Lithium battery separator and preparation method and application thereof

Abstract

The application discloses a lithium battery diaphragm and a preparation method and application thereof, and belongs to the technical field of diaphragms. The lithium battery diaphragm comprises a porous base material and an inorganic ceramic coating arranged on at least one side surface of the porous base material; the inorganic ceramic coating contains a binder and inorganic ceramics coated with a styrene-maleic anhydride copolymer; the area coverage rate of the styrene-maleic anhydride copolymer on the surface of the inorganic ceramics is 10% to 100%, and the mass coverage rate of the styrene-maleic anhydride copolymer on the surface of the inorganic ceramics is 1% to 10%. The styrene-maleic anhydride copolymer can be used to direct coating of the ceramics and reduction of the water content of the ceramics. The styrene-maleic anhydride copolymer not only has a dispersing effect, but also can effectively reduce the water content in the diaphragm; in addition, the granular binder and the non-granular binder can be combined to construct a three-dimensional network, effectively improve the adhesion between the coating and the base film, and improve the electrochemical performance of the battery.

Description

Technical Field

[0001] This invention relates to the field of separator technology, and more specifically, to a lithium battery separator, its preparation method, and its application. Background Technology

[0002] The separator in a lithium-ion battery is a crucial component for ensuring battery safety and ion transport, and its moisture content directly affects the battery's cycle performance and safety. Existing coated separators are typically prepared using aqueous or water-containing systems, especially in ceramic coatings, inorganic / organic composite coatings, and functionalized coatings, where water is widely used as a dispersion medium or process solvent. Under current technological conditions, a certain amount of moisture is inevitably introduced or left behind during the preparation, winding, and storage of coated separators, and this moisture is difficult to remove completely without increasing process costs. Residual moisture in the separator can have several adverse effects on lithium-ion battery performance during cell manufacturing and use. On the one hand, moisture in the electrolyte system can trigger the decomposition reaction of lithium salts (such as LiPF6), generating corrosive byproducts such as HF, thereby exacerbating the corrosion of positive and negative electrode materials and current collectors, damaging the stability of the electrode / electrolyte interface, leading to increased internal resistance, accelerated capacity decay, and reduced cycle life. On the other hand, moisture can also affect the formation quality of the solid electrolyte interface (SEI / CEI), inducing more side reactions, thus reducing battery consistency and reliability. For high-energy-density power batteries and energy storage batteries, the negative impact of moisture in the separator is particularly significant.

[0003] In the prior art, to reduce the moisture content of ceramic-coated diaphragms, amphiphilic polymers are usually added as water-blocking agents to modify the ceramic. However, traditional water-blocking agents mostly rely on physical adsorption to coat the ceramic surface. During high-speed shearing of the slurry or wetting of the electrolyte, the water-blocking layer is prone to fall off or uneven distribution, resulting in a deterioration of the water-blocking effect. In addition, the above methods also greatly increase the production cost and the instability of the slurry system.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of this invention is to provide a lithium battery separator, its preparation method, and its application, so as to solve or improve the above-mentioned technical problems.

[0006] This invention can be implemented as follows: In a first aspect, the present invention provides a lithium battery separator, comprising a porous substrate and an inorganic ceramic coating disposed on at least one surface of the porous substrate; Inorganic ceramic coatings contain binders and inorganic ceramics coated with styrene-maleic anhydride copolymers; Adhesives include particulate adhesives and non-particulate adhesives; The area coverage of styrene-maleic anhydride copolymer on the surface of inorganic ceramics is 10%~100%, and the mass coverage of styrene-maleic anhydride copolymer on the surface of inorganic ceramics is 1%~10%.

[0007] In an optional embodiment, the area coverage of the styrene-maleic anhydride copolymer on the inorganic ceramic surface is 17% to 95%; the mass coverage of the styrene-maleic anhydride copolymer on the inorganic ceramic surface is 1.1% to 5.2%.

[0008] In an optional embodiment, the inorganic ceramic in the inorganic ceramic coating has a mass percentage of 50% to 92%, preferably 87% to 92%.

[0009] In an optional embodiment, the particle size of the inorganic ceramic is 0.01 μm to 5 μm.

[0010] In an optional embodiment, the styrene-maleic anhydride copolymer is present in the inorganic ceramic coating at a mass percentage of 1% to 20%, preferably 1% to 6%.

[0011] In an optional embodiment, the molar ratio of styrene to maleic anhydride in the styrene-maleic anhydride copolymer is 1:10 to 4:10.

[0012] In an optional embodiment, the adhesive contains 33% to 67% particulate adhesive, with the balance being non-particulate adhesive.

[0013] In an optional embodiment, the particle size of the particulate binder is 0.05 μm to 1 μm.

[0014] In an optional embodiment, the lithium battery separator has at least one of the following characteristics: Feature 1: The porosity of the porous substrate is 30%~50%; Feature 2: The thickness of the porous substrate is 1μm~25μm; Feature 3: The thickness of the inorganic ceramic coating is 0.1μm~5μm; Feature 4: The air permeability increment of the lithium battery separator does not exceed 50s / 100cc; Feature 5: The longitudinal thermal shrinkage rate of the lithium battery separator at 120℃ / h is <3.5%; Feature 6: The lateral thermal shrinkage rate of the lithium battery separator at 120℃ / h is <3.0%; Feature 7: The water content of the lithium battery separator does not exceed 700 ppm; Feature 8: The coating peel strength of the lithium battery separator is not less than 72 N / m.

[0015] In a second aspect, the present invention provides a method for preparing a lithium battery separator as described in any of the foregoing embodiments, comprising the following steps: mixing an inorganic ceramic with a styrene-maleic anhydride copolymer activation solution and then subjecting the mixture to heat treatment to obtain a first mixture; mixing the first mixture with a binder to obtain a coating slurry; coating the coating slurry onto at least one side surface of a porous substrate and drying it.

[0016] In an optional embodiment, the styrene-maleic anhydride copolymer activation solution is obtained by high-shear pre-activation of the styrene-maleic anhydride copolymer in a solvent.

[0017] In an optional embodiment, the high-shear pre-activation shear rate is 3000 rpm to 5000 rpm, and the time is 40 min to 90 min.

[0018] In an optional embodiment, the pH of the styrene-maleic anhydride copolymer activation solution is 7.0 to 9.0.

[0019] In an optional embodiment, the inorganic ceramic is added to the styrene-maleic anhydride copolymer activation solution in n separate additions and sheared, wherein the shear rate after the nth addition is greater than the shear rate after the (n-1)th addition.

[0020] In an optional embodiment, the heat treatment temperature is 45°C to 60°C, and the time is 1 hour to 2 hours.

[0021] In an optional embodiment, the preparation of the coating slurry includes: first mixing a first mixture with a non-particulate binder to obtain a second mixture; then mixing the second mixture with a particulate binder to obtain the coating slurry.

[0022] Thirdly, the present invention provides a battery comprising a lithium battery separator according to any of the foregoing embodiments.

[0023] The beneficial effects of this invention include: This application utilizes a styrene-maleic anhydride copolymer to replace conventional dispersants for encapsulating inorganic ceramics. This not only provides superior dispersion but also allows the anhydride groups of maleic anhydride to form strong hydrogen bonds and even chemical bonds with the hydroxyl groups on the ceramic surface under ring-opening conditions. The hydrophobic segments of styrene face outwards, forming steric hindrance and a hydrophobic layer, effectively reducing the water content of the inorganic ceramic coating. By compounding particulate and non-particulate binders, where the particulate binder achieves "point contact" and the non-particulate binder constructs a three-dimensional network through "line / surface contact," the adhesion and peel strength between the coating and the base film are effectively improved. With the combination of the aforementioned styrene-maleic anhydride copolymer and binder, the diaphragm also exhibits superior overall performance in terms of heat resistance and air permeability. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 The image shows a transmission electron microscope (TEM) image of the lithium battery separator prepared in Example 1. Figure 2 for Figure 1 Lattice spacing diagram of Al2O3; Figure 3 for Figure 1 Enlarged view of the local interface between the SMA coating layer and Al2O3. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0027] The following is a detailed description of the lithium battery separator, its preparation method, and its application provided by this invention. In this text, SMA refers to styrene-maleic anhydride copolymer, PAA-Na refers to sodium polyacrylate, PA refers to acrylate emulsion, PVA refers to modified polyvinyl alcohol, and MA refers to maleic anhydride.

[0028] This application provides a lithium battery separator, which includes a porous substrate and an inorganic ceramic coating disposed on at least one side surface of the porous substrate.

[0029] This inorganic ceramic coating contains a binder and inorganic ceramics coated with a styrene-maleic anhydride copolymer. It should be noted that the means of achieving styrene-maleic anhydride copolymer coating of inorganic ceramics include, but are not limited to, the interaction between maleic anhydride and the inorganic ceramic surface through hydrogen bonds and other chemical bonds.

[0030] In this application, the adhesive includes particulate adhesives and non-particulate adhesives.

[0031] In some alternative embodiments, the adhesive may contain 33wt% to 67wt% of particulate adhesive, with the balance being non-particulate adhesive. In other words, the mass percentage of particulate adhesive in the adhesive may be 33wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, or 67wt%, or other values ​​within the range of 33wt% to 67wt%.

[0032] If the adhesive contains too little particulate binder (too much non-particulate binder), it can easily clog the micropores of the coating and worsen its breathability; the non-particulate binder itself has a high moisture content, leading to an increase in the overall moisture content of the coating. If the adhesive contains too much particulate binder (too little non-particulate binder), it can easily lead to a decrease in the peel strength of the coating and cause powdering.

[0033] In some alternative embodiments, the particle size of the particulate binder can be 0.05 μm to 1 μm, such as 0.05 μm, 0.1 μm, 0.2 μm, 0.5 μm, 0.8 μm or 1 μm, or other values ​​within the range of 0.05 μm to 1 μm.

[0034] In some alternative embodiments, particulate binders may, by way of example but not limitation, include modified polyvinyl alcohol; non-particulate binders may, by way of example but not limitation, include acrylate emulsions. The modified polyvinyl alcohol can be obtained by in-situ crosslinking modification of PVA with a silane coupling agent. For example, a silane coupling agent (such as KH560) can be introduced into the PVA slurry, followed by drying. During the drying process, the silanol groups of the silane coupling agent undergo dehydration condensation with the hydroxyl groups of PVA to form a Si-OC or Si-O-Si strongly crosslinked network. This highly crosslinked "network" can physically lock the water-absorbing active sites of the hydroxyl groups, preventing them from forming hydrogen bonds with water molecules in the environment, thereby reducing the water absorption rate.

[0035] In this application, the area coverage of the styrene-maleic anhydride copolymer on the inorganic ceramic surface is 10% to 100%, such as 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 100%, or other values ​​within the range of 10% to 100%. In some typical embodiments, the area coverage of the styrene-maleic anhydride copolymer on the inorganic ceramic surface is 17% to 95%.

[0036] If the area coverage of the styrene-maleic anhydride copolymer on the inorganic ceramic surface is less than 10%, it is not conducive to building an effective hydrophobic barrier on the inorganic ceramic surface, and it cannot fully mask the hydrophilic hydroxyl sites on the inorganic ceramic surface, making it difficult to control the residual moisture of the coated membrane to below 700 ppm.

[0037] In this application, the mass coating rate of the styrene-maleic anhydride copolymer on the inorganic ceramic surface is 1% to 10%, such as 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%, or other values ​​within the range of 1% to 10%. In some typical embodiments, the mass coating rate of the styrene-maleic anhydride copolymer on the inorganic ceramic surface is 1.1% to 5.2%.

[0038] If the mass coverage rate of the styrene-maleic anhydride copolymer on the inorganic ceramic surface is less than 1%, it is not conducive to constructing an effective hydrophobic barrier on the inorganic ceramic surface, and it cannot fully mask the hydrophilic hydroxyl sites on the inorganic ceramic surface, making it difficult to control the residual moisture of the coated membrane below 700 ppm. If the mass coverage rate of the styrene-maleic anhydride copolymer on the inorganic ceramic surface is higher than 10%, the excessive copolymer molecules will undergo multi-layer entanglement and accumulation between the inorganic ceramics, which is not conducive to maintaining the original porous structure of the coating, leading to deterioration of the membrane's permeability; at the same time, excessive free organic phase will also affect the rheological stability of the slurry.

[0039] In this paper, the area coverage and mass coverage can be tested as follows: Thermogravimetric analysis (TGA) is performed on the washed and dried modified ceramic powder (i.e., inorganic ceramic coated with styrene-maleic anhydride copolymer). The mass loss fraction after drying at 600℃ is the mass fraction W of the surface chemically bonded organic matter (SMA). SMA The specific surface area S of the original inorganic ceramic powder was tested. BET Maximum saturated adsorption density F max (Directly obtained from BET testing instruments) and the average repeating unit molecular weight M of SMA SMA Assume that the surface area of ​​the modified ceramic powder does not change significantly before and after modification.

[0040] Based on the following formula: Actual surface molar adsorption capacity (F) = W SMA / [M SMA ×S BET ×(1-W SMA )]; Coverage rate (%) = (F / F max )×100%; Mass coating rate (%) = (m SMA / m 无机陶瓷 )×100%, where m SMA Indicates the mass of SMA added, m 无机陶瓷 This indicates the mass of inorganic ceramic powder added.

[0041] In some optional embodiments, the mass percentage of inorganic ceramics in the inorganic ceramic coating can be 50% to 92%, such as 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, or 92%, or other values ​​within the range of 50% to 92%. In some more typical embodiments, the mass percentage of inorganic ceramics in the inorganic ceramic coating is 87% to 92%.

[0042] In some alternative embodiments, the particle size of the inorganic ceramic can be 0.01μm to 5μm, such as 0.01μm, 0.05μm, 0.1μm, 0.5μm, 1μm, 2μm, 3μm, 4μm or 5μm, or other values ​​within the range of 0.01μm to 5μm.

[0043] In some alternative embodiments, the mass percentage of the styrene-maleic anhydride copolymer in the inorganic ceramic coating can be 1% to 20%, such as 1%, 2%, 5%, 10%, 15%, or 20%, or other values ​​within the range of 1% to 20%. In some more typical embodiments, the mass percentage of the styrene-maleic anhydride copolymer in the inorganic ceramic coating is 1% to 6%.

[0044] If the mass percentage of styrene-maleic anhydride copolymer in the inorganic ceramic coating is less than 1%, it is difficult to achieve an effective water-blocking effect. If the mass percentage of styrene-maleic anhydride copolymer in the inorganic ceramic coating is higher than 20%, it is easy for excessive organic phase to destroy the rigid heat-resistant skeleton formed by the mutual stacking of inorganic ceramics, which increases the thermal shrinkage rate of the membrane under 120℃ / 1h conditions and loses its heat-resistant protection function. Excessive polymer can also block the microporous structure of polyolefin membrane, causing a sharp increase in air permeability and hindering the transport of lithium ions.

[0045] In some alternative embodiments, the molar ratio of styrene to maleic anhydride in the styrene-maleic anhydride copolymer can be from 1:10 to 4:10, such as 1:10, 1.5:10, 2:10, 2.5:10, 3:10, 3.5:10 or 4:10, or other values ​​within the range of 1:10 to 4:10.

[0046] The specific copolymer molar ratio mentioned above ensures that at the molecular chain scale, 2 to 4 styrene hydrophobic barriers are closely arranged between every 1 to 2 chemical anchoring sites (MA ring-opening carboxyl groups), thus constructing a nanoscale alternating chemical pinning-hydrophobic shielding structure on the ceramic surface.

[0047] In some alternative embodiments, the porosity of the porous substrate in the lithium battery separator can be 30% to 50%, such as 30%, 38%, 40%, 45% or 50%, or other values ​​within the range of 30% to 50%.

[0048] In some alternative embodiments, the thickness of the porous substrate can be 1μm to 25μm, such as 1μm, 5μm, 8μm, 10μm, 15μm, 20μm or 25μm, or other values ​​within the range of 1μm to 25μm.

[0049] In some alternative embodiments, the thickness of the inorganic ceramic coating can be 0.1 μm to 5 μm, such as 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm or 5 μm, or other values ​​within the range of 0.1 μm to 5 μm.

[0050] In some alternative implementations, the gas permeability increment of the lithium battery separator does not exceed 50s / 100cc.

[0051] In some alternative implementations, the longitudinal thermal shrinkage rate of the lithium battery separator at 120°C / h is <3.5%.

[0052] In some alternative implementations, the lateral thermal shrinkage rate of the lithium battery separator at 120°C / h is <3.0%.

[0053] In some alternative implementations, the water content of the lithium battery separator does not exceed 700 ppm.

[0054] In some alternative implementations, the coating peel strength of the lithium battery separator is not less than 72 N / m.

[0055] Accordingly, the present invention also provides a method for preparing the above-mentioned lithium battery separator, comprising the following steps: mixing inorganic ceramic with a styrene-maleic anhydride copolymer activation solution and then heat-treating it to obtain a first mixture; mixing the first mixture with a binder to obtain a coating slurry; coating the coating slurry onto at least one side surface of a porous substrate and drying it.

[0056] In some alternative embodiments, the styrene-maleic anhydride copolymer activation solution is obtained by high-shear pre-activation of the styrene-maleic anhydride copolymer in a solvent.

[0057] Unactivated SMA is in a closed-ring state of the anhydride ring. Due to the combined effect of the styrene segment and the closed-ring anhydride, it is insoluble in water and only soluble in organic solvents such as acetone. In this invention, the SMA after pre-activation treatment is in an open-ring state. Specifically, when the styrene-maleic anhydride copolymer is pre-activated under specific energy-enhancing conditions, the maleic anhydride ring undergoes a ring-opening reaction and hydrolyzes into a strongly polar group with two carboxylate groups, making the SMA an amphiphilic polymer. The hydrophobic segment (styrene) remains hydrophobic, providing a barrier against moisture on the ceramic surface in the later stages; the hydrophilic segment (open-ring anhydride) is hydrophilic, allowing it to dissolve perfectly or self-assemble stably in a pure water system.

[0058] In other words, this invention does not contain any additional high molecular weight (weight average molecular weight not less than 10,000 g / mol) amphiphilic water-blocking agents. Instead, it drives the efficient ring-opening of its anhydride ring through in-situ pre-activation of low molecular weight SMA. After ring-opening, the high-density active carboxyl sites form a strong, in-situ chemically bonded molecular brush structure with the hydroxyl groups on the ceramic surface. This dense monolayer or thin-layer directional hydrophobic shield can chemically prevent water molecule adsorption without the need for giant molecular physical filling, thus achieving ultra-low moisture content while maintaining low air permeability increment.

[0059] In some optional embodiments, the shear rate for high shear preactivation can be 3000 rpm to 5000 rpm, such as 3000 rpm, 3500 rpm, 4000 rpm, 4500 rpm, or 5000 rpm, or other values ​​within the range of 3000 rpm to 5000 rpm. The high shear preactivation time can be 40 min to 90 min, such as 40 min, 50 min, 60 min, 70 min, 80 min, or 90 min, or other values ​​within the range of 40 min to 90 min.

[0060] The pH value of the styrene-maleic anhydride copolymer activation solution can be 7.0~9.0, such as 7.0, 7.5, 8.0, 8.5 or 9.0, or other values ​​within the range of 7.0~9.0.

[0061] This process unfolds the compact SMA molecular chains through high-energy shear forces and induces local ring-opening of maleic anhydride groups under specific pH conditions, exposing active sites and providing a thermodynamic basis for subsequent chemical anchoring to the ceramic surface. The pH value can be adjusted using dilute hydrochloric acid or ammonia. If the pH value is too low, due to the nucleophilic OH groups... - Insufficient concentration will prevent the effective overcoming of the steric hindrance of the styrene chain segments, resulting in an extremely slow hydrolysis rate of the maleic anhydride ring and insufficient ring-opening efficiency, thus failing to form high-density hydrogen bond anchoring on the inorganic ceramic surface. If the pH value is too high, excessive alkaline components will cause severe alkali swelling of the aqueous polymer adhesive, increasing the viscosity of the slurry and deteriorating its rheological processability.

[0062] In some alternative embodiments, the inorganic ceramic is added to the styrene-maleic anhydride copolymer activation solution in n separate additions and sheared, wherein the shear rate after the nth addition is greater than the shear rate after the (n-1)th addition.

[0063] For example, the inorganic ceramic is added to the styrene-maleic anhydride copolymer activation solution in three separate additions and sheared. The shear rate after the first addition is 500 rpm, the shear rate after the second addition is 1500 rpm, and the shear rate after the third addition is 3000 rpm.

[0064] In some alternative embodiments, the heat treatment temperature can be 45°C to 60°C, such as 45°C, 50°C, 55°C, or 60°C, or other values ​​within the range of 45°C to 60°C. The heat treatment time can be 1 hour to 2 hours, such as 1 hour, 1.5 hours, or 2 hours, or other values ​​within the range of 1 hour to 2 hours.

[0065] The three additions mentioned above correspond to three stages. The first stage mainly involves low-speed stirring to initially wet the inorganic ceramic; the second stage mainly involves medium-speed shearing to break up powder agglomeration; and the third stage mainly involves high-speed collision. Heat treatment is crucial for inducing the outward orientation of styrene segments (hydrophobic ends) and the inward orientation of maleic anhydride segments (binding ends). Without the aforementioned step-energy enhancement, the water film on the ceramic surface cannot be completely removed, and the SMA cannot form a dense hydrophobic protective layer. This application, through a combination of step-energy enhancement and heat treatment, enables the maleic anhydride groups in the SMA molecular chain to tightly coat the surface of the inorganic ceramic particles via hydrogen bonds or chemical bonds, while the hydrophobic styrene segments are driven outward by polarity differences, forming a nanometer-thick hydrophobic isolation layer on the inorganic ceramic surface.

[0066] It should be noted that if inorganic ceramics are directly mixed with an unactivated styrene-maleic anhydride copolymer solution, uneven coating is likely to occur, with a coating rate of less than 10%. This application uses pre-activation to fully expose the maleic anhydride groups in the SMA segments, forming active micelles with poor hydrophilic-hydrophobic polarity, which is beneficial for achieving a high area coating rate (e.g., 17%~95%).

[0067] Furthermore, it should be noted that although modifying ceramic particles with hydrophobic polymers such as polystyrene can reduce the moisture content of the separator, it faces severe process and safety bottlenecks in actual industrial applications: First, polystyrene is completely insoluble in water, so it cannot be used directly in aqueous slurries. It must first be dissolved in an organic solvent (acetone), then mixed with alumina, vacuum dried, and ground into a dry powder to achieve physical coating. However, acetone is a highly volatile, flammable, and explosive organic solvent. Second, the preparation process is extremely cumbersome, requiring ultrasonic mixing, high-speed centrifugation, washing, and time-consuming vacuum drying to extract the physical composite dry powder, resulting in extremely low production efficiency. Moreover, since the polystyrene and ceramic particles are only weakly physically deposited, the hydrophobic layer is prone to swelling and detachment under high-speed shearing of the slurry and long-term immersion in the electrolyte inside the battery, leading to a decrease in water-blocking performance.

[0068] This invention creatively utilizes aqueous pre-activated styrene-maleic anhydride copolymer to directly induce anhydride group ring-opening during conventional slurry dispersion processes, causing it to undergo strong condensation with hydroxyl groups on the ceramic surface, forming a robust chemical bond. This process completely eliminates hazardous organic reagents such as acetone and avoids any cumbersome intermediate separation and purification steps such as centrifugation and drying, achieving a green, efficient, and continuous one-pot slurrying process. Simultaneously, the chemically anchored directional hydrophobic layer completely solves the problem of easy swelling and peeling of physical coatings in electrolytes, ensuring ultra-low moisture stability of the separator throughout the battery's entire lifespan.

[0069] In some alternative embodiments, the preparation of the coating slurry may include: first mixing a first mixture with a non-particulate binder to obtain a second mixture; then mixing the second mixture with a particulate binder to obtain the coating slurry.

[0070] For example, the first mixture can be cooled to room temperature, and then a non-particulate binder can be added and stirred for 30 minutes at a shear rate of 600 rpm. The non-particulate binder forms a continuous molecular network between the coated ceramics and fills the primary pores. Then, a particulate binder can be added and stirred for 60 minutes.

[0071] By adding a non-particulate binder first, a first flexible barrier is formed around the styrene-maleic anhydride copolymer coating layer. The subsequent addition of a particulate binder provides heat-resistant support through point contact. This "first-line, then-last" composite sequence allows the non-particulate binder to preferentially occupy the active sites on the ceramic surface, effectively filling the dead volume in the coating micropores, further blocking moisture migration channels, and significantly reducing secondary infiltration of environmental moisture. The subsequently added particulate binder is distributed in the interstices of the framework, providing support and effectively controlling the thermal shrinkage rate of the membrane at high temperatures.

[0072] The lithium battery separator provided in this application has a low moisture content (below 700ppm) and high coating peel strength and air permeability, which can avoid the problems of coating porosity deterioration and secondary water absorption caused by conventional water-based non-particulate binders.

[0073] In addition, the present invention also provides a battery comprising the above-mentioned lithium battery separator, which has better electrochemical performance.

[0074] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0075] Example 1 This embodiment provides a lithium battery separator, which is an ultra-low moisture lithium battery separator comprising a porous substrate and an inorganic ceramic coating located on both sides of the porous substrate.

[0076] The inorganic ceramic coating contains 90% inorganic ceramics, 3% styrene-maleic anhydride copolymer, and 7% binder. The styrene-maleic anhydride copolymer has an area coverage of 50% and a mass coverage of 2.5% on the inorganic ceramic surface; the molar ratio of styrene to maleic anhydride in the styrene-maleic anhydride copolymer is 3:10 (0.3:1). The binder contains 50 wt% particulate binder, with the balance being non-particulate binder.

[0077] The preparation method of this lithium battery separator includes: S1: Preparation of coating slurry.

[0078] S1-1: Pre-activation treatment of water-blocking dispersant.

[0079] The styrene-maleic anhydride copolymer was added to deionized water and pre-shear activated at 4000 rpm for 60 min using a high-shear disperser to obtain an activated styrene-maleic anhydride copolymer solution. During this process, the pH of the system was precisely adjusted to 8.0 by adding dilute hydrochloric acid or ammonia.

[0080] S1-2: Stepped directional coating of ceramic particles.

[0081] Inorganic ceramic powder (alumina, particle size 0.7μm~1μm) was added to the above activation solution in three portions at a mass ratio of 1:1:1, and stirred continuously at 50℃ for 2 hours to obtain the first mixture. The shear rate corresponding to the first addition was 500 rpm, the second addition was 1500 rpm, and the third addition was 3000 rpm.

[0082] S1-3: Composite with adhesive.

[0083] After the first mixture cools to room temperature, switch to planetary stirring (shear rate of 600 rpm), first add non-particulate binder (modified polyvinyl alcohol, purchased from Maclean's Reagent Company), and stir for 30 minutes; then add particulate binder (acrylate emulsion), and stir for 60 minutes to obtain the coating slurry.

[0084] S2: Preparation of composite coated membrane Double-sided coating was performed on the surface of a porous substrate with a gap of 1.5 μm on an online rod coating machine. The porous substrate was a commercial polyethylene separator with a porosity of approximately 38% and a thickness of 9 μm. The separator was then dried in a forced-air oven at 60°C for 30 min to obtain a lithium battery separator.

[0085] The transmission electron microscope image of the lithium battery separator prepared in this embodiment is shown below. Figure 1 As shown, the lattice spacing diagram of Al2O3 is as follows: Figure 2 As shown in the enlarged view of the local interface between the SMA coating layer and Al2O3, see below. Figure 3 As shown.

[0086] Figure 1 The medium-dark gray crystals are Al2O3. The left surface of Al2O3 has a light gray, amorphous SMA coating layer (with a thickness of about 2nm~4nm), while the right surface of Al2O3 has no coating layer.

[0087] Depend on Figure 2 It can be seen that the Al2O3 lattice stripes have a d=0.243nm.

[0088] Depend on Figure 3 It can be seen that the SMA coating layer and Al2O3 are tightly bonded at the interface, with no obvious gaps.

[0089] Example 2 The difference between this embodiment and Embodiment 1 is that the inorganic ceramic coating contains 92% inorganic ceramic, 1% styrene-maleic anhydride copolymer, and 7% binder. The area coverage of the styrene-maleic anhydride copolymer on the inorganic ceramic surface is 17%, and the mass coverage of the styrene-maleic anhydride copolymer on the inorganic ceramic surface is 1.1%.

[0090] In step S1-1, the styrene-maleic anhydride copolymer was added to deionized water and pre-sheared and activated for 60 minutes at 4000 rpm using a high-shear disperser to obtain an activated styrene-maleic anhydride copolymer solution. During this process, the pH of the system was precisely adjusted to 8.0 by adding dilute hydrochloric acid or ammonia.

[0091] S1-2: Stepped directional coating of ceramic particles.

[0092] Inorganic ceramic powder (alumina, particle size 0.7μm~1μm) was added to the above activation solution in one go, and stirred continuously at a shear rate of 800 rpm for 2 hours at room temperature. The shear rate corresponding to the first addition was 500 rpm, the second addition was 1500 rpm, and the third addition was 3000 rpm.

[0093] All other conditions and steps are the same as in Example 1.

[0094] Example 3 The difference between this embodiment and Embodiment 1 is that the inorganic ceramic coating contains 87% inorganic ceramic, 6% styrene-maleic anhydride copolymer, and 7% binder. The area coverage of the styrene-maleic anhydride copolymer on the inorganic ceramic surface is 95%, and the mass coverage of the styrene-maleic anhydride copolymer on the inorganic ceramic surface is 5.2%.

[0095] In step S1-1, the styrene-maleic anhydride copolymer was added to deionized water and pre-sheared and activated for 60 minutes at 5000 rpm using a high-shear disperser to obtain an activated styrene-maleic anhydride copolymer solution. During this process, the pH of the system was precisely adjusted to 8.0 by adding dilute hydrochloric acid or ammonia.

[0096] In step S1-2, inorganic ceramic powder (alumina, particle size 0.7μm~1μm) was added to the above activation solution in three portions at a mass ratio of 1:1:1, and the mixture was stirred continuously at 55℃ for 2 hours to obtain the first mixture. The shear rate corresponding to the first addition was 500 rpm, the second addition was 2000 rpm, and the third addition was 4000 rpm.

[0097] All other conditions and steps are the same as in Example 1.

[0098] Example 4 The difference between this embodiment and Embodiment 1 is that the adhesive contains 33wt% particulate adhesive and the remainder is non-particulate adhesive.

[0099] Example 5 The difference between this embodiment and Embodiment 1 is that the adhesive contains 67 wt% particulate adhesive and the remainder is non-particulate adhesive.

[0100] Comparative Example 1 The difference between this comparative example and Example 1 is that SMA dispersant is not used; instead, the dispersant is replaced with the most commonly used water-based dispersant on the market (low molecular weight sodium polyacrylate PAA-Na).

[0101] Comparative Example 2 The difference between this comparative example and Example 1 is that pure maleic anhydride homopolymer (without styrene segments) was used as the dispersant.

[0102] Comparative Example 3 The difference between this comparative example and Example 1 is that no binder compounding is performed; only a single particulate binder (acrylate emulsion) is used.

[0103] Comparative Example 4 The difference between this comparative example and Example 1 is that no binder compounding is performed; only a single non-particulate binder (modified polyvinyl alcohol) is used.

[0104] Comparative Example 5 The difference between this comparative example and Example 1 is that, in the preparation process, in S1, the coating slurry is obtained by adding styrene-maleic anhydride copolymer (styrene / maleic anhydride ratio 3:10) to deionized water, followed by the sequential addition of ceramic powder and binder, and then dispersing it at 1500 rpm for 90 min using a disperser to form a uniformly dispersed coating slurry.

[0105] The selection and dosage of the above materials are the same as in Example 1.

[0106] Step S2 is the same as in Example 1.

[0107] Comparative Example 6 The difference between this comparative example and Example 1 is that, in the preparation process, polystyrene and polymaleic anhydride were added to S1, with a total mass ratio of 3% (polystyrene / polymaleic anhydride molar ratio of 3:10). The mixture was pre-shear activated at 4000 rpm for 60 minutes using a high-shear disperser to obtain dispersions of the two polymers. During this process, the pH of the system was precisely adjusted to 8.0 by adding dilute hydrochloric acid or ammonia.

[0108] Step S2 is the same as in Example 1.

[0109] Test case The lithium battery separators obtained in the above embodiments and comparative examples were subjected to performance tests. The test items, test instruments and test methods are shown in Table 1.

[0110] Table 1. Testing instruments and methods for preparing diaphragms in the examples and comparative examples.

[0111] The amount of substances used and the coating conditions of Examples 1-5 and Comparative Examples 1-6 are shown in Table 2, and the performance test results are shown in Table 3.

[0112] Table 2. Material Dosage and Coating Information

[0113] Table 3. Diaphragm performance results

[0114] As can be seen from Tables 2 and 3, the lithium battery separator provided in this application exhibits significant advantages in terms of comprehensive performance, such as moisture control, heat shrinkage resistance, air permeability, and coating adhesion.

[0115] As can be seen from Examples 1-3, the SMA addition amount in Example 2 was relatively low (area coverage rate of 17%), resulting in poorer integrity of the water-blocking network in the diaphragm, raising the moisture content to 700 ppm compared to Example 1. In Example 3, the SMA addition amount was higher (area coverage rate of 95%), and although the moisture content was extremely low (310 ppm), the thicker SMA coating layer hindered effective contact between the binder and ceramic particles and somewhat damaged the skeletal structure, leading to a decrease in coating peel strength and an increase in thermal shrinkage. Therefore, the solution provided in Example 1 achieves a performance balance between water resistance and coating strength.

[0116] Furthermore, in Example 2, the lower shear force made it difficult to effectively dismantle the SMA molecular coils, and the low ring-opening efficiency of the maleic anhydride group at room temperature resulted in a limited number of hydrogen bonds formed between the maleic anhydride and the hydroxyl groups (-OH) on the ceramic surface, with an area coverage of only 17%. Compared to Example 1, it was more difficult to construct an effective hydrophobic barrier on the inorganic ceramic surface. In Example 3, strong shear and longer heat treatment induced the complete unfolding of the SMA chain segments and large-scale ring-opening of the anhydride groups. The heating process provided the molecular chains with sufficient kinetic energy to overcome steric hindrance, allowing the hydrophobic styrene segments to be neatly oriented outwards. The maleic anhydride segments achieved a high-density chemical bond with the ceramic surface, ultimately forming a continuous and dense coating layer with an area coverage of 95%. The reduced interaction area between the ceramic surface and the adhesive led to a decrease in the peel strength of the coating to 72 N / m.

[0117] As can be seen from Examples 1, 4 and 5, in the adhesive of Example 1, both particulate adhesive and non-particulate adhesive account for 50wt% of the total adhesive. Among them, the particulate adhesive can effectively provide skeleton support, ensuring low air permeability increment and low thermal shrinkage, while the non-particulate adhesive can effectively fill gaps, increase the coating peel force to 120N / m and help seal the pore channels, resulting in better overall performance of the diaphragm.

[0118] A comparison of Example 1 and Comparative Example 1 shows that the moisture content of the membrane prepared in Comparative Example 1 without the addition of SMA is as high as 1300 ppm; while after adding 3% by mass of SMA (Example 1), the moisture content of the membrane prepared is significantly reduced to 450 ppm; this proves that adding 1 wt% to 6 wt% of SMA can effectively shield the hydrophilic groups on the ceramic surface.

[0119] A comparison of Example 1 and Comparative Example 2 shows that the inorganic ceramic in Comparative Example 2 can be dispersed in the coating slurry, but due to the lack of hydrophobic shielding effect of styrene, the moisture content of the resulting membrane is as high as 1200 ppm. This proves that anchoring by maleic anhydride alone cannot effectively reduce the moisture content of the membrane. Instead, true ultra-low moisture barrier can only be achieved by relying on the hydrophobic shielding layer formed by the directional arrangement of styrene segments at the interface in the presence of maleic anhydride.

[0120] As can be seen from Example 1 and Comparative Example 3, Comparative Example 3 only uses a single particulate binder, so there is only "point contact", resulting in insufficient coating cohesion, a coating peel strength of only 70 N / m, and the heat-resistant network collapses, with longitudinal and transverse thermal shrinkage rates as high as 5.1% and 4.78% at 120°C, respectively.

[0121] As can be seen from Example 1 and Comparative Example 4, Comparative Example 4, due to the use of only a single non-particulate binder, the excessive amount of non-particulate binder (usually containing more polar / hydrophilic groups) not only severely blocked the membrane micropores, but also increased the air permeability by as much as 60s / 100cc, affecting ion transport. Its own high water absorption also caused the overall membrane moisture content to rise to 860ppm.

[0122] As can be seen from Example 1 and Comparative Example 5, Comparative Example 5 did not undergo specific process treatment, but instead used a one-pot mixing method, resulting in an area coverage rate of only 8% and a moisture content of 1000 ppm in the diaphragm. This proves that the pre-activation treatment of the water-blocking dispersant and the step-by-step directional coating of ceramic particles in this application have a significant impact on the ceramic layer coverage rate and the moisture content of the diaphragm.

[0123] As can be seen from Example 1 and Comparative Example 6, Comparative Example 6 directly blended polystyrene, hydrolyzed polymaleic anhydride dispersant, and ceramic separately in the aqueous phase. Due to the extreme hydrophobicity of polystyrene, it could only exist in isolation as large agglomerates in the aqueous phase. This led to severe macroscopic phase separation, pore blockage (air permeability increase as high as 145s / 100cc), and water-blocking failure (moisture content as high as 1355ppm). Furthermore, the polystyrene particles floating on the slurry surface and agglomerated over a large area disrupted the three-dimensional network continuity of the compounded binder during coating drying, resulting in deterioration of the membrane's thermal shrinkage performance (MD / TD thermal shrinkage rates both >5%), and the coating's peel strength was only 32N / m.

[0124] In summary, this invention utilizes inorganic ceramics coated with styrene-maleic anhydride copolymer to replace conventional dispersants, and employs a combination of particulate and non-particulate binders. This not only reduces the water content of the separator but also gives the separator superior heat resistance, air permeability, and coating peel strength. On the one hand, this reduces battery baking time and lowers battery manufacturing costs; on the other hand, it improves the electrochemical performance of the battery.

[0125] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A lithium battery separator, characterized in that, It includes a porous substrate and an inorganic ceramic coating disposed on at least one surface of the porous substrate; The inorganic ceramic coating contains an inorganic ceramic coated with a binder and a styrene-maleic anhydride copolymer; The adhesive includes particulate adhesives and non-particulate adhesives; The styrene-maleic anhydride copolymer has an area coverage of 10% to 100% on the inorganic ceramic surface, and a mass coverage of 1% to 10% on the inorganic ceramic surface.

2. The lithium battery separator according to claim 1, characterized in that, The styrene-maleic anhydride copolymer has an area coverage of 17% to 95% on the inorganic ceramic surface; the styrene-maleic anhydride copolymer has a mass coverage of 1.1% to 5.2% on the inorganic ceramic surface.

3. The lithium battery separator according to claim 1, characterized in that, The inorganic ceramic in the inorganic ceramic coating has a mass percentage of 50% to 92%, preferably 87% to 92%. And / or, the particle size of the inorganic ceramic is 0.01μm~5μm.

4. The lithium battery separator according to claim 1, characterized in that, The styrene-maleic anhydride copolymer in the inorganic ceramic coating is 1% to 20% by mass, preferably 1% to 6% by mass. And / or, in the styrene-maleic anhydride copolymer, the molar ratio of styrene to maleic anhydride is 1:10 to 4:

10.

5. The lithium battery separator according to claim 1, characterized in that, The adhesive contains 33wt% to 67wt% of the particulate adhesive, with the balance being the non-particulate adhesive; Preferably, the particle size of the particulate binder is 0.05 μm to 1 μm.

6. The lithium battery separator according to any one of claims 1 to 5, characterized in that, The lithium battery separator has at least one of the following characteristics: Feature 1: The porosity of the porous substrate is 30%~50%; Feature 2: The thickness of the porous substrate is 1μm~25μm; Feature 3: The thickness of the inorganic ceramic coating is 0.1μm~5μm; Feature 4: The air permeability increment of the lithium battery separator does not exceed 50s / 100cc; Feature 5: The longitudinal thermal shrinkage rate of the lithium battery separator at 120℃ / h is <3.5%; Feature 6: The lateral thermal shrinkage rate of the lithium battery separator at 120℃ / h is <3.0%; Feature 7: The water content of the lithium battery separator does not exceed 700 ppm; Feature 8: The coating peel strength of the lithium battery separator is not less than 72 N / m.

7. A method for preparing a lithium battery separator as described in any one of claims 1 to 6, characterized in that, The process includes the following steps: mixing inorganic ceramics with a styrene-maleic anhydride copolymer activation solution and then heat-treating the mixture to obtain a first mixture; mixing the first mixture with a binder to obtain a coating slurry; coating the coating slurry onto at least one side of a porous substrate and then drying it.

8. The preparation method according to claim 7, characterized in that, The styrene-maleic anhydride copolymer activation solution is obtained by high-shear pre-activation of the styrene-maleic anhydride copolymer in a solvent; Preferably, the shear rate for high-shear pre-activation is 3000 rpm to 5000 rpm, and the time is 40 min to 90 min; Preferably, the pH value of the styrene-maleic anhydride copolymer activation solution is 7.0~9.

0.

9. The preparation method according to claim 7, characterized in that, The inorganic ceramic is added to the styrene-maleic anhydride copolymer activation solution in n parts and sheared. The shear rate after the nth addition is greater than the shear rate after the (n-1)th addition. And / or, the heat treatment temperature is 45℃~60℃, and the time is 1h~2h; And / or, the preparation of the coating slurry includes: first mixing the first mixture with a non-particulate binder to obtain a second mixture; then mixing the second mixture with a particulate binder to obtain the coating slurry.

10. A battery, characterized in that, The battery includes the lithium battery separator as described in any one of claims 1 to 6.

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