A method for manufacturing a dry electrode sheet

Abstract

The application discloses a kind of production methods of dry electrode sheet, it is related to electrode manufacturing technical field, it solves the technical problems such as high pollution, high energy consumption of traditional wet process, fiberization is not sufficient, film thickness is uneven, intensity is low, continuous production is difficult and so on of existing dry process.The method includes: active material, conductive agent, binder are mixed in proportion, after low-temperature preliminary mixing, medium-temperature high-speed pre-fiberization, airflow crushing is introduced to carry out depth fiberization;Again, the powder that is fully fiberized is after dense mixing, granulation, adopts multi-roller calender and controls the linear velocity difference between rollers to carry out shearing stretch film, finally, with rubber-coated aluminum foil covering, obtain the sandwich structure of dry electrode.The method ensures the uniformity and strength of fiber network by two-stage fiberization, realizes the high consistency of electrode film thickness and compaction density by differential speed shearing film forming mechanism, effectively overcomes the problems such as uneven fiberization, large film forming fluctuation, low intensity and so on in prior art, and is suitable for continuous production.

Description

Technical Field

[0001] This invention relates to the fields of supercapacitors, lithium batteries and solid-state batteries, and in particular to a method for manufacturing dry electrode sheets. Background Technology

[0002] Currently, the production of electrodes for lithium-ion batteries mainly employs wet coating processes. This process requires organic solvents such as N-methylpyrrolidone (NMP) and subsequent high-temperature drying, resulting in high energy consumption, high cost, VOC emissions, and environmental unfriendliness. Furthermore, solvent residue severely impacts the cycle life and safety of batteries (especially solid-state batteries), hindering the development of high-performance batteries. Dry electrode processes, due to their advantages of being solvent-free, environmentally friendly, residue-free, and having high energy density, have become a key development direction for the industry.

[0003] In the prior art, Chinese patent CN117393704B discloses a dry-process electrode preparation method, which uses PTFE composite binder, internal mixing, low-speed shear granulation, and graded warm-pressing thinning process. This method improves the strength and conductivity of the electrode to a certain extent and has certain industrial application value. However, this method still has obvious technical defects: First, its fiberization mainly relies on the shearing action of the internal mixer, which is a single method and is prone to local insufficient fiberization, material agglomeration, or excessive shearing leading to the breakage of binder (such as PTFE) chains. The degree of fiberization is difficult to control precisely, affecting the uniformity and strength of the electrode. Second, it uses a step-by-step static pressing thinning method with roller spacing. The film thickness and uniformity are directly affected by feeding fluctuations and roller parallelism, which can easily lead to poor thickness consistency and uneven compaction density, requiring extremely high precision in equipment processing and debugging. Third, the above-mentioned static pressing film formation process lacks shearing and stretching action on the internal fiber network of the material, making it difficult to further orient and densify the fibers, thus limiting the upper limit of the optimization of the electrode's mechanical properties and conductive network.

[0004] In addition, conventional airflow fiberization processes suffer from problems such as short fiberization time and uncontrollable fiberization degree, making it difficult to achieve continuous and stable production. Therefore, developing a dry electrode sheet preparation method that achieves fully uniform fiberization, consistent film thickness, high strength, and is suitable for large-scale continuous production has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to solve the above-mentioned problems by designing a dry electrode sheet manufacturing method, which solves the problems of high pollution and high energy consumption of traditional wet processes, as well as insufficient fiberization and uneven film thickness of existing dry processes.

[0006] The technical solution of the present invention to achieve the above objectives is a method for manufacturing a dry electrode sheet, comprising the following steps: (1) Weigh and measure the active material, conductive agent and binder in a mass percentage of 85-95%: 2-5%: 3-10%, and perform preliminary mixing at a preset temperature to obtain a uniformly mixed first powder; (2) The mixing temperature is increased to no more than 80°C for high-speed mixing to form a second powder with preliminary fibrosis; (3) The second powder is placed in an air jet mill and deep fiberized using high-temperature steam or inert gas to obtain a fully fiberized and uniform third powder; (4) The third powder is kneaded at 60-200℃ and 0.5-10MPa for 5-60 minutes to form a molten block material; (5) Granulate the molten block material to obtain particulate powder with a particle size of 100μm-3000μm; (6) The granular powder is calendered into a film by a multi-roll calender. By controlling the speed or diameter of the rolls, a linear speed difference is formed. The speed ratio between the rolls is controlled to be greater than 1 and less than or equal to 3. The film is stretched by the generated shear force and then laminated with coated aluminum foil / copper foil to obtain a sandwich structure dry electrode sheet.

[0007] As a further supplement to the active material, the active material in step (1) includes, but is not limited to, at least one of NCM, graphite, lithium titanate, lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, soft carbon, hard carbon, and activated carbon.

[0008] As a further supplement to the adhesive, the adhesive mentioned in step (1) includes, but is not limited to, at least one of polyethylene, polyvinylidene fluoride, polypropylene, polyvinylidene fluoride, polyethylene oxide, polyphenylene ether, polyethylene-block-polyethylene glycol, polydimethylsiloxane, polytetrafluoroethylene, polydimethylsiloxane-co-alkylmethylsiloxane, and carboxymethyl cellulose.

[0009] Preferably, the adhesive is polytetrafluoroethylene.

[0010] To ensure more uniform mixing of materials, in step (1), the active material, conductive agent, and polytetrafluoroethylene are weighed and measured in proportion, and sent to a high-power shear mixer for low-speed mixing at a speed of 30-200 r / min. The mixing temperature is controlled below 19℃, and the mixing time is 20-60 min.

[0011] In order to achieve the initial fiberization of the first powder, in step (2), the mixing temperature is increased to 25-80℃ for high-speed mixing, the rotation speed is 200-2000r / min, and the mixing time is 5-30min, so as to form the initial fiberized second powder.

[0012] Preferably, the inert gas in the air jet mill in step (3) is argon or nitrogen, with a gas temperature of 80-150℃ and a pressure of 0.4-2MPa.

[0013] As a further supplement to step (5), the molten block material obtained in step (5) is put into a granulation device to obtain granules with a uniform particle size of 100-3000μm. The granulation device is any one of a dry granulator, a swing granulator, a crushing granulator, or an extrusion granulator.

[0014] As one implementation of step (6), the three rolls in step (6) have different diameters but different rotation speeds, which causes a speed difference between the linear velocities of the outer circumference of each roll, and the speed ratio between the rolls is controlled to be greater than 1 and less than or equal to 3.

[0015] As a preferred embodiment of step (6), the diameters of the three rolls in step (6) increase sequentially along the feeding direction. By controlling the rotation speed to be the same or different, a speed difference is generated between the linear velocities of the outer circumference of each roll. The speed ratio between the rolls is controlled to be greater than 1 and less than or equal to 3.

[0016] Its advantages over existing technologies are: The technical solution of this invention features a scientifically designed entire process chain, from low-temperature premixing, two-stage fiberization, and internal mixing to stabilize the network and optimize flowability through granulation. In particular, the granulation step effectively solves the problems of powder agglomeration and bridging, ensuring uniform and stable feeding of materials in the subsequent differential speed rolling process, resulting in a yield rate of over 98% and providing a reliable guarantee for high-speed continuous roll-to-roll production. Specifically, active materials, conductive agents, and binders are mixed in proportion at low speed to form a uniformly mixed material, i.e., the first powder. This first powder is then mixed at high speed below 80°C to obtain a uniformly mixed, pre-fiberized second powder. If the initial mixing is not uniform enough, the fiberization will also be uneven. The second powder is then placed in an air jet mill, where high-speed airflow fully fiberizes it. Finally, the third powder is placed in an internal mixer for internal mixing, forming a molten block material, making the fiberization more uniform. Furthermore, the tensile strength of the subsequently produced electrode film is further improved, greatly enhancing the continuous production of the product. Next, the molten, blocky material is placed into a granulation device for granulation. This step improves material flowability and increases the compaction density of the produced electrode, thereby increasing capacity and reducing product defects caused by powder agglomeration during subsequent film formation. Then, a multi-roll calender is used to calender the granular powder into a film. The multi-roll calender uses the speed difference between the rollers to create shear force between the materials, stretching them into a film. Finally, the resulting electrode film is laminated with coated aluminum or copper foil to obtain a sandwich-structured dry electrode sheet. This method overcomes the limitations of relying solely on intensive mixing and shearing through a two-stage synergistic process of "high-speed mixing and pre-fiberization" and "airflow milling for deep fiberization." Airflow milling allows high-temperature inert gas to fully collide and rub against the powder, achieving uniform deep fiberization and forming a three-dimensional network fiber structure that encapsulates the active particles. This fundamentally avoids the problems of insufficient or excessive fiberization, laying the foundation for preparing high-strength electrode films.

[0017] By dividing the fiberization process into two precise and controllable steps—high-speed pre-fiberization followed by airflow-based deep fiberization—fiberization becomes more thorough and uniform, avoiding binder chain breakage or insufficient fiberization. This significantly improves the tensile strength of the electrode film, and the intensive mixing process makes the fiber network more stable, enabling high-speed continuous roll-to-roll production. During film formation, shear force is generated by the difference in linear speed between the rollers to stretch the film, rather than simply extruding and thinning it. The compaction density fluctuation is less than 2%, reducing the dependence on the parallelism of the rollers. Attached Figure Description

[0018] Figure 1 These are electron microscope images of the activated carbon-based dry electrode sheet of this invention; Figure 2 These are electron microscope images of the ternary dry electrode sheet of this invention. Figure 3 It is a process flow diagram of the equipment. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0020] The fabrication method of this dry electrode sheet mainly includes the following steps: Step 1: The active materials (including but not limited to lithium nickel cobalt manganese oxide (NCM), graphite, lithium titanate, lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, soft carbon, hard carbon, activated carbon, etc.), conductive agents, binders (including but not limited to polyethylene (PE), PVDF, polypropylene (PP), polyvinylidene fluoride (PVDF), polyethylene oxide (PEO), polyphenylene ether (PPO), polyethylene-block polyethylene glycol, polydimethylsiloxane (PDMS), polytetrafluoroethylene (PTFE), polydimethylsiloxane-co-alkylmethylsiloxane, carboxymethyl cellulose (CMC), etc.) and other additives are automatically weighed and metered by positive pressure / negative pressure at a mass percentage ratio of 85%-95%: 2%-5%: 3%-10%.

[0021] Taking polytetrafluoroethylene (PTFE) as a binder as an example, the weighed components are then sent to a high-pressure shear mixer for preliminary mixing. During mixing, the mixing temperature of the equipment is controlled below 19℃ (PTFE binder is more stable below 19℃, while above 19℃ it is easy to produce microfibrillation due to friction between powder particles, forming agglomerated powder that affects the uniformity of mixing). The mixing is carried out at a low speed, with a rotation speed of 30-200 r / min and a mixing time of 20-60 min, to obtain the first powder of preliminary mixing.

[0022] Step 2: After the initial mixing is completed, the temperature is increased to 25-80℃ for high-speed mixing, with a rotation speed of 200-2000 r / min and a mixing time of 5-30 min, to form a second powder with preliminary fiberization, creating conditions for subsequent full fiberization.

[0023] Step 3: The second powder obtained in step 2 is subjected to a jet mill to fully fiberize it again, resulting in a fully fiberized third powder. This step can improve the drawing strength. The gas in the jet mill can be high-temperature steam (dry steam at 150°C) or an inert gas heated by electric heating at a pressure of 0.6-1.8 MPa and a temperature of 80-150°C (the inert gas can be nitrogen or argon, preferably nitrogen).

[0024] Step 4: The third powder obtained in step 3 is placed into an internal mixer for internal mixing to form a molten block material. The mixing temperature is 60-200℃, the pressure is 0.5-10MPa, and the time is 5-60min. This makes the fiberization more uniform and further improves the tensile strength of the electrode film produced in step 6, which greatly improves the continuous production of the product.

[0025] Step 5: Place the molten block material obtained in Step 4 into a granulation device. The granulation device can be a dry granulator, a swing granulator, a crushing granulator, an extrusion granulator, etc., to obtain granules with uniform particle sizes of 100μm / 500μm / 1mm / 200mm / 3mm. This improves the material flowability and increases the compaction density of the produced electrode, thereby increasing the capacity and reducing product defects caused by powder agglomeration in Step 6.

[0026] Step 6: The granular powder obtained in Step 5 is fed into a multi-roll calender (which is an integrated roll-pressing and laminating machine) through a quantitative feeding system. The multi-roll calender calenders the granular powder into a film. The speed of each roll in the multi-roll calender is adjustable, creating a speed difference between the rolls. The speed ratio between the rolls is controlled to be greater than 1 and less than or equal to 3, forming a shear force between the materials and stretching the powder particles into a film. Alternatively, a method of using rolls of different diameters can be used to create a speed difference between the rolls and form a shear force between the materials.

[0027] It should be noted that the speed mentioned in this invention refers to the linear velocity of the outer circumferential surface of the roll, and the speed difference is the difference between the linear velocities of the outer circumferential surfaces of different rolls.

[0028] In practical applications, the second method is preferred; see [link / reference]. Figure 3 The diagram shows the process flow of the equipment. It clearly indicates that the diameters of the three rollers increase sequentially along the flow direction of the electrode film (small rollers can be 100mm / 150mm / 200mm / 250mm in diameter, while other rollers can be 200mm / 250mm / 300mm in diameter). Because the rollers at the powder feeding position use small-diameter rollers, the wrap angle is larger, which greatly reduces surface defects caused by powder agglomeration and bridging during production, thus producing a qualified first electrode film (film thickness between 150μm and 500μm). Then, the first electrode film undergoes a second-stage rolling process using larger-diameter rollers to obtain a second electrode film with uniform thickness and high compaction density (film thickness between 50μm and 150μm). Finally, the second electrode film undergoes a third-stage rolling process and is laminated with coated aluminum foil or copper foil to obtain a sandwich-structured dry electrode.

[0029] Specifically, the second electrode film is formed by two sets of three rollers of different diameters symmetrically distributed on the left and right. The coated foil is unwound and passed between the two rollers of the largest diameter. Then, the two rollers of the largest diameter are used to roll and laminate the second electrode film onto both sides of the coated aluminum foil / copper foil to form a sandwich structure dry electrode.

[0030] Generally speaking, the larger the roller diameter, the more material it can handle, the greater the lateral pressure, and the greater the required drive power, almost in a linear relationship. Therefore, the three rollers are designed with progressively larger diameters, starting with the first pair of small-diameter rollers. This reduces the wrap angle, decreases the material intake, and allows for pre-forming, thus solving the problem of poor thickness consistency caused by the large separation force between the two rollers.

[0031] Example 1 850g of lithium nickel cobalt manganese oxide, 50g of conductive agent, and 100g of PTEF were automatically weighed and metered using a positive / negative pressure method and then sent to a high-pressure shear mixer. The equipment temperature was controlled below 19℃ and the mixture was mixed at a low speed of 30r / min for 20min to obtain the first powder. After the initial mixing is completed, the mixing temperature is increased to 25℃ for high-speed mixing at a speed of 200r / min for 20min to form a second powder with preliminary fibrosis. The second powder obtained in step (2) is subjected to full fiberization again by an air jet mill. The gas in the air jet mill is nitrogen and the pressure is 0.6 MPa, to obtain a fully fiberized third powder. The third powder obtained in step (3) is put into a mixer for internal mixing to form a molten block material. The mixing temperature is 85℃, the pressure is 0.5MPa, and the time is 5min, so that the fiberization is more uniform. The molten block material obtained in step (4) is put into a dry granulator for granulation to obtain granular powder with a particle size of about 0.5 mm. The granular powder obtained in step (5) is fed into a multi-roll calender through a quantitative feeding system, and the granular powder is calendered into a film by the multi-roll calender. The diameter of the three rolls is the same, all 200 mm, and the rotation speed of the three rolls increases sequentially, with a speed ratio of 3:4:5, which creates a speed difference between the linear velocities of the outer circumference of each roll, forming a shear force between the materials. After the first-stage rolling, the first electrode film (film thickness 450 μm) is obtained, and after the second-stage rolling, the second electrode film (film thickness 150 μm) is obtained. The film thickness and performance test data are shown in Table 1. Then, after rolling, the second electrode film is laminated with coated aluminum foil to obtain a sandwich-structured dry electrode sheet.

[0032] Example 2 (1) 900g of lithium iron phosphate, 30g of conductive agent and 70g of PTEF are automatically weighed and metered by positive pressure / negative pressure and sent to a high-pressure shear mixer. The equipment temperature is controlled below 19℃ and the mixture is mixed at a low speed of 100r / min for 40min to obtain the first powder. (2) After the initial mixing is completed, the mixing temperature is increased to 40℃ for high-speed mixing, the rotation speed is 1000r / min, and the mixing time is 25min to form the second powder with initial fiberization; (3) The second powder obtained in step (2) is subjected to full fiberization again by an air jet mill. The gas in the air jet mill is nitrogen and the pressure is 0.65 MPa, to obtain a fully fiberized third powder. (4) The third powder obtained in step (3) is put into a mixer for internal mixing to form a molten block material. The mixing temperature is 150℃, the pressure is 5MPa, and the time is 30min to make the fiberization more uniform. (5) The molten block material obtained in step (4) is put into a dry granulator for granulation to obtain granules with a particle size of about 1 mm. (6) The granular powder obtained in step (5) is fed into a multi-roll calender through a quantitative feeding system, and the granular powder is calendered into a film by the multi-roll calender. The diameter of the three rolls is the same, all 200 mm, and the rotation speed of the three rolls increases sequentially, with a speed ratio of 2:3:4, so that a speed difference is generated between the linear velocities of the outer circumference of each roll, forming a shear force between the materials; after the first rolling, the first electrode film (film thickness 350 μm) is obtained, and after the second rolling, the second electrode film (film thickness 100 μm) is obtained. The film thickness and performance test data are shown in Table 1. Then, after rolling, the second electrode film is laminated with coated aluminum foil to obtain a sandwich structure dry electrode sheet.

[0033] Example 3 (1) 950g of graphite electrode active material, 20g of conductive agent and 30g of PTEF were automatically weighed and metered by positive pressure / negative pressure and sent to a high-pressure shear mixer. The equipment temperature was controlled below 19℃ and the mixture was mixed at a low speed of 200r / min for 60min to obtain the first powder. (2) After the initial mixing is completed, the mixing temperature is increased to 60℃ for high-speed mixing, the rotation speed is 2000r / min, and the mixing time is 30min to form the second powder with initial fiberization; (3) The second powder obtained in step (2) is subjected to full fiberization again by an air jet mill. The gas in the air jet mill is nitrogen and the pressure is 0.7 MPa, to obtain a fully fiberized third powder. (4) The third powder obtained in step (3) is put into a mixer for internal mixing to form a molten block material. The mixing temperature is 60℃, the pressure is 10MPa, and the time is 60min to make the fiberization more uniform. (5) The molten block material obtained in step (4) is put into an extrusion granulator for granulation to obtain granules with a particle size of about 3 mm. (6) The granular powder obtained in step (5) is fed into a multi-roll calender through a quantitative feeding system, and the granular powder is calendered into a film by the multi-roll calender. The diameters of the three rolls along the feeding direction are 150mm, 200mm, and 300mm respectively, and the rotation speed is the same, so that a speed difference is generated between the linear velocities of the outer circumference of each roll, and shear force is generated between the materials. After the first-stage rolling, the first electrode film (film thickness 320μm) is obtained, and after the second-stage rolling, the second electrode film (film thickness 90μm) is obtained. The film thickness and performance test data are shown in Table 1. Then, after rolling, the second electrode film is laminated with the adhesive-coated copper foil to obtain a sandwich structure dry electrode sheet.

[0034] Example 4 (1) 950g activated carbon, 20g conductive agent and 30g PTEF were automatically weighed and metered by positive pressure / negative pressure and sent to a high-pressure shear mixer. The equipment temperature was controlled below 19℃ and the mixture was mixed at a low speed of 200r / min for 60min to obtain the first powder. (2) After the initial mixing is completed, the mixing temperature is increased to 80℃ for high-speed mixing, the rotation speed is 2000r / min, and the mixing time is 30min to form the second powder with initial fiberization; (3) The second powder obtained in step (2) is subjected to full fiberization again by an air jet mill. The gas in the air jet mill is nitrogen and the pressure is 1.2 MPa, to obtain a fully fiberized third powder. (4) The third powder obtained in step (3) is put into a mixer for internal mixing to form a molten block material. The mixing temperature is 200℃, the pressure is 10MPa, and the time is 60min to make the fiberization more uniform. (5) The molten block material obtained in step (4) is put into an extrusion granulator for granulation to obtain granules with a particle size of about 3 mm. (6) The granular powder obtained in step (5) is fed into a multi-roll calender through a quantitative feeding system, and the granular powder is calendered into a film by the multi-roll calender. The diameters of the three rolls along the feeding direction are 100mm, 200mm, and 300mm respectively, and the rotation speed is the same, so that a speed difference is generated between the linear velocities of the outer circumference of each roll, and shear force is generated between the materials. After the first-stage rolling, the first electrode film (film thickness 160μm) is obtained, and after the second-stage rolling, the second electrode film (film thickness 50μm) is obtained. The film thickness and performance test data are shown in Table 1. Then, after rolling, the second electrode film is laminated with coated aluminum foil to obtain a sandwich structure dry electrode sheet.

[0035] Example 5 (1) 900g lithium manganese oxide, 40g conductive agent and 60g PTEF were automatically weighed and metered by positive pressure / negative pressure and sent to a high-pressure shear mixer. The equipment temperature was controlled below 19℃ and the mixture was mixed at a low speed of 150r / min for 50min to obtain the first powder. (2) After the initial mixing is completed, the mixing temperature is increased to 60℃ for high-speed mixing, the rotation speed is 1500r / min, and the mixing time is 30min to form the second powder with initial fiberization; (3) The second powder obtained in step (2) is subjected to full fiberization again by an air jet mill. The gas in the air jet mill is nitrogen and the pressure is 1.0 MPa, to obtain a fully fiberized third powder. (4) The third powder obtained in step (3) is put into a mixer for internal mixing to form a molten block material. The mixing temperature is 150℃, the pressure is 5MPa, and the time is 40min to make the fiberization more uniform. (5) The molten block material obtained in step (4) is put into an extrusion granulator for granulation to obtain granules with a particle size of about 3 mm. (6) The granular powder obtained in step (5) is fed into a multi-roll calender through a quantitative feeding system, and the granular powder is calendered into a film by the multi-roll calender. The diameters of the three rolls along the feeding direction are 150mm, 200mm, and 300mm respectively, and the rotation speed is the same, so that a speed difference is generated between the linear velocities of the outer circumference of each roll, and shear force is generated between the materials. After the first-stage rolling, the first electrode film (film thickness 280μm) is obtained, and after the second-stage rolling, the second electrode film (film thickness 80μm) is obtained. The film thickness and performance test data are shown in Table 1. Then, after rolling, the second electrode film is laminated with coated aluminum foil to obtain a sandwich structure dry electrode sheet.

[0036] Comparative Example 1 (1) Weigh and measure 800g of lithium nickel cobalt manganese oxide, 60g of conductive agent and 140g of PTEF, and mix them evenly at 20℃ using a high-speed shear mixer with a speed of 7000rpm / min for 5min to obtain the mixture. (2) The mixture obtained in step (1) is subjected to intensive mixing to fibrillate the binder through shearing action. The intensive mixing temperature is 150℃ and the intensive mixing time is 2min. (3) The material after intensive mixing is granulated by low-speed shearing, with a stirring speed of 500 rpm / min, a stirring temperature of 20℃, and a particle size of about 0.5 cm. (4) Preparation of film: The granulated material is calendered into a film with a thickness of 800-1000μm by a roller mill. The roller mill spacing is adjusted, and the thinning amount is 100-200μm each time. When the film thickness is higher than 200μm, the roller temperature is 100℃ and the pressure is 15T; when the film thickness is lower than 200μm, the roller temperature is 200℃ and the pressure is 30T. (5) The membrane obtained in step (4) is laminated with aluminum foil at a lamination temperature of 100°C to obtain an electrode membrane.

[0037] The prepared membranes had insufficient and uneven fiberization in the early stage, resulting in insufficient tensile strength after film formation.

[0038] Comparative Example 2 (1) Weigh and measure 850g of graphite electrode active material, 50g of conductive agent and 100g of PTEF, and mix them evenly at 20℃ using a high-speed shear mixer at a speed of 6000rpm / min for 3min to obtain the mixture. (2) The mixture obtained in step (1) is subjected to intensive mixing to fibrillate the binder through shearing action. The intensive mixing temperature is 150℃ and the intensive mixing time is 2min. (3) The material after intensive mixing is granulated by low-speed shearing, with a stirring speed of 600 rpm / min, a stirring temperature of 20℃, and a particle size of about 1 cm. (4) Preparation of film: The granulated material is calendered into a film with a thickness of 800-1000μm by a roller mill. The roller mill spacing is adjusted, and the thinning amount is 100-200μm each time. When the film thickness is higher than 200μm, the roller temperature is 100℃ and the pressure is 15T; when the film thickness is lower than 200μm, the roller temperature is 200℃ and the pressure is 30T. (5) The membrane obtained in step (4) is laminated with a copper foil at a lamination temperature of 100°C to obtain an electrode membrane.

[0039] Comparative Example 3 (1) After weighing and measuring 900g activated carbon, 30g conductive agent and 70g PTEF, mix them evenly at 20℃ using a high-speed shear mixer with a speed of 6000rpm / min for 3min to obtain the mixture. (2) The mixture obtained in step (1) is subjected to intensive mixing to fibrillate the binder through shearing action. The intensive mixing temperature is 150℃ and the intensive mixing time is 2min. (3) The material after intensive mixing is granulated by low-speed shearing, with a stirring speed of 500 rpm / min, a stirring temperature of 20℃, and a particle size of about 1 cm. (4) Preparation of film: The granulated material is calendered into a film with a thickness of 800-1000μm by a roller mill. The roller mill spacing is adjusted, and the thinning amount is 100-200μm each time. When the film thickness is higher than 200μm, the roller temperature is 100℃ and the pressure is 15T; when the film thickness is lower than 200μm, the roller temperature is 200℃ and the pressure is 30T. (5) The membrane obtained in step (4) is laminated with aluminum foil at a lamination temperature of 100°C to obtain an electrode membrane.

[0040] Comparative Example 4 (1) Weigh 950g activated carbon, 30g conductive agent and 20g PTEF and mix them evenly at 20℃ using a high-speed shear mixer at a speed of 6000rpm / min for 3min to obtain the mixture. (2) The mixture obtained in step (1) is subjected to intensive mixing to fibrillate the binder through shearing action. The intensive mixing temperature is 150℃ and the intensive mixing time is 2min. (3) The material after intensive mixing is granulated by low-speed shearing, with a stirring speed of 700 rpm / min, a stirring temperature of 20℃, and a particle size of about 0.5 cm. (4) Preparation of film: The granulated material is calendered into a film with a thickness of 800-1000μm by a roller mill. The roller mill spacing is adjusted, and the thinning amount is 100-200μm each time. When the film thickness is higher than 200μm, the roller temperature is 100℃ and the pressure is 15T; when the film thickness is lower than 200μm, the roller temperature is 200℃ and the pressure is 30T. (5) The membrane obtained in step (4) is laminated with aluminum foil at a lamination temperature of 100°C to obtain an electrode membrane.

[0041] This invention utilizes the difference in linear velocity between rollers to generate shearing and tensile force, rather than simple extrusion, to orient and densify the fibers. Figure 1 , Figure 2As can be seen, the PTEF fibers have a three-dimensional network structure, tightly wrapping the activated carbon particles. The conductive agent is evenly distributed to form a beaded conductive network. The membrane surface is dense and pore-free, and the fibers are evenly distributed without agglomeration defects.

[0042] The results of testing the membranes obtained in the examples and comparative examples are summarized in Table 1.

[0043] The conductivity was measured using an ST2258C multi-functional digital four-probe tester; the reciprocal of resistivity is the conductivity. Three sets of data were measured for each membrane, and the average value was taken. Thickness was measured using a micrometer.

[0044] Table 1 Test data of the membranes obtained in the examples and comparative examples

[0045] As can be seen from the above embodiments, the tensile strength and conductivity of the diaphragm obtained by the technical solution provided by the present invention are significantly improved.

[0046] The electron microscope images shown in the attached figures clearly demonstrate that the PTFE fibers in the electrode sheet prepared by this invention form a continuous and uniform three-dimensional network structure, tightly wrapping the active material particles, with the conductive agent evenly distributed and no visible pores or agglomeration defects.

[0047] This invention fundamentally solves the problems of uneven fiberization, large film thickness fluctuations, low strength, and difficulty in continuous production in existing dry electrode processes through a six-stage process: low-speed premixing, high-speed prefiberization, airflow deep fiberization, intensive mixing, precision granulation, and differential shearing and rolling film formation.

[0048] This film-forming method differs from the traditional "static pressure thinning" method. It applies continuous shear force to the material during calendering, resulting in denser fibers. This not only significantly improves the tensile strength and conductivity of the electrode film, but more importantly, the process is more tolerant of feed fluctuations and reduces the extreme dependence on the absolute parallelism of the rolls.

[0049] The above technical solutions only embody the preferred technical solutions of the present invention. Any modifications that may be made by those skilled in the art to certain parts thereof embody the principles of the present invention and fall within the protection scope of the present invention.

Claims

1. A method for manufacturing a dry electrode sheet, characterized in that, Includes the following steps: (1) Weigh and measure the active material, conductive agent and binder in a mass percentage of 85-95%: 2-5%: 3-10%, and perform preliminary mixing at a preset temperature to obtain a uniformly mixed first powder; (2) The mixing temperature is increased to no more than 80°C for high-speed mixing to form a second powder with preliminary fibrosis; (3) The second powder is placed in an air jet mill and deep fiberized using high-temperature dry steam or inert gas to obtain a fully fiberized and uniform third powder; (4) The third powder is kneaded at 60-200℃ and 0.5-10MPa for 5-60 minutes to form a molten block material; (5) Granulate the molten block material to obtain particulate powder with a particle size of 100μm-3000μm; (6) The granular powder is calendered into a film by a multi-roll calender. By controlling the speed or diameter of the rolls, a linear speed difference is formed. The speed ratio between the rolls is controlled to be greater than 1 and less than or equal to 3. The film is stretched by the generated shear force and then laminated with coated aluminum foil / copper foil to obtain a sandwich structure dry electrode sheet.

2. The method for manufacturing a dry electrode sheet according to claim 1, characterized in that, The active material in step (1) includes, but is not limited to, at least one of NCM, graphite, lithium titanate, lithium cobalt oxide, lithium iron phosphate, lithium manganese oxide, soft carbon, hard carbon, and activated carbon.

3. The method for manufacturing a dry electrode sheet according to claim 2, characterized in that, The adhesive mentioned in step (1) includes, but is not limited to, at least one of polyethylene, polyvinylidene fluoride, polypropylene, polyvinylidene fluoride, polyethylene oxide, polyphenylene ether, polyethylene-block polyethylene glycol, polydimethylsiloxane, polytetrafluoroethylene, polydimethylsiloxane-co-alkylmethylsiloxane, and carboxymethyl cellulose.

4. The method for manufacturing a dry electrode sheet according to claim 3, characterized in that, The adhesive is polytetrafluoroethylene.

5. The method for manufacturing a dry electrode sheet according to claim 4, characterized in that, In step (1), the active material, conductive agent, and polytetrafluoroethylene are weighed and measured according to the proportion, and sent to a high-strength shear mixer for low-speed mixing at a speed of 30-200 r / min. The mixing temperature is controlled below 19℃ and the mixing time is 20-60 min.

6. The method for manufacturing a dry electrode sheet according to claim 5, characterized in that, In step (2), the mixing temperature is increased to 25-80℃ for high-speed mixing, the rotation speed is 200-2000r / min, and the mixing time is 5-30min to form a second powder with preliminary fiberization.

7. The method for manufacturing a dry electrode sheet according to claim 1, characterized in that, The inert gas in the airflow pulverizer in step (3) is argon or nitrogen, with a gas temperature of 80-150℃ and a pressure of 0.6-0.7MPa.

8. The method for manufacturing a dry electrode sheet according to claim 1, characterized in that, In step (5), the obtained molten block material is put into a granulation device to obtain granules with a uniform particle size of 100-3000μm. The granulation device is any one of a dry granulator, a swing granulator, a crushing granulator, or an extrusion granulator.

9. The method for manufacturing a dry electrode sheet according to claim 1, characterized in that, In step (6), the three rolls have different diameters but different rotation speeds, which causes a speed difference between the linear velocities of the outer circumference of each roll. The speed ratio between the rolls is controlled to be greater than 1 and less than or equal to 3.

10. The method for manufacturing a dry electrode sheet according to claim 1, characterized in that, In step (6), the diameters of the three rolls increase sequentially along the feeding direction. By controlling the rotation speed to be the same or different, a speed difference is generated between the linear velocities of the outer circumference of each roll. The speed ratio between the rolls is controlled to be greater than 1 and less than or equal to 3.

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