A method for regulating a dry electrode coating process

Abstract

This invention discloses a method for controlling the dry electrode coating process, belonging to the field of battery technology. The method includes the following steps: before the current collector and the dry film are laminated, a conductive adhesive is coated on the surface of the current collector. The dry film is then laminated with the current collector through the action of the conductive adhesive to obtain a dry electrode sheet. The dry electrode sheet includes the current collector, the conductive adhesive, and the dry film. The aqueous binder in the conductive adhesive is an aqueous binder with a large number of carboxylic acid groups on its surface. These carboxylic acid groups on the surface of the aqueous binder form a large number of hydrogen bonds with both the current collector and the dry film, thereby increasing the adhesion between the dry film and the current collector. The conductive adhesive prepared by this invention is simple and environmentally friendly, requiring no additional composite additives. The conductive adhesive is obtained simply by mixing the aqueous binder and the conductive material, and the prepared conductive adhesive has high adhesion. The conductive adhesive prepared by this invention uses an aqueous binder with a large number of carboxylic acid groups on its surface, which can form hydrogen bonds with both the current collector surface and the dry film to achieve adhesion, thereby increasing the adhesion between the dry film and the current collector, further reducing internal resistance, and improving the rate performance and cycle stability of the battery. The dry electrode coating process of this invention is simple to operate, low in cost, non-toxic, and can be mass-produced.

Description

Technical Field

[0001] This invention belongs to the field of batteries, and particularly relates to a method for controlling a dry electrode coating process. Background Technology

[0002] In recent years, with Tesla, the leading electric vehicle company, acquiring Maxwell, a supercapacitor manufacturer, "dry electrode technology" has become a hot topic in the lithium battery industry. Compared with the traditional wet process of lithium batteries, the biggest feature of dry electrode technology is that it does not use any solvents, and it has outstanding advantages such as being environmentally friendly, having high energy density, good conductivity, and being more suitable for pre-lithiation technology and solid-state battery technology.

[0003] The dry electrode process involves uniformly mixing active particles and conductive agents, then adding a binder. The binder's fibrillation action forms a self-supporting film, which is finally rolled onto the current collector surface. Dry electrodes do not use solvents in their fabrication; the binder exists in a fibrous state and only makes point contact with the surface of the active material particles. This does not affect the internal contact between the active material particles, resulting in tighter contact between the active material particles and with the conductive agent particles, leading to better electrode conductivity.

[0004] Binders are a crucial component of battery electrodes, serving as polymeric compounds that adhere active materials and conductive agents from the electrode sheet to the current collector. They enhance the contact between the active material, conductive agent, and current collector, and stabilize the electrode structure, making them a high-tech additive in battery materials. Studies show that although binders are used in relatively small quantities in electrode sheets, their performance directly impacts battery capacity, lifespan, and safety. Polymer binders bridge the gap between the current collector, conductive carbon black, and active material to ensure the integrity of the electrode components. After adsorption on particle surfaces, binders form boundary layers, cured layers, and free layers. The performance of the cured and free layers primarily depends on the bulk properties of the binder.

[0005] In dry-process electrodes, the binder used for the dry membrane is PTFE, a polymer material with very unique properties. PTFE exhibits extremely high resistance to almost all chemicals, including strong acids, strong alkalis, and organic solvents, making it very popular in chemical industries and laboratory equipment. PTFE possesses excellent mechanical properties and remains stable at extreme temperatures; its continuous operating temperature range is typically between -200°C and 260°C, with shorter-term temperature resistance reaching even higher levels. However, PTFE has a very low surface energy, making it non-sticky on most surfaces. While this characteristic is advantageous in some applications, when used as a binder, the low surface energy can lead to insufficient adhesion between PTFE and other materials, resulting in poor adhesion between the dry membrane and the current collector, affecting the overall battery resistance. The adhesive strength between the dry membrane and the current collector is crucial. In dry-process electrodes, the use of PTFE as the binder in the dry membrane makes it easy for the dry membrane to peel off from the current collector.

[0006] CN116487519A discloses a dry electrode, its preparation method, and a battery. This preparation method involves mixing an adhesive with a conductive material to form a uniform conductive adhesive solution. By adjusting the spray nozzle size and the distance between the nozzle and the foil, the adhesive solution is evenly dispersed on the foil, thereby improving the peel strength of the dry electrode and reducing the electrode impedance. However, the conductive adhesive used in this preparation method is liquid on the current collector, employing a wet coating process. To avoid uneven coating due to the fluidity of the wet coating surface, and to prevent the dry electrode film from becoming wet during lamination, which is detrimental to rolling and leads to problems such as sticking to the rollers after winding and unstable roll density, a dot pattern is used, with the area of ​​a single conductive adhesive layer not exceeding 1 cm². 2 Because the conductive adhesive is applied in dots, its flow on the foil is reduced. However, this method has the following problems: First, the binders used in the conductive adhesive are water-based and oil-based binders, and it is a wet dot application. The selected dry film is a layered oxide cathode material for sodium-ion batteries, which is very sensitive to moisture. This limits the binder used in the conductive adhesive to oil-based PVDF. However, PVDF has poor bonding ability in the electrode, and the mechanical properties, adhesion to the current collector, and cohesion of the electrode film are not high. This limits the scope of application. Ternary materials and sulfide materials are also sensitive to moisture, which also limits their application. Second, the use of spray dot application to spray the conductive adhesive onto the current collector is not conducive to large-scale production. Third, the organic solvents used are volatile and have a certain degree of toxicity, which increases environmental protection costs. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for controlling the dry electrode coating process, thereby improving the adhesion between the dry film and the current collector, enhancing the battery's cycle performance, and reducing the battery's internal resistance.

[0008] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0009] A method for controlling a dry electrode coating process, characterized by the following steps: before the current collector and the dry film are laminated, a conductive adhesive is coated on the surface of the current collector, and the dry film is laminated with the current collector through the action of the conductive adhesive to obtain a dry electrode sheet;

[0010] The water-based adhesive in the conductive adhesive is a water-based adhesive with a large number of carboxylic acid groups on its surface. The carboxylic acid groups on the surface of the water-based adhesive form a large number of hydrogen bonds with the current collector and the dry film respectively, thereby increasing the adhesion between the dry film and the current collector.

[0011] Furthermore, the dry electrode includes a current collector, a conductive adhesive, and a dry film;

[0012] The conductive adhesive is composed of water-based adhesive I and a conductive agent;

[0013] The dry membrane is composed of an active substance, binder II, and a conductive agent.

[0014] Furthermore, the water-based adhesive I in the conductive adhesive is a water-based adhesive with a large number of carboxylic acid groups on its surface, including at least one of polyacrylic acid PAA, sodium carboxymethyl cellulose CMC / styrene-butadiene rubber SBR, and alginate ALG;

[0015] The conductive agent in the conductive adhesive includes any one or a combination of at least two of conductive carbon black, carbon nanofibers, carbon nanotubes, acetylene black, Ketjen black, or graphene.

[0016] Furthermore, the dry membrane has a thickness of 100-250 μm and a composition of 95 wt% active material, 2 wt% binder II, and 3 wt% conductive agent. The active material includes one or a mixture of at least two of graphite, soft carbon, hard carbon, silicon-oxygen composite material, silicon-carbon composite material, and ternary 811 material. The binder II is polytetrafluoroethylene (PTFE) or a combination of PTFE with any one of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polyethylene oxide (PEO), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR). When PTFE is combined with other binders, the PTFE content is at least 50 wt%.

[0017] The conductive agent is any one or a combination of at least two of conductive carbon black, carbon nanofibers, carbon nanotubes, acetylene black, Ketjen black, or graphene.

[0018] The method for controlling the dry electrode coating process of the present invention specifically includes the following steps:

[0019] (1) Dissolve a certain amount of water-based adhesive in a water-based solvent and mix them evenly to obtain a water-based adhesive solution;

[0020] (2) Mix a certain amount of water-based adhesive solution and conductive agent evenly to obtain conductive adhesive;

[0021] (3) Apply conductive adhesive to the current collector using a flatbed coating machine. The thickness of the conductive adhesive coating is 2-30 μm.

[0022] (4) After the moisture in the conductive adhesive on the current collector evaporates, the dry film is applied to the current collector by a hot roller press and a flat plate hot pressing composite process.

[0023] Furthermore, the solid content of the aqueous adhesive in the aqueous adhesive solution in step (1) is 1-20 wt%.

[0024] Furthermore, the mass ratio of the aqueous adhesive solution to the conductive agent in step (2) is (70-98):(1-20).

[0025] Furthermore, in step (3), the coating thickness of the conductive adhesive on the current collector is 2 to 30 μm.

[0026] Furthermore, the current collector is a foil material, such as copper foil and carbon-coated copper foil.

[0027] Furthermore, the method for evaporating the moisture from the conductive adhesive on the current collector in step (4) is to air-dry the current collector coated with conductive adhesive in the air for 5-9 hours, then place it in a forced-air oven at 40°C for 6 hours, and then bake it at 80°C for 1 hour.

[0028] Furthermore, in step (4), the hot roller press temperature is 100℃~150℃, the roller gap distance is adjusted to 80%-90% of the dry film thickness and the total thickness of the conductive adhesive current collector, the hot roller speed is 0.5m / min~3m / min; the flat plate hot pressing temperature is 100℃~180℃, the pressure is 0.5T-2T, and the hot pressing time is 2-10s.

[0029] The beneficial effects of this invention are as follows: The adhesion strength between the dry-process membrane and the current collector is crucial. However, during the composite process of the current collector and the dry-process membrane in a dry-process electrode, the presence of the PTFE binder results in very low surface energy, making adhesion difficult and causing the dry-process membrane to easily peel off from the current collector. This invention coats the surface of the current collector with conductive adhesive before the current collector and the dry-process membrane are composited. After the conductive adhesive on the current collector surface dries, the dry-process membrane is composited with the current collector through the action of the conductive adhesive, resulting in a dry-process electrode. The aqueous binder in the selected conductive adhesive contains a large number of carboxylic acid groups on its surface. These carboxylic acid groups form numerous hydrogen bonds with the current collector and the dry-process membrane, thereby increasing the adhesion between the dry-process membrane and the current collector. Secondly, the conductive adhesive used in this invention is solid on the current collector, employing a dry coating process. The binder in the conductive adhesive forms hydrogen bonds with the current collector and the dry film under high-temperature rolling and hot pressing, increasing adhesion. The method used in this invention not only has stronger adhesion than oil-based binders but also has a wider range of applications, suitable for water-sensitive materials such as ternary cathodes, lithium titanate anodes, solid sulfides, and sodium electrode materials. The dry electrode coating process of this invention is simple to operate, low in cost, non-toxic, and can be mass-produced. Attached Figure Description

[0030] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0031] Figure 1 To compare the effect of drying method on the current collector coating effect of conductive adhesive in Example 1.

[0032] Figure 2 This is Example 1, which illustrates the effect of drying method on the current collector coating effect of conductive adhesive. Detailed Implementation

[0033] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments are merely illustrative of the invention and should not be construed as limiting its scope.

[0034] The dry electrode described in this invention patent includes a current collector, a conductive adhesive, and a dry film.

[0035] According to the technical solution of the present invention, a method for controlling the dry electrode coating process is provided to improve the adhesion between the dry film and the current collector, improve the cycle performance of the battery, and reduce the internal resistance of the battery.

[0036] Example 1

[0037] This embodiment describes a method for controlling a dry electrode coating process, the steps of which are as follows:

[0038] (1) Preparation of conductive adhesive: A certain amount of PAA and water are mixed evenly in a degassing machine according to the following parameters: first, the mixture is rotated at low speeds of 600 rpm, 900 rpm and 1200 rpm for 300 s, 360 s and 180 s respectively, then left to stand for 300 s, and then rotated at high speeds of 1200 rpm, 1500 rpm and 1800 rpm for 300 s, 360 s and 180 s respectively, to obtain a PAA water-based adhesive solution with a solid content of 5 wt%.

[0039] (2) Place the PAA water-based adhesive solution and SP conductive agent with a mass ratio of 95:5 in a degassing machine and mix them according to the following parameters: first, rotate at low speeds of 300 rpm, 600 rpm and 900 rpm for 120 s, 150 s and 120 s respectively, then let it stand for 300 s; then rotate at medium speeds of 600 rpm, 900 rpm and 1200 rpm for 300 s, 360 s and 180 s respectively, then let it stand for 300 s; finally, rotate at high speeds of 1500 rpm, 1800 rpm and 2600 rpm for 300 s, 600 s and 180 s respectively to obtain conductive adhesive.

[0040] (3) Apply conductive adhesive to the copper foil current collector using a flatbed coating machine. The thickness of the conductive adhesive coating is 5 μm, and the coating speed is 3 cm / s. Allow the current collector coated with conductive adhesive to air dry naturally for 5 hours, then place it in a forced-air oven at 40°C for 6 hours, and then at 80°C for 1 hour.

[0041] (4) The graphite dry film is coated onto the copper foil current collector coated with conductive adhesive. The roller gap distance of the roller press is adjusted to 80% of the thickness of the current collector coated with conductive adhesive plus the total thickness of the dry film. The hot rolling speed is 0.5 m / min and the hot rolling temperature is 110℃. The graphite dry film with a thickness of 150 μm is coated onto the copper foil current collector to initially obtain the graphite dry electrode sheet. The graphite dry film is composed of 95 wt% graphite, 2 wt% binder PTFE, and 3 wt% conductive carbon black.

[0042] (5) The graphite dry electrode sheet from step (4) is further reinforced with a flat plate hot press. The hot pressing temperature is set to 130°C, the pressure is 1T, and the hot pressing time is 5s to obtain the graphite dry electrode sheet.

[0043] Example 2

[0044] This embodiment describes a method for controlling a dry electrode coating process, the steps of which are as follows:

[0045] (1) Preparation of conductive adhesive: A certain amount of PAA and water are mixed evenly in a degassing machine. The mixture is mixed according to the following parameters: first, it is rotated at low speeds of 400 rpm, 600 rpm and 900 rpm for 300 s, 360 s and 180 s respectively, then left to stand for 300 s, and then rotated at high speeds of 900 rpm, 1200 rpm and 1500 rpm for 300 s, 360 s and 180 s respectively, to obtain a PAA water-based adhesive solution with a solid content of 1%.

[0046] (2) Place the PAA water-based adhesive solution and SP conductive agent with a mass ratio of 80:1 in a degassing machine and mix them according to the following parameters: first, rotate at low speeds of 300 rpm, 600 rpm and 900 rpm for 120 s, 150 s and 120 s respectively, and then let it stand for 300 s; then rotate at medium speeds of 600 rpm, 900 rpm and 1200 rpm for 300 s, 360 s and 180 s respectively, and then let it stand for 300 s; finally, rotate at high speeds of 1500 rpm, 1800 rpm and 2600 rpm for 300 s, 600 s and 180 s respectively to obtain conductive adhesive.

[0047] (3) Apply conductive adhesive to the copper foil current collector using a flatbed coating machine. The thickness of the conductive adhesive coating is 2μm, and the coating speed is 1cm / s. Allow the current collector coated with conductive adhesive to air dry naturally for 6 hours, then place it in a forced-air oven at 40℃ for 6 hours, and then at 80℃ for 1 hour.

[0048] (4) The silicon-carbon dry film is coated on the copper foil current collector coated with conductive adhesive. The roller gap distance of the roller press is adjusted to 85% of the thickness of the dry film plus the current collector coated with conductive adhesive. The hot rolling speed is 1m / min and the hot rolling temperature is 130℃. The silicon-carbon composite material with a thickness of 180μm is dry coated on the copper foil current collector. The composition of the silicon-carbon composite material dry film is 95wt% silicon-carbon composite material, 2wt% binder PTFE, 2wt% conductive carbon black + 1wt% carbon nanotubes. The silicon-carbon composite material dry electrode is initially obtained.

[0049] (5) The silicon-carbon composite material dry electrode sheet from step (4) is further reinforced with a flat plate hot press. The hot pressing temperature is set to 150°C, the pressure to be 0.5T, and the hot pressing time to be 10s to obtain the silicon-carbon composite material dry electrode sheet.

[0050] Example 3

[0051] This embodiment describes a method for controlling a dry electrode coating process, the steps of which are as follows:

[0052] (1) Preparation of conductive adhesive: A certain amount of ALG and water are mixed evenly in a degassing machine according to the following parameters: first, the mixture is rotated at low speeds of 200 rpm, 600 rpm and 800 rpm for 600 s, 300 s and 180 s respectively, then left to stand for 300 s, and then rotated at high speeds of 600 rpm, 900 rpm and 1200 rpm for 600 s, 300 s and 180 s respectively, to obtain an ALG aqueous adhesive solution with a solid content of 10 wt%.

[0053] (2) Place the PAA water-based adhesive solution and acetylene black conductive agent with a mass ratio of 75:5 in a degassing machine and mix them according to the following parameters: first, rotate at low speeds of 200 rpm, 600 rpm and 800 rpm for 300 s, 150 s and 120 s respectively, and then let it stand for 300 s; then rotate at medium speeds of 600 rpm, 900 rpm and 1200 rpm for 600 s, 300 s and 180 s respectively, and then let it stand for 300 s; finally, rotate at high speeds of 1500 rpm, 1800 rpm and 2600 rpm for 300 s, 600 s and 180 s respectively to obtain conductive adhesive.

[0054] (3) Apply conductive adhesive to the copper foil current collector using a flatbed coating machine. The thickness of the conductive adhesive coating is 10 μm, and the coating speed is 2 cm / s. Allow the current collector coated with conductive adhesive to air dry naturally for 8 hours, then place it in a forced-air oven at 40°C for 6 hours, and then at 80°C for 1 hour.

[0055] (4) A silicon-oxygen dry-process film is coated onto a copper foil current collector coated with conductive adhesive. The roller gap distance of the roller press is adjusted to 90% of the total thickness of the dry-process film plus the thickness of the current collector coated with conductive adhesive. The hot rolling speed is 3 m / min and the hot rolling temperature is 150℃. A silicon-oxygen composite material with a thickness of 200 μm is dry-process coated onto the copper foil current collector. The composition of the silicon-oxygen composite material dry-process film is 95 wt% silicon-oxygen composite material, 1.5 wt% PTFE binder + 0.5 wt% PAA, 2 wt% conductive carbon black + 1 wt% carbon nanotubes. A silicon-oxygen composite material dry-process electrode is initially obtained.

[0056] (5) The silicon-oxygen composite dry electrode sheet from step (4) is further reinforced with a flat plate hot press. The hot pressing temperature is set to 140°C, the pressure to be 2T, and the hot pressing time to be 2s to obtain the silicon-oxygen composite dry electrode sheet.

[0057] Example 4

[0058] This embodiment describes a method for controlling a dry electrode coating process, the steps of which are as follows:

[0059] (1) Preparation of conductive adhesive: A certain amount of CMC / SBR (mass ratio 1:1) and water were mixed evenly in a degassing machine. The mixture was mixed according to the following parameters: first, it was rotated at low speeds of 150 rpm, 300 rpm and 400 rpm for 600 s, 120 s and 180 s respectively, then stopped for 300 s, and then rotated at high speeds of 200 rpm, 400 rpm and 1200 rpm for 600 s, 120 s and 180 s respectively, to obtain a CMC / SBR waterborne adhesive solution with a solid content of 20%.

[0060] (2) Place the PAA aqueous adhesive solution and nano-carbon fiber conductive agent with a mass ratio of 80:20 in a degassing machine and mix them according to the following parameters: first, rotate at low speeds of 150 rpm, 300 rpm and 400 rpm for 600 s, 120 s and 180 s respectively, and then let it stand for 300 s; then rotate at medium speeds of 200 rpm, 400 rpm and 500 rpm for 600 s, 120 s and 180 s respectively, and then let it stand for 300 s; finally, rotate at high speeds of 300 rpm, 500 rpm and 800 rpm for 300 s, 180 s and 120 s respectively to obtain conductive adhesive.

[0061] (3) Apply conductive adhesive to the current collector using a flatbed coating machine. The thickness of the conductive adhesive coating is 25 μm, and the coating speed is 2 cm / s. Allow the current collector coated with conductive adhesive to air dry naturally for 9 hours, then place it in a forced-air oven at 40°C for 6 hours, and then at 80°C for 1 hour.

[0062] (4) A graphite dry film is coated onto a copper foil current collector coated with conductive adhesive. The roller gap distance of the roller press is adjusted to 86% of the total thickness of the dry film plus the current collector coated with conductive adhesive. The hot rolling speed is 1.5 m / min and the hot rolling temperature is 120℃. A graphite material with a thickness of 220 μm is dry coated onto the copper foil current collector. The graphite dry film is composed of 95 wt% graphite, 1.5 wt% PTFE binder + 0.5 wt% PAA, 2 wt% conductive carbon black + 1 wt% carbon nanotubes. A graphite dry electrode sheet is initially obtained.

[0063] (5) The graphite dry electrode sheet from step (4) is further reinforced with a flat plate hot press. The hot pressing temperature is set to 180°C, the pressure to be 0.6T, and the hot pressing time to be 10s to obtain the graphite dry electrode sheet.

[0064] Example 5

[0065] This embodiment describes a method for controlling a dry electrode coating process, the steps of which are as follows:

[0066] (1) Preparation of conductive adhesive: A certain amount of PAA and water are mixed evenly in a degassing machine according to the following parameters: first, the mixture is rotated at low speeds of 600 rpm, 900 rpm and 1200 rpm for 300 s, 360 s and 180 s respectively, then left to stand for 300 s, and then rotated at high speeds of 1200 rpm, 1500 rpm and 1800 rpm for 300 s, 360 s and 180 s respectively, to obtain a PAA water-based adhesive solution with a solid content of 7 wt%.

[0067] (2) Place the PAA water-based adhesive solution and SP conductive agent with a mass ratio of 96:3 in a degassing machine and mix them according to the following parameters: first, rotate at low speeds of 300 rpm, 600 rpm and 900 rpm for 120 s, 150 s and 120 s respectively, and then let it stand for 300 s; then rotate at medium speeds of 600 rpm, 900 rpm and 1200 rpm for 300 s, 360 s and 180 s respectively, and then let it stand for 300 s; finally, rotate at high speeds of 1500 rpm, 1800 rpm and 2600 rpm for 300 s, 600 s and 180 s respectively to obtain conductive adhesive.

[0068] (3) Apply conductive adhesive to the aluminum foil current collector using a flatbed coating machine. The thickness of the conductive adhesive coating is 10 μm, and the coating speed is 3 cm / s. Allow the current collector coated with conductive adhesive to air dry naturally for 6 hours, then place it in a forced-air oven at 40°C for 6 hours, and then at 80°C for 1 hour.

[0069] (4) The graphite dry process film is coated on the aluminum foil current collector coated with conductive adhesive. The roller gap distance of the roller press is adjusted to 90% of the thickness of the current collector coated with conductive adhesive plus the total thickness of the dry process film. The hot rolling speed is 0.5 m / min and the hot rolling temperature is 130℃. The ternary 811 dry process film with a thickness of 150 μm is coated on the aluminum foil current collector to initially obtain the ternary 811 dry process electrode sheet. The composition of the ternary 811 dry process film is 95 wt% ternary 811, 2 wt% binder PTFE, 1 wt% conductive carbon black + 2 wt% carbon nanotubes.

[0070] (5) The ternary 811 dry electrode sheet from step (4) is further reinforced with a flat plate hot press. The hot pressing temperature is set to 130℃, the pressure is 1T, and the hot pressing time is 5s to obtain the ternary 811 dry electrode sheet.

[0071] Comparative Example 1

[0072] This comparative example provides a method for controlling the dry electrode coating process. The method involves coating a conductive adhesive onto a current collector using a flatbed coating machine. The current collector coated with the conductive adhesive is not allowed to air dry naturally, but is directly placed in a forced-air oven at 40°C for 6 hours, followed by drying at 80°C for 1 hour. All other conditions are exactly the same as in Example 1.

[0073] Comparative Example 2

[0074] This comparative example provides a method for controlling the dry electrode coating process. In this method, the conductive adhesive does not use a binder containing carboxylic acid groups; instead, PI (polyimide) is used as the binder, and the corresponding solvent is DMF (N,N-dimethylformamide). Apart from this, all other conditions are exactly the same as in Example 1.

[0075] Comparative Example 3

[0076] This comparative example provides a method for controlling the dry electrode coating process. In this method, the conductive adhesive does not use a binder containing carboxylic acid groups; instead, PVDF (polyvinylidene fluoride) is used as the binder, and NMP (N-methylpyrrolidone) is used as the solvent. Apart from this, all other conditions are exactly the same as in Example 1.

[0077] Comparative Example 4

[0078] This comparative example provides a method for controlling the dry electrode coating process. In this method, the conductive adhesive does not use a binder containing carboxylic acid groups; instead, PVP (polyvinylpyrrolidone) is used as the binder, and water is used as the solvent. All other conditions are exactly the same as in Example 1.

[0079] Comparative Example 5

[0080] This comparative example provides a method for controlling the dry electrode coating process, wherein the conductive adhesive in the method has an SP content of 0. All other conditions are exactly the same as in Example 1.

[0081] Comparative Example 6

[0082] This comparative example provides a method for controlling the dry electrode coating process, wherein the hot roller press temperature in the method is 80°C. Apart from this, all other conditions are exactly the same as in Example 1.

[0083] Comparative Example 7

[0084] This comparative example provides a wet electrode with the same ratio of active material: binder: conductive agent as the dry electrode. In Example 1, the graphite:PTFE: conductive agent ratio is 95:2:3 in the dry electrode and the graphite:CMC:SBR: conductive agent ratio is 95:1:1:3 in the wet electrode. The electrodes are coated on copper foil using a 150μm doctor blade.

[0085] Performance testing

[0086] The adhesion force and impedance test results between the membrane and the current collector in each embodiment and comparative example are shown in Table 1.

[0087] Table 1 shows the adhesive strength and resistance test results for the examples and comparative examples.

[0088] Example 1 0.37 0.02201 Example 2 0.36 0.02698 Example 3 0.38 0.03046 Example 4 0.35 0.03215 Example 5 0.36 0.02886 Comparative Example 1 / / Comparative Example 2 0.13 0.19687 Comparative Example 3 0.15 0.13717 Comparative Example 4 0.12 0.26187 Comparative Example 5 0.38 2.32153 Comparative Example 6 0.03 0.03537 Comparative Example 7 0.14 0.47591

[0089] Dry and wet electrode sheets from each embodiment and comparative example were assembled into a button cell, and the first efficiency, first discharge specific capacity at 0.2C, and specific capacity retention rate after 50 and 100 cycles were tested. The test results are shown in Figure 2.

[0090] Table 2. Electrochemical performance test results of the examples and comparative examples.

[0091]

[0092] The results in Tables 1 and 2 show that the dry electrode prepared by the method of the present invention has a large adhesion, a small impedance, and excellent electrochemical performance.

[0093] As shown in Tables 1-4 and Comparative Example 7, the dry-process electrode of the present invention exhibits stronger adhesion between the active material and the current collector compared to the wet-process electrode. Furthermore, impedance testing reveals that the impedance between the active material and the current collector in the dry-process electrode of the present invention is also lower than that in the wet-process electrode. A comparison of the electrochemical performance of Examples 1-4 and Comparative Example 7 in Tables 2 shows that its performance is comparable to that of wet-process electrodes. However, the dry-process electrode has a significant advantage over the wet-process electrode in terms of manufacturing process and cost.

[0094] Example 5 uses ternary cathode material 811, which is sensitive to moisture. Since the moisture in the conductive adhesive on the current collector is removed during the coating process of this patent, the ternary cathode 811 electrode sheet produced has excellent performance, indicating that the coating process of this invention is applicable to a wide range of fields.

[0095] When the binder in the conductive adhesive of Comparative Examples 2-4 is an oil-based binder or an aqueous binder without carboxylic acid groups during the composite of dry membrane and current collector, the bonding strength decreases and the impedance increases. This is predicted to affect the cycle life. From the specific capacity retention rate at 50 and 100 cycles, Comparative Examples 2-4 have poor cycle performance, which is consistent with the poor bonding strength and high impedance of Comparative Examples 2-4 in Table 1.

[0096] In Comparative Example 5, the conductive adhesive has an SP content of 0, and the dry membrane is connected to the current collector via PAA adhesive. Its interfacial impedance is too high, so there is no need to assemble the button cell to measure its electrochemical performance.

[0097] In Comparative Example 6, the hot roller press temperature in the method is 80°C. The temperature is too low during film coating, which is not conducive to the formation of hydrogen bonds between the binder in the conductive adhesive and the dry film and current collector, resulting in low adhesion to the current collector, which in turn affects the coating effect and other electrochemical properties.

[0098] Figure 1For Comparative Example 1, conductive adhesive was coated onto the current collector using a flatbed coating machine. The current collector coated with conductive adhesive was not air-dried but directly placed in a forced-air oven at 40°C for 6 hours, followed by drying at 80°C for 1 hour. The conductive adhesive remained intact during air drying and oven drying, but began to crack upon removal from the oven. Using the same method, the foil coated with conductive adhesive was air-dried for 1 hour as described in Example 1, then placed in an oven at 40°C for 6 hours, followed by drying at 80°C for 1 hour. The conductive adhesive did not crack in this case. Figure 2 As shown.

[0099] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A method for controlling a dry electrode coating process, characterized in that, Includes the following steps: Before the current collector and the dry film are combined, a conductive adhesive is coated on the surface of the current collector. The dry film is then combined with the current collector through the action of the conductive adhesive to obtain a dry electrode sheet. The water-based adhesive in the conductive adhesive is a water-based adhesive with a large number of carboxylic acid groups on its surface. The carboxylic acid groups on the surface of the water-based adhesive form a large number of hydrogen bonds with the current collector and the dry film respectively, thereby increasing the adhesion between the dry film and the current collector. The conductive adhesive I is an aqueous adhesive with a large number of carboxylic acid groups on its surface, including at least one of polyacrylic acid PAA, sodium carboxymethyl cellulose CMC / styrene-butadiene rubber SBR, and alginate ALG; The control method for the dry electrode coating process includes the following steps: (1) Dissolve a certain amount of water-based adhesive I in a water-based solvent and mix them evenly to obtain a water-based adhesive solution; (2) Mix a certain amount of water-based adhesive solution and conductive agent evenly to obtain conductive adhesive; (3) Apply conductive adhesive to the current collector using a flatbed coating machine. The thickness of the conductive adhesive coating is 2-30 μm. (4) After the moisture in the conductive adhesive on the current collector evaporates, the dry film is applied to the current collector by a hot roller press and a flat plate hot press composite process. In step (4), the method to evaporate the moisture of the conductive adhesive on the current collector is to air-dry the current collector coated with conductive adhesive in the air for 5-9 hours, then place it in a forced-air oven at 40°C for 6 hours, and then at 80°C for 1 hour. In step (4), the hot roller press temperature is 100℃~150℃, the roller gap distance is adjusted to 80%-90% of the dry film thickness and the total thickness of the conductive adhesive current collector, the hot roller speed is 0.5m / min~3m / min; the flat plate hot pressing temperature is 100℃~180℃, the pressure is 0.5T-2T, and the hot pressing time is 2-10s.

2. The method for controlling the dry electrode coating process according to claim 1, characterized in that, The dry electrode includes a current collector, a conductive adhesive, and a dry film; The conductive adhesive is composed of water-based adhesive I and a conductive agent; The dry membrane is composed of an active substance, binder II, and a conductive agent.

3. The method for controlling the dry electrode coating process according to claim 2, characterized in that, The conductive agent in the conductive adhesive includes any one or a combination of at least two of conductive carbon black, carbon nanofibers, carbon nanotubes, acetylene black, Ketjen black, or graphene.

4. The method for controlling the dry electrode coating process according to claim 2, characterized in that, The dry membrane has a thickness of 100-250 μm and is composed of: 95 wt% active material, 2 wt% binder II and 3 wt% conductive agent. The active material includes one or a mixture of at least two of graphite, soft carbon, hard carbon, silicon-oxygen composite material, silicon-carbon composite material and ternary 811 material. The adhesive II is polytetrafluoroethylene (PTFE) or a combination of PTFE with any one of polyvinylidene fluoride (PVDF), polyacrylic acid (PAA), polyethylene oxide (PEO), sodium carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR). When PTFE is combined with other adhesives, the PTFE content is at least 50 wt%. The conductive agent is any one or a combination of at least two of conductive carbon black, carbon nanofibers, carbon nanotubes, acetylene black, Ketjen black, or graphene.

5. The method for controlling the dry electrode coating process according to claim 1, characterized in that, The solid content of the aqueous adhesive in the aqueous adhesive solution in step (1) is 1-20 wt%.

6. The method for controlling the dry electrode coating process according to claim 1, characterized in that, The mass ratio of the aqueous adhesive solution to the conductive agent in step (2) is (70-98):(1-20).

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