Dry binder, method of making and electrode pole piece

Abstract

The present application relates to the technical field of binder materials, in particular to a dry binder, a preparation method thereof and an electrode tab. The dry binder is prepared from raw materials including polyolefin and paraffin in a mass ratio of 1:(0.05-0.8). The polyolefin has a weight average molecular weight of 5*10 4 Da-5*10 7 Da. The paraffin has a weight average molecular weight of 500 Da-3*10 4 Da. The dry binder of the present application uses polyolefin as the main body and paraffin as the auxiliary material, which can reduce the cost of raw materials, show good compatibility with electrode active materials, realize firm and uniform adhesion under the condition of no solvent, and balance the peeling strength, cohesive strength and electrochemical performance of the electrode.

Description

Technical Field

[0001] This invention relates to the field of adhesive materials technology, and in particular to a dry adhesive, its preparation method, and an electrode sheet. Background Technology

[0002] With the rapid development of new energy vehicles and large-scale energy storage industries, the market has placed higher demands on the energy density, manufacturing cost, and production efficiency of lithium-ion batteries. Traditional electrode manufacturing generally employs a wet process, which involves mixing active materials, conductive agents, and binders (such as PVDF) in an organic solvent (such as NMP) to form a slurry, followed by coating, drying, and rolling processes. However, this process has inherent drawbacks: firstly, the high cost and toxicity of the organic solvents require complex recycling systems, increasing production costs and environmental burden; secondly, the drying process is not only energy-intensive but also prone to coating cracking and uneven binder distribution, hindering improvements in battery performance and the design of thick electrode structures. To overcome these problems in the wet process, dry electrode technology, which eliminates the need for solvents and drying processes, has emerged. This technology, through dry powder mixing and direct rolling, can significantly increase production capacity, reduce energy consumption, and avoid solvent pollution, and is considered a key pathway for next-generation high-performance battery manufacturing.

[0003] Existing dry processes primarily rely on fluoropolymers such as polytetrafluoroethylene (PTFE) to achieve bonding through shearing and fiberization to form a physical network. However, fluoropolymers are expensive, and their production and handling pose environmental risks. Furthermore, PTFE's strong insulation and chemical inertness may hinder lithium-ion transport and increase interfacial impedance. In addition, PTFE is extremely sensitive to process parameters, and problems such as uneven bonding or fiber perforation in the electrodes are prone to occur.

[0004] Polyolefin materials are considered ideal candidates for fluorine-free binders due to their low cost, chemical stability, and environmental friendliness. However, conventional polyolefins (such as PE and PP) are nonpolar molecules, which have poor compatibility with electrode active materials and are difficult to form a strong and continuous bonding network under dry processing conditions, resulting in insufficient mechanical strength of the electrodes.

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

[0006] The purpose of this invention is to provide a dry binder, its preparation method, and an electrode sheet. The dry binder of this invention uses polyolefin as the main body and is combined with paraffin. While reducing the cost of raw materials, it exhibits good compatibility with the electrode active material. It can achieve strong and uniform bonding under solvent-free conditions, and takes into account the peel strength, cohesive strength, and electrochemical performance of the electrode.

[0007] To achieve the above-mentioned objectives of the present invention, a first aspect of the present invention provides a dry adhesive, the raw materials of which include polyolefin and paraffin in a mass ratio of 1:(0.05~0.8); The weight-average molecular weight of the polyolefin is 5 × 10⁻⁶. 4 Da~5×10 7 Da; The weight-average molecular weight of the paraffin is 500 Da ~ 3 × 10⁻⁶. 4 Da.

[0008] In a specific embodiment of the present invention, the polyolefin includes at least one of polyethylene, polypropylene, ethylene-α-olefin copolymer, polyolefin elastomer, ethylene-vinyl acetate copolymer and poly4-methyl-1-pentene.

[0009] In a specific embodiment of the present invention, the paraffin wax includes at least one of ordinary paraffin wax, Fischer-Tropsch wax, polyethylene wax, chlorinated paraffin wax, liquid paraffin wax, and microcrystalline wax.

[0010] In a specific embodiment of the present invention, the average particle size of the dry binder is 5~15 μm.

[0011] The second aspect of the present invention provides a method for preparing the dry binder provided in the first aspect of the present invention, comprising the following steps: subjecting a mixture of polyolefin and paraffin to intensive mixing.

[0012] In a specific embodiment of the present invention, the mixing temperature is 70~90℃ and the mixing time is 0.5~2 h.

[0013] A third aspect of the present invention provides an electrode sheet comprising a current collector and an active material layer disposed on at least one surface of the current collector; the active material layer comprises the dry binder, conductive agent and active material provided in the first aspect of the present invention.

[0014] A fourth aspect of the present invention provides a method for preparing the electrode sheet provided in the third aspect of the present invention, comprising the following steps: (a) The dry binder, conductive agent and active material are mixed and kneaded to obtain a mixed powder; (b) The mixed powder is heated and then rolled to obtain an active material layer; the thickness of the active material layer is 100~200 μm; (c) The active material layer and the current collector are subjected to hot pressing to obtain the electrode sheet.

[0015] In a specific embodiment of the present invention, in step (a), the mixing and kneading temperature is 60~200℃, preferably 80~120℃.

[0016] In a specific embodiment of the present invention, in step (c), the temperature during the hot pressing process is 60~200℃, preferably 120~140℃.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The dry binder of the present invention is a composite of polyolefin and paraffin. The low melting point and good fluidity of paraffin allow it to melt preferentially during hot pressing, acting as a processing medium, thereby reducing the processing temperature of polyolefin and widening the process window, and improving compatibility with electrode active materials. After curing, the microscopic "weld points" formed by the resolidification of paraffin (i.e., the point-like bonding nodes that paraffin acts between the polyolefin entanglement network and the active particles, which firmly connect the components like welding) can complement the network structure formed by the physical entanglement of polyolefin molecular chains, improving the flexibility and structural stability of the electrode. At the same time, by controlling the melting point and amount of paraffin, the electrode pore structure can be improved and the ion transport efficiency can be enhanced while ensuring the bonding strength.

[0018] (2) In terms of preparation, the raw material cost of the present invention is low and the manufacturing process is simple and safe.

[0019] (3) The dry electrode sheet prepared by the dry binder of the present invention is not only green and efficient, but also has the advantages of low interface resistance, high peel strength and high cohesive strength, which is beneficial to improving the performance of lithium-ion batteries. Attached Figure Description

[0020] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in 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 the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0021] Figure 1 This is a SEM image of the adhesive prepared in Example 1 of the present invention. Detailed Implementation

[0022] The technical solution of the present invention 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 some embodiments of the present invention, but not all embodiments, and are only used to illustrate the present invention, and should not be regarded as limiting the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. 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.

[0023] The first aspect of the present invention provides a dry adhesive, the raw materials of which include polyolefin and paraffin in a mass ratio of 1:(0.05~0.8); The weight-average molecular weight of the polyolefin is 5 × 10⁻⁶. 4 Da~5×10 7 Da; The weight-average molecular weight of the paraffin is 500 Da ~ 3 × 10⁻⁶. 4 Da.

[0024] The dry adhesive of this invention employs a composite of polyolefin and paraffin wax. The low melting point and good fluidity of paraffin wax allow it to melt preferentially during hot pressing, acting as a processing medium. This reduces the processing temperature of the polyolefin, widens the process window, and improves compatibility with the electrode active material. The microscopic "weld joints" formed after curing complement the network structure of the polyolefin, enhancing the electrode's flexibility and structural stability. Simultaneously, by controlling the melting point and dosage of paraffin wax, the electrode's pore structure can be improved while maintaining bonding strength, thereby enhancing ion transport efficiency.

[0025] The dry binder of this invention, after hot pressing and cooling solidification, forms a network structure with polyolefin physical entanglement as the framework and paraffin microregions dispersed within it. This network has a stable chemical composition, and the size, distribution, and crystal morphology of the paraffin microregions can be controlled by adjusting the melting point and amount of paraffin (i.e., controllable microregion characteristics). When the dry binder of this invention is used in electrodes, this physically entangled network provides strong and uniform mechanical support for the active material, constructing stable ion and electron transport channels. During hot pressing, the softened polyolefin and molten paraffin penetrate and fill the micropores on the surface of the current collector, forming a mechanical interlock upon cooling, thereby achieving strong physical anchoring. This helps optimize the electrode interface, reduce interfacial resistance, and improve cohesive strength and peel strength.

[0026] In a specific embodiment of the present invention, the mass ratio of polyolefin to paraffin in the raw materials is 1:(0.05~0.8), specifically within the range of 1:0.05, 1:0.1, 1:0.2, 1:0.3, 1:0.4, 1:0.5, 1:0.6, 1:0.7, 1:0.8, or any combination thereof. An appropriate amount of paraffin preferentially melts during hot pressing, effectively reducing the processing temperature and widening the process window. After solidification, it complements the polyolefin network structure, thereby improving the electrode's flexibility and structural stability. Simultaneously, by controlling the amount of paraffin, the pore structure is optimized, enhancing ion transport performance. This achieves a synergistic improvement in both the process window and electrode performance. If the paraffin ratio is too high, it will lead to insufficient content of the main polyolefin in the binder, resulting in a significant decrease in mechanical strength and cohesive strength. Excessive paraffin may also increase interfacial resistance. If the paraffin ratio is too low, it will be difficult to fully exert the effects of reducing processing temperature, improving pore structure and enhancing flexibility. The process window will be narrower, and problems such as uneven bonding or insufficient flexibility may easily occur.

[0027] In a specific embodiment of the present invention, the weight-average molecular weight of the polyolefin is 5 × 10⁻⁶. 4 Da~5×10 7 Da, specifically, can be 5 × 10 4 Da, 8×10 4 Da, 1×10 5 Da, 3×10 5 Da, 5×10 5 Da, 8×10 5 Da, 1×10 6 Da, 3×10 6 Da, 5×10 6 Da, 8×10 6 Da, 1×10 7 Da, 3×10 7 Da, 5×10 7 The range of Da or any two thereof is preferably 5 × 10 4 Da~2×10 7 A suitable molecular weight ensures that polyolefins form a continuous and strong bonding network during dry processing, guaranteeing peel strength and cohesive strength. It also allows for uniform flow and curing in conjunction with paraffin under hot pressing conditions. Furthermore, polyolefins within this molecular weight range exhibit good compatibility with the electrode active material, contributing to reduced interfacial impedance. If the molecular weight is too high, the processing window of the polyolefin is narrow, making it difficult to achieve uniform bonding under solvent-free conditions, easily leading to localized bonding defects or decreased flexibility of the electrode. If the molecular weight is too low, the polyolefin molecular chains are too short, making it difficult to form a strong and tough network structure, resulting in insufficient mechanical strength and affecting the long-term stability and electrochemical performance of the electrode.

[0028] Compared to traditional fluorinated materials, polyolefins are inexpensive, widely available, and completely avoid the environmental concerns associated with fluorinated substances. Furthermore, polyolefins possess excellent electrochemical stability and good thermoplastic processing characteristics; when combined with paraffin wax, they can form a bonded network in a dry state through hot pressing.

[0029] In a specific embodiment of the present invention, the polyolefin includes at least one of polyethylene, polypropylene, ethylene-α-olefin copolymer, polyolefin elastomer, ethylene-vinyl acetate copolymer and poly4-methyl-1-pentene, preferably polypropylene or polyethylene.

[0030] In a specific embodiment of the present invention, the paraffin wax has a weight-average molecular weight of 500 Da ~ 3 × 10⁻⁶. 4 Da, specifically, can be 500 Da or 1×10 3 Da, 3×10 3 Da, 5×10 3 Da, 8×10 3 Da, 1×10 4 Da, 1.5×10 4 Da, 2×10 4 Da, 2.5×10 4 Da, 3×10 4 The range of Da or any two thereof is preferably 500 Da ~ 2 × 10 4 Da. Paraffin wax is extremely low in cost and environmentally friendly, further reducing the overall system cost and enhancing its green attributes. In the dry binder system of this invention, paraffin wax not only improves dry processability but also enhances flexibility and structural stability by forming a network structure. Paraffin wax with a molecular weight within the above range has a moderate melting point and good fluidity, allowing it to preferentially melt and disperse uniformly during hot pressing, effectively reducing the processing temperature of polyolefins, widening the process window, and forming a good complement to the polyolefin network structure after curing, improving the flexibility and structural stability of the electrode without excessively clogging the electrode pores, thus maintaining excellent ion transport performance. If the molecular weight of paraffin wax is too high, its melting point increases and its fluidity decreases, easily leading to uneven binder distribution and reduced electrode flexibility; if the molecular weight of paraffin wax is too low, the paraffin wax is too soft and has a too low melting point, easily migrating, precipitating, or melting during processing or battery use, damaging the structural stability of the electrode.

[0031] In a specific embodiment of the present invention, the paraffin wax includes at least one of ordinary paraffin wax, Fischer-Tropsch wax, polyethylene wax, chlorinated paraffin wax, liquid paraffin wax and microcrystalline wax, preferably ordinary paraffin wax or microcrystalline wax.

[0032] In a specific embodiment of the present invention, the average particle size of the dry binder is 5~15 μm, specifically it can be a range of 5 μm, 8 μm, 10 μm, 12 μm, 15 μm or any two of them, preferably 5~10 μm.

[0033] The second aspect of the present invention provides a method for preparing the dry binder provided in the first aspect of the present invention, comprising the following steps: subjecting a mixture of polyolefin and paraffin to intensive mixing.

[0034] In a specific embodiment of the present invention, the mixing temperature is 70~90℃, specifically a range of 70℃, 75℃, 80℃, 85℃, 90℃, or any combination thereof; the mixing time is 0.5~2 h, specifically a range of 0.5h, 0.8h, 1h, 1.2h, 1.5h, 1.8h, 2h, or any combination thereof. Further, the mixing speed is 40~60 rpm, specifically a range of 40 rpm, 45 rpm, 50 rpm, 55 rpm, 60 rpm, or any combination thereof.

[0035] In a specific embodiment of the present invention, the method for preparing a mixture of polyolefin and paraffin wax includes: mixing and ball-milling a polyolefin and paraffin wax in a certain proportion to obtain a mixture of polyolefin and paraffin wax. The specific parameters of the ball milling are not limited, as long as the two materials are mixed uniformly. The present invention provides an optional ball milling condition: ball milling at 1200 rpm for 10 min.

[0036] In a specific embodiment of the present invention, after the mixing process, a crushing process is performed to obtain a dry binder with an average particle size that meets the requirements.

[0037] A third aspect of the present invention provides an electrode sheet comprising a current collector and an active material layer disposed on at least one surface of the current collector; the active material layer comprises the dry binder, conductive agent and active material provided in the first aspect of the present invention.

[0038] This invention does not impose any particular restrictions on the type of current collector; it can be selected conventionally based on the type of electrode.

[0039] In a specific embodiment of the present invention, based on the total mass of the active material layer as 100%, the content of the conductive agent is 1% to 10%, specifically it can be 1%, 3%, 5%, 8%, 10% or any combination thereof.

[0040] In a specific embodiment of the present invention, the conductive agent may include at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon nanotubes, graphene, and carbon nanofibers.

[0041] In a specific embodiment of the present invention, the content of the active material is 80% to 98%, based on the total mass of the active material layer as 100%, specifically it can be a range of 80%, 85%, 90%, 95%, 98% or any two of them.

[0042] This invention does not impose any particular limitation on the type of active material, and conventional selection can be made according to the type of electrode. In a specific embodiment of this invention, the active material includes a positive electrode active material or a negative electrode active material; the positive electrode active material may include at least one of olivine structure materials such as lithium manganese iron phosphate, lithium iron phosphate, and lithium manganese phosphate, and ternary structure materials such as NCM811, NCM622, NCM523, and NCM333; the negative electrode active material may include at least one of graphite, silicon carbide, and silicon oxide materials.

[0043] In a specific embodiment of the present invention, the thickness of the active material layer is 100~200 μm, specifically it can be 100 μm, 120 μm, 150 μm, 180 μm, 200 μm or any combination thereof.

[0044] A fourth aspect of the present invention provides a method for preparing the electrode sheet provided in the third aspect of the present invention, comprising the following steps: (a) The dry binder, conductive agent and active material are mixed and kneaded to obtain a mixed powder; (b) The mixed powder is heated and then rolled to obtain an active material layer; (c) The active material layer and the current collector are subjected to hot pressing to obtain the electrode sheet.

[0045] In a specific embodiment of the present invention, the thickness of the active material layer is 100~200 μm.

[0046] In a specific embodiment of the present invention, in step (a), before the mixing and kneading, the conductive agent and the active material are first mixed and ball-milled, and then a dry binder is added before subsequent mixing and kneading.

[0047] In a specific embodiment of the present invention, in step (a), the ball-to-material ratio in the ball milling is 1:1, the ball milling media includes 5 mm ball milling beads (such as zirconia beads), the ball milling speed is 1500~2000 rpm, and the ball milling time is 3~8 min.

[0048] In a specific embodiment of the present invention, in step (a), the mixing and kneading temperature is 60~200℃, specifically it can be a range of 60℃, 80℃, 100℃, 110℃, 120℃, 140℃, 160℃, 180℃, 200℃ or any two of these, preferably 80~120℃; the mixing and kneading time is 1~10 h, specifically it can be a range of 1 h, 3 h, 5 h, 8 h, 10 h or any two of these; the mixing and kneading speed is 20~60 rpm, specifically it can be a range of 20 rpm, 30 rpm, 40 rpm, 50 rpm, 60 rpm or any two of these.

[0049] In a specific embodiment of the present invention, in step (b), the temperature of the heat treatment is 80~120℃, and the heat treatment time is 2~5 min. Specifically, the mixed powder can be heated on a heating table and then rolled on a roller press until the target thickness, such as 100~200 μm, is achieved.

[0050] In a specific embodiment of the present invention, in step (c), the hot pressing treatment is performed at a temperature of 60~200℃, specifically within the range of 60℃, 80℃, 100℃, 120℃, 150℃, 180℃, 200℃, or any combination thereof, preferably 120~140℃; the hot pressing time is 5~20 min, specifically within the range of 5 min, 8 min, 10 min, 15 min, 20 min, or any combination thereof; the hot pressing pressure is 20~100 MPa, specifically within the range of 20 MPa, 40 MPa, 60 MPa, 80 MPa, 100 MPa, or any combination thereof. The hot pressing treatment can be performed on a flat vulcanizing machine.

[0051] In a specific embodiment of the present invention, step (c) further includes: keeping the hot-pressed electrode sheet at 25~35°C for 10~12 h to allow the paraffin to fully crystallize in this temperature range and form a stable "soldering point" structure, while releasing the residual stress generated during the hot pressing process, thereby optimizing the pore network of the electrode and enhancing the bonding stability of the electrode / current collector interface.

[0052] Example 1 This embodiment provides a method for preparing a dry electrode sheet, including the following steps: (1) Polypropylene particles and microcrystalline wax were mixed at a mass ratio of 1:0.3, then ball-milled at 1200 rpm for 10 min, and then transferred to an internal mixer at 80℃ and 50 rpm for 1 h. After crushing, a dry binder was obtained. The weight-average molecular weight of the polypropylene particles was 7.5 × 10⁻⁶. 4Da (using PPH-T03 homopolymer polypropylene powder from Sinopec Maoming Petrochemical); the dropping melting point of the microcrystalline wax is 70~75℃, and the weight average molecular weight of the microcrystalline wax is 700~1000 Da (purchased from Sinopec Jingmen Petrochemical).

[0053] (2) Weigh the conductive agent (Super P), positive electrode material (lithium iron phosphate), and the dry binder from step (1) at a mass ratio of 3:92:3. Add the conductive agent and positive electrode material to a ball mill, and then add the ball to a 5 mm ball mill at a ball-to-material ratio of 1:1. Ball mill at 2000 rpm for 5 min to obtain a mixture. Add the dry binder to the mixture, transfer it to a mixer, and mix and knead at 80°C and 50 rpm for 3 h to obtain a composite material.

[0054] (3) The composite material obtained in step (2) is heated on a heating table at 90°C for 2 min and then cold rolled; the heating and cold rolling steps are repeated until an active material layer with a thickness of 100 μm is obtained.

[0055] (4) The active material layer obtained in step (3) is spread on an aluminum foil with a thickness of 12 μm, and then placed on a flat vulcanizing machine for hot pressing at 120℃ and 25 MPa for 10 min. After hot pressing, it is placed in a constant temperature box at 30℃ for 11 h.

[0056] Figure 1 The image shows a SEM image of the dry adhesive prepared in this embodiment. As can be seen from the image, the average particle size of the dry adhesive prepared in this embodiment is 10~15 μm. The melting point of the dry adhesive prepared in this embodiment is 55℃~60℃.

[0057] Example 2 This embodiment group provides a method for preparing a dry electrode sheet. Referring to Example 1, the only difference is that the mass ratio of polypropylene particles and microcrystalline wax is different in step (1). The rest are the same as in Example 1. The specific differences are as follows: Example 2a: Polypropylene granules and microcrystalline wax were taken at a mass ratio of 1:0.05; Example 2b: Polypropylene granules and microcrystalline wax were taken at a mass ratio of 1:0.5; Example 2c: Polypropylene particles and microcrystalline wax were taken at a mass ratio of 1:0.8.

[0058] Example 3 This embodiment provides a method for preparing a dry electrode sheet. Referring to Example 1, the only difference is that the type of wax used in step (1) is different. All other aspects are the same as in Example 1. The specific differences are as follows: In this embodiment, polyethylene wax (Mitsui 420P purchased from Mitsui Chemicals, with a weight-average molecular weight of 4000~6000 Da) was used to replace the microcrystalline wax in Example 1 by weight.

[0059] Example 4 This embodiment provides a method for preparing a dry electrode sheet. Referring to Embodiment 1, the only difference is that the mixing temperature in the internal mixer in step (2) is different. All other aspects are the same as in Embodiment 1. The specific differences are as follows: In step (2) of this embodiment, the mixing temperature in the internal mixer is 60°C.

[0060] Example 5 This embodiment provides a method for preparing a dry electrode sheet. Referring to Embodiment 1, the only difference is that the hot pressing temperature in step (4) is different. All other aspects are the same as in Embodiment 1. The specific differences are as follows: In step (4) of this embodiment, the hot pressing temperature is 100°C.

[0061] Comparative Example 1 Comparative Example 1 is the same as Example 1, except that the polypropylene particles in step (1) are different. The other differences are as follows: The weight-average molecular weight of the polypropylene particles in this comparative example is 8.0 × 10⁻⁶. 3 Da (Choose Honeywell's AC 1089).

[0062] Comparative Example 2 Comparative Example 2 was prepared in accordance with the preparation method of Example 1, except that microcrystalline wax was not added in step (1), and all other steps were the same as in Example 1.

[0063] Comparative Example 3 Comparative Example 3 follows the same preparation method as Example 1, except that the type of wax used in step (1) is different. All other aspects are the same as in Example 1. The specific differences are as follows: Comparative Example 3 uses liquid paraffin No. 15 industrial grade white oil (selecting No. 15 industrial grade white oil that conforms to SH / T 0006 standard, with a typical average molecular weight distribution of about 350~450 Da) to replace the microcrystalline paraffin in Example 1 by weight.

[0064] Comparative Example 4 Comparative Example 4 is the same as Example 1, except that the type of microcrystalline wax used in step (1) is different. The other differences are as follows: Comparative Example 4 uses 70# microcrystalline wax (e.g., 70# microcrystalline wax purchased from Sinopec Jingmen Petrochemical, with a weight-average molecular weight of 200~500 Da) to replace the microcrystalline wax in Example 1 by weight.

[0065] Comparative Example 5 Comparative Example 5 follows the same preparation method as Example 1, except that the thickness of the active material layer in step (3) is different. The rest is the same as in Example 1. The specific differences are as follows: The thickness of the active material layer in Comparative Example 5 is 250 μm.

[0066] Experimental Example The performance of the electrode sheets prepared in different embodiments and comparative examples was tested as follows. Specifically, 2.5 cm × 10 cm electrode sheets were cut with scissors and tested as follows. The test results are shown in Table 1.

[0067] 1. Peel strength: Refer to GB / T 2792 The test was conducted according to the 2014 standard "Test Method for Peel Strength of Adhesive Tape". The active material layer of the electrode was attached to a stainless steel plate with double-sided adhesive tape. 3M tape (Scotch 600, 25 mm wide) was attached to the current collector surface of the electrode and rolled back and forth three times with a 1 kg roller. The peel strength at 180° was tested at a peel speed of 100 mm / min. Six parallel tests were performed and the average value was taken.

[0068] 2. Cohesive strength: The current collector side of the electrode is attached to a stainless steel plate with double-sided tape. 3M tape (Scotch 600, 25 mm wide) is attached to the surface of the active material layer of the electrode, and the electrode is rolled back and forth three times with a 1 kg roller. The 180° peel strength is tested at a peeling speed of 100 mm / min. The average value is taken from 6 parallel tests.

[0069] 3. Interface resistance: The interface resistance of the active material layer of the electrode is tested using a resistance tester. A point is taken every 20 mm, and the average value is taken for 30 points.

[0070] Table 1 Performance test results of different electrode plates

[0071] The test results above show that the dry adhesive of the present invention is a composite of polyolefin and paraffin. Paraffin with a suitable molecular weight has a low melting point and good fluidity, which can not only reduce the melting temperature of polyolefin and reduce energy consumption during processing, but also form a uniformly distributed micro-reinforcing phase after curing, thereby improving the bonding strength, flexibility and ion transport performance.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention 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; and these 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 the present invention.

Claims

1. A dry adhesive, characterized in that, The raw materials for preparation include polyolefin and paraffin in a mass ratio of 1:(0.05~0.8); The weight-average molecular weight of the polyolefin is 5 × 10⁻⁶. 4 Da~5×10 7 Da; The weight-average molecular weight of the paraffin is 500 Da ~ 3 × 10⁻⁶. 4 Da.

2. The dry adhesive according to claim 1, characterized in that, The polyolefin includes at least one of polyethylene, polypropylene, ethylene-α-olefin copolymer, polyolefin elastomer, ethylene-vinyl acetate copolymer, and poly4-methyl-1-pentene.

3. The dry adhesive according to claim 1, characterized in that, The paraffin wax includes at least one of ordinary paraffin wax, Fischer-Tropsch wax, polyethylene wax, chlorinated paraffin wax, liquid paraffin wax, and microcrystalline wax.

4. The dry adhesive according to claim 1, characterized in that, The average particle size of the dry binder is 5~15μm.

5. The method for preparing the dry adhesive according to any one of claims 1 to 4, characterized in that, The process includes the following steps: mixing the mixture of polyolefin and paraffin.

6. The preparation method according to claim 5, characterized in that, The mixing temperature is 70~90℃, and the mixing time is 0.5~2 h.

7. An electrode sheet, characterized in that, It includes a current collector and an active material layer disposed on at least one surface of the current collector; the active material layer includes a dry binder, a conductive agent and an active material; the dry binder is the dry binder according to any one of claims 1 to 4 or the dry binder prepared by the preparation method according to any one of claims 5 to 6.

8. The method for preparing the electrode sheet according to claim 7, characterized in that, Includes the following steps: (a) The dry binder, conductive agent and active material are mixed and kneaded to obtain a mixed powder; (b) The mixed powder is heated and then rolled to obtain an active material layer; The thickness of the active material layer is 100~200 μm; (c) The active material layer and the current collector are subjected to hot pressing to obtain the electrode sheet.

9. The preparation method according to claim 8, characterized in that, In step (a), the mixing and kneading temperature is 60~200℃, preferably 80~120℃.

10. The preparation method according to claim 8, characterized in that, In step (c), the hot pressing process is carried out at a temperature of 60~200℃, preferably 120~140℃.

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