Battery positive electrode with low impedance and high liquid absorption performance and preparation method thereof

Abstract

The invention discloses a battery positive electrode with low impedance and high liquid absorption performance and a preparation method thereof, and the preparation method comprises the following steps: slurry pretreatment is matched with coating parameters, the viscosity of the slurry is adjusted to 4000-6000 mPa.s, and the coating speed and the viscosity meet the relation V = K / eta; preheating and homogenizing, wherein infrared radiation heating and hot air circulation are adopted; step-by-step gradient drying, including high-temperature rapid drying, medium-temperature drying and low-temperature stable drying; annealing treatment; and plasma surface modification. Compared with the prior art, by scientifically matching coating parameters, accurately controlling the drying process and optimizing the surface characteristics, the prepared positive electrode has the advantages that the crack length density is smaller than or equal to 0.15%, the interface impedance is smaller than or equal to 10 omega.cm, the electrolyte contact angle is smaller than or equal to 15 degrees, and the positive electrode has the advantages of low impedance and high liquid absorption performance, so that the cycle life of the battery is effectively prolonged.

Description

Technical Field

[0001] The present invention belongs to the technical field of the preparation of the positive electrode of lithium - ion batteries, and particularly relates to a battery positive electrode with low impedance and high liquid absorption performance and a preparation method thereof. Background Art

[0002] With the rapid development of the new energy vehicle industry, as one of the core power sources of new energy vehicles, the performance of lithium - ion batteries directly affects the cruising range and safety of vehicles. Among them, as a key component of lithium - ion batteries, the quality of the coating of the positive electrode material has a decisive impact on the cycle life, energy density and safety of the battery. During the positive electrode manufacturing process, it is usually necessary to uniformly coat a high - solid - content positive electrode slurry on an aluminum foil substrate, and then go through multiple drying processes to remove solvents (such as N - methylpyrrolidone, NMP). However, with the increasing requirements for battery energy density and production efficiency, the coating speed has been continuously increased to 30 m / min and above, resulting in the formation of criss - cross micro - cracks in the coating during the drying process (as shown in Figure 1 ). These cracks not only increase the interface impedance of the battery, reduce the wettability of the electrolyte, but also significantly increase the scrap rate of the positive electrode sheet. Industry statistics show that the scrap rate of positive electrode sheets caused by cracks is as high as 5% - 8%, seriously restricting the large - scale production of high - consistency batteries.

[0003] The formation of cracks is mainly attributed to the mismatch of drying kinetics, uneven temperature field, and the mismatch between the rheological properties of the slurry and the coating process. The traditional constant - temperature and high - wind - speed drying method causes a hard shell to form rapidly on the surface layer of the coating, hindering the escape of internal solvents and leading to the accumulation of internal stress; the temperature difference fluctuation in each section of the oven is large, resulting in uneven heating of the positive electrode sheet and inducing shear cracks; under the condition of high - speed coating of high - solid - content positive electrode slurry, the traditional mode of linearly adjusting the coating speed and viscosity cannot effectively ensure the leveling property of the coating. In addition, existing solutions such as simply adjusting oven parameters, hierarchical drying design, and slurry formula optimization all have common defects such as passive regulation, the contradiction between efficiency and quality, and insufficient technical synergy, making it difficult to comprehensively and effectively solve the crack problem.

[0004] Therefore, there is an urgent need to develop a new positive electrode preparation method that integrates slurry rheological adaptation, gradient drying stress control, and intelligent compensation to improve the integrity of the coating, reduce the battery interface impedance, and improve the wettability of the electrolyte, so as to meet the urgent needs of the new energy vehicle industry for high - performance lithium - ion batteries. Summary of the Invention

[0005] The purpose of the present invention is: aiming at the deficiencies of the prior art, to provide a preparation method of a battery positive electrode with low impedance and high liquid absorption performance, which can effectively prevent cracks from occurring on the surface of the positive electrode coating, thereby reducing the battery interface impedance and improving the wettability of the electrolyte.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A method for preparing a battery positive electrode with low impedance and high liquid absorption performance comprises the following steps:

[0008] S1. Slurry pretreatment and coating parameter adaptation: The positive electrode slurry is sheared and dispersed to adjust the slurry viscosity to 4000~6000 mPa·s; and the coating speed V (m / min) and the slurry viscosity η (mPa·s) satisfy the relationship: V= ‌K / ‌η, where K is a constant, and its value is (1.0~2.0)*10 5 , the unit is mPa·s·m / min; S2. Preheating and homogenizing treatment: after coating, the positive electrode sheet enters the preheating chamber and is pretreated in a composite mode of infrared radiation heating and hot air circulation, with a preheating temperature of 75~85℃, a relative humidity of 30%~50%, and a time of 20~40 s; S3. Segmented gradient drying: after preheating and homogenizing treatment, the positive electrode sheet enters the following three drying zones in sequence:

[0009] The first stage: temperature 90~100℃, wind speed 3~5m / s, time 10~20s, solvent volatilization rate is 50%~60% of the total solvent content;

[0010] The second stage: temperature 75~85℃, wind speed 1~3m / s, time 30~50s;

[0011] The third stage: temperature 60~70℃, wind speed 0.5~1 m / s, time 20~30s, final solvent residue ≤200 ppm;

[0012] S4. Annealing: Annealing is performed under nitrogen protection at a temperature of 120-150°C for 10-20 min at a heating rate of ≤5°C / min.

[0013] S5. Plasma surface modification: The surface of the positive electrode is treated with a mixed gas plasma of argon and oxygen, with a plasma power of 300~500 W and a treatment time of 30~60 s.

[0014] Furthermore, the shearing and dispersing treatment in S1 includes three levels of speed adjustment, namely 2000 rpm, 2500 rpm, and 3000 rpm, and the total treatment time is 30-60 min.

[0015] Furthermore, the wavelength of the infrared radiation in S2 is 2~5 μm, the hot air circulation speed is 0.5~1 m / s, and the solvent volatilization rate during the preheating process is 0.05~0.1 g / (m²·s).

[0016] Further, a periodic negative pressure is applied in the second stage of S3, with the negative pressure ranging from -10 to -5 kPa, the frequency ranging from 0.8 to 1 Hz, and the negative pressure fluctuation range ≤ ±0.5 kPa.

[0017] Further, the total drying time of S3 is controlled within 80 - 100 s, and the temperature gradient difference from the first stage to the third stage ≥ 15°C.

[0018] Further, the nitrogen flow rate during the annealing treatment in S4 is 5 - 10 L / min, and the residual stress of the coating after annealing ≤ 1 MPa.

[0019] Further, the volume mixing ratio of argon to oxygen in S5 is 4:1. After plasma treatment, nano - scale pores with a size of 50 - 200 nm are formed on the coating surface, and the electrolyte contact angle ≤ 15°.

[0020] Further, it further includes step S6. On - line stress detection and compensation: The internal stress of the coating is monitored in real - time. When the local stress ≥ 5 MPa, the temperature or negative pressure intensity in the drying section is dynamically adjusted, and the response time ≤ 1 s.

[0021] Further, in S6, the stress is monitored by a laser Doppler vibrometer with a resolution of 0.1 μm. The temperature range for dynamic adjustment is ±5°C, and the negative pressure adjustment intensity is ±2 kPa.

[0022] Further, the positive active material of the positive electrode paste in S1 is LiNi 0.8 Co 0.1 Mn 0.1 O2, the binder is PVDF, the conductive agent is conductive carbon black, and the solid content of the paste is 60% - 80%.

[0023] In addition, the present invention also provides a battery positive electrode, which is prepared by the preparation method of the battery positive electrode with low impedance and high liquid absorption performance as described above.

[0024] Compared with the prior art, the present invention has at least the following beneficial effects:

[0025] 1) In the present invention, through the slurry adaptation control (S1), the slurry viscosity is adjusted to an appropriate range to ensure good fluidity and leveling property of the slurry during high - speed coating, avoiding the appearance of ripples or unevenness on the coating surface; by establishing a quantitative relationship between the coating speed and the slurry viscosity through a formula, the coating thickness during the coating process is uniform, reducing coating defects caused by the mismatch between speed and viscosity; different from the traditional linear adjustment mode, the present invention guides the setting of coating parameters with a quantitative formula, can adjust the coating speed according to the real - time change of the slurry viscosity, realizes the active control of the coating quality, avoids the problem of deteriorated leveling property in traditional linear adjustment, reduces the coating thickness deviation, and reduces the stress concentration source.

[0026] 2) Through the preheating and homogenization treatment (S2) of the present invention, infrared radiation can penetrate deep into the coating, with uniform heating, accelerating the volatilization of solvents on the surface and inside of the coating, avoiding the situation that the surface forms a film too quickly, which makes it difficult for the internal solvents to escape; under the control of relative humidity, it prevents stress concentration caused by the coating drying too quickly, reducing the risk of crack generation; the preheating process promotes the rearrangement and densification of particles in the slurry, improving the mechanical strength and adhesion of the coating. At the same time, the preheating temperature is adjusted to 75 - 85 °C, forming a gentle transition with the subsequent first-stage drying temperature, avoiding the accumulation of thermal stress caused by sudden temperature changes.

[0027] 3) Through the segmented gradient drying (S3) of the present invention, the drying area is divided into three segments, with different temperatures, wind speeds and times set respectively. At the same time, periodic negative pressure is applied in the second segment. By controlling the temperature gradient of each drying segment, it avoids the generation of thermal stress in the coating due to sudden temperature changes, thereby reducing the formation of cracks, and the temperature gradient design enables the solvents inside the coating to volatilize gradually and evenly, avoiding solvent residue and the accumulation of internal stress; among them, the first-stage high-temperature rapid drying quickly removes the surface solvents, enabling the coating to form a preliminary solidification; the second-stage medium-temperature drying enables the solvents inside the coating to volatilize evenly; the third-stage low-temperature stable drying finally removes the residual solvents (residual amount ≤ 200 ppm), enabling the coating to reach a stable state.

[0028] 4) Through the annealing treatment (S4) of the present invention, the annealing process further releases the residual stress in the coating, significantly improving the mechanical stability of the coating; annealing can promote the perfection of the lattice of the active material, reduce material defects, and improve the electrochemical performance; annealing under nitrogen protection avoids oxidation reactions at high temperatures, maintaining the purity and stability of the cathode material; a slow heating rate (≤ 5 °C / min) ensures that the cathode sheet is heated evenly, preventing thermal stress and material structure damage caused by too rapid temperature rise.

[0029] 5) Through the plasma surface modification (S5) of the present invention, oxygen plasma etching forms hydrophilic nano-pores, argon ion bombardment eliminates the residual stress on the surface layer, and plasma treatment forms nano-scale pores with a size of 50 - 200 nm on the coating surface, increasing the surface specific area and improving the contact interface between the cathode sheet and the electrolyte; the contact angle of the electrolyte on the treated coating surface is reduced to ≤ 15°, greatly improving the wettability and promoting the penetration and infiltration of the electrolyte; by changing the surface microstructure, it improves the kinetic performance of the electrode reaction, enhancing the rate performance and cycle life of the battery. At the same time, by adjusting the power and time, the depth and intensity of the plasma treatment are precisely controlled to avoid excessive impact on the coating. Description of the Drawings

[0030] Figure 1 It is a schematic diagram of the partial structure where cracks exist on the surface of the cathode sheet. Detailed Embodiments

[0031] The technical solution of the present invention will be clearly and completely described below in conjunction with specific embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0032] According to the first aspect of the present application, the present application provides a method for preparing a battery positive electrode with low impedance and high liquid absorption performance, comprising the following steps:

[0033] S1. Slurry pretreatment and coating parameter adaptation: The positive electrode slurry is sheared and dispersed to adjust the slurry viscosity to 4000~6000 mPa·s; and the coating speed V (m / min) and the slurry viscosity η (mPa·s) satisfy the relationship: V= ‌K / ‌η, where K is a constant, and its value is (1.0~2.0)*10 5 , the unit is mPa·s·m / min; S2. Preheating and homogenizing treatment: after coating, the positive electrode sheet enters the preheating chamber and is pretreated in a composite mode of infrared radiation heating and hot air circulation, with a preheating temperature of 75~85℃, a relative humidity of 30%~50%, and a time of 20~40 s; S3. Segmented gradient drying: after preheating and homogenizing treatment, the positive electrode sheet enters the following three drying zones in sequence:

[0034] The first stage: temperature 90~100℃, wind speed 3~5m / s, time 10~20s, solvent volatilization rate is 50%~60% of the total solvent content;

[0035] The second stage: temperature 75~85℃, wind speed 1~3m / s, time 30~50s;

[0036] The third stage: temperature 60~70℃, wind speed 0.5~1 m / s, time 20~30s, final solvent residue ≤200 ppm;

[0037] S4. Annealing: Annealing is performed under nitrogen protection at a temperature of 120-150°C for 10-20 min at a heating rate of ≤5°C / min.

[0038] S5. Plasma surface modification: The surface of the positive electrode is treated with a mixed gas plasma of argon and oxygen, with a plasma power of 300~500 W and a treatment time of 30~60 s.

[0039] In an embodiment according to the present application, the shearing and dispersing treatment in S1 includes three-level rotational speed adjustment, which are 2000 rpm, 2500 rpm, and 3000 rpm in sequence, and the total treatment time is 30 - 60 min. By gradually increasing the rotational speed, the active substances, conductive agents, and binders in the slurry are fully dispersed to obtain a stable slurry system; on the one hand, the agglomerated particles in the slurry are eliminated, the rheological properties of the slurry are improved, and the uniformity and denseness of the coating are ensured; on the other hand, the slurry is prevented from stratifying or settling during storage and use, and the stability of the coating quality is guaranteed.

[0040] In an embodiment according to the present application, the wavelength of the infrared radiation in S2 is 2 - 5 μm, the hot air circulation wind speed is 0.5 - 1 m / s, and the solvent evaporation rate during the preheating process is 0.05 - 0.1 g / (m²·s). Among them, the wavelength range of 2 - 5 μm is selected because this wavelength matches the molecular vibration absorption peak of the NMP solvent, and it can efficiently transfer heat to the inside of the coating to accelerate the uniform evaporation of the solvent. The hot air circulation wind speed is controlled at a relatively low level. The main purpose is to maintain temperature uniformity rather than accelerate solvent evaporation, avoiding rapid film formation on the surface, which makes it difficult for the internal solvent to escape. The temperature uniformity in the preheating cavity is ensured through the design of the circulation air duct, and the temperature difference in the cavity is controlled within ±2℃.

[0041] During the preheating process, the control of the solvent evaporation rate is achieved through the comprehensive adjustment of temperature, relative humidity, and hot air circulation wind speed. Specifically, when the temperature is fixed within the range of 75 - 85℃, the evaporation rate can be controlled by adjusting the relative humidity; the higher the relative humidity, the lower the solvent evaporation rate, and vice versa. For example, at a temperature of 80℃, when the relative humidity is 30%, the evaporation rate is about 0.1 g / (m²·s); when the relative humidity is increased to 50%, the evaporation rate drops to about 0.05 g / (m²·s). The solvent evaporation rate is monitored in real time through a mass flow meter and an on-line near-infrared spectroscopy analyzer, and the working state of the humidifier or dehumidifier is adjusted in combination with the PID control system to achieve precise control of the evaporation rate.

[0042] In an embodiment according to the present application, a periodic negative pressure is applied in the second stage of S3, the negative pressure range is -10 - -5 kPa, the frequency is 0.8 - 1 Hz, and the negative pressure fluctuation range ≤ ±0.5 kPa. Applying a periodic negative pressure promotes the escape of internal solvent. Under the action of the negative pressure, the internal solvent is more likely to diffuse to the surface and be carried away, reducing the stress caused by the internal residual solvent; at the same time, the introduction of the periodic negative pressure adjusts the pressure difference between the inside and outside of the coating, preventing cracks caused by stress accumulation. The selection of the negative pressure frequency is based on the experimental optimization results. Too high a frequency will cause the coating to deform frequently, increasing stress, and too low a frequency will reduce the solvent extraction effect.

[0043] Among them, the realization of periodic negative pressure can be completed through a closed negative pressure cavity system, which mainly consists of the following parts:

[0044] 1) Closed cavity: It adopts a structure of two-layer sealing plates up and down. The length of the cavity matches the length of the drying section, and the width is slightly larger than the width of the positive electrode sheet. A flexible sealing device is provided on the side to adapt to positive electrode sheets of different widths and ensure the tightness of the negative pressure environment.

[0045] 2) Vacuum pump and buffer tank system: The vacuum pump works continuously to pump the air in the cavity to the buffer tank to form a stable basic negative pressure.

[0046] 3) Electro-magnetic proportional valve and PID control system: The opening and closing degree of the electro-magnetic proportional valve is driven by the control system to realize the periodic change of negative pressure. The sampling frequency of the PID controller is ≥10 Hz, and the valve opening is adjusted in real time according to the feedback information of the pressure sensor to ensure that the negative pressure fluctuation range is ≤±0.5 kPa.

[0047] In an embodiment according to the present application, the total drying time of S3 is controlled within 80 - 100 s, the temperature gradient difference between adjacent two sections from the first section to the third section is ≥15°C, and the temperature and wind speed of each section are adjusted through real-time feedback to ensure the uniformity of the coating and the gradual release of internal stress. Among them, the high-temperature and rapid dehydration in the first section (50% - 60% of the solvent is removed) shortens the total duration, and the low-temperature and balanced curing in the third section prevent rebound cracks. Among them, the setting of the temperature gradient difference is based on the results of thermal stress theory and experimental verification in materials science. When the temperature difference between adjacent two sections from the first section to the third section is above 15°C, it can promote the gradient migration of solvents inside the coating, form a solvent volatilization path from the inside to the outside, and reduce the accumulation of internal pressure.

[0048] The design of gradually decreasing temperature from the first section to the third section conforms to the principle of solvent evaporation kinetics. In the initial stage, the solvent content is high and the evaporation resistance is small. At this time, high temperature and high wind speed can effectively accelerate the removal of solvents. As the solvent content decreases, it becomes more and more difficult to volatilize. If the high temperature is maintained at this time, it will cause excessive drying on the surface while the solvents remain inside, forming a "hard shell effect". Therefore, the temperature gradient design makes the drying rate match the difficulty of solvent volatilization to achieve uniform drying.

[0049] In an embodiment according to the present application, the nitrogen flow rate during the annealing treatment in S4 is 5 - 10 L / min, and the residual stress of the coating after annealing is ≤1 MPa. Among them, an appropriate nitrogen flow rate ensures that the oxygen content in the annealing environment is extremely low to prevent oxidation. The annealing process further releases the residual stress inside the coating, and the residual stress of the coating after annealing is reduced to ≤1 MPa.

[0050] Among them, the selection range of the annealing temperature (120~150°C) is based on a comprehensive consideration of the stability of the high-nickel ternary material. On the one hand, a sufficiently high temperature is required to promote stress release and structural reorganization; on the other hand, too high a temperature that may cause material structure damage needs to be avoided. Through X-ray diffraction (XRD) and differential scanning calorimetry (DSC) tests, it is verified that within this temperature range, LiNi 0.8 Co 0.1 Mn 0.1 O2 material maintains structural stability. For example, under the annealing condition of 130°C, the weight loss of the material ≤0.1%, and the lattice parameter change ≤0.1%, proving that no obvious structural change or oxygen detachment phenomenon occurs. Weak structural changes may start to be observed during long-term (>30 min) annealing at 140°C. Therefore, in the present invention, the annealing time is controlled within the range of 10~20 min to ensure the structural stability of the material.

[0051] Among them, a slow heating rate (≤5°C / min) is the key to preventing coating cracking caused by thermal shock. According to the thermal stress theory, when the temperature change rate is too fast, the temperature difference between the inside and outside of the material is large, and the generated thermal stress is likely to exceed the strength limit of the material. Experimental verification shows that when the heating rate >8°C / min, the probability of microcracks appearing in the coating increases significantly; while when the heating rate is controlled at ≤5°C / min, the yield rate of the coating maintaining integrity ≥99.5%.

[0052] In an embodiment according to the present application, the volume mixing ratio of argon to oxygen in S5 is 4:1. After plasma treatment, nano-scale pores with a size of 50~200 nm are formed on the coating surface, and the electrolyte contact angle ≤15°.

[0053] Among them, the ratio selection of argon to oxygen is based on the different action mechanisms of the two gases in plasma treatment: the plasma generated by argon mainly acts through physical bombardment to eliminate the residual stress on the surface layer and increase the surface roughness at the same time; the plasma generated by oxygen mainly acts through chemical reaction to form oxygen-containing functional groups on the surface, improve the hydrophilicity, and etch to form nano-pores.

[0054] The mechanism of forming nano-pores by plasma treatment mainly includes the following processes:

[0055] 1) Activation stage: Active particles such as high-energy electrons, ions, and free radicals in the oxygen plasma bombard the coating surface, break the chemical bonds between surface molecules, and form active sites;

[0056] 2) Oxidation stage: Reactive oxygen reacts with surface active sites to form oxygen-containing functional groups (such as -OH, -COOH, etc.), enhancing the surface hydrophilicity;

[0057] 3) Etching stage: The reactive oxygen continues to react, partially oxidizing and decomposing the surface organic components (such as PVDF binder), forming volatile products that leave the surface, leaving nano-scale pores;

[0058] 3) Modification stage: Argon ion bombardment further adjusts the surface morphology, eliminates tiny stress concentration points, and optimizes the pore distribution.

[0059] By systematically adjusting the plasma power, treatment time, and gas ratio, the size and distribution of nano-pores can be precisely controlled. Experiments show that when the power is 300 - 500 W, the treatment time is 30 - 60 s, and the argon-oxygen ratio is 4:1, uniformly distributed nano-pores with a diameter of 50 - 200 nm and a depth of 20 - 100 nm can be formed on the coating surface, and the porosity reaches 15 - 25%. These nano-pores significantly increase the surface specific area (the increase amplitude ≥ 30%), improve the wettability of the electrolyte, and the contact angle of the treated electrolyte decreases from the original 60 - 80° to ≤ 15°.

[0060] The key to power selection for plasma treatment is to balance effective modification and avoid excessive damage. When the power is lower than 300 W, the treatment effect is not obvious, and the improvement of the contact angle is limited; when the power is higher than 500 W, it may lead to excessive etching of the coating, damage the surface of the active material, and even reduce the battery capacity. Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analyses show that within the power range of 300 - 500 W, the surface structure of the active material particles remains intact, and only partial etching of the PVDF binder and surface carbon black occurs, which ensures that the electrochemical activity of the material is not affected.

[0061] Another significant effect of plasma treatment is to improve the kinetic performance of the electrode / electrolyte interface. Through electrochemical impedance spectroscopy testing, it is found that the interface impedance of the treated positive electrode is reduced by 30% - 50%, which is beneficial to improving the rate performance and cycle life of the battery.

[0062] In an embodiment according to the present application, it further includes step S6. On-line stress detection and compensation: The internal stress of the coating is monitored in real time. When the local stress ≥ 5 MPa, the drying section temperature or negative pressure intensity is dynamically adjusted, and the response time ≤ 1 s. Among them, the high-precision stress detection and fast-response compensation mechanism can timely eliminate stress concentration and prevent the generation of cracks; dynamically adjusting the drying parameters according to the coating stress condition realizes the adaptive control of the drying process, improves the consistency of the coating quality, and reduces the quality fluctuations caused by human factors.

[0063] In an embodiment according to the present application, in S6, a laser Doppler vibrometer is used to monitor stress, with a resolution of 0.1 μm, a dynamically adjustable temperature range of ±5°C, and a negative pressure adjustment intensity of ±2 kPa. A dynamic stress nephogram can be generated in real time. When the detected stress ≥ 5 MPa, compensation is triggered, and the temperature is adjusted by ±5°C or the negative pressure by ±2 kPa to improve the process fault tolerance rate.

[0064] Among them, the online stress detection and compensation system mainly consists of the following parts:

[0065] 1) Laser Doppler vibrometer: Arranged between the first and second drying zones in S3, it uses a scanning spot for monitoring, with a resolution of 0.1 μm and a sampling frequency ≥ 10 kHz. This device calculates the surface strain field distribution by measuring the frequency and amplitude of the minute vibrations on the surface of the positive electrode sheet. The measurement principle is based on the Doppler effect. When a laser beam irradiates the vibrating surface, the frequency of the reflected light changes, and this change is proportional to the surface vibration velocity. By analyzing the frequency change, surface micro-vibration information can be obtained in real time.

[0066] 2) Stress analysis system: Converts the vibration measurement data into stress distribution through the following finite element model to generate a dynamic stress nephogram: a) Establish a coating mechanical model, considering parameters such as material elastic modulus (3 - 5 GPa) and Poisson's ratio (0.3 - 0.35); b) Input the measured surface displacement / velocity data as boundary conditions into the model; c) Solve the stress distribution through the equations of elasticity to calculate the internal stress state; d) Display the calculation results in the form of a stress nephogram in real time, with a resolution reaching 0.1 μm. This calculation process uses a simplified linear elastic model and a fast solution algorithm, with a calculation delay ≤ 0.2 s, meeting the requirements of real-time monitoring.

[0067] 3) Feedback control system: When the detected local stress ≥ 5 MPa, a compensation mechanism is triggered to dynamically adjust the temperature (±5°C) or negative pressure intensity (±2 kPa) in the drying section. The system response time ≤ 1 s, and it is mainly achieved by the following components: a) High-speed PLC controller, with a scanning cycle ≤ 10 ms; b) Temperature adjustment actuator: A heating element or cooling valve with fast response; c) Negative pressure adjustment device: A combination of a high-precision proportional solenoid valve and a pressure sensor; d) Parameter optimization algorithm: Based on fuzzy control theory, select the optimal adjustment strategy according to the stress distribution characteristics.

[0068] When a high-stress area is detected, the system will automatically select the optimal compensation strategy according to the stress distribution characteristics. For example, if the stress is mainly concentrated on the surface layer, the system will preferentially lower the temperature; if the stress distribution is relatively uniform, the negative pressure will be preferentially enhanced. This real-time monitoring and dynamic compensation mechanism enables the drying process to be self-adaptive, automatically adjusting the process parameters according to the characteristics of different batches of materials, ensuring the consistency of product quality, and significantly reducing the risk of cracks caused by stress concentration.

[0069] In an embodiment according to the present application, the cathode active material of the cathode slurry in S1 is LiNi 0.8 Co 0.1 Mn 0.1 O2 (90 - 98 wt%), the binder is PVDF (1 - 5 wt%), the conductive agent is conductive carbon black (1 - 5 wt%), the solvent is NMP, and the solid content of the slurry is 60% - 80%.

[0070] Among them, the high-nickel ternary material LiNi 0.8 Co 0.1 Mn 0.1 O2 has a high specific capacity, which helps to improve the energy density of the battery and meet the demand for long endurance of new energy vehicles; PVDF has good chemical stability and adhesion performance, ensuring the stable distribution of active substances in the coating and enhancing the mechanical strength of the coating; the solid content is increased to 60% - 80%, which is beneficial to improving the compaction density of the coating and further enhancing the volume specific energy of the battery.

[0071] In a second aspect according to the present application, the present application also provides a lithium-ion battery cathode, including an aluminum foil current collector and a cathode active material layer coated on the aluminum foil. The surface of the cathode active material layer has a nanoscale pore structure with a size of 50 - 200 nm, a crack length density ≤ 0.15%, an interfacial impedance ≤ 10 Ω·cm², and an electrolyte contact angle ≤ 15°. It is prepared by the preparation method of the battery cathode with low impedance and high liquid absorption performance described above.

[0072] The following will specifically describe the implementation manners and mechanisms of each step in the cathode preparation method of the present application in detail as follows:

[0073] S1. Slurry pretreatment and coating parameter adaptation

[0074] In the present invention, the slurry pretreatment and coating parameter adaptation are based on the matching of the rheological properties of the slurry and the coating process parameters. Through theoretical analysis and experimental verification, an inverse relationship between the slurry viscosity and the optimal coating speed is found. This relationship can be expressed as: V = K / η, where V is the coating speed (m / min), η is the slurry viscosity (mPa·s), and K is a constant related to the slurry composition, solid content, and equipment characteristics. The value range determined by experiments is (1.0 - 2.0)×105 mPa·s·m / min.

[0075] Among them, when the slurry flows through the coating head at a speed V, the shear stress it receives is proportional to the velocity gradient, and the velocity gradient is inversely proportional to the viscosity. To ensure the uniformity of the coating, a constant shear condition needs to be maintained. Therefore, the speed and viscosity need to maintain an inverse relationship. Through this formula, the coating speed can be dynamically adjusted according to the real-time measured viscosity of the slurry to ensure the stability of the coating quality.

[0076] The positive electrode slurry is subjected to shear dispersion treatment to adjust the slurry viscosity to 4000 - 6000 mPa·s. Specifically, this shear dispersion treatment includes three-stage rotational speed adjustment, which are 2000 rpm, 2500 rpm, and 3000 rpm in sequence, and the total treatment time is 30 - 60 min. By gradually increasing the rotational speed, the active substances, conductive agents, and binders in the slurry are fully dispersed to obtain a stable slurry system. During the treatment process, a high-precision online viscometer is used to monitor the change of the slurry viscosity in real time to ensure that the viscosity is controlled within the target range.

[0077] For example, when the slurry viscosity reaches 5000 mPa·s, if K = 1.5×10 5 mPa·s·m / min, then the optimal coating speed is V = 1.5×10 5 / 5000 = 30 m / min. This parameter optimization method based on the theoretical formula is significantly better than the traditional empirical adjustment method, ensuring the uniformity of the coating under high-speed coating conditions.

[0078] S2. Preheating and homogenization treatment

[0079] After coating, the positive electrode sheet enters the preheating chamber and is pre-treated in a composite mode of infrared radiation heating and hot air circulation. The preheating temperature is controlled at 75 - 85°C, the relative humidity is 30% - 50%, and the time is 20 - 40 s. The selection of the preheating temperature range is based on two considerations: on the one hand, a high enough temperature is needed to promote the preliminary volatilization of the solvent; on the other hand, a relatively gentle transition needs to be formed with the subsequent first-stage drying temperature (90 - 100°C) to avoid the accumulation of thermal stress caused by sudden temperature changes.

[0080] The wavelength of the infrared radiation is 2 - 5μm, and this wavelength range matches the molecular vibration absorption peak of the NMP solvent, enabling efficient heat transfer to the inside of the coating. The hot air circulation wind speed is 0.5 - 1 m / s, and a special designed air duct distributor is used to ensure the temperature uniformity in the preheating chamber, and the temperature difference in the chamber is controlled within ±2°C.

[0081] During the preheating process, the solvent evaporation rate is monitored in real time through a mass flow meter and an online near-infrared spectroscopy analyzer, and is controlled at 0.05 - 0.1 g / (m 2·s), which allows the coating to be heated evenly and avoids the problem of rapid film formation on the surface while solvent remaining inside, creating good initial conditions for subsequent staged gradient drying.

[0082] S3. Staged Gradient Drying

[0083] The preheated and homogenized positive electrode sheets enter three drying zones in sequence, and the parameters for each zone are set as follows:

[0084] The first stage: temperature 90 - 100 °C, wind speed 3 - 5 m / s, time 10 - 20 s, and the solvent evaporation rate is 50% - 60% of the total solvent content. High temperature and high wind speed are adopted in this stage to quickly remove most of the solvents on the surface and form a preliminary solidified structure. Through the design of the air duct deflector, it is ensured that the wind speed uniformity ≥ 95% to avoid stress concentration caused by uneven local drying.

[0085] The second stage: temperature 75 - 85 °C, wind speed 1 - 3 m / s, time 30 - 50 s. The most significant feature of this stage is the application of periodic negative pressure, with the negative pressure range of -10 - -5 kPa and the frequency of 0.8 - 1 Hz, and the negative pressure fluctuation range ≤ ±0.5 kPa. The periodic negative pressure is achieved through a pulse control system composed of a vacuum pump and a solenoid valve. This system mainly consists of a vacuum pump, a buffer tank, an electromagnetic proportional valve, and a PID controller, which can achieve precise control of ±0.5 kPa with a response time ≤ 0.1 s.

[0086] The mechanism of action of the periodic negative pressure: Under negative pressure, there is a pressure difference between the inside and outside of the coating, which promotes the migration of internal solvent molecules to the surface; when the negative pressure is released, the coating obtains a short relaxation, reducing the accumulation of internal stress. This periodic "suction - relaxation" process effectively promotes the uniform escape of internal solvents and avoids the common "surface dry and internal wet" phenomenon in traditional drying.

[0087] The third stage: temperature 60 - 70 °C, wind speed 0.5 - 1 m / s, time 20 - 30 s, and the final solvent residue ≤ 200 ppm. Low temperature and low wind speed are adopted in this stage to gently remove the residual solvents and relieve the internal stress of the coating at the same time. The solvent residue is monitored in real time by an on - line near - infrared spectroscopy analyzer, with a sampling frequency ≥ 1 Hz and an accuracy ≤ 50 ppm to ensure accurate control of the drying end point.

[0088] The total time of the entire staged gradient drying is controlled within 80 - 100 s, and the temperature gradient difference from the first stage to the third stage ≥ 15 °C. This gradient drying design follows the principle of "fast first and then slow", which not only ensures production efficiency but also avoids the stress accumulation problem in traditional drying.

[0089] S4. Annealing Treatment

[0090] Annealing treatment is carried out under nitrogen protection. The annealing temperature is 120 - 150 °C, the time is 10 - 20 min, and the heating rate is ≤5 °C / min. The nitrogen flow rate is 5 - 10 L / min, and the oxygen content is controlled at ≤100 ppm. A specially designed roller annealing furnace is used in the annealing process to ensure that the positive electrode sheet is heated evenly during movement.

[0091] The main purpose of the annealing treatment is to further release the residual stress in the coating, optimize the crystal structure of the active material, and improve the electrochemical performance of the material. The residual stress of the coating after annealing is ≤1 MPa, which is measured by X-ray diffraction stress analysis method. This measurement method is based on the relationship between the displacement of the X-ray diffraction peak and the internal stress of the material, and can non-destructively measure the internal stress distribution of the coating.

[0092] Experiments have proved that the annealing treatment can reduce the residual stress of the coating from 3 - 5 MPa to ≤1 MPa, significantly improve the mechanical stability of the coating, and reduce the risk of cracking during subsequent battery assembly and use. At the same time, the annealing under nitrogen protection avoids the oxidation reaction that may occur to the high-nickel material at high temperature, and maintains the electrochemical activity and stability of the positive electrode material.

[0093] S5. Plasma surface modification

[0094] The surface of the positive electrode sheet is treated with a mixed gas plasma of argon and oxygen. The plasma power is 300 - 500 W, and the treatment time is 30 - 60 s. The volume mixing ratio of argon to oxygen is 4:1, and the working pressure is controlled at 20 - 50 Pa.

[0095] The mechanism of plasma surface modification mainly includes two aspects: on the one hand, the oxygen plasma reacts chemically with the coating surface to form hydrophilic functional groups and etch out nanoscale pores at the same time; on the other hand, the physical bombardment of argon ions eliminates the surface residual stress and increases the surface roughness at the same time.

[0096] By systematically studying the relationship between the plasma power, treatment time and surface morphology, it is found that when the power is 300 - 500 W and the treatment time is 30 - 60 s, 50 - 200 nm nanoscale pores can be formed on the coating surface in a uniform distribution. These pores significantly increase the surface specific area and improve the wettability of the electrolyte, and the contact angle of the electrolyte after treatment is reduced to ≤15°.

[0097] Another significant effect of plasma treatment is to improve the kinetic performance of the electrode / electrolyte interface. It is found through electrochemical impedance spectroscopy testing that the interfacial impedance of the treated positive electrode is reduced by 30% - 50%, which is beneficial to improving the rate performance and cycle life of the battery.

[0098] S6. Online Stress Detection and Compensation

[0099] The present invention also includes an online stress detection and compensation system, which monitors the internal stress of the coating in real time. When the local stress ≥ 5 MPa, it dynamically adjusts the temperature or negative pressure intensity in the drying section. This system mainly consists of the following parts:

[0100] 1) Laser Doppler vibrometer: Arranged between the first and second drying zones in S3, it uses a scanning spot for monitoring, with a resolution of 0.1 μm and a sampling frequency ≥ 10 kHz. This device can non-contact measure the micro-vibrations on the surface of the positive electrode sheet, and then calculate the surface strain distribution.

[0101] 2) Real-time data processing system: It converts the vibration measurement data into stress distribution through a finite element model and generates a dynamic stress nephogram. The calculation process is based on the theory of elasticity mechanics, considering factors such as the thickness and elastic modulus of the coating, and the conversion accuracy ≤ 5%.

[0102] 3) Feedback control system: When the detected local stress ≥ 5 MPa, it triggers a compensation mechanism to dynamically adjust the temperature in the drying section (±5°C) or the negative pressure intensity (±2 kPa). The system response time ≤ 1 s, and closed-loop control is achieved through a PLC controller and an actuator.

[0103] This real-time monitoring and dynamic compensation mechanism makes the drying process self-adaptive, capable of automatically adjusting process parameters according to the characteristics of different batches of materials, ensuring the consistency of product quality, and significantly reducing the risk of cracks caused by stress concentration.

[0104] The implementation and advantages of the present application will be further described below in combination with specific embodiments.

[0105] Embodiment 1

[0106] A preparation method of a battery positive electrode with low impedance and high liquid absorption performance provided in this embodiment includes the following steps:

[0107] 1. Slurry pretreatment and coating parameter adaptation

[0108] 1) Slurry preparation:

[0109] Positive electrode active material: LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811), with a specific surface area of 3 m² / g and a mass ratio of 95%;

[0110] Conductive agent: Super P, with a mass ratio of 2%;

[0111] Binder: PVDF, with a mass ratio of 3%;

[0112] Solvent: NMP;

[0113] Solid content of the slurry: 70%.

[0114] 2) Three - stage shear dispersion:

[0115] First stage: 2000 rpm, 10 min, preliminarily disperse agglomerated particles;

[0116] Second stage: 2500 rpm, 20 min, refine the particle size of the slurry (D50 ≤ 3μm);

[0117] Third stage: 3000 rpm, 10 - 30 min, stabilize the viscosity to 5000 mPa·s (25℃).

[0118] 3) Coating speed calculation:

[0119] According to the relationship V = K / η, when η = 5000 mPa·s and K = 1.5×10 5 , V = 30 m / min.

[0120] 2. Pre - heating and homogenization treatment

[0121] Pre - heating cavity design:

[0122] The wavelength of the infrared radiation plate is 3.5μm, and the power density is 1.5 W / cm²;

[0123] The wind speed of the hot - air circulation system is 0.75 m / s, the temperature is 80℃, and the temperature uniformity is ≤ ±2℃;

[0124] The treatment time is 30 s, and the relative humidity is 40%;

[0125] The solvent evaporation rate is monitored in real - time by a mass flowmeter and controlled to be 0.08 g / (m²·s).

[0126] 3. Segmented gradient drying

[0127] 1) The first stage (rapid dehydration):

[0128] Temperature 95℃, wind speed 4 m / s, time 15 s, solvent evaporation rate 55% - 60%;

[0129] The wind speed uniformity is adjusted to ≥95% by the air duct deflector.

[0130] 2) The second stage (negative - pressure stress release):

[0131] Temperature 80℃, wind speed 2 m / s, negative pressure - 8 kPa, frequency 0.8 Hz, time 40 s;

[0132] The negative - pressure fluctuation range is ≤ ±0.5 kPa, which is realized by a vacuum pump cooperating with a PID controller.

[0133] 3) The third stage (equilibrium curing):

[0134] Temperature 65°C, wind speed 0.8 m / s, time 25 s, total drying time 80 s;

[0135] The solvent residue is 180 ppm, which is monitored in real time by an on-line near-infrared spectrometer with a sampling frequency of 2 Hz.

[0136] 4. On-line stress detection and compensation

[0137] 1) Detection device:

[0138] Laser Doppler vibrometer (Polytec PSV-500), resolution 0.1μm, sampling frequency 10 kHz;

[0139] The finite element model (ANSYS Mechanical) calculates the stress distribution with an error ≤5%.

[0140] 2) Dynamic compensation logic:

[0141] When the local stress ≥5 MPa, trigger a temperature reduction of 3 - 5°C or an increase in negative pressure of 1 - 2 kPa;

[0142] The response time ≤1 s (PLC controller + pneumatic actuator).

[0143] 5. Annealing treatment

[0144] Annealing furnace parameters:

[0145] Nitrogen purity ≥99.999%, flow rate 8 L / min;

[0146] Heating rate 3°C / min, holding temperature 135°C, time 15 min;

[0147] The residual stress of the coating after annealing is 0.8 MPa, which is measured by X-ray diffraction stress analysis method.

[0148] 6. Plasma surface modification

[0149] Plasma equipment:

[0150] Radio frequency power supply (13.56 MHz), power 400 W, argon / oxygen mixing ratio 4:1;

[0151] Working pressure 30 Pa, treatment time 45 s;

[0152] Uniform nano-pores are formed on the surface of the positive electrode sheet, with an average pore diameter of 120 nm, a surface coverage rate ≥80%, and an electrolyte contact angle of 10°.

[0153] Example 2

[0154] Different from Example 1, the relevant parameters of this example are as follows:

[0155] 1) Slurry solid content: 75%, viscosity 6000 mPa·s;

[0156] 2) According to the relationship V = K / η, when η = 6000 mPa·s and K = 1.5×10 5 , V = 25 m / min;

[0157] 3) Negative pressure parameter: -10 kPa, frequency 1 Hz;

[0158] 4) Annealing heating rate: 2°C / min, final temperature 145°C;

[0159] 5) Plasma power: 450 W, treatment time 40 s;

[0160] 6) Average diameter of nano-pores on the surface of the positive electrode sheet is 100 nm, and the electrolyte contact angle is 12°.

[0161] Others are the same as Example 1 and will not be elaborated here.

[0162] Example 3

[0163] Different from Example 1, the relevant parameters of this example are as follows:

[0164] 1) Total drying time: 90 s (15 s for the first stage, 50 s for the second stage, 25 s for the third stage);

[0165] 2) Solvent residue: 150 ppm;

[0166] 3) Plasma power: 350 W, treatment time 50 s;

[0167] 4) Average diameter of nano-pores on the surface of the positive electrode sheet is 150 nm, and the electrolyte contact angle is 15°.

[0168] Others are the same as Example 1 and will not be elaborated here.

[0169] Example 4

[0170] Different from Example 1, this example uses non-negative pressure drying, that is, the segmented drying temperature is the same as that in Example 1, but there is no negative pressure in the second stage.

[0171] Others are the same as Example 1 and will not be elaborated here.

[0172] Comparative Example 1

[0173] Different from Example 1, this comparative example uses traditional oven drying with the following parameters:

[0174] Constant temperature drying: 100 °C, wind speed 3 m / s, time 120 s, no negative pressure;

[0175] Annealing temperature 150 °C, time 20 min;

[0176] No plasma surface modification treatment.

[0177] Other conditions are the same as those in Example 1 and will not be elaborated here.

[0178] Comparative Example 2

[0179] Different from Example 1, this comparative example does not apply the coating speed formula to establish the adaptation between the coating speed and the slurry viscosity, and uses a fixed coating speed of 45 m / min and a slurry viscosity of 5000 mPa·s.

[0180] Other conditions are the same as those in Example 1 and will not be elaborated here.

[0181] The following performance tests were respectively carried out on the positive electrode sheets prepared in the above examples and comparative examples, and the test results are shown in Table 1.

[0182] 1) Detection of crack length density:

[0183] Equipment: Laser confocal microscope (Keyence VK-X1000), scanning area 10 mm × 10 mm;

[0184] Standard: Cracks with a length ≥ 50 μm are counted as effective defects, and the density = total crack length / detection area × 100%.

[0185] 2) Cycle performance test:

[0186] Assemble a button cell (CR2032), electrolyte 1M LiPF6 (EC:DMC = 1:1), cycling conditions: 0.5C charge / discharge, voltage 3.0~4.3 V;

[0187] Capacity retention rate = discharge capacity at the 500th cycle / initial discharge capacity × 100%.

[0188] 3) Interface impedance test:

[0189] Equipment: Electrochemical workstation (Solartron 1260), frequency range 100 kHz~0.01 Hz, amplitude 10 mV;

[0190] Calculate the diameter of the semi-circle in the high-frequency region as the interface impedance (unit: Ω·cm²).

[0191] 4) Electrolyte wettability test:

[0192] Equipment: Contact angle measuring instrument (Krüss DSA100), measurement conditions: room temperature, 1 μL of standard electrolyte; take the average value of 5-point measurements as the final result.

[0193] Table 1 Group Crack length density (%) Drying time (s) Cycle capacity retention rate (%) Interface impedance (Ω·cm²) Electrolyte contact angle (°) Example 1 0.08 80 95.6 6.3 10 Example 2 0.12 70 94.8 6.9 12 Example 3 0.15 90 93.5 7.6 15 Example 4 0.14 80 92.2 8.0 13 Comparative Example 1 5.8 140 87.5 12.8 65 Comparative Example 2 4.1 95 88.7 11.2 50

[0194] Among them, the analysis of the above test results is as follows:

[0195] 1. Comparative analysis between the examples and the comparative examples:

[0196] 1) Crack length density: The crack length density in Example 1 is significantly lower than that in Comparative Example 1, proving that the synergistic effect of segmented gradient drying and online compensation has a significant effect on preventing crack formation.

[0197] 2) Cycling performance: The capacity retention rate of Example 1 is 95.6%, significantly higher than that of Comparative Example 1, which benefits from the stable interface and good structural integrity brought by the complete coating; due to the mismatch between the coating speed and the slurry viscosity in Comparative Example 2, the interfacial impedance reaches 11.2 Ω·cm², and the cycling performance deteriorates, verifying the necessity of slurry adaptation control.

[0198] 3) Drying efficiency: The drying time of each example is lower than that of Comparative Example 1. Especially, the drying time of Example 3 is compressed to 60 s, significantly lower than that of Comparative Example 1, indicating that the gradient drying design greatly improves the production efficiency while ensuring the quality.

[0199] 4) Interfacial impedance: The interfacial impedance of Example 1 is much lower than that of Comparative Example 1, proving that the preparation method of the present application can effectively prevent crack generation through designs such as speed-slurry viscosity and segmented gradient drying, thereby reducing the interfacial impedance.

[0200] 5) Electrolyte infiltration performance: The electrolyte contact angle of Example 1 is significantly lower than that of Comparative Example 1, indicating that plasma surface modification can effectively improve the surface microstructure, increase the surface specific area, improve the contact interface between the positive electrode sheet and the electrolyte, greatly improve the liquid wettability of the positive electrode sheet, and is conducive to the uniform infiltration and ion transport of the electrolyte.

[0201] 2. Comparative analysis between the examples

[0202] 1) Compared with Example 1, in Example 2, due to the increase in the solid content of the slurry to 75% and the increase in viscosity to 6000 mPa·s, the coating speed is correspondingly reduced to 25 m / min, but the crack density still remains at a low level (0.12%), maintaining a good crack suppression effect, reflecting the adaptability of the process of the present invention to different conditions; the slight increase in interfacial impedance is related to the reduction in the porosity of the high-solid-content coating, but it is still within a good range.

[0203] 2) Compared with Example 1, the drying time in Example 3 was extended to 90 s, and the solvent residue decreased, indicating that the solvent residue can be further reduced by appropriately extending the treatment time. However, the crack density increased slightly (0.15%), indicating that it is necessary to balance the drying thoroughness and stress control to find the optimal process window.

[0204] 3) Compared with Example 1, in Example 4, the lack of negative pressure led to insufficient stress release, resulting in the crack length density and interface impedance still being higher than those in Example 1, indicating that the introduction of periodic negative pressure helps to inhibit crack formation.

[0205] Based on the disclosure and teachings of the above specification, those skilled in the art to which the present invention pertains are also able to make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments, and any obvious improvements, substitutions or variations made by those skilled in the art on the basis of the present invention all fall within the protection scope of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A method for preparing a battery positive electrode with low impedance and high liquid absorption performance, characterized in that, It includes the following steps: S1. Slurry pretreatment and coating parameter adaptation: The positive electrode slurry is subjected to shear dispersion treatment to adjust the slurry viscosity to 4000 - 6000 mPa·s; and the coating speed V (m / min) and the slurry viscosity η (mPa·s) satisfy the relationship: V = K / η, where K is a constant, and its value is (1.0 - 2.0) * 10 5 , with the unit of mPa·s·m / min; S2. Preheating and homogenization treatment: After coating, the positive electrode sheet enters the preheating cavity and is pretreated in a composite mode of infrared radiation heating and hot air circulation. The preheating temperature is 75 - 85°C, the relative humidity is 30% - 50%, and the time is 20 - 40 s; S3. Step - gradient drying: The positive electrode sheet after preheating and homogenization treatment sequentially enters the following three drying zones: The first stage: temperature 90~100°C, wind speed 3~5 m / s, time 10~20 s; The second stage: temperature 75~85°C, wind speed 1~3 m / s, time 30~50 s; The third stage: temperature 60~70°C, wind speed 0.5~1 m / s, time 20~30 s; S4. Annealing treatment: Annealing treatment is carried out under nitrogen protection, annealing temperature 120~150°C, time 10~20 min, heating rate ≤5°C / min; S5. Plasma surface modification: The surface of the positive electrode sheet is treated with a mixed gas plasma of argon and oxygen, plasma power 300~500 W, treatment time 30~60 s.

2. The preparation method of the battery positive electrode with low impedance and high liquid absorption performance according to claim 1, wherein, The shear dispersion treatment in the said S1 includes three-stage speed regulation, which are 2000 rpm, 2500 rpm, and 3000 rpm in sequence, and the total treatment time is 30~60 min.

3. The preparation method of the battery positive electrode with low impedance and high liquid absorption performance according to claim 1, characterized in that The wavelength of the infrared radiation in the said S2 is 2~5 μm, the hot air circulation wind speed is 0.5~1 m / s, and the solvent evaporation rate during the preheating process is 0.05~0.1 g / (m²·s).

4. The preparation method of the battery positive electrode with low impedance and high liquid absorption performance according to claim 1, characterized in that, In the second stage of the said S3, periodic negative pressure is applied, the negative pressure range is -10~-5 kPa, and the frequency is 0.8~1 Hz.

5. The preparation method of the battery positive electrode with low impedance and high liquid absorption performance according to claim 1, characterized in that, The total drying time of the said S3 is controlled within 80~100 s, and the temperature gradient difference from the first stage to the third stage is ≥15°C.

6. The preparation method of the battery positive electrode with low impedance and high liquid absorption performance according to claim 1, characterized in that, The nitrogen flow rate for the annealing treatment in the said S4 is 5~10 L / min, and the residual stress of the coating after annealing is ≤1 MPa.

7. The preparation method of the battery positive electrode with low impedance and high liquid absorption performance according to claim 1, characterized in that, In the said S5, the volume mixing ratio of argon and oxygen is 4:1, and nano-scale pores of 50~200 nm are formed on the surface of the coating after plasma treatment, and the electrolyte contact angle is ≤15°.

8. The preparation method of the battery positive electrode with low impedance and high liquid absorption performance according to claim 1, characterized in that, It also includes step S6. On-line stress detection and compensation: The internal stress of the coating is monitored in real time. When the local stress ≥5 MPa, the drying section temperature or the negative pressure intensity is dynamically adjusted.

9. The preparation method of the battery positive electrode with low impedance and high liquid absorption performance according to claim 8, characterized in that, In the said S6, the stress is monitored by a laser Doppler vibrometer, the resolution is 0.1 μm, the temperature range for dynamic adjustment is ±5°C, and the negative pressure adjustment intensity is ±2 kPa.

10. A battery positive electrode, characterized in that, It is obtained by the preparation method of the battery positive electrode with low impedance and high liquid absorption performance according to any one of claims 1~9.

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