A composite conductive agent for lithium ion batteries, a composite conductive agent slurry, and a method for preparing the same

Abstract

The present application belongs to the technical field of lithium ion battery electrode material, and particularly relates to a composite conductive agent for lithium ion battery, a composite conductive agent slurry and a preparation method thereof. The present application is prepared by compounding various conductive agents in the form of a slurry, thereby comprehensively exerting the advantages of different conductive agents, reducing the contact resistance of the electrode, accelerating electron transfer, improving the lithium ion migration rate, and thus improving the charge-discharge efficiency of the electrode. The present application also performs pitch coating treatment on the conductive agent (whisker carbon tube) for lithium ion battery negative electrode material, coats a layer of pitch on the surface of the whisker carbon tube through physical coating, and then performs high-temperature heat treatment, thereby improving the dispersibility of the whisker carbon tube in the slurry, achieving better conductivity, reducing the contact resistance of the electrode material, improving the electron migration rate, effectively improving the lithium ion migration rate, and thus improving the high-rate charge-discharge performance of the negative electrode material.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery electrode material technology, specifically relating to a composite conductive agent for lithium-ion batteries, a composite conductive agent slurry, and a method for preparing the same. Background Technology

[0002] Lithium-ion batteries are one of the commonly used energy storage devices. Because the conductivity of the active materials in existing lithium-ion batteries is insufficient to meet the electron migration rate requirements, conductive agents need to be added to improve this rate. These conductive agents can collect microcurrents between active materials and between the active materials and the current collector, thereby reducing electrode contact resistance and improving the fast charge / discharge performance of lithium-ion batteries.

[0003] Currently, most commercially available lithium-ion batteries use graphite-based carbon materials as the negative electrode material. However, due to the volume expansion and contraction of graphite-based carbon materials during charge and discharge, the gaps between the materials increase after several cycles. Particulate carbon black, acetylene black, or fibrous conductive agents can effectively fill the gaps between carbon negative electrode materials, maintaining the stability of the electrode during cycling.

[0004] Commonly used conductive agents for lithium-ion batteries can be categorized into conductive carbon black, conductive graphite, vapor-grown carbon fibers, carbon nanotubes, and graphene. Carbon black and conductive graphite are traditional conductive agents, forming a conductive network through point-to-point contact between particles. Vapor-grown carbon fibers, carbon nanotubes, and graphene are advanced conductive agents. Carbon fibers and carbon nanotubes are one-dimensional materials that exhibit point-to-line contact with the active material, providing both short-range and long-range conductivity. Graphene, on the other hand, presents point-to-surface contact with the active material, resulting in better conductivity and allowing for a reduction in the proportion of conductive agents required.

[0005] Carbon whisker nanotubes (also known as carbon whisker nanotubes, a common abbreviation used in the industry for ease of explanation) are similar to carbon fibers, both being one-dimensional materials. However, unlike carbon fibers, carbon whisker nanotubes exhibit a vertically stacked, hollow structure, allowing for better electrolyte wetting of the electrodes and facilitating rapid lithium-ion insertion, which is beneficial for high-rate charge and discharge. Furthermore, using carbon nanotubes as a conductive agent creates a more complete conductive network, resulting in excellent electrical contact with the active material. This improves material capacity, rate performance, battery cycle life, and reduces battery interface impedance.

[0006] Carbon nanotubes possess high mechanical strength, and the conductive network they form exhibits a degree of toughness. This allows them to suppress the expansion of active materials during battery charging, discharging, and cycling, and to maintain lithium-ion conduction pathways within the active materials, ensuring uninterrupted electron and ion transport and improving cycle life and battery safety. Furthermore, their high electrical and thermal conductivity can enhance the thermal conductivity of both positive and negative electrodes, facilitating heat dissipation during high-current charging and discharging.

[0007] Each of the aforementioned conductive agents has its advantages, but relying on a single conductive agent is insufficient to meet the actual requirements of lithium-ion batteries. By mixing different conductive agents, their advantages can be combined, further improving the conductivity of lithium-ion batteries. Therefore, it is necessary to develop novel composite conductive agents. Summary of the Invention

[0008] The purpose of this invention is to propose a carbon whisker / SWCNTs / Super-P composite conductive agent, a composite conductive agent slurry, and a method for preparing the same for power lithium-ion batteries. By combining multiple conductive agents in the form of a slurry, the advantages of different conductive agents are comprehensively utilized, thereby reducing the contact resistance of the electrode, accelerating electron transfer, and increasing the lithium-ion migration rate, thus improving the charge and discharge efficiency of the electrode.

[0009] Furthermore, the application of the composite conductive agent or composite conductive agent slurry in the preparation of lithium-ion batteries is also provided.

[0010] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution: A carbon nanotube / SWCNTs / Super-P composite conductive agent is composed of carbon nanotubes, single-walled carbon nanotubes (SWCNTs), and carbon black (Super-P); the mass percentage of carbon nanotubes is 0.01%~40%; the mass percentage of carbon black (Super-P) is 0.01%~70%, and the balance is single-walled carbon nanotubes (SWCNTs).

[0011] Specifically, the carbon whisker tubes in the composite conductive agent are a novel type of carbon nanotube, also known as vapor-grown carbon fiber. The carbon whisker tubes have a linear structure, do not entangle with each other, and have extremely high crystallinity and purity. This novel carbon whisker tube has excellent electrical conductivity, thermal conductivity, corrosion resistance, and high-temperature stability.

[0012] Specifically, the single-walled carbon nanotubes (SWCNTs) in the composite conductive agent are entirely composed of carbon atoms, and their geometry can be considered as being formed by rolling up a single layer of graphene. As a novel conductive agent, SWCNTs have characteristics such as high light transmittance, low resistance, and high carrier mobility. However, SWCNTs themselves have poor dispersibility. The dispersibility of SWCNTs in the matrix can be improved by adding surfactants, thereby enhancing their electrical and mechanical properties. Furthermore, the surfactant is selected from one of sodium carboxymethyl cellulose (CMC), sodium dodecyl sulfate (SDS), polyacrylic acid (PAA), hexadecyltrimethylammonium bromide (HTAB), polyethyleneimine (PEI), sodium dodecylbenzene sulfonate (SDBS), and ethanol.

[0013] Specifically, Super-P in the composite conductive agent is a conductive carbon black prepared by furnace method (MMM method). It is made by agglomerating primary particles (primary structure) with a diameter of about 40 nm into primary aggregates (secondary structure) with a diameter of 150-200 nm, and then processing them through soft agglomeration and artificial compression, etc. The whole is in the form of grape-like chains.

[0014] Furthermore, based on a general inventive concept, the present invention also provides a composite conductive agent slurry, comprising the above-mentioned carbon nanotube / SWCNTs / Super-P composite conductive agent and a solvent; the percentage content of the composite conductive agent in the composite conductive agent slurry is ≤10%.

[0015] Preferably, the percentage content of the composite conductive agent in the composite conductive agent slurry is 5%.

[0016] Preferably, the solvent is selected from deionized water, ethanol, and N-methylpyrrolidone (NMP).

[0017] Furthermore, based on a general inventive concept, the present invention also provides a method for preparing a carbon whisker / SWCNTs / Super-P composite conductive agent slurry, comprising the following steps: (1) Weigh a certain amount of carbon whisker tubes, a certain amount of carbon black (Super-P), and a certain amount of single-walled carbon nanotubes (SWCNTs), place the three in a container, and obtain composite conductive agent powder; (2) Add solvent to the composite conductive agent powder obtained in step (1), ultrasonically disperse it at a power of 80~100 W, and then magnetically stir it at a speed of 300~400 r / min to disperse the carbon whisker, carbon black Super-P and single-walled carbon nanotubes SWCNTs evenly to obtain the composite conductive agent slurry.

[0018] Preferably, the carbon nanotubes are carbon nanotubes without surface-modified hydroxyl groups (AH) or carbon nanotubes with surface-modified hydroxyl groups (BH).

[0019] Preferably, the solvent is selected from deionized water, ethanol, and NMP.

[0020] Preferably, the mass ratio of composite conductive agent powder to solvent in step (2) is (1~5):(30~50), and more preferably 1:6, 1:10, 1:30, or 1:50.

[0021] Preferably, in the composite conductive agent slurry obtained in step (2), the mass ratio of carbon nanotubes / SWCNTs / Super-P is (2~3):7:(0.05~0.1).

[0022] Preferably, in step (2), the specific method steps are as follows: the mixed composite conductive agent powder and solvent are ultrasonically dispersed at a power of 80~100 W for 8~12 min, and then polytetrafluoroethylene magnets are placed in the container and magnetically stirred at a speed of 300~400 r / min for 8~12 h to make the carbon whisker, carbon black (Super-P) and single-walled carbon nanotubes (SWCNTs) dispersed evenly.

[0023] Furthermore, based on a general inventive concept, the present invention also provides the application of the composite conductive agent or the composite conductive agent slurry in the preparation of lithium-ion batteries.

[0024] Furthermore, based on a general inventive concept, the present invention also provides a method for preparing a lithium-ion battery using the composite conductive agent or the composite conductive agent slurry, comprising the following steps: a) Preparation of electrode sheet: The active material, composite conductive agent slurry and binder are mixed to form an electrode slurry, which is then uniformly coated on copper foil and dried at 60~80 ℃ for 8~12 h to form an electrode sheet; b) Button cell assembly: Using lithium metal sheets as the counter electrode, assemble them into button cells. The battery model is a CR2032 type button cell.

[0025] Specifically, the active material mentioned in step a) is graphite, carbon-coated silicon suboxide, or a mixture of both.

[0026] Specifically, the adhesive in step a) is a mixture of carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) in a mass ratio of 1:(1~2), preferably 1:1.

[0027] Specifically, the weight ratio of the active material, composite conductive agent slurry, and binder in step a) is (18~20):(1~2):1, preferably 90:5:5.

[0028] Specifically, the loading of active material in the electrode sheet prepared in step a) is no greater than 2 mg cm⁻¹. -2 .

[0029] Specifically, in the battery assembled in step b), the separator type is Celgard2500, and the electrolyte is 1M LiPF6 in EC:DEC=1:1 vol% with 5% FEC.

[0030] Furthermore, the present invention also provides a method for preparing a modified conductive agent for a lithium-ion battery negative electrode, wherein the conductive agent is a modified carbon whisker, comprising the following steps: 1) Mix carbon nanotubes and pitch, add ethanol, and use mechanical stirring to disperse the carbon nanotubes and pitch evenly to obtain a mixture; 2) Dry the mixture from step 1) to obtain a uniformly dispersed mixture of carbon nanotubes and pitch; 3) Place the mixture obtained in step 2) in a tube furnace, heat it under an inert atmosphere to carbonize it, and finally let it cool naturally to room temperature to obtain the modified conductive agent.

[0031] Specifically, in step 1), the carbon whisker is a carbon whisker without surface-modified hydroxyl groups (AH) or a carbon whisker with surface-modified hydroxyl groups (BH).

[0032] Specifically, in step 1), the mass ratio of carbon nanotubes to pitch is (2~9):1, preferably (7~9):(1~3), and more preferably 7:3 or 9:1.

[0033] Specifically, in step 1), the mass ratio of ethanol to carbon whisker is (15~20):1, preferably 20:1.

[0034] Specifically, in step 3), the inert atmosphere is formed by argon or nitrogen; during the ventilation process, the gas flow rate is 0.1~0.2 L / min. -1 .

[0035] Specifically, in step 3), during carbonization, the temperature is first raised to 300~320℃ and held for 1~2 hours in an inert atmosphere, and then held at 800~1000℃ for 1~2 hours for carbonization.

[0036] Preferably, the carbonization temperature is 800℃, 900℃ or 1000℃.

[0037] Furthermore, based on a general inventive concept, the present invention also provides the application of the modified conductive agent for the negative electrode of the lithium-ion battery in the preparation of lithium-ion batteries.

[0038] Specifically, the conductive agent is modified carbon whisker tubes coated with asphalt.

[0039] Compared with the prior art, the advantages of the present invention are: In this invention, carbon nanotubes, acting as a conductive agent, possess a long, linear carbon structure that is easily dispersed. They exhibit high strength, high electrical conductivity, and high thermal conductivity, and also possess extremely high electrolyte adsorption capacity, enabling them to significantly improve the rate capability and cycle performance of lithium-ion batteries. The conductive agent Super-P ensures optimal contact between the active oxide particles and the current collector, as well as better contact between the internal particles, controlling the porosity of the lithium battery negative electrode and allowing the electrolyte to ideally contact the oxide particles.

[0040] In lithium-ion battery applications, single-walled carbon nanotubes, when used as conductive agents, not only effectively connect more active materials due to their unique network structure, but also significantly reduce impedance due to their excellent conductivity. Furthermore, carbon nanotubes with a larger aspect ratio have a larger specific surface area.

[0041] Single-walled carbon nanotubes (SUVs) offer several advantages as conductive agents in lithium-ion batteries: 1. As a one-dimensional tubular structure, SUVs allow for the formation of conjugated carbon rings, enabling the creation of a conductive network that fully connects active materials with a small amount, thus improving battery capacity and cycle stability. 2. The double-layer effect of SUVs enhances the battery's high-rate charge-discharge performance. 3. The excellent thermal conductivity of SUVs aids in heat dissipation and reduces internal polarization, thereby improving high- and low-temperature performance, safety, and extending battery life. 4. The high aspect ratio of SUVs means that the amount required to achieve the same percolation threshold is less than that of other conductive agents. 5. The lithium storage capacity of SUVs is significantly greater than that of traditional carbon materials such as natural graphite, artificial graphite, and amorphous carbon. Therefore, using SUVs as a conductive agent in lithium-ion batteries can substantially improve battery capacity and cycle life.

[0042] The unique structure of carbon nanotubes enables them to conduct electricity over long distances. The one-dimensional tubular structure of carbon nanotubes has a large aspect ratio and a large specific surface area. The unique structure allows even a small number of carbon nanotubes to form a conductive network that fully connects the active material. The grape-like chain-like Super-P fills the gaps between carbon nanotubes and single-walled carbon nanotubes, and the three combine to form a unique three-dimensional conductive network.

[0043] This invention generates a novel ternary hybrid conductive agent by mixing three different conductive agents in a certain proportion. The mixing method is simple and highly practical. The generated novel ternary hybrid conductive agent has good dispersibility, avoiding the stacking and agglomeration of carbon nanotubes, SWCNTs, and Super-P, forming a conductive network with good conductivity. This improves the contact between the conductive agent and the active material, and forms a smoother electron conduction path, thereby increasing electronic conductivity, reducing electrode contact resistance, accelerating electron movement speed, increasing lithium ion migration rate, and thus improving the charge and discharge efficiency of the negative electrode.

[0044] In addition, the present invention also performs asphalt coating treatment on the conductive agent (carbon whisker) of the lithium-ion battery negative electrode material. By means of physical coating, a layer of asphalt is coated on the surface of the carbon whisker and then subjected to high temperature heat treatment, which improves its dispersibility in the slurry, resulting in better conductivity, reducing the contact resistance of the electrode material, increasing the electron migration rate, effectively improving the lithium-ion migration rate, and thus improving the high-rate charge and discharge performance of the negative electrode material. Attached Figure Description

[0045] Figure 1The following are the rate constant current charge-discharge diagrams of the negative electrode material when Examples 1, 2, and Comparative Examples 1, 2, and 3 are used as conductive agents; Figure 2 The following are the rate constant current charge-discharge diagrams of the negative electrode material when Examples 3, 4, and Comparative Examples 4, 5, and 6 are used as conductive agents; Figure 3 SEM image of carbon nanotube AH; Figure 4 SEM image of carbon nanotube BH; Figure 5 The rate constant current charge-discharge diagram of the negative electrode material when the target product of Example 5 (modified carbon whisker AH and pitch) and the original sample (carbon whisker AH without surface-modified hydroxyl groups) are used as conductive agents. Figure 6 SEM image of the target product (modified carbon whisker) in Example 5; Figure 7 SEM image of the target product (modified carbon whisker) in Example 7; Figure 8 The Raman spectra of the target products (modified carbon whisker AH and pitch) in Examples 5, 6, and 7 are compared with the original sample (carbon whisker AH without surface-modified hydroxyl groups). Detailed Implementation

[0046] The following examples, in conjunction with the accompanying drawings, further illustrate the present invention. These embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and processes; however, the scope of protection of the present invention is not limited to the following embodiments.

[0047] Unless otherwise specified, the experimental methods in the following examples are generally performed under conventional conditions, and the raw materials and reagents used are all commercially available products unless otherwise specified.

[0048] Example 1 A method for preparing a carbon nanotube / SWCNTs / Super-P composite conductive agent slurry, the specific steps of which are as follows: (1) Weigh a certain amount of surface-modified hydroxyl-modified carbon nanotubes (i.e., BH carbon nanotubes, which are prepared by referring to carbon nanotubes in the patent document (CN 101027434 A Preparation method and apparatus for vapor-grown carbon fibers), a certain amount of carbon black (Super-P, Shenzhen Kejing Zhida Technology Co., Ltd., CAS1333-86-4), and a certain amount of single-walled carbon nanotubes (SWCNTs, OCSIAL, TUBALL™), and place the three in a container in sequence to obtain composite conductive agent powder; (2) In step (1), solvent (deionized water) is added to the composite conductive agent powder. The mass ratio of composite conductive agent powder to solvent is 1:10. The mixture is ultrasonically dispersed at 100 W for 8 min. Then, polytetrafluoroethylene magnets are placed in a container and stirred at 400 r / min for 12 h to make the carbon nanotubes, carbon black (Super-P) and single-walled carbon nanotubes (SWCNTs) dispersed evenly, so as to obtain a composite conductive agent slurry with a mass ratio of carbon nanotubes / SWCNTs / Super-P of 2.95:7:0.05.

[0049] The specific steps for performance testing are as follows: a) Preparation of electrode sheet: The active material carbon-coated silicon sub-substrate (Anhui Keda New Material Co., Ltd., DVC-55), the composite conductive agent slurry prepared in step (2), and the binder (CMC+SBR, mass ratio of 1:1) are mixed in a weight ratio of 90:5:5 to prepare an electrode slurry (for specific preparation methods and processes, please refer to patent literature (CN 114447271 A Preparation method of electrode sheet and electrode sheet and lithium-ion battery)). The mixture is stirred on a stirrer for 10 h to further mix it. Then it is evenly coated on copper foil and dried in a vacuum oven at 80 ℃ for 12 h to prepare an electrode sheet, wherein the loading of the active material is not greater than 2 mg / cm³. -2 .

[0050] b) Button cell assembly and rate performance testing (test method see patent document (CN115692686A A novel lithium battery negative electrode material and its preparation method and application)): Using a CR2032 type button cell model, with a lithium metal sheet as the counter electrode, a Celgard 2500 separator, and a 1M LiPF6 in EC:DEC=1:1 vol% with 5% FEC, a button cell was assembled. Its rate performance was tested at room temperature using a constant current charge-discharge method. The test voltage range was 2.0V~0.1V, and the test currents, expressed as rates, were 0.1 C, 0.2 C, 0.3 C, 0.5 C, 1.0 C, and 2 C. The test results are as follows: Figure 1 As shown, the composite conductive agent in Example 1 exhibits excellent performance in improving the rate performance of lithium-ion batteries, with a discharge specific capacity of up to 1750 mAh g at 0.1 C. -1 The discharge specific capacity at 1.0 C is 900 mAh g. -1 The discharge specific capacity at 2.0 C is 600 mAh g. -1 Test results show that the composite conductive agent in Example 1 is superior to the carbon nanotube conductive agent (Comparative Example 1), SWCNTs conductive agent (Comparative Example 2), and Super-P conductive agent (Comparative Example 3) in improving the rate performance of lithium-ion batteries.

[0051] Example 2 Example 2 provides a method for preparing a carbon nanotube / SWCNTs / Super-P composite conductive agent slurry. The difference between Example 2 and Example 1 is that by adjusting the amount of each raw material in step (1), the mass ratio of carbon nanotubes / SWCNTs / Super-P in the prepared composite conductive agent slurry is 2.9:7:0.1. The performance testing method of Example 2 is the same as that of Example 1.

[0052] The test results are as follows: Figure 1 As shown, the composite conductive agent with a mass ratio of carbon nanotubes / SWCNTs / Super-P of 2.9:7:0.1 exhibits excellent performance in improving the rate performance of lithium-ion batteries, with the lithium-ion battery achieving a discharge specific capacity of up to 1750 mAh g⁻¹ at 0.1 C. -1 The discharge specific capacity at 1.0 C is 950 mAh g. -1 The discharge specific capacity at 2.0 C is 600 mAh g. -1 .

[0053] Example 3 Example 3 provides a method for preparing a carbon nanotube / SWCNTs / Super-P composite conductive agent slurry. The difference between Example 3 and Example 1 is that the raw materials used to prepare the electrode sheet are different during performance testing. The specific steps are as follows: a) Electrode sheet preparation: Active materials (graphite and carbon-coated silicon suboxide in a mass ratio of 97:3), composite conductive agent slurry, and binder (CMC+SBR, mass ratio of 1:1) are mixed in a weight ratio of 90:5:5 to prepare an electrode slurry (for specific preparation methods and processes, please refer to patent literature (CN 114447271 A Preparation method of electrode sheet and electrode sheet and lithium-ion battery)). The slurry is then stirred on a stirrer for 10 h to further mix it. The mixture is then uniformly coated onto copper foil and dried in a vacuum oven at 80 ℃ for 12 h to prepare the electrode sheet. The loading of the active material is no more than 2 mg / cm³. -2 .

[0054] b) Button cell assembly and rate performance testing (test method is described in patent document CN115692686A A novel lithium battery anode material and its preparation method and application): Using a CR2032 type button cell model, with a lithium metal sheet as the counter electrode, a Celgard 2500 separator, and a 1M LiPF6 in EC:DEC=1:1 vol% electrolyte with 5% FEC, a button cell was assembled. Its rate performance was tested at room temperature using a constant current charge-discharge method. The test voltage range was 2.0V to 0.1V, and the test currents, expressed as rates, were 0.1 C, 0.2 C, 0.3 C, 0.5 C, 1.0 C, and 2 C.

[0055] The test results are as follows: Figure 2 As shown, the composite conductive agent in Example 3 exhibits excellent performance in improving the rate performance of lithium-ion batteries, with a discharge specific capacity of up to 400 mAh g⁻¹ at 0.1 C. -1 The discharge specific capacity at 1.0 C is 320 mAh g. -1 The discharge specific capacity at 2.0 C is 235 mAh g. -1 The composite conductive agent in Example 3 is superior to the whisker carbon nanotube conductive agent (Comparative Example 4), SWCNTs conductive agent (Comparative Example 5), and Super-P conductive agent (Comparative Example 6) with the same active material in improving the rate performance of lithium-ion batteries.

[0056] Example 4 Example 4 provides a method for preparing a carbon nanotube / SWCNTs / Super-P composite conductive agent slurry. The difference between Example 4 and Example 2 is that the performance test method is the same as that in Example 3.

[0057] The test results are as follows: Figure 2 As shown, the composite conductive agent in Example 4 exhibits excellent performance in improving the rate performance of lithium-ion batteries, with a discharge specific capacity of up to 370 mAh g⁻¹ at 0.1 C. -1 The discharge specific capacity at 1.0 C is 310 mAh g. -1 The discharge specific capacity at 2.0 C is 235 mAh g. -1 .

[0058] Comparative Example 1 Comparative Example 1 provides a method for preparing a carbon nanotube conductive agent slurry, the specific steps of which are as follows: A certain amount of surface-modified hydroxyl-coated carbon nanotubes (i.e., BH carbon nanotubes, which are prepared by referring to the carbon nanotubes in the patent document (CN101027434A Preparation method and apparatus for vapor-grown carbon fibers), and the inventors further modified them with hydroxyl to obtain surface-modified hydroxyl-coated carbon nanotubes with a diameter of 150 nm, the material being from Henan Kelaiwei Nanocarbon Materials Co., Ltd.) were placed in a container to obtain conductive agent powder; a solvent (deionized water) was added to the conductive agent powder, the mass ratio of the conductive agent powder to the solvent being 1:50, and the mixture was ultrasonically dispersed at a power of 100 W for 8 min. Then, a polytetrafluoroethylene magnet was placed in the container and stirred at a speed of 400 r / min for 12 h to obtain a carbon nanotube conductive agent slurry.

[0059] The performance testing method for Comparative Example 1 is the same as that for Example 1. The test results are as follows: Figure 1 As shown, the lithium-ion battery has a discharge specific capacity as high as 1200 mAh g at 0.1 C. -1 The discharge specific capacity at 1.0 C is 65 mAh g. -1 The discharge specific capacity at 2.0 C is 37 mAh g. -1 .

[0060] Comparative Example 2 Comparative Example 2 provides a method for preparing a single-walled carbon nanotube (SWCNT) conductive agent slurry, the specific steps of which are as follows: A certain amount of single-walled carbon nanotubes (SWCNTs) were weighed and placed in a container to obtain conductive agent powder. Solvent (deionized water) was added to the conductive agent powder, with a mass ratio of conductive agent powder to solvent of 1:30. The mixture was ultrasonically dispersed at a power of 80~100 W for 8 min~12 min. Then, a polytetrafluoroethylene magnet was placed in the container and stirred at a speed of 300~400 r / min for 8~12 h to obtain a whisker carbon nanotube conductive agent slurry.

[0061] The performance testing method for Comparative Example 2 is the same as that for Example 1. The test results are as follows: Figure 1 As shown, the lithium-ion battery has a discharge specific capacity as high as 1350 mAh g at 0.1 C. -1 The discharge specific capacity at 1.0 C is 162 mAh g. -1 The discharge specific capacity at 2.0 C is 67 mAh g. -1 .

[0062] Comparative Example 3 Comparative Example 3 provides a method for preparing a carbon black (Super-P) conductive agent slurry, the specific steps of which are as follows: Weigh a certain amount of carbon black (Super-P) and place it in a container to obtain conductive agent powder; add solvent (deionized water) to the conductive agent powder, with a mass ratio of conductive agent powder to solvent of 1:50, and ultrasonically disperse at a power of 80~100 W for 8 min~12 min. Then, place a polytetrafluoroethylene magnet in the container and stir at a speed of 300~400 r / min for 8~12 h to obtain a whisker carbon nanotube conductive agent slurry.

[0063] The performance testing method for Comparative Example 3 is the same as that for Example 1. The test results are as follows: Figure 1 As shown, the lithium-ion battery has a discharge specific capacity as high as 800 mAh g at 0.1 C. -1 The discharge specific capacity at 1.0 C is 8 mAh g. -1 The discharge specific capacity at 2.0 C is 3 mAh g. -1 .

[0064] Comparative Example 4 Comparative Example 4 provides a method for preparing a conductive agent slurry for carbon nanotubes. The preparation method of Comparative Example 4 is the same as that of Comparative Example 1, and the testing method of Comparative Example 4 is the same as that of Example 3. The test results are as follows: Figure 2 As shown, the lithium-ion battery has a discharge specific capacity as high as 380 mAh g⁻¹ at 0.1 C. -1 The discharge specific capacity at 1.0 C is 292 mAh g. -1 The discharge specific capacity at 2.0 C is 195 mAh g. -1 .

[0065] Comparative Example 5 Comparative Example 5 provides a method for preparing a single-walled carbon nanotube (SWCNT) conductive agent slurry. The preparation method of Comparative Example 5 is the same as that of Comparative Example 2, and the testing method of Comparative Example 5 is the same as that of Example 3. The test results are as follows: Figure 2 As shown, the lithium-ion battery has a discharge specific capacity as high as 388 mAh g⁻¹ at 0.1C. -1 The discharge specific capacity at 1.0 C is 220 mAh g. -1The discharge specific capacity at 2.0 C is 116 mAh g. -1 .

[0066] Comparative Example 6 Comparative Example 6 provides a method for preparing a carbon black (Super-P) conductive agent slurry. The preparation method of Comparative Example 6 is the same as that of Comparative Example 3, and the testing method of Comparative Example 6 is the same as that of Example 3. The test results are as follows: Figure 2 As shown, the lithium-ion battery has a discharge specific capacity as high as 372 mAh g⁻¹ at 0.1 C. -1 The discharge specific capacity at 1.0 C is 286 mAh g. -1 The discharge specific capacity at 2.0 C is 205 mAh g. -1 .

[0067] Example 5 Example 5 provides a method for preparing a modified conductive agent for a lithium-ion battery negative electrode, wherein the conductive agent is a modified carbon nanotube whisker, and the specific steps are as follows: 1) Carbon nanotubes without surface-modified hydroxyl groups (i.e., AH carbon nanotubes, which are prepared with reference to the carbon nanotubes in patent document (CN101027434A Preparation method and apparatus for vapor-grown carbon fibers), without hydroxyl modification, with a tube diameter of 75 nm, the material being from Henan Kelaiwei Nanocarbon Materials Co., Ltd., such as... Figure 3 , Figure 4 As shown, Figure 3 It's AH. Figure 4 It is BH, and it can be seen that the surface of BH is modified with hydroxyl groups, while the surface of AH has no hydroxyl groups. Using asphalt as raw material, the carbon nanotubes and asphalt are mixed at a mass ratio of 7:3. An appropriate amount of ethanol is added (the mass ratio of ethanol to carbon nanotubes is 20:1). The carbon nanotubes and asphalt are dispersed evenly by mechanical stirring to obtain a mixture. 2) Place the container containing the mixture from step 1) in an oven to dry it, and obtain a mixture of carbon whiskers and pitch that is evenly dispersed. 3) Place the mixture obtained in step 2) in a tube furnace and introduce argon gas at a flow rate of 0.1 L / min. -1 The modified conductive agent was first heated to 310℃ and held for 2 hours in an argon atmosphere, then held at 800℃ for 2 hours for carbonization, and finally cooled to room temperature naturally.

[0068] Example 6 Example 6 provides a method for preparing a modified conductive agent for the negative electrode of a lithium-ion battery. The difference between Example 6 and Example 5 is that the carbonization temperature in step (3) is 900 °C.

[0069] Example 7 Example 7 provides a method for preparing a modified conductive agent for a lithium-ion battery negative electrode. The difference between Example 7 and Example 5 is that the carbonization temperature in step 3) is 1000 °C.

[0070] Example 8 Example 8 provides a method for preparing a modified conductive agent for a lithium-ion battery negative electrode. The difference between Example 8 and Example 5 is that the ratio of carbon nanotubes to pitch in step 1) is 9:1.

[0071] Example 9 Example 9 provides a method for preparing a modified conductive agent for a lithium-ion battery negative electrode. The difference between Example 9 and Example 8 is that the carbonization temperature in step 3) is 900 °C.

[0072] Example 10 Example 10 provides a method for preparing a modified conductive agent for a lithium-ion battery negative electrode. The difference between Example 10 and Example 8 is that the carbonization temperature in step 3) is 1000 °C.

[0073] Performance testing The modified conductive agents obtained in Examples 5, 6, 7, 8, 9, and 10 were used as negative electrode materials to make batteries, and performance tests were conducted.

[0074] For specific steps, please refer to the performance testing method in Example 1, except that in step a), the modified conductive agent is used instead of the composite conductive agent slurry.

[0075] Figure 5 The graph shows the rate constant current charge-discharge performance of the anode material when the target product of Example 5 and the original sample are used as conductive agents. It can be seen from the graph that when the target product of Example 5 is used as a conductive agent, the anode material exhibits superior constant current charge-discharge performance at 2 C, with a specific capacity reaching 180 mAh g⁻¹. -1 The original sample has a specific capacity of 155 mAh g at 2 C. -1 .

[0076] Figure 6 This is an SEM image of the target product in Example 5. Figure 6 a is a SEM image of the target product of Example 5 taken under a low-magnification scanning electron microscope. Figure 6 b is a SEM image of the target product of Example 5 taken under a high-magnification scanning electron microscope. Figure 7 This is an SEM image of the target product in Example 7. Figure 7 a is a SEM image of the target product of Example 7 taken under a low-magnification scanning electron microscope. Figure 7 b is a high-magnification scanning electron microscope (SEM) image of the target product of Example 7. As can be seen from the image, the sample surface is coated with asphalt, and the coating effect is relatively uniform.

[0077] Figure 8 This is the Raman spectrum of the target product in Example 5. Compared to the original sample, the D peak intensity is enhanced, resulting in a lower I peak intensity in the target product of Example 5. D / I G Value, I D / I G The larger the ratio, the greater the degree of defect, the easier it is for electrons to conduct, and the better the cycle efficiency of the electrode.

[0078] This invention combines multiple conductive agents in a slurry form, leveraging the advantages of each to reduce electrode contact resistance, accelerate electron transfer, and increase lithium-ion migration rate, thereby improving electrode charge-discharge efficiency. The composite conductive agent of this invention has significant application value in the field of lithium-ion batteries and is suitable for industrial-scale application.

[0079] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A carbon nanotube / SWCNTs / Super-P composite conductive agent, characterized in that, It is composed of carbon whisker tubes, single-walled carbon nanotubes (SWCNTs), and carbon black Super-P; the mass percentage of carbon whisker tubes is 0.01%~40%; the mass percentage of carbon black Super-P is 0.01%~70%, and the balance is single-walled carbon nanotubes (SWCNTs).

2. A slurry of carbon nanotubes / SWCNTs / Super-P composite conductive agent, characterized in that, It includes the carbon nanotube / SWCNTs / Super-P composite conductive agent as described in claim 1 and a solvent; the percentage content of the composite conductive agent in the composite conductive agent slurry is ≤10%.

3. The method for preparing the carbon nanotube / SWCNTs / Super-P composite conductive agent slurry according to claim 2, characterized in that, Includes the following steps: (1) Weigh a certain amount of carbon whisker, a certain amount of carbon black Super-P, and a certain amount of single-walled carbon nanotubes (SWCNTs), place the three in a container, and obtain composite conductive agent powder. (2) Add solvent to the composite conductive agent powder obtained in step (1), ultrasonically disperse it at a power of 80~100 W, and then magnetically stir it at a speed of 300~400 r / min to disperse the carbon whisker, carbon black Super-P and single-walled carbon nanotubes SWCNTs evenly to obtain the composite conductive agent slurry.

4. The preparation method according to claim 3, characterized in that, In step (2), the mass ratio of composite conductive agent powder to solvent is (1~5): (30~50); the solvent is selected from deionized water, ethanol and NMP; in the composite conductive agent slurry obtained in step (2), the mass ratio of carbon whisker tubes / SWCNTs / Super-P is (2~3):7: (0.05~0.1).

5. The application of the composite conductive agent of claim 1, the composite conductive agent slurry of claim 2, or the composite conductive agent slurry prepared by the method of claim 3 or 4 in the preparation of lithium-ion batteries.

6. A method for preparing a lithium-ion battery using the composite conductive agent of claim 1, the composite conductive agent slurry of claim 2, or the composite conductive agent slurry prepared by the method of claim 3 or 4, comprising the following steps: a) Preparation of electrode sheet: The active material, composite conductive agent slurry and binder are mixed to form an electrode slurry, which is then uniformly coated on copper foil and dried at 60~80 ℃ for 8~12 h to form an electrode sheet; b) Button cell assembly: Using lithium metal sheets as the counter electrode, assemble them into button cells. The battery model is a CR2032 type button cell.

7. The preparation method according to claim 6, characterized in that, The weight ratio of the active material, composite conductive agent slurry, and binder in step a) is (18~20):(1~2):1.

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