Solid electrolyte composite diaphragm and preparation method thereof

Abstract

The preparation method comprises the following steps: mixing a first monomer and a second monomer in a solvent to obtain monomer slurry, mixing an activated inorganic salt whisker and a lithium salt to obtain filler slurry, mixing the two types of slurry, adding a photoinitiator to obtain electrolyte precursor slurry, coating the electrolyte precursor slurry on the surface of a diaphragm base material, and drying to obtain the solid electrolyte composite diaphragm. Carrying out UV induced crosslinking to obtain the inorganic salt whisker doped solid electrolyte composite diaphragm; proper addition of the monofunctional first monomer avoids the problems of too long polymeric chain, too brittle and hard material and the like of a multifunctional monomer, and endows the composite diaphragm with better flexibility; the mechanical strength and the ionic conductivity of the composite diaphragm are improved by doping the activated inorganic salt whiskers; the coating work is completed before monomer polymerization, the system molecular weight is small, the viscosity is low, construction is convenient, part of monomers and doping materials can better permeate into base material pores, finally UV induced polymerization improves the adhesion performance of the coating, and meanwhile the comprehensive performance of the diaphragm is further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of diaphragms, and particularly relates to a solid electrolyte composite diaphragm and a preparation method thereof. Background Art

[0002] Liquid batteries rely on flammable organic electrolytes. When the diaphragm is damaged under overcharge, collision or high temperature, it will cause short circuit or even explosion. Conventional diaphragms have problems such as low ionic conductivity and poor high-temperature resistance. Therefore, it is necessary to modify them to further improve their comprehensive performance. For example, CN 113937417 A discloses a photocured modified lithium-ion battery diaphragm and a preparation method thereof. By using a combination of specific photocurable monomers and pore-forming agents on the lithium-ion battery diaphragm, a porous structure is formed, which solves the problem of reduced air permeability of the diaphragm in the prior art, and realizes the improvement of heat resistance, adhesion and wettability, while maintaining the air permeability of the diaphragm. In addition, to improve the adhesion between the ceramic layer and the base film, CN 115312962 A adds a photocuring agent and a resin to the ceramic layer and the polymer layer of the lithium-ion battery diaphragm to achieve crosslinking curing, solves the problem of ceramic layer peeling, improves the heat resistance and stability of the diaphragm, and ensures the safety performance of the lithium battery.

[0003] Improving the heat resistance, adhesion and wettability of the diaphragm is one aspect, and on the other hand, it is necessary to improve its ionic conduction performance. Especially with the current need for the development of high-energy density batteries, the requirements for diaphragms are becoming increasingly stringent. Conventional wet-process PE diaphragms, in order to obtain high energy density and high porosity, often lead to a reduction in their mechanical strength, resulting in poor puncture resistance of the diaphragm, and thus prone to problems such as internal short circuit of the battery. In view of this, CN119133592 A discloses a solid electrolyte, a lithium battery using the solid electrolyte and a preparation method thereof. By using a polymer monomer containing unsaturated bonds to prepare a solid electrolyte in the lithium battery and using it in conjunction with a composite current collector to form an electron insulation layer, the problem of thermal runaway in the lithium battery during the needle puncture test is solved, and the safety and energy density of the battery are improved.

[0004] The present invention develops a novel solid electrolyte composite diaphragm, which improves the ionic conductivity of the diaphragm while improving its mechanical properties, in order to reduce the use of liquid electrolyte and improve the energy density of the battery and reduce the safety risk. Summary of the Invention

[0005] The present invention discloses a solid electrolyte composite separator and a preparation method thereof. First, a first monomer and a second monomer are mixed in a solvent to obtain a monomer slurry, and an activated inorganic salt whisker and a lithium salt are mixed to obtain a filler slurry. After mixing the two slurries, a photoinitiator is added to obtain an electrolyte precursor slurry. The electrolyte precursor slurry is coated on the surface of a separator substrate, and through UV light irradiation, the polymer is further crosslinked to obtain a composite separator coated with a solid electrolyte coating doped with inorganic salt whiskers. The corresponding preparation process schematic diagram is as shown in the appendix Figure 1 as follows

[0006] On the one hand, a solid electrolyte composite separator includes a separator substrate and a coating covering the substrate; The coating is obtained by coating an electrolyte precursor slurry on the surface of a separator substrate and drying it after UV light-induced crosslinking.

[0007] The electrolyte precursor slurry includes a monomer slurry, a filler slurry, and a photoinitiator; Furthermore, the solid content of the electrolyte precursor slurry is 30-50%.

[0008] The monomer slurry is obtained by dissolving a first monomer having at least one photocurable reaction group and a second monomer having at least two photocurable reaction groups in a solvent and mixing them.

[0009] The solvent is dichloromethane.

[0010] The photoinitiator is one or more of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone.

[0011] The first monomer is one or more of methyl methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate, and n-propyl acrylate; The second monomer is one or more of 1,6-hexanediol diacrylate, triethylene glycol diacrylate, and dipropylene glycol diacrylate.

[0012] The dosage of the first monomer and the second monomer is in a mass ratio of 3-1:7-9.

[0013] The filler slurry includes activated inorganic salt whiskers and lithium salts; The dosage of the activated inorganic salt whiskers in the electrolyte precursor slurry, calculated based on the dosage of the modified inorganic salt whiskers, accounts for 5-15% of the total amount of polymer monomers.

[0014] The activated inorganic salt whiskers are obtained by first treating with a borate coupling agent to obtain modified inorganic salt whiskers, and then reacting with a branched compound; The inorganic whiskers are one or more of magnesium borate whiskers, calcium borate whiskers, aluminum borate whiskers, copper aluminum borate whiskers, basic magnesium sulfate whiskers, magnesium carbonate whiskers, calcium carbonate whiskers, and calcium sulfate whiskers; Preferably, the diameter of the inorganic whiskers is 0.01 - 10 μm, and the aspect ratio is 2 - 100; Preferably, the diameter of the inorganic whiskers is 0.01 - 1 μm, and the aspect ratio is 2 - 30.

[0015] The branched - chain compound is one or more of pentaerythritol triacrylate (PET3A), pentaerythritol tetraacrylate (PET4A), and pentaerythritol tetrakis(3 - mercaptopropionate) (PETMP).

[0016] By mass, the dosage ratio of the borate coupling agent to the inorganic whiskers is 0.8 - 1.2:40 - 60; By mass, the dosage of the branched - chain compound is 5 - 10% of the modified inorganic whiskers; Specifically, the corresponding preparation steps are as follows: Place the flask containing the coupling agent in an ultrasonic oscillator with a water temperature of 50 °C. After dissolving with absolute ethanol, add the inorganic whiskers dried at 120 °C for 4 h. Stir electrically and ultrasonically vibrate for 1 - 2 h, then filter, wash, and dry to obtain modified inorganic whiskers with C=C modification; Then pre - polymerize the modified inorganic whiskers with C=C modification and the branched - chain compound in a dichloromethane solvent system to endow multiple active sites, obtaining activated inorganic whiskers; Furthermore, the specific steps for pre - polymerizing the modified inorganic whiskers with C=C modification and the branched - chain compound are: Place in the dark, in a dichloromethane solvent system, add the modified inorganic whiskers, the branched - chain compound, and a photo - initiator (2% based on the mass of the branched - chain compound), then seal and ultrasonically treat under ultraviolet light for 1 - 5 minutes.

[0017] Furthermore, add the lithium salt solution to the above - mentioned activated inorganic whiskers reaction system and continue ultrasonically treating for 5 minutes to obtain a filler slurry; Preferably, the lithium salt solution is a lithium salt / acetonitrile solution with a solid content of 50%.

[0018] The lithium salt includes one or more of lithium bis(oxalato)borate (LiBOB), lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium perchlorate (LiClO4); Preferably, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4).

[0019] The dosage of the lithium salt is 10 - 20% of the total amount of polymer monomers.

[0020] The diaphragm substrate is a PE, PP or PET diaphragm with ultra-high porosity and ultra-large pore size, the porosity is ≥65%, the pore size is >85 nm, and the thickness is 8-12 μm; Preferably, the pore size of the diaphragm substrate is >100 nm.

[0021] Preferably, the borate coupling agent includes one or more of 2-allyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, dibutyl vinyl borate, and 2-methyl-2,4-pentanediol vinyl borate.

[0022] Finally, the monomer slurry and the filler slurry are mixed, and a photoinitiator is added to obtain a precursor slurry for the solid electrolyte; by mass, the amount of the photoinitiator used is 2-6% of the total amount of monomers in the monomer slurry.

[0023] On the other hand, a method for preparing a solid electrolyte composite diaphragm includes the following steps: First, a monomer slurry is obtained by mixing a first monomer and a second monomer in a solvent, a filler slurry is obtained by activating and mixing inorganic salt whiskers and a lithium salt, the two slurries are mixed and then a photoinitiator is added to obtain a precursor slurry for the solid electrolyte, the precursor slurry for the electrolyte is coated on the surface of the diaphragm substrate, and UV light irradiation is carried out to promote further cross-linking of the polymer to obtain a composite diaphragm coated with a solid electrolyte coating doped with inorganic salts. The specific steps are as follows: Step 1: Preparation of the precursor slurry for the electrolyte: (1) Preparation of the monomer slurry Under nitrogen protection, using dichloromethane as a solvent, a first monomer and a second monomer with a mass ratio of 3-1:7-9 are added to a reaction vessel and stirred at room temperature for 10-30 minutes to obtain a uniformly mixed monomer slurry; (2) Preparation of the filler slurry Placed in the dark, in a dichloromethane solvent system, a borate coupling agent-modified inorganic salt whisker accounting for 5-15% of the total amount of polymer monomers, a branched-chain compound accounting for 5-10% of the modified inorganic salt whisker, and a photoinitiator based on 2% of the mass of the branched-chain compound are added, and then sealed and ultrasonically treated under ultraviolet light for 1-5 minutes; The inorganic salt whisker material is one or more of magnesium borate whisker, calcium borate whisker, aluminum borate whisker, copper aluminum borate whisker, basic magnesium sulfate whisker, magnesium carbonate whisker, calcium carbonate whisker, and calcium sulfate whisker; The photoinitiator is one or more of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone.

[0024] Finally, a lithium salt solution with a lithium salt content of 10-20% based on the total amount of polymer monomers is prepared, and the lithium salt / acetonitrile solution is added to the above-activated inorganic salt whisker reaction system, followed by ultrasonic treatment for 5 minutes to obtain a filler slurry; Preferably, the lithium salt / acetonitrile solution has a solid content of 50%.

[0025] Preparation of the borate coupling agent-modified inorganic salt whiskers: Place the flask containing the coupling agent in an ultrasonic oscillator with a water temperature of 50 °C. After dissolving with absolute ethanol, add the inorganic salt whiskers dried at 120 °C for 4 h. Stir electrically and ultrasonically vibrate for 1-2 h, then filter, wash, and dry to obtain; wherein, by mass, the dosage of the coupling agent to the inorganic salt whiskers is 0.8-1.2:40-60; the dosage of absolute ethanol is 3-5 times that of the inorganic salt whiskers; the coupling agent is one or more of 2-allyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, dibutyl vinyl borate, and 2-methyl-2,4-pentanediol vinyl borate.

[0026] (3) Preparation of the electrolyte precursor slurry In the dark, mix the monomer slurry obtained in step (1) and the filler slurry obtained in step (2), control the solid content of the slurry to be 30-50%, and add a photoinitiator after mixing evenly; the photoinitiator is one or more of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone, and its dosage is 2-6% of the total amount of monomers in the monomer slurry.

[0027] Step 2. Preparation of a composite separator coated with a solid electrolyte coating Coat the electrolyte precursor slurry obtained in the above step on the surface of the separator substrate, control the thickness to be 3-7 μm, and irradiate with UV light to promote UV-induced crosslinking of the polymer and drying to obtain a composite separator coated with a solid electrolyte coating doped with inorganic salt whiskers.

[0028] Preferably, the separator substrate is a PE, PP, or PET separator with ultra-high porosity and ultra-large pore size, the porosity is ≥65%, and the pore size > 100 nm.

[0029] The UV light irradiation uses two-stage UV light sources. The energy of the first-stage light source is 20 mW / cm 2 , the photocuring wavelength is the mercury lamp 365 nm light source, the machine speed is 2 m / min, and the length is 1 m; at this time, the polymer is pre-cured, and during this period, small molecule monomers and lithium salts can still further penetrate into the pore structure of the substrate; the energy of the second-stage light source is 25 mW / cm 2, the photocuring wavelength is a mercury lamp 365nm light source, the machine speed is 1.2m / min, and the length is 3 m; after completing UV-induced crosslinking, the composite separator is placed in an oven and maintained at 85 °C for 2 to 4 hours to remove the solvent, so that the coating adheres to the surface of the separator substrate to obtain a solid electrolyte composite separator.

[0030] The present invention provides the application of the solid electrolyte composite separator prepared by the above method in the preparation of liquid batteries; The present invention further provides the application of the solid electrolyte composite separator prepared by the above method in the preparation of solid or semi-solid batteries; The liquid, solid or semi-solid battery is a lithium battery or a lithium-ion battery.

[0031] A solid electrolyte composite separator and a preparation method thereof provided by the present invention have the following beneficial effects: (1) The first monomer and the second monomer are used in a ratio. The first monomer is a monofunctional monomer, and the second monomer is a polyfunctional monomer. The appropriate addition of the monofunctional monomer can significantly reduce the viscosity of the system, improve the fluidity, and facilitate construction; the polyfunctional monomer is used as a crosslinking agent, containing multiple polymerizable functional groups that can promote the crosslinking of the polymer to form a high crosslinking degree network structure; in addition, the coating work is completed before the slurry polymerization. At this time, the molecular weight of the monomer is small, and the fluidity of the slurry is better. Especially driven by the solvent, it can enter the pores of the separator. Finally, UV-induced polymerization is completed to further crosslink the polymer, endowing the polymer composite with high ionic conductivity and excellent mechanical properties.

[0032] (2) The doping of activated inorganic salt whiskers. On the one hand, the inorganic salt whisker material itself has good heat resistance and flame retardancy, which can improve the safety performance of the composite separator, and the unique aspect ratio structure of the whiskers can significantly improve the mechanical strength of the composite material; secondly, the Lewis acid center of the inorganic salt whiskers can interact with the lithium salt anions, thereby weakening the interaction between Li + and the anions, promoting the dissociation of the lithium salt to release more Li + , which is beneficial to improving the ionic conductivity of the composite solid electrolyte; after modification, the compatibility with the organic system is improved to form a good dispersion, and at the same time, the activation treatment promotes the crosslinking and combination of the whiskers and the polymer system to further improve the mechanical properties of the composite material, which can effectively inhibit the growth of lithium dendrites and avoid the problem of the porous membrane being pierced.

[0033] (3) A solid electrolyte composite separator with a uniform coating is obtained based on the co-doping of fibrous inorganic salt whiskers and lithium salts, which has high ionic conductivity and excellent mechanical properties at the same time. Description of the Drawings

[0034] Figure 1 Schematic diagram of the preparation process of a solid electrolyte composite separator.

[0035] 1 - First monomer; 2 - Second monomer; 3 - Activated inorganic salt whisker; 4 - Lithium salt. Specific embodiments

[0036] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific embodiments.

[0037] In the present invention, unless otherwise specified, all devices and raw materials can be purchased from the market or are commonly used in this industry. The methods in the following embodiments are conventional methods in this field unless otherwise specified.

[0038] Magnesium borate, aluminum borate, magnesium carbonate trihydrate whisker: Yingkou Xiongdi Boron-Magnesium Chemical Co., Ltd.; Magnesium carbonate trihydrate whisker: purity ≥ 99%, diameter 0.02 - 1.0 μm, length 0.2 - 20.0 μm; Magnesium borate whisker: purity ≥ 99%, diameter 0.01 - 1.0 μm, length 0.1 - 20.0 μm; In addition, magnesium borate whisker with purity ≥ 99%, diameter 1.0 - 2.0 μm, and length 2.0 - 40.0 μm was selected for comparison; Aluminum borate whisker: purity ≥ 99%, diameter 0.05 - 1.0 μm, length 0.5 - 20.0 μm; Preparation of borate coupling agent-modified Mg2B2O5 whisker: Add 0.5 g of vinyl borate dibutyl ester coupling agent to a 250 mL flask, place it in an ultrasonic oscillator with a water temperature of 50 °C, dissolve it with 100 mL of absolute ethanol, then add 25 g of magnesium borate whisker dried at 120 °C for 4 h. While stirring electrically, perform ultrasonic oscillation for 1 h, then filter, wash, and dry at 90 °C for 6 h to obtain the modified magnesium borate material; the dosage of absolute ethanol is 3 - 5 times that of the Mg2B2O5 whisker.

[0039] Perform modification treatment on aluminum borate and magnesium carbonate trihydrate in the same method as above for comparison.

[0040] Lithium salt (LiTFSI): Shanghai Macklin Biochemical Co., Ltd.

[0041] PE separator, Hefei New Energy Materials Co., Ltd., porosity ≥ 65%, pore diameter > 100 nm.

[0042] Methyl methacrylate and triethylene glycol diacrylate, analytical pure, Shanghai Aladdin Biochemical Technology Co., Ltd.

[0043] Example 1 A solid electrolyte composite separator. First, a monomer slurry is obtained by mixing a first monomer and a second monomer in a solvent. Then, an activated Mg2B2O5 whisker and a lithium salt are mixed to obtain a filler slurry. Next, the two slurries are mixed and a photoinitiator is added to obtain a solid electrolyte precursor slurry. The solid electrolyte precursor slurry is coated on the surface of a separator substrate, and through UV light irradiation, the polymer is further crosslinked and dried to obtain a composite separator coated with a solid electrolyte coating doped with Mg2B2O5. The specific preparation steps are as follows: Step 1. Preparation of the solid electrolyte precursor slurry: (1) Preparation of the monomer slurry Under nitrogen protection, using dichloromethane as the solvent, methyl methacrylate and triethylene glycol diacrylate with a mass ratio of 3:7, that is, 30 g of methyl methacrylate and 70 g of triethylene glycol diacrylate, are added to a reaction vessel and stirred at room temperature for 10 - 30 minutes to obtain a uniformly mixed monomer slurry; (2) Preparation of the filler slurry In the dark, in a dichloromethane solvent system, 10% (10 g) of borate coupling agent - modified Mg2B2O5 whiskers, 7.5% (0.75 g) of PETMP, and 2% (0.015 g) of 2,2 - dimethoxy - 2 - phenylacetophenone are added, then sealed and ultrasonically treated for 3 minutes under UV light with a light source energy of 25 mW; Subsequently, a lithium salt / acetonitrile solution formed by 15% (15 g) of LiTFSI is added to the above - mentioned activated Mg2B2O5 whisker reaction system, and ultrasonically treated for another 5 minutes to obtain a filler slurry; the solid content of the lithium salt / acetonitrile solution is 50%; (3) Preparation of the solid electrolyte precursor slurry In the dark, the monomer slurry obtained in step (1) and the filler slurry obtained in step (2) are mixed, controlling the solid content of the slurry to be 40% ±. After mixing evenly, 3 g of 2,2 - dimethoxy - 2 - phenylacetophenone is added and ultrasonically treated until the mixture is homogeneous.

[0044] Step 2. Preparation of the composite separator coated with a solid electrolyte coating The solid electrolyte precursor slurry is coated on one side surface of the separator substrate, controlling the thickness to be 5 μm. Through UV light irradiation, the energy of the first - stage light source is 20 mW / cm 2 , the light - curing wavelength is a mercury lamp 365 nm light source, the machine speed is 2 m / min, and the length is 1 m; the energy of the second - stage light source is 25 mW / cm 2 , the light - curing wavelength is a mercury lamp 365 nm light source, the machine speed is 1.2 m / min, and the length is 3 m; after completing UV - induced crosslinking, the composite separator is placed in an oven and maintained at 85 °C for 2 - 4 hours to remove the solvent; Coat the other surface of the substrate according to the above operations to obtain a solid electrolyte composite separator.

[0045] Example 2 Adjust the mass ratio of methyl methacrylate to triethylene glycol diacrylate in step (1) of Example 1 to 2:8, and keep the remaining steps unchanged.

[0046] Example 3 Adjust the mass ratio of methyl methacrylate to triethylene glycol diacrylate in step (1) of Example 1 to 1:9, and keep the remaining steps unchanged.

[0047] Example 4 Adjust the dosage of LiTFSI in step (2) of Example 2 to 10%, and keep the remaining steps unchanged.

[0048] Example 5 Adjust the dosage of LiTFSI in step (2) of Example 2 to 20%, and keep the remaining steps unchanged.

[0049] Example 6 Adjust the dosage of modified magnesium borate whiskers in step (2) of Example 2 to 5%, and keep the remaining steps unchanged.

[0050] Example 7 Adjust the dosage of modified magnesium borate whiskers in step (2) of Example 2 to 15%, and keep the remaining steps unchanged.

[0051] Example 8 Adjust to modified aluminum borate whiskers in step (2) of Example 2, and keep the remaining steps unchanged.

[0052] Example 9 Adjust to modified magnesium carbonate trihydrate whiskers in step (2) of Example 2, and keep the remaining steps unchanged.

[0053] Comparative Example 1 Adjust the mass ratio of methyl methacrylate to triethylene glycol diacrylate in step (1) of Example 1 to 0:10, and keep the remaining steps unchanged.

[0054] Comparative Example 2 Adjust that the modified magnesium borate in step (2) of Example 2 is not activated, that is, the dosage of PETMP is 0 g, and keep the remaining steps unchanged.

[0055] Comparative Example 3 Adjust to unmodified magnesium borate in step (2) of Example 2, that is, Mg2B2O5 whiskers without any treatment, and keep the remaining steps unchanged.

[0056] Comparative Example 4 In (2) of Step 1, no modified magnesium borate is added, that is, 0 g of magnesium borate whiskers modified with borate coupling agent, and the remaining steps are the same as those in Example 2.

[0057] Comparative Example 5 Add 3 g of 2,2-dimethoxy-2-phenylacetophenone to the monomer slurry in (1) of Step 1, and irradiate it with UV light with a light source energy of 25 mW in the dark and ultrasonically treat it for 5 min until the mixture is uniform. In Step 3, no 2,2-dimethoxy-2-phenylacetophenone is added, and the remaining steps are the same as those in Example 2.

[0058] Comparative Example 6 Adjust the dosage of LiTFSI in (2) of Step 1 of Example 2 to 0%, and keep the remaining steps unchanged.

[0059] Comparative Example 7 Adjust the inorganic salt whiskers in Step 1 (2) of Example 2 to magnesium borate whiskers modified with borate coupling agent with a diameter of 1.0 - 2.0 μm and a length of 2.0 - 40.0 μm, and keep the remaining steps unchanged.

[0060] Comparative Example 8 PE separator without any coating treatment.

[0061] The separators prepared in the above Examples 1 - 9 and Comparative Examples 1 - 8 are cut into A4 size for testing various performances. The test items are as follows: (1) Tensile strength & elongation at break: According to "GB / T 36363 - 2018", use a Xieqiang CTM universal testing machine to test the longitudinal and transverse tensile strength and elongation at break of the separator. Test 5 samples in each direction and calculate their average value; (2) Puncture strength: According to "GB / T 36363 - 2018", use a Xieqiang CTM universal testing machine to test the puncture strength of the separator. Test 5 samples and calculate their average value; (3) Ionic conductivity: Refer to the relevant ionic conductivity test method in "GB / T 36363 - 2018" to test the ionic conductivity of each composite separator; (4) Peel strength: Test according to the method in the national standard "GB / T 2792 - 2014 Adhesive tape peel strength", and use a Xieqiang CTM universal material testing machine.

[0062] The test results of the samples in Examples 1 - 9 and Comparative Examples 1 - 8 are shown in Table 1.

[0063] Table 1 Test results of the samples in Examples 1 - 9 and Comparative Examples 1 - 8

[0064] From the data comparison between Examples 1 to 9 and Comparative Example 8 in Table 1, it can be found that the solid electrolyte composite separator modified by doping coatings based on activated magnesium borate whiskers, aluminum borate whiskers, and magnesium carbonate whiskers of the present invention has high ionic conductivity and more excellent mechanical properties.

[0065] Among them, Examples 1 to 3 and Comparative Examples 1 and 5 were investigated by adjusting different ratios of polymerization monomers and comparing whether UV polymerization was completed before coating or after coating. From the relevant data, it can be seen that the addition of a certain proportion of monofunctional polymerization monomers, on the one hand, the appropriate addition of monofunctional monomers can avoid problems such as too long polymerization chains of polyfunctional monomers and the composite material being too brittle and hard. It endows the composite separator with better flexibility and elongation at break, ensuring that the separator is not easily broken during the charge and discharge process of the battery, and making the separator easier to operate during processing such as winding and laminating; on the other hand, polyfunctional monomers, as cross-linking agents, contain two polymerizable functional groups to promote polymer cross-linking. After UV-induced polymerization in the later stage, a highly cross-linked network structure is formed to improve the mechanical properties of the composite material and increase the puncture and coating peel strength. Completing the coating work before monomer polymerization, at this time, the molecular weight of the system is small, the viscosity is low, and the fluidity is high, which is convenient for construction. And some monomers and fillers can better penetrate into the pores of the substrate. Finally, UV-induced polymerization is completed, so that the coating can firmly adhere to the substrate (the coating peel strength is better), and the electrolyte material enters the substrate to improve the overall ionic conductivity of the separator.

[0066] From the data comparison between Examples 2, 8, 9 and Comparative Examples 2 to 4, it can be seen that the addition of activated Mg2B2O5 whiskers can improve the ionic conductivity, and its effect is more significant than that of aluminum borate and magnesium carbonate; at the same time, after the Mg2B2O5 whiskers are activated, it is more beneficial to the improvement of ionic conductivity. This means that a part of the polymer cross-links with the Mg2B2O5 whiskers, and the interaction between the polymer phase and the inorganic phase can more fully play the role of promoting the dissociation of lithium salts, fixing anionic groups, and transporting lithium ions. The dissociation of inorganic whiskers introduces more binding sites, which combine with the polymer to form continuous ion channels or networks. These channels provide paths for the transport of lithium ions. Therefore, when compared with unactivated or unmodified Mg2B2O5 whiskers, the increase in the transference number of Li + and the improvement of ionic conductivity of the composite material after the Mg2B2O5 whiskers are activated may be due to the further expansion of ion channels.

[0067] In addition, by comparing the data of Example 2 with those of Examples 4 to 7 and Comparative Examples 5, 6, and 7, it is found that the addition of a certain amount of activated Mg2B2O5 whiskers and lithium salts significantly improves the ionic conductivity. At the same time, the introduction of fibrous whisker materials significantly helps to improve the overall mechanical strength of the materials. This may be because the doping of whisker materials with a certain aspect ratio structure in the polymer system enables them to be uniformly and orderly combined with the coating, thereby improving the properties such as tensile strength and puncture strength.

[0068] In summary, a solid electrolyte composite separator disclosed by the present invention has relatively excellent mechanical strength and ionic conductivity.

Claims

1. A solid electrolyte composite diaphragm, comprising a diaphragm substrate and a coating covering the surface of the substrate, wherein the coating is obtained by coating an electrolyte precursor slurry on the surface of the diaphragm substrate, and then undergoing UV light-induced crosslinking and drying, wherein: The electrolyte precursor slurry includes monomer slurry, filler slurry and photoinitiator; the monomer slurry is a first monomer including at least one group that can participate in photocuring reaction and a second monomer including at least two groups that can participate in photocuring reaction; the filler slurry includes activated inorganic salt whiskers and lithium salt; the activated inorganic salt whiskers are first treated with a borate coupling agent to obtain modified inorganic salt whiskers, and then activated by reaction with a branched compound; the branched compound is one or more of pentaerythritol triacrylate, pentaerythritol tetraacrylate, and pentaerythritol tetra(3-mercaptopropionic acid) ester.

2. A solid electrolyte composite diaphragm according to claim 1, characterized in that: The first monomer is one or more of methyl methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate, and n-propyl acrylate; the second monomer is one or more of 1,6-hexanediol diacrylate, triethylene glycol diacrylate, and tripropylene glycol diacrylate; the monomer slurry is obtained by dissolving the first monomer and the second monomer in a solvent; the amount of the first monomer and the second monomer is 3 to 1:7 to 9 in a mass ratio; the photoinitiator is one or more of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone.

3. A solid electrolyte composite diaphragm according to claim 2, characterized in that: The inorganic salt whiskers are one or more of magnesium borate whiskers, calcium borate whiskers, aluminum borate whiskers, copper aluminum borate whiskers, basic magnesium sulfate whiskers, magnesium carbonate whiskers, calcium carbonate whiskers and calcium sulfate whiskers.

4. A solid electrolyte composite diaphragm according to claim 3, characterized in that: The filler slurry is obtained by adding lithium salt to the prepolymerization reaction system of the modified inorganic salt whisker and the branched compound, and the specific steps are: placing it in a dark place, adding the modified inorganic salt whisker, the branched compound and a photoinitiator based on 2% of the mass of the branched compound in a dichloromethane solvent system, then sealing and ultrasonically treating it under ultraviolet light for 1 to 5 minutes, and then adding the lithium salt / acetonitrile solution to the above-mentioned activated inorganic salt whisker reaction system and continuing ultrasonically treating it for 5 minutes to obtain it.

5. A solid electrolyte composite diaphragm according to claim 4, characterized in that: The borate coupling agent includes one or more of 2-allyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, dibutyl vinyl borate, and 2-methyl-2,4-pentanediol vinyl borate.

6. A solid electrolyte composite membrane according to claim 5, characterized in that: The amount of the activated inorganic salt whiskers in the electrolyte precursor slurry, calculated as the amount of the modified inorganic salt whiskers, accounts for 5 to 15% of the total amount of polymer monomers; the amount ratio of the borate coupling agent to the inorganic salt whiskers is 0.8 to 1.2:40 to 60 by mass; the amount of the branched compound is 5 to 10% of the modified inorganic salt whiskers; and the amount of the lithium salt is 10 to 20% of the total amount of polymer monomers.

7. A solid electrolyte composite diaphragm according to claim 6, characterized in that: The lithium salt includes one or more of lithium bis(oxalatoborate), lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonylimide), and lithium perchlorate; the solid content of the electrolyte precursor slurry is 30-50%; and the diaphragm substrate is a PE or PP or PET diaphragm with a porosity of ≥65% and a pore size of >85 nm.

8. The method for preparing a solid electrolyte composite membrane according to any one of claims 1 to 7, characterized in that: The specific preparation steps include: Step 1: Preparation of electrolyte precursor slurry: (1) Preparation of monomer slurry: under nitrogen protection, using dichloromethane as solvent, adding the first monomer and the second monomer in a mass ratio of 3-1:7-9 into a reaction container and stirring at room temperature for 10-30 minutes to obtain a uniformly mixed monomer slurry; (2) Preparation of filler slurry: Place in a dark place, add 5-15% of borate coupling agent modified inorganic salt whiskers, 5-10% of branched compounds based on the weight of the modified inorganic salt whiskers, and 2% of photoinitiator based on the weight of the branched compounds in a dichloromethane solvent system, then seal and ultrasonically treat under ultraviolet light for 1-5 minutes; Finally, 10-20% of lithium salt based on the total amount of polymer monomers is prepared into a lithium salt / acetonitrile solution, added into the activated inorganic salt whisker reaction system, and ultrasonic treatment is continued for 5 minutes to obtain a filler slurry; (3) Preparation of electrolyte precursor slurry: In a dark place, mix the monomer slurry obtained in step (1) and the filler slurry obtained in step (2), control the solid content of the slurry to be 30-50%, and after mixing evenly, add 2-6% of a photoinitiator based on the total amount of the monomers; The photoinitiator in step (2) or (3) of step 1 is one or more of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone; Step 2: Preparation of composite diaphragm coated with solid electrolyte coating: The electrolyte precursor slurry obtained in the above step is coated on the surface of the diaphragm substrate with a thickness of 3 to 7 μm. The polymer is irradiated with UV light to induce UV crosslinking and dried to obtain a composite diaphragm coated with a solid electrolyte coating doped with an inorganic salt.

9. The method for preparing a solid electrolyte composite diaphragm according to claim 8, characterized in that: Preparation of borate coupling agent modified inorganic salt whiskers in step 1 (2): placing a flask containing the coupling agent in an ultrasonic oscillator at a water temperature of 50°C, dissolving it with anhydrous ethanol, adding inorganic salt whiskers dried at 120°C for 4 hours, stirring it electrically and ultrasonically oscillating it for 1 to 2 hours, filtering it, washing it, and drying it to obtain the product; wherein, in parts by weight, the amount of coupling agent to inorganic salt whiskers is 0.8 to 1.2:40 to 60; the amount of anhydrous ethanol is 3 to 5 times that of the inorganic salt whiskers; and the coupling agent is one or more of 2-allyl-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, dibutyl vinyl borate, and 2-methyl-2,4-pentanediol vinyl borate.

10. The method for preparing a solid electrolyte composite membrane according to claim 9, characterized in that: The UV irradiation in step 2 is carried out using two sections of UV light source, wherein the energy of the first section of the light source is 20 mW / cm 2 The light curing wavelength is a mercury lamp with a wavelength of 365 nm, a machine speed of 2 m / min, and a length of 1 m; the energy of the second light source is 25 mW / cm 2 The photocuring wavelength is a mercury lamp with a light source of 365 nm, the machine speed is 1.2 m / min, and the length is 3 m. After the UV-induced cross-linking is completed, the composite diaphragm is placed in a drying oven at 85 °C for 2 to 4 hours to remove the solvent, so that the coating adheres to the surface of the diaphragm substrate to obtain a solid electrolyte composite diaphragm.

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