Dry binder and preparation method therefor, and electrode sheet and preparation method therefor

Abstract

The present application relates to the technical field of secondary ion batteries, and in particular relates to a dry binder and a preparation method therefor, and an electrode sheet and a preparation method therefor. The preparation method for a dry binder comprises the following steps: mixing a graft polymer and a metal salt, and granulating same to obtain a dry binder, wherein the graft polymer comprises maleic-anhydride-grafted polypropylene. In the present application, maleic-anhydride-grafted polypropylene is used as a polymer matrix, and is blended with a metal salt to prepare a solvent-free dry binder by means of a mixing process; and the prepared dry binder exhibits a good adhesive strength and lithium-ion conductivity, a high use safety, as well as low raw material costs.

Description

Dry adhesives and their preparation methods, as well as electrode sheets and their preparation methods. Technical Field

[0001] This application relates to the field of secondary ion battery technology, and in particular to a dry binder and its preparation method, as well as an electrode sheet and its preparation method. Background Technology

[0002] Rechargeable lithium-ion batteries (LIBs) have become an important energy storage technology, especially against the backdrop of increasing global focus on green technologies and environmental issues. While lithium-ion batteries are widely regarded as clean energy storage devices, their manufacturing processes are not yet fully sustainable. A significant environmental and health concern stems from the toxic and volatile solvents used in the electrode manufacturing stage.

[0003] In traditional lithium-ion battery electrode manufacturing, metal current collectors are typically coated with a slurry composed of active materials, conductive agents, and polymer binders (such as polyvinylidene fluoride, PVDF) mixed with N-methyl-2-pyrrolidone (NMP) solvent. While NMP is an effective solvent for PVDF, it is both expensive and toxic. NMP evaporates slowly, making drying and recycling processes time-consuming and costly. Furthermore, NMP is harmful to health, for example, causing male infertility, and is flammable, increasing the risk of fire. Long-term exposure to NMP not only threatens worker health but also increases production costs and environmental impact; therefore, finding safer and more sustainable alternatives in lithium-ion battery manufacturing is imperative.

[0004] Dry processing is considered a novel manufacturing method for next-generation lithium-ion battery electrodes due to its unparalleled advantages in operating costs and energy efficiency compared to traditional solvent-based processes. Furthermore, by eliminating the use of solvents, dry processing can increase the maximum loading threshold of active materials, enabling electrode manufacturing with higher loading capacities and paving the way for battery miniaturization. However, while dry processing is solvent-free, current industrial manufacturing processes for its auxiliary binder materials involve significant amounts of solvents and fluoropolymers, such as the PTFE dry binders and acrylate dry binders disclosed in Chinese patent applications with publication numbers CN117777343A, CN117691110A, and CN117438531A. Moreover, because dry binders involve a high-temperature shear fiberization process, the binders require superior thermal and mechanical stability, as well as electrolyte resistance. PTFE binder fiberization requires high-temperature and high-pressure conditions, while acrylate binders suffer from poor mechanical properties.

[0005] In view of the above, this application is hereby submitted. Summary of the Invention

[0006] The following is an overview of the subject matter described in detail herein. This overview is not intended to limit the scope of the claims.

[0007] The purpose of this application is to provide a dry binder and its preparation method, as well as an electrode sheet and its preparation method, which can prepare binder masterbatch through a solvent-free dry process, thereby reducing manufacturing costs and increasing electrode sheet load.

[0008] To achieve the above objectives, the first aspect of this application provides a method for preparing a dry adhesive, comprising the following steps:

[0009] The grafted polymer is mixed with a metal salt and granulated to obtain a dry binder.

[0010] The grafted polymer includes maleic anhydride-grafted polypropylene.

[0011] In specific embodiments of this application, the grafted polymers include maleic anhydride-grafted polypropylene and maleic anhydride-grafted polystyrene.

[0012] In a specific embodiment of this application, the mass ratio of maleic anhydride-grafted polypropylene to maleic anhydride-grafted polystyrene in the grafted polymer is (80-98):(20-2).

[0013] In a specific embodiment of this application, the proportion of grafted group units in the grafted polymer is 0.01wt% to 5wt%.

[0014] In a specific embodiment of this application, the metal salt is composed of cations and anions; the cations include Li + Na + K + Zn 2+ Al 3+ Mg 2+ Mn 2+ and Ga 2+ The anion comprises any one of the following: hydroxide, bis(trifluoromethanesulfonyl)imide, bis(fluorosulfonyl)imide, chloride, sulfate, carbonate, nitrate, perchlorate, tetrafluorophosphate, hexafluorophosphate, bis(oxalate-borate), and difluoro(oxalate-borate). Further, the metal salt comprises at least one of LiOH, LiTFSI, LiFSI, LiClO4, LiBF4, LiPF6, LiBOB, LiDFOB, NaOH, NaClO4, NaPF6, and Na2CO3.

[0015] In a specific embodiment of this application, the molar ratio of the grafting group unit in the grafted polymer to the cation in the metal salt is (0.1~30):1.

[0016] In a specific embodiment of this application, the grafted polymer is first melt-treated, and then mixed with the metal salt. Further, the melting temperature is 120–200°C, and the mixing temperature is 60–150°C.

[0017] The second aspect of this application provides a dry adhesive prepared using the dry adhesive preparation method of the first aspect.

[0018] The third aspect of this application provides an electrode sheet prepared using a dry binder obtained by the preparation method of the first aspect of this application or a dry binder of the second aspect.

[0019] The fourth aspect of this application provides a method for preparing the electrode sheet of the third aspect, comprising the following steps:

[0020] (a) A dry binder, electrode active material, conductive agent and optional filler are mixed in proportion and blended by screw shearing to obtain a fibrous solid.

[0021] (b) The solid material is heated and rolled into a sheet, and then hot-pressed onto the surface of the current collector to obtain an electrode sheet.

[0022] In a specific embodiment of this application, the mass ratio of the dry binder, electrode active material and conductive agent is (1-10):(80-95):(5-10).

[0023] Compared with the prior art, the beneficial effects of this application are as follows:

[0024] This application utilizes maleic anhydride-grafted polypropylene as a polymer matrix, and prepares a solvent-free dry binder by blending it with metal salts through a mixing process. On the one hand, maleic anhydride-grafted polypropylene has excellent electrolyte resistance. On the other hand, the solvent-free mixing process, the good solvation ability of maleic anhydride groups for metal ions, and the unique microphase structure of the grafted side chains enable the polymer matrix to accommodate and dissociate electrolyte salts. This ensures the bonding strength of the binder while forming an ion-aggregated conductive network, significantly improving the room temperature ionic conductivity and helping to improve the rate performance of the battery.

[0025] After reading and understanding the accompanying diagrams and detailed descriptions, the other aspects can be understood. Attached Figure Description

[0026] The accompanying drawings are provided to further understand the technical solutions herein and form part of the specification. They are used together with the embodiments of this application to explain the technical solutions herein and do not constitute a limitation on the technical solutions herein.

[0027] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0028] Figure 1 is a schematic diagram of a twin-screw extruder for preparing dry electrode sheets according to an embodiment of this application. Detailed Implementation

[0029] The technical solution of this application will be clearly and completely described below with reference to the accompanying drawings and specific embodiments. However, those skilled in the art will understand that the embodiments described below are only some embodiments of this application, not all embodiments, and are only used to illustrate this application, and should not be regarded as limiting the scope of this application. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall be followed. Where the manufacturers of reagents or instruments are not specified, they are all conventional products that can be purchased commercially.

[0030] In the description of this application, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0031] In the description of this application, it should be noted that, unless otherwise expressly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0032] The first aspect of this application provides a method for preparing a dry adhesive, comprising the following steps:

[0033] The grafted polymer is mixed with a metal salt and granulated to obtain a dry binder.

[0034] Grafted polymers include maleic anhydride-grafted polypropylene.

[0035] In the preparation method of this application, a grafted polymer is selected as the main polymer of the dry binder. Compared with the existing PTFE dry fiber binder, the grafted polymer has a mature synthesis process, low cost, and excellent ion conduction properties. It can be mass-produced by solvent-free hot melt grafting. Furthermore, this application uses maleic anhydride grafted polypropylene, which has good electrolyte resistance and adhesion properties. The grafted maleic anhydride groups can ensure stable adhesion to the powder active material and current collector, and the maleic anhydride groups can also interact with metal salts to promote ion conduction. This improves performance while being compatible with existing production line processes, and has a superior cost advantage.

[0036] In specific embodiments of this application, the grafted polymers include maleic anhydride-grafted polypropylene and maleic anhydride-grafted polystyrene. The combined use of maleic anhydride-grafted polystyrene and maleic anhydride-grafted polypropylene forms a unique microphase structure, which can further improve the cohesive strength and room-temperature ionic conductivity of the binder.

[0037] There are many types of maleic anhydride-grafted polymers, such as maleic anhydride-grafted polyethylene, maleic anhydride-grafted polyolefin elastomers, maleic anhydride-grafted ethylene-vinyl acetate copolymers, maleic anhydride-grafted acrylonitrile-butadiene-styrene copolymers, maleic anhydride-grafted polyphenylene ether, and maleic anhydride-grafted ethylene propylene diene monomer (EPDM) rubber. The inventors of this application have discovered that using maleic anhydride-grafted polypropylene and maleic anhydride-grafted polystyrene can not only ensure the electrolyte resistance of the resulting adhesive, but also ensure the bonding performance and cost.

[0038] In a specific embodiment of this application, the mass ratio of maleic anhydride-grafted polypropylene to maleic anhydride-grafted polystyrene in the grafted polymer is (80-98):(20-2), for example, it can be a range of 80:20, 82:18, 85:15, 88:12, 90:10, 92:8, 95:5, 98:2 or any two of these, thereby improving the dry processability, the bonding performance, cohesive strength and room temperature ionic conductivity of the obtained dry adhesive.

[0039] In a specific embodiment of this application, the weight-average molecular weight of the grafted polymer is 5 × 10⁻⁶. 5 ~2×10 7 Da, for example, can be 5×10 5 Da, 8×10 5 Da, 1×10 6 Da, 3×10 6 Da, 5×10 6 Da, 8×10 6 Da, 1×107 Da, 1.2×10 7 Da, 1.5×10 7 Da, 1.8×10 7 Da, 2×10 7 The range is defined as Da or any combination of both. Further, the weight-average molecular weight of the grafted polymer is 5 × 10⁻⁶. 5 ~1.5×10 7 Da.

[0040] In specific embodiments of this application, the proportion of grafted group units in the grafted polymer is 0.01 wt% to 5 wt%, for example, it can be 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, or any combination thereof. Further, the proportion of grafted group units in the grafted polymer is 0.1 wt% to 2 wt%, which helps to improve battery performance by interacting with metal salts while ensuring the bonding strength of the binder to the active material and the current collector.

[0041] The grafting polymer used in this application can be a commercially available grafting polymer, provided that the type, molecular weight, grafting rate, etc., meet the above conditions.

[0042] In a specific embodiment of this application, the metal salt is composed of cations and anions; the cations include Li + Na + K + Zn 2+ Al 3+ Mg 2+ Mn 2+ and Ga 2+ Any of the following; anions include hydroxide (OH-) - ), bis(trifluoromethanesulfonyl)imide (TFSI) - ), difluorosulfonamide (FSI) - ), chloride ions (Cl) - ), sulfate ions (SO4) 2- ), carbonate ions (CO3) 2- ), nitrate ions (NO3) - ), perchlorate ions (ClO4) - ), tetrafluorophosphate ions (BF4) - ), hexafluorophosphate ions (PF6) - ), bis(oxalate)borate ion (BOB) - ) and difluorooxalate borate ion (DFOB) -Any one of the following. Further, the metal salt includes at least one of LiOH, LiTFSI, LiFSI, LiClO4, LiBF4, LiPF6, LiBOB, LiDFOB, NaOH, NaClO4, NaPF6, and Na2CO3.

[0043] In a specific embodiment of this application, the molar ratio of the grafting group unit in the grafted polymer to the cation in the metal salt is (0.1–30):1, for example, it can be a range of 0.1:1, 0.5:1, 1:1, 3:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1, or any combination thereof, and further, (0.5–5):1. Regulating the molar ratio of the grafting group unit to the cation in the metal salt within the above range balances the need to ensure both adhesive performance and improved room-temperature ionic conductivity; it avoids the degradation of adhesive performance caused by excessive cations in the metal salt, and also avoids the insignificant improvement in room-temperature ionic conductivity caused by insufficient cations in the metal salt.

[0044] In a specific embodiment of this application, the grafted polymer is first melt-treated and then mixed with a metal salt. Further, the melting temperature is 120–200°C, for example, a range of 120°C, 140°C, 150°C, 180°C, 200°C, or any combination thereof; the mixing temperature is 60–150°C, for example, a range of 60°C, 80°C, 100°C, 120°C, 140°C, 150°C, or any combination thereof.

[0045] In practice, the melt treatment and mixing process can be carried out using a twin-screw extruder. Specifically, the grafted polymer and metal salt can be dried and dehydrated first. Then, the dried and dehydrated grafted polymer is added to the twin-screw extruder and set to the melt treatment temperature. After the grafted polymer melts, the metal salt is added to the molten grafted polymer through the feeding hopper in proportion. The mixing temperature is set, and the temperature and shear force of the screw cause the maleic anhydride groups of the grafted polymer to open the ring and complex with the metal salt to form an ionic polymer. After extrusion and cooling through the extrusion die, the dry binder is granulated using a granulator.

[0046] In a specific embodiment of this application, the drying and dehydration temperature can be 100 to 140°C, for example, 100°C, 110°C, 120°C, 130°C, 140°C or any combination thereof.

[0047] The second aspect of this application provides a dry adhesive prepared using the dry adhesive preparation method of the first aspect.

[0048] The third aspect of this application provides an electrode sheet prepared using a dry binder obtained by the preparation method of the first aspect of this application or a dry binder of the second aspect.

[0049] The fourth aspect of this application provides a method for preparing the electrode sheet of the third aspect, comprising the following steps:

[0050] (a) A dry binder, electrode active material, conductive agent and optional filler are mixed in proportion and blended by screw shearing to obtain a fibrous solid.

[0051] (b) After heating and rolling the solid into a sheet, it is hot-pressed onto the surface of the current collector to obtain an electrode sheet.

[0052] Blending can be carried out using a screw extruder, heated calendering can be carried out using a roller press, and hot pressing can be carried out using a hot roller press. Specifically, in shear blending, the mixture can be stirred and mixed at 200-300 rpm for 5-15 minutes, and then stirred and mixed at 300-400 rpm for 20-40 minutes.

[0053] When preparing a dry-process negative electrode sheet, the electrode active material can be any negative electrode active material; when preparing a dry-process positive electrode sheet, the electrode active material can be any positive electrode active material. The following examples use graphite as an example of a negative electrode active material, but are not limited to this.

[0054] Figure 1 is a schematic diagram of a twin-screw extruder for preparing dry electrode sheets according to an embodiment of this application. Dry binder, electrode active material, conductive agent, etc. can be added to the twin-screw extruder through different feeding hoppers to obtain fibrous solids. Then, the solids are heated and calendered into finished products, and then hot-pressed onto the surface of the current collector to obtain electrode sheets.

[0055] In a specific embodiment of this application, the temperature during shear blending is 30 to 90°C, for example, it can be a range of 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, or any combination thereof.

[0056] In a specific embodiment of this application, the temperature during the heated calendering process can be 140–160°C, and the pressure can be 3–8 MPa.

[0057] In a specific embodiment of this application, the thickness of the heated calendered sheet is 20 to 120 μm, for example, it can be 20 μm, 40 μm, 60 μm, 80 μm, 100 μm, 120 μm or any combination thereof.

[0058] In the specific embodiments of this application, the temperature in the hot pressing bonding process can be 100-140°C, and the time can be 5-20 minutes.

[0059] In a specific embodiment of this application, the mass ratio of dry binder, electrode active material and conductive agent is (1-10):(80-95):(5-10). The specific mass ratio of dry binder, electrode active material and conductive agent can be adjusted according to the composition requirements of the electrode sheet and is not limited thereto.

[0060] In specific embodiments of this application, the filler includes, but is not limited to, solid electrolyte particles, such as oxide solid electrolyte particles (LLZO) and sulfide solid electrolyte particles (LGPS). The specific amount of filler is adjusted according to the composition requirements of the electrode sheet, for example, it can be 1wt% to 5wt% of the total material (mass of dry binder, electrode active material, conductive agent and filler), but is not limited to this.

[0061] In specific embodiments of this application, the electrode active material includes at least one of graphite, silicon-carbon materials, silicon-oxygen materials, lithium iron phosphate materials, and ternary cathode materials; the conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene, and carbon nanofibers.

[0062] The current collector used in this application is conventionally selected based on the type of electrode.

[0063] Examples 1-6

[0064] This embodiment provides a method for preparing a dry binder and an electrode sheet, including the following steps:

[0065] (1) The grafted polymer is dried at 120°C to remove water, and then added to a twin-screw extruder. The screw is heated to the set temperature of 150°C to soften and melt the polymer.

[0066] (2) Add the metal salt to the polymer obtained in step (1) through the hopper and mix for 70 minutes. The screw speed during mixing is 120 rpm and the temperature is 150°C. Then, after extrusion through the co-extrusion die, cooling and drying are performed, and then dry binder is obtained through a granulator.

[0067] (3) Weigh the negative electrode active material graphite, conductive agent carbon black and dry binder in a mass ratio of 92:5:3. Add graphite and carbon black to the extruder and stir at 120 rpm for 10 min. Then add the dry binder and stir at 250 rpm for 10 min, followed by stirring at 350 rpm for 30 min to obtain fibrous solids.

[0068] (4) The fibrous solid obtained in step (3) is placed into a roller press and hot-rolled at 150°C / 5MPa pressure to form a dry electrode film with a thickness of 20-120μm (specifically 80μm). Then the dry electrode film is bonded to the negative electrode current collector (such as copper foil) and hot-rolled at 120°C for 10min to obtain a dry negative electrode sheet.

[0069] In the preparation of the dry adhesives in Examples 1-6, the grafted polymer used was maleic anhydride-grafted polypropylene (PP-MAH, weight-average molecular weight approximately 600,000 Da) with a grafting rate of 1%, and the metal salt was LiOH. The amounts of PP-MAH and LiOH, as well as the grafting groups MAH in PP-MAH and the cationic Li in LiOH, were also specified. + The molar amounts are shown in Table 1.

[0070] Table 1. Raw material usage information for different embodiments

[0071] Examples 7-11

[0072] Examples 7-11 refer to the preparation method of dry adhesive and electrode sheet in Example 5, except that PP-MAH is replaced with a mixture of PP-MAH with a grafting rate of 1% and maleic anhydride-grafted polystyrene (PS-MAH, weight average molecular weight of about 600,000 Da) with a grafting rate of 1%, and the specific amounts are shown in Table 2.

[0073] Table 2. Raw material usage information for different embodiments

[0074] Examples 12-16

[0075] Examples 12-16 refer to the preparation methods of the dry binder and electrode sheet of Example 10, the only difference being the type and amount of metal salt used. Specific information is shown in Table 3.

[0076] Table 3. Raw material usage information for different embodiments

[0077] Comparative Example 1

[0078] Comparative Example 1 follows the preparation method of Example 5, except that the grafted polymer is replaced with PTFE.

[0079] Experimental Example 1

[0080] The dry binders and electrodes prepared in different embodiments and comparative examples were tested as follows, and the test results are shown in Table 4.

[0081] Room temperature ionic conductivity: Dry binders prepared in different embodiments and comparative examples were added to a mixer to soften and obtain a solid binder. The solid binder was then placed in a roller press and hot-pressed at 5 MPa and 160°C to form a film. The film was then cut into 17 mm diameter discs (adhesive film) and assembled with stainless steel sheets to form a sandwich-like battery clamping device. The room temperature (25°C) ionic conductivity of the binder was tested according to the formula... Calculate the ionic conductivity at room temperature, where σ is the ionic conductivity, l is the thickness of the adhesive film, S is the contact surface area of ​​the tested adhesive film, and R corresponds to the intrinsic impedance of the adhesive film obtained by impedance spectroscopy.

[0082] Cohesive peel strength: The cohesive peel strength of the electrodes prepared in different embodiments was tested according to GB / T 2792-2014 "Test Method for 180° Peel Strength of Adhesives". Specifically, the electrodes were cut into test samples (200mm x 25mm). The metal side of the current collector was adhered to a stainless steel plate with double-sided tape. 3M tape (Scotch 600 / 25mm wide) was adhered to the coating surface, and the sample was rolled back and forth three times using a 1kg roller. The cohesive force between the coating and the current collector was tested using a universal tensile testing machine according to the test conditions of national standard GB / T 2792-2014.

[0083] Table 4 Test results for different embodiments

[0084] The room temperature ionic conductivity and cohesive strength of the PTFE binder in Comparative Example 1 are lower than those of the binder in the same formulation of this application, indicating that the binder of this application has higher cost and performance advantages.

[0085] According to the test results of Examples 1-6, the room temperature ionic conductivity of the adhesive films varies significantly with different LiOH contents. When the molar ratio of graft groups in the grafted polymer to cations in the metal salt (MAH:Li) is (0.5-2.6):1, the room temperature ionic conductivity of the corresponding adhesive film is significantly higher than that of adhesive films with other ratios. The cohesive strength shows a trend of first increasing and then decreasing with the increase of LiOH content, especially when MAH:Li is 1.3:1.

[0086] In the mixing of different grafted polymers with LiOH, the type of grafted polymer and the ratio of the grafted polymers affect the room temperature ionic conductivity of the binder film and the cohesive strength of the electrode. According to the test results of Examples 7-11, when the mass ratio of PP-MAH to PS-MAH is 9:1, the room temperature ionic conductivity of the binder and the cohesive strength of the electrode are optimal, which is due to the unique microphase structure of the two polymers after blending contributing to the performance improvement.

[0087] According to the test results of Examples 10 and 12-16, when LiOH is used as the metal salt, it can achieve both better ionic conductivity and cohesive strength.

[0088] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a dry adhesive, comprising the following steps: The grafted polymer is mixed with a metal salt and granulated to obtain a dry binder. The grafted polymer includes maleic anhydride-grafted polypropylene.

2. The method for preparing the dry adhesive according to claim 1, wherein, The grafted polymers include maleic anhydride-grafted polypropylene and maleic anhydride-grafted polystyrene.

3. The method for preparing the dry adhesive according to claim 2, wherein, In the grafted polymer, the mass ratio of maleic anhydride-grafted polypropylene to maleic anhydride-grafted polystyrene is (80-98):(20-2).

4. The method for preparing the dry adhesive according to claim 1, wherein, It has at least one of the following characteristics: (1) In the grafted polymer, the proportion of grafted group units is 0.01wt% to 5wt%; (2) The metal salt is composed of cations and anions; the cations include Li + Na + K + Zn 2+ Al 3+ Mg 2+ Mn 2+ and Ga 2+ Any one of the following; the anion includes any one of hydroxide, bis(trifluoromethanesulfonyl)imide, bis(fluorosulfonyl)imide, chloride, sulfate, carbonate, nitrate, perchlorate, tetrafluorophosphate, hexafluorophosphate, bis(oxalateborate) and difluorooxalateborate. (3) The metal salt includes at least one of LiOH, LiTFSI, LiFSI, LiClO4, LiBF4, LiPF6, LiBOB, LiDFOB, NaOH, NaClO4, NaPF6 and Na2CO3.

5. The method for preparing the dry adhesive according to claim 4, wherein, The molar ratio of the grafting group unit in the grafted polymer to the cation in the metal salt is (0.1~30):

1.

6. The method for preparing the dry adhesive according to claim 1, wherein, The grafted polymer is first melt-treated, and then mixed with the metal salt. The melting temperature is 120–200°C, and the mixing temperature is 60–150°C.

7. A dry adhesive prepared by the preparation method according to any one of claims 1 to 6.

8. An electrode sheet prepared by the preparation method according to any one of claims 1 to 6, or by the dry binder according to claim 7.

9. The method for preparing the electrode sheet according to claim 8, comprising the following steps: (a) A dry binder, electrode active material, conductive agent and optional filler are mixed in proportion and blended by screw shearing to obtain a fibrous solid. (b) The solid material is heated and rolled into a sheet, and then hot-pressed onto the surface of the current collector to obtain an electrode sheet.

10. The preparation method according to claim 9, wherein, The mass ratio of the dry binder, electrode active material and conductive agent is (1-10):(80-95):(5-10).

Images