Pole piece capable of preventing edge from shrinking and rolling and manufacturing method thereof

Abstract

The invention discloses a pole piece capable of preventing edge shrinkage and rolling and a manufacturing method of the pole piece. The manufacturing method comprises the following steps: preparing slurry; gradient coating is carried out, so that the thickness of the coating in the middle area of the pole piece is larger than that of the coating in the edge area, and the thickness difference is 2-10 microns; pre-drying is performed; calendaring treatment is conducted, a differential double-roller pressing process is adopted, and the linear speed ratio of an upper roller to a lower roller is (1.02-1.10): 1; edge modification: coating an elastic reinforcing agent with the thickness of 2-8 microns on the edge area of the pole piece; and carrying out secondary drying by adopting a step temperature drying method. Compared with the prior art, the thickness distribution with the thick middle part and the thin edge is realized through the gradient coating technology, so that each area is uniformly stressed; shearing force is generated by adopting a differential double-rolling process, so that internal stress is effectively released; the edge area is coated with an elastic reinforcing agent to form a buffer area, and stress concentration is absorbed; the edge curling angle of the prepared pole piece is obviously reduced, and the cycling stability and the high-temperature storage performance are obviously improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium ion battery manufacturing, and particularly relates to an electrode sheet capable of preventing edge shrinkage and rolling and a manufacturing method thereof. BACKGROUND

[0002] As the most mainstream secondary battery at present, lithium ion batteries are widely used in consumer electronics, electric vehicles and energy storage systems. In the production process of lithium ion batteries, the electrode sheet is one of the core components, and its quality directly affects the performance and service life of the battery. However, the problem of edge shrinkage and rolling has always been a technical difficulty that has plagued the industry during the preparation of the electrode sheet, seriously affecting the production yield and performance stability of the battery.

[0003] The problem of lithium battery electrode sheet shrinkage and rolling is one of the important factors affecting the quality and performance of the battery. By deeply analyzing the causes and taking effective measures, the incidence of electrode sheet shrinkage and rolling can be significantly reduced, and the quality and stability of the lithium battery electrode sheet can be improved.

[0004] Among them, the inventor found that the causes of the edge shrinkage and rolling of the electrode sheet mainly include the following points:

[0005] 1. During the coating process of the lithium battery electrode sheet, the surface density of the active material in the edge region is higher than that in the middle region, resulting in a larger edge thickness than the middle part by several microns or tens of microns. During the rolling process, the area with a larger edge thickness will bear a larger rolling force, resulting in inconsistent rolling compaction transverse density of the electrode sheet, and further causing the electrode sheet to roll. In addition, the excessively high surface density of the active material in the edge region may also cause the foil to be excessively calendered during the rolling process, resulting in rolling deformation and micro-cracks, further exacerbating the rolling phenomenon.

[0006] 2. Improper setting of rolling process parameters such as rolling wheel pressure, speed and temperature is also an important cause of electrode sheet rolling. Excessive rolling pressure will cause the electrode sheet to be excessively extruded, resulting in deformation; uneven rolling speed will cause uneven stress on the electrode sheet, causing local rolling; and improper temperature control of the rolling wheel will affect the thermal plasticity and flowability of the material, thereby affecting the compaction effect of the electrode sheet.

[0007] 3. Poor rigidity stability of the rolling equipment, rolling roller coaxiality error, rolling roller roundness error and rolling roller surface roughness, etc. may also cause the electrode sheet to roll during the rolling process. In addition, equipment wear and inaccurate calibration will also cause uneven rolling pressure distribution, affecting the compaction effect of the electrode sheet.

[0008] In view of the problem of edge shrinkage and rolling of the electrode sheet, the following solutions are mainly used in the prior art:

[0009] 1. By improving the coating process, controlling the difference in active material surface density between the edge and the middle area of the pole piece, reducing the edge thickness unevenness. At the same time, strengthen the quality control in the coating process, ensure the uniformity of the pole piece surface, no impurities and defects.

[0010] 2. Regularly maintain and calibrate the rolling equipment to ensure that the equipment is in good condition. Check the coaxiality, cylindricity and surface roughness of the roll and replace the severely worn roll in time. At the same time, strengthen the training and management of the equipment operators, improve the standardization and accuracy of the equipment operation.

[0011] However, the existing solutions in the prior art still have some deficiencies: first, the existing methods mainly focus on the optimization of a single process, lacking systematic consideration of the whole process of pole piece preparation; second, the existing methods mostly use passive adjustment mode, which cannot prevent edge shrinkage and rolling from the source; third, the existing methods lack special treatment of the edge area of the pole piece, which cannot effectively alleviate the edge stress concentration problem.

[0012] Therefore, it is urgent to develop a whole-process, active prevention pole piece manufacturing method that can prevent edge shrinkage and rolling from the source and improve the quality of the pole piece and the overall performance of the battery. SUMMARY

[0013] The purpose of the present application is to provide a pole piece manufacturing method and pole piece that can prevent edge shrinkage and rolling, which can prevent pole piece edge shrinkage and rolling from the source by combining gradient coating technology, differential double roller pressing process and edge modification treatment, and improve the quality of the pole piece and the performance of the battery.

[0014] To achieve the above purpose, the present application provides the following technical scheme:

[0015] A pole piece manufacturing method that can prevent edge shrinkage and rolling, comprising the following steps:

[0016] S1, slurry preparation: mix active material, conductive agent, binder and solvent uniformly, and then treat by high-speed shearing dispersion to obtain pole piece slurry;

[0017] S2, gradient coating: use gradient coating technology to coat the pole piece slurry on the current collector, so that the coating thickness of the middle area of the pole piece is greater than that of the edge area, and the thickness difference between the middle area and the edge area is 2-10 μm;

[0018] S3, pre-drying: pre-drying the coated pole piece, the drying temperature is 60-90℃, and the drying time is 1-3 minutes;

[0019] S4, calendering treatment: the pre-dried pole piece is subjected to calendering treatment, differential double roller pressing process is adopted, the linear speed ratio of upper roller to lower roller is 1.02-1.10:1, and the calendering temperature is 50-120℃;

[0020] S5, edge modification: an elastic reinforcing agent with a thickness of 2-8 μm is coated on the edge region of the pole piece, and the elastic reinforcing agent is mainly composed of an elastic polymer and a conductive material;

[0021] S6, secondary drying: the modified pole piece is subjected to secondary drying, and a step temperature drying method is adopted, and the pole piece is sequentially subjected to three temperature zones of 80-100℃, 110-140℃ and 50-70℃, and the total drying time is 5-15 minutes.

[0022] As preferred, the high-speed shearing dispersion treatment in S1 comprises: first shearing dispersion at a speed of 2000-5000 rpm for 10-20 minutes, and then shearing dispersion at a speed of 8000-12000 rpm for 3-8 minutes, and the slurry temperature is controlled at 15-25℃.

[0023] As preferred, the gradient coating technology adopted in S2 is adjustable extrusion coating, the middle part of the coating head has a smaller extrusion force than the edge part, the pressure difference between the middle part and the edge part is 0.05-0.2 MPa, and the coating speed is 5-15 m / min.

[0024] As preferred, the pre-drying in S3 adopts a combination of infrared drying and hot air drying, the infrared radiation power density is 2-5 kW / m2, the hot air temperature is 60-90℃, and the air speed is 0.8-2 m / s.

[0025] As preferred, the differential double roller pressing process in S4 further comprises: the roller pressing pressure is gradiently distributed along the width direction, the edge region pressure is 80%-95% of the middle region pressure, the total pressure is 5-15 kN / cm, and the roller pressing times are 2-4 times.

[0026] As preferred, the elastic reinforcing agent in S5 is made of the following raw materials in parts by weight: 60-80 parts of an elastic polymer, 15-30 parts of a conductive material, 3-8 parts of a dispersant, and 200-300 parts of a solvent; the elastic polymer is selected from one or more of polyvinylidene fluoride, polyacrylate, styrene-butadiene rubber, polyurethane and epoxy resin; and the conductive material is selected from one or more of conductive carbon black, graphite, carbon nanotube and metal powder.

[0027] As preferred, the elastic reinforcing agent coating in S5 adopts precise dispensing technology, the dispensing precision is ±0.1 mm, the coating width is 1-5 mm, and the coating position is located at 0.5-3 mm inside the pole piece edge.

[0028] As preferred, in the step S6, the length ratio of the three temperature zones is 2:5:1, the temperature of the first temperature zone is 80-100 DEG C, the temperature of the second temperature zone is 110-140 DEG C, and the temperature of the third temperature zone is 50-70 DEG C.

[0029] As preferred, before the step S4, 0.5-2wt% lubricant solution is sprayed on the surface of the pole piece, and the lubricant is selected from one or more of carboxymethyl cellulose, polyethylene glycol and polyvinyl alcohol.

[0030] As preferred, in the step S4, the calendering treatment adopts micro-vibration assisted calendering technology, and micro-vibration is applied to the calendering roller during the calendering process, with a frequency of 20-100 Hz and an amplitude of 10-50 μm.

[0031] As preferred, after the step S6, the step S7 of surface treatment of the pole piece is further included, and the surface of the pole piece is treated by plasma, the plasma gas is oxygen or argon, the power is 100-300 W, and the treatment time is 10-60 s.

[0032] As preferred, 0.5-3wt% stress buffer is further added to the pole piece slurry, and the stress buffer is selected from one or more of nano-SiO2, nano-Al2O3 and nano-ZrO2.

[0033] As preferred, in the step S2, a tension of 10-50 N is applied to the current collector during the coating process, and the current collector is kept at an angle of 85-89 DEG with the coating direction.

[0034] As preferred, before the step S5, the step S4' of edge ultrasonic treatment is further included, and the edge region of the pole piece is treated by ultrasonic wave with a frequency of 20-60 kHz, a treatment time of 1-5 s and an ultrasonic power of 50-200 W.

[0035] The application further provides a pole piece capable of preventing edge shrinkage and rolling, which is prepared by the above method, and the coating thickness of the middle region of the pole piece is greater than that of the edge region, the thickness difference between the middle region and the edge region is 2-10 μm, the edge region of the pole piece is coated with an elastic reinforcing agent with a thickness of 2-8 μm, and the elastic reinforcing agent is mainly composed of elastic polymer and conductive material.

[0036] Compared with the prior art, the application has at least the following beneficial effects:

[0037] 1) The present application realizes the structure design of the middle region of the pole piece coating thickness being greater than the edge region coating thickness by gradient coating technology, effectively solving the problem of the edge thickness being greater than the middle thickness in the traditional coating process. This reverse thickness gradient design makes the stress of each region of the pole piece more uniform in the subsequent calendering process, preventing the edge shrinkage and rolling phenomenon from the source. The thickness difference between the middle region and the edge region is controlled within the range of 2-10 μm, which can effectively balance the calendering force distribution, and also will not excessively affect the overall capacity and performance of the pole piece.

[0038] 2) The present application adopts differential double roller pressing process, and the linear speed ratio of the upper roller to the lower roller is controlled within 1.02-1.10:1. This differential design generates shear force in the calendering process, making the pole piece material form shear rheology in the thickness direction, effectively releasing the internal stress, and improving the density and uniformity of the material. In addition, differential calendering can also form micro shear texture on the surface of the pole piece, enhancing the flexibility and anti-deformation ability of the pole piece.

[0039] 3) The present application innovatively introduces an edge modification process, coating an elastic reinforcing agent in the edge region of the pole piece to form an elastic buffer zone, effectively absorbing and dispersing the stress concentration in the edge region, preventing edge shrinkage and rolling. The conductive material in the elastic reinforcing agent ensures that the electrical conductivity of the edge region is not affected, while the elastic polymer provides the necessary mechanical support and deformation buffer capacity, and the two work together to significantly improve the structural stability of the edge region of the pole piece. DETAILED DESCRIPTION

[0040] The technical solutions of the present application will be described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0041] The present application provides a method for manufacturing a pole piece that can prevent edge shrinkage and rolling, comprising the following steps:

[0042] S1, slurry preparation: mix active material, conductive agent, binder and solvent uniformly, and then treat by high-speed shearing dispersion to obtain pole piece slurry.

[0043] In this step, different active materials, conductive agents and binders are selected according to the need to prepare positive or negative electrodes. For positive electrode slurry, the active material can be selected from NCM811, LFP or NCA, etc.; the conductive agent can be selected from conductive carbon black, graphite, carbon nanotube, etc.; and the binder can be selected from PVDF, etc. For negative electrode slurry, the active material can be selected from artificial graphite, natural graphite, silicon-carbon composite material, etc.; the conductive agent can be selected from conductive carbon black, etc.; and the binder can be selected from SBR, CMC, etc.

[0044] The high-speed shearing dispersion process adopts a two-stage process: first, shearing dispersion at a speed of 2000-5000 rpm for 10-20 minutes, and then shearing dispersion at a speed of 8000-12000 rpm for 3-8 minutes. This two-stage shearing process can first break up large agglomerates and then further refine the particles, while avoiding overheating and material damage caused by excessive shearing. During the shearing process, the slurry temperature is controlled at 15-25℃ by an external cooling system to prevent excessive solvent evaporation and adhesive performance changes caused by high temperature.

[0045] Specifically, the high-speed shearing dispersion process uses a high-speed dispersion machine, which mainly consists of a variable frequency motor, a high-speed dispersion shaft, a dispersion disc, a cooling system and a temperature monitoring system. The first stage of low-speed shearing mainly uses a large-aperture dispersion disc with a diameter of 80-120 mm, a pore size of 3-5 mm and an edge tooth depth of 5-8 mm. The second stage of high-speed shearing uses a small-aperture dispersion disc with a diameter of 60-80 mm, a pore size of 1-2 mm and an edge tooth depth of 3-5 mm. The cooling system uses a jacket design to control the slurry temperature within the set range by circulating cooling water. The temperature monitoring system monitors the slurry temperature in real time through a thermocouple and adjusts the cooling water flow and stirring speed through an automatic control system to ensure stable slurry temperature.

[0046] S2, Gradient coating: using gradient coating technology to coat the pole piece slurry on the current collector, so that the coating thickness of the middle region of the pole piece is greater than that of the edge region, and the thickness difference between the middle region and the edge region is 2-10 μm.

[0047] The gradient coating technology adopted by the present application is adjustable extrusion coating technology. Through commercially available or customized coating heads, a gradient pressure distribution is achieved, in which the middle extrusion pressure is less than the edge extrusion pressure, and the pressure difference between the middle and edge is controlled within the range of 0.05-0.2 MPa. This gradient pressure distribution makes the coating thickness of the middle region greater than that of the edge region, forming a thickness distribution pattern opposite to that of traditional coating, which lays the foundation for preventing edge roll in the subsequent process. The coating speed is controlled at 5-15 m / min, which ensures both production efficiency and coating quality.

[0048] Specifically, the coating head used in the adjustable extrusion coating technology mainly consists of a coating die body, an adjustable extrusion module, a slurry supply system, and a precision control system. The coating die body is made of stainless steel, with a length of 100-300 mm designed according to the width of the pole piece, and has a flow channel system inside to ensure uniform distribution of the slurry. The coating die body is divided into 5-9 independent areas along the width direction, each area is equipped with an independent pressure adjustment mechanism, and the pressure of the middle area (60-70% of the total width) and the edge area (15-20% of the total width, one on each side) is independently adjusted by a precision screw and a spring assembly. The pressure adjustment mechanism consists of a precision screw (pitch 0.5 mm, diameter 8-10 mm), a pressure sensor, a spring assembly, and an adjustment hand wheel. By rotating the adjustment hand wheel to change the spring compression amount, the extrusion pressure of each area can be accurately controlled. Each area is equipped with a high-precision pressure sensor (accuracy ±0.01 MPa) to monitor the actual pressure value in real time, and the control system automatically adjusts according to the feedback data to ensure that the pressure difference between the middle and edge areas is stable at the set value.

[0049] During the coating process, a tension of 10-50 N is also applied to the current collector, and the current collector is kept at an angle of 85-89° with the coating direction. Proper tension and angle settings can ensure the flatness of the current collector, reduce wave-like deformation, and help the uniform distribution and adhesion of the slurry on the surface of the current collector. The tension control uses a precision tension control roller, which monitors the tension value in real time through a sensor and automatically adjusts the position of the tension roller by a motor to maintain constant tension. The angle control is achieved by adjustable guide rollers installed on a precision angle adjustment mechanism, which can adjust the angle between the current collector and the coating direction with an accuracy of 0.1°.

[0050] S3, pre-drying: the coated pole piece is subjected to pre-drying treatment, the drying temperature is 60-90°C, and the drying time is 1-3 minutes.

[0051] The pre-drying uses a combination of infrared drying and hot air drying, with an infrared radiation power density of 2-5 kW / m2, a hot air temperature of 60-90°C, and a wind speed of 0.8-2 m / s. Infrared drying can quickly heat the inside of the coating, promoting the diffusion of solvents from the inside to the outside; hot air drying accelerates the evaporation of surface solvents, and the two work together to achieve uniform drying from the inside to the outside, avoiding the problems of surface crust and internal solvent retention that may be caused by traditional single drying methods.

[0052] Specifically, the pre-drying device mainly consists of an infrared heating module, a hot air system and a temperature control system. The infrared heating module adopts a medium wave infrared lamp tube with a wavelength range of 2-4 pm, a power density adjustable in the range of 2-5 kW / m2, a lamp tube spacing of 100-150 mm and an installation height distance of 150-200 mm from the surface of the pole piece. The hot air system consists of a hot air generator, an air duct and an air outlet, the hot air temperature is accurately controlled within the set range by a PID controller, the air speed is adjusted by a frequency conversion fan, and the air duct is designed as an air distribution device to ensure uniform distribution of hot air. The temperature control system uses a multi-point temperature sensor to monitor the temperature distribution of the drying area in real time, and automatically adjusts the infrared power and hot air temperature through a closed-loop control system to ensure stable and controllable drying process.

[0053] The purpose of pre-drying is to remove most of the solvent, so that the coating has enough strength for subsequent calendering process, while retaining an appropriate amount of solvent to facilitate the rheology and densification of the material during calendering. The drying time is controlled within 1-3 minutes, which can achieve the purpose of pre-drying without causing the coating to be too dry and brittle.

[0054] S4, calendering treatment: the pre-dried pole piece is subjected to calendering treatment, the calendering adopts differential double roller pressing process, the linear speed ratio of the upper roller to the lower roller is 1.02-1.10:1, and the calendering temperature is 50-120℃.

[0055] Before the calendering treatment, 0.5-2wt% of a lubricant solution is sprayed on the surface of the pole piece, and the lubricant is selected from one or more of carboxymethyl cellulose, polyethylene glycol and polyvinyl alcohol. The addition of lubricant can reduce the friction between the pole piece and the calendering roller, reduce the damage to the surface of the pole piece, and at the same time help the uniform transmission of the calendering force. The lubricant spraying adopts an ultrasonic atomizing spraying device, the nozzle distance from the surface of the pole piece is 150-200 mm, and the spraying amount is controlled within 5-15 mL / m2 to ensure uniform distribution of the lubricant on the surface of the pole piece.

[0056] The differential double roller pressing process device adopted by the present application mainly includes: two upper and lower calendering rollers, independent variable frequency motor driving system, precision gear transmission mechanism, pressure regulating system and temperature control device. Among them, the upper roller and the lower roller are respectively driven by independent variable frequency motors, the motor speed is accurately controlled by the frequency converter to realize different linear speeds of the upper and lower rollers. The pressure between the upper and lower rollers is controlled by a hydraulic system, 5-7 independent pressure control areas are arranged along the width direction, and the pressure of each area can be adjusted individually to realize the gradient distribution of pressure. Temperature control adopts built-in heating element and temperature sensor to ensure uniform distribution of calendering temperature within the set range.

[0057] The calendering roller adopts high-strength alloy steel material, and the surface is precisely ground and hardened. The surface roughness Ra is less than or equal to 0.2 μm, the roundness tolerance is less than or equal to 5 μm, and the cylindrical tolerance is less than or equal to 10 μm. The roller diameter is 200-300 mm, and the roller surface width is designed according to the width of the pole piece, generally 100-400 mm. The parallelism between the upper and lower rollers is controlled within ±5 μm, ensuring uniform transmission of the calendering force.

[0058] By setting different linear speeds of the upper roller and the lower roller (ratio 1.02-1.10:1), shear force is generated during the calendering process, which forms shear flow in the thickness direction of the material, effectively releases internal stress, and improves the density and uniformity of the material. The linear speed difference is realized by an independent frequency conversion motor driving system. The upper roller and the lower roller are respectively driven by independent frequency conversion motors. The motor power is 5-10 kW, and the rotation speed accuracy is ±0.1%. The motor rotation speed is adjusted in real time through a closed-loop control system to keep the set linear speed ratio stable.

[0059] In addition, the roller pressure is distributed in a gradient along the width direction, and the edge area pressure is 80%-95% of the central area pressure. The total pressure is 5-15 kN / cm, and the roller pressure times is 2-4 times. This gradient pressure design matches the gradient coating technology, further ensuring that the stress of each area of the pole piece is uniform, and preventing edge rolling. The pressure gradient is realized by a hydraulic system. 5-7 independent hydraulic cylinders are arranged along the width direction of the roller surface. Each hydraulic cylinder is controlled by an independent proportional valve. A pressure sensor monitors the actual pressure of each area in real time. The control system automatically adjusts according to the feedback data to ensure that the pressure gradient is stable within the set range.

[0060] The calendering temperature is controlled within 50-120 ℃. The temperature selection is determined according to the characteristics of the pole piece material. Generally, the positive electrode material needs a higher temperature (80-120 ℃), and the negative electrode material needs a lower temperature (50-90 ℃). Appropriate temperature can improve the rheological property of the material, which is beneficial to obtain higher compaction density and more uniform pole piece structure. Temperature control adopts built-in heating elements and temperature sensors. The heating element adopts an electric heating tube with a power of 3-5 kW, which is uniformly distributed along the roller surface axis. The temperature sensor adopts PT100 with an accuracy of ±0.1 ℃. 3-5 sensors are installed on each roller surface to monitor the temperature distribution of the roller surface in real time. The control system accurately controls the heating power through the PID algorithm to ensure uniform and stable temperature.

[0061] In the calendering process, a micro-vibration assisted calendering technology is also used. The micro-vibration is applied to the calendering roller with a frequency of 20-100 Hz and an amplitude of 10-50 pm. The micro-vibration can reduce the yield strength of the material, promote particle rearrangement and densification, and reduce internal stress accumulation, further preventing edge shrinkage and rolling. The micro-vibration assisted device is composed of a vibration motor, an eccentric wheel, an elastic support, and a sensor. The vibration motor has a power of 0.5-1 kW, and the rotation speed is controlled by a frequency converter to achieve adjustable frequency. The mass and eccentricity of the eccentric wheel are adjustable to adjust the amplitude. The elastic support uses a specially designed spring-damping system to ensure efficient transmission of vibration energy to the calendering roller without affecting the calendering precision. The vibration sensor monitors the vibration parameters in real time, and the control system automatically adjusts according to the feedback data to ensure that the vibration frequency and amplitude are stable at the set value.

[0062] S4', edge ultrasonic treatment: using ultrasonic waves with a frequency of 20-60 kHz to treat the edge region of the pole piece, the treatment time is 1-5 seconds, and the ultrasonic power is 50-200 W.

[0063] This step is optional and mainly used for further processing of the edge region of the pole piece. Ultrasonic treatment can redistribute and fuse the active materials and adhesives in the edge region, reduce micro defects, and enhance the structural stability of the edge region. The energy of the ultrasonic waves is mainly concentrated on the surface of the pole piece, and will not cause damage to the current collector.

[0064] Specifically, the edge ultrasonic treatment uses a customized ultrasonic treatment device, mainly including: an ultrasonic generator, a transducer, a focused acoustic head, and a positioning system. The ultrasonic generator generates a high-frequency electric signal of 20-60 kHz, with a power adjustable in the range of 50-200 W, a frequency stability of ±0.1%, and an output power stability of ±2%. The transducer uses piezoelectric ceramic material to convert the electric signal into mechanical vibration, with a conversion efficiency of ≥95%. The focused acoustic head uses a specially designed acoustic lens to concentrate the vibration energy on the edge region of the pole piece. The working end of the acoustic head has a diameter of 3-5 mm, the acoustic intensity distribution is uniform, and the edge acoustic intensity attenuation is ≤10%.

[0065] During processing, the pole piece is fixed on a precision positioning platform, and the ultrasonic focusing head is kept at a working distance of 0.5-1 mm from the edge of the pole piece. The ultrasonic head moves at a uniform speed of 5-10 mm / s along the edge of the pole piece to ensure that the ultrasonic energy is uniformly applied to the entire edge area. The positioning system uses CCD visual recognition technology to automatically identify the edge position of the pole piece and control the ultrasonic head to accurately track the edge profile, with a positioning accuracy of ±0.1 mm. The ultrasonic power is accurately adjusted through the control system, and the temperature is monitored in real time during processing to prevent overheating damage to the pole piece. When the temperature at the detection point exceeds the set threshold value (generally 80°C), the system automatically reduces the power or pauses the processing to ensure that the pole piece is not damaged due to overheating. The entire processing process is controlled by a computer and automatically completed according to the preset processing path and parameters to ensure uniform and consistent processing.

[0066] S5, edge modification: coating a thickness of 2-8 μm of an elastic reinforcing agent on the edge area of the pole piece, the elastic reinforcing agent mainly composed of an elastic polymer and a conductive material.

[0067] The elastic reinforcing agent is made from the following raw materials by weight: 60-80 parts of an elastic polymer, 15-30 parts of a conductive material, 3-8 parts of a dispersing agent, and 200-300 parts of a solvent. The elastic polymer is selected from one or more of polyvinylidene fluoride, polyacrylate, butadiene styrene rubber, polyurethane, and epoxy resin; the conductive material is selected from one or more of conductive carbon black, graphite, carbon nanotubes, and metal powder.

[0068] The elastic polymer provides the necessary elasticity and adhesion properties, the conductive material ensures that the modified area has good electrical conductivity, the dispersing agent improves the dispersion stability of the material, and the solvent adjusts the overall rheological properties to make it suitable for precise coating. The preparation process of the elastic reinforcing agent includes: first, dissolving the elastic polymer in a suitable solvent and stirring until completely dissolved; then adding the dispersing agent and continuing to stir for 5-10 minutes; finally, adding the conductive material and dispersing it for 30-60 minutes with a high-speed dispersing machine to obtain a uniform and stable elastic reinforcing agent.

[0069] The elastic reinforcing agent is coated using precision dispensing technology, with a dispensing accuracy of ±0.1 mm and a coating width of 1-5 mm. The coating position is located 0.5-3 mm inside the edge of the pole piece. This precise edge modification forms an elastic buffer zone that effectively absorbs and disperses stress concentration in the edge area, preventing edge shrinkage and rolling.

[0070] Specifically, the precision dispensing technology adopts a computer-controlled three-axis dispensing device, mainly including: a precision dispensing head, a three-axis motion platform, a visual positioning system and a pressure control system. The dispensing head adopts a precision screw valve design, the valve needle diameter is 0.1-0.3 mm, the valve body adopts a corrosion-resistant alloy material, and the sealing ring adopts a fluororubber material, which can realize accurate control of micro glue, and the minimum dispensing amount is 0.001 mL. The three-axis motion platform is driven by a high-precision linear motor, the X / Y axis positioning accuracy is ±0.01 mm, the repeat positioning accuracy is ±0.005 mm, the Z axis positioning accuracy is ±0.005 mm, the maximum running speed is 500 mm / s, and the acceleration is 5000 mm / s2. The visual positioning system captures the edge position of the pole piece in real time through a high-resolution CCD camera (pixel ≥ 2 million), and the image processing algorithm automatically identifies the edge profile to ensure accurate dispensing position, and the system resolution is 0.01 mm. The pressure control system adopts a precision air pressure regulation technology, the pressure control accuracy is ±0.001 MPa, the glue extrusion pressure is stable, and the consistency of the coating thickness is ensured.

[0071] The whole dispensing process is controlled by a computer program, first, the edge profile of the pole piece is scanned by the visual system to generate a dispensing path; then the edge modification work is automatically completed according to the preset dispensing parameters (pressure, speed, height, etc.). During the dispensing process, the system monitors the dispensing amount and position in real time, automatically adjusts the parameters to ensure uniform and consistent coating. After coating is completed, the quality is checked by the visual system to ensure that the coating position and width meet the requirements.

[0072] The elastic reinforcing agent used in the application not only has excellent mechanical properties, but also has good electrochemical stability and compatibility with electrolyte. The elastic polymer material is selected from varieties with wide electrochemical window and stability to lithium ion battery electrolyte, and the addition of conductive material ensures that the modified area has good electronic conductivity. Experiments show that the edge area of the pole piece coated with the elastic reinforcing agent can normally participate in the electrochemical reaction in the battery and will not hinder the migration and embedding / detaching process of lithium ions.

[0073] The inventors conducted immersion tests on the pole piece coated with the elastic reinforcing agent. After the pole piece was immersed in electrolyte (1M LiPF6 EC / DMC / EMC, volume ratio 1:1:1) for 30 days, the elastic reinforcing agent had no obvious dissolution, expansion or peeling phenomenon, and the weight loss was less than 0.5%, proving that it has good electrochemical stability. In addition, the ion conductivity test results of the modified area show that the ion conductivity after coating the elastic reinforcing agent is more than 85% of that of the uncoated area, and the electronic conductivity is more than 90% of that of the uncoated area, which can meet the demand of normal operation of the battery. The cyclic voltammetry test results show that the elastic reinforcing agent has no obvious oxidation-reduction peak in the voltage range of 0.01-4.5 V, proving that it is electrochemically stable in the working voltage range of the battery.

[0074] S6, Secondary drying: The modified electrode sheet is subjected to secondary drying. The ladder temperature drying method is adopted, and the electrode sheet is sequentially subjected to three temperature zones of 80-100°C, 110-140°C, and 50-70°C. The total drying time is 5-15 minutes.

[0075] In the ladder temperature drying method, the length ratio of the three temperature zones is 2:5:1, the first temperature zone is 80-100°C, the second temperature zone is 110-140°C, and the third temperature zone is 50-70°C. The first temperature zone is a preheating zone, mainly to remove most of the solvent; the second temperature zone is a main drying zone, to completely dry and solidify the coating; and the third temperature zone is a cooling zone, to control the cooling rate of the electrode sheet, preventing the accumulation of internal stress and deformation caused by rapid cooling.

[0076] Specifically, the secondary drying equipment is composed of three independently temperature-controlled drying zones, each equipped with an independent heating system, temperature control system, and air circulation system. The heating system uses electric heating pipes with a power density of 2-5 kW / m2, evenly distributed at the top and bottom of the drying zone; the temperature control system uses multi-point temperature sensors and PID controllers with a temperature control accuracy of ±1°C; the air circulation system consists of a variable frequency fan, air duct, and guide vanes to ensure uniform distribution of hot air, with a wind speed adjustable within 0.5-2 m / s. The conveying system uses a mesh belt conveyor with a speed adjustable within 0.5-3 m / min, set according to the drying time requirements. The entire drying system adopts closed-loop control, automatically adjusting the temperature, air speed, and conveying speed according to the type, thickness, and coating composition of the electrode sheet, to ensure the best drying effect.

[0077] This ladder temperature drying method can achieve uniform drying and stress release of the electrode sheet, avoiding the uneven drying of the surface and interior that may be caused by traditional single temperature drying, further reducing the risk of edge shrinkage and rolling. During the drying process, the first temperature zone has a lower temperature, mainly to remove most of the solvent, preventing surface bubbles and cracking caused by rapid solvent evaporation; the second temperature zone has a higher temperature, completely drying and solidifying the coating to ensure stable coating structure; and the third temperature zone has a lower temperature, mainly to control the cooling rate of the electrode sheet, preventing the accumulation of internal stress and deformation caused by a large temperature gradient.

[0078] S7, Electrode sheet surface treatment: The electrode sheet surface is treated by plasma, with oxygen or argon as the plasma gas, a power of 100-300 W, and a treatment time of 10-60 s.

[0079] This step is optional and mainly used to improve the wettability and interfacial properties of the electrode sheet surface. Plasma treatment can change the chemical composition and physical morphology of the surface without affecting the structure of the electrode sheet, enhancing the compatibility with the electrolyte, and improving the charge and discharge performance and cycle stability of the battery.

[0080] Specifically, the plasma processing equipment is composed of a plasma generator, a gas supply system, a processing chamber and a control system. The plasma generator adopts a radio frequency (RF) power source with a frequency of 13.56 MHz and a power adjustable in a range of 100-300 W and a power stability of ±2%. The gas supply system includes gas cylinders, pressure reducing valves, mass flow controllers and pipelines, which can accurately control the gas flow (1-100 sccm) and pressure (1-100 Pa). The processing chamber is made of stainless steel and is internally provided with an electrode and a sample stage. The electrode adopts a parallel plate design, and the sample stage can adjust the height to ensure the optimal interaction distance between the electrode and the plasma. The control system adopts a PLC controller, which can set the processing power, time, gas type and flow and other parameters and monitor the processing process in real time.

[0081] During the processing, the electrode plate is placed on the sample stage, vacuumized to a basic pressure (<1 Pa), and then the working gas (oxygen or argon) is introduced, and the gas flow is adjusted to stabilize the processing chamber pressure at 10-50 Pa. The plasma generator is started to generate uniform and stable plasma. The processing time is set according to the type of electrode plate and processing requirements, generally 10-60 s. After the processing is completed, the plasma power is turned off, nitrogen gas is introduced to replace the processing chamber gas, and then the electrode plate is taken out.

[0082] The plasma processing can form active functional groups such as hydroxyl and carboxyl on the surface of the electrode plate, which can improve the wettability of the electrode plate surface, improve the contact and infiltration with the electrolyte. At the same time, the plasma processing can also remove the organic contaminants on the surface of the electrode plate, increase the surface roughness, and further improve the electrochemical performance of the battery. Experiments show that the contact angle of the electrode plate treated by plasma with the electrolyte is reduced from 60-80° to 10-30°, and the infiltration speed is increased by 2-3 times, which has a positive significance for improving the rate performance and cycle stability of the battery.

[0083] The electrode plate prepared by the above steps has a coating thickness in the middle region greater than that in the edge region, and the thickness difference between the middle region and the edge region is 2-10 μm. The edge region of the electrode plate is coated with an elastic reinforcing agent with a thickness of 2-8 μm. This special structural design fundamentally solves the problem of edge shrinkage and rolling of the electrode plate, and significantly improves the quality of the electrode plate and the performance of the battery.

[0084] The application will be further described below in conjunction with specific examples.

[0085] Example 1 (positive electrode plate)

[0086] S1: Preparation of slurry

[0087] NCM811 positive electrode active material 94 parts by weight, conductive carbon black 3 parts by weight, PVDF binder 3 parts by weight, NMP solvent 100 parts by weight were mixed, first sheared and dispersed at a speed of 3000 rpm for 15 minutes, then sheared and dispersed at a speed of 10000 rpm for 5 minutes, and the slurry temperature was controlled at 20℃. At the same time, 1.5wt% of nano-SiO2 was added as a stress buffer.

[0088] S2: Gradient coating

[0089] An adjustable extrusion coating technology was used, the middle extrusion pressure of the coating head was 0.3MPa, the edge extrusion pressure was 0.4MPa, and the coating speed was 10m / min. A tension of 30N was applied to the aluminum foil current collector during the coating process, and the current collector was kept at an angle of 87° with the coating direction. After coating, the thickness of the middle region was 85μm, the thickness of the edge region was 80μm, and the thickness difference was 5μm.

[0090] S3: Pre-drying

[0091] The infrared drying and hot air drying were combined, the infrared radiation power density was 3.5kW / m2, the hot air temperature was 80℃, the air speed was 1.5m / s, and the drying time was 2 minutes.

[0092] S4: Calendering treatment

[0093] A 1wt% polyethylene glycol solution was sprayed on the surface of the pole piece as a lubricant, and then calendering treatment was carried out. The differential double roller pressing process was used, the linear speed ratio of the upper roller to the lower roller was 1.05:1, and the calendering temperature was 100℃. The roll pressure was gradiently distributed along the width direction, the middle region pressure was 10kN / cm, the edge region pressure was 8.5kN / cm(85% of the middle), and the roll pressure times was 3 times. A micro-vibration with a frequency of 50Hz and an amplitude of 30μm was applied to the calendering roller during the calendering process.

[0094] S4': Edge ultrasonic treatment

[0095] The edge region of the pole piece was treated with ultrasonic waves with a frequency of 40kHz, the treatment time was 3 seconds, and the ultrasonic power was 120W.

[0096] S5: Edge modification

[0097] An elastic reinforcing agent was coated on the edge region of the pole piece, which was made of the following raw materials: polyvinylidene fluoride 70 parts, conductive carbon black 20 parts, dispersant 5 parts, NMP solvent 250 parts. Precise dispensing technology was used for coating, the coating width was 3mm, the position was located 2mm inside the edge of the pole piece, and the coating thickness was 5μm.

[0098] S6: Secondary drying

[0099] The length ratio of the three temperature zones is 2:5:1, the temperature of the first temperature zone is 90℃, the temperature of the second temperature zone is 130℃, and the temperature of the third temperature zone is 60℃. The total drying time is 10 minutes.

[0100] S7: Surface treatment of the pole piece

[0101] The surface of the pole piece is treated by oxygen plasma, the power is 200W, and the treatment time is 30s.

[0102] Example 2 (negative pole piece)

[0103] S1: Preparation of slurry

[0104] 95 parts by weight of artificial graphite negative active material, 1.5 parts by weight of conductive carbon black, 1.5 parts by weight of SBR binder, 2 parts by weight of CMC binder, and 110 parts by weight of deionized water are mixed. First, shear dispersion is carried out at a speed of 4000 rpm for 12 minutes, and then shear dispersion is carried out at a speed of 9000 rpm for 4 minutes, with the slurry temperature controlled at 18℃. At the same time, 2wt% of nano-Al2O3 is added as a stress buffer.

[0105] S2: Gradient coating

[0106] An adjustable extrusion coating technique is used, with the middle extrusion pressure of the coating head being 0.25MPa and the edge extrusion pressure being 0.4MPa, and the coating speed being 12m / min. A tension of 35N is applied to the copper foil current collector during the coating process, and the current collector is kept at an angle of 86° with the coating direction. After coating, the thickness of the middle region is 90μm, the thickness of the edge region is 82μm, and the thickness difference is 8μm.

[0107] S3: Pre-drying

[0108] An infrared drying and hot air drying combination method is used, with the infrared radiation power density being 4kW / m2, the hot air temperature being 75℃, the air speed being 1.2m / s, and the drying time being 1.5 minutes.

[0109] S4: Calendering treatment

[0110] A 1.5wt% carboxymethyl cellulose solution is sprayed on the surface of the pole piece as a lubricant, and then calendering treatment is carried out. Differential double roller pressing process is used, with the linear speed ratio of the upper roller to the lower roller being 1.08:1, and the calendering temperature being 70℃. The roller pressure is gradiently distributed along the width direction, with the pressure in the middle region being 12kN / cm and the pressure in the edge region being 10.2kN / cm (85% of the middle), and the number of roller pressing is 2 times. A micro-vibration with a frequency of 60Hz and an amplitude of 25μm is applied to the calendering roller during the calendering process.

[0111] S4': Edge ultrasonic treatment

[0112] The edge region of the pole piece is treated using ultrasonic waves with a frequency of 30 kHz, a treatment time of 2 seconds, and an ultrasonic wave power of 150 W.

[0113] S5: Edge modification

[0114] An elastic enhancer is coated on the edge region of the pole piece, the elastic enhancer being made from the following raw materials: styrene-butadiene rubber 65 parts, graphite 25 parts, dispersant 6 parts, deionized water 270 parts. The coating is performed using precision dispensing technology, the coating width is 4 mm, the position is located 1.5 mm inside the edge of the pole piece, and the coating thickness is 6 μm.

[0115] S6: Secondary drying

[0116] A step temperature drying method is used, the length ratio of the three temperature zones is 2:5:1, the first temperature zone temperature is 85°C, the second temperature zone temperature is 120°C, the third temperature zone temperature is 55°C, and the total drying time is 8 minutes.

[0117] S7: Pole piece surface treatment

[0118] The surface of the pole piece is treated using argon plasma, the power is 150 W, and the treatment time is 40 s.

[0119] Example 3 (silicon-carbon negative pole piece)

[0120] S1: Slurry preparation

[0121] Silicon-carbon composite negative active material 92 parts by weight, conductive carbon black 2 parts by weight, SBR binder 2 parts by weight, CMC binder 4 parts by weight, and deionized water 120 parts by weight are mixed, first sheared and dispersed at a speed of 3500 rpm for 18 minutes, and then sheared and dispersed at a speed of 11000 rpm for 6 minutes, with the slurry temperature controlled at 16°C. 2.5 wt% of nano-ZrO2 is added as a stress buffer.

[0122] S2: Gradient coating

[0123] Adjustable extrusion coating technology is used, the middle extrusion pressure of the coating head is 0.2 MPa, the edge extrusion pressure is 0.35 MPa, and the coating speed is 8 m / min. A tension of 40 N is applied to the copper foil current collector during the coating process, and the current collector is kept at an angle of 88° to the coating direction. After coating, the middle region thickness is 75 μm, the edge region thickness is 67 μm, and the thickness difference is 8 μm.

[0124] S3: Pre-drying

[0125] The infrared drying and hot air drying are combined, the infrared radiation power density is 3 kW / m2, the hot air temperature is 70 °C, the air speed is 1 m / s, and the drying time is 2.5 minutes.

[0126] S4: Calendering treatment

[0127] A 2 wt% polyvinyl alcohol solution is sprayed on the surface of the pole piece as a lubricant, and then a calendering treatment is performed. The calendering adopts a differential double roller pressing process, the linear speed ratio of the upper roller to the lower roller is 1.10:1, and the calendering temperature is 60 °C. The roller pressing pressure is gradiently distributed along the width direction, the pressure in the middle region is 8 kN / cm, the pressure in the edge region is 7.2 kN / cm (90% of the middle), and the roller pressing number is 4 times. Micro-vibration with a frequency of 80 Hz and an amplitude of 40 μm is applied to the calendering roller during the calendering process.

[0128] S4': Edge ultrasonic treatment

[0129] The edge region of the pole piece is treated by using an ultrasonic wave with a frequency of 50 kHz, the treatment time is 4 seconds, and the ultrasonic power is 180 W.

[0130] S5: Edge modification

[0131] An elastic reinforcing agent is coated on the edge region of the pole piece, the elastic reinforcing agent is made of the following raw materials: polyurethane 75 parts, carbon nanotube 18 parts, dispersant 7 parts, and deionized water 280 parts. Precise dispensing technology is used for coating, the coating width is 2.5 mm, the position is located 1 mm inside the edge of the pole piece, and the coating thickness is 7 μm.

[0132] S6: Secondary drying

[0133] A step temperature drying method is adopted, the length ratio of the three temperature zones is 2:5:1, the temperature of the first temperature zone is 85 °C, the temperature of the second temperature zone is 115 °C, the temperature of the third temperature zone is 60 °C, and the total drying time is 12 minutes.

[0134] S7: Pole piece surface treatment

[0135] The surface of the pole piece is treated by using oxygen plasma, the power is 250 W, and the treatment time is 20 s.

[0136] Comparative Example 1 (traditional positive pole piece preparation method)

[0137] S1: Preparation of slurry

[0138] NCM811 positive active material 94 parts by weight, conductive carbon black 3 parts by weight, PVDF binder 3 parts by weight, and NMP solvent 100 parts by weight are mixed and sheared and dispersed for 30 minutes at a speed of 5000 rpm, and the slurry temperature is controlled at room temperature (about 25 °C).

[0139] S2: Conventional coating

[0140] The conventional extrusion coating technology was adopted, the extrusion pressure of the coating head was uniform, 0.4 MPa, and the coating speed was 8 m / min. After coating, the thickness was uniform, about 85 μm.

[0141] S3: Drying

[0142] The single temperature drying was adopted, the temperature was 120 ℃, and the drying time was 10 minutes.

[0143] S4: Calendering treatment

[0144] The conventional calendering process was adopted, the linear speeds of the upper roller and the lower roller were equal, the calendering temperature was room temperature (about 25 ℃). The roller pressure was uniform, 10 kN / cm, and the roller pressure times was 1.

[0145] Comparative Example 2 (conventional negative electrode sheet preparation method)

[0146] S1: Preparation of slurry

[0147] The artificial graphite negative active material 95 parts by weight, the conductive carbon black 1.5 parts by weight, the SBR binder 1.5 parts by weight, the CMC binder 2 parts by weight, and the deionized water 110 parts by weight were mixed, and sheared and dispersed at a speed of 6000 rpm for 25 minutes, and the slurry temperature was controlled at room temperature (about 25 ℃).

[0148] S2: Conventional coating

[0149] The conventional extrusion coating technology was adopted, the extrusion pressure of the coating head was uniform, 0.35 MPa, and the coating speed was 10 m / min. After coating, the thickness was uniform, about 90 μm.

[0150] S3: Drying

[0151] The single temperature drying was adopted, the temperature was 100 ℃, and the drying time was 8 minutes.

[0152] S4: Calendering treatment

[0153] The conventional calendering process was adopted, the linear speeds of the upper roller and the lower roller were equal, the calendering temperature was room temperature (about 25 ℃). The roller pressure was uniform, 12 kN / cm, and the roller pressure times was 1.

[0154] Comparative Example 3 (partially improved electrode sheet preparation method)

[0155] S1: Preparation of slurry

[0156] NCM811 positive active material 94 parts by weight, conductive carbon black 3 parts by weight, PVDF binder 3 parts by weight, NMP solvent 100 parts by weight were mixed, first sheared and dispersed at a speed of 3000 rpm for 15 minutes, and then sheared and dispersed at a speed of 10000 rpm for 5 minutes, and the slurry temperature was controlled at 20℃.

[0157] S2: conventional coating

[0158] The conventional extrusion coating technology was adopted, the extrusion pressure of the coating head was uniform, and was 0.4 MPa, and the coating speed was 10 m / min. After coating, the thickness was uniform, and was about 85 μm.

[0159] S3: pre-drying

[0160] The hot air drying method was adopted, the temperature was 80℃, and the drying time was 2 minutes.

[0161] S4: calendering treatment

[0162] The differential double roller pressing process was adopted, the linear speed ratio of the upper roller to the lower roller was 1.05:1, and the calendering temperature was 100℃. The calendering pressure was uniform, and was 10 kN / cm, and the calendering times was 2 times.

[0163] S5: secondary drying

[0164] The single temperature drying method was adopted, the temperature was 130℃, and the drying time was 10 minutes.

[0165] The performance of the pole piece prepared in the above examples and comparative examples was tested, and the specific test method was as follows, and the specific test results were shown in Tables 1-3.

[0166] 1. Edge curling angle test method:

[0167] 10 pieces of pole piece prepared in each batch were taken, the curling angles of the left and right edges of each piece were measured, and a total of 20 data points were averaged. The curling angle was measured by an angle measuring instrument, the pole piece was placed on the water platform, and the included angle between the edge of the pole piece and the horizontal plane was measured. The smaller the curling angle, the lighter the edge shrinkage and curling degree of the pole piece. When measuring, the pole piece was placed in the center of the measuring platform, a fixed clamp was used to ensure that the main body of the pole piece was flat, and then the measuring arm of the angle measuring instrument was used to touch the edge of the pole piece, and the display value was read. Each measurement point was measured repeatedly for 3 times to take the average value, so as to reduce the measurement error.

[0168] 2. Compaction density test method:

[0169] The compaction density of the electrode sheet is measured by Archimedes drainage method. First, the mass of the electrode sheet is measured (using an analytical balance with a precision of 0.0001 g), then the electrode sheet is cut into small pieces with a known area (usually 4 cm x 4 cm), the thickness is measured using a precision micrometer (with a precision of 0.001 mm), 5 points are measured at different positions of the electrode sheet and the average value is taken, the volume is calculated, and finally the density is calculated. When testing, first weigh the mass m of the electrode sheet, then measure the thickness h of the electrode sheet (deducting the thickness of the current collector), calculate the area S, then the compaction density p = m / (S x h). Each sample is measured 5 times and the average value is taken.

[0170] 3. Battery capacity test method:

[0171] The prepared electrode sheet is cut into a size of 4 cm x 5 cm, assembled into a 2032 type button cell, and the electrolyte is a 1 mol / L LiPF6 EC / DMC / EMC (volume ratio 1:1:1) solution, assembled in an argon gas glove box (oxygen and moisture content <0.1 ppm). Using a new battery test system (model: CT-4008), charge and discharge at 0.1C rate at 25°C for 3 times, measure the discharge capacity, and calculate the capacity density (mAh / g). The charge cut-off voltage is 4.2V (positive half-cell) or 0.01V (negative half-cell), and the discharge cut-off voltage is 3.0V (positive half-cell) or 1.5V (negative half-cell).

[0172] 4. Cycle performance test method:

[0173] Using a new battery test system (model: CT-4008), charge and discharge at 1C rate for 500 times at 25°C, measure the capacity retention rate. Capacity retention rate (%) = (discharge capacity after 500 cycles / first discharge capacity) x 100%. The charge and discharge conditions are the same as in the capacity test method. Every 50 cycles, a reference test at 0.1C rate is performed to evaluate the capacity decay of the battery.

[0174] 5. High temperature storage performance test method:

[0175] After charging the battery to 50% SOC state, store it in a 60°C high temperature oven for 30 days, and test the capacity loss before and after storage. Capacity loss rate (%) = (capacity before storage - capacity after storage) / capacity before storage x 100%. Before and after storage, 3 times of 0.1C rate charge and discharge cycles are performed to obtain stable capacity values for comparison.

[0176] 6. Rate performance test method:

[0177] The discharge capacity of the battery was tested at 0.2C, 0.5C, 1C, 2C, 5C and 10C rates, respectively, and the high-rate capacity retention rate was calculated. The high-rate capacity retention rate (%) = (10C rate discharge capacity / 0.2C rate discharge capacity) x 100%. Each rate test was repeated 3 times to take the average value, and the test sequence was from low rate to high rate, and 1 reference cycle of 0.2C rate was performed between each rate.

[0178] Table 1 Edge curling angle and compaction density test results of the electrode sheet

[0179]

[0180]

[0181] Table 2 Battery capacity and cycle performance test results

[0182]

[0183] Table 3 High-temperature storage performance and rate performance test results

[0184] Sample High temperature storage capacity loss rate (%) 10C / 0.2C capacity retention rate (%) Example 1 3.2 82.5 Example 2 2.8 85.3 Example 3 4.5 78.6 Comparative Example 1 8.7 68.3 Comparative Example 2 7.5 72.1 Comparative Example 3 5.6 75.8

[0185] Among them, the above test results are analyzed as follows:

[0186] 1) Comparative analysis of edge curling angle: The edge curling angle of the electrode sheet prepared by the three examples of the present application is significantly smaller than that of the three comparative examples. The edge curling angles of Example 1, Example 2 and Example 3 are 2.3°, 1.8° and 3.1°, respectively, while the edge curling angles of Comparative Example 1, Comparative Example 2 and Comparative Example 3 are 15.7°, 12.6° and 7.4°, respectively. This shows that the preparation method of the present application can effectively prevent the edge shrinkage and curling of the electrode sheet, and the effect of Example 2 is the best. This is mainly due to the synergistic effect of the gradient coating technology, differential double-roller pressing process and edge modification treatment adopted in the present application, which prevents the edge shrinkage and curling problem from the source.

[0187] The gradient coating technology realizes the coating distribution of the thickness of the middle region being greater than that of the edge region, which is contrary to the case of the edge thickness being greater than the middle thickness in the traditional coating, and fundamentally changes the stress situation of each region in the subsequent calendering process. The differential double-roller pressing process generates shear force through the different linear speeds of the upper and lower rollers, so that the coating material forms shear flow in the thickness direction, effectively releasing the internal stress. The edge modification treatment forms an elastic buffer zone at the edge region of the electrode sheet, which can absorb and disperse the stress concentration of the edge region. The synergistic effect of these three technical measures ensures uniform stress distribution of the electrode sheet during the entire preparation process, thereby effectively preventing the edge shrinkage and curling problem.

[0188] 2) Compaction density comparison analysis: The compaction density of the electrode prepared by the inventive example is generally higher than that of the corresponding comparative example. For example, the compaction density of Example 1 is 3.65 g / cm3, while that of Comparative Example 1 is 3.45 g / cm3; the compaction density of Example 2 is 1.75 g / cm3, while that of Comparative Example 2 is 1.62 g / cm3. This shows that the differential double roller pressing process and the micro-vibration assisted calendering technology of the present application can effectively improve the compaction density of the electrode sheet and improve the energy density of the battery.

[0189] In the differential double roller pressing process, the shear force generated by the different linear speeds of the upper and lower rollers can promote the rearrangement and densification between the particles, while the micro-vibration assisted calendering technology can reduce the yield strength of the material, further promoting the close packing of the particles. In addition, the gradient pressure distribution design adopted in the calendering process also ensures that each region obtains appropriate compaction density, avoiding the problem of excessive compaction of the edge or insufficient compaction of the middle in traditional calendering due to uniform pressure. High compaction density means that more active materials are contained in a unit volume, which is beneficial to improve the energy density of the battery. At the same time, appropriate compaction density also helps to improve the electronic conductivity and ion transport performance inside the electrode.

[0190] 3) Battery capacity and first charge-discharge efficiency comparison analysis: The first discharge capacity and first charge-discharge efficiency of the battery prepared by the inventive example are slightly higher than those of the corresponding comparative example. For example, the first discharge capacity of Example 1 is 195.3 mAh / g, and the first charge-discharge efficiency is 89.7%; while the first discharge capacity of Comparative Example 1 is 191.5 mAh / g, and the first charge-discharge efficiency is 88.5%. This shows that the preparation method of the present application not only prevents edge rolling, but also improves the capacity and efficiency of the battery.

[0191] The improvement of the first discharge capacity is mainly due to the higher compaction density and more uniform electrode structure, which enables more active materials to effectively participate in the electrochemical reaction. The improvement of the first charge-discharge efficiency is related to the optimization of the electrode structure and the surface treatment. The uniform electrode structure reduces the irreversible capacity loss, and the plasma surface treatment improves the interface performance between the electrode and the electrolyte, reducing the interface side reaction. In addition, the stress buffer (such as nano-SiO2, nano-Al2O3, etc.) used in the present application can also improve the structural stability of the electrode and reduce the structural damage during charging and discharging, thereby improving the first charge-discharge efficiency.

[0192] 4) Cycle performance comparison analysis: The capacity retention rate of the batteries prepared in the examples of the present application after 500 cycles is significantly higher than that of the corresponding comparative examples. The capacity retention rates of Example 1, Example 2 and Example 3 after 500 cycles are 88.6%, 91.5% and 82.4% respectively, while those of Comparative Example 1, Comparative Example 2 and Comparative Example 3 are 76.2%, 78.9% and 81.5% respectively. This shows that the preparation method of the present application can significantly improve the cycle stability of the battery, which is mainly due to the more stable structure of the electrode sheet, reducing the shedding of active material and performance decay caused by edge rolling during the cycle process.

[0193] The improvement of cycle performance is mainly due to the following aspects: first, the gradient coating and differential double roller pressing process of the present application makes the electrode sheet structure more uniform and stable, reduces the local stress concentration and reduces the risk of structure collapse during the cycle process; second, the elastic buffer zone formed by the edge modification treatment can effectively absorb and disperse the stress change during the charging and discharging process, protecting the edge area from damage; third, the micro vibration assisted calendering technology forms micro shear texture, which enhances the flexibility and structural stability of the electrode sheet, and improves the adaptability to volume change; finally, the step temperature drying method reduces the residual stress in the electrode sheet, further improving the structural stability. These factors work together to make the battery maintain a high capacity retention rate during long cycle process.

[0194] 5) High temperature storage performance comparison analysis: The high temperature storage capacity loss rate of the batteries prepared in the examples of the present application is significantly lower than that of the corresponding comparative examples. The high temperature storage capacity loss rates of Example 1, Example 2 and Example 3 are 3.2%, 2.8% and 4.5% respectively, while those of Comparative Example 1, Comparative Example 2 and Comparative Example 3 are 8.7%, 7.5% and 5.6% respectively. This shows that the preparation method of the present application can improve the high temperature storage stability of the battery and reduce the self-discharge and side reactions.

[0195] The improvement of high temperature storage performance is mainly due to the more uniform and stable electrode structure and better interface performance. The gradient coating and differential double roller pressing process used in the present application makes the electrode sheet structure more uniform and dense, reducing the excessive penetration and reaction of electrolyte in the electrode; the elastic buffer zone formed by the edge modification treatment can prevent the structural deformation and material shedding of the edge area in high temperature environment; the plasma surface treatment improves the chemical composition and physical morphology of the electrode surface, reducing the interface side reactions; in addition, the stress buffer added in the present application can also improve the structural stability of the electrode in high temperature environment. These factors work together to make the battery maintain high stability and reduce capacity loss during high temperature storage process.

[0196] 6) Rate capability comparison: The 10C / 0.2C capacity retention of the batteries prepared in the examples of the present application is higher than that of the corresponding comparative examples. The 10C / 0.2C capacity retention of Example 1, Example 2 and Example 3 is 82.5%, 85.3% and 78.6% respectively, while that of Comparative Example 1, Comparative Example 2 and Comparative Example 3 is 68.3%, 72.1% and 75.8% respectively. This indicates that the preparation method of the present application can improve the rate capability of the battery, which may be related to the more stable structure of the electrode sheet and the more uniform electrolyte infiltration.

[0197] The improvement of rate capability is mainly due to the following aspects: First, the microstructure formed by the differential double roller pressing process and the micro-vibration assisted calendering technology of the present application is beneficial to the uniform infiltration of electrolyte and the rapid transmission of ions; Second, the appropriate compaction density not only ensures sufficient active material content, but also retains appropriate porosity, which is beneficial to the rapid migration of ions; Third, the plasma surface treatment improves the wettability of the electrode surface, promotes the infiltration of electrolyte and the interfacial ion transmission; Finally, the uniform and stable electrode structure reduces local polarization and improves the transmission efficiency of electrons and ions. These factors work together to enable the battery to maintain a high capacity output under high-rate charging and discharging conditions.

[0198] 7) Comparison analysis between different examples: Among the three examples, Example 2 (negative electrode sheet) has the best overall performance, especially in terms of edge curling angle, cycle performance and rate capability. This may be related to the structural characteristics of the graphite material, which has a good layered structure and flexibility, making it more suitable for the preparation method of the present application. Although Example 3 (silicon-carbon negative electrode sheet) has the highest initial discharge capacity, its cycle performance and high-temperature storage performance are slightly inferior, which may be related to the large volume change of silicon material during the cycle process.

[0199] The layered structure of graphite material makes it more easily form an ordered arrangement under the action of shear force, and the shear force generated by the differential double roller pressing process can make the graphite layer arrange more orderly, reduce the interlayer defects, and improve the electronic conductivity and lithium ion diffusion rate. In addition, the flexibility of graphite material makes its volume change smaller during charging and discharging, and the structure is more stable, making it more suitable for the preparation method of the present application. In contrast, although silicon-carbon material has higher theoretical capacity, its volume change during charging and discharging is large (more than 300%), which challenges the stability of the electrode structure. However, the preparation method of the present application still significantly improves the structural stability and electrochemical performance of the silicon-carbon electrode sheet through gradient coating, differential double roller pressing and edge modification, etc. Technical measures, especially compared with traditional preparation methods, the cycle performance and high-temperature storage performance are significantly improved.

[0200] 8) Process parameter optimization analysis:

[0201] (1) In the gradient coating technology, the pressure difference between the middle and the edge is controlled in the range of 0.05-0.2 MPa. If the pressure difference is too small, it is difficult to form an effective thickness gradient; if the pressure difference is too large, it will lead to uneven coating and quality problems. Experiments show that when the pressure difference is 0.1 MPa, the thickness difference between the middle and the edge is about 5 μm, which is the most suitable thickness difference, which can effectively balance the distribution of rolling force and will not excessively affect the overall capacity and performance of the pole piece.

[0202] (2) In the differential double roller pressing process, the linear speed ratio of the upper roller to the lower roller is in the range of 1.02-1.10:1. If the ratio is lower than 1.02, the shear effect is not obvious; if the ratio is higher than 1.10, it will cause damage to the surface of the pole piece and material peeling. Experiments show that when the linear speed ratio is 1.05-1.08:1, it can produce enough shear force to release internal stress and will not cause obvious damage to the surface of the pole piece, which is the best process parameter range.

[0203] (3) In the edge modification process, the thickness of the elastic reinforcing agent is controlled in the range of 2-8 μm. If the thickness is too small, the buffering effect is not obvious; if the thickness is too large, it will affect the overall structure and assembly of the pole piece. Experiments show that when the thickness of the elastic reinforcing agent is 5-6 μm, it can provide sufficient elastic buffering effect and will not excessively increase the thickness of the pole piece, which is the best process parameter range. In addition, the coating position is located 1-2 mm inside the edge of the pole piece, which is the best position, which can effectively cover the stress concentration area and will not affect the effective area of the pole piece.

[0204] (4) In the step temperature drying method, the temperature gradient and residence time ratio of the three temperature zones have a significant effect on the quality of the pole piece. If the temperature of the first temperature zone is too low, the solvent removal is not sufficient; if it is too high, it may cause surface crust and bubbles. If the temperature of the second temperature zone is too low, the coating solidification is not sufficient; if it is too high, it may cause the decomposition of the binder and damage to the active material. If the temperature of the third temperature zone is too low, the cooling effect is not obvious; if it is too high, it cannot effectively reduce the temperature. Experiments show that when the temperature of the first temperature zone is 85-90 °C, the temperature of the second temperature zone is 120-130 °C, the temperature of the third temperature zone is 55-60 °C, and the length ratio of the three temperature zones is 2:5:1, the drying effect is the best and the pole piece structure is the most stable.

[0205] (5) In the micro-vibration assisted calendering technology, the vibration frequency and amplitude need to be optimized according to the characteristics of the pole piece material. If the frequency is too low, the vibration effect is not obvious; if the frequency is too high, it may cause equipment resonance and control difficulty. If the amplitude is too small, the promotion effect on the material rheology is insufficient; if the amplitude is too large, it may cause damage to the surface of the pole piece and structural instability. Experiments show that for the positive electrode material, the vibration parameters with the best effect are 40-60 Hz in frequency and 20-30 μm in amplitude; for the negative electrode material, the vibration parameters with the best effect are 60-80 Hz in frequency and 25-40 μm in amplitude. This difference is mainly related to the mechanical properties and rheological properties of different materials.

[0206] (6) In the edge ultrasonic treatment, the ultrasonic frequency, power and treatment time need to be optimized according to the type and thickness of the pole piece. If the frequency is too low, the penetration depth is large but the energy concentration is low; if the frequency is too high, the energy is concentrated but the penetration depth is limited. If the power is too low, the treatment effect is not obvious; if the power is too high, it may cause the pole piece to overheat and be damaged. If the treatment time is too short, the effect is insufficient; if the treatment time is too long, it may cause over-treatment and material damage. Experiments show that for the positive electrode pole piece, the treatment parameters with the best effect are 30-40 kHz in frequency, 100-150 W in power and 2-3 seconds in treatment time; for the negative electrode pole piece, the treatment parameters with the best effect are 40-50 kHz in frequency, 150-200 W in power and 3-4 seconds in treatment time.

[0207] The electrochemical performance test shows that the pole piece prepared by the present application is superior to the pole piece prepared by the traditional preparation method in various performance indicators. In particular, the improvement effect is most significant in the cycle stability and high-rate performance. This is mainly due to the synergistic effect of the gradient coating technology, the differential double-roller pressing process and the edge modification treatment adopted by the present application, which optimizes the structure and performance of the pole piece from multiple aspects. The gradient coating technology realizes the thickness distribution of thick in the middle and thin at the edge, so that the pole piece is more uniform in stress during the calendering process; the differential double-roller pressing process releases internal stress by generating shear force, thereby improving the density and uniformity of the material; the edge modification treatment forms an elastic buffer zone in the edge region of the pole piece, which effectively absorbs and disperses the stress concentration in the edge region. The organic combination of the three technical measures successfully solves the problem of edge shrinkage and rolling of the pole piece, and at the same time improves various performance indicators of the battery.

[0208] In addition, the elastic reinforcing agent used in the present application not only has excellent mechanical properties, but also has good electrochemical stability and compatibility with electrolyte. The elastic reinforcing agent coating area can normally participate in electrochemical reaction and will not hinder the migration of lithium ions and the embedding / extraction process. The electrochemical impedance spectroscopy test results show that the interface impedance of the electrode sheet coated with the elastic reinforcing agent only increases by 5-10% compared with the uncoated area, which will not significantly affect the electrochemical performance of the battery. Long-term cycle test also proves that the elastic reinforcing agent remains stable during long-term charging and discharging process and will not significantly degrade or peel off. These results show that the edge modification treatment provided by the present application not only prevents the edge shrinkage and curling of the electrode sheet, but also is compatible with the electrochemical system of the battery and will not introduce new problems.

[0209] In summary, the manufacturing method of the electrode sheet capable of preventing edge shrinkage and curling provided by the present application successfully solves the problem of edge shrinkage and curling of the electrode sheet through the organic combination of gradient coating technology, differential double roller pressing process and edge modification treatment, significantly improves the quality of the electrode sheet and the performance of the battery. Especially in the aspects of cycle stability, high-temperature storage performance and rate performance, the present application has obvious advantages and provides a new technical path for the performance improvement of lithium ion batteries.

[0210] It is apparent for those skilled in the art that the present application is not limited to the details of the above exemplary embodiments, but can be implemented in other concrete forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered as exemplary and non-limiting, and the scope of the present application is defined by the appended claims rather than the above description, and all changes falling within the meaning and range of equivalent elements of the claims are intended to be included in the present application.

[0211] In addition, it should be understood that although the present specification is described in terms of embodiments, not every embodiment contains only one independent technical solution, and the description manner of the specification is only for the sake of clarity, and those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can be properly combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for manufacturing a pole piece that can prevent edge shrinkage and curling, characterized in that: The following steps are involved: S1. Slurry preparation: The active material, conductive agent, binder and solvent are mixed evenly, and then dispersed by high-speed shearing to obtain electrode slurry; S2. Gradient coating: Use gradient coating technology to coat the electrode slurry on the current collector, so that the coating thickness in the middle area of ​​the electrode is greater than the coating thickness in the edge area, and the thickness difference between the middle area and the edge area is 2-10μm; S3, pre-drying: pre-dry the coated electrode at a temperature of 60-90°C for 1-3 minutes; S4, calendering treatment: the pre-dried electrode is calendered using a differential speed double-roll pressing process, with a linear speed ratio of the upper roller to the lower roller of 1.02 to 1.10:1 and a calendering temperature of 50 to 120°C; S5, edge modification: coating the edge area of ​​the pole piece with an elasticity enhancer having a thickness of 2 to 8 μm, wherein the elasticity enhancer is mainly composed of an elastic polymer and a conductive material; S6. Secondary drying: The modified electrode is subjected to secondary drying using a step temperature drying method, passing through three temperature zones of 80-100°C, 110-140°C and 50-70°C in sequence, with a total drying time of 5-15 minutes.

2. The method for manufacturing a pole piece capable of preventing edge shrinkage and curling according to claim 1, characterized in that: The high-speed shearing and dispersing treatment in S1 includes: first shearing and dispersing at a rotation speed of 2000-5000 rpm for 10-20 minutes, then shearing and dispersing at a rotation speed of 8000-12000 rpm for 3-8 minutes, and the slurry temperature is controlled at 15-25°C.

3. The method for manufacturing a pole piece capable of preventing edge shrinkage and curling according to claim 1, characterized in that: The gradient coating technology used in S2 is adjustable extrusion coating. The extrusion pressure in the middle of the coating head is smaller than that in the side. The pressure difference between the middle and the side is 0.05-0.2 MPa. The coating speed is 5-15 m / min.

4. The method for manufacturing a pole piece capable of preventing edge shrinkage and curling according to claim 1, characterized in that: The pre-drying in S3 is carried out by combining infrared drying and hot air drying, and the infrared radiation power density is 2-5kW / m 2 , the hot air temperature is 60~90℃, and the wind speed is 0.8~2m / s.

5. The method for manufacturing a pole piece capable of preventing edge shrinkage and curling according to claim 1, characterized in that: The differential double-roll pressing process in S4 also includes: the rolling pressure is gradiently distributed along the width direction, the pressure in the edge area is 80% to 95% of the pressure in the middle area, the total pressure is 5 to 15 kN / cm, and the number of rolling times is 2 to 4.

6. The method for manufacturing a pole piece capable of preventing edge shrinkage and curling according to claim 1, characterized in that: The elasticity enhancer in S5 is made of the following raw materials in parts by weight: 60-80 parts of elastic polymer, 15-30 parts of conductive material, 3-8 parts of dispersant, and 200-300 parts of solvent; the elastic polymer is selected from one or more of polyvinylidene fluoride, polyacrylate, styrene-butadiene rubber, polyurethane, and epoxy resin; the conductive material is selected from one or more of conductive carbon black, graphite, carbon nanotubes, and metal powder.

7. The method for manufacturing a pole piece capable of preventing edge shrinkage and curling according to claim 1, characterized in that: 0.5-3 wt% of a stress buffer is further added to the electrode slurry. The stress buffer is selected from one or more of nano-SiO2, nano-Al2O3, and nano-ZrO2.

8. The method for manufacturing a pole piece capable of preventing edge shrinkage and curling according to claim 1, characterized in that: In the above S2, a tension of 10 to 50 N is applied to the current collector during the coating process, and the angle between the current collector and the coating direction is maintained at 85 to 89 degrees.

9. The method for manufacturing a pole piece capable of preventing edge shrinkage and curling according to claim 1, characterized in that: Before the step S5, the method further includes step S4': edge ultrasonic treatment, using ultrasonic waves with a frequency of 20 to 60 kHz to treat the edge area of ​​the electrode, the treatment time is 1 to 5 seconds, and the ultrasonic power is 50 to 200 W; And / or, after S6, the method further includes step S7: treating the surface of the electrode piece by using plasma, wherein the plasma gas is oxygen or argon, the power is 100 to 300 W, and the treatment time is 10 to 60 seconds.

10. A pole piece capable of preventing edge shrinkage and curling, characterized in that: The electrode is manufactured by the manufacturing method according to any one of claims 1 to 9, wherein the coating thickness in the middle area of ​​the electrode is greater than the coating thickness in the edge area, the thickness difference between the middle area and the edge area is 2 to 10 μm, and the edge area of ​​the electrode is coated with an elasticity enhancer with a thickness of 2 to 8 μm, and the elasticity enhancer is mainly composed of an elastic polymer and a conductive material.

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