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CN-122025222-A - Composite conductive material containing carbon nano tube and preparation method and application thereof

CN122025222ACN 122025222 ACN122025222 ACN 122025222ACN-122025222-A

Abstract

The invention discloses a composite conductive material containing carbon nanotubes, a preparation method and application thereof, and belongs to the technical field of polymer composite materials. The method comprises the steps of carrying out surface pretreatment and mild depolymerization on the multiwall carbon nanotube to obtain a pre-dispersed carbon nanotube, carrying out grafting reaction on the pre-dispersed carbon nanotube and a hydroxyl-terminated prepolymer to obtain a carbon nanotube with a high molecular chain grafted on the surface, and carrying out controllable compounding with an electrode active material through planetary stirring to obtain the electrode slice. The invention solves the dispersion problem under the premise of maintaining the structural integrity of the carbon nano tube by the synergistic effect of selective oxidation and polymer grafting, and the constructed three-dimensional elastic conductive network taking a polymer chain as an anchor point can effectively adapt to the volume change of an active material and maintain the structural stability and the smoothness of a conductive path in the circulation process. The material is particularly suitable for a silicon-based negative electrode or a high-voltage positive electrode with high volume expansion, and can obviously improve the multiplying power performance and the cycle life of a solid-state battery.

Inventors

  • XU LILI
  • XU SHAN

Assignees

  • 连云港中科景合新能源科技有限责任公司

Dates

Publication Date
20260512
Application Date
20260408

Claims (10)

  1. 1. The composite conductive material containing the carbon nano tube and the preparation method thereof are characterized by comprising the following steps: Step 1, carrying out surface pretreatment on a multi-wall carbon nano tube, and carrying out oxidation treatment on the multi-wall carbon nano tube at a temperature of between 40 and 60 ℃ by using a mixed oxidant solution containing organic weak acid and oxidizing salt to obtain a pre-dispersed carbon nano tube with carboxyl and hydroxyl modified on the surface; step 2, after the carboxyl on the surface of the pre-dispersed carbon nano tube is activated, carrying out grafting reaction with a hydroxyl-terminated prepolymer to obtain the carbon nano tube with a high molecular chain grafted on the surface; And 3, premixing the carbon nano tube grafted with the polymer chains on the surface with electrode active material powder, adding a solvent and a polymer binder, mechanically fusing through planetary stirring to form uniform slurry, and coating and drying to obtain the composite conductive material electrode slice.
  2. 2. The composite conductive material containing carbon nanotubes and the method for preparing the same according to claim 1, wherein in the step 1, the organic weak acid is selected from one of citric acid, tartaric acid and oxalic acid, the oxidizing salt is selected from potassium persulfate and ammonium persulfate, the molar ratio of the organic weak acid to the oxidizing salt is determined by fixing the concentration of the oxidizing salt, changing the ratio of the organic weak acid, respectively treating a multi-walled carbon nanotube sample, measuring the raman spectrum IG/ID value of the multi-walled carbon nanotube after the treatment and the turbidity of the dispersion in water after the dispersion for 24 hours, selecting the molar ratio of the organic weak acid to the oxidizing salt such that the IG/ID value is reduced by less than 5% with respect to the original multi-walled carbon nanotube and the turbidity is reduced to 30% or less of the original multi-walled carbon nanotube dispersion.
  3. 3. The method according to claim 1, wherein in the step 1, the oxidation treatment is performed in a constant temperature reactor and stirring is continued, the reaction end point is determined by monitoring the pH value of the reaction system and the Zeta potential of the pre-dispersed carbon nanotube dispersion, when the pH value of the reaction system is stabilized and the Zeta potential absolute value of the pre-dispersed carbon nanotube dispersion reaches a plateau value in the range of-30 mV to-50 mV, the oxidation treatment is stopped, after the oxidation treatment is completed, the product is vacuum filtered and washed until the filtrate is neutral, the filter cake is redispersed in absolute ethanol, and the filter cake is treated in an ultrasonic bath with a power lower than 200W for 5 minutes to 10 minutes, and then centrifugally separated and dried, thereby obtaining the pre-dispersed carbon nanotubes.
  4. 4. The composite conductive material containing carbon nanotubes and the method for preparing the same according to claim 1, wherein in the step 2, the hydroxyl-terminated prepolymer is selected from one of a hydroxyl-terminated polybutadiene-acrylonitrile copolymer, a polyurethane prepolymer or a polyimide prepolymer having a molecular weight ranging from 3000 g/mol to 10000 g/mol, the grafting reaction is performed in an aprotic polar solvent, the activator used for carboxyl activation is a mixture of N, N' -dicyclohexylcarbodiimide and 4-dimethylaminopyridine, and the hydroxyl-terminated prepolymer is dissolved in the same aprotic polar solvent and is added dropwise to the activated pre-dispersed carbon nanotube dispersion at a temperature ranging from 0 ℃ to 10 ℃.
  5. 5. The composite conductive material containing carbon nanotubes according to claim 4, wherein in the step 2, the grafting reaction is performed at a temperature of 60 to 80 ℃, the progress of the reaction is monitored by fourier transform infrared spectroscopy, the monitored characteristic peaks include a characteristic peak at about 1730 cm-1 representing stretching vibration of the ester bond c=o and a characteristic peak at about 3450 cm-1 representing stretching vibration of the hydroxyl-terminated prepolymer hydroxyl-terminated O-H, when the characteristic peak intensity at about 1730 cm-1 is not significantly increased and the characteristic peak intensity at about 3450 cm-1 is weakened to a stable level, the completion of the grafting reaction is judged, the reaction mixture is poured into a precipitant after the completion of the reaction, a solid product is collected by centrifugation and filtration, washed with the precipitant, and finally vacuum-dried to obtain the carbon nanotubes grafted with high molecular chains on the surface.
  6. 6. The composite conductive material containing carbon nanotubes and the preparation method thereof according to claim 1, wherein in the step 3, the electrode active material powder is a silicon-carbon composite negative electrode material or a high-nickel ternary positive electrode material, the addition amount of the carbon nanotubes grafted with polymer chains on the surface accounts for 0.5 to 5.0% of the mass of the electrode active material powder based on the mass of the carbon nanotubes, and the chemical type of the polymer binder has chemical compatibility with the polymer chain segments grafted on the carbon nanotubes grafted with polymer chains on the surface.
  7. 7. The composite conductive material containing carbon nanotubes and the method for preparing the same according to claim 1, wherein in the step 3, the mechanical fusion process of planetary stirring is performed under the temperature control condition of 25 ℃ to 40 ℃, the total time and speed parameter of planetary stirring are determined by monitoring the rheological property of the uniform slurry, the specific method of monitoring is that sampling is periodically performed, a glass rod is used for picking up the slurry to observe the wiredrawing length when the slurry drops down, and the time required for naturally leveling the slurry drops to a mirror surface is measured on the glass plate, and when the wiredrawing length reaches the stable range of 3 cm to 5 cm and the time required for naturally leveling to the mirror surface meets the requirement of the subsequent coating process, stirring is stopped.
  8. 8. The method for preparing the composite conductive material containing the carbon nanotubes according to claim 1, wherein in the step 3, after the uniform slurry is formed, the method further comprises a step of vacuum defoaming the uniform slurry, wherein the drying is a step heating drying process, a majority of solvents are firstly dried at 80 ℃, then residual solvents are removed under a vacuum condition at 120 ℃ and the curing of a polymer binder is promoted, and the final composite conductive material electrode plate is obtained after the drying and rolling.
  9. 9. The composite conductive material containing carbon nanotubes according to claim 1, wherein the number of carboxyl and hydroxyl functional groups modified on the surface of the pre-dispersed carbon nanotubes obtained in step 1 is indirectly characterized by the plateau value of the Zeta potential reaching the range of-30 mV to-50 mV, so as to ensure that the pre-dispersed carbon nanotubes have enough reaction sites in the grafting reaction of step 2.
  10. 10. The composite conductive material containing carbon nanotubes according to any one of claims 1 to 9 and its preparation and application, wherein the electrode sheet of the composite conductive material, the solid electrolyte membrane and the counter electrode are assembled into a solid battery, and the electrode of the solid battery is a high-volume expansion silicon-based negative electrode or a high-voltage positive electrode.

Description

Composite conductive material containing carbon nano tube and preparation method and application thereof Technical Field The invention relates to the technical field of polymer composite materials, in particular to a composite conductive material containing carbon nano tubes, a preparation method and application thereof. Background Carbon Nanotubes (CNTs) are considered ideal fillers for constructing high performance conductive networks of polymer-based composites due to their excellent one-dimensional conductivity, high mechanical strength, and large aspect ratio. In the field of new energy, in particular to lithium ion batteries and solid-state batteries, the carbon nano tube is used as a conductive additive, and plays a key role in improving the electron conduction capacity, mechanical integrity and cycle stability of an electrode. However, the conversion of the excellent theoretical properties of carbon nanotubes into practical application performance faces a series of technical bottlenecks that have not been properly solved for a long time. First, the inherent van der Waals forces of carbon nanotubes make them very susceptible to agglomeration, forming aggregates on a macroscopic scale. This agglomeration severely impedes its uniform dispersion in the polymer matrix or electrode slurry. Traditional physical dispersion methods, such as high-speed shearing and stirring, often can only realize macroscopic mixing and cannot effectively dissociate nanoscale agglomerates. While more intense dispersion means, such as long-time ball milling or high-power ultrasonic treatment, are more effective in destroying agglomeration, they are extremely prone to irreversible mechanical damage to the one-dimensional tubular structure of the carbon nanotubes themselves, such as breakage, bending, or the creation of a large number of structural defects, which in turn can significantly reduce their intrinsic conductivity and mechanical strength. For example, studies have shown that improper sonication can reduce the IG/ID values in the raman spectra of carbon nanotubes that characterize the degree of graphitization and result in an increase in slurry resistivity. Therefore, how to maintain the structural integrity and performance of the carbon nanotubes to the maximum while achieving efficient dispersion is the first core contradiction. Secondly, in specific electrode application scenes, particularly when facing new generation battery material systems such as silicon-carbon negative electrodes, high-nickel positive electrodes or solid-state electrolytes, the requirements on the conductive network are more severe. The carbon nanotube composite material prepared by simple physical mixing (melt blending or solution blending) has a random and unstable conductive network. In the process of charging and discharging the electrode, the active material can undergo significant volume expansion and contraction (for example, the volume change of the silicon material can reach more than 300%), and the repeated stress can damage the randomly distributed carbon nano tube network connection points, so that the conductive path is interrupted, the electrode impedance is rapidly increased, and the battery capacity is rapidly attenuated. In addition, in solid-state batteries, there is a solid-solid contact between the electrode and the solid-state electrolyte, which has a large interface impedance, and a more efficient and stable three-dimensional continuous path requirement for ion and electron transport inside the electrode is created. The existing simple blending material is difficult to construct a stable network which can adapt to volume change and simultaneously ensure high-speed transmission of electrons and ions. Furthermore, for the role that carbon nanotubes play in electrodes, the prior art is mostly limited to conductive "wires" that are considered inert. In fact, the closed tube wall of the carbon nanotube and the ultra-long one-dimensional diffusion path of lithium ions obstruct the intercalation of lithium ions from the graphite layers of the tube wall, so that the utilization rate of the carbon nanotube as a lithium storage active site is extremely low, and the waste of material functions is caused. In summary, the composite conductive material based on carbon nanotubes and the preparation method thereof in the prior art generally have the problems that the dispersibility and the structural integrity of the carbon nanotubes are difficult to be compatible, the formed conductive network is unstable in an electrochemical circulation environment, and the carbon nanotubes have single function (only conductive). This limits its application in new generation high performance batteries, especially solid state batteries, requiring high energy density, high power density and long cycle life. Disclosure of Invention Based on the above object, the present invention provides a method for preparing a composite conductive material containing ca