A safe and protective lithium-supplementing positive electrode material and its preparation method

Abstract

The present invention discloses a safety-protective lithium-supplementing cathode material and its preparation method. The safety-protective lithium-supplementing cathode material comprises the following components by weight: 80-120 parts of a lithium-rich nickel-manganese-cobalt layered oxide active material, 30-40 parts of a lithium-supplementing agent, 10-15 parts of a protective agent, 10-15 parts of a conductive agent, 8-12 parts of a binder, and 55-65 parts of a solvent. The protective agent comprises carbon fibers loaded with carbon black and aluminum powder. In the present invention, the safety-protective lithium-supplementing cathode material utilizes the aluminum powder loaded on the carbon fibers to consume oxygen, thereby reducing the risk of thermal runaway. This effectively improves the safety of the battery and provides the battery with excellent electrochemical cycling performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium batteries, and in particular relates to a safety-protective lithium-supplementing positive electrode material and a preparation method thereof. Background Art

[0002] Lithium-rich layered oxide cathode materials have cation and anion redox reactions, thus having ultra-high specific capacity and are one of the key cathode materials to be studied in future lithium-ion batteries.

[0003] However, lithium-rich layered oxide cathode materials also have defects. For example, the cathode materials decompose under high temperature and high pressure, and a large amount of oxygen is released, which leads to a serious decline in the cathode performance. In addition, a large amount of heat and energy is released rapidly, endangering the safety of the battery and triggering thermal runaway.

[0004] Therefore, how to further improve the safety of cathode materials is a problem that needs to be solved at present. Summary of the Invention

[0005] The object of the present invention is to provide a safety-protective lithium-supplementing cathode material and a preparation method thereof, wherein the safety-protective lithium-supplementing cathode material can effectively reduce the risk of thermal runaway and improve the safety of the battery.

[0006] In order to achieve the above object, a specific embodiment of the present invention provides the following technical solutions:

[0007] A safety and protective lithium-supplementing positive electrode material, comprising the following components by weight: 80-120 parts of a lithium-rich nickel-manganese-cobalt layered oxide active material, 30-40 parts of a lithium-supplementing agent, 10-15 parts of a protective agent, 10-15 parts of a conductive agent, 8-12 parts of a binder, and 55-65 parts of a solvent;

[0008] Wherein, the protective agent comprises carbon fiber loaded with carbon black and aluminum powder.

[0009] In one or more embodiments of the present invention, the mass ratio of the carbon fiber to the carbon black is 1:(0.1-0.3), and the mass ratio of the carbon fiber to the aluminum powder is 1:(0.1-0.3).

[0010] In one or more embodiments of the present invention, in the carbon fiber, the mass ratio of carbon black to aluminum powder is 1:(1-2).

[0011] In one or more embodiments of the present invention, the diameter of the carbon fiber is 3-7 μm and the length is 1-2 mm; the particle size of the carbon black is 20-40 nm; and the particle size of the aluminum powder is 20-50 nm.

[0012] In one or more embodiments of the present invention, the protective agent is prepared as follows: aluminum powder and carbon black are dispersed in anhydrous ethanol, and then carbon fiber is added, impregnated under vacuum, and then dried in an inert atmosphere to obtain carbon fiber loaded with carbon black and aluminum powder.

[0013] In one or more embodiments of the present invention, the protective agent further comprises spiral carbon fibers, which are entangled with carbon fibers loaded with carbon black and aluminum powder, and the mass ratio of the carbon fibers loaded with carbon black and aluminum powder to the spiral carbon fibers is 1:(2-3).

[0014] In one or more embodiments of the present invention, the diameter of the carbon fiber is 3-7 μm and the length is 1-2 mm; the average spiral diameter of the spiral carbon fiber is 8-10 μm and the average length is 2-3 mm.

[0015] In one or more embodiments of the present invention, the protective agent is obtained by mixing and grinding the spiral carbon fiber with the carbon fiber loaded with carbon black and aluminum powder, with the grinding speed being 150-200 rpm and the grinding time being 1-2 hours.

[0016] In one or more embodiments of the present invention, the lithium-rich nickel-manganese-cobalt layered oxide active material is prepared as follows:

[0017] A nickel source, a cobalt source, and a manganese source are mixed with water in a molar ratio of nickel atoms, cobalt atoms, and manganese atoms of 1:1:(2-4) to prepare an ion solution, the ion solution is mixed with an alkali to react to form a precipitate, and the precipitate is filtered, washed, and dried to obtain a precursor;

[0018] The precursor and lithium salt are mixed, and when mixing, the ratio of the total molar amount of nickel atoms, cobalt atoms and manganese atoms to the molar amount of lithium atoms is 1: (1.2-1.5), and then sintered to obtain a lithium-rich nickel-manganese-cobalt layered oxide active material.

[0019] Another specific embodiment of the present invention provides a technical solution as follows:

[0020] A method for preparing a safety-protective lithium-supplementing positive electrode material comprises mixing various raw material components according to a proportion to obtain the safety-protective lithium-supplementing positive electrode material.

[0021] Compared with the existing technology, the safety protection type lithium supplement positive electrode material in the present invention consumes oxygen through the aluminum powder loaded on the carbon fiber to reduce the risk of thermal runaway, effectively improving the safety of battery use and making the battery have excellent electrochemical cycle performance. DETAILED DESCRIPTION

[0022] To help those skilled in the art better understand the technical solutions of the present invention, the following clearly and completely describes the technical solutions in the embodiments of the present invention. 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 those skilled in the art without creative work should fall within the scope of protection of the present invention.

[0023] A specific embodiment of the present invention provides a safety and protective lithium-supplementing positive electrode material, comprising the following components by weight: 80-120 parts of a lithium-rich nickel-manganese-cobalt layered oxide active material, 30-40 parts of a lithium-supplementing agent, 10-15 parts of a protective agent, 10-15 parts of a conductive agent, 8-12 parts of a binder, and 55-65 parts of a solvent; wherein the protective agent is carbon fiber loaded with carbon black and aluminum powder.

[0024] Specifically, the lithium-rich nickel-manganese-cobalt layered oxide active material is doped with manganese and cobalt metal elements, which can reduce the material's active oxygen content and improve thermal stability. Adding an appropriate amount of lithium supplement can further increase the battery's energy density and improve cycling performance. Conductive agents can enhance the conductivity of the positive electrode material and improve rate performance. Binders can effectively bond the various raw material components, improving the structural stability of the positive electrode material, slowing its volume expansion and contraction during charge and discharge, and enhancing the battery's cycling stability.

[0025] The functions of the protective agent used in the present invention are as follows: first, the carbon fiber itself has excellent electrical conductivity, which can improve the electron transmission efficiency of the positive electrode material; second, the carbon fiber has a porous structure, and aluminum powder can be loaded on the carbon fiber. When the positive electrode material releases oxygen due to thermal runaway, the aluminum powder on the carbon fiber can react with oxygen to generate aluminum oxide, thereby reducing the possibility of oxygen igniting the combustible electrolyte; moreover, when the positive electrode material experiences thermal runaway, the temperature rises, and the carbon fiber has excellent thermal conductivity, which can quickly transfer heat to the aluminum powder. At higher temperatures, the reaction between the aluminum powder and oxygen is faster, thereby quickly consuming oxygen and effectively reducing the risk of thermal runaway; in addition, the electrical conductivity of aluminum oxide is weaker than that of aluminum powder. When the aluminum powder generates aluminum oxide, the electrical conductivity of the carbon fiber decreases, while carbon black has better electrical conductivity. Therefore, by loading carbon black on the carbon fiber, the decrease in conductivity caused by the generation of aluminum oxide by the aluminum powder can be compensated, and it can be ensured that the positive electrode material can maintain a high electrical conductivity; moreover, the generated aluminum oxide helps to improve the capacity retention rate of the positive electrode material, which is beneficial to improving the cycle performance of the battery.

[0026] Furthermore, in the protective agent, the mass ratio of carbon fiber to carbon black is 1:(0.1-0.3), and the mass ratio of carbon fiber to aluminum powder is 1:(0.1-0.3). Preferably, the mass ratio of carbon black to aluminum powder is 1:(1-2).

[0027] Specifically, by controlling the loading amount of carbon black and aluminum powder on the carbon fiber, while ensuring that the aluminum powder can effectively consume oxygen, the conductivity caused by the formation of aluminum oxide can be greatly reduced, ensuring that the positive electrode material has high conductivity.

[0028] Furthermore, the diameter of the carbon fiber is 3-7 μm and the length is 1-2 mm; the particle size of the carbon black is 20-40 nm; and the particle size of the aluminum powder is 20-50 nm. By controlling the specifications of the carbon fiber, carbon black, and aluminum powder, the carbon black and aluminum powder can be effectively loaded on the carbon fiber.

[0029] Furthermore, the protective agent is prepared as follows: aluminum powder and carbon black are dispersed in anhydrous ethanol, then carbon fibers are added, impregnated under vacuum, and dried in an inert atmosphere to obtain carbon fibers loaded with carbon black and aluminum powder. Dispersing the aluminum powder in anhydrous ethanol reduces the possibility of aluminum powder oxidation, while drying in an inert atmosphere also reduces oxidation. The inert atmosphere is specifically nitrogen or argon, and the drying temperature is 70-80°C.

[0030] Furthermore, the protective agent also includes spiral carbon fibers, which are entangled with carbon fibers loaded with carbon black and aluminum powder, and the mass ratio of the carbon fibers loaded with carbon black and aluminum powder to the spiral carbon fibers is 1:(2-3).

[0031] Furthermore, the carbon fibers have a diameter of 3-7 μm and a length of 1-2 mm, and the spiral carbon fibers have an average spiral diameter of 8-10 μm and an average length of 2-3 mm. The spiral carbon fibers are mixed and ground with carbon fibers loaded with carbon black and aluminum powder at a grinding speed of 150-200 rpm for 1-2 hours.

[0032] Specifically, the carbon fiber and the spiral carbon fiber are wound together through grinding, and after the two are wound together, the aluminum powder is wrapped, so that the two can transfer heat to the aluminum powder more quickly, promoting the oxidation of the aluminum powder to consume oxygen. In addition, when the aluminum powder is oxidized to generate aluminum oxide, the volume will increase to a certain extent. The spiral structure of the spiral carbon fiber allows it to undergo micro-deformation. Therefore, when the aluminum powder generates aluminum oxide and the volume changes, the spiral carbon fiber can slow down the negative impact of this sudden volume change on the structure of the positive electrode material through micro-deformation, so that the positive electrode material maintains normal electrochemical properties. Moreover, in addition to slowing down the volume change caused by the oxidation of aluminum powder, the spiral carbon fibers dispersed in the system also help maintain the integrity of the positive electrode material structure, reduce the expansion or contraction of the positive electrode material during the charge and discharge process, and help maintain the cycle performance of the battery.

[0033] Furthermore, the preparation of lithium-rich nickel-manganese-cobalt layered oxide active material is as follows:

[0034] A nickel source, a cobalt source, and a manganese source are mixed with water in a molar ratio of nickel atoms, cobalt atoms, and manganese atoms of 1:1:(2-4) to prepare an ion solution, the ion solution is mixed with an alkali to react to form a precipitate, and the precipitate is filtered, washed, and dried to obtain a precursor;

[0035] The precursor and lithium salt are mixed, and when mixing, the ratio of the total molar amount of nickel atoms, cobalt atoms and manganese atoms to the molar amount of lithium atoms is 1: (1.2-1.5), and then sintered to obtain a lithium-rich nickel-manganese-cobalt layered oxide active material.

[0036] Specifically, the precursor is prepared by coprecipitation to ensure uniform dispersion of nickel, cobalt, and manganese atoms. The precursor is then sintered with a lithium salt at 750-850°C for 10-15 hours to obtain a lithium-rich nickel-manganese-cobalt layered oxide active material. The base is specifically sodium carbonate aqueous solution or ammonia.

[0037] Furthermore, the lithium supplement agent is selected from lithium quarate, lithium oxalate, lithium iron phosphate, and lithium manganese iron phosphate; the conductive agent is selected from graphene, conductive carbon black, and carbon nanotubes; the binder is selected from polyvinylidene fluoride, polyacrylonitrile, and polyimide; and the solvent is N-methyl-2-pyrrolidone.

[0038] Another specific embodiment of the present invention provides a method for preparing a safety-protective lithium-supplementing positive electrode material, wherein the raw material components are mixed uniformly according to a ratio to obtain the safety-protective lithium-supplementing positive electrode material.

[0039] The present invention is further described in detail below with reference to specific embodiments.

[0040] The carbon fiber used in the present invention is activated carbon fiber purchased from Wanlixiang Carbon Fiber Co., Ltd. in Dongguan City; the average diameter of a single fiber of the spiral carbon fiber is 200 nm, the average spiral diameter is 10 μm, and the average length is 2 mm.

[0041] Preparation Example 1

[0042] Nickel sulfate hexahydrate (NiSO4·6H2O), cobalt sulfate heptahydrate (CoSO4·7H2O), and manganese sulfate monohydrate (MnSO4·H2O) were dissolved in water at a molar ratio of 1:1:4 (nickel, cobalt, and manganese) to form an ionic solution. The total concentration of nickel, cobalt, and manganese ions in the ionic solution was 2 mol / L. A 2 mol / L sodium carbonate aqueous solution was then prepared and mixed with the ionic solution. Ammonia was added to adjust the pH of the solution to 8.0. The mixture was then reacted at 60°C for 45 hours to form carbonate co-precipitates of all the nickel, cobalt, and manganese ions. The amount of sodium carbonate aqueous solution used was in 10% excess relative to the stoichiometric ratio in the carbonate co-precipitation. The filtered carbonate co-precipitate was washed with deionized water and then dried at 120°C for 12 hours to obtain the precursor.

[0043] The precursor and lithium carbonate were mixed in a ratio of the total molar amount of nickel atoms, cobalt atoms and manganese atoms to the molar amount of lithium atoms of 1:1.4, and then sintered at 500°C for 5 hours and then at 830°C for 12 hours to obtain a lithium-rich nickel-manganese-cobalt layered oxide active material.

[0044] Preparation Example 2

[0045] Take 10L of anhydrous ethanol, add 10g of carbon black and 10g of aluminum powder, make a dispersion after ultrasonic treatment, then add 100g of carbon fiber, soak under vacuum for 15 minutes, take out and dry at 70°C for 30 minutes under nitrogen protection to obtain a protective agent.

[0046] Preparation Example 3

[0047] Take 10L of anhydrous ethanol, add 30g of carbon black and 20g of aluminum powder, make a dispersion after ultrasonic treatment, then add 100g of carbon fiber, soak under vacuum for 15 minutes, take out and dry at 70℃ for 30 minutes under nitrogen protection to obtain the protective agent.

[0048] Preparation Example 4

[0049] Take 10L of anhydrous ethanol, add 20g of carbon black and 30g of aluminum powder, make a dispersion after ultrasonication, then add 100g of carbon fiber, impregnate under vacuum for 15 minutes, take out and dry at 70°C for 30 minutes under nitrogen protection to obtain a protective agent.

[0050] Preparation Example 5

[0051] Take 10L of anhydrous ethanol, add 10g of carbon black and 20g of aluminum powder, make a dispersion after ultrasonic treatment, then add 100g of carbon fiber, soak under vacuum for 15 minutes, take out and dry at 70°C for 30 minutes under nitrogen protection to obtain a protective agent.

[0052] Preparation Example 6

[0053] The carbon fiber in Preparation Example 2 was taken, and the carbon fiber and the spiral carbon fiber were mixed in a mass ratio of 1:2, placed in a ball mill, and ground at a speed of 150 rpm for 1 hour to obtain a protective agent.

[0054] Preparation Example 7

[0055] The carbon fiber in Preparation Example 2 was taken, and the carbon fiber and the spiral carbon fiber were mixed in a mass ratio of 1:3, placed in a ball mill, and ground at a speed of 200 rpm for 2 hours to obtain a protective agent.

[0056] Example 1

[0057] In parts by weight, 80 parts of the lithium-rich nickel-manganese-cobalt layered oxide active material in Preparation Example 1, 35 parts of lithium carbonate, 10 parts of the protective agent in Preparation Example 2, 13 parts of conductive carbon black, 10 parts of polyvinylidene fluoride, and 55 parts of N-methyl-2-pyrrolidone were mixed to obtain a safe and protective lithium-supplementing positive electrode material.

[0058] Example 2

[0059] In parts by weight, 100 parts of the lithium-rich nickel-manganese-cobalt layered oxide active material in Preparation Example 1, 40 parts of lithium carbonate, 12 parts of the protective agent in Preparation Example 2, 15 parts of conductive carbon black, 8 parts of polyvinylidene fluoride and 60 parts of N-methyl-2-pyrrolidone were taken and mixed to obtain a safe and protective lithium-supplementing positive electrode material.

[0060] Example 3

[0061] In parts by weight, 120 parts of the lithium-rich nickel-manganese-cobalt layered oxide active material in Preparation Example 1, 30 parts of lithium carbonate, 15 parts of the protective agent in Preparation Example 2, 10 parts of conductive carbon black, 12 parts of polyvinylidene fluoride, and 65 parts of N-methyl-2-pyrrolidone were mixed to obtain a safe and protective lithium-supplementing positive electrode material.

[0062] Example 4

[0063] In parts by weight, 80 parts of the lithium-rich nickel-manganese-cobalt layered oxide active material in Preparation Example 1, 35 parts of lithium carbonate, 10 parts of the protective agent in Preparation Example 3, 13 parts of conductive carbon black, 10 parts of polyvinylidene fluoride, and 55 parts of N-methyl-2-pyrrolidone were mixed to obtain a safe and protective lithium-supplementing positive electrode material.

[0064] Example 5

[0065] In parts by weight, 80 parts of the lithium-rich nickel-manganese-cobalt layered oxide active material in Preparation Example 1, 35 parts of lithium carbonate, 10 parts of the protective agent in Preparation Example 4, 13 parts of conductive carbon black, 10 parts of polyvinylidene fluoride and 55 parts of N-methyl-2-pyrrolidone were taken and mixed to obtain a safe and protective lithium-supplementing positive electrode material.

[0066] Example 6

[0067] In parts by weight, 80 parts of the lithium-rich nickel-manganese-cobalt layered oxide active material in Preparation Example 1, 35 parts of lithium carbonate, 10 parts of the protective agent in Preparation Example 5, 13 parts of conductive carbon black, 10 parts of polyvinylidene fluoride and 55 parts of N-methyl-2-pyrrolidone were taken and mixed to obtain a safe and protective lithium-supplementing positive electrode material.

[0068] Example 7

[0069] In parts by weight, 80 parts of the lithium-rich nickel-manganese-cobalt layered oxide active material in Preparation Example 1, 35 parts of lithium carbonate, 10 parts of the protective agent in Preparation Example 6, 13 parts of conductive carbon black, 10 parts of polyvinylidene fluoride and 55 parts of N-methyl-2-pyrrolidone were taken and mixed to obtain a safe and protective lithium-supplementing positive electrode material.

[0070] Example 8

[0071] In parts by weight, 80 parts of the lithium-rich nickel-manganese-cobalt layered oxide active material in Preparation Example 1, 35 parts of lithium carbonate, 10 parts of the protective agent in Preparation Example 7, 13 parts of conductive carbon black, 10 parts of polyvinylidene fluoride, and 55 parts of N-methyl-2-pyrrolidone were mixed to obtain a safe and protective lithium-supplementing positive electrode material.

[0072] Comparative Example 1

[0073] In parts by weight, 80 parts of the lithium-rich nickel-manganese-cobalt layered oxide active material in Preparation Example 1, 35 parts of lithium carbonate, 10 parts of a protective agent, 13 parts of conductive carbon black, 10 parts of polyvinylidene fluoride, and 55 parts of N-methyl-2-pyrrolidone were taken, wherein the protective agent included carbon fiber, carbon black, and aluminum powder in a mass ratio of 10:1:1. The above raw materials were mixed to obtain a safe and protective lithium-supplementing positive electrode material.

[0074] Comparative Example 2

[0075] Take 10L of anhydrous ethanol, add 20g of aluminum powder, make a dispersion after ultrasonication, then add 100g of carbon fiber, impregnate under vacuum for 15 minutes, take out and dry at 70°C for 30 minutes under nitrogen protection to obtain a protective agent.

[0076] In parts by weight, 80 parts of the lithium-rich nickel-manganese-cobalt layered oxide active material in Preparation Example 1, 35 parts of lithium carbonate, 10 parts of a protective agent, 13 parts of conductive carbon black, 10 parts of polyvinylidene fluoride, and 55 parts of N-methyl-2-pyrrolidone were mixed to obtain a safe and protective lithium-supplementing positive electrode material.

[0077] The positive electrode material was evenly coated on aluminum foil and dried at 80°C for 12 hours to obtain a positive electrode sheet, which was assembled into a button battery. The electrolyte was LiPF6 (1.0M) as a solute dissolved in a mixture of ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) with a volume ratio of 1:1:1. The negative electrode used a lithium sheet and the separator used a PE separator.

[0078] TG-MS test: The temperature was raised from room temperature to 300°C at a heating rate of 10°C / min in an argon atmosphere, and the temperature at which the cathode material began to release oxygen was measured.

[0079] Under the conditions of charging voltage 3.0-4.3V and current 0.1C, the capacity retention rate of the button battery was tested after 50 cycles at 25°C.

[0080] Table 1 Performance test results

[0081]

[0082] It can be seen from Table 1 that, compared with Comparative Example 1, the present invention can inhibit oxygen release from the positive electrode material and reduce the risk of thermal runaway of the battery by adding carbon fibers loaded with carbon black and aluminum powder, while ensuring the cycle stability of the battery.

[0083] It can be seen from Example 1 and Examples 4-6 that loading carbon black and aluminum powder on carbon fibers in an appropriate mass ratio can better inhibit oxygen release from the positive electrode material and reduce the risk of thermal runaway.

[0084] It can be seen from Example 1, Example 7 and Example 8 that the use of carbon fiber loaded with carbon black and aluminum powder and spiral carbon fiber can further reduce the risk of thermal runaway of the battery.

[0085] 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 invention can be embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations that come within the meaning and range of equivalents of the claims be embraced therein.

[0086] In addition, it should be understood that although this specification is described in terms of implementation methods, not every implementation method contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

Claims

1. A safety protection type lithium supplement positive electrode material, characterized in that: The invention comprises the following components in parts by weight: 80-120 parts of lithium-rich nickel-manganese-cobalt layered oxide active material, 30-40 parts of lithium supplement agent, 10-15 parts of protective agent, 10-15 parts of conductive agent, 8-12 parts of binder and 55-65 parts of solvent; Wherein, the protective agent comprises carbon fiber loaded with carbon black and aluminum powder; The protective agent is prepared as follows: aluminum powder and carbon black are dispersed in anhydrous ethanol, then carbon fiber is added, impregnated under vacuum, and then dried in an inert atmosphere to obtain carbon fiber loaded with carbon black and aluminum powder.

2. The safety protection type lithium supplementing positive electrode material according to claim 1, characterized in that: The mass ratio of the carbon fiber to the carbon black is 1:(0.1-0.3), and the mass ratio of the carbon fiber to the aluminum powder is 1:(0.1-0.3).

3. The safety protection type lithium supplementing positive electrode material according to claim 1, characterized in that: In the carbon fiber, the mass ratio of carbon black to aluminum powder is 1:(1-2).

4. The safety protection type lithium supplementing positive electrode material according to claim 1, characterized in that: The diameter of the carbon fiber is 3-7 μm and the length is 1-2 mm; the particle size of the carbon black is 20-40 nm; and the particle size of the aluminum powder is 20-50 nm.

5. The safety protection type lithium supplementing positive electrode material according to claim 1, characterized in that: The protective agent further comprises spiral carbon fibers, which are entangled with carbon fibers loaded with carbon black and aluminum powder, and the mass ratio of the carbon fibers loaded with carbon black and aluminum powder to the spiral carbon fibers is 1:(2-3).

6. The safety protection type lithium supplementing positive electrode material according to claim 5, characterized in that: The diameter of the carbon fiber is 3-7 μm, and the length is 1-2 mm; the average spiral diameter of the spiral carbon fiber is 8-10 μm, and the average length is 2-3 mm.

7. The safety protection type lithium supplementing positive electrode material according to claim 5, characterized in that: The protective agent is obtained by mixing and grinding spiral carbon fiber with carbon fiber loaded with carbon black and aluminum powder, with a grinding speed of 150-200 rpm and a grinding time of 1-2 hours.

8. The safety protection type lithium supplementing positive electrode material according to claim 1, characterized in that: The preparation of the lithium-rich nickel-manganese-cobalt layered oxide active material is as follows: A nickel source, a cobalt source, and a manganese source are mixed with water in a molar ratio of nickel atoms, cobalt atoms, and manganese atoms of 1:1:(2-4) to prepare an ion solution, the ion solution is mixed with an alkali to react to form a precipitate, and the precipitate is filtered, washed, and dried to obtain a precursor; The precursor and lithium salt are mixed, and when mixing, the ratio of the total molar amount of nickel atoms, cobalt atoms and manganese atoms to the molar amount of lithium atoms is 1: (1.2-1.5), and then sintered to obtain a lithium-rich nickel-manganese-cobalt layered oxide active material.

9. A method for preparing the safety protection type lithium supplementing positive electrode material according to any one of claims 1 to 8, characterized in that: The raw material components are mixed evenly according to the proportion to obtain a safe and protective lithium-supplementing positive electrode material.

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