Preparation method for conductive carbon-coated additive for lithium battery positive electrode material, and use thereof

Abstract

The present application relates to the technical field of lithium battery positive electrode materials, and specifically relates to a preparation method for a conductive carbon-coated additive for a lithium battery positive electrode material, and a use thereof. The preparation method comprises: step I, using a gas plasma process to carry out surface modification on a carbon nanotube so as to obtain a modified carbon nanotube, wherein the modified carbon nanotube is a hydrogenated carbon nanotube or an ammoniated carbon nanotube; step II, using a sulfur trioxide sulfonation method to carry out sulfonation treatment on organic carbon and the modified carbon nanotube so as to obtain a sulfonated carbon material; and step III, mixing the sulfonated carbon material and water, carrying out sanding treatment on the mixed solution, and uniformly dispersing to obtain a conductive carbon-coated additive as a lithium iron phosphate or lithium manganese iron phosphate carbon-coated additive. The conductive performance of positive electrode materials can be effectively improved.

Description

Preparation method and application of conductive carbon coating additive for lithium battery positive electrode material

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 6, 2023, with application number 202311665592.4 and invention name “Preparation method and application of conductive carbon-coated additives for lithium battery positive electrode materials”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the technical field of lithium battery positive electrode materials, and in particular to a preparation method and application of a conductive carbon-coated additive for lithium battery positive electrode materials. Background Art

[0003] Lithium-ion batteries (LIBs) are a new generation of green, high-energy batteries with superior performance. They have become a key focus of high-tech development and are receiving increasing attention and recognition due to their high specific capacity, high voltage, and high safety. Lithium-ion battery cathode materials are a crucial component and directly impact their performance. To achieve excellent discharge performance, LIBs require cathode materials with enhanced ionic and electronic conductivity. Lithium iron phosphate and lithium iron manganese phosphate are both LIB cathode materials and are widely used in electric vehicles and energy storage systems. However, LIP and LMP cathode materials exhibit poor conductivity. Existing technologies primarily utilize carbon coating to enhance their conductivity. However, the synthesis temperature of LIP and LMP is around 700°C, while the carbon materials used for coating generally require high-temperature treatment at 800°C to achieve ideal electronic conductivity. This results in limited electronic conductivity for existing cathode materials. Furthermore, undoped carbon materials also have limited ionic conductivity. Therefore, it is necessary to develop additives that enhance the ionic and electronic conductivity of the conductive carbon coating layer.

[0004] Application Contents

[0005] The purpose of the embodiments of the present application is to provide a preparation method and application of a conductive carbon coating additive for lithium battery positive electrode materials, aiming to solve the technical problem that the existing carbon coating layer has poor electronic conductivity and ionic conductivity at around 700°C. Technical Solutions

[0006] The technical solution adopted in the embodiment of this application is:

[0007] In a first aspect, the present invention provides a method for preparing a conductive carbon coating additive for a lithium battery positive electrode material, comprising the following steps:

[0008] Step 1: Using a gas plasma process to modify the surface of carbon nanotubes to obtain modified carbon nanotubes; the modified carbon nanotubes are hydrogenated carbon nanotubes or ammoniated carbon nanotubes;

[0009] Step 2: Using sulfur trioxide sulfonation method, the organic carbon and the modified carbon nanotubes are sulfonated to obtain a sulfonated carbon material;

[0010] Step 3: Mix the sulfonated carbon material and water, sand-mill the mixed solution, and obtain a conductive carbon-coated additive after uniform dispersion.

[0011] In some embodiments, the specific method of step one is: placing carbon nanotubes in a reaction chamber of a plasma system, introducing reaction gas into the plasma system, controlling the plasma system power to 25-1000W, the gas pressure to 10-150Pa, the reaction time to 20-30min, and the reaction temperature to 20-150°C to obtain modified carbon nanotubes.

[0012] In some embodiments, the reaction gas is at least one of hydrogen and ammonia.

[0013] In some embodiments, the mass ratio of the ventilation volume of the reaction gas to the carbon nanotubes is 1-100 sccm / g.

[0014] In some embodiments, the carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

[0015] In some embodiments, the carbon nanotubes have a diameter ranging from 2 nm to 50 nm.

[0016] In some embodiments, the specific method of step 2 is: the modified carbon nanotubes and organic carbon are ball-milled and mixed evenly in a mass ratio of 1-2:8-9, and then a mixed gas containing sulfur trioxide and air is introduced, the reaction temperature is controlled to 30-60°C, the reaction time is 0.5-1h, and finally the reacted carbon material is washed and filtered.

[0017] In some embodiments, in step 2, the ball milling speed is 400-600 r / min, the ball milling medium is a zirconium ball with a diameter of 0.3-0.8 mm, and the ball milling time is 20-30 min.

[0018] In some embodiments, the volume ratio of sulfur trioxide to air is 5-6:100.

[0019] In some embodiments, the ratio of the ventilation volume of the mixed gas to the total mass of the modified carbon nanotubes and the organic carbon is 50-150 sccm / g.

[0020] In some embodiments, the organic carbon is at least one of alkanes, olefins, aromatic hydrocarbons, polymer resins, asphalt, and tar.

[0021] In some embodiments, in step three, the mass ratio of the sulfonated carbon material to water is 1:9-10.

[0022] In some embodiments, in step three, the sand milling conditions include: the grinding medium includes zirconium balls with a diameter range of 0.7-1.4 mm, the sand milling speed is 600-800 rpm, and the sand milling time is 0.5-1 h.

[0023] In a second aspect, an embodiment of the present application provides a lithium-ion battery positive electrode material, including the additive prepared by the above preparation method.

[0024] In the embodiments of the present application, hydrogenated / ammoniated carbon nanotubes are prepared by hydrogenating / ammoniating carbon nanotubes. Experiments have shown that hydrogenated / ammoniated carbon nanotubes can improve the dispersion of carbon nanotubes and shorten the dispersion time of carbon nanotubes. Subsequently, when the carbon nanotubes are mixed with organic carbon for sulfonation, a uniformly mixed material can be obtained without the need for prolonged grinding and dispersion of the carbon nanotubes. Furthermore, the hydrogenated / ammoniated carbon nanotubes are dispersed with each other, which is more conducive to improving the sulfonation effect and ultimately improving the conductivity of the carbon coating layer of the positive electrode material. Furthermore, hydrogenated / ammoniated carbon nanotubes increase the amount of hydrogen / ammonia atoms attached to the surface of the carbon nanotubes. During the sulfonation treatment, more sulfonic acid groups replace hydrogen / ammonia atoms on the surface of the carbon nanotubes, thereby increasing the degree of sulfonation of the carbon nanotubes. Carbon nanotubes with multiple sulfonic acid groups attached to their surfaces have better dispersion, enabling the carbon nanotubes to be uniformly mixed with other components of the positive electrode material and uniformly dispersed in the carbon coating layer, thereby improving the conductivity of the carbon coating layer. Furthermore, the multiple sulfonic acid groups provide more ionic conduction paths, further improving the ionic conductivity of the carbon coating layer.

[0025] The present application adopts the sulfur trioxide sulfonation method to reduce the generation of impurities and prevent the impurities in the additives from affecting the conductive properties of the positive electrode material.

[0026] The preparation method of the present application is beneficial to improving the dispersion performance of carbon nanotubes and organic carbon by sulfonating carbon nanotubes and organic carbon, and preparing an aqueous solution as an additive for the carbon coating layer of lithium iron phosphate or lithium iron manganese phosphate, and mixing it with the lithium iron phosphate precursor. After simple mechanical stirring, a uniformly dispersed mixture can be obtained. After calcination, a carbon-coated lithium iron phosphate positive electrode material with high electronic conductivity and high ionic conductivity can be obtained, which can effectively improve the conductive performance of the positive electrode material. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solutions and advantages of this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit this application.

[0028] It should be noted that when a component is referred to as being "fixed on" or "disposed on" another component, it may be directly on the other component or indirectly on the other component. When a component is referred to as being "connected to" another component, it may be directly or indirectly connected to the other component. The terms "upper", "lower", "left", "right", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of description and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation. Therefore, they cannot be understood as limitations on this application. For ordinary technicians in this field, the specific meanings of the above terms can be understood according to the specific circumstances. The terms "first" and "second" are only used for the purpose of convenience of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features. "Multiple" means two or more, unless otherwise clearly and specifically defined.

[0029] The present invention provides a method for preparing a conductive carbon coating additive for a lithium battery positive electrode material, comprising the following steps:

[0030] Step 1: Using a gas plasma process to modify the surface of carbon nanotubes to obtain modified carbon nanotubes; the modified carbon nanotubes are hydrogenated carbon nanotubes or ammoniated carbon nanotubes;

[0031] Step 2: Using sulfur trioxide sulfonation method, the organic carbon and the modified carbon nanotubes are sulfonated to obtain a sulfonated carbon material;

[0032] Step 3: Mix the sulfonated carbon material and water, sand-mill the mixed solution, and obtain a conductive carbon-coated additive after uniform dispersion.

[0033] Specifically, the embodiment of the present application prepares hydrogenated / ammoniated carbon nanotubes by hydrogenating / ammoniating carbon nanotubes. On the one hand, experiments have found that hydrogenated / ammoniated carbon nanotubes can improve the dispersion effect of carbon nanotubes and shorten the dispersion time of carbon nanotubes. When the carbon nanotubes are subsequently mixed with organic carbon for sulfonation treatment, it is not necessary to grind and disperse the carbon nanotubes for a long time to obtain a uniformly mixed material. The carbon nanotubes after hydrogenation / ammoniation are dispersed with each other, which is more conducive to improving the sulfonation effect and ultimately improving the conductivity of the carbon coating layer of the positive electrode material. On the other hand, the hydrogenated / ammoniated carbon nanotubes increase the amount of hydrogen / ammonia atoms connected to the surface of the carbon nanotubes, so that during the sulfonation treatment, more sulfonic acid groups replace the hydrogen / ammonia atoms on the surface of the carbon nanotubes, thereby improving the degree of sulfonation of the carbon nanotubes. The carbon nanotubes with multiple sulfonic acid groups connected to the surface have better dispersion, which can enable the carbon nanotubes to be uniformly mixed with other components of the positive electrode material and uniformly dispersed in the carbon coating layer, thereby improving the conductivity of the carbon coating layer. The multiple sulfonic acid groups provide more ion conduction paths, which can further improve the ion conductivity of the carbon coating layer.

[0034] The present application adopts the sulfur trioxide sulfonation method to reduce the generation of impurities and prevent the impurities in the additives from affecting the conductive properties of the positive electrode material.

[0035] The preparation method of the present application is beneficial to improving the dispersion performance of carbon nanotubes and organic carbon by sulfonating carbon nanotubes and organic carbon, and preparing an aqueous solution as an additive for the carbon coating layer of lithium iron phosphate or lithium iron manganese phosphate, and mixing it with the lithium iron phosphate precursor. After simple mechanical stirring, a uniformly dispersed mixture can be obtained. After calcination, a carbon-coated lithium iron phosphate positive electrode material with high electronic conductivity and high ionic conductivity can be obtained, which can effectively improve the conductive performance of the positive electrode material.

[0036] In some embodiments of the present application, the specific method of step one is: placing carbon nanotubes in a reaction chamber of a plasma system, introducing reaction gas into the plasma system, controlling the plasma system power to 25-1000W, the gas pressure to 10-150Pa, the reaction time to 20-30min, and the reaction temperature to 20-150°C to obtain modified carbon nanotubes.

[0037] By controlling the above reaction conditions, it is more conducive to the connection of hydrogen / ammonia atoms on the surface of carbon nanotubes, increasing the degree of sulfonation reaction, and thus making the additive of the present invention more conducive to improving the ionic conductivity and electronic conductivity of the positive electrode material. When the plasma power is too high, or the reaction time is too long, or the temperature is too high, the carbon nanotubes will be etched, resulting in a decrease in the conductivity of the carbon nanotubes; when the plasma power or temperature is too low, or the reaction time is too short, only a small number of hydrogen / ammonia atoms can be connected to the surface of the carbon nanotubes, affecting the subsequent sulfonation reaction. As a result, the additive of the present invention has limited effect on the improvement of the ionic conductivity and electronic conductivity of the positive electrode material, and the conductivity is difficult to meet the requirements.

[0038] In some embodiments, the plasma system power may be, but is not limited to, 25 W, 100 W, 200 W, 300 W, 400 W, 500 W, 600 W, 700 W, 800 W, 900 W, or 1000 W. The gas pressure may be, but is not limited to, 10 Pa, 30 Pa, 50 Pa, 70 Pa, 90 Pa, 100 Pa, 120 Pa, or 150 Pa. The reaction time may be, but is not limited to, 20 min, 21 min, 23 min, 25 min, 27 min, or 30 min. The reaction temperature of the plasma process may be, but is not limited to, 20° C., 50° C., 70° C., 100° C., 120° C., or 150° C.

[0039] In some embodiments, the reaction gas is at least one of hydrogen and ammonia.

[0040] In some embodiments, in step 1, the mass ratio of the reactant gas flow rate to the carbon nanotubes is 1-100 sccm / g, specifically, but not limited to, 1 sccm / g, 10 sccm / g, 20 sccm / g, 30 sccm / g, 50 sccm / g, 70 sccm / g, and 100 sccm / g. Controlling the mass ratio of the reactant gas flow rate to the carbon nanotubes is beneficial for improving the hydrogenation / ammoniation of the carbon nanotubes and increasing the number of hydrogen / ammonia atoms attached to the carbon nanotube sidewalls.

[0041] In some embodiments, the carbon nanotubes are single-walled carbon nanotubes or multi-walled carbon nanotubes. The diameter of the carbon nanotubes is 2-50 nm. Specifically, the diameter may be, but is not limited to, 2 nm, 10 nm, 20 nm, 30 nm, 40 nm, or 50 nm. If the diameter of the carbon nanotubes is too small, they are easily etched and fragmented during the hydrogen plasma process, affecting the conductivity of the carbon nanotubes and, in turn, the conductivity of the positive electrode material.

[0042] In some embodiments, the specific method of step 2 is: ball-milling the hydrogenated carbon nanotubes and organic carbon in a mass ratio of 1-2:8-9 to mix them evenly, then introducing a mixed gas containing sulfur trioxide and air, controlling the reaction temperature to 30-60°C, the reaction time to 0.5-1h, and finally washing and filtering the reacted carbon material with water.

[0043] In some embodiments, the ball milling speed of hydrogenated carbon nanotubes is 400-600 r / min, the ball milling medium is zirconium balls with a diameter of 0.3-0.8 mm, and the ball milling time is 20-30 min.

[0044] In some embodiments, the volume ratio of sulfur trioxide to air is 5-6:100.

[0045] In some embodiments, the mass ratio of the mixed gas flow rate to the total mass of the hydrogenated carbon nanotubes and the organic carbon is 50-150 sccm / g.

[0046] In some embodiments, the organic carbon is at least one of alkanes, olefins, aromatic hydrocarbons, polymer resins, asphalt, and tar.

[0047] In some embodiments, in step three, the mass ratio of the sulfonated carbon material to water is 1-5:10.

[0048] In some embodiments, in step three, the grinding medium for sand milling is a zirconium ball with a diameter of 0.7-1.4 mm, the sand milling speed is 600-800 rpm, the sand milling time is 0.5-1 h, the dispersion pressure for homogenization is 650-850 bar, and the homogenization time is 0.5-1 h.

[0049] Some embodiments of the present application also provide a lithium-ion battery positive electrode material, which includes the additive prepared by the above preparation method.

[0050] In the embodiments of the present application, hydrogenated / ammoniated carbon nanotubes are prepared by hydrogenating / ammoniating carbon nanotubes. Experiments have shown that hydrogenated / ammoniated carbon nanotubes can improve the dispersion of carbon nanotubes and shorten the dispersion time of carbon nanotubes. Subsequently, when the carbon nanotubes are mixed with organic carbon for sulfonation, a uniformly mixed material can be obtained without the need for prolonged grinding and dispersion of the carbon nanotubes. Furthermore, the hydrogenated / ammoniated carbon nanotubes are dispersed with each other, which is more conducive to improving the sulfonation effect and ultimately improving the conductivity of the carbon coating layer of the positive electrode material. Furthermore, hydrogenated / ammoniated carbon nanotubes increase the amount of hydrogen / ammonia atoms attached to the surface of the carbon nanotubes. During the sulfonation treatment, more sulfonic acid groups replace hydrogen / ammonia atoms on the surface of the carbon nanotubes, thereby increasing the degree of sulfonation of the carbon nanotubes. Carbon nanotubes with multiple sulfonic acid groups attached to their surfaces have better dispersion, enabling the carbon nanotubes to be uniformly mixed with other components of the positive electrode material and uniformly dispersed in the carbon coating layer, thereby improving the conductivity of the carbon coating layer. Furthermore, the multiple sulfonic acid groups provide more ionic conduction paths, further improving the ionic conductivity of the carbon coating layer.

[0051] The embodiment of the present application adopts the sulfur trioxide sulfonation method to reduce the generation of impurities and prevent the impurities in the additives from affecting the conductive properties of the positive electrode material.

[0052] The preparation method of the embodiment of the present application is beneficial to improving the dispersion performance of carbon nanotubes and organic carbon by sulfonating the carbon nanotubes and organic carbon, and preparing an aqueous solution as an additive for the carbon coating layer of lithium iron phosphate or lithium iron manganese phosphate, and mixing it with the lithium iron phosphate precursor. After simple mechanical stirring, a uniformly dispersed mixture can be obtained. After calcination, a carbon-coated lithium iron phosphate positive electrode material with high electronic conductivity and high ionic conductivity can be obtained, which can effectively improve the conductive performance of the positive electrode material.

[0053] The following describes the details in conjunction with specific embodiments.

[0054] Example 1

[0055] A method for preparing a positive electrode material for a lithium battery with high ionic and electronic conductivity, comprising the following steps:

[0056] Step 1: Prepare hydrogenated carbon nanotubes using a hydrogen plasma process: Place carbon nanotubes in a reaction chamber of a plasma system, introduce hydrogen into the plasma system, control the plasma system power to 25 W, the gas pressure to 10 Pa, the reaction time to 30 min, and the reaction temperature to 150°C to obtain hydrogenated carbon nanotubes; wherein the mass ratio of the hydrogen flow rate to the carbon nanotubes is 100 sccm / g; and the diameter of the carbon nanotubes is 2 nm.

[0057] Step 2: The hydrogenated carbon nanotubes and polyethylene are evenly mixed by ball milling in a mass ratio of 3:7, the ball milling speed is 400r / min, the ball milling medium is a zirconium ball with a diameter of 0.3mm, the ball milling number is 1, and then a mixed gas containing sulfur trioxide and air is introduced for sulfonation treatment. The volume ratio of sulfur trioxide to air is 5:100, and the ventilation volume of the mixed gas and the total mass ratio of hydrogenated carbon nanotubes and organic carbon are 50sccm / g. The reaction temperature is controlled at 30°C and the reaction time is 1h. Finally, the reacted carbon material is washed and filtered to obtain a sulfonated carbon material.

[0058] Step 3: Mix the sulfonated carbon material and water in a mass ratio of 1:10, and sand-mill the mixed solution in sequence. The grinding medium for the sand-milling treatment is a zirconium ball with a diameter of 0.7 mm, the sand-milling speed is 600 rpm, and the sand-milling time is 1 h. After uniform dispersion, a conductive carbon-coated additive is obtained;

[0059] Step 4: Mix the lithium iron phosphate precursor, glucose and conductive carbon coating additive in a mass ratio of 100:10:0.1, sinter for 3 hours under an argon inert atmosphere at a calcination temperature of 700°C to obtain a lithium battery positive electrode material.

[0060] Example 2

[0061] A method for preparing a positive electrode material for a lithium battery with high ionic and electronic conductivity, comprising the following steps:

[0062] Step 1: Prepare hydrogenated carbon nanotubes using an ammonia plasma process: Place carbon nanotubes in a reaction chamber of a plasma system, introduce ammonia into the plasma system, control the plasma system power to 500 W, the gas pressure to 80 Pa, the reaction time to 25 min, and the reaction temperature to 85°C to obtain ammoniated carbon nanotubes; the mass ratio of the ammonia flow rate to the carbon nanotubes is 50 sccm / g; and the diameter of the carbon nanotubes is 5 nm.

[0063] Step 2: Ball-mill the ammoniated carbon nanotubes and asphalt in a mass ratio of 3.5:6.5 to mix them evenly. The ball milling speed is 500 r / min. The ball milling medium is a zirconium ball with a diameter of 0.5 mm. The ball milling number is 1. Then, a mixed gas containing sulfur trioxide and air is introduced for sulfonation treatment. The volume ratio of sulfur trioxide to air is 5.6:100. The ventilation volume of the mixed gas and the total mass ratio of the ammoniated carbon nanotubes and organic carbon is 100 sccm / g. The reaction temperature is controlled at 45°C and the reaction time is 0.75 h. Finally, the reacted carbon material is washed and filtered to obtain a sulfonated carbon material.

[0064] Step 3: Mix the sulfonated carbon material and water in a mass ratio of 1:9, and sand-mill the mixed solution. The grinding medium for the sand-milling treatment is a zirconium ball with a diameter of 1.0 mm. The sand-milling speed is 700 rpm, and the sand-milling time is 0.75 h. After uniform dispersion, a conductive carbon-coated additive is obtained;

[0065] Step 4: Sand-mill the lithium iron phosphate precursor, asphalt and conductive carbon coating additive in a mass ratio of 100:10:0.3. The grinding medium for the sand-milling treatment is a zirconium ball with a diameter of 0.3 mm. The sand-milling speed is 2000 rpm and the sand-milling time is 4 hours. After spray drying, sintering is carried out in an argon inert atmosphere for 3.5 hours at a calcination temperature of 725°C to obtain a high-performance fast-charging and discharging lithium battery positive electrode material.

[0066] Example 3

[0067] A method for preparing a high ionic and electronic conductive lithium battery positive electrode material. The difference between Example 3 and Example 2 is that in step 4 of Example 3, the lithium iron phosphate precursor, asphalt and conductive carbon coating additive are mixed and sand-milled in a mass ratio of 100:10:3. The other step conditions of Example 3 are the same as those of Example 2.

[0068] Comparative Example 1

[0069] A method for preparing a positive electrode material for a lithium battery comprises sand grinding a lithium iron phosphate precursor and asphalt in a mass ratio of 100:10, using zirconium balls with a diameter of 0.3 mm as a grinding medium, a sand grinding speed of 2000 rpm, and a sand grinding time of 4 hours. After spray drying, the mixture is sintered in an argon inert atmosphere for 3.5 hours at a calcination temperature of 725°C to obtain a positive electrode material for a lithium battery.

[0070] Comparative Example 2

[0071] A method for preparing a positive electrode material for a lithium battery. The difference between Comparative Example 2 and Example 2 is that the preparation method of Comparative Example 2 does not perform gas plasma treatment on carbon nanotubes. The other preparation steps and conditions of Comparative Example 2 are the same as those of Example 2.

[0072] Performance Testing

[0073] Experimental method: The positive electrode materials of Examples 1-3 and Comparative Examples 1-2 were added to the organic solvent N-methylpyrrolidone with acetylene black and a binder at a mass ratio of 8:1:1, stirred thoroughly and evenly, and then coated on aluminum foil. After drying, lithium-ion batteries were made with a graphite negative electrode. The gram capacity, rate performance, and low-temperature tests were performed. The test results are shown in the following table.

[0074] Table 1. Test results of positive electrode sheet resistivity

[0075] Table 2 Battery charge and discharge capacity test results

[0076] Table 3 Battery performance test results

[0077] The above are merely optional embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present application should be included within the scope of the claims of the present application.

Claims

1. A method for preparing a conductive carbon-coated additive for a lithium battery positive electrode material, characterized in that: The method comprises the following preparation steps: Step 1: using a gas plasma process to modify the surface of carbon nanotubes to obtain modified carbon nanotubes; the modified carbon nanotubes are hydrogenated carbon nanotubes or ammoniated carbon nanotubes; Step 2: Using sulfur trioxide sulfonation method, sulfonating the organic carbon and the modified carbon nanotubes to obtain a sulfonated carbon material; Step 3: Mix the sulfonated carbon material and water, sand-mill the mixed solution, and obtain a conductive carbon-coated additive after uniform dispersion.

2. The method for preparing the conductive carbon coated additive for lithium battery positive electrode material according to claim 1, characterized in that: The specific method of step one is: placing carbon nanotubes in the reaction chamber of the plasma system, introducing reaction gas into the plasma system, controlling the plasma system power to 25-1000W, the gas pressure to 10-150Pa, the reaction time to 20-30min, the reaction temperature to 20-150°C, and obtaining modified carbon nanotubes.

3. The method for preparing the conductive carbon coated additive for lithium battery positive electrode material according to claim 2, characterized in that: The reaction gas is at least one of hydrogen and ammonia.

4. The method for preparing the conductive carbon coated additive for lithium battery positive electrode material according to claim 2, characterized in that: The mass ratio of the ventilation volume of the reaction gas to the carbon nanotubes is 1-100 sccm / g.

5. The method for preparing the conductive carbon coated additive for lithium battery positive electrode material according to claim 1, characterized in that: The carbon nanotubes include at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

6. The method for preparing the conductive carbon coated additive for lithium battery positive electrode material according to claim 5, characterized in that: The diameter of the carbon nanotubes ranges from 2 to 50 nm.

7. The method for preparing the conductive carbon-coated additive for lithium battery positive electrode material according to claim 1, characterized in that: The specific method of step 2 is: the modified carbon nanotubes and organic carbon are evenly mixed by ball milling at a mass ratio of 1-2:8-9, and then introduced into a mixed gas containing sulfur trioxide and air, the reaction temperature is controlled to be 30-60°C, the reaction time is 0.5-1h, and finally the reacted carbon material is washed and filtered.

8. The method for preparing the conductive carbon-coated additive for lithium battery positive electrode material according to claim 7, characterized in that: In step 2, the ball milling speed is 400-600 r / min, the ball milling medium is a zirconium ball with a diameter of 0.3-0.8 mm, and the ball milling time is 20-30 min.

9. The method for preparing the conductive carbon-coated additive for lithium battery positive electrode material according to claim 8, characterized in that: The volume ratio of the sulfur trioxide to air is 5-6:

100.

10. The method for preparing the conductive carbon coated additive for lithium battery positive electrode material according to claim 7, characterized in that: The ratio of the ventilation volume of the mixed gas to the total mass of the modified carbon nanotubes and the organic carbon is 50-150 sccm / g.

11. The method for preparing the conductive carbon coated additive for lithium battery positive electrode material according to claim 1, characterized in that: The organic carbon is at least one of alkanes, olefins, aromatic hydrocarbons, polymer resins, asphalt, and tar.

12. The method for preparing the conductive carbon coated additive for lithium battery positive electrode material according to claim 1, characterized in that: In step three, the mass ratio of the sulfonated carbon material to water is 1:9-10.

13. The method for preparing the conductive carbon coated additive for lithium battery positive electrode material according to claim 1, characterized in that: In step three, the sand milling conditions include: the grinding medium includes zirconium balls with a diameter range of 0.7-1.4 mm, the sand milling speed is 600-800 rpm, and the sand milling time is 0.5-1 h.

14. A positive electrode material for a lithium ion battery, characterized in that: The additive comprises an additive prepared by the preparation method according to any one of claims 1 to 13.

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