Preparation method for inhibiting generation of shrinkage cavities on surface of pole piece and pole piece

Abstract

The invention discloses a preparation method for inhibiting generation of shrinkage cavities on the surface of a pole piece and the pole piece. The method comprises the following steps: S1, pre-activating a base material, and generating a hydrophobic-oleophylic gradient layer by argon and hexamethyldisiloxane mixed plasma; s2, slurry modification: adding a zwitterionic block copolymer and silane modified nano titanium dioxide, and adjusting the surface tension of the slurry to 25-30 mN / m; s3, dynamic flow field coating is conducted, an ultrasonic generator restrains vortex, and the coating speed ranges from 20 m / min to 60 m / min; s4, gradient drying, three-section temperature control and wind speed decreasing are matched with solvent volatilization; and S5, defect repairing, wherein the shrinkage cavity is repaired through laser micro-area remelting in combination with the piezoelectric micro-roller. Compared with the prior art, through cooperation of surface energy gradient matching, flow field regulation and control and online repair, the shrinkage cavity phenomenon of the pole piece can be effectively inhibited, so that the quality and consistency of the pole piece are improved, and the method is suitable for efficient production of high-energy-density batteries.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery electrode sheet preparation, and particularly relates to a preparation method and an electrode sheet for suppressing the generation of shrinkage holes on the surface of the electrode sheet. Background Art

[0002] With the wide application of lithium-ion batteries in the fields of new energy vehicles and energy storage, the electrode sheet, as the core component of the battery, its manufacturing quality directly affects the energy density, cycle life and safety of the battery. As Figures 1 - 2 shown, in the electrode sheet coating process, shrinkage hole defects (including craters and pits) are one of the key problems leading to uneven electrode surface and reducing battery performance. The formation of shrinkage holes stems from the surface tension mismatch between pollutants (such as oil droplets, dust, etc.) and the slurry during the coating process. The slurry in the pollutant area migrates towards the direction of high surface tension, resulting in local coating collapse. Such defects not only destroy the uniformity of the active material distribution, but also cause local stress concentration during the charge and discharge process, accelerate the growth of lithium dendrites, and increase the risk of battery short circuit.

[0003] Currently, the industry mainly reduces shrinkage holes through traditional means such as coating liquid filtration, environmental dust control, and substrate cleaning. However, these methods have the following deficiencies:

[0004] 1) Lack of dynamic regulation of surface tension: Traditional processes cannot actively regulate the surface tension gradient between the slurry and the substrate, and it is difficult to suppress the local tension imbalance caused by pollutants;

[0005] 2) Insufficient process synergy: The process parameters of coating, drying, etc. (such as viscosity, wind speed) are independently optimized, lacking the coordinated control of the rheology of the slurry and the drying kinetics, resulting in the risk of surface collapse;

[0006] 3) Lack of defect repair means: Existing technologies rely on pre-prevention and lack the online repair ability for the already formed shrinkage holes. Especially during high-speed coating, the defect miss rate is high;

[0007] 4) Conflict between efficiency and quality: Increasing the coating speed will exacerbate the slurry vortex and drying non-uniformity, and traditional solutions are difficult to balance the requirements of high-speed production and defect suppression.

[0008] For example, the conventional coating process improves the leveling property by reducing the viscosity of the slurry, but this will exacerbate the surface tension gradient during the drying process and instead increase the probability of shrinkage holes; while increasing the drying temperature can shorten the process time, but it is easy to cause premature curing of the surface layer, hinder the volatilization of internal solvents, and form hidden shrinkage holes. In addition, the control of substrate cleanliness is limited by the workshop environment, and it is difficult to completely eliminate micron-sized pollutants.

[0009] Therefore, there is an urgent need for an electrode sheet preparation method that can systematically regulate the surface tension, optimize the flow field distribution, and integrate online repair to meet the strict requirements of high-energy density batteries for the consistency of electrode sheets. Summary of the Invention

[0010] The object of the present invention is to provide a preparation method for suppressing the generation of shrinkage holes on the surface of a pole piece, which can effectively inhibit the generation of shrinkage holes on the pole piece, thereby improving the quality and consistency of the pole piece, aiming at the deficiencies of the prior art.

[0011] To achieve the above object, the present invention provides the following technical solutions:

[0012] A preparation method for suppressing the generation of shrinkage holes on the surface of a pole piece, comprising the following steps:

[0013] S1. Substrate pre-activation treatment: Place the substrate in a plasma treatment chamber, introduce a mixture of argon and hexamethyldisiloxane, the volume ratio of argon to hexamethyldisiloxane is (8 - 10):1, apply a radio frequency power of 50 - 200 W, and the treatment time is 30 - 60 seconds to form a hydrophobic-lipophilic gradient layer on the surface of the substrate, and the surface energy difference of the gradient layer from the surface to the bottom layer is 20 - 40 mN / m; S2. Slurry modification treatment: Add 0.1% - 0.5% by mass of an amphiphilic block copolymer and 0.05% - 0.2% by mass of nano-titanium dioxide particles to the active material slurry, and adjust the surface tension of the slurry to 25 - 30 mN / m, and the particle size of the nano-titanium dioxide is 20 - 50 nm; S3. Dynamic flow field coating: Use a slit extrusion coater for coating. An annular ultrasonic generator is integrated at the outlet of the coating head of the coater. The working frequency of the ultrasonic generator is 20 - 50 kHz, the power density is 0.5 - 2.0 W / cm², the coating speed is 20 - 60 m / min, and a wet film thickness of 50 - 100 μm is formed; S4. Gradient drying and curing: The wet film is successively subjected to three-stage drying treatment. The specific parameters are: the temperature in the first stage is 50 - 60°C, the wind speed is 2 - 4 m / s, and the surface solvent is quickly evaporated to form a dense surface layer; the temperature in the second stage is 70 - 80°C, the wind speed is 1 - 2 m / s, and the internal solvent is driven to diffuse directionally through the temperature gradient to avoid surface collapse; the temperature in the third stage is 90 - 100°C, the wind speed is 0.5 - 1 m / s, and high-temperature curing is carried out to eliminate residual stress; S5. On-line defect repair: Use a laser scanning detection system to identify the position of shrinkage holes, use picosecond laser to remelt the defect area in a micro-region, and then apply a pressure of 3 - 5 N / cm² and vibrate at a frequency of 10 - 20 kHz through a piezoelectric micro-roller for local compaction.

[0014] Further, the pressure in the plasma treatment chamber in S1 is 10 - 30 Pa, and the radio frequency frequency is 13.56 MHz.

[0015] Further, the zwitterionic block copolymer in S2 is poly(sulfobetaine)-poly(ethylene oxide), and the molar ratio of its hydrophilic segment to hydrophobic segment is (2-4):1.

[0016] Further, the surface of the nano-titanium dioxide in S2 is modified with a silane coupling agent, and the hydroxyl density measured by X-ray photoelectron spectroscopy is ≥5 per nm².

[0017] Further, the gap between the coating head and the substrate in S3 is 100-200 μm, the angle between the ultrasonic propagation direction and the coating direction is 20°-40°, and the slurry viscosity is adjusted in real time to 1000-4000 mPa·s.

[0018] Further, the humidity control in each drying section of S4 is: 30% in the first stage, 20% in the second stage, and 10% in the third stage, and the length ratio of the three drying zones is 2:1:1.

[0019] Further, in S5, the wavelength of the picosecond laser is 355 nm, the pulse width is 10 ps, and the energy density is 0.05-0.1 J / cm²; the scanning path of the picosecond laser is concentric circle diffusion type, the scanning spacing is 10-20 μm, and the micro-region remelting depth ≤5 μm.

[0020] Further, the surface of the piezoelectric micro-roller in S5 is coated with a hard tungsten carbide coating, the surface roughness Ra of the coating ≤0.1 μm, and the vibration direction is perpendicular to the rolling direction.

[0021] Further, it further includes step S6: performing nitrogen plasma post-treatment on the repaired electrode sheet, with the treatment power being 100-150 W and the time being 10-30 seconds.

[0022] Further, an infrared temperature measurement module is provided at the outlet of the coater in S3 to monitor the wet film temperature in real time and feedback to adjust the ultrasonic power, with the temperature control accuracy being ±1°C.

[0023] Further, the laser scanning detection system in S5 uses a convolutional neural network to identify shrinkage holes, and the identification accuracy ≥99%.

[0024] Further, the substrate in S1 is etched aluminum foil or copper foil with a surface roughness Ra ≤0.3 μm and a thickness of 10-20 μm.

[0025] In addition, the present invention also provides an electrode sheet prepared by the above method for suppressing the generation of shrinkage holes on the surface of the electrode sheet.

[0026] Compared with the prior art, the present invention has at least the following beneficial effects:

[0027] 1) In the present invention, through the plasma treatment of argon and hexamethyldisiloxane (volume ratio 8 - 10:1), a hydrophobic - lipophilic gradient layer (surface energy difference 20 - 40 mN / m) is generated, which actively matches the surface tension of the slurry, making it difficult to form a tension difference in the pollutant area, reducing the probability of surface tension mismatch caused by pollutants, and effectively suppressing the root cause of shrinkage holes. Moreover, the hydrophobic end in the gradient layer repels oily pollutants, and the lipophilic end adsorbs the slurry, reducing the requirement for substrate cleanliness and enhancing the resistance to pollutants.

[0028] 2) In the present invention, zwitterionic block copolymers (such as polysulfobetaine - polyethylene oxide) reduce the interfacial tension through the charge neutralization effect, and nano - titanium dioxide (20 - 50 nm) enhances the rheology of the slurry, synergistically suppressing the shrinkage holes induced by tension imbalance.

[0029] 3) In the present invention, an ultrasonic generator (20 - 50 kHz) induces laminar shear of the slurry layer, eliminates the interference of eddy currents. When the coating speed is increased to 20 - 60 m / min, the flow velocity fluctuation of the slurry is lower than that of the traditional process.

[0030] 4) In the present invention, segmented temperature control (50 - 100 °C) and decreasing wind speed (4 → 0.5 m / s) match the solvent evaporation kinetics, avoid premature curing of the surface layer, reduce the shrinkage rate of the wet film, and improve the uniformity of the internal stress distribution.

[0031] 5) In the present invention, picosecond laser is used to precisely vaporize the edges of shrinkage holes, combined with the high - frequency vibration compaction of a piezoelectric micro - roller (pressure 3 - 5 N / cm²), and the porosity deviation in the repaired area is relatively low. Description of the Drawings

[0032] Figure 1 It is a schematic structural diagram of a pole piece surface with shrinkage hole defects;

[0033] Figure 2 It is a schematic diagram of the formation mechanism of shrinkage holes on the pole piece surface. Detailed Embodiments

[0034] Next, specific embodiments will be combined to clearly and completely describe the technical solutions of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present invention.

[0035] In the first aspect according to the present application, the present application provides a preparation method for suppressing the generation of shrinkage holes on the pole piece surface, including the following steps:

[0036] S1. Substrate pre-activation treatment: Place the substrate in a plasma treatment chamber, introduce a mixture of argon and hexamethyldisiloxane, where the volume ratio of argon to hexamethyldisiloxane is (8 - 10):1, apply a radio frequency power of 50 - 200 W, and treat for 30 - 60 seconds to form a hydrophobic-lipophilic gradient layer on the substrate surface. The surface energy difference of the gradient layer from the surface to the bottom layer is 20 - 40 mN / m; S2. Slurry modification treatment: Add 0.1% - 0.5% by mass of zwitterionic block copolymer and 0.05% - 0.2% by mass of nano-titanium dioxide particles to the active material slurry, and adjust the surface tension of the slurry to 25 - 30 mN / m. The particle size of the nano-titanium dioxide is 20 - 50 nm; S3. Dynamic flow field coating: Use a slot die coater for coating. An annular ultrasonic generator is integrated at the outlet of the coating head of the coater. The working frequency of the ultrasonic generator is 20 - 50 kHz, the power density is 0.5 - 2.0 W / cm², and the coating speed is 20 - 60 m / min to form a wet film thickness of 50 - 100 μm; S4. Gradient drying and curing: Pass the wet film through three-stage drying treatment successively. The specific parameters are: the temperature in the first stage is 50 - 60°C, the wind speed is 2 - 4 m / s, quickly evaporate the surface solvent to form a dense surface layer; the temperature in the second stage is 70 - 80°C, the wind speed is 1 - 2 m / s, drive the directional diffusion of the internal solvent through the temperature gradient to avoid surface collapse; the temperature in the third stage is 90 - 100°C, the wind speed is 0.5 - 1 m / s, cure at high temperature to eliminate residual stress; S5. On-line defect repair: Use a laser scanning detection system to identify the position of the shrinkage hole, and use picosecond laser with a wavelength of 355 nm, a pulse width of 10 ps, and an energy density of 0.05 - 0.1 J / cm² to perform micro-region remelting on the defect area, and then apply a pressure of 3 - 5 N / cm² through a piezoelectric micro-roller and perform local compaction at a vibration frequency of 10 - 20 kHz.

[0037] In an embodiment according to the present application, the pressure in the plasma treatment chamber in S1 is 10 - 30 Pa. At low pressure, the plasma uniformity is improved, and the thickness fluctuation of the gradient layer is reduced from ±15 nm to ±5 nm; the radio frequency frequency is 13.56 MHz, which matches the decomposition energy of hexamethyldisiloxane (HMDSO) to increase the grafting rate of hydrophobic groups (-CH3).

[0038] In an embodiment according to the present application, the zwitterionic block copolymer in S2 is poly(sulfobetaine)-poly(ethylene oxide), and the molar ratio of its hydrophilic chain segment to hydrophobic chain segment is (2 - 4):1; balance the slurry dispersibility and interfacial tension regulation ability, and the slurry Zeta potential is stabilized at -30 mV, and the particle aggregation rate ≤ 3%.

[0039] In one embodiment according to the present application, the surface of the nano-titanium dioxide in S2 is modified with a silane coupling agent, and the hydroxyl density measured by X-ray photoelectron spectroscopy is ≥5 per nm²; the hydrogen bond binding force between the nano-particles and the slurry is enhanced, the yield stress of the slurry is increased, and the capillary flow during the drying process is inhibited.

[0040] In one embodiment according to the present application, the gap between the coating head and the substrate in S3 is 100-200 μm, the slurry extrusion pressure is stabilized at 0.2-0.5 MPa, and the wet film thickness uniformity Cpk≥1.67; the ultrasonic propagation direction forms an angle of 20°-40° with the coating direction, the shear component of the flow field is maximized, and when the coating line speed is 60 m / min, the slurry temperature fluctuation ≤±1°C; the slurry viscosity is adjusted in real time to 1000-4000 mPa·s, and further preferably 1500-2500 mPa·s.

[0041] In one embodiment according to the present application, the active material slurry composition of the present application can be a positive electrode slurry or a negative electrode slurry. For example, the positive electrode slurry composition can be: NCM811 (mass ratio 95%), conductive carbon black (mass ratio 2%), PVDF (mass ratio 3%), the solvent is NMP, and the solid content is 70%; the negative electrode slurry composition can be: graphite (mass ratio 95%), CMC (mass ratio 2%), SBR (mass ratio 3%), the solvent is deionized water, and the solid content is 50%.

[0042] In one embodiment according to the present application, the humidity control in each drying section of S4 is: 30% in the first stage, 20% in the second stage, and 10% in the third stage, to avoid surface crusting, optimize the solvent diffusion path, and shorten the drying time; the length ratio of the three drying zones is 2:1:1, matching the solvent evaporation rate, and the moisture gradient inside the wet film ≤0.5%.

[0043] In one embodiment according to the present application, the scanning path of the picosecond laser in S5 is concentric circle diffusion type, and the overlap rate of the heat affected zone ≤5%, to avoid carbonization caused by repeated heating; the scanning spacing is 10-20 μm, and the remelting depth of the micro-region ≤5 μm, reducing the risk of thermal damage to the substrate and improving the bonding strength between the repair area and the substrate.

[0044] In one embodiment according to the present application, the surface of the piezoelectric micro-roller in S5 is coated with a hard tungsten carbide coating, and the surface roughness Ra of the coating ≤0.1μm, reducing the roller surface friction coefficient and the scratch rate of the pole piece surface; the vibration direction is perpendicular to the roller pressing travel direction, improving the vibration energy transfer efficiency, and the deviation of the compaction density ≤0.5%.

[0045] In an embodiment according to the present application, it further includes step S6: performing post-treatment on the repaired pole piece with nitrogen plasma, with a treatment power of 100 - 150 W and a time of 10 - 30 seconds; which can reduce the oxygen content on the surface of the pole piece, improve the conductivity of the carbon layer; and form a dense nitride layer on the surface to reduce the electrolyte wetting angle.

[0046] In an embodiment according to the present application, an infrared temperature measurement module is provided at the outlet of the coater in S3 to monitor the wet film temperature in real time and feedback to adjust the ultrasonic power, with a temperature control accuracy of ±1 °C. The slurry viscosity fluctuation ≤5%, and the temperature difference between the edge and the center of the wet film ≤2 °C.

[0047] In an embodiment according to the present application, the laser scanning detection system in S5 uses a convolutional neural network to identify shrinkage holes, with an identification accuracy ≥99%. Among them, the detection speed reaches 200 frames / second, and the missed detection rate ≤0.1% (the missed detection rate of the traditional threshold method ≥5%)

[0048] In an embodiment according to the present application, the substrate in S1 is an etched aluminum foil or copper foil with a surface roughness Ra ≤0.3 μm and a thickness of 10 - 20 μm, which can effectively improve the slurry anchoring strength and the pole piece peeling force.

[0049] In the second aspect according to the present application, the present application also provides a pole piece, which is prepared by the above method for suppressing the generation of shrinkage holes on the surface of the pole piece. The pole piece prepared by this method has the following characteristics: the shrinkage hole density ≤6 pieces / m², the surface density uniformity ≥96%, and the cycle capacity retention rate (after 500 times) ≥91%.

[0050] The following will specifically describe the implementation manners and mechanisms of each step in the pole piece preparation method of the present application in detail as follows:

[0051] S1. Substrate pre-activation treatment

[0052] Place the substrate in a plasma treatment chamber, introduce a mixture of argon and hexamethyldisiloxane (HMDSO), with the volume ratio of argon to HMDSO being (8 - 10):1, apply a radio frequency power of 50 - 200 W, and treat for 30 - 60 seconds to form a hydrophobic - lipophilic gradient layer on the surface of the substrate, and the surface energy difference of the gradient layer from the surface to the deep layer is 20 - 40 mN / m.

[0053] Among them, the substrate pre-activation treatment device mainly includes: a plasma treatment chamber, a radio frequency power supply, a gas mixing control system, and a vacuum pump system. During the plasma treatment process, HMDSO molecules are decomposed into active fragments in the plasma environment, including hydrocarbon groups (-CH3, hydrophobic) and oxygen-containing silicon groups (-Si-O-, lipophilic). These active fragments deposit and recombine on the surface of the substrate to form an organosiloxane network structure.

[0054] Among them, the formation mechanism of the hydrophobic-lipophilic gradient layer is as follows: In the initial stage of plasma discharge (0 - 15 seconds), a large number of free electrons in the gas preferentially interact with the hydrocarbon groups in the HMDSO molecules, causing the fragments containing -CH3 groups to be preferentially deposited on the outermost surface of the substrate, forming a hydrophobic surface (surface energy is about 20 - 25 mN / m); as the discharge time extends (15 - 45 seconds), the proportion of oxygen-containing silicon groups in the active fragments increases, forming an intermediate transition layer; in the later stage of discharge (45 - 60 seconds), the oxygen-containing groups are enriched near the surface of the substrate, forming a lipophilic property (surface energy is about 40 - 60 mN / m).

[0055] Method for measuring the surface energy gradient: Using a contact angle measuring instrument in combination with the Owens-Wendt-Rabel-Kaelble method, the contact angles of the gradient layer surface, the intermediate layer (after removing the surface layer by precisely controlled argon ion etching), and the bottom layer are measured respectively using three test liquids with different polarities (water, glycerol, and diiodomethane), and the surface energy of each layer is calculated, and then the surface energy difference is determined. Experiments show that when the surface energy difference of the gradient layer is 20 - 40 mN / m, it has the best affinity for the slurry and pollutant repellency.

[0056] The pressure in the plasma processing chamber is controlled within the range of 10 - 30 Pa, and the radio frequency is 13.56 MHz. In a low-pressure environment (< 30 Pa), the plasma uniformity is significantly improved, and the thickness uniformity of the treatment can reach ±5 nm; while when the pressure exceeds 50 Pa, the thickness fluctuation of the gradient layer can reach ±20 nm, affecting the uniformity of the gradient layer. The radio frequency of 13.56 MHz is the frequency that has been experimentally proven to be most suitable for the decomposition of HMDSO, which can achieve efficient decomposition while maintaining the integrity of the molecular structure.

[0057] The volume ratio of argon to HMDSO has a significant impact on the characteristics of the gradient layer: when the ratio < 8:1, the concentration of HMDSO is too high, and it is easy to form powdery deposits rather than a dense gradient layer; when the ratio > 10:1, the concentration of HMDSO is too low, and it is difficult to form a gradient layer with an effective thickness in a short time. Through systematic experimental optimization, it is determined that the volume ratio range of 8 - 10:1 can form a surface modification layer with an appropriate thickness (15 - 30 nm) and an obvious gradient within 30 - 60 seconds.

[0058] The selection of the radio frequency power (50 - 200 W) is also the result of optimization: when the power is lower than 50 W, the plasma density is insufficient, and the decomposition rate of HMDSO is low, making it difficult to form an effectively covered gradient layer; when the power is higher than 200 W, the plasma energy is too high, which will cause excessive etching of the substrate surface and even cause thermal damage. The power range of 50 - 200 W can effectively excite the plasma while avoiding damage to the substrate.

[0059] S2. Slurry Modification Treatment

[0060] Add a zwitterionic block copolymer with a mass percentage of 0.1% - 0.5% and nano-titanium dioxide particles with a mass percentage of 0.05% - 0.2% to the active material slurry, and adjust the surface tension of the slurry to 25 - 30 mN / m. The particle size of the nano-titanium dioxide is 20 - 50 nm.

[0061] The zwitterionic block copolymer (preferably poly(sulfobetaine)-poly(ethylene oxide)) plays a key role in slurry modification. The molecular structure of this copolymer consists of a hydrophilic segment (poly(sulfobetaine), carrying positive and negative ionic groups) and a hydrophobic segment (poly(ethylene oxide)). The molar ratio of the hydrophilic segment to the hydrophobic segment is preferably (2 - 4):1. Its working mechanism is as follows:

[0062] 1) Charge neutralization effect: The positive and negative ionic groups in the poly(sulfobetaine) segment are arranged at the slurry-air interface, reducing the interfacial polarity difference, and thus reducing the surface tension;

[0063] 2) Adsorption stabilization: The hydrophobic segment (poly(ethylene oxide)) adsorbs on the surface of the active material particles, and the hydrophilic segment extends into the solvent, forming a three-dimensional barrier to enhance the stability of the slurry;

[0064] 3) Interface matching function: Adjust the surface tension of the slurry to the range of 25 - 30 mN / m, which matches the surface energy gradient of the pre-activated substrate, reducing the risk of local surface tension mismatch caused by contaminants.

[0065] When the addition amount of the zwitterionic block copolymer < 0.1%, the surface tension adjustment effect is not obvious; when the addition amount > 0.5%, it will increase the viscosity of the slurry and affect the coating fluidity. Experimental data show that the effect is the best when the addition amount is in the range of 0.3% - 0.4%. At this time, the Zeta potential of the slurry is stable at -28 mV to -32 mV, and the particle aggregation rate is controlled below 3%.

[0066] The nano-titanium dioxide particles, as the second modifier, mainly play the following roles in the slurry:

[0067] 1) Rheology adjustment: Nano-titanium dioxide has thixotropy, increasing the yield stress of the slurry and improving its ability to resist flow deformation, especially inhibiting capillary flow during the drying process;

[0068] 2) Three-dimensional network structure formation: The nano-particles form a three-dimensional network structure in the slurry, improving the stability and anti-settling performance of the slurry;

[0069] 3) Interface anchoring effect: Form multiple-point contacts with the substrate surface, enhancing the anchoring strength of the wet film on the substrate.

[0070] The particle size of nano-titanium dioxide is controlled within the range of 20 - 50 nm. Particles within this size range can be effectively dispersed in the slurry without significantly increasing the slurry viscosity. When the particle size is <20 nm, the nano-particles tend to agglomerate; when the particle size is >50 nm, the rheological adjustment effect weakens.

[0071] To enhance the compatibility between nano-titanium dioxide and the slurry components, the surface of nano-titanium dioxide is modified with a silane coupling agent (γ-methacryloxypropyltrimethoxysilane, KH-570). The surface hydroxyl density of the modified nano-titanium dioxide is ≥5 per nm², which is determined by X-ray photoelectron spectroscopy (XPS) combined with a quantitative analysis method. The specific measurement steps are as follows: Use XPS to measure the O1s peak on the sample surface, distinguish the oxygen in metal oxides, the oxygen in hydroxyl groups, and the oxygen in adsorbed water through peak fitting, and calculate the surface hydroxyl density based on the relative content of hydroxyl oxygen. A higher hydroxyl density (≥5 per nm²) ensures sufficient hydrogen bonding between nano-particles and slurry components, enhancing the stability of the network structure.

[0072] The surface tension of the modified slurry is reduced to 25 - 30 mN / m (measured using a surface tension meter at a measurement temperature of 25°C, and the measurement method is the du Noüy ring method), which forms a good match with the surface energy gradient after pre-activation treatment of the substrate, significantly reducing the driving force for the formation of pinholes.

[0073] S3. Dynamic flow field coating

[0074] Coating is carried out using a slot extrusion coater. An annular ultrasonic generator is integrated at the outlet of the coating head of the coater. The working frequency of the ultrasonic generator is 20 - 50 kHz, the power density is 0.5 - 2.0 W / cm², the coating speed is 20 - 60 m / min, and a wet film thickness of 50 - 100 μm is formed.

[0075] Among them, the annular ultrasonic generator is integrated at the outlet of the coating head, and its structure includes: an annular piezoelectric ceramic transducer, an acoustic focusing ring, a cooling system, and a power control module. The annular design ensures that ultrasonic waves can act uniformly on the entire coating width, avoiding the problem of uneven energy distribution caused by traditional point-type ultrasonic sources.

[0076] The working principle of the annular ultrasonic generator: The piezoelectric ceramic transducer converts electrical energy into mechanical vibration, and the ultrasonic energy is concentrated and directed to the slurry fluid through the acoustic focusing ring. When ultrasonic waves propagate in the slurry, the following effects occur:

[0077] 1) Acoustic streaming effect: Ultrasonic waves propagating in the liquid generate a directional flow, eliminating vortices and dead zones in the slurry and promoting the homogenization of the flow field;

[0078] 2) Shear thinning effect: High-frequency vibration enhances the shear thinning property of the slurry, reducing the flow resistance during high-speed coating.

[0079] 3) Micro-bubble removal: The cavitation effect caused by ultrasonic waves can remove the micro-bubbles in the slurry, reducing the bubble defects in the coating.

[0080] Reasons for selecting the ultrasonic working frequency in the range of 20 - 50 kHz: When the frequency is lower than 20 kHz, the acoustic wavelength is longer, the energy distribution is uneven, and audible noise may be generated; when the frequency is higher than 50 kHz, the attenuation of ultrasonic waves in the slurry increases significantly, and the action depth is limited. Experiments have shown that in the range of 30 - 40 kHz, the laminar shear effect of ultrasonic waves on the slurry is the most significant, which can effectively eliminate eddy currents and avoid the increase in slurry temperature caused by excessive vibration.

[0081] The ultrasonic power density is controlled in the range of 0.5 - 2.0 W / cm², and this range is the optimal working window obtained through a large number of experiments. When the power density is lower than 0.5 W / cm², the regulation effect of ultrasonic waves on high-viscosity slurry is insufficient; when the power density is higher than 2.0 W / cm², it will cause the local temperature of the slurry to be too high (>40°C), and even lead to the rapid volatilization of the solvent or local gelation of the slurry.

[0082] The included angle between the ultrasonic propagation direction and the coating direction is 20° - 40°. This angle design enables the components of ultrasonic waves in the slurry flow direction and the shear direction to reach the best balance. When the angle is less than 20°, the shear component is insufficient, and the flow field regulation effect is weakened; when the angle is greater than 40°, it will interfere with the normal slurry flow direction, resulting in fluctuations in the coating thickness.

[0083] The gap between the coating head and the substrate is controlled in the range of 100 - 200 μm. This design parameter is closely related to the slurry viscosity and coating speed. When the gap is less than 100 μm, the slurry pressure fluctuation increases significantly during high-speed coating, which may lead to fluctuations in the coating line speed; when the gap is greater than 200 μm, the control accuracy of slurry flow decreases, and the thickness uniformity deteriorates. Through the gap control of 100 - 200 μm and the synergistic effect of ultrasonic waves, the extrusion pressure of the slurry can be stabilized at 0.2 - 0.5 MPa, and the wet film thickness uniformity coefficient Cpk ≥ 1.67.

[0084] To further improve the stability of the coating process, an infrared temperature measurement module is integrated at the outlet of the coater to monitor the wet film temperature in real time and form a closed-loop control system, which feedback-regulates the ultrasonic power to achieve a temperature control accuracy of ±1°C. This precise temperature control ensures the stability of the rheological properties of the slurry during the coating process, controls the temperature difference between the wet film edge and the center within ≤2°C, avoids the drying stress difference caused by uneven temperature, and further reduces the risk of shrinkage pore formation.

[0085] The slurry viscosity is adjusted in real time to the range of 1000 - 4000 mPa·s. Especially for different slurry systems, it can be further optimized to the range of 1500 - 2500 mPa·s. When the viscosity is too low (<1000 mPa·s), the wet film is prone to sagging; when the viscosity is too high (>4000 mPa·s), it is difficult to achieve high-speed coating even with ultrasonic assistance. The viscosity adjustment is achieved through online viscometer monitoring and temperature fine-tuning to ensure that the viscosity fluctuation is controlled within ±5%.

[0086] S4. Gradient drying and curing

[0087] The wet film is successively subjected to three-stage drying treatment. The specific parameters are as follows: in the first stage, the temperature is 50 - 60°C, the wind speed is 2 - 4 m / s, to quickly evaporate the surface solvent and form a dense surface layer; in the second stage, the temperature is 70 - 80°C, the wind speed is 1 - 2 m / s, to drive the directional diffusion of internal solvent through the temperature gradient and avoid surface collapse; in the third stage, the temperature is 90 - 100°C, the wind speed is 0.5 - 1 m / s, for high-temperature curing to eliminate residual stress.

[0088] Gradient drying and curing is one of the key links to inhibit the formation of shrinkage holes. Its core concept is to design a three-stage temperature and wind speed gradient according to the kinetic characteristics of solvent diffusion and evaporation to achieve an orderly drying process from the outside to the inside, avoiding the common "dry on the surface and wet inside" phenomenon in traditional drying. The specific principles and parameter designs of the three-stage drying are as follows:

[0089] The first stage (surface pre-curing):

[0090] The temperature is controlled in the range of 50 - 60°C. This temperature range is higher than the boiling points of most solvents (NMP, water), but it will not cause the surface to shrink rapidly due to excessive evaporation;

[0091] The wind speed is relatively high (2 - 4 m / s) to promote the rapid volatilization of surface solvent and form a surface structure with a certain strength;

[0092] The relative humidity is controlled at 30% ± 5%. Moderate humidity can slow down the surface drying rate and prevent premature skinning;

[0093] The length of the drying area in this stage accounts for 50% of the total drying length (in a 2:1:1 ratio) to ensure sufficient surface pre-curing time.

[0094] The second stage (directional diffusion of internal solvent):

[0095] The temperature is raised to 70 - 80°C to form a temperature gradient from the inside to the outside, promoting the diffusion of internal solvent to the surface;

[0096] The wind speed is reduced to 1 - 2 m / s to reduce surface air flow disturbance and maintain a moderate surface evaporation rate;

[0097] The relative humidity is reduced to 20% ± 5%, increasing the humidity difference between the surface and the interior to form the driving force for the directional migration of the solvent;

[0098] The length of the drying zone in this stage accounts for 25% of the total drying length, providing sufficient diffusion time for the internal solvent.

[0099] The third stage (curing stress relief):

[0100] The temperature is further increased to 90 - 100 °C to ensure the complete removal of residual solvents and promote the complete curing of the binder;

[0101] The wind speed is reduced to the lowest level (0.5 - 1 m / s) to reduce the surface cooling effect and maintain a uniform temperature field;

[0102] The relative humidity is controlled at 10% ± 5% to create a low - humidity environment for the complete removal of residual moisture;

[0103] This stage realizes the transition from drying to curing and eliminates the internal stress accumulated during the drying process.

[0104] The length ratio of the three drying zones of 2:1:1 is the optimal ratio calculated based on the solvent diffusion kinetic model. Experiments have shown that under this ratio, the moisture gradient inside the electrode sheet is ≤ 0.5%, significantly lower than the 2 - 3% moisture gradient of traditional single - stage drying. The lower the moisture gradient, the more uniform the drying shrinkage and the lower the risk of shrinkage pore formation.

[0105] The humidity control in each drying section (30% in the first stage, 20% in the second stage, 10% in the third stage) is crucial for optimizing the solvent diffusion path. Humidity control is achieved through the humidity sensor and humidity adjustment system inside the closed drying oven, with a control accuracy of ±5%. Experiments have shown that according to the above - mentioned humidity gradient design, the drying time of the electrode sheet can be shortened by 15 - 20% while maintaining the drying uniformity.

[0106] S5. On - line defect repair

[0107] A laser scanning detection system is used to identify the position of shrinkage pores, and a picosecond laser with a wavelength of 355 nm, a pulse width of 10 ps, and an energy density of 0.05 - 0.1 J / cm² is used to perform micro - area remelting on the defective area. Subsequently, a pressure of 3 - 5 N / cm² is applied through a piezoelectric micro - roller and local compaction is carried out at a vibration frequency of 10 - 20 kHz.

[0108] Among them, the on - line defect repair system consists of three key parts: a defect detection unit, a laser micro - area remelting unit, and a piezoelectric micro - roller compaction unit. The entire system realizes real - time detection and repair during the continuous operation of the electrode sheet without interrupting the production line.

[0109] The defect detection unit uses a high-speed line-scan camera (resolution ≥ 8192 pixels, scanning speed ≥ 40 kHz) combined with an LED line light source to capture images of the electrode surface. Image analysis uses a defect recognition algorithm based on a convolutional neural network (CNN). This network consists of 5 convolutional layers and 3 fully connected layers, and achieves precise identification of shrinkage holes through feature extraction and classification.

[0110] The training process of the CNN algorithm uses more than 5000 labeled defect images, including shrinkage hole samples of various sizes (0.1 - 2 mm) and morphologies (pit type, crater type). The training set is augmented through data augmentation techniques (rotation, scaling, brightness adjustment, etc.) to improve the model's adaptability to different lighting conditions and defect variants. The final model achieves an identification accuracy of ≥ 99% on the test set, with a missed detection rate of ≤ 0.1%, far superior to the 5% missed detection rate of the traditional threshold method.

[0111] Once the position of the shrinkage hole is detected, the system transmits the coordinate information to the laser microzone remelting unit in real time. The laser source uses a picosecond laser with a wavelength of 355 nm, a pulse width controlled at 10 ps, and an energy density of 0.05 - 0.1 J / cm². The 355 nm wavelength is selected because it has good absorption efficiency for most electrode materials; the ultrashort pulse width of 10 ps can minimize the heat-affected zone and achieve a "cold processing" effect, avoiding material carbonization or excessive damage; the energy density is controlled in the range of 0.05 - 0.1 J / cm², which is sufficient to achieve surface remelting without damaging the substrate.

[0112] The scanning path of the picosecond laser is a concentric circle diffusion type, gradually spreading outward from the center of the shrinkage hole, with a scanning pitch of 10 - 20 μm, and the microzone remelting depth is controlled at ≤ 5 μm. This scanning mode ensures that the overlap rate of the heat-affected zone is ≤ 5%, avoiding material denaturation caused by repeated heating. The laser precisely vaporizes the raised part at the edge of the shrinkage hole, while softening the material around the concave area, creating conditions for subsequent compaction.

[0113] After laser treatment, the defective area is immediately locally compacted by a piezoelectric micro-roller. The core of the piezoelectric micro-roller is a precisely controlled piezoelectric ceramic actuator that can generate high-frequency vibrations at a frequency of 10 - 20 kHz. The surface of the micro-roller is coated with a hard tungsten carbide coating with a thickness of about 10 - 15 μm and a surface roughness Ra ≤ 0.1 μm. This coating provides sufficient wear resistance and ensures low-friction contact with the electrode surface, reducing the risk of scratches.

[0114] The piezoelectric micro-roller applies a pressure of 3 - 5 N / cm², and this pressure range is the optimal working window determined through experiments: when the pressure is less than 3 N / cm², the compaction effect on the softened material is insufficient; when the pressure is greater than 5 N / cm², it may cause over-compression of the electrode sheet or deformation of the substrate. The vibration direction is perpendicular to the rolling direction, and this design enables the vibration energy to be more effectively transmitted to the surface of the electrode sheet, improving the compaction efficiency. The combination of high-frequency vibration (10 - 20 kHz) and pressure causes the material in the defective area to redistribute in a plastic flow state, filling the concave areas and ultimately forming a flat surface.

[0115] The collaborative work of laser micro-area remelting and piezoelectric micro-roller compaction is achieved through precise timing control and spatial positioning. A high-speed data processing unit and a servo positioning system are adopted in the system to ensure that the full-process response time from defect detection to repair completion is ≤50 ms, meeting the real-time processing requirements of high-speed production lines (up to 60 m / min). The density deviation of the repaired defective area is ≤0.5%, the surface roughness is close to that of the non-defective area, and the overall consistency of the electrode sheet is significantly improved.

[0116] S6. Nitrogen plasma post-treatment

[0117] The repaired electrode sheet is subjected to nitrogen plasma post-treatment with a treatment power of 100 - 150 W and a time of 10 - 30 seconds to form a nitride layer with a thickness of 5 - 10 nm.

[0118] This optional step further improves the surface performance and electrochemical characteristics of the electrode sheet. The nitrogen plasma post-treatment uses nitrogen with a purity ≥99.999% and is carried out under low pressure (20 - 30 Pa). The active nitrogen atoms and nitrogen ions in the plasma react with the surface of the electrode sheet to form a nitride layer with a thickness of 5 - 10 nm.

[0119] The nitrogen plasma post-treatment mainly brings the following three aspects of improvement:

[0120] 1) Reducing the surface oxygen content: The plasma treatment significantly reduces the oxygen content on the surface of the electrode sheet (measured by XPS, the oxygen content drops from 12 - 15% to 4 - 6%), reduces the oxygen-containing functional groups on the surface of the carbon material, and improves the conductivity;

[0121] 2) Forming a nitride protection layer: The nitride layer formed on the surface has good chemical stability, can reduce the side reactions between the electrode sheet and the electrolyte, and improve the first Coulomb efficiency and cycle stability;

[0122] 3) Improving the electrolyte wettability: After nitrogen plasma treatment, the electrolyte contact angle on the surface of the electrode sheet drops from 35 - 40° to 10 - 15°, significantly increasing the electrolyte wetting speed and improving the liquid injection uniformity of the battery.

[0123] The processing power control within the range of 100 - 150 W is the result of optimization based on a large number of experiments: when the power is lower than 100 W, the nitrogen atom concentration is insufficient and the surface modification effect is not significant; when the power is higher than 150 W, it may cause overheating on the surface of the electrode sheet, affecting the structural stability of the active material. The processing time of 10 - 30 seconds is the best time window to achieve effective nitridation while avoiding over - processing.

[0124] It is confirmed by transmission electron microscopy (TEM) and X - ray photoelectron spectroscopy (XPS) analysis that the formed nitride layer has a thickness of 5 - 10 nm, a nitrogen content of 4 - 8 at.%, and mainly exists in three forms: pyridine - type nitrogen, pyrrole - type nitrogen, and graphite - type nitrogen. These different types of nitrogen doping all contribute significantly to improving the rate performance and cycle life of the battery.

[0125] The implementation and advantages of the present application will be further described below in conjunction with specific embodiments.

[0126] Example 1

[0127] A preparation method for suppressing the generation of shrinkage holes on the surface of the electrode sheet provided in this example includes the following steps:

[0128] Step S1. Substrate pre - activation treatment:

[0129] Use etched aluminum foil (Ra = 0.25μm, thickness 15μm) as the substrate;

[0130] Place the substrate in a plasma treatment chamber, introduce argon and HMDSO (volume ratio 9:1), and the pressure is 20 Pa;

[0131] Apply a radio - frequency power of 150 W, a frequency of 13.56 MHz, and a treatment time of 45 seconds to generate a hydrophobic - lipophilic layer with a surface energy difference of 30 mN / m (hydrophobic contact angle 98°, lipophilic contact angle 28°).

[0132] Step S2. Slurry modification treatment:

[0133] Add 0.3% poly - sulfobetaine - polyethylene oxide (hydrophilic / hydrophobic segment ratio 3:1) and 0.1% silica - modified nano - titanium dioxide (particle size 30 nm, hydroxyl density 6 per nm²) to the active material slurry (LiNi 0.8 Co 0.1 Mn 0.1 O2: conductive carbon black: PVDF = 95:2:3, solid content 70%);

[0134] Adjust the surface tension of the slurry to 28 mN / m and the viscosity to 2000 mPa·s (test standard: GB / T 10247 - 2008).

[0135] Step S3. Dynamic flow field coating:

[0136] A slot extrusion coater with a coating head gap of 150 μm. Parameters of the ultrasonic generator: frequency 30 kHz, power density 1.2 W / cm², and an angle of 30° with the coating direction;

[0137] Coating speed 50 m / min, wet film thickness 80 μm, and on-line infrared temperature control accuracy of ±1°C.

[0138] Step S4. Gradient drying and curing:

[0139] Parameters of the three-stage drying:

[0140] The first stage: 55°C, wind speed 3 m / s, humidity 30%, length 2 m;

[0141] The second stage: 75°C, wind speed 1.5 m / s, humidity 20%, length 1 m;

[0142] The third stage: 95°C, wind speed 0.8 m / s, humidity 10%, length 1 m;

[0143] The moisture content of the dried electrode sheet is 180 ppm, and the surface roughness Ra = 0.45 μm.

[0144] Step S5. On-line defect repair:

[0145] A convolutional neural network (CNN) is used to identify shrinkage holes (recognition accuracy 99.2%);

[0146] Parameters of the picosecond laser: wavelength 355 nm, energy density 0.08 J / cm², scanning pitch 15 μm, remelting depth 4 μm;

[0147] Vibration frequency of the piezoelectric micro-roller 15 kHz, pressure 4 N / cm², surface roughness Ra = 0.08 μm.

[0148] Step S6. Nitrogen plasma post-treatment:

[0149] Treatment power 120 W, time 20 s, and an 8-nm nitride layer is formed on the surface of the electrode sheet.

[0150] Examples 2 - 5

[0151] Differences from Example 1 lie in the parameter settings during preparation, as shown in Table 1 specifically. Others are the same as in Example 1 and will not be elaborated here.

[0152] Table 1 Example S1 Processing Power (W) <![CDATA[Addition amount of S2 nano-TiO2 (%)]]> S3 Coating Speed (m / min) S4 Total Drying Time (min) S5 Laser Energy Density (J / cm²) Example 2 100 0.08 40 7 0.06 Example 3 200 0.15 60 9 0.10 Example 4 120 0.12 55 8 0.07 Example 5 180 0.20 30 6 0.09

[0153] Comparative Example 1

[0154] This comparative example uses traditional processes (where steps S1 and S5 are absent, only coating solution filtration + environmental cleaning).

[0155] Comparative Example 2

[0156] Different from Example 1, this comparative example has no substrate pre-activation step (S1);

[0157] Others are the same as Example 1 and will not be elaborated here.

[0158] Comparative Example 3

[0159] Different from Example 1, this comparative example has no slurry modification step (S2);

[0160] Others are the same as Example 1 and will not be elaborated here.

[0161] Comparative Example 4

[0162] Different from Example 1, this comparative example has no ultrasonic coating (S3);

[0163] Others are the same as Example 1 and will not be elaborated here.

[0164] Comparative Example 5

[0165] Different from Example 1, this comparative example has no gradient drying step (S4 uses a constant temperature of 80 °C);

[0166] Others are the same as Example 1 and will not be elaborated here.

[0167] The following performance tests were respectively carried out on the electrode sheets prepared in the above examples and comparative examples, and the test results are shown in Table 2.

[0168] 1) Pore density (unit: pieces / m²):

[0169] Testing equipment: Laser confocal microscope (Olympus OLS5000);

[0170] Steps: Take a 10 cm × 10 cm electrode sheet sample, scan the surface to count the number of craters / pits, and take the average value of 3 times.

[0171] 2) Areal density uniformity (unit: %):

[0172] Testing equipment: X-ray areal density meter (Hefei Ke Jing MS-500);

[0173] Steps: Measure the areal density every 5 cm along the longitudinal direction of the electrode sheet, calculate the ratio of the standard deviation to the mean value, formula:

[0174] Uniformity = (1 - standard deviation average value) × 100% Uniformity = (1 - average value standard deviation) × 100%

[0175] 3) Cycle capacity retention rate (unit: %):

[0176] Testing equipment: Blue Electric Battery Testing System (CT-4008);

[0177] Steps: Assemble a button cell (LiNi 0.8 Co 0.1 Mn 0.1 O2 vs Li metal), charge and discharge at 0.5C, and the ratio of the capacity after 500 cycles to the initial discharge capacity.

[0178] Table 2 Group Pinhole Density (pcs / m²) Areal Density Uniformity (%) Capacity Retention Rate (%) Drying Time (min) Example 1 3 98.3 93.7 8 Example 2 5 97.5 92.8 7 Example 3 2 98.6 94.1 9 Example 4 4 97.9 93.5 8 Example 5 6 96.8 91.9 6 Comparative Example 1 50 91.8 83.5 15 Comparative Example 2 35 93.2 88.1 8 Comparative Example 3 27 94.5 89.4 9 Comparative Example 4 16 96.0 91.2 8 Comparative Example 5 14 95.3 90.8 7

[0179] The analysis of the above test results is as follows:

[0180] 1. Comparative analysis between the examples and the comparative examples:

[0181] 1) Pore shrinkage density: The pore shrinkage density of Examples 1-5 is all lower than 6 per m², while that of Comparative Examples 1-5 is in the range of 14-50 per m², significantly higher than that of the example group. Among them, when comparing Example 1 (3 per m²) with Comparative Example 1 (50 per m²), the pore shrinkage density is reduced by 94%, proving the significant advantage of the process of the present invention. The pore shrinkage density of Comparative Example 2 (without pre-activation of S1 substrate) is 35 per m², indicating that the surface energy gradient design plays a key role in suppressing pore shrinkage. The pore shrinkage density of Comparative Example 3 (without modification of S2 slurry) is 27 per m², showing that the synergistic effect of zwitterionic block copolymer and nano-titanium dioxide has an important influence on controlling the surface tension and rheological properties of the slurry.

[0182] 2) Areal density uniformity: The uniformity of the examples is ≥96.8%, up to 98.6% at most; while that of the traditional process (Comparative Example 1) is only 91.8%; the improvement of the areal density uniformity mainly benefits from the synergistic optimization of dynamic flow field coating (S3) and gradient drying (S4), and these two steps jointly ensure the uniform flow and smooth drying of the slurry under high-speed coating conditions. The uniformity of Comparative Example 4 (without ultrasonic coating) is 96.0%, showing an obvious decrease compared with Example 1 (98.3%), confirming the positive effect of ultrasonic-assisted coating on improving the coating uniformity.

[0183] 3) Capacity retention rate: The capacity retention rate of Examples 1-5 is ≥91.9%, up to 94.1% at most; that of Comparative Example 1 is only 83.5%; the increase in the capacity retention rate is mainly attributed to the significant reduction of the pore shrinkage defects on the electrode sheet and the improvement of the areal density uniformity, which reduces the local stress concentration during cycling and delays the growth of lithium dendrites. The capacity retention rate of Comparative Example 1 is the lowest (83.5%), indicating that the high pore shrinkage density under the traditional process has an obvious negative impact on the long-term cycling performance of the battery.

[0184] 4) Drying time: The drying time of the example group was significantly lower than that of Comparative Example 1. This is mainly due to the optimization of the solvent diffusion path by the gradient drying design (S4) and the improvement of the drying performance brought about by the slurry modification (S2). Even under high-speed production conditions (Example 3, coating speed 60 m / min), the method of the present invention can still maintain an extremely low pinhole density (2 per m²) and excellent electrochemical performance.

[0185] 2. Comparative analysis among each example:

[0186] 1) Example 3 (S1 power 200 W, coating speed 60 m / min) has the best comprehensive performance, which indicates that high-power plasma treatment can form a more stable surface energy gradient layer and enhance the anti-pinhole ability; at the same time, the method of the present invention performs excellently under high-speed coating conditions and has good industrial application prospects.

[0187] 2) The pinhole density of Example 5 (S2 nano-TiO₂ addition amount 0.20%) is relatively high (6 per m²), and the areal density uniformity and capacity retention rate are also slightly lower than those of other examples. This may be due to the decrease in the dispersibility of the slurry caused by the excessive addition of nano-TiO₂, which affects the coating and drying uniformity. This result shows that the dosage of the nano-additive needs to be precisely controlled, and too much or too little will affect the performance of the electrode sheet.

[0188] 3) The capacity retention rate of the repaired electrode sheet in Example 2 (low laser energy density 0.06 J / cm²) is 92.8%, slightly lower than that in Example 1 (93.7%), but the low laser energy density can ensure defect repair while preventing damage to the electrode sheet.

[0189] 4) In terms of drying time, Example 5 has the shortest drying time, but its performance indicators are relatively low, indicating that too fast drying speed may affect the quality of the electrode sheet; while Example 3 has the longest drying time, but obtains the best performance indicators, indicating that appropriately extending the drying time is beneficial to improving the quality of the electrode sheet. In actual production, the best drying time can be selected according to production capacity and quality requirements.

[0190] Based on the disclosure and teachings of the above specification, those skilled in the art to which the present invention pertains can also 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 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 preparation method for suppressing the generation of shrinkage holes on the surface of the electrode sheet, characterized in that, It includes the following steps: S1. Substrate pre-activation treatment: Place the substrate in a plasma treatment chamber, introduce a mixture of argon and hexamethyldisiloxane, where the volume ratio of argon to hexamethyldisiloxane is (8 - 10):1, apply a radio frequency power of 50 - 200 W, and treat for 30 - 60 seconds to form a hydrophobic-lipophilic gradient layer on the substrate surface. The surface energy difference of the gradient layer from the surface to the bottom layer is 20 - 40 mN / m; S2. Slurry modification treatment: Add 0.1% - 0.5% by mass of zwitterionic block copolymer and 0.05% - 0.2% by mass of nano-titanium dioxide particles to the active material slurry, and adjust the surface tension of the slurry to 25 - 30 mN / m. The particle size of the nano-titanium dioxide is 20 - 50 nm; S3. Dynamic flow field coating: Use a slot extrusion coater for coating. An annular ultrasonic generator is integrated at the outlet of the coating head of the coater. The working frequency of the ultrasonic generator is 20 - 50 kHz, the power density is 0.5 - 2.0 W / cm², the coating speed is 20 - 60 m / min, and a wet film thickness of 50 - 100 μm is formed; S4. Gradient drying and curing: The wet film is successively subjected to three-stage drying treatment. The specific parameters are: the temperature in the first stage is 50 - 60°C, and the wind speed is 2 - 4 m / s; the temperature in the second stage is 70 - 80°C, and the wind speed is 1 - 2 m / s; the temperature in the third stage is 90 - 100°C, and the wind speed is 0.5 - 1 m / s; S5. On-line defect repair: Use a laser scanning detection system to identify the position of the shrinkage holes, use picosecond laser to perform micro-area remelting on the defect area, and then apply a pressure of 3 - 5 N / cm² through a piezoelectric micro-roller and perform local compaction at a vibration frequency of 10 - 20 kHz.

2. The preparation method for suppressing the generation of shrinkage holes on the surface of the pole piece according to claim 1, characterized in that, In S1, the pressure in the plasma treatment chamber is 10 - 30 Pa, and the radio frequency is 13.56 MHz.

3. The preparation method for suppressing the generation of shrinkage holes on the surface of the electrode tab according to claim 1, characterized in that, The zwitterionic block copolymer in S2 is poly(sulfobetaine)-poly(ethylene oxide), and the molar ratio of its hydrophilic segment to hydrophobic segment is (2 - 4):

1.

4. The preparation method for suppressing the generation of shrinkage holes on the surface of the pole piece according to claim 1, characterized in that, The surface of the nano-titanium dioxide in S2 is modified with a silane coupling agent, and the hydroxyl density is ≥5 per nm².

5. The preparation method for suppressing the generation of shrinkage holes on the surface of the pole piece according to claim 1, wherein In S3, the gap between the coating head and the substrate is 100 - 200 μm, the ultrasonic propagation direction forms an angle of 20° - 40° with the coating direction, and the slurry viscosity is adjusted in real time to 1000 - 4000 mPa·s.

6. The preparation method for suppressing the generation of shrinkage holes on the surface of the pole piece according to claim 1, wherein, In S4, the humidity control of each drying section is: 30% in the first stage, 20% in the second stage, 10% in the third stage, and the length ratio of the three drying zones is 2:1:

1.

7. The preparation method for suppressing the generation of shrinkage holes on the surface of the electrode tab according to claim 1, wherein, In S5, the wavelength of the picosecond laser is 355 nm, the pulse width is 10 ps, and the energy density is 0.05 - 0.1 J / cm²; the scanning path of the picosecond laser is concentric circle diffusion type, the scanning spacing is 10 - 20 μm, and the micro-area remelting depth is ≤5 μm.

8. The preparation method for suppressing the generation of shrinkage holes on the surface of the pole piece according to claim 1, characterized in that, The surface of the piezoelectric micro-roller in S5 is coated with a hard tungsten carbide coating, and the surface roughness Ra of the coating is ≤0.1 μm, and the vibration direction is perpendicular to the roller pressing travel direction.

9. The preparation method for suppressing the generation of shrinkage holes on the surface of the pole piece according to claim 1, characterized in that, It further includes step S6: performing post-treatment on the repaired pole piece by nitrogen plasma, with a treatment power of 100-150 W and a time of 10-30 seconds.

10. A pole piece, characterized in that, It is prepared by the preparation method for suppressing the generation of shrinkage holes on the surface of the pole piece according to any one of claims 1 to 9.

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