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

Abstract

The present invention relates to the technical field of secondary ion batteries, and in particular to a dry binder, a preparation method thereof, an electrode sheet and a preparation method thereof. The preparation method of the dry binder comprises the following steps: kneading and granulating a graft polymer and a metal salt to obtain the dry binder; the graft polymer comprises maleic anhydride grafted polypropylene. The present invention uses maleic anhydride grafted polypropylene as a polymer matrix, and is blended with a metal salt to prepare a solvent-free dry binder through a kneading process, which has excellent bonding strength, lithium ion conduction ability, high use safety, and low raw material cost.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary ion batteries, and in particular to a dry binder, a preparation method thereof, an electrode sheet and a preparation method thereof. Background Art

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

[0003] In the traditional manufacturing of lithium-ion battery electrodes, a metal current collector is usually coated with a slurry composed of an active material, a conductive agent, and a polymer binder (such as polyvinylidene fluoride, PVDF) mixed with an N-methyl-2-pyrrolidone (NMP) solvent. Although NMP is an effective solvent for PVDF, it is both expensive and toxic. NMP evaporates slowly, making the drying and recycling processes time-consuming and costly. In addition, NMP is also harmful to health, for example, it can cause male infertility, and it is flammable, increasing the fire risk. Long-term exposure to NMP not only threatens the health of workers but also increases production costs and environmental impacts. Therefore, in the manufacturing of lithium batteries, it is imperative to find safer and more sustainable alternatives.

[0004] The dry process is regarded as a new manufacturing method for the next generation of lithium-ion battery electrodes because it has incomparable advantages in terms of operating costs and energy efficiency compared with the traditional solvent process. In addition, since no solvent is used, the dry process can increase the maximum loading threshold of the active material, thus enabling the manufacture of electrodes with higher loadings, paving the way for the miniaturization of batteries. However, although the dry process does not involve solvents, its auxiliary binder currently involves the use of a large amount of solvents and fluoropolymers in the industrial manufacturing process, such as the PTFE dry binder and acrylate dry binder involved in Chinese patent applications with publication numbers CN117777343A, CN117691110A, and CN117438531A. In addition, due to the dry binder involving a high-temperature shear fibrillation process, the binder is required to have better thermal stability, mechanical stability, and electrolyte resistance. The fibrillation of the PTFE binder requires high-temperature and high-pressure conditions, and the acrylate binder has problems such as poor mechanical properties.

[0005] In view of this, the present invention is specifically proposed. Summary of the Invention

[0006] The object of the present invention is to provide a dry binder, a preparation method thereof, an electrode sheet and a preparation method thereof, which can prepare a binder masterbatch through a solvent-free dry process, reduce the manufacturing cost and increase the loading of the electrode sheet.

[0007] To achieve the above object of the present invention, the first aspect of the present invention provides a preparation method of a dry binder, comprising the following steps:

[0008] Mix and granulate a graft polymer and a metal salt to obtain a dry binder;

[0009] The graft polymer includes maleic anhydride grafted polypropylene.

[0010] In a specific embodiment of the present invention, the graft polymer includes maleic anhydride grafted polypropylene and maleic anhydride grafted polystyrene.

[0011] In a specific embodiment of the present invention, in the graft polymer, the mass ratio of the maleic anhydride grafted polypropylene to the maleic anhydride grafted polystyrene is (80-98):(20-2).

[0012] In a specific embodiment of the present invention, in the graft polymer, the proportion of the graft group units is 0.01 wt%-5 wt%.

[0013] In a specific embodiment of the present invention, the metal salt consists of a cation and an anion; the cation includes Li + , Na + , K + , Zn 2+ , Al 3+ , Mg 2+ , Mn 2+ and Ga 2+ ; the anion includes any one of hydroxide, bis(trifluoromethanesulfonyl)imide, bis(fluorosulfonyl)imide, chloride ion, sulfate ion, carbonate ion, nitrate ion, perchlorate ion, tetrafluorophosphate ion, hexafluorophosphate ion, bis(oxalato)borate ion and difluoro(oxalato)borate ion. Further, the metal salt includes at least one of LiOH, LiTFSI, LiFSI, LiClO 4 , LiBF 4 , LiPF 6 , LiBOB, LiDFOB, NaOH, NaClO 4 , NaPF 6 and Na 2 CO 3 .

[0014] In a specific embodiment of the present invention, the molar ratio of the graft group units in the graft polymer to the cations in the metal salt is (0.1 to 30):1.

[0015] In a specific embodiment of the present invention, the graft polymer is first melt-treated and then kneaded with the metal salt. Further, the temperature of the melt treatment is 120 to 200 °C, and the temperature of the kneading is 60 to 150 °C.

[0016] The second aspect of the present invention provides a dry binder prepared by the preparation method of the dry binder of the first aspect.

[0017] The third aspect of the present invention provides an electrode sheet prepared by using the dry binder prepared by the preparation method of the first aspect of the present invention or the dry binder of the second aspect.

[0018] The fourth aspect of the present invention provides a preparation method of the electrode sheet of the third aspect, comprising the following steps:

[0019] (a) Mixing a dry binder, an electrode active material, a conductive agent and optionally a filler in proportion, and performing screw shear blending to obtain a fibrillar solid;

[0020] (b) Heating and rolling the solid into a sheet and then thermally pressing and laminating it on the surface of a current collector to obtain an electrode sheet.

[0021] In a specific embodiment of the present invention, the mass ratio of the dry binder, the electrode active material and the conductive agent is (1 to 10):(80 to 95):(5 to 10).

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] The present invention uses maleic anhydride grafted polypropylene as a polymer matrix and kneads it with a metal salt to prepare a solvent-free dry binder. On the one hand, maleic anhydride grafted polypropylene has excellent electrolyte resistance. On the other hand, the solvent-free kneading process, the good solvation ability of maleic anhydride groups for metal ions, and the unique microphase structure of the graft side chains enable the polymer matrix to accommodate and dissociate electrolyte salts. While ensuring the bonding strength of the binder, an ion-aggregation conduction network is formed, significantly improving the room-temperature ionic conductivity and contributing to improving the rate performance of the battery. Description of the Drawings

[0024] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0025] Figure 1 Schematic diagram of a twin-screw extruder for preparing a dry electrode sheet provided by an embodiment of the present invention. Specific embodiments

[0026] The following will clearly and completely describe the technical solutions of the present invention in conjunction with the drawings and specific embodiments. However, those skilled in the art will understand that the described embodiments are some embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention. For those conditions not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer can be obtained as conventional products through commercial purchase.

[0027] In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the present invention. In addition, the terms "first", "second", "third" are only used for descriptive purposes and cannot be construed as indicating or implying relative importance.

[0028] In the description of the present invention, it should be noted that unless otherwise clearly specified and defined, the terms "installation", "connection", "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific situations.

[0029] The first aspect of the present invention provides a preparation method of a dry binder, including the following steps:

[0030] Mix and granulate the graft polymer and the metal salt to obtain a dry binder;

[0031] The graft polymer includes maleic anhydride grafted polypropylene.

[0032] In the preparation method of the present invention, a graft polymer is selected as the main polymer of the dry binder. Compared with the existing PTFE dry fiber binder, the graft polymer synthesis process is mature, the cost is low, it has excellent ion conduction characteristics, and can be prepared in batches by a solvent-free hot melt grafting method. Moreover, the present invention uses maleic anhydride grafted polypropylene, which has good electrolyte resistance characteristics and bonding characteristics; the grafted maleic anhydride group can ensure stable bonding with the powder active material and the current collector, and at the same time, the maleic anhydride group can interact with metal salts to promote ion conduction, improve performance while being compatible with the existing production line process, and has a relatively excellent cost advantage.

[0033] In a specific embodiment of the present invention, the graft polymer includes maleic anhydride grafted polypropylene and maleic anhydride grafted polystyrene. Using maleic anhydride grafted polystyrene in combination with maleic anhydride grafted polypropylene forms a unique microphase structure, which can further improve the cohesive strength and room temperature ionic conductivity of the binder, etc.

[0034] There are many types of maleic anhydride graft polymers, such as maleic anhydride grafted polyethylene, maleic anhydride grafted polyolefin elastomer, maleic anhydride grafted ethylene-vinyl acetate copolymer, maleic anhydride grafted acrylonitrile-butadiene-styrene copolymer, maleic anhydride grafted polyphenylene ether, maleic anhydride grafted ethylene propylene diene monomer, etc. The inventors of the present invention have found that using maleic anhydride grafted polypropylene and maleic anhydride grafted polystyrene can not only ensure the electrolyte resistance performance of the obtained binder, but also ensure the bonding performance and cost.

[0035] In a specific embodiment of the present invention, in the graft polymer, the mass ratio of maleic anhydride grafted polypropylene to maleic anhydride grafted polystyrene is (80-98):(20-2), for example, it can be 80:20, 82:18, 85:15, 88:12, 90:10, 92:8, 95:5, 98:2 or the range composed of any two of them, thereby taking into account the improvement of the dry processability, the bonding performance, cohesive strength and room temperature ionic conductivity of the obtained dry binder.

[0036] In a specific embodiment of the present invention, the weight average molecular weight of the graft polymer is 5×10 5 ~2×10 7 Da, for example, it can be 5×10 5 Da, 8×10 5 Da, 1×10 6 Da, 3×10 6 Da, 5×10 6 Da, 8×106 Da, 1×10 7 Da, 1.2×10 7 Da, 1.5×10 7 Da, 1.8×10 7 Da, 2×10 7 Da or the range composed of any two of them. Further, the weight-average molecular weight of the graft polymer is 5×10 5 ~1.5×10 7 Da.

[0037] In a specific embodiment of the present invention, in the graft polymer, the proportion of the graft group units is 0.01 wt% to 5 wt%, and 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 the range composed of any two of them. Further, in the graft polymer, the proportion of the graft group units is 0.1 wt% to 2 wt%, which helps to promote ion conduction by interacting with metal salts and improve battery performance while ensuring the adhesion strength of the binder to the active material and the current collector.

[0038] The graft polymer of the present invention can adopt commercial graft polymers, as long as the type, molecular weight, grafting rate, etc. meet the above conditions.

[0039] In a specific embodiment of the present invention, the metal salt is composed of a cation and an anion; the cation includes Li + 、Na + 、K + 、Zn 2+ 、Al 3+ 、Mg 2+ 、Mn 2+ and Ga 2+ any one of them; the anion includes hydroxide (OH - ), bis(trifluoromethanesulfonyl)imide (TFSI - ), bis(fluorosulfonyl)imide (FSI - ), chloride ion (Cl - ), sulfate ion (SO 4 2- ), carbonate ion (CO 3 2- ), nitrate ion (NO 3 - ), perchlorate ion (ClO 4 - ), tetrafluorophosphate ion (BF 4 - ), hexafluorophosphate ion (PF 6- ), bis(oxalato)borate ion (BOB - ), and difluoro(oxalato)borate ion (DFOB - ). Further, the metal salt includes LiOH, LiTFSI, LiFSI, LiClO 4 , LiBF 4 , LiPF 6 , LiBOB, LiDFOB, NaOH, NaClO 4 , NaPF 6 and Na 2 CO 3 at least one of them.

[0040] In a specific embodiment of the present invention, the molar ratio of the graft group unit in the graft polymer to the cation in the metal salt is (0.1 - 30):1. For example, it can be 0.1:1, 0.5:1, 1:1, 3:1, 5:1, 10:1, 15:1, 20:1, 25:1, 30:1 or the range composed of any two of them. Further, it is (0.5 - 5):1. Adjusting the molar ratio of the graft group unit to the cation in the metal salt within the above range takes into account ensuring the improvement of the bonding performance and the room temperature ionic conductivity; avoiding the deterioration of the bonding performance caused by too many cations in the metal salt, and also avoiding the insignificant improvement of the room temperature ionic conductivity caused by too few cations in the metal salt.

[0041] In a specific embodiment of the present invention, the graft polymer is first melt - treated and then kneaded with the metal salt. Further, the temperature of the melt - treatment is 120 - 200 °C. For example, it can be 120 °C, 140 °C, 150 °C, 180 °C, 200 °C or the range composed of any two of them; the temperature of the kneading is 60 - 150 °C. For example, it can be 60 °C, 80 °C, 100 °C, 120 °C, 140 °C, 150 °C or the range composed of any two of them.

[0042] In actual operation, the melt - treatment and kneading processes can be carried out using a twin - screw extruder. Specifically, the graft polymer, metal salt, etc. can be dried to remove water first, and then the dried graft polymer is added to the twin - screw extruder, set to the temperature of the melt - treatment. After the graft polymer melts, the metal salt is added to the molten graft polymer through the feeding hopper according to the proportion, set to the temperature of the kneading, and the maleic anhydride groups of the graft polymer are promoted to open - ring and complex with the metal salt to form an ionic polymer through the temperature and shear force of the screw. After extrusion through the extrusion die head and cooling, it is granulated using a granulator to obtain a dry - process binder.

[0043] In a specific embodiment of the present invention, the temperature for drying and water removal can be 100 - 140 °C, such as 100 °C, 110 °C, 120 °C, 130 °C, 140 °C or the range composed of any two of them.

[0044] The second aspect of the present invention provides a dry binder prepared by the preparation method of the dry binder of the first aspect.

[0045] The third aspect of the present invention provides an electrode sheet prepared by using the dry binder prepared by the preparation method of the first aspect of the present invention or the dry binder of the second aspect.

[0046] The fourth aspect of the present invention provides a preparation method of the electrode sheet of the third aspect, including the following steps:

[0047] (a) Mix the dry binder, electrode active material, conductive agent and optionally filler in proportion, and obtain a fibrillar solid through screw shear blending.

[0048] (b) After heating and rolling the solid into a sheet, hot press and laminate it on the surface of the current collector to obtain the electrode sheet.

[0049] Among them, the blending can be carried out by a screw extruder, the heating and rolling into a sheet can be carried out by a roll press, and the hot press lamination can be carried out by a hot roll press. Specifically, in the shear blending, it can be first stirred and mixed at a speed of 200 - 300 rpm for 5 - 15 min, and then stirred and mixed at a speed of 300 - 400 rpm for 20 - 40 min.

[0050] When preparing a dry negative electrode sheet, the electrode active material can be a negative electrode active material; when preparing a dry positive electrode sheet, the electrode active material can be a positive electrode active material. In the following examples, the negative electrode active material graphite is taken as an example for illustration, but it is not limited thereto.

[0051] Figure 1 It is a schematic diagram of a twin-screw for preparing a dry electrode sheet provided by an embodiment of the present invention. The dry binder, electrode active material, conductive agent, etc. can be added into the twin-screw extruder through different feeding hoppers to obtain a fibrillar solid, and then after heating and rolling the solid into a finished product, hot press and laminate it on the surface of the current collector to obtain the electrode sheet.

[0052] In a specific embodiment of the present invention, in the shear blending, the temperature is 30 - 90 °C, such as it can be 30 °C, 40 °C, 50 °C, 60 °C, 70 °C, 80 °C, 90 °C or the range composed of any two of them.

[0053] In a specific embodiment of the present invention, in the heating and rolling into a sheet, the temperature can be 140 - 160 °C, and the pressure can be 3 - 8 MPa.

[0054] In a specific embodiment of the present invention, in the heating and calendering into sheets, the thickness is 20 - 120 μm, for example, it can be 20 μm, 40 μm, 60 μm, 80 μm, 100 μm, 120 μm or the range composed of any two of them.

[0055] In a specific embodiment of the present invention, in the hot pressing and laminating, the temperature can be 100 - 140 °C, and the time can be 5 - 20 min.

[0056] In a specific embodiment of the present invention, the mass ratio of the dry binder, the electrode active material, and the conductive agent is (1 - 10):(80 - 95):(5 - 10). Specifically, the mass ratio of the dry binder, the electrode active material, and the conductive agent is adjusted according to the composition requirements of the electrode sheet, and is not limited thereto.

[0057] In a specific embodiment of the present invention, the filler includes but is not limited to solid electrolyte particles, etc., for example, it can be oxide solid electrolyte particles LLZO, sulfide solid electrolyte particles LGPS, etc. The dosage of the specific filler is adjusted according to the composition requirements of the electrode sheet. For example, it can be 1 wt% - 5 wt% of the total amount of the materials (the mass sum of the dry binder, the electrode active material, the conductive agent, and the filler), but is not limited thereto.

[0058] In a specific embodiment of the present invention, the electrode active material includes at least one of graphite, silicon-carbon material, silicon-oxygen material, lithium iron phosphate material, and ternary cathode material; the conductive agent includes at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene, and carbon nanofibers.

[0059] The current collector adopted in the present invention is conventionally selected according to the type of the electrode sheet.

[0060] Examples 1 - 6

[0061] This example provides a preparation method of a dry binder and an electrode sheet, including the following steps:

[0062] (1) Pre-dry the graft polymer at 120 °C to remove water, then add it into a twin-screw extruder, heat the screw to the set temperature of 150 °C to soften and melt the polymer.

[0063] (2) Add the metal salt to the polymer obtained in step (1) through a hopper for mixing for 70 min. The screw speed during mixing is 120 rpm, and the temperature is 150 °C; then extrude through a co-extrusion die head, cool and dry, and obtain the dry binder through a granulator.

[0064] (3) Weigh the anode active material graphite, conductive agent carbon black, and dry binder according to a mass ratio of 92:5:3. Add graphite and carbon black into an extruder, stir and mix at 120 rpm for 10 min, then add the dry binder. First, stir and mix at 250 rpm for 10 min, and then stir and mix at 350 rpm / min for 30 min to obtain a fibrous solid.

[0065] (4) Put the fibrous solid obtained in step (3) into a roll press, and hot roll press it at 150 °C / 5 MPa to form a dry electrode film layer with a layer thickness of 20 - 120 μm (specifically, it can be 80 μm). Then attach the dry electrode film layer to the anode current collector (such as copper foil) and hot roll press it at 120 °C for 10 min to obtain a dry anode electrode sheet.

[0066] In the preparation of the dry binder in Examples 1 - 6, the graft polymer used is maleic anhydride grafted polypropylene (PP-MAH with a grafting rate of 1%, weight average molecular weight of about 600000 Da), the metal salt is LiOH, the dosages of PP-MAH and LiOH, and the molar ratio of the graft group unit MAH in PP-MAH to the cation Li + in LiOH are shown in Table 1.

[0067] Table 1 Raw material dosage information for different examples

[0068]

[0069] Examples 7 - 11

[0070] Examples 7 - 11 refer to the preparation method of the dry binder and electrode sheet in Example 5, with the only difference being that PP-MAH is replaced with a mixture of PP-MAH with a grafting rate of 1% and maleic anhydride grafted polystyrene (PS-MAH with a grafting rate of 1%, weight average molecular weight of about 600000 Da). The specific dosages are shown in Table 2.

[0071] Table 2 Raw material dosage information for different examples

[0072]

[0073] Examples 12 - 16

[0074] Examples 12 - 16 refer to the preparation method of the dry binder and electrode sheet in Example 10, with the only difference being that the types and dosages of the metal salts are different. The specific information is shown in Table 3.

[0075] Table 3 Raw material dosage information for different examples

[0076]

[0077] Comparative Example 1

[0078] The preparation method of Comparative Example 1 refers to Example 5, with the difference that the graft polymer is replaced by PTFE.

[0079] Experimental Example 1

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

[0081] Room temperature ionic conductivity: The dry adhesives prepared in different examples and comparative examples were added to a mixer to be softened to obtain a solid adhesive, and then placed in a roll press and hot-pressed into a film at 5 MPa and 160 °C. Then, the film was cut into circular pieces with a diameter of 17 mm (adhesive film), and assembled with a stainless steel sheet into a sandwich battery clamping device to test the room temperature (25 °C) ionic conductivity of the adhesive. According to the formula , the ionic conductivity at room temperature was calculated, 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, R corresponds to the intrinsic impedance of the adhesive film obtained by impedance spectroscopy test.

[0082] Cohesive peel strength: The cohesive peel strength of the electrode sheets prepared in different examples was tested with reference to GB / T 2792-2014 "Test Method for 180° Peel Strength of Adhesives"; specifically, the electrode sheets were cut into test samples (length and width: 200 mm × 25 mm), and the metal side of the current collector was pasted on a stainless steel plate with double-sided tape. A 3M tape (Scotch 600 / 25 mm wide) was pasted on the coating surface, and the sample was rolled back and forth three times with a 1 kg roller. According to the test conditions of the national standard GB / T 2792-2014, a universal tensile machine was used to test the cohesive force between the coating / current collector.

[0083] Table 4 Test Results of Different Examples

[0084]

[0085] The room temperature ionic conductivity and cohesive strength of the PTFE adhesive in Comparative Example 1 are lower than those of the adhesive of the present invention under the same ratio, indicating that the adhesive of the present invention has higher cost advantages and performance advantages.

[0086] According to the test results of Examples 1 to 6, it can be seen that at different LiOH contents, there are obvious differences in the room-temperature ionic conductivity of the corresponding binder films. When the molar ratio of the graft group unit in the graft polymer to the cation in the metal salt (MAH﹕Li) is (0.5 to 2.6)﹕1, the room-temperature ionic conductivity of the corresponding binder film is significantly higher than that of the binder films with other ratios. The corresponding cohesive strength first increases and then decreases with the increase of the LiOH dosage, and it is optimal when MAH﹕Li is 1.3﹕1.

[0087] In the mixing of different graft polymers and LiOH, the type and compounding ratio of the graft polymer have an impact on the room-temperature ionic conductivity of the binder film and the cohesive strength of the electrode sheet. According to the test results of Examples 7 to 11, when the mass ratio of PP-MAH and PS-MAH is 9﹕1, the room-temperature ionic conductivity of the binder and the cohesive strength of the electrode sheet are the best, because the unique microphase structure of the two-phase polymer after blending helps to improve the performance.

[0088] According to the test results of Examples 10, 12 to 16, it can be seen that when the metal salt is LiOH, better ionic conductivity and cohesive strength can be achieved simultaneously.

[0089] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a dry binder, characterized in that: The steps include: The grafted polymer and the metal salt are mixed and granulated to obtain a dry binder; The grafted polymer includes maleic anhydride grafted polypropylene and maleic anhydride grafted polystyrene; in the grafted polymer, the proportion of the grafted group unit is 0.01wt% to 5wt%; In the grafted polymer, the mass ratio of the maleic anhydride grafted polypropylene to the maleic anhydride grafted polystyrene is (82-98): (18-2); The molar ratio of the grafted group unit in the grafted polymer to the cation in the metal salt is (0.5-5):1; The metal salt includes at least one of LiOH, LiTFSI, NaOH and KOH.

2. The method for preparing a dry binder according to claim 1, characterized in that: Firstly, the grafted polymer is melt-treated, and then mixed with the metal salt; The temperature of the melting treatment is 120-200°C, and the temperature of the mixing is 60-150°C.

3. A dry adhesive, characterized in that: The preparation method is adopted according to any one of claims 1 to 2.

4. An electrode sheet, characterized in that: It is prepared by the dry binder prepared by the preparation method according to any one of claims 1 to 2 or the dry binder according to claim 3.

5. The method for preparing the electrode sheet according to claim 4, characterized in that: The steps include: (a) mixing a dry binder, an electrode active material, a conductive agent and optionally a filler in proportion, and blending by screw shearing to obtain a fiberized solid; (b) The solid material is heated and rolled into a sheet, and then hot-pressed and bonded to the surface of a current collector to obtain an electrode sheet.

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

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