Process method for improving dry-method diaphragm wrinkles and lithium ion battery

Abstract

The invention relates to a process method for improving dry-method diaphragm wrinkles and a lithium ion battery. According to the method, collaborative optimization of diaphragm wrinkle elimination, structure protection and infiltration efficiency improvement is realized by sequentially coupling processes such as plasma pretreatment on a diaphragm before winding, dynamic tension-temperature collaborative control during winding, multi-stage gradient hot pressing (combined with ultrasonic vibration) on a core package, multi-step stepped vacuumizing liquid injection during liquid injection and the like; the performance of the lithium ion battery is improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion batteries, specifically to a process method for improving dry-process separator wrinkles and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries have become a key development direction in the lithium-ion battery field due to their advantages such as high energy density, thinness, and flexible shape. However, in the winding or stacking process, the problem of separator wrinkles has long constrained battery performance and safety, especially when using dry-process separators (such as polypropylene and polyethylene materials). Due to the characteristics of the manufacturing process, dry-process separators exhibit significant anisotropy in thermal shrinkage (e.g., the difference between longitudinal (MD) and transverse (TD) shrinkage rates reaches 1% to 3%), and have low surface energy and high porosity (40% to 60%). This makes them susceptible to tension fluctuations, thermal stress, and uneven friction coefficients during the winding process, resulting in local wrinkles or microcracks. These defects not only exacerbate uneven electrolyte wetting but also cause problems such as internal short circuits and lithium plating, severely reducing battery cycle life and safety threshold.

[0003] Traditional improvement methods mainly focus on adjusting process parameters, such as optimizing winding tension or using single-stage hot pressing. However, fixed tension modes are difficult to adapt to the dynamic deformation requirements of the diaphragm, especially in the tab area or corners where stress concentration easily occurs, leading to wrinkle recurrence. While high-temperature hot pressing (e.g., >100℃) can temporarily eliminate macroscopic wrinkles, it may damage the microporous structure of the diaphragm, causing pore collapse or edge warping, which in turn deteriorates the wetting performance. In addition, existing technologies mostly use single process optimization, lacking coordinated control of diaphragm material properties (such as thermal shrinkage rate and surface energy) and equipment parameters, resulting in limited treatment effects and poor process compatibility. For example, although published patent CN116072983 proposes to improve wrinkles through hot pressing, it does not solve the problem of interfacial stress mismatch between the diaphragm and the electrode during hot pressing; another document uses plasma treatment to improve the hydrophilicity of the diaphragm, but ignores the protection of the mechanical strength of the dry-process diaphragm, which can easily cause secondary deformation.

[0004] In lithium-ion battery manufacturing, separator wrinkles are a key issue affecting battery performance and safety. Traditional processes mainly assemble cells through winding or stacking, but due to the characteristics of separator materials (such as the anisotropy of dry-process separators) and process parameters (such as tension and temperature), the separator is prone to wrinkles due to factors such as uneven stress and differences in electrolyte wetting. Specifically, this manifests as: a) Thermal shrinkage anisotropy: Dry-process separators exhibit significant differences in thermal shrinkage rates in the transverse (TD) and longitudinal (MD) directions (TD shrinkage rate 1%–3%, MD shrinkage rate 0.5%–2%), leading to uneven stress release after electrolyte wetting and wrinkle formation. b) Electrolyte wetting defects: Electrolyte (such as DMC) causes localized bulging of the separator under capillary action, while residual gas forms bubbles, further exacerbating wrinkles. c) Insufficient process tension control: Traditional fixed tension modes cannot adapt to dynamic winding processes, especially in the tab area where stress concentration easily occurs, leading to wrinkle recurrence. In existing technologies, methods to improve separator wrinkles mostly focus on adjusting a single process parameter. For example: 1. Tension optimization: Fixed tension control reduces diaphragm stretching deformation, but it is difficult to adapt to dynamic winding processes, especially stress concentration in the tab area; 2. Hot pressing: High-temperature hot pressing (>100℃) eliminates macroscopic wrinkles, but it easily damages the diaphragm microporous structure, leading to pore collapse or edge warping; 3. Surface modification: Plasma treatment improves the hydrophilicity of the diaphragm, but it does not solve the problems of mechanical strength loss and secondary deformation during the treatment process. 4. During the electrolyte injection process, traditional single-stage vacuuming can easily lead to diaphragm displacement or worsening of local wrinkles due to sudden pressure changes. This is especially true for dry-process diaphragms, which, due to their high porosity (40%–60%) and low surface energy, make it difficult for the electrolyte to quickly wet the pores. Residual air bubbles can exacerbate uneven stress on the diaphragm. 5. Electrolyte pre-wetting and constraint force formation: Microscopic wrinkles are repaired through pre-wetting with a low-viscosity electrolyte, and constraint forces (such as clamp torque of 0.1–5 N·m) are applied during the formation stage to maintain diaphragm flatness. This process has a long cycle: pre-wetting requires 30–60 minutes of resting time, and the formation stage requires staged charging (totaling over 8 hours), reducing production efficiency. Battery volume increases: adding an elastic layer (such as 0.5–2 mm thick) may sacrifice battery energy density. However, all of the above methods have limitations: traditional hot-pressing and electrolyte injection processes struggle to balance wrinkle elimination and structural protection; single parameter adjustments cannot synergistically control diaphragm thermal shrinkage, surface energy, and dynamic stress. Therefore, there is an urgent need for a multi-dimensional synergistic process that can eliminate wrinkles while maintaining the integrity of the membrane structure and efficient electrolyte wetting. Summary of the Invention

[0005] To address the problems of material damage, poor process compatibility, and insufficient long-term performance in existing diaphragm wrinkle improvement processes, this invention relates to a multi-dimensional synergistic treatment process for improving dry-process diaphragm wrinkles. This process is achieved by coupling the processes of diaphragm plasma pretreatment, dynamic tension-temperature synergistic control (for diaphragms that have been wound or stacked), multi-level gradient hot pressing shaping, and multi-step stepped vacuum injection on diaphragms.

[0006] The diaphragm plasma pretreatment includes: performing double-sided plasma treatment on the diaphragm in a low humidity environment to reduce the surface friction coefficient, and using ion wind to eliminate static electricity; The diaphragm is one of the following: dry-process PP, dry-process PE, coated diaphragm, or ceramic diaphragm.

[0007] In the diaphragm plasma pretreatment, the low humidity environment is ≤5%, the power of the double-sided plasma treatment of the diaphragm is 50-100W, the time is 5-15s, the surface friction coefficient is reduced from 0.35 to 0.15-0.2, and the surface voltage of the ion wind to eliminate static electricity is ≤50V.

[0008] Dynamic tension-temperature coordinated control includes: adjusting the tension according to the real-time temperature of the diaphragm during the winding process, with segmented tension control used in the tab area. Further, the dynamic tension-temperature coordinated control includes: adjusting the tension according to the real-time temperature of the diaphragm during the winding process as follows: predicting the tab position based on the diaphragm displacement length feedback from the encoder, and reducing the winding tension from the reference value (F_base) to the tab area tension value (F_tab) by 30%-50% before the tab arrives. The tension reduction process is completed within 100-200ms. The diaphragm temperature T_web is monitored in real-time using an infrared thermometer, and the reference value (F_base) and / or the tab area tension value (F_tab) are compensated in real-time based on the temperature value. The compensation coefficient (k) is 0.01-0.03 / ℃, and F_actual=F_set. [1-k [(T_web-T_room)], F_set is the currently set target tension temperature, and T_room is the ambient room temperature (e.g., 25°C). For every 5°C increase, the tension decreases by 0.2N, and the tension in the tab area decreases by 30% to 50%.

[0009] The multi-stage gradient hot pressing forming process includes: hot pressing forming of the wound or stacked core package: Phase 1: Low-temperature pre-compression to eliminate macroscopic wrinkles; The second stage is high-temperature shaping, which uses a porous silicone pressure plate and combines ultrasonic vibration to disperse pressure, while simultaneously using air cooling to lock in the shape.

[0010] Furthermore, in the multi-stage gradient hot pressing shaping process, the first stage low-temperature pre-pressing conditions are: 60-70℃, 0.3~0.5MPa, 3~5s, to eliminate macroscopic wrinkles; the second stage high-temperature shaping conditions are: 90~110℃, 0.8~1.2MPa, 8~12s, using a porous silicone pressure plate with a pore size of 50~200μm and a porosity of 30%-60%, combined with ultrasonic vibration of 20~40kHz to disperse pressure, and simultaneously using air cooling at a rate ≥10℃ / s to lock the shape.

[0011] The multi-step step vacuum injection process includes: 1) pre-vacuuming; 2) secondary step vacuuming; 3) gradient recovery to normal pressure.

[0012] Furthermore, the multi-step stepped vacuum injection process includes the following steps: 1) Pre-vacuuming: The vacuum level is reduced from atmospheric pressure to -50 kPa in three steps, from -20 kPa to -35 kPa to -50 kPa, with each step held for 2 to 3 minutes, gradually removing air from the battery cell; The initial electrolyte injection volume is 40% to 50% of the total electrolyte volume, and pressure-maintaining permeation is performed; after injection, the vacuum degree is adjusted back to -10 kPa and maintained for 5 to 8 minutes. 2) Secondary step vacuuming: Parameters: The vacuum level is reduced to -70 kPa in two steps by operating from -50 kPa to -60 kPa to -70 kPa, with each step held for 1 to 2 minutes; when the vacuum level reaches -70 kPa, the remaining electrolyte is injected. 3) Gradient recovery to normal pressure: The pressure is gradually restored to normal at a rate of 10 kPa / min, in three stages: from -70 kPa to -40 kPa to -10 kPa to 0 kPa; the diaphragm and the electrode are gradually bonded together by slowly releasing the pressure.

[0013] This invention also relates to the application of the above-mentioned process for improving dry-process separator wrinkles in lithium-ion batteries, wherein the lithium-ion battery is one of a pouch battery or a square aluminum-cased battery.

[0014] The process method for improving dry-process separator wrinkles described in this invention achieves synergistic optimization of separator wrinkle elimination, structural protection and wetting efficiency improvement through process coupling including separator plasma pretreatment, dynamic tension-temperature coordinated control, multi-level gradient hot pressing shaping and multi-step step vacuum injection. It breaks through the technical bottleneck of adjusting a single process parameter and provides a low-cost and highly compatible solution for the manufacturing of high-consistency soft-pack batteries.

[0015] This invention provides a multi-stage synergistic process that solves the wrinkling problem of dry-process membranes through the dynamic coupling of physical treatment and chemical modification. Specifically, it may include the following steps: 1. Diaphragm plasma pretreatment: Under low humidity environment (humidity ≤5%), the diaphragm is subjected to double-sided plasma treatment (power 50~100W, time 5~15s) to reduce the surface friction coefficient (from 0.35 to 0.15~0.2), and static electricity is eliminated by ion wind (surface voltage ≤50V). The diaphragm can be one of the following: dry PP, dry PE, coated diaphragm, ceramic diaphragm, etc.

[0016] 2. Dynamic tension-temperature coordinated control: During the winding process, the tension is adjusted according to the real-time temperature of the diaphragm fed back by the infrared thermometer (the tension is reduced by 0.2N for every 5°C increase in temperature), and segmented tension control is adopted in the tab area (reduced by 30% to 50%). 3. Multi-stage gradient hot pressing shaping Hot pressing is performed on the core package after winding or stacking: First stage: Low temperature pre-compression (60-70℃, 0.3-0.5MPa, 3-5s) to eliminate macroscopic wrinkles; The second stage: high temperature setting (90~110℃, 0.8~1.2MPa, 8~12s), using a porous silicone pressure plate (pore diameter 50~200μm, porosity: 30%-60%) combined with ultrasonic vibration (20~40kHz) to disperse pressure, and simultaneously air cooling (rate ≥10℃ / s) to lock in the shape; The equipment structure is as follows: 1) Multi-hole pressure plate design Materials and Pore Structure: Porous pressure plates are typically made of high-temperature resistant, high-thermal-conductivity materials (such as porous silicone, ceramics, or metal alloys), and their pore structure design must meet the following requirements: Aperture range: 50-200μm, ensuring uniform pressure distribution while preventing material collapse; Porosity: 30%-60%, balancing air permeability and mechanical strength; Surface treatment: Adjusting the surface hydrophilicity / hydrophobicity through plasma treatment or coating technology to optimize contact characteristics with materials.

[0017] Functional positioning: The porous pressure plate is mainly used to disperse pressure, promote gas discharge, and serve as a transmission medium for ultrasonic vibration.

[0018] The optimal parameters for the porous silicone pressure plate used in the experimental verification of this invention are as follows: The pressure plate is made of high-temperature vulcanized silicone rubber with a pore size of 180μm, a porosity of 50%, and a hardness of 40-50 Shore A. The surface of the pressure plate is covered with a PTFE (Teflon) non-stick coating. The coating is formed on the silicone surface by spraying or impregnation, resulting in a 15±3μm PTFE coating, which is then cured at high temperature.

[0019] 2) Ultrasonic vibration system Ultrasonic generator: usually integrated inside or outside the pressure plate, with a frequency range of 20-40kHz, preferably 35kHz, and the power is selected according to the material properties (e.g., 1800W-3000W).

[0020] Vibration transmission path: Ultrasonic waves are transmitted to the material surface through the gaps in the pressure plate, forming high-frequency micro-vibrations, which excite the material molecules to generate heat through friction, and at the same time, non-contact pressure is achieved through sound wave pressure.

[0021] Collaborative control: The ultrasonic and hot-press parameters are linked and controlled through a PLC or LabVIEW system to ensure dynamic matching of vibration intensity with temperature and pressure.

[0022] 4. Multi-step stepped vacuum injection 1) Pre-vacuuming stage: Parameters: The vacuum level is gradually reduced from atmospheric pressure to -50 kPa in three stages (-20 kPa → -35 kPa → -50 kPa), with each stage held for 2–3 minutes. This gradually removes air from the cell, reducing gas resistance between the separator and the electrode, and preventing the separator from stretching and deforming due to instantaneous negative pressure.

[0023] Initial injection + pressure-maintaining permeation: Injection volume: 40% to 50% of the total electrolyte volume (viscosity ≤ 2.5 cP).

[0024] Vacuum control: After injection, the vacuum level is adjusted back to -10 kPa and maintained for 5~8 minutes.

[0025] Mechanism: Under low pressure, the electrolyte diffuses rapidly through the capillary action of the diaphragm pores, while the negative pressure inhibits the accumulation of bubbles on the diaphragm surface.

[0026] 2) Secondary step vacuuming: Parameters: The vacuum level is reduced to -70 kPa in two steps (-50 kPa → -60 kPa → -70 kPa), and the holding time for each step is 1 to 2 minutes.

[0027] Synchronous action: When the vacuum reaches -70kPa, inject the remaining electrolyte (50%~60%).

[0028] The high pressure differential stage of electrolyte injection utilizes the "pressure differential drive" effect to promote the penetration of electrolyte into the deep layers of the diaphragm; the step-down pressure reduction avoids the diaphragm from rebounding and wrinkling due to a sudden drop in pressure.

[0029] 3) Gradient recovery to normal pressure: Parameters: The pressure is gradually restored to normal at a rate of 10 kPa / min, in three stages (-70 kPa → -40 kPa → -10 kPa → 0 kPa). Slow pressure release allows the diaphragm and electrode to gradually adhere, reducing interfacial stress concentration.

[0030] The lithium-ion battery described in this invention can be one of a pouch battery, a square aluminum-cased battery, etc.

[0031] Beneficial effects: This invention provides a multi-dimensional synergistic treatment process for improving wrinkles in dry-process diaphragms. This process is achieved through the coupling of several steps, including diaphragm plasma pretreatment, dynamic tension-temperature synergistic control, multi-level gradient hot-pressing shaping, and multi-step stepped vacuum injection. The resulting technical effects are as follows: 1. Balancing wrinkle elimination and structural protection: Overcoming the problems of membrane micropore collapse or edge warping caused by high temperature and high pressure in traditional hot pressing processes, non-contact pressure is applied by combining low-temperature multi-stage hot pressing (such as 60-110℃ gradient temperature control) with ultrasonic vibration (20-40kHz) to eliminate macroscopic wrinkles while maintaining the integrity of the membrane pore structure.

[0032] 2. Dynamic stress coordination control: This solves the problem of wrinkle recurrence caused by stress concentration in the tab area during the winding process in the fixed tension mode. Through temperature-tension linkage adjustment (e.g., reducing tension by 0.2N for every 5℃ increase in temperature) and segmented tension control (reducing tension in the tab area by 30% to 50%), it adapts to the anisotropic characteristics of diaphragm thermal shrinkage and achieves dynamic stress balance.

[0033] 3. Improve electrolyte wetting efficiency: Overcome the defect of uneven wetting caused by the low surface energy of the diaphragm in the traditional process. By introducing polar groups (such as -OH, -COOH, etc.) on the diaphragm surface through plasma pretreatment (power 50-100W, time 5-15s), the contact angle is reduced from 130° to 25°. Combined with porous platen gradient hot pressing and multi-step stepped vacuum injection, the pore filling rate is ≥98%.

[0034] 4. Adaptation of process cost and scale: By avoiding the limitations of existing high-cost technologies (such as plasma coating and multi-layer hot pressing equipment modification), through modular design (such as ultrasonic vibration integrated into the multi-hole pressure plate), PLC dynamic parameter control and conventional production line compatibility optimization (such as no need to add complex equipment), the process modification cost is reduced by more than 40%, and the yield rate is increased to 96%.

[0035] In summary, the process method for improving separator wrinkles described in this invention sequentially couples together processes such as plasma pretreatment of the separator before winding / stacking, dynamic tension-temperature coordinated control during winding, multi-level gradient hot pressing of the core pack (combined with ultrasonic vibration), and multi-step stepped vacuum injection during liquid injection. This achieves synergistic optimization of separator wrinkle elimination, structural protection, and improved wetting efficiency, thereby improving the performance of lithium-ion batteries. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 This is a process flow diagram related to Embodiment 1 of this application. Detailed Implementation

[0038] To facilitate understanding of the present invention, various exemplary embodiments of the present invention are now described in detail. This detailed description should not be regarded as a specific limitation of the present invention, but should be understood as a more detailed description of certain aspects, features and embodiments of the present invention.

[0039] Example 1: Taking a 50Ah pouch cell (positive electrode LFP + negative electrode graphite, dry-process PP separator, thickness 16μm, porosity 50%) as an example: 1. Plasma treatment parameters: power 80W, time 10s; 2. Winding tension control: During normal winding, the tension is maintained at 1.5N. When the encoder detects that the tab is about to arrive, the PLC triggers a command, and the tension smoothly decreases from 1.5N to 0.8N (a reduction of about 47%) within 150ms. At the same time, the infrared thermometer detects that the temperature of the diaphragm at the tab has risen to 40℃. The system finally controls the real-time tension in the tab area at 0.56N. After the tab passes, the tension smoothly returns to 1.5N. 3. Hot pressing parameters: First stage 65℃ / 0.4MPa / 4s; Second stage 100℃ / 1.0MPa / 10s, ultrasonic vibration 25kHz.

[0040] 4. Multi-step stepped vacuum injection: Pre-vacuuming: atmospheric pressure → -20 kPa (hold for 2 min) → -35 kPa (hold for 2.5 min) → -50 kPa (hold for 3 min); Initial injection: Inject 22.5 mL of electrolyte (45% of the total injection volume), and maintain the pressure at -10 kPa for 6 min; Secondary vacuuming: -50kPa → -60kPa (1min) → -70kPa (1.5min), while simultaneously injecting the remaining 27.5mL of electrolyte; Pressure relief: Pressure relief was carried out in three stages at a rate of 10 kPa / min: -70 kPa → -40 kPa → -10 kPa → 0 kPa, with a total time of 7 minutes.

[0041] The testing method is as follows (the same applies below): The electrolyte wetting process was monitored using the dynamic impedance method. The cell internal resistance was continuously monitored at a frequency of 1 kHz using an external electrochemical workstation (Gamry Reference 3000). The time required for the internal resistance to decrease and stabilize to within 105% of its final value was recorded as the complete wetting time. The test was conducted at a constant temperature of 25°C.

[0042] To quantify the uniformity of electrolyte distribution, non-destructive testing of the battery cells after impregnation was performed using X-ray imaging. Two-dimensional images of the battery cells were acquired using an X-ray CT system at 100 kV, 8 μA, and 1 μm resolution. The core region of the battery cell was divided into a 5×5 grid using ImageJ software, and the average grayscale value of each grid was extracted. The relative standard deviation (RSD) of these grayscale values ​​was calculated, and the uniformity was determined using the formula: Uniformity (%) = (1 - RSD) The calculation yields 100% accuracy in determining the electrolyte distribution uniformity. Simultaneously, it can acquire three-dimensional images of the battery cell, observe the state of the diaphragm in all two-dimensional virtual cross-sections, and determine the diaphragm wrinkling situation.

[0043] The battery cell after liquid injection in the example was disassembled, the diaphragm was cleaned and dried by DMC, and the contact angle was tested with an optical contact angle meter. The test standard refers to GB / T 30693-2014. The finished battery cells undergo the following performance tests: 1) 25℃ storage test: stored at 25±2℃ for 28 days at 100% SOC, and the retention rate is tested. 2) 25℃ cycle test: charged at 1C current with constant current and constant voltage to the upper limit voltage, cut off current 0.05C, rested for 30 minutes, discharged at 1C current with constant current to the lower limit voltage, and the cycle capacity retention rate is recorded. The cell thickness is tested after 100 cycles, and the cycle expansion rate is recorded.

[0044] The finished battery cells are subjected to a needle penetration test: a 5Φmm high-temperature resistant steel needle (with a cone angle of 45°~60° at the needle tip, and a smooth surface free of rust, oxide layer and oil) is used to penetrate a single cell at a speed of (25±5) mm / s from a direction perpendicular to the battery plates (the steel needle remains in the single cell). The cell is observed for 1 hour. The tested battery is considered qualified if it does not explode or catch fire.

[0045] Test results: The diaphragm contact angle decreased from 130° to 25°, X-ray inspection showed zero wrinkles in the diaphragm, electrolyte distribution uniformity >95%, electrolyte complete immersion time 45 min, retention rate 98% after 28 days of storage at 25℃, capacity retention rate 94% after 500 cycles, expansion rate ≤1.5%, and needle penetration test pass rate 100%.

[0046] Comparative Example 1: Taking a 50Ah pouch cell (positive electrode LFP + negative electrode graphite, dry-process PP separator, thickness 16μm, porosity 50%) as an example: No plasma pretreatment; Winding tension control: Fixed tension 1.5N (adjustable in the stepless tab area); Single-stage hot pressing: 90℃ / 0.8MPa / 10s; Traditional single-stage vacuum injection: directly vacuum to -70 kPa, maintain for 5 min; inject all electrolyte (44 mL); directly restore to normal pressure (time < 1 min).

[0047] Test results: X-ray inspection showed a wrinkle rate of 12% and obvious warping in the tab area; the electrolyte was fully wetted for 120 minutes, the contact angle remained at 95°, the retention rate was 94% after 28 days of storage at 25°C, the capacity retention rate was 87% after 500 cycles at 1C, and the expansion rate was 3.8%.

[0048] Comparative Example 2: Taking a 50Ah pouch cell (positive electrode LFP + negative electrode graphite, dry-process PP separator, thickness 16μm, porosity 50%) as an example: Plasma pretreatment: power 80W, time 10s; Winding tension control: Fixed tension 1.5N (adjustable in the stepless tab area); Single-stage hot pressing: 90℃ / 0.8MPa / 10s; Traditional single-stage vacuum injection: directly vacuum to -70 kPa, maintain for 5 min; inject all electrolyte (44 mL); directly restore to normal pressure (time < 1 min).

[0049] Test results: X-ray inspection showed a wrinkle rate of 10% and obvious warping in the tab area; the electrolyte was fully wetted for 100 minutes, the contact angle was 55°, the retention rate was 94.6% after 28 days of storage at 25℃, the capacity retention rate was 88.5% after 500 cycles at 1C, and the expansion rate was 3.2%.

[0050] Comparative Example 3: Taking a 50Ah pouch cell (positive electrode LFP + negative electrode graphite, dry-process PP separator, thickness 16μm, porosity 50%) as an example: Plasma pretreatment: power 80W, time 10s; Winding tension control: Same as in Example 1, the reference tension is 1.5N, and the tension in the tab area is 0.8N; Single-stage hot pressing: 90℃ / 0.8MPa / 10s; Traditional single-stage vacuum injection: directly vacuum to -70 kPa and hold for 5 minutes; Inject all electrolyte (44 mL); restore atmospheric pressure directly (time < 1 min).

[0051] Test results: X-ray inspection showed a wrinkle rate of 6% and no obvious warping in the tab area; the electrolyte complete wetting time was 96 min, the contact angle was 55°, the retention rate was 95.2% after 28 days of storage at 25℃, the capacity retention rate was 90% after 500 cycles at 1C, and the expansion rate was 2.8%.

[0052] Comparative Example 4: Taking a 50Ah pouch cell (positive electrode LFP + negative electrode graphite, dry-process PP separator, thickness 16μm, porosity 50%) as an example: Plasma pretreatment: power 80W, time 10s; Winding tension control: Same as in Example 1, the reference tension is 1.5N, and the tension in the tab area is 0.8N; Multi-stage hot pressing: Hot pressing parameters: First stage 65℃ / 0.4MPa / 4s; Second stage 100℃ / 1.0MPa / 10s, ultrasonic vibration 25kHz.

[0053] Traditional single-stage vacuum injection: directly vacuum to -70 kPa, maintain for 5 min; inject all electrolyte (44 mL); directly restore to normal pressure (time < 1 min).

[0054] Test results: X-ray inspection showed a wrinkle rate of 4%, a complete electrolyte wetting time of 80 min, a residual contact angle of 45°, a retention rate of 96.4% after 28 days of storage at 25℃, a capacity retention rate of 92% after 500 cycles at 1C, and an expansion rate of 2.2%.

[0055] Table 1 Comparison of Test Data

[0056] Table 1 shows that when manufacturing lithium-ion batteries using the processes of Example 1, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4, the total injection time, separator wrinkle rate, electrolyte uniformity, lithium-ion battery internal resistance, storage retention rate, 1C cycle capacity retention rate, and cell expansion rate after 500 cycles are all superior to those of Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4. With the superposition and coupling of multiple processes, separator wrinkles and performance are significantly improved. Through the process coupling of plasma pretreatment, dynamic tension-temperature synergistic control, multi-level gradient hot pressing, and multi-step stepped vacuum injection, the synergistic optimization of separator wrinkle elimination, structural protection, and wetting efficiency improvement is achieved, thus enhancing the performance of lithium-ion batteries.

[0057] Obviously, the above embodiments are merely examples for clear illustration and are not intended to limit the embodiments. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all embodiments here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A process for improving wrinkles in dry-process diaphragms, characterized in that, This is achieved by coupling processes including plasma pretreatment, multi-level gradient hot pressing and shaping, and multi-step stepped vacuum injection for diaphragms that are wound or stacked. For wound diaphragms, a dynamic tension-temperature coordinated control process is also included between plasma pretreatment and multi-level gradient hot pressing and shaping.

2. The process method for improving dry-process diaphragm wrinkles as described in claim 1, characterized in that, The diaphragm plasma pretreatment includes: performing double-sided plasma treatment on the diaphragm in a low humidity environment to reduce the surface friction coefficient, and using ion wind to eliminate static electricity; The diaphragm is one of the following: dry-process PP, dry-process PE, coated diaphragm, or ceramic diaphragm.

3. The process method for improving dry-process diaphragm wrinkles as described in claim 2 is further characterized in that, in the diaphragm plasma pretreatment, the low humidity environment is ≤5%, the power of the double-sided plasma treatment of the diaphragm is 50-100W, the time is 5-15s, the surface friction coefficient is reduced from 0.35 to 0.15-0.2, and the surface voltage for ion wind to eliminate static electricity is ≤50V.

4. The process method for improving wrinkles in dry-process diaphragms as described in claim 1, characterized in that, Dynamic tension-temperature coordinated control includes: adjusting the tension according to the real-time temperature of the diaphragm during the winding process, and using segmented tension control in the tab area.

5. The process method for improving dry-process diaphragm wrinkles as described in claim 4, further characterized in that the dynamic tension-temperature coordinated control includes: During the winding process, the tension is adjusted according to the real-time temperature of the diaphragm as follows: for every 5°C increase in temperature, the tension is reduced by 0.2N, and the tension in the tab area is reduced by 30% to 50%.

6. The process method for improving dry-process diaphragm wrinkles as described in claim 1, characterized in that, The multi-stage gradient hot pressing forming process includes: hot pressing forming of the wound or stacked core package: Phase 1: Low-temperature pre-compression to eliminate macroscopic wrinkles; The second stage is high-temperature shaping, which uses a porous silicone pressure plate and combines ultrasonic vibration to disperse pressure, while simultaneously using air cooling to lock in the shape.

7. The process method for improving dry-process diaphragm wrinkles as described in claim 6, further characterized in that, in the multi-stage gradient hot pressing shaping process, the first stage low-temperature pre-pressing conditions are: 60-70℃, 0.3-0.5MPa, 3-5s, to eliminate macroscopic wrinkles; the second stage high-temperature shaping conditions are: 90-110℃, 0.8-1.2MPa, 8-12s, using a porous silicone pressure plate with a pore size of 50-200μm and a porosity of 30%-60%, combined with ultrasonic vibration of 20-40kHz to disperse pressure, and simultaneously using air cooling at a rate ≥10℃ / s to lock the shape.

8. The process method for improving dry-process diaphragm wrinkles as described in claim 1, characterized in that, The multi-step step vacuum injection process includes: 1) pre-vacuuming; 2) secondary step vacuuming; 3) gradient recovery to normal pressure.

9. The process method for improving dry-process diaphragm wrinkles as described in claim 8, further characterized in that the multi-step stepped vacuum injection process includes the following steps: 1) Pre-vacuuming: The vacuum level is reduced from atmospheric pressure to -50 kPa in three steps, from -20 kPa to -35 kPa to -50 kPa, with each step held for 2 to 3 minutes, gradually removing air from the battery cell; The initial electrolyte injection volume is 40% to 50% of the total electrolyte volume, and pressure-maintaining permeation is performed; after injection, the vacuum degree is adjusted back to -10 kPa and maintained for 5 to 8 minutes. 2) Secondary step vacuuming: Parameters: The vacuum level is reduced to -70 kPa in two steps by operating from -50 kPa to -60 kPa to -70 kPa, with each step held for 1 to 2 minutes; when the vacuum level reaches -70 kPa, the remaining electrolyte is injected. 3) Gradient recovery to normal pressure: The pressure is gradually restored to normal at a rate of 10 kPa / min, in three stages: from -70 kPa to -40 kPa to -10 kPa to 0 kPa; the diaphragm and the electrode are gradually bonded together by slowly releasing the pressure.

10. The application of the process for improving dry-process separator wrinkles as described in any one of claims 1-9 in a lithium-ion battery, wherein the lithium-ion battery is a pouch battery or a square aluminum-cased battery.

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