 10 batteries were taken from each of the examples and comparative examples. All batteries that did not catch fire or explode were considered qualified. The results are shown in Table 1.

[0104] Table 1

[0105]

[0106] This invention provides a lithium cobalt oxide coated cathode material and the cathode sheet prepared therefrom. By limiting the process and composition, the cathode sheet of the lithium battery is endowed with excellent cycle stability, thereby improving the durability and safety of the battery.

[0107] Comparing Example 3 with Comparative Example 1, it can be seen that a binder with dynamic reversible bonds such as hydrogen bonds and disulfide bonds was synthesized through free radical polymerization of acrylamide, acrylic acid, and a compound with double bond end-capping containing disulfide bonds. The compound with double bond end-capping containing disulfide bonds was prepared from 4,4-diaminodiphenyl disulfide and ethyl 2-isocyanate methacrylate. This effectively improves the mechanical and rheological properties of the cathode material and enhances the stability of the electrode. At the same time, the abundant polar groups on the binder can form a covalent-non-covalent cross-linked network between the conductive particles and the copolymer chains, effectively buffering the volume expansion of silica and ensuring that the structural integrity of the electrode remains unchanged after cycling.

[0108] Comparing Example 3 with Comparative Example 2, it can be seen that in order to improve the stability of lithium cobalt oxide, Mg is first used for doping to stabilize its crystal structure and suppress its irreversible phase transition under high voltage. Then, the conductive polymer polypyrrole is coated on its surface. Then, the large π bond of polypyrrole is used to coat its surface with an organic porous polymer prepared by the quaternary linker 5,10,15,20-tetra(4-aminophenyl)porphyrin and pyromellitic anhydride, thereby improving its performance in cycle performance and rate performance.

[0109] Comparing Example 3 with Comparative Example 3, it can be seen that by modifying the conductive agent, firstly by mercaptoizing it with (3-mercaptopropyl)trimethoxysilane, and then by using mercapto-double bond photoclicking to graft a disulfide bond-terminated compound with reversible double bonds, the stability and safety of battery performance are improved.

[0110] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the present invention's specification under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for preparing a lithium cobalt oxide coated cathode material, characterized in that, Includes the following steps: S1: Add the self-healing adhesive to deionized water, stir, and then vacuum defoam to obtain the self-healing adhesive solution. Divide it into two parts, denoted as self-healing adhesive solution a and self-healing adhesive solution b. S2: Mix self-healing adhesive a and composite lithium cobalt oxide, stir ultrasonically, add modified conductive agent and self-healing adhesive b in sequence, stir ultrasonically to obtain a lithium cobalt oxide coated cathode material; The preparation of the composite lithium cobalt oxide includes: first, Mg doping, then surface coating with polypyrrole, and then surface coating again with an organic porous polymer prepared by the quaternary linker 5,10,15,20-tetra(4-aminophenyl)porphyrin and pyromellitic anhydride; The preparation of the self-healing adhesive includes the following steps: Under a nitrogen atmosphere, acrylamide, acrylic acid, a compound with disulfide bonds at double bond end, and deionized water are mixed, and ammonium persulfate is added. The mixture is kept in an oil bath at 48-52℃ for 7-8 hours, washed with ethanol 3-5 times, and freeze-dried to obtain a self-healing adhesive. The preparation of the modified conductive agent includes the following steps: 1) Mix the conductive agent, isopropanol, and deionized water, sonicate for 30-40 min, add (3-mercaptopropyl)trimethoxysilane, adjust the pH to 2.9-3.1, keep warm in a water bath at 58-62℃ for 5-6 h, filter, wash, and dry to obtain the mercapto-based conductive agent. 2) Mix the mercapto-conductive agent and n-hexane, keep warm in a 60°C water bath for 3-4 hours, add a mixture of double-bond-terminated disulfide compounds and n-hexane, stir for 5-6 hours, add benzoin dimethyl ether, treat with ultraviolet light, wash and dry to obtain the modified conductive agent.

2. The method for preparing a lithium cobalt oxide coated cathode material according to claim 1, characterized in that, The mass ratio of the self-healing adhesive a to the self-healing adhesive b is 3:

1.

3. The method for preparing a lithium cobalt oxide coated cathode material according to claim 1, characterized in that, The components in the cathode material are as follows, by weight: 77-87 parts of composite lithium cobalt oxide, 6-9 parts of modified conductive agent, 4-8 parts of self-healing binder, and 21-26 parts of deionized water.

4. The method for preparing a lithium cobalt oxide coated cathode material according to claim 1, characterized in that, The preparation of the composite lithium cobalt oxide includes the following steps: (1) Mix cobalt tetroxide powder, lithium carbonate powder and magnesium oxide, grind them, and keep them at 1000℃ for 10h in air atmosphere to obtain magnesium-doped lithium cobalt oxide; (2) Pyrrole, magnesium-doped lithium cobalt oxide and anhydrous ethanol are mixed, sodium persulfate is added, and the mixture is stirred in an ice-water bath for 5-6 hours. After filtration, washing and drying, pyrrole-coated magnesium-doped lithium cobalt oxide is obtained. (3) Mix 5,10,15,20-tetra(4-aminophenyl)porphyrin, pyromellitic anhydride, N-methylpyrrolidone, and 1,3,5-trimethylbenzene, add isoquinoline, sonicate for 10-20 min, transfer to a reaction tube, freeze-degas and cycle 3-5 times, keep warm at 150℃ for 5 days, cool, centrifuge, wash with N,N-dimethylformamide and methanol 3-5 times in sequence, add tetrahydrofuran and pyrrole-coated magnesium-doped lithium cobalt oxide, sonicate for 1-2 h, centrifuge, wash and dry to obtain composite lithium cobalt oxide.

5. The method for preparing a lithium cobalt oxide coated cathode material according to claim 1, characterized in that, In the preparation of the modified conductive agent, the conductive agent is obtained by compounding carbon black and silica in a mass ratio of 2:

1.

6. The method for preparing a lithium cobalt oxide coated cathode material according to claim 1, characterized in that, The preparation of the double-bond-terminated disulfide compound includes the following steps: Under a nitrogen atmosphere, 4,4-diaminodiphenyl disulfide and acetone were mixed, and ethyl 2-isocyanate methacrylate was added. The mixture was stirred at 18-25°C for 20-21 h, washed, and dried to obtain a compound with double-bond-terminated disulfide bonds.

7. A lithium cobalt oxide coated cathode material, characterized in that, Prepared by the preparation method according to any one of claims 1-6.

8. A positive electrode sheet coated with lithium cobalt oxide, characterized in that, The lithium cobalt oxide cathode material is prepared according to claim 7. The preparation method includes the following steps: coating the lithium cobalt oxide cathode material on both sides of a metal foil and drying it to obtain a lithium cobalt oxide cathode sheet.

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