Composite conductive binder, preparation method thereof and dry electrode

Abstract

The invention discloses a composite conductive binder, a preparation method thereof and a dry-method electrode. The composite conductive binder is composed of polypyrrole, a modified conductive agent and hydroxyl-containing polyisobutene. The chemical formula of the hydroxyl-containing polyisobutene is-[CH8-] n-O-CH4O2-CH-CHOH-CHOH, and the chemical formula of the hydroxyl-containing polyisobutene is-[CH8-] n-O-CH4O2-CH-CHOH-CHOH. The composite conductive binder has better compatibility, the agglomeration problem of the conductive agent is reduced, the conductivity is remarkably improved, the internal resistance is reduced, the charge and discharge efficiency is improved, the dispersity is improved, the conductive agent is ensured to be uniformly distributed in an electrode, the mechanical strength and the battery stability are improved, and the cycle life of the battery is prolonged. The conductivity, the mechanical property and the cycling stability of the dry-method electrode can be effectively improved, and a new solution is provided for the development of a high-efficiency battery.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy batteries, and particularly to a composite conductive binder, a preparation method thereof, and a dry electrode. Background Art

[0002] In the manufacturing process of lithium-ion batteries, the key to the dry electrode preparation technology lies in eliminating the use of organic solvents, thus avoiding the solvent pollution and solvent recovery problems in the wet process. In early studies, scholars attempted to use solid binders such as Polytetrafluoroethylene (abbreviated as PTFE). Its excellent chemical stability and mechanical properties make it an ideal binding material. By mixing PTFE powder with active materials and processing under high temperature and high pressure conditions, these materials can be effectively combined into an electrode film. During the preparation of dry electrodes, the selection and dosage of the binder directly affect the performance of the electrodes. For example, the distribution uniformity and bonding strength of the binder in the electrode determine the electrical conductivity and mechanical strength of the electrode. Therefore, researchers strive to improve the overall performance of dry electrodes by optimizing the type and addition method of the binder.

[0003] In dry electrodes, due to the absence of solvents, the selection of conductive agents and binders is particularly important. The conductive agent needs to be tightly combined with the active material under the action of the binder to ensure the stability of the conductive network and the efficient operation of the electrode.

[0004] The dry electrode preparation technology provides an environmentally friendly and efficient solution for battery manufacturing, and the selection and optimization of binders and conductive agents play a crucial role in the performance of dry electrodes.

[0005] PTFE as a binder itself is a very good insulator, and its electrical conductivity is almost zero. Although the conductive agent can provide electronic conductivity, due to its uneven dispersion, agglomeration, and low compatibility with PTFE, the overall conductivity of the electrode is limited.

[0006] Due to the low surface energy of PTFE and the high hydrophilicity of the conductive agent, there is a lack of effective interaction between the two during the dispersion process, resulting in the difficulty of evenly dispersing the conductive agent in the PTFE matrix. The adhesion force of the binder is not sufficient to overcome the electrostatic or van der Waals forces between the conductive agent particles, leading to uneven dispersion of the conductive agent in the electrode material. The conductive filler is prone to agglomeration in the PTFE matrix, forming larger particle clusters, which further reduces the conductivity of the material. The agglomerated conductive agent cannot effectively form a conductive network, causing the conduction path of the electrode material to be interrupted, thereby resulting in a decrease in conductivity. Summary of the Invention

[0007] The technical problem to be solved by the embodiments of the present invention is to provide a composite conductive binder, a preparation method thereof, and a dry electrode to improve the performance and stability of the battery.

[0008] To solve the above technical problem, an embodiment of the present invention provides a composite conductive binder, which is composed of polypyrrole, a modified conductive agent, and hydroxyl-containing polyisobutylene.

[0009] Further, the chemical formula of the hydroxyl-containing polyisobutylene is: –[C4H8–] n –O–C4H4O2–CH2–CHOH–CH2OH.

[0010] Further, the modified conductive agent is obtained by treating the conductive agent with a silane coupling agent, and the conductive agent includes one or more of carbon black, conductive graphite, graphene, and carbon nanotubes.

[0011] Correspondingly, an embodiment of the present invention also provides a preparation method of a composite conductive binder, including: Graft product preparation step: Take an appropriate amount of polyisobutylene and maleic anhydride for graft reaction, so that the double bond of maleic anhydride reacts with the carbon atom in the polyisobutylene molecular chain to obtain PIB-g-MA; Mix PIB-g-MA and glycerol in a molar ratio for a nucleophilic reaction to obtain hydroxyl-containing polyisobutylene; Modified conductive agent preparation step: Treat the conductive agent with a silane coupling agent so that the silane coupling agent covers the surface of the conductive agent to obtain a modified conductive agent; Polymerization reaction step: Prepare a solution of the modified conductive agent and hydroxyl-containing polyisobutylene according to the obtained hydroxyl-containing polyisobutylene and modified conductive agent, dissolve pyrrole in ethanol to form a pyrrole solution, slowly add it to the solution of the modified conductive agent and polyisobutylene, and then add an oxidant to initiate the polymerization reaction of pyrrole. After the polymerization reaction is completed, dry to obtain the composite conductive binder.

[0012] Further, the graft product preparation step includes the following steps: Add polyisobutylene and maleic anhydride in a molar ratio to an appropriate solvent, then add an initiator, and heat the reaction system to 70-120 °C. Under the protection of an inert gas, carry out the reaction for 2 to 6 hours; After the reaction is completed, cool the reaction system to room temperature, remove the solvent, and remove the unreacted maleic anhydride and by-products by solvent extraction to obtain PIB-g-MA; PIB-g-MA was mixed with glycerol in a molar ratio for a nucleophilic reaction, and an appropriate amount of solvent was added to help dissolve the reactants. The reaction temperature was 120 - 160 °C, and the reaction time was 3 to 5 hours. After the reaction, it was cooled to room temperature, the reaction solvent was removed by solvent exchange, and then the moisture was removed by vacuum drying to obtain hydroxyl-containing polyisobutene.

[0013] Furthermore, the preparation steps of the modified conductive agent include the following: The conductive agent and the solvent were mixed to prepare a mixed solution, and the mass fraction of the conductive agent in the solution was 5% - 50%; The silane coupling agent was added to the mixed solution, and the mass proportion of the silane coupling agent was 1% - 5%; The solution was subjected to ultrasonic or stirring treatment and heated, and the heating temperature was 40 °C - 75 °C, so that the silane coupling agent uniformly covered the surface of the conductive agent to obtain a modified conductive agent solution.

[0014] Furthermore, the solvent is one or more of isopropyl alcohol, ethanol, deionized water, acetone, methanol, toluene, dimethyl sulfoxide, cyclohexane, the conductive agent is one or more of carbon black, conductive graphite, graphene, carbon nanotubes, and the silane coupling agent is one or more of 3-glycidoxypropylsilane, 3-chloropropyltriethoxysilane, 3-silylacrylate, 3-aminopropyltriethoxysilane, 3-isocyanatopropyltriethoxysilane.

[0015] Furthermore, the polymerization reaction steps include the following steps: The hydroxyl-containing polyisobutene was slowly added to the modified conductive agent solution and stirred and mixed. The mass ratio of polyisobutene to the modified conductive agent solution was 10 - 30%; Pyrrole was dissolved in ethanol to form a pyrrole solution, and then slowly added to the solution of the modified conductive agent and hydroxyl-containing polyisobutene and stirred. The mass ratio of the pyrrole solution to the solution of the modified conductive agent and hydroxyl-containing polyisobutene was 10 - 30%; An oxidant with a mass fraction of 5 - 10% was added to initiate the polymerization reaction of pyrrole to obtain a composite; After the polymerization reaction was completed, the composite was vacuum dried to remove the solvent in the composite to obtain a composite conductive binder.

[0016] Furthermore, the oxidant is one or more of persulfate, potassium persulfate, sodium persulfate, ammonium bisulfate, calcium persulfate, hydrogen peroxide.

[0017] Correspondingly, the embodiment of the present invention also provides a dry electrode, including the composite conductive binder prepared by the preparation method of the above composite conductive binder.

[0018] The beneficial effects of the present invention are as follows: In traditional dry electrode binders, there is usually a problem of poor interfacial bonding between the conductive agent and the binder, which affects the mechanical strength and cycling stability of the electrode. By grafting maleic anhydride (MAH) onto polyisobutylene (PIB) and introducing hydroxyl (-OH) functional groups, the polarity of PIB is significantly enhanced, enabling it to form a closer bond with the conductive agent and silane coupling agent, improving the interfacial bonding strength, and thus enhancing the mechanical strength and stability of the electrode.

[0019] In traditional conductive binders, the conductive agent usually relies on physical mixing and interfacial crosslinking, and its conductivity is affected by the binder itself. In the present invention, by introducing polypyrrole (PPy), it is in-situ polymerized on the surface of the conductive agent (such as Super P) to form a continuous conductive network, significantly improving the conductivity of the electrode material. By this method of the present invention, not only can a high conductivity be ensured, but also the compatibility between the conductive agent and the binder can be enhanced, enabling the electrode to maintain excellent conductivity even at high loadings.

[0020] Compared with traditional non-polar polymers such as polytetrafluoroethylene (PTFE), the present invention enables PIB to form stronger chemical bonds with the conductive agent and silane coupling agent, enhancing the compatibility and adhesion between PIB and the conductive agent, and solving the problem of weak interfaces in the traditional system.

[0021] The composite binder scheme of the present invention using polyisobutylene binder, silane coupling agent-modified conductive agent, and pyrrole to enhance conductivity has significant advantages: Better compatibility, reducing the agglomeration problem of the conductive agent, significantly enhancing conductivity, reducing internal resistance, improving charge and discharge efficiency, improving dispersibility, ensuring uniform distribution of the conductive agent in the electrode, increasing mechanical strength and battery stability, and extending the cycle life of the battery. The design of the composite conductive binder in this scheme can effectively improve the conductivity, mechanical properties, and cycling stability of the dry electrode, providing a new solution for the development of high-performance batteries. Description of the Drawings

[0022] Figure 1 is the electron micrograph of the mixed dry electrode material in Example 1 of the present invention.

[0023] Figure 2 is the electron micrograph of the mixed dry electrode material in Example 2 of the present invention.

[0024] Figure 3 is the electron micrograph of the mixed dry electrode material in Example 3 of the present invention.

[0025] Figure 4 is the electron micrograph of the mixed dry electrode material in Example 4 of the present invention.

[0026] Figure 5It is the electron microscope image after the dry electrode material of Comparative Example 1 of the present invention is mixed. Detailed implementation manners

[0027] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present invention will be further described in detail below with reference to specific embodiments.

[0028] The strong cohesive force between PTFE molecules and the low surface energy make the physical and chemical interactions between it and many conductive fillers (such as carbon black, carbon nanotubes) weak. Even when mixed under high shear force, it is difficult for the conductive agent to be evenly distributed. Uneven dispersion of the conductive agent often leads to too high a concentration of the conductive agent in local areas of the electrode, while other areas may lack sufficient conductive agent. This uneven distribution forms the problem of uneven conductivity inside the battery, resulting in non-uniform conduction of current during the battery discharge process, thereby affecting the performance and stability of the battery.

[0029] Due to the uneven dispersion and poor conductivity of PTFE as a binder and the conductive agent, the battery performance will be affected in many aspects, including poor conductivity, low battery efficiency, shortened cycle life, accelerated capacity decay, decreased mechanical properties, and poor thermal stability. Therefore, in the design and production process of the battery, it is necessary to ensure the reasonable ratio, dispersibility, and compatibility with the active material of the binder and the conductive agent to ensure the optimization and stability of the battery performance.

[0030] The composite conductive binder of the embodiment of the present invention is composed of polypyrrole, a modified conductive agent, and hydroxyl-containing polyisobutylene. The preparation method of the composite conductive binder of the embodiment of the present invention includes a graft product preparation step, a modified conductive agent preparation step, and a polymerization reaction step.

[0031] Graft product preparation step: Take appropriate amounts of polyisobutylene and maleic anhydride for graft reaction, so that the double bond of maleic anhydride reacts with the carbon atoms in the polyisobutylene molecular chain to obtain PIB-g-MA; mix PIB-g-MA with glycerol in a molar ratio for a nucleophilic reaction to obtain hydroxyl-containing polyisobutylene.

[0032] In the graft reaction of PIB and MAH, the end of the PIB molecular chain reacts with the double bond of maleic anhydride to generate a PIB graft product PIB-g-MA with an ester group (–COO). This grafting step effectively introduces reactive functional groups, providing a basis for subsequent modification.

[0033] PIB-g-MA and glycerol introduce a hydroxyl group (–OH) functional group through a nucleophilic reaction. This makes PIB-g-MA have higher polarity and enhances the compatibility between PIB and the conductive agent. The introduced hydroxyl group (–OH) can further enhance its binding force with other materials (conductive agent, silane coupling agent).

[0034] Steps for preparing the modified conductive agent: Treat the conductive agent with a silane coupling agent so that the silane coupling agent covers the surface of the conductive agent, obtaining the modified conductive agent. In the present invention, the modification of the conductive agent by the silane coupling agent enhances the bonding force between the conductive agent and the binder through the reaction of the silyl group with the surface of the conductive agent. Thereby, the dispersibility of the conductive agent in the composite material is improved, the conductivity is increased, and the mechanical properties are enhanced.

[0035] Polymerization reaction steps: Prepare a solution of the modified conductive agent and hydroxyl-containing polyisobutene according to the obtained hydroxyl-containing polyisobutene and the modified conductive agent. Dissolve pyrrole in ethanol to form a pyrrole solution, slowly add it to the solution of the modified conductive agent and polyisobutene, then add an oxidant to initiate the polymerization reaction of pyrrole. After completing the polymerization reaction, dry to obtain the composite conductive binder.

[0036] In the present invention, the pyrrole solution is added to the solution of the modified conductive agent and polyisobutene. As the polymerization reaction proceeds, polypyrrole will form a conductive network. During the polymerization of pyrrole, by adjusting the temperature, reaction time, and solvent concentration, the structure and coagulation process of the composite are controlled. By slowly cooling the solution, the coagulation rate is controlled to form a uniform conductive binder structure.

[0037] First, prepare polyisobutene (PIB), maleic anhydride (MAH), and a necessary initiator (di-tert-butyl peroxide). Add PIB and maleic anhydride in a molar ratio to an appropriate solvent, and the solvent is tetrahydrofuran (THF) or benzene. Then, add the initiator, and heat the reaction system to 70 - 120 °C. Under the protection of an inert gas (such as nitrogen), carry out the reaction. During the reaction, the double bond of maleic anhydride reacts with the carbon atoms in the PIB molecular chain to form a PIB-g-MA graft product. This graft reaction incorporates maleic anhydride into the PIB chain through a chemical bond, providing a terminal group that can react with other chemical substances. The reaction time is 2 to 6 hours. After the reaction ends, cool the reaction system to room temperature, remove the solvent, and remove the unreacted maleic anhydride and by-products through solvent extraction. Finally, obtain the PIB-g-MA graft product. After grafting, the anhydride group remains in a closed ring and can be hydrolyzed into a carboxylic acid group later.

[0038] The reaction formula for the grafting of maleic anhydride onto polyisobutene is as follows: ; Glycerol is introduced into the PIB molecular chain through a nucleophilic reaction. PIB-g-MA and glycerol are mixed in a molar ratio, and an appropriate amount of solvent (such as xylene, tetrahydrofuran, etc.) is added to help dissolve the reactants. During the reaction, the hydroxyl group (–OH) of glycerol acts as a nucleophile, attacking the ester group in the grafted maleic anhydride and opening the ring structure. Through this reaction, the grafted maleic anhydride part on the PIB-g-MA chain is replaced by the hydroxyl group of glycerol. This reaction is usually carried out at 120 - 160 °C for 3 to 5 hours to ensure complete reaction. After the reaction, it is cooled to room temperature, the reaction solvent is removed by solvent exchange method, and then water is removed by vacuum drying. Finally, a PIB grafted product containing hydroxyl group (–OH) is obtained, and its chemical formula is: –[C4H8–] n –O–C4H4O2–CH2–CHOH–CH2OH.

[0039] The nucleophilic reaction formula of PIB-g-MA and glycerol is as follows: .

[0040] The conductive agent is treated with a silane coupling agent. By treating the conductive agent with a silane coupling agent, the compatibility between the conductive agent and the modified polyisobutylene (PIB) binder is enhanced, the dispersibility of the conductive agent is improved, and agglomeration is avoided.

[0041] Conductive agent: one or more of carbon black, conductive graphite, graphene, carbon nanotubes.

[0042] Silane coupling agent: one or more of 3-glycidoxypropyltrimethoxysilane (GPTMS), 3-chloropropyltriethoxysilane (CPTS), 3-silylacrylate (Si-AME), 3-aminopropyltriethoxysilane (APS), 3-isocyanatopropyltriethoxysilane (IPTS). These silane coupling agents have active groups and can react with the hydroxyl groups or other functional groups on the surface of the conductive agent.

[0043] Solvent: one or more of isopropanol, ethanol, deionized water, acetone, methanol, toluene, dimethyl sulfoxide amide, cyclohexane.

[0044] Treatment process: The conductive agent and the solvent are mixed to obtain a mixed solution. The mass fraction of the conductive agent in the solution is 5% - 50%. The silane coupling agent is added to the mixed solution, and the mass ratio of the silane coupling agent is 1% - 5%.

[0045] The solution is treated by ultrasonic treatment or mechanical stirring, and the solution is heated. The heating temperature is 40 - 75 °C to ensure that the silane coupling agent can uniformly cover the surface of the conductive agent.

[0046] Mixing of hydroxyl-containing polyisobutene and modified conductive agent. The modified conductive agent is fully mixed with the hydroxyl-containing polyisobutene binder to form a stable composite conductive binder material.

[0047] Polyisobutene (PIB): Polyisobutene with a low molecular weight of 1000 - 40000, and its viscosity is determined according to the required electrode performance.

[0048] Mixing process: Slowly add the liquid hydroxyl-containing polyisobutene to the modified conductive agent solution. The mass ratio of the hydroxyl-containing polyisobutene to the modified conductive agent solution is 10 - 30%. Use a mechanical stirrer to promote mixing. The mixing process needs to ensure the uniform dispersion of the conductive agent in the polyisobutene to avoid affecting the conductivity due to uneven dispersion. The stirring time is 1 - 6 hours.

[0049] Temperature control: Ensure that the mixing temperature is within the range of 50 - 75 °C to avoid the degradation of polyisobutene caused by too high temperature.

[0050] Pyrrole itself has good electrical conductivity and can form a conductive polypyrrole network through chemical polymerization. During the composite process, pyrrole will act together with the hydroxyl-containing polyisobutene and the modified conductive agent, and interact with the surface of the conductive agent or the hydroxyl-containing polyisobutene through chemical polymerization.

[0051] Oxidant selection: Use one or more of persulfates, such as potassium persulfate, sodium persulfate, ammonium persulfate, calcium persulfate, and hydrogen peroxide, as oxidants to promote the polymerization reaction of pyrrole.

[0052] Dissolve pyrrole in ethanol to form a pyrrole solution, and slowly add it to the solution of the modified conductive agent and the hydroxyl-containing polyisobutene, while keeping stirring to ensure the uniform dispersion of the pyrrole solution in the mixture of the hydroxyl-containing polyisobutene and the conductive agent. The mass ratio of the pyrrole solution to the solution of the modified conductive agent and the hydroxyl-containing polyisobutene is 10 - 30%.

[0053] After adding the pyrrole solution to the mixture, add an oxidant with a mass fraction of 5 - 10% to initiate the polymerization reaction of pyrrole. During the polymerization process of pyrrole, control the structure and coagulation process of the composite by adjusting the temperature, reaction time, and solvent concentration.

[0054] As the polymerization reaction proceeds, polypyrrole will form a conductive network and coagulate with the conductive agent and the hydroxyl-containing polyisobutene into a solid composite material. By slowly cooling the solution and controlling the coagulation rate, a uniform conductive binder structure is formed.

[0055] After the polymerization reaction is completed, the composite material may still contain solvents. Put the composite into a vacuum drying oven at a temperature of 100 - 180 °C for 1 - 10 hours to completely remove the solvents and obtain the composite conductive binder.

[0056] Example 1: Prepare polyisobutylene (PIB) with a molecular weight of 2000, maleic anhydride (MAH), and an appropriate amount of initiator (di-tert-butyl peroxide); Example 2: Prepare polyisobutylene (PIB) with a molecular weight of 5000, maleic anhydride (MAH), and an appropriate amount of initiator (di-tert-butyl peroxide). Example 3: Prepare polyisobutylene (PIB) with a molecular weight of 15000, maleic anhydride (MAH), and an appropriate amount of initiator (di-tert-butyl peroxide). Example 4: Prepare polyisobutylene (PIB) with a molecular weight of 35000, maleic anhydride (MAH), and an appropriate amount of initiator (di-tert-butyl peroxide).

[0057] Add the PIB and MAH of each example in an appropriate ratio (1:1 molar ratio) to a solvent (tetrahydrofuran), add the initiator and heat to 100 °C, and react for 2 hours under an inert gas atmosphere to ensure that maleic anhydride reacts with the end of the PIB chain to form a PIB-g-MA graft product, where PIB and maleic anhydride are connected by an ester group (–COO). After the reaction, cool to room temperature and use solvent extraction to remove unreacted maleic anhydride and by-products.

[0058] Mix the obtained PIB-g-MA with glycerol in a ratio (1:1 molar ratio) and heat to 120 °C in a solvent (xylene) and react for 3 hours. Through this nucleophilic reaction, the hydroxyl group (–OH) of glycerol will replace the oxygen atom in the ester group, and finally introduce a hydroxyl group (–OH) functional group on the PIB chain. After the reaction is completed, cool to room temperature, use solvent exchange to remove the reaction solvent, and remove moisture by vacuum drying to obtain a PIB graft product containing a hydroxyl group (–OH) functional group.

[0059] Add the silane coupling agent 3-glycidoxypropylsilane, carbon black (conductive agent), and absolute ethanol to a heated beaker, heat at a temperature of 60 °C for 1 h, and continuously stir. The mass fraction of the conductive agent in the solution is 10%, and the mass ratio of the silane coupling agent is 1%.

[0060] Slowly add the modified polyisobutylene (i.e., polyisobutylene containing hydroxyl groups) to the modified conductive agent solution. The modified polyisobutylene accounts for 10% of the mass of the modified conductive agent solution. Use a mechanical stirrer to promote mixing for 1 hour. Ensure that the mixing temperature is 50 °C to avoid degradation of polyisobutylene due to excessive temperature. After stirring evenly, gradually cool down at a rate of 2 °C / min, and continue stirring during the cooling process to obtain a solid composite conductive binder material formed by the condensation of modified polyisobutylene and the conductive agent.

[0061] Dissolve pyrrole in ethanol to form a pyrrole solution, and slowly add it to the solution of the modified conductive agent and modified polyisobutene while stirring. The mass ratio of the pyrrole solution to the solution of the modified conductive agent and polyisobutene is 10%. Add potassium persulfate with a mass fraction of 5%. During the polymerization of pyrrole, it coagulates with the conductive agent and polyisobutene to form a solid composite material. Slow cooling is carried out at a cooling rate of 1 °C / min to form a uniform conductive binder structure.

[0062] After completing the polymerization reaction, put the composite into a vacuum drying oven. The drying temperature is 120 °C and the time is 18 h to completely remove the solvent, obtaining a composite conductive binder.

[0063] Homogeneously mix the cathode active material lithium nickel manganese cobalt ternary material (NCM) and the composite conductive binder prepared in each example according to a weight ratio of 9:1, and use a roll press to hot-press and prepare a dry film. Place the dry film on an aluminum foil (current collector), and hot-press to obtain the cathode electrode sheets of each example. Use a Hoki electrode resistance test system to test the volume resistivity of the dressing layer, that is, the volume resistivity of the film.

[0064] Assemble the cathode electrode sheets in each example into coin cells and test their relevant electrochemical properties. The rate performance test method is as follows: At room temperature, charge at a constant current of 0.1C to 4.3V, and charge at a constant voltage of 4.3V until the current ≤ 0.02C. Then discharge at a constant current of 0.1C, 1C, and 3C respectively to 3.0V. Each discharge rate is cycled for 3 weeks. Record the discharge capacity of the battery in the third week at different discharge rates, and calculate the discharge capacity retention rates of the battery at 1C and 3C relative to 0.1C respectively.

[0065] The dry electrode of the present invention is prepared by homogeneously mixing a composite conductive binder and an active material.

[0066] The electron microscope photos of the composite conductive binder and the active material homogeneously mixed in Examples 1, 2, 3, and 4 are respectively as Figure 1 , Figure 2 , Figure 3 , Figure 4 shown.

[0067] Comparative Example 1: Homogeneously mix the cathode active material lithium nickel manganese cobalt ternary material (NCM), conductive agent sp, and binder PTFE according to a weight ratio of 9:0.5:0.5. The electron microscope photo is as Figure 5 , and use a roll press to hot-press and prepare a dry film. Place the dry film on an aluminum foil (current collector), and hot-press to obtain the cathode electrode sheet. Use a Hoki electrode resistance test system to test the volume resistivity of the dressing layer, that is, the volume resistivity of the film.

[0068] The positive electrode sheet in Comparative Example 1 was assembled into a button cell, and its related electrochemical performance was tested. The rate performance test method is as follows: at room temperature, it was charged at a constant current of 0.1C to 4.3V, and then charged at a constant voltage of 4.3V until the current ≤ 0.02C. Then, it was discharged at a constant current of 0.1C, 1C, and 3C to 3.0V respectively. Each discharge rate was cycled for 3 weeks. The discharge capacity of the battery in the third week at different discharge rates was recorded, and the discharge capacity retention rates of the battery at 1C and 3C relative to 0.1C were calculated respectively.

[0069] The test results of the volume resistivity and discharge capacity of each example and comparative example are shown in Table 1 and Table 2 respectively.

[0070]

[0071]

[0072] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalent scope.

Claims

1. A composite conductive adhesive, characterized in that: It is composed of polypyrrole, modified conductive agent and hydroxyl-containing polyisobutylene.

2. The composite conductive adhesive according to claim 1, characterized in that: The chemical formula of the hydroxyl-containing polyisobutylene is: –[C4H8–] n –O–C4H4O2–CH2–CHOH–CH2OH.

3. The composite conductive adhesive according to claim 1, characterized in that: The modified conductive agent is obtained by treating a conductive agent with a silane coupling agent, and the conductive agent includes one or more of carbon black, conductive graphite, graphene, and carbon nanotubes.

4. A method for preparing a composite conductive adhesive, characterized in that: include: The preparation steps of the grafted product are as follows: taking appropriate amounts of polyisobutylene and maleic anhydride for grafting reaction, so that the double bonds of maleic anhydride react with the carbon atoms in the polyisobutylene molecular chain to obtain PIB-g-MA; mixing PIB-g-MA and glycerol in a molar ratio for nucleophilic reaction to obtain hydroxyl-containing polyisobutylene; The modified conductive agent preparation step is: treating the conductive agent with a silane coupling agent so that the silane coupling agent covers the surface of the conductive agent to obtain the modified conductive agent; Polymerization reaction step: prepare a solution of modified conductive agent and hydroxyl-containing polyisobutylene according to the obtained hydroxyl-containing polyisobutylene and modified conductive agent, dissolve pyrrole in ethanol to form a pyrrole solution, slowly add the solution to the modified conductive agent and polyisobutylene, then add an oxidant to initiate the polymerization reaction of pyrrole, and after the polymerization reaction is completed, dry to obtain a composite conductive adhesive.

5. The method for preparing the composite conductive adhesive according to claim 4, characterized in that: The graft product preparation step comprises the following steps: Adding polyisobutylene and maleic anhydride in a molar ratio to a suitable solvent, then adding an initiator, and heating the reaction system to 70-120° C., reacting under the protection of an inert gas, and the reaction time is 2 to 6 hours; after the reaction is completed, cooling the reaction system to room temperature, removing the solvent, and removing unreacted maleic anhydride and by-products by solvent extraction to obtain PIB-g-MA; PIB-g-MA and glycerol are mixed in a molar ratio to carry out a nucleophilic reaction, and a proper amount of solvent is added to help dissolve the reactants. The reaction temperature is 120-160° C. and the reaction time is 3 to 5 hours. After the reaction is completed, the mixture is cooled to room temperature, the reaction solvent is removed by a solvent exchange method, and then the moisture is removed by vacuum drying to obtain a hydroxyl-containing polyisobutylene.

6. The method for preparing the composite conductive adhesive according to claim 4, characterized in that: The steps for preparing the modified conductive agent include the following: Mixing a conductive agent and a solvent to prepare a mixed solution, wherein the mass fraction of the conductive agent in the solution is 5%-50%; Add silane coupling agent to the mixed solution, the mass proportion of silane coupling agent is 1%-5%; The solution is subjected to ultrasonic or stirring treatment and heated at a temperature of 40° C. to 75° C., so that the silane coupling agent is evenly covered on the surface of the conductive agent to obtain a modified conductive agent solution.

7. The method for preparing the composite conductive adhesive according to claim 6, characterized in that: The solvent is one or more of isopropanol, ethanol, deionized water, acetone, methanol, toluene, dimethylsulfamide, and cyclohexane; the conductive agent is one or more of carbon black, conductive graphite, graphene, and carbon nanotubes; and the silane coupling agent is one or more of 3-glycidyl ether silane, 3-chloropropyltriethoxysilane, 3-silyl acrylate, 3-aminopropyltriethoxysilane, and 3-isocyanatepropyltriethoxysilane.

8. The method for preparing the composite conductive adhesive according to claim 6, characterized in that: The polymerization step comprises the following steps: Slowly add hydroxyl-containing polyisobutylene to the modified conductive agent solution and stir to mix, wherein the mass ratio of polyisobutylene to the modified conductive agent solution is 10-30%; Dissolving pyrrole in ethanol to form a pyrrole solution, then slowly adding the solution to the modified conductive agent and the hydroxyl-containing polyisobutylene and stirring, wherein the mass ratio of the pyrrole solution to the solution of the modified conductive agent and the hydroxyl-containing polyisobutylene is 10-30%; Adding an oxidant with a mass fraction of 5-10% to initiate a polymerization reaction of pyrrole to obtain a complex; After the polymerization reaction is completed, the composite is vacuum dried to remove the solvent in the composite to obtain a composite conductive adhesive.

9. The method for preparing the composite conductive adhesive according to claim 8, characterized in that: The oxidant is one or more of persulfate, potassium persulfate, sodium persulfate, ammonium bisulfate, calcium persulfate, and hydrogen peroxide.

10. A dry electrode, characterized in that: A composite conductive adhesive prepared by the method for preparing a composite conductive adhesive as claimed in any one of claims 4 to 9.

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