Dry-method electrode plate, preparation method thereof and secondary battery

Abstract

The invention relates to the technical field of new energy, in particular to a dry-method electrode plate, a preparation method thereof and a secondary battery. The preparation method of the dry-method electrode pole piece comprises the following steps: mixing an electrode active material, a conductive agent and carboxymethyl cellulose, and performing primary stirring to obtain a first mixture; mixing the first mixture and polyacrylic acid, and performing secondary stirring to obtain a second mixture; mixing the second mixture and polytetrafluoroethylene, and stirring for the third time to obtain a composite material; the composite material is subjected to fibrillation treatment, and a fibrillated material is obtained; and preparing the dry-method electrode plate by using the fiberized material and the current collector. The dry-method electrode plate prepared by the method not only has excellent mechanical strength, chemical stability and viscoelasticity, but also can improve the compaction density of the electrode plate, thereby better adapting to the large-scale preparation requirement of a thick-film electrode, and finally improving the energy density and cycle performance of a battery.

Description

Technical Field

[0001] This application relates to the field of new energy technology, and in particular to dry electrode sheets and their preparation methods and secondary batteries. Background Technology

[0002] In recent years, my country's energy storage industry has experienced rapid development. All-solid-state batteries, which use solid electrolytes instead of traditional flammable electrolytes, are expected to improve energy density while ensuring safety, and are considered an important future development direction for energy storage batteries. Against this backdrop, dry electrode technology, as one of the key technologies that must be mastered in the development of all-solid-state batteries, is becoming an emerging research hotspot in the battery field. Currently, traditional electrode manufacturing mainly uses a wet coating process, including slurry preparation, coating drying, and rolling. This process requires the use of a large amount of N-methylpyrrolidone (NMP) as a solvent for homogenization, and the solvent is removed in a long-term, energy-intensive process during subsequent drying, which not only increases production costs but also brings certain environmental pressures. Although wet processes are mature and widely used, their inherent defects still limit further breakthroughs in lithium battery performance and continuous cost optimization.

[0003] Dry electrode technology exhibits significant environmental advantages due to its complete avoidance of solvents in the production process. Lithium-ion batteries fabricated using dry film deposition technology, compared to traditional liquid lithium-ion batteries, not only promise to significantly improve energy density but also substantially reduce production costs. Currently, polytetrafluoroethylene (PTFE) is widely used as a binder, forming adhesive fibrils through shear mixing during its preparation, thereby achieving a tight bond between PTFE and conductive carbon and active materials. However, single-component PTFE, limited by its viscoelasticity, cannot adequately guarantee the interfacial bonding force between the active material and conductive carbon, nor can it achieve strong adhesion to the current collector. This deficiency easily leads to voids in the active material during volume changes during charge and discharge, or detachment during cycling, resulting in battery capacity decay and decreased cycle stability. Summary of the Invention

[0004] Based on this, the first aspect of this application provides a method for preparing a dry electrode sheet, the technical solution of which is as follows:

[0005] A method for preparing a dry electrode sheet includes the following steps:

[0006] The electrode active material, conductive agent, and carboxymethyl cellulose are mixed and stirred once to obtain the first mixture;

[0007] The first mixture and polyacrylic acid are mixed and stirred a second time to obtain the second mixture;

[0008] The second mixture and polytetrafluoroethylene were mixed and stirred three times to obtain the composite material;

[0009] The composite material is subjected to fibrillation treatment to obtain fibrous material;

[0010] Dry electrode sheets are prepared using the aforementioned fibrous material and current collector.

[0011] The second aspect of this application provides a method for preparing a dry electrode sheet, which is prepared by the method described above.

[0012] A third aspect of this application provides a secondary battery comprising the dry electrode plates described above.

[0013] Compared with traditional solutions, this application has the following advantages:

[0014] The dry electrode preparation method provided in this application employs a step-by-step mixing process. First, electrode active materials, conductive agents, and granular carboxymethyl cellulose (CMC) are initially stirred and mixed. After uniform dispersion, long-chain polyacrylic acid (PAA) is added for a second stirring and mixing. Finally, a second long-chain molecule, polytetrafluoroethylene (PTFE), is introduced. After three stirring and mixing processes, a homogeneous composite material is obtained. This composite material undergoes fibrillation treatment and is then combined with a current collector to ultimately produce a dense, uniformly thick dry electrode. In this bonding system, CMC is mixed first, primarily acting as a point contact adhesive. Then, PAA is added, followed by PTFE, causing the long-chain molecular structures to entangle and construct a three-dimensional network framework. This improves the contact tightness between the electrode active material and the conductive agent, reduces impedance, and enhances conductivity. More importantly, the carboxyl groups (-COOH) and hydroxyl groups (-OH) abundant in the three binder molecules can undergo cross-linking reactions and form a stable and robust bonding network through hydrogen bonding. This improves the adhesion between the electrode active layer and the current collector, reducing the risk of the electrode active layer detaching during charging and discharging. This multi-component synergistic mechanism effectively enhances the interfacial bonding force between electrode components. After fibrillation treatment, the resulting dry electrode sheet not only possesses excellent mechanical strength, chemical stability, and viscoelasticity, but also improves the compaction density of the electrode sheet, thereby better adapting to the requirements of large-scale preparation of thick film electrodes and ultimately improving the energy density and cycle performance of the battery. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in the embodiments of this application and to more completely understand this application and its beneficial effects, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1This is a schematic diagram showing the thickness of the dry electrode sheet prepared in Example 1 at various points.

[0017] Figure 2 The adhesion performance test results are for the electrode sheets prepared in each embodiment and comparative example;

[0018] Figure 3 The AC impedance spectra of the electrode sheets prepared in each embodiment and comparative example after being assembled into a battery;

[0019] Figure 4 The first charge-discharge curves of the battery after the electrode sheets prepared for each embodiment and comparative example are assembled into batteries;

[0020] Figure 5 The results of charge-discharge cycles were performed on the electrode sheets prepared for each embodiment and comparative example after they were assembled into batteries. Detailed Implementation

[0021] The present application will be further described in detail below with reference to specific embodiments. The present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the disclosure of this application.

[0022] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0023] Unless otherwise stated or in case of contradiction, the terms or phrases used herein shall have the following meanings:

[0024] In this application, the terms "optionally," "optionally," and "optional" refer to options that are optional, meaning they can be selected from either "with" or "without." If multiple "optional" options appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "optional" option is independent.

[0025] In this application, the terms "first aspect," "second aspect," "third aspect," and "fourth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," and "fourth," etc., serve only a non-exhaustive enumeration purpose and should be understood not to constitute a closed limitation on quantity.

[0026] In this application, numerical intervals (i.e. numerical ranges) are involved. Unless otherwise specified, the selected numerical distributions within the above-mentioned numerical intervals are considered continuous, and include the two numerical endpoints (i.e., the minimum value and the maximum value) of the numerical range, as well as every value between the two numerical endpoints.

[0027] To address the problems of weak interfacial bonding and poor cycle stability caused by insufficient binder performance in dry-process electrodes, this application provides a method for preparing a dry-process electrode sheet. This method employs a strategy of synergistic modification using a distributed mixture of multi-component binders, combined with fibrillation under dry-process conditions, to prepare a dry-process electrode sheet with excellent chemical stability and mechanical properties, meeting the requirements of secondary batteries, such as lithium batteries, under repeated charge-discharge conditions. In one embodiment, the method for preparing the dry-process electrode sheet includes the following steps:

[0028] S1. Mix the electrode active material, conductive agent and carboxymethyl cellulose, and stir once to obtain the first mixture.

[0029] S2. Mix the first mixture and polyacrylic acid, and stir twice to obtain the second mixture.

[0030] S3. Mix the second mixture and polytetrafluoroethylene, and stir three times to obtain the composite material.

[0031] Optionally, the mass ratio of carboxymethyl cellulose, polyacrylic acid, and polytetrafluoroethylene is (1~9):(1~9):(1~9). Optionally, the mass ratio of the total mass of carboxymethyl cellulose, polyacrylic acid, and polytetrafluoroethylene, to the mass ratio of the electrode active material to the conductive agent is 3:(92~96):(1~5). Within the above range, it is beneficial to prepare electrode sheets with good mechanical properties and viscoelasticity.

[0032] Understandably, primary, secondary, and tertiary mixing can be performed in a mixer or blade mixer. Optionally, the primary mixing speed is 4000-8000 rpm, preferably 5000-6000 rpm. The primary mixing time is 5-20 minutes, preferably 10-15 minutes. Optionally, the secondary mixing speed is 5000-10000 rpm, preferably 7000-8000 rpm. The secondary mixing time is 5-20 minutes, preferably 10-15 minutes. Optionally, the tertiary mixing speed is 5000-10000 rpm, preferably 8000-9000 rpm; the tertiary mixing time is 1-5 minutes, preferably 2-3 minutes. After tertiary mixing, the material agglomerates.

[0033] By mixing multiple binders in stages, the contact effect between the electrode active material and the conductive agent can be improved, and the compaction density of the electrode sheet can be increased. This better meets the requirements for large-scale preparation of thick film electrodes, and ultimately improves the energy density and cycle performance of the battery.

[0034] Optionally, the electrode active material is selected from positive electrode active materials or negative electrode active materials; the positive electrode active material is selected from one or more of lithium iron phosphate, lithium manganese iron phosphate, ternary nickel cobalt manganese, lithium titanate, ternary nickel cobalt aluminum, lithium cobalt oxide and lithium alloy, wherein the alloying elements contained in the lithium alloy include one or more of tin, titanium and silicon; the negative electrode active material is selected from one or more of activated carbon, graphite, hard carbon, soft carbon and silicon suboxide.

[0035] Optionally, the conductive agent is selected from one or more of acetylene black, Super P, carbon nanotubes, carbon fibers, Ketjen black, graphite, and graphene.

[0036] S4. The composite material is subjected to fibrillation treatment to obtain fibrous material.

[0037] The composite material is subjected to fibrillation treatment, comprising the following steps: the composite material is sequentially passed through the feeding zone, mixing zone, and discharge zone of a twin-screw extruder. Optionally, the screw speed in the feeding zone is 50-200 rpm, preferably 150-200 rpm; the screw speed in the mixing zone is 200-500 rpm, preferably 300-350 rpm; and the screw speed in the discharge zone is 100-300 rpm, preferably 200-250 rpm. Optionally, the processing temperature in the feeding zone is controlled between room temperature and 60°C, wherein room temperature refers to 10-40°C. Preferably, the processing temperature in the feeding zone is controlled below 30°C; the processing temperature in the mixing zone is controlled between 50-90°C, preferably 70-80°C; and the processing temperature in the discharge zone is controlled between 80-100°C, preferably not exceeding 90°C. Optionally, the filling rate of the composite material in the feeding zone, mixing zone and discharge zone is maintained between 50% and 80%; preferably between 60% and 70%.

[0038] The above method uses a twin-screw kneading pair to perform fibrillation treatment, and the feed rate and rotation speed can be controlled in conjunction.

[0039] S5. Dry electrode sheets are prepared using the fibrous material and the current collector.

[0040] Optionally, the dry electrode sheet is prepared using the fibrous material and the current collector, comprising the following steps:

[0041] S51. Grind the fibrous material to obtain abrasive.

[0042] The fibrous material can be placed in a grinding mill for grinding. Optionally, the grinding speed is 10,000 to 28,000 rpm, preferably 20,000 to 25,000 rpm.

[0043] S52. The abrasive material is subjected to roll pressing to obtain a support film;

[0044] Optionally, the roll forming process includes preliminary roll forming and hot roll thinning, which can be processed between the rolls of a three-roll mill. Optionally, the roll forming temperature for preliminary roll forming is room temperature to 150°C, where room temperature refers to 10 to 40°C, preferably 80 to 120°C; the inter-roll pressure is 2 to 10 t, preferably 6 to 8 t. Optionally, the hot roll thinning temperature is 60 to 200°C, preferably 100 to 160°C; the linear pressure is 0 to 1.5 t / mm, preferably 1.2 to 1.5 t / mm; on a laboratory scale, the rolling speed is 0.05 to 5 m / min, preferably 0.05 to 0.2 m / min; the thinned thickness is 15 to 150 μm, preferably 15 to 50 μm. Understandably, the roll forming process employs alternating transverse and longitudinal rolling.

[0045] S53. The self-supporting film and the current collector are hot-pressed together to obtain the dry electrode sheet.

[0046] Optionally, the current collector is aluminum foil.

[0047] Optionally, the temperature for hot pressing is 110~200℃, preferably 140~170℃; the pressure is 5~30t, preferably 10~20t.

[0048] Understandably, after hot-pressing the self-supporting membrane with the current collector, the process further includes the following step: slitting the wide electrode roll into the required width.

[0049] The dry electrode preparation method provided in this embodiment employs a step-by-step mixing process. First, the electrode active material, conductive agent, and granular carboxymethyl cellulose (CMC) are initially stirred and mixed. After uniform dispersion, long-chain polyacrylic acid (PAA) is added for a second stirring and mixing. Finally, a second long-chain molecule, polytetrafluoroethylene (PTFE), is introduced. After three stirring and mixing processes, a composite material with uniform composition is obtained. This composite material undergoes fibrillation treatment and is then combined with a current collector to ultimately produce a dry electrode with a dense structure and uniform thickness. In this bonding system, CMC is mixed first, primarily acting as a point contact adhesive. Then, PAA is added, followed by PTFE, causing the long-chain molecular structures to entangle and construct a three-dimensional network framework. This improves the contact tightness between the electrode active material and the conductive agent, reduces impedance, and enhances conductivity. More importantly, the carboxyl groups (-COOH) and hydroxyl groups (-OH) abundant in the three binder molecules can undergo cross-linking reactions and form a stable and robust bonding network through hydrogen bonding. This improves the adhesion between the electrode active layer and the current collector, reducing the risk of the electrode active layer detaching during charging and discharging. This multi-component synergistic mechanism effectively enhances the interfacial bonding force between electrode components. After fibrillation treatment, the resulting dry electrode sheet not only possesses excellent mechanical strength, chemical stability, and viscoelasticity, but also improves the compaction density of the electrode sheet, thereby better adapting to the requirements of large-scale preparation of thick film electrodes and ultimately improving the energy density and cycle performance of the battery.

[0050] The second aspect of this application provides a method for preparing a dry electrode sheet, which is prepared by the method described above.

[0051] A third aspect of this application provides a secondary battery comprising the dry electrode plates described above.

[0052] The following description is further illustrated with specific embodiments and comparative examples. Unless otherwise specified, the raw materials involved in the following specific embodiments and comparative examples are all commercially available. Unless otherwise specified, the instruments used are all commercially available. Unless otherwise specified, the processes involved are conventionally selected by those skilled in the art.

[0053] Example 1

[0054] This embodiment provides a dry electrode sheet and its preparation method, the steps of which are as follows:

[0055] S1. Place 94g of electrode active material lithium iron phosphate (LFP), 3g of conductive agent Superp and 1g of carboxymethyl cellulose (CMC) in a mixer and mix at 6000rpm for 10min at a time to obtain the first mixture.

[0056] S2. Add 1g of polyacrylic acid (PAA) to the first mixture of S1, and stir for 10 minutes at 8000rpm to obtain the second mixture.

[0057] S3. Add 1g of polytetrafluoroethylene (PTFE) to the second mixture of S2, and stir at 8000rpm for 3 minutes three times to obtain the composite material.

[0058] S4. The composite material described in S3 is added to a twin-screw extruder and subjected to fibrillation treatment through twin-screw kneading to obtain fibrous material. The screw speed in the feeding zone is set to 200 rpm, the screw speed in the mixing zone to 350 rpm, and the screw speed in the discharge zone to 250 rpm. The processing temperature in the feeding zone is controlled at 30℃, the processing temperature in the mixing zone is 70℃, and the processing temperature in the discharge zone is 90℃. The feeding speed and screw speed are linked and controlled, and the filling rate is maintained at 65%.

[0059] S5. Dry electrode sheets are prepared using the fibrous material and the current collector.

[0060] The fibrous material of S4 was finely ground in a mill at a speed of 25,000 rpm to obtain abrasive material. This abrasive material was then subjected to roll forming, which included preliminary roll forming and hot roll forming for thinning. The preliminary roll forming temperature was 120℃, and the inter-roll pressure was 8t. The hot roll forming temperature was 160℃, the linear pressure was 1.5t / mm, and the rolling speed was 0.2m / min. The process was repeated three times, alternating between transverse and longitudinal directions, resulting in a thickness of 50μm, thus obtaining a self-supporting film.

[0061] The self-supporting membrane and the current collector (aluminum foil) are hot-pressed together at a temperature of 170°C and a pressure of 20t to finally obtain a dry electrode sheet.

[0062] Examples 2-3

[0063] Examples 2 and 3 respectively provide a dry-process electrode sheet and its preparation method, which are basically the same as those in Example 1, except that the quality of carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and polytetrafluoroethylene (PTFE) used is different, as detailed below:

[0064] In Example 2, the mass of carboxymethyl cellulose (CMC) was 1g, the mass of polyacrylic acid (PAA) was 0.5g, and the mass of polytetrafluoroethylene (PTFE) was 1.5g.

[0065] In Example 3, the mass of carboxymethyl cellulose (CMC) was 1g, the mass of polyacrylic acid (PAA) was 1.5g, and the mass of polytetrafluoroethylene (PTFE) was 0.5g.

[0066] Comparative Example 1

[0067] This comparative example provides a wet electrode sheet and its preparation method, the steps of which are as follows:

[0068] S1. Disperse 94g of electrode active material lithium iron phosphate (LFP), 3g of conductive agent Superp, 1g of carboxymethyl cellulose (CMC), 1g of polyacrylic acid (PAA) and 1g of polytetrafluoroethylene (PTFE) in organic solvent N-methylpyrrolidone (NMP) and perform high-speed shear stirring to form a uniform slurry with stable viscosity.

[0069] S2. The slurry is uniformly coated onto the same current collector (aluminum foil) as in Example 1 using a slit extrusion process. It is then placed in a long, multi-temperature oven for drying. After drying, it is compacted using a high-tonnage cold press roller to form a 50μm thick active layer on the current collector. A second drying process is then performed to thoroughly remove any residual trace amounts of moisture and solvent from the electrode sheet. This yields a wet-process electrode sheet.

[0070] Comparative Example 2

[0071] This comparative example provides a dry electrode sheet and its preparation method, the steps of which are as follows:

[0072] S1. Place 94g of electrode active material lithium iron phosphate (LFP), 3g of conductive agent Superp, 1g of carboxymethyl cellulose (CMC), 1g of polyacrylic acid (PAA) and 1g of polytetrafluoroethylene (PTFE) in a mixer and mix at 8000rpm for 23min to obtain the composite material.

[0073] S2, the same as S4 in Example 1.

[0074] S3, the same as S5 in Example 1.

[0075] The performance of the dry electrode sheets of the above embodiments and comparative examples was tested. The test items and methods are as follows:

[0076] Project 1: The thickness of the dry electrode sheet prepared in Example 1 was measured at different locations, and the results are as follows. Figure 1 As shown in the figure. The results show that the maximum deviation between the six points is ±1 μm, indicating that the prepared dry electrode sheet has good consistency.

[0077] Project 2: Adhesion test of the electrode active layer to the current collector was conducted according to standard ASTM D3359. Results are shown below. Figure 2The results showed that Example 1 exhibited the highest adhesion, demonstrating that the addition of a suitable ratio of carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and polytetrafluoroethylene (PTFE) in the dry electrode can improve mechanical properties. This is because the two long chains of PAA and PTFE cross-link through hydrogen bonds and ester groups formed between carboxyl groups (-COOH) and hydroxyl groups (-OH), thus forming a stable fibrous network. Therefore, the ratio of the two long-chain materials needs to be controlled to obtain the optimal cross-linking effect.

[0078] Project 3: Using the dry electrode sheets of the above embodiments and comparative examples as positive electrode sheets, assemble the battery as follows: In an argon-filled glove box, use a lithium metal sheet as the counter electrode, a Celgard 2400 polypropylene membrane as the separator, and a 1M LiPF6 EC / DEC solution as the electrolyte to assemble a CR2032 type coin cell.

[0079] 1. Following the operating procedures of the electrochemical workstation, AC impedance tests were performed on the batteries of each embodiment and comparative example within a frequency range of 100kHz to 10mHz and a perturbation amplitude of 5mV. The results are shown in [reference needed]. Figure 3 .

[0080] The results showed that the charge transfer impedance of Example 1 was lower than that of Comparative Example 1. This indicates that the appropriate ratio of carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and polytetrafluoroethylene (PTFE) effectively dispersed the conductive agent. At the same time, this dry electrode preparation method made the contact between the entire active material and the conductive agent closer, thus better reducing the impedance of the composite material.

[0081] 2. Perform charge and discharge tests on the battery. The charge and discharge procedure is as follows: charge at a constant current of 0.1C to 4.2V, then charge at a constant voltage of 4.2V until the cutoff current is 0.05C; then discharge at a constant current of 0.1C to 2.5V, and repeat the charge and discharge cycle 300 times.

[0082] The voltage-capacity curves for the first charge-discharge tests of each embodiment and comparative example are as follows: Figure 4 As shown in the figure. The results show that the initial coulombic efficiency of Example 1 is 100.0%, while that of Comparative Example 1 is 99.6%, with little difference. However, the discharge specific capacity of Example 1 is higher than that of Comparative Example 1, which indicates that the dry electrode prepared in Example 1 improves the contact effect between the electrode active material and the conductive agent, thereby improving the conductivity of lithium iron phosphate, which originally had poor conductivity, and greatly increasing the discharge specific capacity.

[0083] The discharge specific capacity of each embodiment and comparative example after 300 charge-discharge cycles is as follows: Figure 5As shown. The results show that under 1C charge-discharge conditions, the capacity of Example 1 is higher than that of Comparative Example 1, proving that the obtained dry electrode sheet not only has excellent mechanical strength, chemical stability and viscoelasticity, but also can improve the contact effect between the electrode material and the conductive agent, improve the conductivity of the material, and ultimately improve the energy density and cycle performance of the battery.

[0084] In summary, the dry electrode preparation method provided in this application employs a step-by-step mixing process. First, the electrode active material, conductive agent, and granular carboxymethyl cellulose (CMC) are initially stirred and mixed. After uniform dispersion, long-chain polyacrylic acid (PAA) is added for a second stirring and mixing. Finally, a second long-chain molecule, polytetrafluoroethylene (PTFE), is introduced. After three stirring and mixing processes, a homogeneous composite material is obtained. This composite material undergoes fibrillation treatment and is then compounded with a current collector to ultimately produce a dense, uniformly thick dry electrode. In this bonding system, CMC is mixed first, primarily acting as a point contact adhesive. Then, PAA is added for mixing, followed by PTFE, causing the long-chain molecular structures to entangle and construct a three-dimensional network framework. This improves the contact tightness between the electrode active material and the conductive agent, reduces impedance, and enhances conductivity. More importantly, the carboxyl groups (-COOH) and hydroxyl groups (-OH) abundant in the three binder molecules can undergo cross-linking reactions and form a stable and robust bonding network through hydrogen bonding. This improves the adhesion between the electrode active layer and the current collector, reducing the risk of electrode active layer detachment during charge and discharge. This multi-component synergistic mechanism effectively enhances the interfacial bonding force between electrode components. After fibrillation treatment, the resulting dry-process electrode sheet not only possesses excellent mechanical strength, chemical stability, and viscoelasticity, but also increases the compaction density of the electrode sheet, thus better meeting the requirements of large-scale fabrication of thick-film electrodes, ultimately improving the energy density and cycle performance of the battery.

[0085] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0086] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A method for preparing a dry electrode sheet, characterized in that, Includes the following steps: The electrode active material, conductive agent, and carboxymethyl cellulose are mixed and stirred once to obtain the first mixture; The first mixture and polyacrylic acid are mixed and stirred a second time to obtain the second mixture; The second mixture and polytetrafluoroethylene were mixed and stirred three times to obtain the composite material; The composite material is subjected to fibrillation treatment to obtain fibrous material; Dry electrode sheets are prepared using the aforementioned fibrous material and current collector.

2. The method for preparing dry electrode sheets according to claim 1, characterized in that, The mass ratio of carboxymethyl cellulose, polyacrylic acid and polytetrafluoroethylene is (1~9):(1~9):(1~9).

3. The method for preparing dry electrode sheets according to claim 1, characterized in that, The total mass of the carboxymethyl cellulose, polyacrylic acid and polytetrafluoroethylene, and the mass ratio of the electrode active material to the conductive agent are 3:(92~96):(1~5).

4. The method for preparing dry electrode sheets according to claim 1, characterized in that, Includes at least one of the following features: (1) The stirring speed for one stirring cycle is 4000~8000 rpm; (2) The stirring time for one session is 5 to 20 minutes; (3) The stirring speed for the second stirring is 5000~10000 rpm; (4) The second stirring time is 5~20 min; (5) The stirring speed for the three stirrings is 5000~10000 rpm; (6) The stirring time for the three times is 1~5 minutes.

5. The method for preparing a dry electrode sheet according to any one of claims 1 to 4, characterized in that, The fibrillation treatment of the composite material includes the following steps: passing the composite material sequentially through the feed zone, mixing zone, and discharge zone of a twin-screw extruder, including at least one of the following characteristics: (1) The screw speed in the feeding zone is 50~200 rpm; the screw speed in the mixing zone is 200~500 rpm; and the screw speed in the discharge zone is 100~300 rpm. (2) The processing temperature of the feeding zone is controlled at room temperature to 60°C; the processing temperature of the mixing zone is controlled at 50°C to 90°C; and the processing temperature of the discharging zone is controlled at 80°C to 100°C. (3) The filling rate of the composite material in the feeding zone, mixing zone and discharge zone is maintained between 50% and 80%.

6. The method for preparing a dry electrode sheet according to any one of claims 1 to 4, characterized in that, The preparation of dry electrode sheets using the aforementioned fibrous material and current collector includes the following steps: The fibrous material is ground to obtain abrasive; The abrasive material is subjected to roll pressing to obtain a support film; The self-supporting membrane is hot-pressed together with the current collector to obtain the dry electrode sheet.

7. The method for preparing a dry electrode sheet according to claim 6, characterized in that, Includes at least one of the following features: (1) The grinding speed is 10,000~28,000 rpm; (2) Roll forming process includes preliminary roll forming and hot roll forming for thinning; the rolling temperature for preliminary roll forming is room temperature to 150℃, and the inter-roll pressure is 2 to 10t; the rolling temperature for hot roll forming for thinning is 60 to 200℃; the linear pressure is 0 to 1.5t / mm; and the rolling speed is 0.05 to 5m / min. (3) The temperature for hot pressing composite is 110~200℃; (4) The pressure of hot pressing composite is 5~30t.

8. The method for preparing a dry electrode sheet according to any one of claims 1 to 4 and 7, characterized in that, The electrode active material is selected from positive electrode active materials or negative electrode active materials; The positive electrode active material is selected from one or more of lithium iron phosphate, lithium manganese iron phosphate, ternary nickel cobalt manganese, lithium titanate, ternary nickel cobalt aluminum, lithium cobalt oxide, and lithium alloys, and the alloying elements contained in the lithium alloy include one or more of tin, titanium, and silicon. The negative electrode active material is selected from one or more of activated carbon, graphite, hard carbon, soft carbon, and silicon suboxide.

9. The method for preparing a dry electrode sheet according to any one of claims 1 to 4, characterized in that, The conductive agent is selected from one or more of acetylene black, Super P, carbon nanotubes, carbon fibers, Ketjen black, graphite, and graphene.

10. A dry-process electrode sheet, characterized in that, It is prepared by any one of the preparation methods according to claims 1 to 9.

11. A secondary battery, characterized in that, Includes the dry electrode sheet as described in claim 10.

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