Aqueous ceramic lithium battery coating slurry and preparation method thereof

Abstract

The present invention belongs to the technical field of diaphragm coating slurries, and specifically relates to a water-based ceramic lithium battery coating slurry and a preparation method thereof. The composition includes the following components: Al2O3 ceramic particles, an amphiphilic CNC skeleton, 2-hydroxyethyl methacrylate phosphate, butyl acrylate, a transfer agent, azobisisobutyronitrile, a fluorocarbon surfactant FS-30, hydroxyethyl cellulose, Al(NO3)3·9H2O, NH4H2PO4, a photoinitiator, and a crosslinking agent. The present invention integrates an organic-inorganic interpenetrating network, gradient crosslinking, and dynamic interface bonding through a biomimetic mineralized binder system to solve the problems of weak bonding, poor stress buffering, and insufficient environmental adaptability of traditional water-based slurries. Amphiphilic cellulose nanocrystals and phosphate group copolymers form a double network structure. The all-aqueous system combines with the CNC skeleton to reduce VOCs. The gradient distribution of the photoinitiator and the thermal crosslinker does not require layered coating, and has both efficient interface bonding and environmental advantages.

Description

Technical Field

[0001] The present invention belongs to the technical field of diaphragm coating slurries, and in particular relates to a water-based ceramic lithium battery coating slurry and a preparation method thereof. Background Art

[0002] With the rapid development of the new energy industry, the large-scale application of lithium-ion batteries in electric vehicles and energy storage systems has placed higher demands on safety and energy density. As the core component that separates the positive and negative electrodes within the battery, the thermal stability and mechanical strength of the separator directly determine the battery's resistance to short circuits and thermal runaway. While the current mainstream polyolefin (PE / PP) separators offer excellent electrolyte wettability and ion conductivity, their heat deformation temperatures (PE approximately 130°C / PP approximately 160°C) are insufficient to meet the demands of high-energy-density battery systems. If abnormal internal heating within the battery causes the separator to melt and shrink, contact between the positive and negative electrodes could trigger a cascading thermal runaway event.

[0003] Ceramic coating technology has become a mainstream solution for improving the high-temperature tolerance of diaphragms by adding an inorganic protective layer to polyolefin-based membranes. Currently, the industry generally uses an organic solvent system (such as NMP-based slurry) composed of ceramic materials such as alumina and boehmite and a PVDF binder. Although this process can increase the temperature resistance of the diaphragm to above 200°C, it has bottlenecks such as high solvent toxicity, high coating energy consumption, and easy peeling of the coating. What is more serious is that the interface bonding between the ceramic particles and the organic binder in the traditional slurry is weak. The coating layer is prone to microcracks due to stress concentration during the battery cycle, which not only increases the risk of lithium dendrite penetration, but the residual metal impurities (such as iron and nickel ions) will also significantly increase the probability of battery micro-short circuits.

[0004] ‌Water-based ceramic coating slurries are considered an important direction to break through the shackles of traditional technologies due to their environmentally friendly properties and strong interfacial bonding. ‌Through the synergistic effect of water-based binders and ceramic particles, a functional coating with both thermal stability and ion conductivity efficiency can be constructed on the surface of the diaphragm. However, water-based systems still face multiple challenges in practical applications: poor slurry stability caused by environmental humidity sensitivity, coating defects caused by uneven dispersion of ceramic particles, and coating swelling under long-term electrolyte immersion. These problems may weaken the physical barrier effect of the diaphragm on lithium dendrites. ‌Therefore, based on the above-mentioned defects, it is extremely necessary to develop an environmentally friendly and highly stable water-based coating slurry. Summary of the Invention

[0005] In view of the defects of the prior art, the object of the present invention is to provide an aqueous ceramic lithium battery coating slurry and a preparation method thereof.

[0006] The technical effects of the present invention are achieved through the following technical scheme: a water-based ceramic lithium battery coating slurry, which comprises the following components: Al2O3 ceramic particles, an amphiphilic CNC skeleton, 2-hydroxyethyl methacrylate phosphate, butyl acrylate, a transfer agent, azobisisobutyronitrile, a fluorocarbon surfactant FS-30, hydroxyethyl cellulose, Al(NO3)3·9H2O, NH4H2PO4, a photoinitiator and a cross-linking agent.

[0007] Preferably, the specific preparation steps of the amphiphilic CNC skeleton are as follows:

[0008] S1: Cellulose nanocrystals are added to deionized water and dispersed uniformly by ultrasonic treatment to obtain a 5 wt% dispersion. Tetramethylpiperidinium oxide and sodium bromide are then added to the dispersion, the pH is adjusted to 9-10, and after uniform mixing, a 5 wt% sodium hypochlorite solution is slowly added dropwise. The mixture is reacted at room temperature for 6-8 h, centrifuged, filtered, washed until neutral, and freeze-dried at -40°C for 12-18 h to obtain carboxylated cellulose nanocrystals.

[0009] S2: The carboxylated cellulose nanocrystals prepared in step S1 were dispersed in 0.1 M MES buffer at pH 5, EDC and NHS were added, and the mixture was activated at room temperature for 1-2 h. Then, methoxypolyethylene glycol amino was added and the mixture was reacted at 30-40°C for 10-12 h. The mixture was centrifuged, filtered, and washed three times with 0.1 M sodium chloride solution to obtain an amphiphilic CNC framework.

[0010] Preferably, in step S1, the ratio of the amount of the cellulose nanocrystals, tetramethylpiperidinium oxide, sodium bromide and sodium hypochlorite solution is 1 g: 0.015-0.02 g: 0.01-0.02 g: 5-6 mL;

[0011] Preferably, in step S2, the ratio of the amount of the carboxylated cellulose nanocrystals, MES buffer, EDC, NHS and methoxypolyethylene glycol amino is 1 g:200 mL:0.3-0.38 g:0.34-0.43 g:0.3-0.4 g;

[0012] Preferably, the transfer agent is 4-cyano-4-(phenylthiocarbamoylthio)pentanoic acid;

[0013] Preferably, the photoinitiator is phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide;

[0014] Preferably, the cross-linking agent is trimethylolpropane triglycidyl ether;

[0015] Preferably, another aspect of the present invention is to provide a method for preparing a water-based ceramic lithium battery coating slurry, the specific preparation steps are as follows:

[0016] S101: 2-Hydroxyethyl methacrylate phosphate and butyl acrylate were added to N,N-dimethylformamide, mixed evenly, and then a transfer agent and azobisisobutyronitrile were added. The mixture was reacted in an oil bath at 70°C under a nitrogen atmosphere for 18-24 hours, and then rapidly cooled to 0°C. The mixture was then poured into a 5-fold volume of an 80 wt% methanol solution, and a white solid was collected by filtration. The solid was washed with ethanol three times, and then dried in a vacuum at 40°C for 36-48 hours to obtain a phosphate group copolymer.

[0017] S102: adding the amphiphilic CNC skeleton to deionized water and dispersing it uniformly by ultrasonic treatment to obtain a 10 wt% amphiphilic CNC suspension; adding the phosphate group copolymer prepared in step S101 to deionized water and dispersing it uniformly by ultrasonic treatment to obtain a 15 wt% copolymer suspension; mixing the amphiphilic CNC suspension and the copolymer suspension, adding 0.2% fluorocarbon surfactant FS-30, stirring at 300 rpm for 2 h, repeating the high-pressure homogenization at 1000 bar for 3 times, shearing, and then standing for 24 h to obtain a composite network system;

[0018] S103: adding Al2O3 ceramic particles to a 5wt% hydrogen peroxide solution, treating at 80°C for 2-4h, centrifuging, washing, and drying at 60°C to constant weight to obtain activated Al2O3 ceramic particles; mixing Al(NO3)3·9H2O and NH4H2PO4 uniformly, then adding them to the composite network system prepared in step S102, ultrasonically dispersing them, and then performing gradient mineralization treatment to obtain a mineralized AlPO4 slurry;

[0019] S104: adding 1-1.5% of a photoinitiator and 2-3% of a cross-linking agent to the mineralized AlPO4 slurry prepared in step S103, stirring at room temperature until completely dispersed, and then adding 0.2% of hydroxyethyl cellulose and 0.1M Tris-HCl buffer to maintain the pH at 7.5 to obtain a water-based ceramic lithium battery coating slurry;

[0020] Preferably, in step S101, the ratio of the amount of 2-hydroxyethyl methacrylate phosphate, butyl acrylate, N,N-dimethylformamide, transfer agent and azobisisobutyronitrile is 30-35 g:45 g:400-500 mL:0.12-0.15 g:0.03-0.06 g;

[0021] Preferably, in step S102, the volume ratio of the amphiphilic CNC suspension to the copolymer suspension is 1:1;

[0022] Preferably, in step S102, the shearing treatment parameters are a shearing rate of 200 to 300 s -1 , time 8 to 10 minutes;

[0023] Preferably, in step S103, the ratio of the amount of the activated Al2O3 ceramic particles, Al(NO3)3·9H2O, NH4H2PO4 and the composite network system is 1g:4-4.5g:1.8-2g:100mL;

[0024] Preferably, in step S103, the ultrasonic dispersion treatment parameters are 200-300W, 40kHz, and time 20-30min;

[0025] Preferably, in step S103, the specific parameters of the gradient mineralization treatment are: first adjust the pH to 4.5 with acetic acid and stay for 4 to 5 minutes; then adjust the pH to 6 with ammonia water and stay for 6 to 8 minutes; finally adjust the pH to 7.5 with ammonia water and stay for 4 to 5 minutes.

[0026] The beneficial effects of the present invention are as follows:

[0027] The present invention integrates the triple technical effects of organic-inorganic interpenetrating network, gradient cross-linking and dynamic interface bonding by constructing a biomimetic mineralized binder system, and systematically solves the defects of weak bonding force, poor stress buffering capacity and insufficient environmental adaptability of traditional water-based coating slurries. First, the amphiphilic cellulose nanocrystals (CNC) form hydrophobic associations with the hydrophobic units (butyl acrylate) of the phosphate group polymer (HEMAP-co-BA) through the surface-grafted polyethylene glycol segments. At the same time, its hydrophilic skeleton combines with deionized water through hydrogen bonds to form a double network structure with a continuous phase. Under the induction of the shear flow field, the structure self-assembles into a layered-fiber interwoven nacre topology, providing multi-scale mechanical interlocking and ion transmission channels for ceramic particles. The phosphate groups in the phosphate group copolymer are preferentially adsorbed on the hydroxyl-rich sites on the surface of the pretreated Al2O3 ceramic particles, and form a chemical anchoring layer through the dual effects of coordination bonds (PO-Al) and hydrogen bonds (P-OH···HO-Al), effectively improving the interface bonding strength; under this interface induction, Al 3+ With PO4 3-Nano-AlPO4 crystals are generated in situ through a pH gradient mineralization reaction. Their crystal faces are lattice-matched with those of CNC to achieve epitaxial growth, forming an atomic-level interlocking of the inorganic and organic phases. In addition, the AlPO4 mineralized layer acts as a rigid bridge to connect the ceramic particles to the polymer network. Through crack deflection and interfacial debonding mechanisms, the external shear stress is converted into multi-level energy dissipation, thereby improving the fracture toughness of the coating. The present invention utilizes a fully aqueous system and a renewable CNC skeleton to effectively reduce VOC emissions, maintains slurry stability through double-layer repulsion and steric hindrance effects, and completely abandons dependence on organic solvents while achieving efficient interfacial bonding, thus making up for the environmental friendliness shortcomings of the existing technology. The photoinitiator added to the slurry of the present invention is enriched in the surface layer of the slurry (contacting the air interface) through a surfactant (FS-30), while the thermal crosslinker is evenly dispersed throughout the system. This distribution difference causes the surface layer to preferentially crosslink after coating, forming a dense hard shell that inhibits sagging, and the underlying epoxy groups gradually open to form a flexible network. This gradient design is achieved through the distribution of the slurry's own components, without the need for additional layered coating. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only for the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0029] Figure 1 1 is a graph showing the high temperature and high humidity performance test results of the aqueous ceramic lithium battery coating slurry prepared in Example 2 of the present invention and Comparative Examples 1 to 3;

[0030] Figure 2 This is an SEM image of the sample after coating with the aqueous ceramic lithium battery coating slurry prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0031] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention. It should be noted that unless otherwise specified, the raw materials involved in the present invention were purchased through conventional commercial channels.

[0032] Example 1: A water-based ceramic lithium battery coating slurry, comprising the following components: Al2O3 ceramic particles, an amphiphilic CNC skeleton, 2-hydroxyethyl methacrylate phosphate, butyl acrylate, a transfer agent, azobisisobutyronitrile, a fluorocarbon surfactant FS-30, hydroxyethyl cellulose, Al(NO3)3·9H2O, NH4H2PO4, a photoinitiator, and a crosslinking agent.

[0033] The specific preparation steps of the amphiphilic CNC framework are as follows:

[0034] S1: 10 g of cellulose nanocrystals were added to 200 mL of deionized water and dispersed uniformly by ultrasonic treatment to obtain a 5 wt% dispersion. 0.15 g of tetramethylpiperidinium oxide and 0.1 g of sodium bromide were then added to the dispersion, the pH was adjusted to 9, and after uniform mixing, 50 mL of a 5 wt% sodium hypochlorite solution was slowly added dropwise. The mixture was reacted at room temperature for 6 h, centrifuged, filtered, washed until neutral, and freeze-dried at -40 °C for 12 h to obtain carboxylated cellulose nanocrystals.

[0035] S2: 10 g of carboxylated cellulose nanocrystals prepared in step S1 were dispersed in 2000 mL of 0.1 M MES buffer at pH 5, 3 g of EDC and 3.4 g of NHS were added, and the mixture was activated at room temperature for 1 h. Then, 3 g of methoxypolyethylene glycol amino was added and the mixture was reacted at 30°C for 10 h. The mixture was centrifuged, filtered, and washed three times with 0.1 M sodium chloride solution to obtain an amphiphilic CNC framework.

[0036] The specific preparation steps of aqueous ceramic lithium battery coating slurry are as follows:

[0037] S101: 30 g of 2-hydroxyethyl methacrylate phosphate and 45 g of butyl acrylate were added to 400 mL of N,N-dimethylformamide and mixed evenly. 0.12 g of 4-cyano-4-(phenylthiocarbamoylthio)valeric acid and 0.03 g of azobisisobutyronitrile were added, and the mixture was reacted in an oil bath at 70°C under a nitrogen atmosphere for 18 h. The mixture was then rapidly cooled to 0°C and poured into 5 times the volume of 80 wt% methanol solution. The white solid was collected by filtration, washed with ethanol three times, and dried under vacuum at 40°C for 36 h to obtain a phosphate group copolymer.

[0038] S102: 10 g of the amphiphilic CNC skeleton was added to 100 mL of deionized water and dispersed uniformly by ultrasonic treatment to obtain a 10 wt% amphiphilic CNC suspension; 15 g of the phosphate group copolymer prepared in step S101 was added to 100 mL of deionized water and dispersed uniformly by ultrasonic treatment to obtain a 15 wt% copolymer suspension; 100 mL of the amphiphilic CNC suspension and 100 mL of the copolymer suspension were mixed, 0.4 g of fluorocarbon surfactant FS-30 was added, and the mixture was stirred at 300 rpm for 2 h, and the high-pressure homogenization was repeated 3 times at 1000 bar, and sheared at a shear rate of 200 s. -1 , time 10min, then let it stand for 24h to obtain a composite network system;

[0039] S103: 2 g of Al2O3 ceramic particles were added to 200 mL of 5 wt% hydrogen peroxide solution, treated at 80°C for 2 h, centrifuged, washed, and dried at 60°C to constant weight to obtain activated Al2O3 ceramic particles; 2 g of activated Al2O3 ceramic particles, 8 g of Al(NO3)3·9H2O, and 3.6 g of NH4H2PO4 were mixed evenly, and then added to 200 mL of the composite network system prepared in step S102, and ultrasonically dispersed at 200 W, 40 kHz, and for 20 min, and then subjected to gradient mineralization treatment, first adjusting the pH to 4.5 with acetic acid and staying for 4 min; then adjusting the pH to 6 with ammonia water and staying for 6 min, and finally adjusting the pH to 7.5 with ammonia water and staying for 5 min to obtain a mineralized AlPO4 slurry;

[0040] S104: Add 3 g of phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide and 4 mL of trimethylolpropane triglycidyl ether to the mineralized AlPO4 slurry prepared in step S103, stir at room temperature until completely dispersed, then add 0.4 g of hydroxyethyl cellulose and 0.1 M Tris-HCl buffer to maintain the pH to 7.5 to obtain an aqueous ceramic lithium battery coating slurry.

[0041] Example 2: A water-based ceramic lithium battery coating slurry, comprising the following components: Al2O3 ceramic particles, an amphiphilic CNC skeleton, 2-hydroxyethyl methacrylate phosphate, butyl acrylate, a transfer agent, azobisisobutyronitrile, a fluorocarbon surfactant FS-30, hydroxyethyl cellulose, Al(NO3)3·9H2O, NH4H2PO4, a photoinitiator, and a crosslinking agent.

[0042] The specific preparation steps of the amphiphilic CNC framework are as follows:

[0043] S1: 10 g of cellulose nanocrystals were added to 200 mL of deionized water and dispersed uniformly by ultrasonic treatment to obtain a 5 wt% dispersion. 0.2 g of tetramethylpiperidinium oxide and 0.2 g of sodium bromide were then added to the dispersion, the pH was adjusted to 9.5, and after uniform mixing, 55 mL of a 5 wt% sodium hypochlorite solution was slowly added dropwise. The mixture was reacted at room temperature for 8 h, centrifuged, filtered, washed until neutral, and freeze-dried at -40°C for 18 h to obtain carboxylated cellulose nanocrystals.

[0044] S2: 10 g of carboxylated cellulose nanocrystals prepared in step S1 were dispersed in 2000 mL of 0.1 M MES buffer at pH 5, 3.8 g of EDC and 4.3 g of NHS were added, and the mixture was activated at room temperature for 2 h. Then, 3.5 g of methoxypolyethylene glycol amino was added, and the mixture was reacted at 40°C for 12 h. The mixture was centrifuged, filtered, and washed three times with 0.1 M sodium chloride solution to obtain an amphiphilic CNC framework.

[0045] The specific preparation steps of aqueous ceramic lithium battery coating slurry are as follows:

[0046] S101: 35 g of 2-hydroxyethyl methacrylate phosphate and 45 g of butyl acrylate were added to 500 mL of N,N-dimethylformamide and mixed evenly. Then, 1.5 g of 4-cyano-4-(phenylthiocarbamoylthio)valeric acid and 0.05 g of azobisisobutyronitrile were added. The mixture was reacted in an oil bath at 70° C. under a nitrogen atmosphere for 20 h. The mixture was then rapidly cooled to 0° C. and poured into 5 times the volume of 80 wt% methanol solution. The white solid was collected by filtration, washed with ethanol three times, and dried under vacuum at 40° C. for 48 h to obtain a phosphate group copolymer.

[0047] S102: 10 g of the amphiphilic CNC skeleton was added to 100 mL of deionized water and dispersed uniformly by ultrasonic treatment to obtain a 10 wt% amphiphilic CNC suspension; 15 g of the phosphate group copolymer prepared in step S101 was added to 100 mL of deionized water and dispersed uniformly by ultrasonic treatment to obtain a 15 wt% copolymer suspension; 100 mL of the amphiphilic CNC suspension and 100 mL of the copolymer suspension were mixed, 0.4 g of the fluorocarbon surfactant FS-30 was added, and the mixture was stirred at 300 rpm for 2 h, and the high-pressure homogenization was repeated 4 times at 1000 bar, and sheared at a shear rate of 300 s. -1 , time 8min, then let it stand for 24h to obtain a composite network system;

[0048] S103: 2 g of Al2O3 ceramic particles were added to 200 mL of 5 wt% hydrogen peroxide solution, treated at 80°C for 3 h, centrifuged, washed, and dried at 60°C to constant weight to obtain activated Al2O3 ceramic particles; 2 g of activated Al2O3 ceramic particles, 9 g of Al(NO3)3·9H2O, and 4 g of NH4H2PO4 were mixed evenly, and then added to 200 mL of the composite network system prepared in step S102, and ultrasonically dispersed at 300 W, 40 kHz, and for 20 min, and then subjected to gradient mineralization treatment, first adjusting the pH to 4.5 with acetic acid and staying for 5 min; then adjusting the pH to 6 with ammonia water and staying for 8 min, and finally adjusting the pH to 7.5 with ammonia water and staying for 5 min to obtain a mineralized AlPO4 slurry;

[0049] S104: Add 3 g of phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide and 6 mL of trimethylolpropane triglycidyl ether to the mineralized AlPO4 slurry prepared in step S103, stir at room temperature until completely dispersed, then add 0.4 g of hydroxyethyl cellulose and 0.1 M Tris-HCl buffer to maintain the pH to 7.5 to obtain an aqueous ceramic lithium battery coating slurry.

[0050] Example 3: A water-based ceramic lithium battery coating slurry, comprising the following components: Al2O3 ceramic particles, an amphiphilic CNC skeleton, 2-hydroxyethyl methacrylate phosphate, butyl acrylate, a transfer agent, azobisisobutyronitrile, a fluorocarbon surfactant FS-30, hydroxyethyl cellulose, Al(NO3)3·9H2O, NH4H2PO4, a photoinitiator, and a crosslinking agent.

[0051] The specific preparation steps of the amphiphilic CNC framework are as follows:

[0052] S1: 10 g of cellulose nanocrystals were added to 200 mL of deionized water and dispersed uniformly by ultrasonic treatment to obtain a 5 wt% dispersion. 0.18 g of tetramethylpiperidinium oxide and 0.15 g of sodium bromide were then added to the dispersion, the pH was adjusted to 10, and after uniform mixing, 60 mL of a 5 wt% sodium hypochlorite solution was slowly added dropwise. The mixture was reacted at room temperature for 7 h, centrifuged, filtered, washed until neutral, and freeze-dried at -40 °C for 15 h to obtain carboxylated cellulose nanocrystals.

[0053] S2: 10 g of carboxylated cellulose nanocrystals prepared in step S1 were dispersed in 2000 mL of 0.1 M MES buffer at pH 5, 3.5 g of EDC and 4.1 g of NHS were added, and the mixture was activated at room temperature for 1.5 h. Then, 4 g of methoxypolyethylene glycol amino was added and the mixture was reacted at 35°C for 11 h. The mixture was centrifuged, filtered, and washed three times with 0.1 M sodium chloride solution to obtain an amphiphilic CNC framework.

[0054] The specific preparation steps of aqueous ceramic lithium battery coating slurry are as follows:

[0055] S101: 32 g of 2-hydroxyethyl methacrylate phosphate and 45 g of butyl acrylate were added to 450 mL of N,N-dimethylformamide and mixed evenly. Then, 1.4 g of 4-cyano-4-(phenylthiocarbamoylthio)valeric acid and 0.06 g of azobisisobutyronitrile were added. The mixture was reacted in an oil bath at 70°C under a nitrogen atmosphere for 24 h, and then rapidly cooled to 0°C. The mixture was then poured into 5 times the volume of 80 wt% methanol solution, and the white solid was collected by filtration. The solid was washed with ethanol three times and dried under vacuum at 40°C for 42 h to obtain a phosphate group copolymer.

[0056] S102: 10 g of the amphiphilic CNC skeleton was added to 100 mL of deionized water, and the mixture was dispersed evenly by ultrasonic treatment to obtain a 10 wt% amphiphilic CNC suspension; 15 g of the phosphate group copolymer prepared in step S101 was added to 100 mL of deionized water, and the mixture was dispersed evenly by ultrasonic treatment to obtain a 15 wt% copolymer suspension; 100 mL of the amphiphilic CNC suspension and 100 mL of the copolymer suspension were mixed, 0.4 g of the fluorocarbon surfactant FS-30 was added, and the mixture was stirred at 300 rpm for 2 h, and the high-pressure homogenization was repeated 5 times at 1000 bar, and sheared at a shear rate of 250 s. -1 , time 9min, then let it stand for 24h to obtain a composite network system;

[0057] S103: 2 g of Al2O3 ceramic particles were added to 200 mL of 5 wt% hydrogen peroxide solution, treated at 80°C for 4 h, centrifuged, washed, and dried at 60°C to constant weight to obtain activated Al2O3 ceramic particles; 2 g of activated Al2O3 ceramic particles, 8.5 g of Al(NO3)3·9H2O, and 3.8 g of NH4H2PO4 were mixed evenly, and then added to 200 mL of the composite network system prepared in step S102, and ultrasonically dispersed at 250 W, 40 kHz, and for 25 min, and then subjected to gradient mineralization treatment, first adjusting the pH to 4.5 with acetic acid and staying for 4.5 min; then adjusting the pH to 6 with ammonia water and staying for 7 min, and finally adjusting the pH to 7.5 with ammonia water and staying for 4.5 min to obtain a mineralized AlPO4 slurry;

[0058] S104: Add 2.5 g of phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide and 5 mL of trimethylolpropane triglycidyl ether to the mineralized AlPO4 slurry prepared in step S103, stir at room temperature until completely dispersed, then add 0.4 g of hydroxyethyl cellulose and 0.1 M Tris-HCl buffer to maintain the pH to 7.5 to obtain an aqueous ceramic lithium battery coating slurry.

[0059] Comparative Example 1: The operation of this comparative example 1 is basically the same as that of Example 2, except that there is no mineralization treatment system in comparative example 1, that is, the addition of Al(NO3)3·9H2O and NH4H2PO4 in step S103 is omitted, Al2O3 is directly mixed with the composite network, and the pH gradient mineralization step is removed.

[0060] Comparative Example 2: The operation of Comparative Example 2 is basically the same as that of Example 2, except that a traditional aqueous binder system is used in Comparative Example 2, i.e., polyacrylic acid is used instead of HEMAP-co-BA copolymer, and Al2O3 particles are directly mixed without pH gradient mineralization treatment.

[0061] Comparative Example 3: The operation of Comparative Example 3 is basically the same as that of Example 2, except that unmodified carboxylated cellulose nanocrystals without PEG grafting are used instead of amphiphilic cellulose nanocrystals in Comparative Example 3.

[0062] Performance test: The aqueous ceramic lithium battery coating slurry prepared in Examples 1 to 3 and Comparative Examples 1 to 3 was coated on a 20 μm polyethylene film with a coating thickness of 15 μm, a wavelength of 365 nm, a light intensity of 80 mW / cm², an energy density of 500 mJ / cm², and UV curing for 10 seconds. The diaphragm samples were then cured at 60°C for 30 minutes and at 100°C for 60 minutes. The following tests were then performed:

[0063] The puncture strength of the diaphragm samples was tested according to GB / T 36363-2018; the thermal shrinkage of the diaphragm samples was tested according to GB / T 36363-2018; the air permeability of the diaphragm samples was tested according to GB / T 36363-2018; the VOC emission test of the diaphragm samples was tested according to GB 33372-2020; and the peel strength of the diaphragm samples was tested according to GB / T 2792-2014 using a universal material testing machine with a peeling speed of 50 mm / min, a sample width of 10 mm, and a data acquisition frequency of 100 Hz. The test results are shown in Table 1 below.

[0064] Table 1. Test results of water-based ceramic slurry performance

[0065]

[0066] As can be seen from the results in Table 1, the water-based ceramic slurry prepared by the present invention exhibits excellent thermal shrinkage performance and high strength after coating and curing through multi-level synergistic effects, good air permeability, low VOC emissions, and is relatively environmentally friendly and safe; ‌As can be seen from the results of Example 2 and Comparative Example 1, there is a lack of rigid support: the lack of rigid inhibition of the AlPO4 mineralized layer and the thermal shrinkage inhibition is significantly reduced by relying solely on the physical filling of Al2O3. In addition, the lack of AlPO4-CNC lattice matching reduces the constraint force of the CNC network, further affecting the thermal shrinkage rate; As can be seen from the results of Example 2 and Comparative Example 2, although polyacrylic acid does not melt at high temperature, its carboxyl dehydration cross-linking reaction Shrinkage stress is generated; and polyacrylic acid is only combined with Al2O3 through hydrogen bonds, which cannot inhibit the slip of the particle-matrix interface; the lack of rigid support of AlPO4 significantly affects the thermal deformation resistance; from the results of Comparative Example 3 and Example 2, it can be seen that the unmodified cellulose nanocrystals are prone to agglomeration in the aqueous system due to the lack of hydrophobicity, forming local defects that induce stress concentration. In addition, there is no PEG chain segment buffering on the surface of the cellulose nanocrystals, which may cause the AlPO4-CNC interface to be easy to crack under thermal stress, and the unmodified CNC cannot effectively form a layered-fiber interwoven network, resulting in a decrease in stress buffering efficiency, which in turn affects the thermal shrinkage rate.

[0067] High temperature and high humidity stability test: The aqueous ceramic lithium battery coating slurry prepared in Example 2 and Comparative Examples 1 to 3 was treated at 85°C and 90% humidity for 144 hours. Samples were taken at 48 hours, 96 hours, and 144 hours for testing. The change rate of bonding strength (%) = (bonding strength before test - bonding strength after test) / bonding strength before test × 100%. The results are as follows: Figure 1 shown.

[0068] Depend on Figure 1 The results show that the aqueous ceramic lithium battery coating slurry prepared by the present invention has excellent resistance, good stability, and can be effectively preserved for a long time; from the results of Comparative Example 1 and Example 2, it can be seen that the lack of AlPO4 mineralization layer allows water to quickly penetrate through the Al2O3 / polymer physical interface, triggering hydrogen bonding between the hydroxyl groups on the surface of the Al2O3 particles and water molecules, thereby causing the particles to detach from the matrix; and the swelling of the polymer chain leads to concentration of interfacial shear stress, further affecting stability; from the results of Example 2 and Comparative Example 2, it can be seen that the carboxylic acid group of polyacrylic acid is ionized after absorbing moisture under hot and humid conditions, causing the binder to plasticize and become brittle, and the weak hydrogen bond with Al2O3 is destroyed by water molecules, resulting in the detachment of particles into pieces, and the stability is significantly affected; from the results of Comparative Example 3 and Example 2, it can be seen that the carboxylated cellulose nanocrystals without PEG grafting have strong hydrophilicity, which may preferentially adsorb water, resulting in the formation of microcracks around the cellulose nanocrystal agglomerates, and then the hydrogen bond between the cellulose nanocrystals and the polymer is replaced by water molecules, resulting in interfacial debonding, and the stability is significantly affected.

[0069] Spectrum test: The SEM spectrum of the sample coated with the aqueous ceramic lithium battery coating slurry prepared in Example 2 was tested using a scanning electron microscope. The test results are as follows: Figure 2 shown.

[0070] Depend on Figure 2 The results show that the granular material shown in the figure coexists with the fiber interweaving of the amphiphilic CNC skeleton with a fibrous network structure, which is consistent with the interpenetrating structure of inorganic particles and organic networks in the slurry; and there are many irregular porous structures in the figure, which is consistent with the expected porosity of the slurry; the multi-phase composite, porous and particle-fiber coexistence morphology in the figure is obvious with the fiber interweaving of the amphiphilic CNC skeleton in the slurry, the rigid support of the AlPO4 mineralized layer and the gradient cross-linking structure of the composite network.

[0071] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A water-based ceramic lithium battery coating slurry, characterized in that: The composition includes the following components: Al2O3 ceramic particles, amphiphilic CNC skeleton, 2-hydroxyethyl methacrylate phosphate, butyl acrylate, transfer agent, azobisisobutyronitrile, fluorocarbon surfactant FS-30, hydroxyethyl cellulose, Al(NO3)3·9H2O, NH4H2PO4, photoinitiator and cross-linking agent; The specific preparation steps of the amphiphilic CNC skeleton are as follows: S1: adding cellulose nanocrystals to deionized water, dispersing them uniformly with ultrasonic treatment to obtain a dispersion, then adding tetramethylpiperidinium oxide and sodium bromide to the dispersion, adjusting the pH, mixing uniformly, slowly adding sodium hypochlorite solution dropwise, reacting at room temperature, centrifuging after the reaction is complete, filtering, washing to neutrality, and freeze-drying to obtain carboxylated cellulose nanocrystals; S2: The carboxylated cellulose nanocrystals prepared in step S1 were dispersed in MES buffer, EDC and NHS were added, and the mixture was activated at room temperature. Then, methoxypolyethylene glycol amino groups were added and reacted. After the reaction was completed, the mixture was centrifuged, filtered, and washed with sodium chloride solution three times to obtain an amphiphilic CNC framework. In step S1, the ratio of the amount of the cellulose nanocrystals, tetramethylpiperidinium oxide, sodium bromide and sodium hypochlorite solution is 1 g: 0.015-0.02 g: 0.01-0.02 g: 5-6 mL; In step S2, the ratio of the amount of the carboxylated cellulose nanocrystals, MES buffer, EDC, NHS and methoxy polyethylene glycol amino is 1 g:200 mL:0.3-0.38 g:0.34-0.43 g:0.3-0.4 g; The preparation steps of the aqueous ceramic lithium battery coating slurry are as follows: S101: 2-Hydroxyethyl methacrylate phosphate and butyl acrylate are added to N,N-dimethylformamide, mixed evenly, and then a transfer agent and azobisisobutyronitrile are added. The mixture is reacted in an oil bath under a nitrogen atmosphere, rapidly cooled, and then poured into a methanol solution. The white solid is collected by filtration, repeatedly washed with ethanol, and vacuum dried to obtain a phosphate group copolymer. S102: adding the amphiphilic CNC skeleton to deionized water, and dispersing it uniformly by ultrasonic treatment to obtain an amphiphilic CNC suspension; adding the phosphate group copolymer prepared in step S101 to deionized water, and dispersing it uniformly by ultrasonic treatment to obtain a copolymer suspension; mixing the amphiphilic CNC suspension and the copolymer suspension, adding a fluorocarbon surfactant FS-30, stirring, repeating high-pressure homogenization, shearing, and then standing to obtain a composite network system; S103: adding Al2O3 ceramic particles to a hydrogen peroxide solution, heating, centrifuging, washing, and drying to a constant weight to obtain activated Al2O3 ceramic particles; uniformly mixing Al(NO3)3·9H2O and NH4H2PO4, then adding the mixture to the composite network system prepared in step S102, ultrasonically dispersing the mixture, and then performing a gradient mineralization treatment to obtain a mineralized AlPO4 slurry; S104: Add a photoinitiator and a cross-linking agent to the mineralized AlPO4 slurry prepared in step S103, stir at room temperature until completely dispersed, then add hydroxyethyl cellulose, and maintain the pH to 7.5 with Tris-HCl buffer to obtain an aqueous ceramic lithium battery coating slurry.

2. The aqueous ceramic lithium battery coating slurry according to claim 1, characterized in that: In step S101, the ratio of the amount of 2-hydroxyethyl methacrylate phosphate, butyl acrylate, N,N-dimethylformamide, transfer agent and azobisisobutyronitrile is 30-35 g:45 g:400-500 mL:0.12-0.15 g:0.03-0.06 g.

3. The aqueous ceramic lithium battery coating slurry according to claim 2, characterized in that: In step S102, the volume ratio of the amphiphilic CNC suspension and the copolymer suspension is 1:1; the parameters of the shear treatment are a shear rate of 200 to 300 s-1 and a time of 8 to 10 min.

4. The aqueous ceramic lithium battery coating slurry according to claim 3, characterized in that: In step S103, the ratio of the amount of the activated Al2O3 ceramic particles, Al(NO3)3·9H2O, NH4H2PO4 and the composite network system is 1g:4~4.5g:1.8~2g:100mL; in step S103, the parameters of the ultrasonic dispersion treatment are 200~300W, 40kHz, and time 20~30min.

5. The aqueous ceramic lithium battery coating slurry according to claim 4, characterized in that: In step S103, the specific parameters of the gradient mineralization treatment are: first adjust the pH to 4.5 with acetic acid and keep it for 4 to 5 minutes; then adjust the pH to 6 with ammonia water and keep it for 6 to 8 minutes; finally adjust the pH to 7.5 with ammonia water and keep it for 4 to 5 minutes.

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