CN112038637B - Composite conductive agent, preparation method thereof and lithium ion battery - Google Patents

Composite conductive agent, preparation method thereof and lithium ion battery Download PDF

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CN112038637B
CN112038637B CN202010789482.9A CN202010789482A CN112038637B CN 112038637 B CN112038637 B CN 112038637B CN 202010789482 A CN202010789482 A CN 202010789482A CN 112038637 B CN112038637 B CN 112038637B
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conductive agent
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CN112038637A (en
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项胜
曹勇
王义飞
董骄
马仁良
鲁冰冰
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Hefei Gotion High Tech Power Energy Co Ltd
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Hefei Guoxuan High Tech Power Energy Co Ltd
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Abstract

The invention discloses a composite conductive agent, a preparation method thereof and a lithium ion battery, and relates to the technical field of lithium ion batteries, wherein the composite conductive agent is prepared by growing a metal organic framework 2-methylimidazole zinc salt on the surface of an initial conductive agent, and then carrying out high-temperature carbonization and acid etching on the metal organic framework zinc salt to obtain a composite conductive agent with a porous amorphous carbon-coated surface; wherein the initial conductive agent is composed of a granular conductive agent and a linear conductive agent. According to the invention, the granular conductive agent is anchored on the linear conductive agent carbon nano tube, and the dispersion capacity of the carbon nano tube is improved through steric hindrance repulsion; in the positive and negative electrode slurry, the granular conductive agent is filled among the active material particles, and the linear conductive agent remotely connects the granular conductive agent together to form a dotted line three-dimensional net-shaped conductive network, so that the contact performance of the conductive agent and the active material is improved, the electron transmission efficiency is improved, and the probability of insufficient contact caused by expansion of the active material in the charging and discharging process is reduced.

Description

Composite conductive agent, preparation method thereof and lithium ion battery
Technical Field
The invention relates to the technical field of lithium ion batteries, in particular to a composite conductive agent, a preparation method thereof and a lithium ion battery.
Background
With the increasing crisis of energy and environment, clean and sustainable energy use and storage become a research hotspot. Lithium ion batteries have many advantages such as high energy density, flexible size, high cycling stability, unlimited application field, etc., and have received great attention from various industries. Currently, the cathode active material commonly used in high specific energy lithium ion batteries is high nickel transition metal oxide, and since most of them are semiconductors or insulators, the conductivity thereof is 10-3～10-9S/cm, and the slow solid-phase diffusion rate of lithium ions seriously affects the internal resistance, multiplying power and capacity of the lithium ionsStable volatilization and circulation and the like. Therefore, it is necessary to add a conductive agent to improve electron conductivity. The kind, dosage and distribution state of the conductive agent have great influence on the utilization rate of active substances, the cycling stability, the multiplying power and the low-temperature discharge performance.
The commonly used lithium ion battery conductive agent comprises a granular conductive agent and a linear conductive agent, wherein the granular conductive agent comprises carbon black (SP), Ketjen Black (KB), conductive graphite (KS-6) and the like, the linear conductive agent comprises vapor deposition carbon nanofibers (VGCF), Carbon Nanotubes (CNTs) and the like, the granular conductive agent belongs to point contact and can only provide short-range electron transmission, the linear conductive agent can provide long-range point-to-line conductive paths, and the good effect is that the two types of conductive agents are matched to form a three-dimensional mesh conductive network.
The carbon nano-tube has better crystallinity, excellent electron transport property and lower resistivity (3.5 multiplied by 10)2Omega cm), etc., is an excellent lithium ion battery conductive agent, and the carbon nano tube is used as a novel fibrous conductive agent, can form a more complete three-dimensional conductive network, has higher electronic conductivity compared with the traditional conductive agent such as conductive carbon black, etc., and correspondingly reduces the required dosage, thereby improving the capacity and energy density. However, the carbon nanotubes as a conductive agent improve the performance of the battery, and the application difficulty is sufficient contact and uniform dispersion with the active material particles. If the dispersion is not uniform, the conductive properties cannot be sufficiently exerted, so whether the conductive agent can exert its excellent conductive properties largely depends on its dispersion state in the active material. Carbon nanotubes have small diameter and large length-diameter ratio, and are easy to agglomerate under the action of van der waals force, and generally, the carbon nanotubes exist in an entangled aggregate state, which is not favorable for uniform dispersion.
The dispersion of carbon nanotubes can be classified into physical and chemical methods. The method for physically dispersing the carbon nanotubes mainly comprises the steps of ultrasonic dispersion, shearing mixing, grinding and the like, and has the advantages of large treatment capacity, no damage to the surface of the carbon nanotubes and the like, but single physical dispersion only can macroscopically mix the carbon nanotube aggregates with matrix powder, and has no effect on the dispersion of the carbon nanotube aggregates. The chemical dispersion is mainly to modify hydrophilic functional groups such as hydroxyl, carboxyl or polymers with hydrophilic ends on the surface of the carbon nanotube so as to improve the dispersibility of the carbon nanotube. The invention provides a high-dispersion lithium ion battery conductive slurry, which can well solve the dispersion problem of carbon nanotubes, improve the electrical property of a battery and the utilization rate of the carbon nanotubes and has an industrial application prospect.
Disclosure of Invention
Based on the technical problems in the background art, the invention provides a composite conductive agent, a preparation method thereof and a lithium ion battery, wherein the dispersion capacity of the linear conductive agent is improved by anchoring a granular conductive agent on the linear conductive agent; in the anode and cathode slurry, the granular conductive agent is filled among the active material particles, and the linear conductive agent remotely connects the granular conductive agent to form a dotted three-dimensional netted conductive network, so that the contact performance of the conductive agent and the active material is improved.
The invention provides a composite conductive agent, which is prepared by growing a metal organic framework 2-methylimidazole zinc salt on the surface of an initial conductive agent, and then carrying out high-temperature carbonization and acid etching on the metal organic framework 2-methylimidazole zinc salt to obtain the composite conductive agent with the surface coated with porous amorphous carbon; wherein the initial conductive agent is composed of a granular conductive agent and a linear conductive agent.
Preferably, the linear conductive agent is a carbon nanotube or a modified carbon nanotube; preferably, the linear conductive agent is a composition of single-walled carbon nanotubes and multi-walled carbon nanotubes which are subjected to acidification treatment; preferably, the weight ratio of the single-walled carbon nanotubes to the multi-walled carbon nanotubes is 1: 30-60.
Preferably, the granular conductive agent is one or more of carbon black, ketjen black and conductive graphite.
In the present invention, the composition of the acidified single-walled carbon nanotubes and multi-walled carbon nanotubes can be prepared as follows: adding single-walled carbon nanotubes and multi-walled carbon nanotubes into a concentrated nitric acid solution, and heating, stirring, cooling and washing to obtain acidified carbon nanotubes; wherein the heating temperature is 40-60 ℃, and the stirring time is 1-4 h.
Preferably, the weight ratio of the linear conductive agent to the particulate conductive agent is 1: 7 to 13.
The invention also provides a preparation method of the composite conductive agent, which comprises the following steps:
s1, mixing the granular conductive agent and the linear conductive agent to obtain the initial conductive agent, ball milling, and adding Zn (NO)3)2Adjusting the pH value to 8.5-9.5 in the anhydrous methanol solution, performing ultrasonic dispersion, standing and aging to obtain a mixed solution;
s2, dripping 2-methylimidazole into the mixed solution of S1, stirring for reaction to obtain a precipitate, and centrifuging, washing and drying to obtain solid powder;
s3, pyrolyzing the solid powder at high temperature in an inert gas protective atmosphere to obtain black powder;
s4, carrying out acid washing on the black powder to remove Zn-containing compounds, washing with water, and drying to obtain the Zn-containing zinc oxide.
Preferably, in S1, the ball milling time is 12-48 h; preferably, the initial conductive agent and Zn (NO)3)2The weight ratio of the methanol solution is 1: 50 to 100, Zn (NO)3)2The weight concentration of the anhydrous methanol solution is 0.5-1.2%; preferably, the pH is adjusted to 8.5-9.5 with ammonia; preferably, the standing and aging time is 6-24 h.
Preferably, in S2, the weight ratio of 2-methylimidazole to the mixed solution is 1: 50 to 125 parts; preferably, the reaction time is 3-12 h.
Preferably, in S3, the pyrolysis temperature is 600-900 ℃, and the pyrolysis time is 1-3 h; preferably, the heating rate of the high-temperature pyrolysis is 1-5 ℃/min.
Preferably, dilute hydrochloric acid is adopted for acid washing in S4, and the acid washing time is 12-24 hours; preferably, the concentration of the dilute hydrochloric acid is 0.2 mol/L.
The invention also provides a lithium ion battery, which comprises a positive plate, a negative plate, a diaphragm and electrolyte, wherein the positive plate and the negative plate comprise positive current collectors, negative current collectors and positive slurry and negative slurry coated on the current collectors, and the positive slurry and the negative slurry comprise the composite conductive agent; preferably, the composite conductive agent accounts for 1.2-2.0% of the weight of the anode slurry, and the composite conductive agent accounts for 0.3-0.8% of the weight of the cathode slurry.
In the invention, in order to avoid dust raising of the conductive agent powder, the composite conductive agent can be dispersed into the binder solution to prepare conductive slurry, and then the conductive slurry is used for preparing the anode slurry and the cathode slurry.
Compared with the prior art, the beneficial effects of the invention are embodied in the following aspects:
1. the invention makes the linear conductive agent carbon nanotube and the granular conductive agent fully mixed by ball milling, and a small amount of metal organic framework 2-methylimidazol zinc salt ZIF-8 grows on the surface of the linear conductive agent carbon nanotube, and then the linear conductive agent carbon nanotube and the granular conductive agent are coated by porous amorphous carbon obtained by high-temperature carbonization and acid etching, and the granular conductive agent is anchored on the carbon nanotube; the composite conductive agent is added into the slurry of the positive electrode and the negative electrode of the lithium ion battery, the granular conductive agent is filled among active material particles, and the linear conductive agent carbon nano tube is used for lapping the remote granular conductive agent, so that a solid dotted three-dimensional netted conductive network is formed, the contact performance of the conductive agent and the active materials of the positive electrode and the negative electrode of the lithium ion battery is improved, the internal resistance is reduced, the electron transmission efficiency is improved, and the multiplying power and the cycle performance of the lithium ion battery are improved.
2. The composite conductive agent is closely contacted with the active material, so that the probability of insufficient contact caused by expansion of the active material in the charging and discharging processes can be reduced. Under the long-term charge-discharge cycle condition, the carbon particles and the graphite flakes can still be well connected together, and the formation of an island is avoided.
3. According to the invention, SP is anchored on the carbon nano tube, and the state of carbon nano tube entangled aggregate is destroyed through steric hindrance repulsion, so that the dispersing capability of the carbon nano tube is improved, and the problem that the carbon nano tube is difficult to disperse in practical application is solved; and the carbon nano tube is slightly acidified and partially coated with carbon, the high crystallinity of the carbon nano tube is not damaged, the original good conductivity is still maintained, the utilization rate of the conductive agent is improved, the content of the conductive agent is reduced, and the capacity and the energy density of the battery cell are improved.
4. The composite conductive agent material has large specific surface area, contains N and other heteroatoms, improves the liquid retention capacity of the conductive agent, has better affinity for an electrolyte solvent, can enhance the electrolyte wettability of a pole piece, reduces electronic polarization and ionic polarization, and improves the cycle performance of a battery.
Drawings
FIG. 1 is a diagram of normal temperature cycle performance of a lithium ion battery prepared in an embodiment of the present invention;
fig. 2 is a rate performance diagram of a lithium ion battery manufactured in an example of the present invention.
Detailed Description
The technical solution of the present invention will be described in detail below with reference to specific examples.
Example 1
The method comprises the following steps: weighing 5g of SWCNTs and 150g of MWCNTs, adding the weighed SWCNTs and MWCNTs into a reactor containing concentrated nitric acid solution, heating and stirring the mixture at 50 ℃ for reaction for 3 hours, cooling the mixture, washing the mixture until the pH value is approximately equal to 7, and drying the mixture to obtain an acidified carbon nanotube;
step two: ball-milling the obtained acidified carbon nano-tube with 1.2Kg SP for 24h, fully mixing uniformly, and then ultrasonically stirring and dispersing in 67.75Kg Zn (NO) with the mass concentration of 0.5 wt%3)2Adjusting the pH to be approximately equal to 9 by ammonia water in the anhydrous methanol, standing and aging for 12 hours to obtain a mixed solution;
step three: slowly adding 800g of 2-methylimidazole into the mixed solution obtained in the second step under the stirring condition, stirring and reacting for 6 hours to obtain a precipitate, and centrifuging, washing and drying at 80 ℃ to obtain solid powder;
step four: putting the solid powder obtained in the third step into pure N2Pyrolyzing at 800 ℃ for 2h in a gas environment at a high temperature, heating at a speed of 5 ℃/min to obtain black powder, then placing the black powder into a dilute hydrochloric acid solution with the concentration of 0.2mol/L for acid washing for 12h to fully react, washing with deionized water, and drying to obtain the composite conductive agent;
step five: respectively dispersing the composite conductive agent obtained in the fourth step in CMC + H2In glue solution prepared by O, NMP and PVDF, the weight percentage of the composite conductive agent in the glue solution is controlled to be 1.5 percent and 2.0 percent respectively, the stirring and dispersing rotating speeds are respectively 10rpm and 1200rpm, and the time is 6 hours, so that the conductive adhesive is obtainedConductive slurry for the negative electrode and the positive electrode of the lithium ion battery;
step six: stirring and dispersing the negative conductive slurry obtained in the fifth step, graphite, water, CMC and SBR uniformly to obtain negative slurry, then coating the negative slurry on copper foil, and rolling and slitting to obtain a negative pole piece; stirring and dispersing the positive conductive slurry, NCM811, PVDF and NMP uniformly to obtain positive slurry, then coating the positive slurry on an aluminum foil, and rolling and slitting to obtain a positive pole piece;
step seven: and matching the negative pole piece, the positive pole piece, the electrolyte and the diaphragm to manufacture the soft package lithium ion battery. The proportion of the composite conductive agent in the negative plate is controlled to be 0.7%, and the proportion of the composite conductive agent in the positive plate is controlled to be 1.2%.
Example 2
The method comprises the following steps: weighing 5g of SWCNTs and 300g of MWCNTs, adding the weighed SWCNTs and MWCNTs into a reactor containing concentrated nitric acid solution, heating and stirring the mixture at 50 ℃ for reaction for 3 hours, cooling the mixture, washing the mixture until the pH value is approximately equal to 7, and drying the mixture to obtain an acidified carbon nanotube;
step two: ball-milling the obtained acidified carbon nano-tube with 2.44Kg SP for 24h, fully mixing uniformly, and then ultrasonically stirring and dispersing the mixture in 122Kg Zn (NO) with the mass concentration of 0.4 wt%3)2In the anhydrous methanol, adjusting the pH to be approximately equal to 9 by using ammonia water, standing and aging for 24 hours to obtain a mixed solution;
step three: slowly adding 1.22Kg of 2-methylimidazole into the mixed solution obtained in the step two under the stirring condition, stirring for reacting for 6 hours to obtain a precipitate, and centrifuging, washing and drying at 80 ℃ to obtain solid powder;
step four: putting the solid powder obtained in the third step into pure N2Pyrolyzing at 900 ℃ for 1h in a gas environment at a high temperature, raising the temperature at a speed of 5 ℃/min to obtain black powder, then placing the black powder into a dilute hydrochloric acid solution with the concentration of 0.2mol/L for acid washing for 12h until the black powder is fully reacted, washing with deionized water, and drying to obtain the composite conductive agent;
step five: respectively dispersing the composite conductive agent obtained in the fourth step in CMC + H2In glue solution prepared by O, NMP and PVDF, the weight percentage of the composite conductive agent in the glue solution is controlled to be 1.5 percent and 2.0 percent respectively, and the stirring and dispersing rotating speeds are respectively 10rpm and 1200rpmPerforming the reaction for 6 hours to obtain conductive slurry for the cathode and the anode of the lithium ion battery;
step six: stirring and dispersing the negative conductive slurry obtained in the fifth step, graphite, water, CMC and SBR uniformly to obtain negative slurry, then coating the negative slurry on copper foil, and rolling and slitting to obtain a negative pole piece; stirring and dispersing the positive conductive slurry, NCM811, PVDF and NMP uniformly to obtain positive slurry, then coating the positive slurry on an aluminum foil, and rolling and slitting to obtain a positive pole piece;
step seven: and matching the negative pole piece, the positive pole piece, the electrolyte and the diaphragm to manufacture the soft package lithium ion battery. The proportion of the composite conductive agent in the negative plate is controlled to be 0.5%, and the proportion of the composite conductive agent in the positive plate is controlled to be 1.3%.
Example 3
The method comprises the following steps: weighing 5g of SWCNTs and 250g of MWCNTs, adding the weighed SWCNTs and 250g of MWCNTs into a reactor containing concentrated nitric acid solution, heating and stirring the mixture at 50 ℃ for reaction for 3 hours, cooling the mixture, washing the mixture until the pH value is approximately equal to 7, and drying the mixture to obtain an acidified carbon nanotube;
step two: ball-milling the obtained acidified carbon nano-tube with 1.54Kg SP for 24h, fully mixing uniformly, and then ultrasonically stirring and dispersing in 67.75Kg Zn (NO) with the mass concentration of 0.5 wt%3)2Adjusting the pH to be approximately equal to 9 by ammonia water in the anhydrous methanol, standing and aging for 12 hours to obtain a mixed solution;
step three: slowly adding 945g of 2-methylimidazole into the mixed solution obtained in the second step under the stirring condition, stirring for reacting for 6 hours to obtain a precipitate, and centrifuging, washing and drying at 80 ℃ to obtain solid powder;
step four: putting the solid powder obtained in the third step into pure N2Pyrolyzing at 600 ℃ for 2h in a gas environment at the temperature rise speed of 5 ℃/min to obtain black powder, then placing the black powder into a dilute hydrochloric acid solution with the concentration of 0.2mol/L for acid washing for 12h to fully react, washing with deionized water, and drying to obtain the composite conductive agent;
step five: respectively dispersing the composite conductive agent obtained in the fourth step in CMC + H2In glue solution prepared by O, NMP and PVDF, the weight percentage of the composite conductive agent in the glue solution is controlled to be 1.5 percent and 2.0 percent respectively, and the stirring and dispersing rotating speeds are respectively 10rpm and 101200rpm for 6h to obtain conductive slurry for the cathode and the anode of the lithium ion battery;
step six: stirring and dispersing the negative conductive slurry obtained in the fifth step, graphite, water, CMC and SBR uniformly to obtain negative slurry, then coating the negative slurry on copper foil, and rolling and slitting to obtain a negative pole piece; stirring and dispersing the positive conductive slurry, NCM811, PVDF and NMP uniformly to obtain positive slurry, then coating the positive slurry on an aluminum foil, and rolling and slitting to obtain a positive pole piece;
step seven: and matching the negative pole piece, the positive pole piece, the electrolyte and the diaphragm to manufacture the soft package lithium ion battery. The proportion of the composite conductive agent in the negative plate is controlled to be 0.6%, and the proportion of the composite conductive agent in the positive plate is controlled to be 1.25%.
Example 4
The method comprises the following steps: weighing 5g of SWCNTs and 250g of MWCNTs, adding the weighed SWCNTs and 250g of MWCNTs into a reactor containing concentrated nitric acid solution, heating and stirring the mixture at 50 ℃ for reaction for 3 hours, cooling the mixture, washing the mixture until the pH value is approximately equal to 7, and drying the mixture to obtain an acidified carbon nanotube;
step two: ball-milling the obtained acidified carbon nano-tube with 1.87Kg SP for 24h, fully mixing uniformly, and then ultrasonically stirring and dispersing in 67.75Kg Zn (NO) with the mass concentration of 0.5 wt%3)2Adjusting the pH to be approximately equal to 9 by ammonia water in the anhydrous methanol, standing and aging for 12 hours to obtain a mixed solution;
step three: slowly adding 1053g of 2-methylimidazole into the mixed solution obtained in the second step under the stirring condition, stirring for reacting for 6 hours to obtain a precipitate, and centrifuging, washing and drying at 80 ℃ to obtain solid powder;
step four: putting the solid powder obtained in the third step into pure N2Pyrolyzing at 700 ℃ for 2h in a gas environment at a high temperature, raising the temperature at a speed of 5 ℃/min to obtain black powder, then placing the black powder into a dilute hydrochloric acid solution with the concentration of 0.2mol/L for acid washing for 12h to fully react, washing with deionized water, and drying to obtain the composite conductive agent;
step five: respectively dispersing the composite conductive agent obtained in the fourth step in CMC + H2In glue solution prepared by O, NMP and PVDF, the weight percentage of the composite conductive agent in the glue solution is controlled to be 1.5 percent and 2.0 percent respectively, and stirring and dispersion rotating speed are dividedRespectively at 10rpm and 1200rpm for 6h to obtain conductive slurry for the cathode and the anode of the lithium ion battery;
step six: stirring and dispersing the negative conductive slurry obtained in the fifth step, graphite, water, CMC and SBR uniformly to obtain negative slurry, then coating the negative slurry on copper foil, and rolling and slitting to obtain a negative pole piece; stirring and dispersing the positive conductive slurry, NCM811, PVDF and NMP uniformly to obtain positive slurry, then coating the positive slurry on an aluminum foil, and rolling and slitting to obtain a positive pole piece;
step seven: and matching the negative pole piece, the positive pole piece, the electrolyte and the diaphragm to manufacture the soft package lithium ion battery. The proportion of the composite conductive agent in the negative plate is controlled to be 0.6%, and the proportion of the composite conductive agent in the positive plate is controlled to be 1.25%.
Comparative example 1
Comparative example 1 differs from example 1 in that: the method does not comprise the first four steps, the composite conductive agent prepared by the method is not used in the fifth step, and the mixed conductive agent of SP, MWCNTs and SWCNTs is used, wherein the mass ratio is respectively 240: 30: 1.
comparative example 2
Comparative example 2 differs from example 2 in that: the method does not comprise the first four steps, the composite conductive agent prepared by the method is not used in the fifth step, and the mixed conductive agent of SP, MWCNTs and SWCNTs is used, wherein the mass ratio is 488: 60: 1.
the performance of the conductive agent, the electrode sheet and the lithium ion battery prepared in examples 1 to 2 of the present invention and comparative examples 1 to 2 was tested.
TABLE 1 Properties of conductive agent and electrode sheet obtained in examples 1-2 and comparative examples 1-2
Figure BDA0002623246520000091
Figure BDA0002623246520000101
As can be seen from Table 1, the composite conductive agent prepared in the embodiment of the invention has larger specific surface area, smaller resistivity and better conductivity, which shows that the composite conductive agent and the pole piece prepared by the invention have good electrochemical properties.
Fig. 1 and 2 are a normal temperature cycle performance diagram and a cell rate performance diagram of the lithium ion batteries manufactured in examples 1 to 2 of the present invention and comparative examples 1 to 2, respectively. It can be seen that the rate and cycle performance of the lithium ion battery prepared by using the composite conductive agent of the invention are obviously higher than those of the battery prepared by using the conventional conductive agent.
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art should be considered to be within the technical scope of the present invention, and the technical solutions and the inventive concepts thereof according to the present invention should be equivalent or changed within the scope of the present invention.

Claims (9)

1. A composite conductive agent is characterized in that a metal organic framework 2-methyl imidazole zinc salt grows on the surface of an initial conductive agent, and then the composite conductive agent with the surface coated with porous amorphous carbon is obtained through high-temperature carbonization and acid etching; wherein the initial conductive agent is composed of a granular conductive agent and a linear conductive agent;
the linear conductive agent is a composition of single-walled carbon nanotubes and multi-walled carbon nanotubes which are subjected to acidification treatment; the weight ratio of the single-walled carbon nanotube to the multi-walled carbon nanotube is 1: 30-60.
2. The composite conductive agent according to claim 1, wherein the particulate conductive agent is one or more of carbon black and conductive graphite.
3. The composite conductive agent according to claim 1 or 2, wherein the weight ratio of the linear conductive agent to the particulate conductive agent is 1: 7 to 13.
4. A method for preparing the composite conductive agent according to any one of claims 1 to 3, comprising the steps of:
S1、mixing granular conductive agent and linear conductive agent to obtain initial conductive agent, ball-milling, and adding Zn (NO)3)2Adjusting the pH value to 8.5-9.5 in the anhydrous methanol solution, performing ultrasonic dispersion, standing and aging to obtain a mixed solution;
s2, dripping 2-methylimidazole into the mixed solution of S1, stirring for reaction to obtain a precipitate, and centrifuging, washing and drying to obtain solid powder;
s3, carbonizing the solid powder at high temperature in an inert gas protective atmosphere to obtain black powder;
and S4, carrying out acid washing on the black powder to remove Zn-containing compounds, washing with water, and drying to obtain the zinc-containing zinc oxide.
5. The preparation method of the composite conductive agent according to claim 4, wherein in S1, the ball milling time is 12-48 h; initial conductive agent and Zn (NO)3)2The weight ratio of the methanol solution is 1: 50 to 100 of Zn (NO)3)2The weight concentration of the anhydrous methanol solution is 0.5-1.2%; adjusting pH to 8.5-9.5 with ammonia water; standing and aging for 6-24 h.
6. The method for producing the composite conductive agent according to claim 4, wherein the weight ratio of the 2-methylimidazole to the mixed solution in S2 is 1: 50 to 125 parts; the reaction time is 3-12 h.
7. The preparation method of the composite conductive agent according to claim 4, wherein in S3, the carbonization temperature is 600-900 ℃, and the carbonization time is 1-3 h; the temperature rise rate of the high-temperature carbonization is 1-5 ℃/min.
8. The preparation method of the composite conductive agent according to claim 4, wherein dilute hydrochloric acid is adopted for acid washing in S4, and the acid washing time is 12-24 h; the concentration of the dilute hydrochloric acid is 0.2 mol/L.
9. A lithium ion battery comprises a positive plate, a negative plate, a diaphragm and electrolyte, wherein the positive plate and the negative plate comprise a positive current collector, a negative current collector and positive slurry and negative slurry coated on the current collectors, and the lithium ion battery is characterized in that the positive slurry and the negative slurry comprise the composite conductive agent of any one of claims 1 to 3 or the composite conductive agent prepared by the method of any one of claims 4 to 8; the composite conductive agent accounts for 1.2-2.0% of the weight of the anode slurry, and the composite conductive agent accounts for 0.3-0.8% of the weight of the cathode slurry.
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