Lithium battery safety coating slurry and preparation method thereof

Abstract

The invention relates to lithium battery safety coating slurry and a preparation method thereof, and belongs to the technical field of battery diaphragms. The slurry is prepared from the following components in percentage by weight: 9.2 to 10.8 percent of PVDF (Polyvinylidene Fluoride) resin, 2.6 to 3.3 percent of modified filler, 0.55 to 0.7 percent of dispersing agent, 0.15 to 0.22 percent of wetting agent, 0.25 to 0.35 percent of defoaming agent and the balance of solvent, according to the modified filler, alkenylated bacterial cellulose and nano aluminum oxide are used as raw materials, a micro-crosslinked cellulose network which takes aluminum oxide as nodes and is covalently connected through flexible trisulfide chain segments is constructed by virtue of crosslinking and chelation effects of thiodimercaptan, and a unique rigid-flexible synergistic structure of the micro-crosslinked cellulose network can effectively dissipate stress and inhibit crack initiation and expansion, so that the mechanical property of the micro-crosslinked cellulose network is improved, and the service life of the micro-crosslinked cellulose network is prolonged. Therefore, the diaphragm is endowed with excellent dendrite puncture resistance and tear resistance, the thermal runaway time of the diaphragm under extreme abuse conditions such as needling is greatly prolonged, and the safety performance of the battery is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of battery separator technology, specifically, it relates to a lithium battery safety coating slurry and its preparation method. Background Technology

[0002] As a highly efficient electrochemical energy storage device, the safety of lithium-ion batteries is a core factor restricting their large-scale application, especially in high-risk scenarios such as electric vehicles and energy storage power stations. Within the internal structure of a lithium-ion battery, the separator acts as a physical barrier separating the positive and negative electrodes to prevent direct contact and short circuits. Its structural integrity and functional stability directly determine the overall safety level of the battery.

[0003] Currently, the mainstream material for commercial lithium-ion battery separators is polyolefin microporous membranes, mainly including polyethylene, polypropylene, and their multilayer composite membranes. These materials are widely used due to their good mechanical strength, excellent chemical and electrochemical stability, mature manufacturing processes, and low cost. However, polyolefin separators have two inherent drawbacks: First, their low melting point means that when the battery experiences excessive temperature rise due to overcharging, internal short circuits, or external thermal shock, the separator is prone to melting and shrinkage, leading to large-area contact between the positive and negative electrodes and causing thermal runaway, posing a serious safety hazard. Second, polyolefins are non-polar materials with poor wettability to polar electrolytes. This not only increases the difficulty of electrolyte injection but also deteriorates the electrode / electrolyte interface, resulting in reduced ion transport efficiency and battery performance degradation.

[0004] To overcome the aforementioned shortcomings, the industry commonly employs functional coating techniques on the surface of polyolefin-based membranes. Among these, polyvinylidene fluoride (PVDF) and its copolymers have become important organic coating materials due to their excellent electrochemical stability, chemical stability, high dielectric constant, and good electrolyte affinity. PVDF coatings can effectively improve the thermal stability of the separator and electrolyte wettability, thereby enhancing battery safety and cycle life. However, as an organic polymer, PVDF is inherently soft. When lithium dendrites form due to uneven lithium deposition during long-term cycling, or when subjected to external mechanical impact, the relatively soft PVDF coating cannot provide sufficient rigidity to resist dendrite growth or puncture by sharp objects, resulting in insufficient physical barrier function.

[0005] To enhance the mechanical strength of PVDF coatings, existing technologies typically employ the introduction of hard inorganic ceramic fillers (such as nano-alumina and boehmite) to form a PVDF-ceramic composite coating. This "polymer matrix + rigid particles" composite approach can indeed improve the overall hardness and puncture resistance threshold of the coating to some extent. However, this approach suffers from a fundamental mechanical flaw: the rigid ceramic filler and the flexible PVDF matrix are primarily bonded through physical adsorption or weak van der Waals forces, resulting in limited interfacial bonding strength. Under sustained or severe localized stress, the hard filler particles cannot adapt to the deformation of the PVDF matrix, leading to significant stress concentration at the filler / matrix interface. This stress concentration easily triggers the initiation and propagation of microcracks, ultimately causing the coating to tear at the interface or even break completely, thus losing its protective function. In other words, while traditional composite coatings improve macroscopic strength, they sacrifice the system's toughness and deformation compatibility, resulting in a "strong but not tough" disadvantage.

[0006] In addition, although high-strength, high-modulus organic coating materials, such as aramid and polyimide, can theoretically provide better puncture resistance, these materials usually face problems such as complex construction processes (such as the need for special solvent systems or complex film-forming processes), high raw material costs (such as aramid), difficulty in bonding with the base film, or increased battery internal resistance, which pose significant challenges in terms of economy and practicality for large-scale production.

[0007] Therefore, developing a novel coating material that can significantly improve the puncture and tear resistance of diaphragm coatings, while also possessing good deformation compatibility and interfacial stability, and with feasible processing and controllable cost, has become a pressing technical problem in this field. The starting point of this invention is to fundamentally improve the shortcomings of the mechanical properties of PVDF-based coatings through innovative filler design and composite mechanisms. Summary of the Invention

[0008] In order to solve the technical problems mentioned in the background art, the purpose of this invention is to provide a lithium battery safety coating slurry and its preparation method.

[0009] The objective of this invention can be achieved through the following technical solutions:

[0010] A lithium battery safety coating slurry, specifically composed of: 9.2-10.8 wt% PVDF resin, 2.6-3.3 wt% modified filler, 0.55-0.7 wt% dispersant, 0.15-0.22 wt% wetting agent, and 0.25-0.35 wt% defoamer, with the balance being solvent.

[0011] Preferably, the dispersant is a high molecular weight polymer formulation, which provides good dispersibility while having little impact on the viscosity of the slurry, thus maintaining the dispersion stability of the modified filler.

[0012] Preferably, the wetting agent is a non-ionic formulation, which has a low impact on the electrical properties of the diaphragm.

[0013] Preferably, the defoamer is a non-silicone formulation to avoid potential impact on electrochemical performance.

[0014] A method for preparing a lithium battery safety coating slurry specifically involves: premixing a dispersant, a wetting agent, a defoamer, and a solvent, then adding a modified filler for dispersion, followed by adding PVDF resin for grinding and mixing, and finally degassing under negative pressure to obtain the slurry.

[0015] The modified filler is prepared by the following method:

[0016] Step A1: Disperse bacterial cellulose in dimethylformamide, add tetramethylethylenediamine and mix well. Heat to 80-100℃ under nitrogen protection, slowly add allyl glycidyl ether and stir for 6-8 hours. After the reaction is completed, add deionized water to wash and dilute, centrifuge and take the bottom precipitate for filtration to obtain alkenylated cellulose.

[0017] Furthermore, the ratio of bacterial cellulose, allyl glycidyl ether, tetramethylethylenediamine, and dimethylformamide is 5g:0.9-1.2mL:0.4-0.5mL:180-240mL. Under the promotion of tetramethylethylenediamine, allyl glycidyl ether undergoes ring-opening grafting with bacterial cellulose, introducing an allyl structure into the side chain, while simultaneously forming side chain hydroxyl and ether structures, retaining the polarity of the molecular chain.

[0018] Preferably, the bacterial cellulose fiber length is 20-40 μm. Cellulose of this specification provides good reinforcement while having a low impact on the surface quality of the coating.

[0019] Step A2: Premix nano-alumina, alkenyl cellulose, thiodiglycol and acetone-ethanol composite solvent, then add photosensitizer and mix well. Stir and react under ultraviolet light for 12-15 hours. After the reaction is completed, centrifuge to collect the precipitate, wash with water and dry to obtain the modified filler.

[0020] Furthermore, the ratio of nano-alumina, alkenylated cellulose, thiodiglycol, and acetone-ethanol composite solvent is 50g:3.8-4.6g:0.5-0.7mL:400-500mL, and the photosensitizer is 0.07-0.09wt% of the reaction system; this reaction mechanism is the core technology of this invention.

[0021] The thiol groups at both ends of the thiodiglycol molecule and the thioether bond in the molecule have a strong tendency to coordinate and chelate with the aluminum ions or Lewis acid sites on the surface of nano-alumina. In the dispersion system, thiodiglycol molecules preferentially migrate and adsorb onto the surface of nano-alumina particles, forming an accumulation. Under ultraviolet light initiation, the thiol groups of thiodiglycol adsorbed on the surface of alumina particles undergo a highly efficient "thiol-ene" addition reaction with the allyl groups of the alkenylated bacterial cellulose side chains dispersed in the solvent. This reaction covalently bonds the thiodiglycol molecule to the cellulose molecular chain, while simultaneously binding and weaving the nano-alumina particles into the micro-crosslinked network, forming an organic-inorganic complex.

[0022] Preferably, the specific surface area of ​​nano-alumina is 80-110 m². 2 / g, the nanoparticles in this specification all have usable dispersibility while maintaining good reinforcement effect.

[0023] The beneficial effects of this invention are:

[0024] The lithium battery safety coating slurry provided by this invention has a core innovation compared to existing technical solutions: a fundamental change to the traditional physical blending enhancement mode. By constructing a multi-scale synergistic composite structure, it endows the coating system with excellent mechanical properties, thermal stability, and safety and reliability under extreme conditions.

[0025] Specifically, this invention, based on a filler reinforcement mechanism, breaks through the traditional paradigm of simple physical blending of rigid particles and flexible polymer matrices. By functionally modifying bacterial cellulose with alkenylation and utilizing the dithiol structure of thiodiglycol and its specific chelating effect on the surface of nano-alumina, a thiol-alkene click chemistry reaction is achieved in situ under UV light initiation. This process is not a simple component mixing, but rather the construction of a three-dimensional bacterial cellulose micronetwork at the nanoscale, linked by covalent bonds, with nano-alumina particles as crosslinking nodes. When this micronetwork is introduced into the polyvinylidene fluoride (PVDF) matrix as a reinforcing phase, it undergoes deep physical entanglement and interpenetration with the matrix molecular chains, transforming the bonding between the two phases from weak interfacial physical adsorption to a strongly interacting network interlocking structure, effectively strengthening the coating structure.

[0026] Furthermore, this unique filler network structure brings excellent rigid-flexibility synergy and damage tolerance characteristics to the coating. The trisulfide segments introduced into the crosslinking agent molecules possess extremely high flexibility and conformational freedom, effectively buffering stress between the rigid cellulose skeleton and the rigid alumina nodes. Simultaneously, the dynamic chelation between thiodiglycol and the alumina surface provides the nanoparticles with a reversible interfacial bond, somewhere between strong covalent bonds and weak van der Waals forces. This design allows the entire filler network to achieve multi-level stress dissipation and redistribution through the extension and rotation of flexible segments and the limited slippage of nanoparticles at the nodes when subjected to localized concentrated loads such as dendrite growth or external puncture, thereby effectively suppressing the initiation and propagation of microcracks. Even under high stress and localized damage, the dynamic chelating interface possesses a certain degree of adaptive adjustment capability, preventing rapid crack instability propagation.

[0027] Beyond breakthroughs in mechanical and safety performance, this invention also demonstrates a balanced advantage in terms of overall performance and process feasibility. The modification of bacterial cellulose retains its polar characteristics, maintaining good wettability with nanoparticles for compatibility with polyvinylidene fluoride (PVDF). This directly translates to lower battery interfacial impedance, improved rate performance, and superior long-cycle capacity retention. In terms of the preparation process, the main raw materials used are already industrially produced. The core solution mixing and UV curing technologies are mature and reliable. The process flow is highly compatible with existing separator coating production lines, requiring no complex or expensive specialized equipment, thus possessing excellent economic viability and prospects for large-scale production.

[0028] In summary, this invention, through original filler structure design and composite mechanism, successfully prepared a lithium-ion battery separator coating that combines high mechanical strength, high toughness, high thermal stability, and a high safety threshold. This technology not only provides an effective material solution for improving the intrinsic safety level of lithium-ion batteries, but its revealed "rigid node-flexible network" synergistic reinforcement mechanism also has universal reference value for the design of polymer composite materials. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Example 1: Preparation of a safety coating slurry for lithium batteries. The specific implementation method is as follows:

[0031] I. Preparation of Modified Fillers

[0032] Step A1: Bacterial cellulose and dimethylformamide were premixed and then ultrasonically dispersed to form a uniform dispersion. Tetramethylethylenediamine was then added and stirred until homogeneous. Nitrogen gas was introduced for protection and the temperature was raised to 80°C. Allyl glycidyl ether was slowly added and stirred for 8 hours. Commercially available dry powder raw material was used for bacterial cellulose, with a typical fiber diameter of 70 nm and a fiber length of 30 μm. The ratio of bacterial cellulose, allyl glycidyl ether, tetramethylethylenediamine, and dimethylformamide was 5 g: 0.9 mL: 0.4 mL: 180 mL. After the reaction was completed, three times the mass of deionized water was added to wash and dilute the mixture. The bottom precipitate was then centrifuged and filtered to obtain alkenylated cellulose.

[0033] Step A2: Nano-alumina, alkenylated cellulose, thiodiglycol, and acetone-ethanol composite solvent were added and stirred with ultrasonic stirring for premixing. Then, a photosensitizer was added to the dispersion system and stirred until homogeneous. The mixture was then irradiated and stirred for 15 hours using a 150W, 365nm ultraviolet light source. The nano-alumina used was commercially available Aluna-100HF type raw material with a specific surface area of ​​approximately 90 m². 2 / g, the composite solvent is a mixture of acetone and ethanol in a volume ratio of 3:1, the photosensitizer is photoinitiator 1173, the ratio of nano alumina, alkenyl cellulose, thiodiglycol and acetone-ethanol composite solvent is 50g:3.8g:0.5mL:400mL, and the photosensitizer is 0.07wt% of the reaction system; after the reaction is completed, the precipitate is collected by centrifugation, the precipitate is washed with water and dried to obtain the modified filler.

[0034] II. Preparation of Coating Slurry

[0035] Materials: By weight percentage, PVDF resin 9.2wt%, Kynar® 761 type raw material is selected; modified filler 2.6wt%, prepared in this example; dispersant 0.55wt%, BYK-170 type polymer dispersant is selected; wetting agent 0.15wt%, ANTI-TERRA-202 type nonionic wetting agent is selected; defoamer 0.25wt%, Efka® PB 2020 AN type non-silicone defoamer is selected; the balance is solvent, industrial grade N-methylpyrrolidone.

[0036] Pulping: Dispersant, wetting agent, defoamer and solvent are added and stirred evenly. Modified filler is added and dispersed by high-speed stirring at 1200 rpm. Then PVDF resin is added and ground and mixed evenly. After degassing under negative pressure, slurry is obtained.

[0037] Example 2: Preparation of a safety coating slurry for lithium batteries. The specific implementation method is as follows:

[0038] I. Preparation of Modified Fillers

[0039] Step A1: Bacterial cellulose and dimethylformamide were premixed and then ultrasonically dispersed to form a uniform dispersion. Tetramethylethylenediamine was then added and stirred until homogeneous. Nitrogen gas was introduced for protection and the temperature was raised to 90°C. Allyl glycidyl ether was slowly added and stirred for 7 hours. Commercially available dry powder raw material was used for bacterial cellulose, with a typical fiber diameter of 70 nm and a fiber length of 30 μm. The ratio of bacterial cellulose, allyl glycidyl ether, tetramethylethylenediamine, and dimethylformamide was 5 g: 1.1 mL: 0.5 mL: 220 mL. After the reaction was completed, three times the mass of deionized water was added to wash and dilute the mixture. The bottom precipitate was then centrifuged and filtered to obtain alkenylated cellulose.

[0040] Step A2: Nano-alumina, alkenylated cellulose, thiodiglycol, and acetone-ethanol composite solvent were added and stirred with ultrasonic stirring for premixing. Then, a photosensitizer was added to the dispersion system and stirred until homogeneous. The mixture was then irradiated and stirred for 13 hours using a 150W, 365nm ultraviolet light source. The nano-alumina used was commercially available Aluna-100HF type raw material with a specific surface area of ​​approximately 90 m². 2 / g, the composite solvent is a mixture of acetone and ethanol in a volume ratio of 3:1, the photosensitizer is photoinitiator 1173, the ratio of nano alumina, alkenyl cellulose, thiodiglycol and acetone-ethanol composite solvent is 50g:4.2g:0.6mL:450mL, and the photosensitizer is 0.08wt% of the reaction system; after the reaction is completed, the precipitate is collected by centrifugation, the precipitate is washed with water and dried to obtain the modified filler.

[0041] II. Preparation of Coating Slurry

[0042] Materials: By weight percentage, PVDF resin 9.8wt%, using Kynar® 761 raw material; modified filler 3.1wt%, prepared in this example; dispersant 0.6wt%, using BYK-170 polymer dispersant; wetting agent 0.2wt%, using ANTI-TERRA-202 nonionic wetting agent; defoamer 0.32wt%, using Efka® PB 2020 AN non-silicone defoamer; the balance is solvent, industrial grade N-methylpyrrolidone.

[0043] Pulping: Dispersant, wetting agent, defoamer and solvent are added and stirred evenly. Modified filler is added and dispersed by high-speed stirring at 1200 rpm. Then PVDF resin is added and ground and mixed evenly. After degassing under negative pressure, slurry is obtained.

[0044] Example 3: Preparation of a safety coating slurry for lithium batteries. The specific implementation method is as follows:

[0045] I. Preparation of Modified Fillers

[0046] Step A1: Bacterial cellulose and dimethylformamide were premixed and then ultrasonically dispersed to form a uniform dispersion. Tetramethylethylenediamine was then added and stirred until homogeneous. Nitrogen gas was introduced for protection and the temperature was raised to 100°C. Allyl glycidyl ether was slowly added and stirred for 6 hours. Commercially available dry powder raw material was used for bacterial cellulose, with a typical fiber diameter of 70 nm and a fiber length of 30 μm. The ratio of bacterial cellulose, allyl glycidyl ether, tetramethylethylenediamine and dimethylformamide was 5 g: 1.2 mL: 0.5 mL: 240 mL. After the reaction was completed, three times the mass of deionized water was added to wash and dilute the mixture. The bottom precipitate was then centrifuged and filtered to obtain alkenylated cellulose.

[0047] Step A2: Nano-alumina, alkenylated cellulose, thiodiglycol, and acetone-ethanol composite solvent were added and stirred with ultrasonic stirring for premixing. Then, a photosensitizer was added to the dispersion system and stirred until homogeneous. The mixture was then irradiated and stirred for 12 hours using a 150W, 365nm ultraviolet light source. The nano-alumina used was commercially available Aluna-100HF type raw material with a specific surface area of ​​approximately 90 m². 2 / g, the composite solvent is a mixture of acetone and ethanol in a volume ratio of 3:1, the photosensitizer is photoinitiator 1173, the ratio of nano alumina, alkenyl cellulose, thiodiglycol and acetone-ethanol composite solvent is 50g:4.6g:0.7mL:500mL, and the photosensitizer is 0.09wt% of the reaction system; after the reaction is completed, the precipitate is collected by centrifugation, the precipitate is washed with water and dried to obtain the modified filler.

[0048] II. Preparation of Coating Slurry

[0049] Materials: By weight percentage, PVDF resin 10.8wt%, using Kynar® 761 raw material; modified filler 3.3wt%, prepared in this example; dispersant 0.7wt%, using BYK-170 polymer dispersant; wetting agent 0.22wt%, using ANTI-TERRA-202 nonionic wetting agent; defoamer 0.35wt%, using Efka® PB 2020 AN non-silicone defoamer; the balance is solvent, industrial grade N-methylpyrrolidone.

[0050] Pulping: Dispersant, wetting agent, defoamer and solvent are added and stirred evenly. Modified filler is added and dispersed by high-speed stirring at 1200 rpm. Then PVDF resin is added and ground and mixed evenly. After degassing under negative pressure, slurry is obtained.

[0051] Example 4: Preparation of a safety coating slurry for lithium batteries. The specific implementation method is as follows:

[0052] I. Preparation of Modified Fillers

[0053] Step A1: Bacterial cellulose and dimethylformamide were premixed and then ultrasonically dispersed to form a uniform dispersion. Tetramethylethylenediamine was then added and stirred until homogeneous. Nitrogen gas was introduced for protection and the temperature was raised to 85°C. Allyl glycidyl ether was slowly added and the mixture was stirred for 8 hours. The bacterial cellulose was a commercially available dry powder raw material with a typical fiber diameter of 70 nm and a fiber length of 30 μm. The ratio of bacterial cellulose, allyl glycidyl ether, tetramethylethylenediamine, and dimethylformamide was 5 g: 1.0 mL: 0.5 mL: 200 mL. After the reaction was completed, three times the mass of deionized water was added to wash and dilute the mixture. The bottom precipitate was then centrifuged and filtered to obtain alkenylated cellulose.

[0054] Step A2: Nano-alumina, alkenylated cellulose, thiodiglycol, and acetone-ethanol composite solvent were added and stirred with ultrasonic stirring for premixing. Then, a photosensitizer was added to the dispersion system and stirred until homogeneous. The mixture was then irradiated and stirred for 14 hours using a 150W, 365nm ultraviolet light source. The nano-alumina used was commercially available Aluna-100HF type raw material with a specific surface area of ​​approximately 90 m². 2 / g, the composite solvent is a mixture of acetone and ethanol in a volume ratio of 3:1, the photosensitizer is photoinitiator 1173, the ratio of nano alumina, alkenyl cellulose, thiodiglycol and acetone-ethanol composite solvent is 50g:4.4g:0.6mL:420mL, and the photosensitizer is 0.08wt% of the reaction system; after the reaction is completed, the precipitate is collected by centrifugation, the precipitate is washed with water and dried to obtain the modified filler.

[0055] II. Preparation of Coating Slurry

[0056] Materials: By weight percentage, PVDF resin 10.3wt%, using Kynar® 761 raw material; modified filler 3.0wt%, prepared in this example; dispersant 0.65wt%, using BYK-170 polymer dispersant; wetting agent 0.18wt%, using ANTI-TERRA-202 nonionic wetting agent; defoamer 0.3wt%, using Efka® PB 2020 AN non-silicone defoamer; the balance is solvent, industrial grade N-methylpyrrolidone.

[0057] Pulping: Dispersant, wetting agent, defoamer and solvent are added and stirred evenly. Modified filler is added and dispersed by high-speed stirring at 1200 rpm. Then PVDF resin is added and ground and mixed evenly. After degassing under negative pressure, slurry is obtained.

[0058] Comparative Example 1 follows the same implementation process as Example 4, but without adding modified fillers; the remaining amount is made up by solvent. The rest of the implementation process is exactly the same.

[0059] Comparative Example 2 follows the same implementation process as Example 4, except that the modified filler was replaced with 2.7 wt% nano-alumina and 0.3 wt% bacterial cellulose, while the rest of the implementation process was exactly the same.

[0060] A 12μm polyethylene membrane was used as the base membrane. The slurry prepared above was coated on both sides of the base membrane using a coating machine. The membrane was then dried sequentially at 80℃ / 10min + 100℃ / 3min + 120℃ / 1min. Composite membranes were fabricated according to the 3+12+3μm specification, and samples were prepared for the following tests:

[0061] Referring to Appendix of GB / T 36363-2018, a 100mm × 100mm sample was placed in a forced-air drying oven and treated at 150℃ for 1 hour, and the heat shrinkage rate was measured. Using a Göller-Leigh air permeability meter, under a pressure difference of 1.2 kPa, the permeability of 100 mL of air was recorded as 6.45 cm. 2 The time required for sample preparation was recorded as air permeability. A 1.0 mm diameter spherical needle was used to vertically puncture the fixed diaphragm at a speed of 100 mm / min, and the maximum force at the moment of puncture was recorded. The specific test results are shown in Table 1.

[0062] Table 1

[0063] Heat shrinkage rate / % Breathability / s Puncture resistance strength / N Example 1 1.12 185 6.4 Example 2 1.07 182 6.6 Example 3 0.88 170 7.1 Example 4 0.96 179 6.8 Comparative Example 1 2.82 195 3.7 Comparative Example 2 1.55 182 5.5

[0064] As shown in Table 1, the test data indicates that after the slurry prepared in the example forms a coating on the surface of the polyolefin membrane, the thermal shrinkage rate of the composite membrane is significantly reduced, the puncture resistance is significantly improved, and the air permeability is similar, thus effectively improving the stability of the membrane.

[0065] The above-mentioned separator, along with NCM811 positive electrode, graphite negative electrode, and 1M LiPF6 electrolyte (EC / EMC / DMC=1:1:1, containing 2% VC), were assembled into a 2032 type coin cell in an argon glove box. The coin cell was subjected to 500 constant-current charge / discharge cycles at 1C within a voltage window of 2.75-4.25V, and the capacity retention rate was calculated. A 2.0Ah soft-pack battery was fabricated using a winding process. Following the GB38031-2025 standard, the fully charged soft-pack battery was fixed, and a 3mm diameter high-temperature resistant steel needle was used to vertically pierce the central area of ​​the battery at a speed of 25mm / s, while the voltage and battery surface temperature were monitored in real time. Specific test data are shown in Table 2.

[0066] Table 2

[0067] Capacity retention rate / % Voltage collapse time / s Maximum cell temperature / °C Example 1 94.6 130 100 Example 2 93.3 122 112 Example 3 90.5 73 130 Example 4 94.2 105 95 Comparative Example 1 88.7 8 355 Comparative Example 2 90.9 45 270

[0068] As shown in Table 2, the slurry prepared in the example was used for lithium battery separators, and the battery capacity retention rate was noticeably improved after 500 cycles. This may be related to the stability of the separator maintaining the normal charging and discharging of the battery. In addition, in the puncture test, the voltage collapse time was significantly prolonged, no significant fire phenomenon occurred, and the cell temperature did not rise sharply, indicating extremely high safety.

[0069] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0070] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described, or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined in the claims, all of which should fall within the protection scope of the present invention.

Claims

1. A lithium battery safety coating slurry, characterized in that, The specific components are: 9.2-10.8 wt% PVDF resin, 2.6-3.3 wt% modified filler, 0.55-0.7 wt% dispersant, 0.15-0.22 wt% wetting agent, and 0.25-0.35 wt% defoamer, with the balance being solvent; The modified filler is prepared by the following method: Step A1: Disperse bacterial cellulose in dimethylformamide, add tetramethylethylenediamine and mix well. Under nitrogen protection, heat to 80-100℃, slowly add allyl glycidyl ether and stir for 6-8 hours to prepare alkenylated cellulose. Step A2: Premix nano-alumina, alkenyl cellulose, thiodiglycol and acetone-ethanol composite solvent, then add photosensitizer and mix well. Stir and react under ultraviolet light for 12-15 hours to prepare modified filler.

2. The lithium battery safety coating slurry according to claim 1, characterized in that, The ratio of bacterial cellulose, allyl glycidyl ether, tetramethylethylenediamine and dimethylformamide is 5g:0.9-1.2mL:0.4-0.5mL:180-240mL.

3. The lithium battery safety coating slurry according to claim 2, characterized in that, Bacterial cellulose fibers have a length of 20-40 μm.

4. The lithium battery safety coating slurry according to claim 2, characterized in that, The ratio of nano-alumina, alkenyl cellulose, thiodiglycol and acetone-ethanol composite solvent is 50g: 3.8-4.6g: 0.5-0.7mL: 400-500mL, and the photosensitizer is 0.07-0.09wt% of the reaction system.

5. The lithium battery safety coating slurry according to claim 4, characterized in that, The specific surface area of ​​nano-alumina is 80-110 m² / g.

6. The lithium battery safety coating slurry according to claim 1, characterized in that, The dispersant is a high molecular weight polymer formulation.

7. The lithium battery safety coating slurry according to claim 1, characterized in that, The wetting agent is a non-ionic formulation.

8. The lithium battery safety coating slurry according to claim 1, characterized in that, The defoamer is a non-silicone formulation.

9. A method for preparing a lithium battery safety coating slurry according to any one of claims 1-8, characterized in that, Specifically, the dispersant, wetting agent, defoamer and solvent are premixed, then modified filler is added and dispersed, then PVDF resin is added and ground and mixed evenly, and the slurry is obtained after degassing under negative pressure.