Graphene modified resin binder for dry-method electrode as well as preparation method and application of graphene modified resin binder

Abstract

The invention provides a graphene modified resin binder for a dry-method electrode as well as a preparation method and application of the graphene modified resin binder, and relates to the technical field of binders. The preparation method of the graphene modified resin adhesive comprises the following steps: carrying out hydrophilic modification on a resin adhesive to obtain a hydrophilic modified resin adhesive, then mixing the hydrophilic modified resin adhesive with graphene oxide, and adsorbing the graphene oxide to the surface of the hydrophilic modified resin adhesive to form full coating, functional groups on the surface of the hydrophilic modified resin adhesive and functional groups on the surface of the graphene oxide are combined to form a stable structure; and finally, reducing the graphene oxide into reduced graphene oxide through a reduction method to obtain the graphene modified resin binder. With the adoption of the technical scheme, the graphene oxide is driven by negative charges carried by the graphene oxide to be adsorbed on the surface of the resin adhesive to form full coating of the graphene on the surface of the resin adhesive, so that the problems of poor dispersity and agglomeration of nano graphene in a dry-method mixing process are solved.

Description

Technical Field

[0001] The present invention relates to the technical field of binders, and in particular to a graphene-modified resin binder for dry-process electrodes, and a preparation method and application thereof. Background Art

[0002] The dry electrode process uses solid adhesive to form a three-dimensional "net" structure, so that the electrode powder is cross-linked by this three-dimensional grid structure to achieve the bonding function. At present, the best choice of adhesive is polytetrafluoroethylene (PTFE). The active material is mixed with the conductive agent and PTFE, and then the PTFE is fiberized under the action of shear force. The diameter of the fiber is only a few nanometers and the length is tens of microns. The active material and carbon black are polymerized together to form a mixture by forming a three-dimensional network structure. Finally, the mixture is rolled to form a film hundreds of microns thick. As for the conductive agent, compared with the commonly used granular and fibrous conductive agents, the graphene conductive agent has better conductivity and higher specific surface area. The addition amount is significantly lower than other conductive agents. A small amount can achieve the same conductive effect. Therefore, the use of graphene-based composite conductive agents instead of traditional carbon black, carbon nanotubes, etc. has become an effective way to improve the performance of lithium-ion batteries. It has been widely recognized by the industry and has huge market potential.

[0003] However, the preparation process of the dry electrode process in the prior art has the following technical problems, including: (1) In the active material particle matrix, the conductive agent and the binder need to be dry-mixed, and how to achieve their uniform dispersion is particularly critical; however, the dispersion of the conductive agent graphene is one of the key factors affecting the conductivity of the electrode. The role of the conductive agent in the electrode system is to build a conductive network for electron transmission. If the conductive agent itself cannot be well dispersed and agglomerates during the mixing process, then the advantages of the "extremely soft and thin" structural characteristics will be difficult to fully exert, not only will the utilization rate of graphene be greatly reduced, but it will also be difficult to build an effective conductive network; in addition, graphene is a nano-scale material. In addition to the characteristics of large specific surface area, there are also strong van der Waals forces between its layers, so it is easy for the sheets to agglomerate, making it difficult to disperse during the dry mixing process. The subsequent thermal compounding of unevenly dispersed graphene prefabricated powder may cause the problem of sheet overlap, which will ultimately affect the actual performance of graphene. How to ensure that graphene has good dispersion stability in the dry system has become one of the problems that need to be solved in the dry electrode process.

[0004] (2) The dry electrode process uses PTFE that can be fiberized as a binder. Density functional theory calculations show that PTFE has a high electron accepting capacity and is prone to reduction reaction. During the battery charging and discharging process, PTFE is unstable at low potentials. After electron reduction, the CF bond breaks and the generated F + With Li in the electrolyte+ The reaction generates LiF, which undergoes an irreversible reaction, causing the electrode to lithiate and consume active lithium when used as the negative electrode, thereby weakening the adhesion effect and reducing the electrode capacity; to overcome the problem of the reaction between PTFE and lithium ions, the prior art usually coats a coating material on the surface of PTFE to passivate the binder and improve the stability of PTFE at low potentials, thereby avoiding the generation of F + ; for example, Chinese invention patent CN117384567A provides a preparation method of a composite binder for a dry electrode and an electrode membrane. A conductive paste formed by adding hydrophilic conductive carbon to deionized water is mixed with a polytetrafluoroethylene dispersion stock solution, and after adding a demulsifier, it is stirred and demulsified and coagulated to obtain a composite binder for a dry electrode. This method solves the problems of increased resistance of the electrode sheet and reduced overall rate performance of the battery after using PTFE as the electrode sheet binder. The coating material used in the prior art selects conductive carbon, including electrical conductors (such as conductive carbon and carbon black) and particulate materials (powdered carbon materials); however, since the requirement for volume energy density in lithium-ion batteries is much more urgent than that for mass energy density, conductive carbon cannot provide capacity inside the battery. Due to its low density, even a small amount will occupy a large electrode space, greatly reducing the volume energy density of the entire system. Therefore, the method of coating conductive carbon further increases the usage amount of the conductive agent and further reduces the volume energy density of the lithium-ion battery.

[0005] In summary, the technical problems to be solved in the dry electrode process mainly include the problem of uneven dispersion of nano-scale graphene powder and the problem of how to reduce the usage amount of the conductive agent to effectively improve the volume energy density of the battery.

[0006] Therefore, based on the above analysis of the prior art, the present invention provides a graphene-modified resin binder suitable for dry electrodes, with graphene oxide coated on the modified resin adhesive, and the graphene oxide is reduced. The unique two-dimensional planar structure of graphene produces a "steric effect" on the transport of lithium ions inside the electrode, solving the problem of the reaction between the resin adhesive and lithium ions. Summary of the Invention

[0007] To solve the above problems, the present invention provides a graphene-modified resin binder for dry electrodes, its preparation method and application.

[0008] To achieve the above object, the present invention provides a method for preparing a graphene-modified resin binder for a dry electrode, which includes obtaining a hydrophilic-modified resin binder by subjecting a resin adhesive to hydrophilic modification, and then mixing it with graphene oxide. The graphene oxide is adsorbed onto the surface of the hydrophilic-modified resin binder to form a complete coating. Finally, the graphene oxide (GO) is reduced to reduced graphene oxide (rGO) by a reduction method, thereby obtaining the graphene-modified resin binder.

[0009] The adsorption includes driving the graphene oxide to attach to the surface of the hydrophilic-modified resin binder through electrostatic interaction by the negative charge carried by the graphene oxide, and the functional groups on the surface of the hydrophilic-modified resin binder combine with the functional groups on the surface of the graphene oxide to form a stable structure.

[0010] The surface functional groups of the hydrophilic-modified resin binder include but are not limited to carbonyl, carboxyl, etc.; the surface of the graphene oxide contains a large number of hydroxyl groups Preferably, the resin adhesive includes any one or a combination of two or more of polytetrafluoroethylene, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, and tetrafluorohexene-hexafluoropropylene copolymer.

[0011] Preferably, the reduction method includes any one of, but is not limited to, chemical reduction method with a reducing agent, high-temperature heat treatment deoxidation method, solvothermal reduction method, electrochemical reduction method, photoreduction method, and microwave-assisted reduction method.

[0012] Preferably, in the chemical reduction method with a reducing agent, the reducing agent is selected from any one of, but is not limited to, hydrazine hydrate, sodium borohydride, lithium aluminum hydride zinc and aluminum powder, ammonia gas, vitamin C, potassium hydroxide, sodium oxide, dimethylhydrazine, p-phenylenediamine, hydroiodic acid, and phenylhydrazine.

[0013] As a preferred implementation manner, the method for hydrophilic modification of the adhesive includes: Step (1): After uniformly mixing dimethyl sulfoxide and acetophenone, add potassium tert-butoxide in small amounts several times, stir with a glass rod while adding, and perform water bath ultrasonic treatment until completely dissolved to obtain an acetophenone dianion solution; utilize the inductive effect of the three methyl groups of C4H9OK to react with C9H 10 O to prepare an acetophenone dianion solution for reducing the resin adhesive powder.

[0014] Step (2): Add the resin adhesive powder into the acetophenone dianion solution, heat it in a water bath, and after post-treatment, oxidize it with an oxidizing agent to obtain the hydrophilic-modified adhesive.

[0015] Preferably, in step (1), the mass ratio of dimethyl sulfoxide, acetophenone, and potassium tert-butoxide is 20:3:10.

[0016] Preferably, in step (2), the molar ratio of the resin adhesive to acetophenone is 1:1.5 to 2.

[0017] More preferably, the molar ratio of the resin adhesive to acetophenone is 1:1.5.

[0018] Preferably, the time of water bath heating is 16 - 24 h, and the temperature is 50 - 60 °C.

[0019] Preferably, the post - treatment includes: first washing with tetrahydrofuran to remove excess acetophenone, then washing with deionized water 2 - 3 times, and placing it in a vacuum oven for baking for 12 - 14 h, with the temperature set at 70 - 90 °C.

[0020] Preferably, the powdery resin adhesive in step (2) is pretreated before hydrophilic modification; Preferably, the pretreatment includes: adding the resin adhesive to ethanol, removing surface impurities by ultrasonic treatment; then freeze - drying and sieving to obtain the resin adhesive powder and placing it in an oven for standby.

[0021] Preferably, the time of ultrasonic treatment is 0.5 - 1 h.

[0022] Preferably, the time of freeze - drying is 8 - 12 h.

[0023] Preferably, the temperature of freeze - drying is - 55 °C to - 75 °C.

[0024] More preferably, the temperature of freeze - drying is - 60 °C.

[0025] Preferably, the oxidant is acidic potassium permanganate solution.

[0026] More preferably, the oxidant is a mixed solution containing 0.5 mol·L -1 potassium permanganate (KMnO4) and 1 mol·L -1 sulfuric acid (H2SO4).

[0027] Preferably, the mass ratio of the resin adhesive to the oxidant is 1:(0.9 - 1.1).

[0028] As a preferred embodiment, the specific preparation method of the graphene - modified resin binder includes: S1. Provide a graphene oxide suspension; Disperse graphene oxide powder in deionized water, and obtain the graphene oxide suspension by ultrasonic stirring; S2. Provide a hydrophilic - modified resin adhesive solution; S3. Add the graphene oxide suspension to the hydrophilic - modified resin adhesive solution, and obtain a dispersion by ultrasonic dispersion; S4. Add a reducing agent to the dispersion obtained in S3. After mixing evenly, perform water bath heating. The resulting precipitate is the graphene-modified resin binder with reduced graphene oxide coated on the resin adhesive.

[0029] Preferably, in S1, the content of graphene oxide in the graphene oxide suspension is 90 - 120 mg·mL -1 .

[0030] As a preferred embodiment, in S3, the mass ratio of graphene oxide to the hydrophilic-modified resin adhesive is 1:2.2×10 5 ~2.2×10 6 ; More preferably, it is 1:2.2×10 6 .

[0031] As a preferred embodiment, the time of ultrasonic dispersion is 1.5 - 1.5 h.

[0032] As a preferred embodiment, in S4, the mass ratio of the reducing agent to the graphene oxide powder is 1:1 - 3.

[0033] As a preferred embodiment, the water bath heating includes a temperature of 70 - 90 °C and a time of 2 - 4 h.

[0034] As one of the invention purposes, the present invention also provides a graphene-modified resin binder, which is prepared by the preparation method described above; wherein, the reduced graphene oxide uniformly wraps the surface of the resin adhesive.

[0035] As one of the invention purposes, the present invention also provides a dry-type positive electrode film, which is prepared by mixing the graphene-modified resin binder, positive electrode active material and conductive agent described above evenly, and then obtaining a fibrillated positive electrode mixed powder under stirring and shearing, and then roll-pressing into a film.

[0036] Specifically, first stir and disperse the positive electrode active material and the conductive agent evenly, then add the binder, control the temperature < 18 °C, stir evenly and then turn off the cooling system, and then fibrillate the binder under natural shearing during stirring to obtain a fibrillated positive electrode mixed powder; the fibrillated positive electrode mixed powder is roll-pressed into a film to obtain a dry-type positive electrode film.

[0037] As one of the invention purposes, the present invention also provides a positive electrode sheet, which is a dry-type positive electrode sheet obtained by thermally roll-pressing and compounding the dry-type positive electrode film described above with a current collector.

[0038] As one of the invention purposes, the present invention also provides a battery, including a positive electrode and a negative electrode; the positive electrode is the dry-type positive electrode sheet described above.

[0039] Binders, taking polytetrafluoroethylene as an example, are widely used as binders for this cathode material due to their good chemical inertness, thermal stability, mechanical strength, and environmental tolerance. However, due to their poor electrical conductivity and strong hydrophobicity, they have a significant impact on the chemical properties of the battery, such as interfacial impedance and slow electrolyte penetration, which leads to the blockage of ion transport channels.

[0040] Graphene oxide (GO) is a two-dimensional material with a single atomic layer thickness and is a derivative of graphene. It has various oxygen-containing functional groups such as hydroxyl, carbonyl, and carboxyl groups. Different from hydrophobic graphene, the surface of GO contains a large number of oxygen-containing functional groups, making it hydrophilic. Therefore, it can be dispersed in water. On the other hand, GO is negatively charged, which drives GO to adsorb onto the surface of the resin adhesive after hydrophilic modification. Further, the oxygen-containing functional groups (such as hydroxyl groups) on the surface of GO combine with the functional groups (such as carboxyl and carbonyl groups) on the surface of the modified hydrophilic resin adhesive to form a stable structure, thereby forming an all-enveloping structure. However, the large number of oxygen-containing functional groups on the surface of GO will not only hinder the electron transport, increase the liquid absorption capacity of the electrolyte, and generate a large number of side reactions with the electrolyte, reducing the electrical conductivity of the material. Therefore, the reduced graphene oxide (rGO) obtained by reduction treatment in the present invention is used to provide higher electrical conductivity and stability.

[0041] Based on the above analysis, in the present invention, after the resin adhesive is subjected to hydrophilic modification, graphene oxide is adsorbed onto its surface to form a stable coating structure, and then the GO coated on the surface of the resin adhesive is reduced to eliminate the excess oxygen-containing functional groups, obtaining an rGO-coated resin adhesive composite material, effectively solving the side reactions caused by too many functional groups on the surface of graphene oxide.

[0042] On the one hand, the present invention utilizes the fact that graphene is a sheet structure and the "plane-point" contact mode between graphene and the active substance. The low conductivity threshold enables a small amount of graphene to effectively improve the electronic conductivity of the electrode, thereby significantly reducing the usage amount of the conductive agent as a non-active substance and effectively increasing the volume energy density of the battery. On the other hand, the present invention reduces the graphene oxide coated on the surface of the resin adhesive. By using the unique two-dimensional planar structure of graphene to generate a "steric hindrance effect" on the transport of lithium ions inside the electrode, after the resin adhesive fibrillates, graphene will still adhere to the particle surface due to the intermolecular interaction force, preventing the reaction between the resin adhesive and Li + and solving the problem of the reaction between the resin adhesive and lithium ions, enhancing the adhesion effect, and avoiding capacity attenuation during subsequent cycling.

[0043] The beneficial technical effects obtained by the present invention: 1. By adopting the technical solution of the present invention, after hydrophilic modification of the resin adhesive, a large number of hydrophilic oxygen-containing functional groups (such as carbonyl, carboxyl, etc.) exist on its surface, which combine with the oxygen-containing functional groups (hydroxyl, carbonyl, carboxyl) on the surface of graphene oxide to form a stable structure. Moreover, graphene oxide is negatively charged, thus driving graphene oxide to adsorb on the surface of the resin adhesive, forming a complete coating of reduced graphene oxide on the surface of the resin adhesive, thereby solving the problems of poor dispersion and agglomeration of nano-graphene during the dry mixing process.

[0044] 2. By adopting the technical solution of the present invention, the graphene oxide coated on the surface of the resin adhesive is reduced to eliminate excess functional groups, and a resin adhesive composite material coated with reduced graphene oxide is obtained, effectively solving the side reactions caused by excessive subsequent functional groups and providing higher conductivity and stability.

[0045] 3. By adopting the technical solution of the present invention, the unique two-dimensional planar structure of graphene produces a "steric effect" on the transport of lithium ions inside the electrode. After the resin adhesive fibrillates, due to the intermolecular interaction force, graphene will still adhere to the particle surface, preventing the reaction between the resin adhesive and Li + and solving the problem of the reaction between the resin adhesive and lithium ions, enhancing the adhesion effect, and avoiding capacity attenuation during subsequent cycles. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 FIG. is a schematic diagram of the preparation process simulation of the graphene-modified resin adhesive provided in Example 1 of the present invention.

[0047] Figure 2 FIG. is an SEM image of the graphene-coated resin adhesive prepared in Example 1 of the present invention.

[0048] Figure 3 FIG. is a comparison chart of 1C cycle and rate charge-discharge tests of the examples and comparative examples of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0049] To make the objectives, technical solutions, and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some, but not all, of the embodiments of the present application.

[0050] The present invention provides a method for preparing a graphene-modified binder, which includes subjecting a resin adhesive to hydrophilic modification to obtain a hydrophilic-modified resin adhesive, and then mixing it with graphene oxide. The graphene oxide is adsorbed onto the surface of the hydrophilic-modified resin adhesive to form a complete coating, and the functional groups on the surface of the hydrophilic-modified resin adhesive combine with the functional groups on the surface of the graphene oxide to form a stable structure. Finally, the graphene oxide (GO) is reduced to reduced graphene oxide (rGO) by a reduction method, thereby obtaining a graphene-modified resin binder.

[0051] Specifically, taking the adhesive (PTFE) as an example, the preparation method includes: adding hydrazine hydrate to the dispersion mixture of the hydrophilic-modified adhesive (PTFE) and graphene oxide (GO) and performing ultrasonic reaction. After the adhesive (PTFE) is hydrophilically modified, a large number of hydroxyl groups are contained on its surface, and a large number of oxygen-containing functional groups (hydroxyl groups, carbonyl groups, carboxyl groups, etc.) on the surface of the graphene oxide (GO) drive its adsorption on the surface of the adhesive (PTFE). The graphene oxide (GO) is reduced to obtain an adhesive (PTFE) coated with reduced graphene oxide (rGO), that is, the binder (PTFE@rGO).

[0052] As a preferred embodiment, the method for hydrophilic modification of the adhesive includes: 1. Pretreatment: Add the resin adhesive powder into a container filled with an ethanol solution, and perform ultrasonic treatment for 0.5 - 1 h to remove surface impurities. Then, freeze-dry for 8 - 12 h, and use a 400 - 600 mesh sieve to sieve the dried powder to obtain a clean resin adhesive powder, which is placed in an oven for standby.

[0053] 2. Provide a reducing agent: Using dimethyl sulfoxide (C2H6OS) as a stable solvent for organic polymer synthesis, mix dimethyl sulfoxide, acetophenone (C9H 10 O), and potassium tert-butoxide (C4H9OK) in a mass ratio of 20:3:10. Utilize the inductive effect of the three methyl groups of C4H9OK to react with C9H 10 O to prepare an acetophenone dianion solution for reducing the resin adhesive powder. The specific mixing method includes: first add the dimethyl sulfoxide C2H6OS solution and C9H 10 O into a container and stir evenly, then add C4H9OK in multiple small amounts, stir with a glass rod while adding, and perform water bath ultrasonic treatment until completely dissolved to obtain an acetophenone dianion solution. The acetophenone dianion has strong reducibility and can reduce the unsaturated C-C bonds in organic compounds. The main covalent bond in the PTFE molecule is the C-C bond.

[0054] 3. Add the PTFE powder obtained in step 1 to the phenylacetone dianion solution obtained in step ②, heat in a water bath for 16-24 hours, and set the temperature to 50-60°C; then wash twice with tetrahydrofuran (C4H8O) to remove excess C9H 10 O; then, the product was washed with deionized water for 2 to 3 times, placed in a vacuum oven and baked for 12 to 14 hours at a temperature of 70 to 90° C. to obtain a resin adhesive powder with a reduced surface.

[0055] 4. Hydrophilic modification: The resin adhesive powder with reduced surface obtained after baking in step 3 is immersed in an acidic potassium permanganate solution at a ratio of 1:0.9~1.1, and heated in a water bath for 3~6 hours at a temperature of 60~85°C to obtain the modified resin adhesive powder for use; hydrophilic functional groups are introduced on the surface of the modified resin adhesive powder. The hydrophilic functional groups introduced on the surface can serve as "anchor points" to react chemically and / or physically adsorb with the functional groups on the surface of graphene oxide through chemical and physical interactions between polar groups to significantly improve the interfacial bonding force, so that graphene oxide is adsorbed on the surface of the modified numerical adhesive to form a graphene fully encapsulated structure.

[0056] Preferably, the resin adhesive includes polytetrafluoroethylene, polyvinylidene fluoride, ethylene-tetrafluoroethylene copolymer, tetrafluoroethylene-hexafluoropropylene copolymer.

[0057] More preferably, the resin adhesive is polytetrafluoroethylene.

[0058] As a preferred embodiment, the method for graphene-modified resin adhesive comprises: ① Add GO powder into deionized water solution and stir ultrasonically to form a uniform suspension of 90~120 mg·mL -1 spare.

[0059] ② Add the modified resin adhesive powder into a beaker containing a mixed solution of anhydrous ethanol and deionized water and perform water bath ultrasonic dispersion for 0.5-1.5h; ③ Add the above GO suspension into the mixed solution and disperse it by ultrasonic for 1-3h, and stir for 7-9h; ④ Add the reducing agent in a mass ratio of 1:1 to 3 with GO powder into the mixed solution and perform water bath sonication.

[0060] ⑤Then heat the mixed solution in a water bath, set the temperature to 70-90°C, and the time to 2-4h.

[0061] ⑥ The reduced graphene-coated resin adhesive precipitate is obtained, and washed with deionized water for 6 times to remove residual hydrazine hydrate, reduction products and other substances; then, freeze-dried for 8-12 hours, the dried powder is sieved with a 400-mesh sieve to obtain a graphene-modified resin adhesive composite material.

[0062] As a preferred embodiment, the present invention also uses the graphene-modified resin adhesive composite material prepared by the above technical solution as an adhesive in the preparation of dry electrodes.

[0063] Specifically, first, a dry positive electrode film is prepared from the graphene-modified resin adhesive composite material, a positive electrode active material, and a conductive agent (conductive graphite); then the dry positive electrode film is hot-rolled to form a dry positive electrode sheet; finally, the dry positive electrode sheet is die-cut and assembled with a negative electrode sheet to form a battery.

[0064] As a preferred embodiment, the method for preparing the dry positive electrode film includes: mixing a positive electrode active material and a conductive agent, adding an adhesive thereto, stirring at a temperature <18°C and 800 rpm for 15 min, then closing the cooling system, and stirring at 3000 rpm to naturally shear and heat up to 90°C to obtain a fibrillated positive electrode mixed powder; adding the fibrillated positive electrode mixed powder to a roller press, and hot-rolling / thinning it into a self-supporting film at 130°C to obtain a dry positive electrode film.

[0065] As a preferred embodiment, the above dry positive electrode film is hot-rolled at 130°C and laminated with a coated aluminum foil having a thickness of (12 + 1 + 1) μm to obtain a continuously wound dry positive electrode sheet.

[0066] As a preferred embodiment, the above dry positive electrode sheet is die-cut and assembled with a negative electrode sheet (a slurry obtained by uniformly dispersing a mixture of a negative electrode active material graphite: a conductive agent carbon black: an adhesive carboxymethyl cellulose + styrene-butadiene rubber (CMC + SBR) in a mass fraction ratio of 95:2:3 is coated on a 6-μm-thick copper foil, and the coated copper foil is roll-pressed and slit to obtain a graphite negative electrode sheet) to form a soft-pack battery.

[0067] The technical solution of the present invention will be described in detail below through specific examples.

[0068] Example 1 This example provides an adhesive (PTFE@rGO), see Figure 1The figure shows a schematic diagram of the preparation process simulation of the binder. First, after mixing the hydrophilic modified adhesive (PTFE) dispersion with the graphene oxide (GO) suspension, the adhesive (PTFE) has a large number of hydrophilic functional groups (such as carbonyl, carboxyl, etc.) on its surface after hydrophilic modification, and the surface of graphene oxide (GO) also has a large number of oxygen-containing functional groups (such as hydroxyl, carbonyl, carboxyl, etc.), which drives it to adsorb on the surface of the adhesive (PTFE). Graphene oxide adsorbs onto the surface of the adhesive and forms a stable structure. Then, hydrazine hydrate is added as a reducing agent for ultrasonic reaction, and the graphene oxide (GO) on the surface is reduced. Finally, reduced graphene oxide (rGO) is obtained and coated on the surface of the adhesive (PTFE), that is, the binder (PTFE@rGO) is obtained.

[0069] After the binder (PTFE@rGO) is mixed with the active substance, it forms a three-dimensional "network" structure by fibrillation under the action of stirring and shearing, and the activity is cross-linked by this fibrous three-dimensional grid structure to achieve the bonding effect.

[0070] Specifically, the preparation steps include: (1) Hydrophilic modification of the resin adhesive: ① Add the resin adhesive (PTFE MP1200) powder into a container filled with ethanol solution, and after ultrasonic treatment for 0.5 h to remove surface impurities; then freeze-dry for 10 h, and use a 450-mesh sieve to sieve the dried powder to obtain clean resin adhesive powder and place it in an oven for standby.

[0071] ② First, add the dimethyl sulfoxide C2H6OS solution and C9H 10 O into a container and stir evenly, then add C4H9OK in small amounts several times, stirring with a glass rod while adding, and perform water bath ultrasonic treatment until completely dissolved to obtain the benzylacetone dianion solution.

[0072] ③ Add the PTFE powder obtained in step ① into the benzylacetone dianion solution obtained in step ②, heat in a water bath for 18 h, set the temperature at 50 - 60 °C, then wash with tetrahydrofuran (C4H8O) twice to remove the excess C9H 10 O, wash the obtained product with deionized water 2 - 3 times again, and place it in a vacuum oven for baking for 12 - 14 h, setting the temperature at 70 - 90 °C.

[0073] ④ Immerse the resin adhesive powder obtained after baking in step ③ in a solution containing 0.5 mol·L -1 potassium permanganate (KMnO4) and 1 mol·L -1 sulfuric acid (H2SO4) at a ratio of 1:1.5. Heat in a water bath for 4 h, set the temperature at 70 °C, to obtain the modified resin adhesive powder for standby.

[0074] (2)Graphene Oxide Coated Resin Adhesive: ① Add GO powder into deionized water solution, and form a uniform GO suspension by ultrasonic stirring at 100mg·mL -1 for standby.

[0075] ② Add the modified resin adhesive powder into a beaker containing a mixed solution of anhydrous ethanol and deionized water (the volume ratio of ethanol to water is 1:1, and the mass ratio of the modified resin adhesive powder to the mixed solution is 1:9), and perform water bath ultrasonic dispersion for 1h. Then add the above GO suspension into the mixed solution, and the addition ratio is: the mass ratio of GO in the GO suspension to the modified resin adhesive powder in the mixed solution is 1:2.2*10 6 , ultrasonic disperse for 2h, and stir for 8h to obtain graphene oxide coated resin adhesive. In this step, graphene is adsorbed on the surface of the resin adhesive to form a fully coated structure.

[0076] (3)Reduction of Graphene Oxide.

[0077] Add hydrazine hydrate into the graphene oxide coated resin adhesive obtained in step (2), where the mass ratio of GO powder to hydrazine hydrate is 1:1.5, and then form a uniform mixed solution by water bath ultrasonic, and reduce graphene oxide by adding the reducing agent hydrazine hydrate.

[0078] ③ Then heat the mixed solution in a water bath to 80°C for 2.5h to obtain a precipitate of reduced graphene coated resin adhesive, wash it 6 times with deionized water to remove residual hydrazine hydrate, reduction products and other substances. Then freeze-dry for 10h and sieve the dried powder through a 400-mesh sieve to obtain the PTFE@rGO composite material.

[0079] Refer to Figure 2 for the SEM image of the PTFE@rGO composite material. As can be seen from the figure, the selected resin adhesive is PTFE, and graphene is evenly and fully coated on the surface of PTFE.

[0080] This embodiment provides a preparation method of a graphite positive electrode sheet by a dry electrode process. The specific steps include: First, use high-nickel ternary (NCM811) positive active material, binder (PTFE@rGO) and conductive agent (conductive graphite) as raw materials, and prepare a dry positive electrode film according to a mass ratio of 95:4:1. Specifically, it includes: Mixing: First, add the positive active material and the conductive agent into a blender, set the dispersion speed at 3000rpm and stir for 10 minutes, then slow stir at 150rpm to cool down to 18°C; then add the binder, control the temperature <18°C, stir at 800rpm for 15min, then turn off the cooling system, and stir at 3000rpm to naturally shear and heat up to 90°C to obtain a fibrillated positive electrode mixed powder.

[0081] Film formation: Put the above-mentioned mixed powder into a primary film-forming / thinning roll press, and perform primary hot roll pressing / thinning at 130 °C to form a self-supporting film, obtaining a dry-process cathode film; wherein, the film-forming roll gap is set to 110 μm, the thinning roll gap is 70 μm, the film-forming differential speed is 1:1.5, the thinning differential speed is 1:1, the film-forming pressure is 6 T, and the thinning pressure is 9 T.

[0082] Then, use the dry-process cathode film prepared by the above steps to prepare a dry-process cathode sheet.

[0083] Laminating the above-mentioned dry-process cathode film with a coated aluminum foil with a thickness of (12 + 1 + 1) μm under hot roll pressing at 130 °C to obtain a continuously wound dry-process cathode sheet, wherein the roll gap is set to 140 μm and the pressure is 40 T.

[0084] Finally, perform battery assembly.

[0085] Graphite anode sheet: The negative electrode active material graphite: conductive agent carbon black: binder carboxymethyl cellulose + styrene-butadiene rubber (CMC + SBR) are mixed according to a mass fraction ratio of 95:2:3, and the mixture is uniformly dispersed in a slurry using deionized water solvent and coated on a 6-μm-thick copper foil, and then roll pressed and slit to obtain a graphite anode sheet.

[0086] After die-cutting the above-mentioned dry-process cathode sheet, assemble it with the graphite anode sheet to form a soft-pack battery, and perform cycle and rate charge-discharge tests.

[0087] Example 2 The difference between this example and Example 1 is that in step (2), the mass ratio of GO in the GO suspension to the modified resin adhesive powder in the mixed solution is 1:2.2×10 5 . Other steps are the same.

[0088] Comparative Example 1 This comparative example provides a preparation method for preparing a graphite cathode sheet by a dry-process electrode process. The specific steps include: First, use high-nickel ternary (NCM811) cathode active material, binder (PTFE), and conductive agent (conductive graphite) as raw materials, and prepare a dry-process cathode film sheet according to a mass ratio of 95:4:1. Specifically, it includes: Mixing: First, add the cathode active material and the conductive agent into a mixer, set the dispersion speed to 3000 rpm and stir for 10 minutes, then slow stir at 150 rpm to cool down to 18 °C; then add the binder, control the temperature <18 °C, stir at 800 rpm for 15 min, and then turn off the cooling system; stir at 3000 rpm and shear naturally to raise the temperature to 90 °C to obtain a fibrillated cathode mixed powder.

[0089] Film formation: Put the above-mentioned fibrillated positive electrode mixed powder into a primary film formation / thinning roll press, and thermally roll press / thin it into a self-supporting film at 130 °C to obtain a dry-process positive electrode film. Among them, the film formation roll gap is set to 110 μm, the thinning roll gap is 70 μm, the film formation differential speed is 1:1.5, the thinning differential speed is 1:1, the film formation pressure is 6 T, and the thinning pressure is 9 T.

[0090] Then, use the dry-process positive electrode film prepared in the above steps to prepare a dry-process positive electrode sheet.

[0091] Laminating the above-mentioned dry-process positive electrode film with a coated aluminum foil with a thickness of (12 + 1 + 1) μm under hot roll pressing at 130 °C to obtain a continuously wound dry-process positive electrode sheet. Among them, the roll gap is set to 140 μm and the pressure is 40 T.

[0092] Finally, perform battery assembly.

[0093] Graphite negative electrode sheet: The negative active material graphite: conductive agent carbon black: binder carboxymethyl cellulose + styrene-butadiene rubber (CMC + SBR) are mixed according to a mass fraction ratio of 95:2:3. The slurry obtained by uniformly dispersing the mixture using deionized water solvent is coated on a 6-μm-thick copper foil, and then roll pressed and slit to obtain a graphite negative electrode sheet.

[0094] After die-cutting the above-mentioned dry-process positive electrode sheet, assemble it with the graphite negative electrode sheet to form a soft-pack battery, and perform cyclic and rate charge-discharge tests.

[0095] Refer to Figure 3 , after the batteries assembled in Example 1 and Comparative Example 1 are cycled 400 times at 1C, the battery capacity attenuation of Comparative Example 1 is much more serious than that of Example 1. The capacity retention rate of Example 1 is 93.96%, while that of Comparative Example 1 is only 89.12%, indicating that the graphene-coated PTFE fibrils play a role in suppressing the attenuation of battery capacity during the cycling process.

[0096] Comparative Example 2 The difference between this comparative example and Example 1 is only that in step (2), the mass ratio of GO in the GO suspension to the modified resin adhesive powder in the mixed solution is 1:2.2×10 7 . Other steps are the same.

[0097] This comparative example shows that for full coating, the effect is not good, and the ratio can be adjusted to supplement the electrochemical performance Adopting the technical solution of Comparative Example 2, since the addition ratio of reduced graphene oxide is reduced, the density of graphene covering the surface of the resin adhesive decreases significantly, resulting in a significant decline in the electrochemical performance of the battery. In addition, when the mass ratio of reduced graphene oxide to the resin adhesive is greater than 1:2.2×10 5, the performance cannot be significantly improved, indicating that the adsorption amount on the surface of the resin adhesive has reached saturation, and there is no obvious improvement in the cycle performance and capacity of the battery, which will not be elaborated here.

[0098]

[0099] The above are only the preferred embodiments of the present invention, and it does not limit the protection scope of the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any changes, modifications, substitutions, integrations, and parameter changes made to these embodiments by means of conventional substitutions or capable of achieving the same functions without departing from the principle and spirit of the present invention fall within the protection scope of the present invention.

Claims

1. A preparation method of a graphene-modified resin binder for a dry electrode, characterized in that, It includes obtaining a hydrophilic modified resin adhesive by hydrophilic modification of a resin adhesive, then adsorbing graphene oxide onto the surface of the hydrophilic modified resin adhesive to form an all - enveloping structure; finally, reducing the graphene oxide to reduced graphene oxide by a reduction method, thus obtaining a graphene - modified resin binder.

2. The preparation method of the graphene-modified resin binder according to claim 1, characterized in that, The adsorption includes the functional groups on the surface of the hydrophilic modified resin adhesive combining with the functional groups on the surface of graphene oxide to form a stable structure; and / or, the resin adhesive includes any one or a combination of two or more of polytetrafluoroethylene, polyvinylidene fluoride, ethylene - tetrafluoroethylene copolymer, and tetrafluoroethylene - hexafluoropropylene copolymer; and / or, the reduction method includes any one of a reducing agent chemical reduction method, a high - temperature heat treatment deoxidation method, a solvothermal reduction method, an electrochemical reduction method, a photoreduction method, and a microwave - assisted reduction method; and / or, in the reducing agent chemical reduction method, the reducing agent is selected from any one of hydrazine hydrate, sodium borohydride, lithium aluminum zinc hydride and aluminum powder, ammonia, vitamin C, potassium hydroxide, sodium oxide, dimethylhydrazine, p - phenylenediamine, hydroiodic acid, and phenylhydrazine.

3. The preparation method of the graphene-modified resin binder according to claim 1, wherein, The method for hydrophilic modification of the adhesive includes: Step (1): After mixing an organic solvent and acetophenone uniformly, add a strong base in small amounts multiple times, stir while adding, and perform water - bath ultrasonic treatment until completely dissolved to obtain an acetophenone di - anion solution; Step (2): Add the resin adhesive powder to the acetophenone di - anion solution, heat in a water - bath, after post - treatment, and then oxidize with an oxidant to obtain the hydrophilic modified resin adhesive.

4. The preparation method of the graphene-modified resin binder according to claim 3, wherein In step (1) , the strong base is potassium tert - butoxide or sodium hydride; the organic solvent is dimethyl sulfoxide; the molar ratio of acetophenone to the strong base is 1:2 - 1:4; the mass ratio of the organic solvent to acetophenone is 20:3; and / or, in step (2), the molar ratio of the resin adhesive powder to acetophenone is 1:1.5 - 2; preferably, the molar ratio is 1:1.5; the time for water - bath heating is 16 - 24 h, and the temperature is 50 - 60 °C; the post - treatment includes: first washing with tetrahydrofuran to remove excess acetophenone, then washing with deionized water 2 - 3 times, and placing it in a vacuum oven for baking for 12 - 14 h, with the temperature set at 70 - 90 °C; Preferably, before the hydrophilic modification of the powdery resin adhesive in step (2), a pre - treatment is also included; The pre - treatment includes: adding the resin adhesive to ethanol, performing ultrasonic treatment to remove surface impurities; then freeze - drying and sieving to obtain a resin adhesive powder and placing it in an oven for standby; the time for ultrasonic treatment is 0.5 - 1 h; the time for freeze - drying is 8 - 12 h, and the temperature is - 55 - 75 °C; preferably, the temperature is - 60 °C; the oxidant is an acidic potassium permanganate solution; preferably, the oxidant is an acidic potassium permanganate solution; more preferably, the mass ratio of the resin adhesive to the oxidant is 1:(0.9 - 1.1).

5. The preparation method of the graphene-modified resin binder according to any one of claims 1-4, characterized in that The specific preparation method includes: S1. Provide a graphene oxide suspension; Disperse graphene oxide powder in deionized water, and perform ultrasonic stirring to obtain the graphene oxide suspension; S2. Provide a hydrophilic modified resin adhesive solution; S3. Add the graphene oxide suspension to the hydrophilic modified resin adhesive solution and disperse it by ultrasonic wave to obtain a dispersion; S4. Add a reducing agent to the dispersion in S3, mix evenly, and then carry out water bath heating. The obtained precipitate is the graphene modified resin binder with reduced graphene oxide coating the resin adhesive.

6. The preparation method of the graphene modified resin binder according to claim 5, wherein In S1, the content of graphene oxide in the graphene oxide suspension is 90~120 mg·mL -1 ; In S3, the mass ratio of graphene oxide to the hydrophilic modified resin adhesive is 1:2.2×10 5 ~2.2×10 6 ; the time of ultrasonic dispersion is 1.5 - 1.5h; in S4, the mass ratio of the reducing agent to the graphene oxide powder is 1:1 - 3; the water bath heating includes a temperature of 70 - 90 °C and a time of 2 - 4h.

7. A graphene-modified resin binder, which is prepared by using the preparation method described in any one of claims 1-6; wherein, Reduced graphene oxide uniformly wraps the surface of the resin adhesive.

8. A dry-type positive electrode film is prepared by mixing the graphene modified resin binder as claimed in claim 7, a positive electrode active material, and a conductive agent evenly, obtaining a fibrillated positive electrode mixed powder under stirring and shearing, and then rolling it into a film.

9. A positive electrode sheet is obtained by laminating the dry-type positive electrode film as claimed in claim 8 with a current collector by hot rolling.

10. A battery includes a positive electrode and a negative electrode; the positive electrode is the positive electrode sheet as claimed in claim 9.

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