A solid electrolyte composite diaphragm and preparation method thereof

Abstract

The invention discloses a solid electrolyte composite diaphragm and a preparation method thereof. The monomer slurry is obtained by mixing a first monomer and a second monomer in a solvent, and activated inorganic salt whiskers and lithium salt are mixed to obtain a filler slurry. After the two slurries are mixed, a photoinitiator is added to obtain an electrolyte precursor slurry, which is then coated on the surface of a diaphragm substrate. After UV-induced crosslinking, an inorganic salt whisker-doped solid electrolyte composite diaphragm is obtained. The proper addition of a monofunctional first monomer avoids problems such as excessively long polymerization chains of multifunctional monomers and excessive brittleness of the material, thereby giving the composite diaphragm better flexibility. The doping of activated inorganic salt whiskers improves the mechanical strength and ion conductivity of the composite diaphragm. The coating work is completed before monomer polymerization, the system has a small molecular weight and low viscosity, is easy to construct, and some monomers and doping materials can better penetrate into the pores of the substrate. Finally, UV-induced polymerization improves the adhesion performance of the coating while further improving the comprehensive performance of the diaphragm.

Description

Technical Field

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

[0002] Liquid batteries rely on flammable organic electrolytes. When overcharged, collided or at high temperatures, the diaphragm is damaged, causing a short circuit or even an explosion. Conventional diaphragms have problems such as low ion conductivity and not being able to withstand high temperatures. Therefore, it is necessary to modify it to further improve its overall performance. For example, CN 113937417 A discloses a photocurable modified lithium-ion battery diaphragm and a preparation method thereof. By using a combination of a specific photocurable monomer and a pore-forming agent on a lithium-ion battery diaphragm, a porous structure is formed, which solves the problem of reduced permeability of the diaphragm in the prior art, achieves improved heat resistance, adhesion and wettability, and maintains the permeability of the diaphragm. In addition, in order to improve the adhesion between the ceramic layer and the base film, CN 115312962 A achieves cross-linking and curing by adding a photocuring agent and a resin to the ceramic layer and the polymer layer of the lithium-ion battery diaphragm, thereby solving the problem of ceramic layer shedding, improving the heat resistance and stability of the diaphragm, and ensuring 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 ion conductivity. 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 circuits in the battery. In view of this, CN119133592 A discloses a solid electrolyte, a lithium battery using a solid electrolyte, and a preparation method thereof. By using a polymer monomer containing an unsaturated bond in a lithium battery to prepare a solid electrolyte, and using it in conjunction with a composite current collector to form an electronic insulating layer, the problem of thermal runaway of the lithium battery in the needle puncture test is solved, and the safety and energy density of the battery are improved.

[0004] The present invention develops a new type of solid electrolyte composite diaphragm, which improves the ion conductivity of the diaphragm while improving its mechanical properties, so as to reduce the use of liquid electrolyte, increase the energy density of the battery, and reduce safety risks. Summary of the Invention

[0005] The present invention discloses a solid electrolyte composite diaphragm and a preparation method thereof. First, a first monomer and a second monomer are mixed in a solvent to obtain a monomer slurry. Activated inorganic salt whiskers and lithium salt are mixed to obtain a filler slurry. After the two slurries are mixed, a photoinitiator is added to obtain an electrolyte precursor slurry. The electrolyte precursor slurry is coated on the surface of the diaphragm substrate. After UV light is applied to promote further cross-linking of the polymer, a composite diaphragm coated with a solid electrolyte coating doped with inorganic salt whiskers is obtained. The corresponding preparation process diagram is shown in the attached figure. Figure 1 shown.

[0006] In one aspect, a solid electrolyte composite membrane comprises a membrane substrate and a coating covering the substrate;

[0007] The coating is obtained by coating the electrolyte precursor slurry on the surface of the diaphragm substrate, and drying after UV light-induced cross-linking.

[0008] The electrolyte precursor slurry includes monomer slurry, filler slurry and photoinitiator;

[0009] Furthermore, the solid content of the electrolyte precursor slurry is 30-50%.

[0010] The monomer syrup is obtained by mixing a first monomer including at least one group capable of participating in a photocuring reaction and a second monomer including at least two groups capable of participating in a photocuring reaction in a solvent.

[0011] The solvent is dichloromethane.

[0012] The photoinitiator is one or more of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone.

[0013] The first monomer is one or more of methyl methacrylate, ethyl methacrylate, methyl acrylate, ethyl acrylate, and n-propyl acrylate;

[0014] The second monomer is one or more of 1,6-hexanediol diacrylate, triethylene glycol diacrylate, and tripropylene glycol diacrylate.

[0015] The mass ratio of the first monomer to the second monomer is 3-1:7-9.

[0016] The filler slurry includes activated inorganic salt whiskers and lithium salt;

[0017] 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.

[0018] The activated inorganic salt whiskers are first treated with a borate coupling agent to obtain modified inorganic salt whiskers, and then reacted with a branched compound to obtain;

[0019] 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;

[0020] Preferably, the diameter of the inorganic salt whiskers is 0.01 to 10 μm, and the aspect ratio is 2 to 100;

[0021] Preferably, the inorganic salt whiskers have a diameter of 0.01 to 1 μm and an aspect ratio of 2 to 30.

[0022] The branched compound is one or more of pentaerythritol triacrylate (PET3A), pentaerythritol tetraacrylate (PET4A), and pentaerythritol tetrakis(3-mercaptopropionate) (PETMP).

[0023] The ratio of the borate coupling agent to the inorganic salt whisker is 0.8-1.2:40-60 by mass;

[0024] The amount of the branched compound is 5 to 10% of the modified inorganic salt whisker by mass;

[0025] Specifically, the corresponding preparation steps are as follows: placing a flask containing a 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, washing, and drying to obtain modified inorganic salt whiskers with C=C modifications; then pre-polymerizing the modified inorganic salt whiskers with C=C modifications with a branched compound in a dichloromethane solvent system to impart multiple active sites, thereby obtaining activated inorganic salt whiskers;

[0026] Furthermore, the specific steps of pre-polymerizing the modified inorganic salt whiskers with C=C modification and the branched compound are: placing in a dark place, adding the modified inorganic salt whiskers, the branched compound and the photoinitiator (2% based on the mass of the branched compound) in a dichloromethane solvent system, and then sealing and ultrasonically treating under ultraviolet light for 1 to 5 minutes.

[0027] Further, a lithium salt solution was added to the activated inorganic salt whisker reaction system and ultrasonic treatment was continued for 5 minutes to obtain a filler slurry;

[0028] Preferably, the lithium salt solution is a lithium salt / acetonitrile solution with a solid content of 50%.

[0029] The lithium salt includes one or more of lithium bis(oxalatoborate) (LiBOB), lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethanesulfonylimide) (LiTFSI), and lithium perchlorate (LiClO4);

[0030] Preferably, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), or lithium perchlorate (LiClO4).

[0031] The amount of the lithium salt used is 10-20% of the total amount of polymer monomers.

[0032] The diaphragm substrate is a PE, PP or PET diaphragm with ultra-high porosity and ultra-large pore size, with a porosity of ≥65%, a pore size of >85 nm, and a thickness of 8 to 12 μm;

[0033] Preferably, the pore size of the diaphragm substrate is greater than 100 nm.

[0034] 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.

[0035] Finally, the monomer slurry and the filler slurry are mixed, and a photoinitiator is added to obtain a solid electrolyte precursor slurry; the amount of the photoinitiator is 2 to 6% of the total amount of monomers in the monomer slurry by mass.

[0036] On the other hand, a method for preparing a solid electrolyte composite diaphragm includes the following steps: first, mixing a first monomer and a second monomer in a solvent to obtain a monomer slurry, mixing activated inorganic salt whiskers and lithium salt to obtain a filler slurry, mixing the two slurries and adding a photoinitiator to obtain a solid electrolyte precursor slurry, coating the electrolyte precursor slurry on the surface of the diaphragm substrate, and irradiating the polymer with UV light to further crosslink to obtain a composite diaphragm coated with an inorganic salt-doped solid electrolyte coating. The specific steps are as follows:

[0037] Step 1: Preparation of electrolyte precursor slurry:

[0038] (1) Preparation of monomer slurry

[0039] Under nitrogen protection, using dichloromethane as solvent, add the first monomer and the second monomer in a mass ratio of 3-1:7-9 into a reaction container and stir at room temperature for 10-30 minutes to obtain a uniformly mixed monomer slurry;

[0040] (2) Preparation of filler slurry

[0041] Place in a dark place, add 5-15% of borate coupling agent-modified inorganic salt whiskers, 5-10% of branched compound based on the weight of the modified inorganic salt whiskers, and 2% of photoinitiator based on the weight of the branched compound in a dichloromethane solvent system, then seal and ultrasonicate under ultraviolet light for 1-5 minutes;

[0042] The inorganic salt whisker material is 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;

[0043] The photoinitiator is one or more of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone.

[0044] Finally, a lithium salt / acetonitrile solution containing 10-20% of lithium salt based on the total amount of polymer monomers was added to the activated inorganic salt whisker reaction system and ultrasonic treatment was continued for 5 minutes to obtain a filler slurry;

[0045] Preferably, the lithium salt / acetonitrile solution has a solid content of 50%.

[0046] The borate coupling agent-modified inorganic salt whiskers are prepared by placing a flask containing a coupling agent in an ultrasonic oscillator at a water temperature of 50°C, dissolving the coupling agent in anhydrous ethanol, adding inorganic salt whiskers dried at 120°C for 4 hours, stirring the mixture electrically and ultrasonically oscillating the mixture for 1-2 hours, filtering, washing, and drying the mixture. The ratio of the coupling agent to the inorganic salt whiskers is 0.8-1.2:40-60 by weight, and the amount of anhydrous 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.

[0047] (3) Preparation of electrolyte precursor slurry

[0048] In a dark place, the monomer slurry obtained in step (1) and the filler slurry obtained in step (2) are mixed, the solid content of the slurry is controlled to be 30-50%, and a photoinitiator is added after mixing evenly; the photoinitiator is one or more of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone, and the amount thereof is 2-6% of the total amount of monomers in the monomer slurry.

[0049] Step 2: Preparation of composite diaphragm coated with solid electrolyte coating

[0050] The electrolyte precursor slurry obtained in the above steps is coated on the surface of the diaphragm substrate with a controlled thickness of 3 to 7 μm. The polymer is UV-induced cross-linked and dried to obtain a composite diaphragm coated with a solid electrolyte coating doped with inorganic salt whiskers.

[0051] Preferably, the diaphragm substrate is a PE, PP or PET diaphragm with ultra-high porosity and ultra-large pore size, with a porosity of ≥65% and a pore size of >100 nm.

[0052] The UV light irradiation adopts two sections of UV light source irradiation, wherein the energy of the first section of the light source is 20mW / cm 2 The light curing wavelength is a mercury lamp with a wavelength of 365nm, a machine speed of 2m / min, and a length of 1m. At this time, the polymer is pre-cured, during which small molecular monomers and lithium salts can still further penetrate into the pore structure of the substrate. The energy of the second light source is 25mW / cm 2 The light curing wavelength is a mercury lamp with a 365nm light source, the machine speed is 1.2m / min, and the length is 3m; after completing the UV-induced cross-linking, the composite membrane is placed in a drying oven at 85 °C for 2 to 4 hours to remove the solvent and allow the coating to adhere to the surface of the membrane substrate to obtain a solid electrolyte composite membrane.

[0053] The present invention provides the use of the solid electrolyte composite diaphragm prepared based on the above method in the preparation of liquid batteries;

[0054] The present invention further provides the use of the solid electrolyte composite diaphragm prepared based on the above method in the preparation of solid-state or semi-solid-state batteries;

[0055] The liquid, solid or semi-solid battery is a lithium battery or a lithium ion battery.

[0056] The present invention provides a solid electrolyte composite diaphragm and a preparation method thereof, which have the following beneficial effects:

[0057] (1) The first monomer and the second monomer are used in a ratio, wherein the first monomer is a monofunctional monomer and the second monomer is a multifunctional monomer. The appropriate addition of the monofunctional monomer can significantly reduce the viscosity of the system, improve the fluidity, and facilitate construction; the multifunctional monomer acts as a cross-linking agent, contains multiple polymerizable functional groups, and can promote the cross-linking of the polymer to form a highly cross-linked network structure; in addition, the coating work is completed before the slurry is polymerized. At this time, the monomer molecular weight is small and the slurry has good fluidity, especially under the influence of the solvent, it can enter the pores of the diaphragm, and finally the UV-induced polymerization is completed to further cross-link the polymer, giving the polymer composite material high ionic conductivity and excellent mechanical properties.

[0058] (2) 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 membrane, and the unique aspect ratio structure of the whisker can significantly improve the mechanical strength of the composite material; secondly, the Lewis acid center of the inorganic salt whisker can interact with the lithium salt anion, thereby weakening the Li + The interaction between the lithium salt and the anion promotes 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 cross-linking 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 porous membrane being punctured.

[0059] (3) Based on the co-doping of fibrous inorganic salt whiskers and lithium salts, a solid electrolyte composite membrane with uniform coating is obtained, which has high ionic conductivity and excellent mechanical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 Schematic diagram of the preparation process of a solid electrolyte composite membrane.

[0061] 1——first monomer; 2——second monomer; 3——activated inorganic salt whiskers; 4——lithium salt. DETAILED DESCRIPTION

[0062] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with specific implementation methods.

[0063] In the present invention, unless otherwise specified, all equipment and raw materials can be purchased from the market or are commonly used in the industry. The methods in the following embodiments, unless otherwise specified, are all conventional methods in the art.

[0064] Magnesium borate, aluminum borate, magnesium carbonate trihydrate whiskers: Yingkou Brothers Boron Magnesium Chemical Co., Ltd.

[0065] Magnesium carbonate trihydrate whiskers: purity ≥99%, diameter 0.02-1.0 μm, length 0.2-20.0 μm;

[0066] Magnesium borate whiskers: purity ≥99%, diameter 0.01-1.0 μm, length 0.1-20.0 μm; in addition, magnesium borate whiskers with purity ≥99%, diameter 1.0-2.0 μm, and length 2.0-40.0 μm were selected for comparison;

[0067] Aluminum borate whiskers: purity ≥99%, diameter 0.05-1.0 μm, length 0.5-20.0 μm;

[0068] Preparation of borate coupling agent-modified Mg2B2O5 whiskers: 0.5 g of vinyl borate dibutyl ester coupling agent was added to a 250 mL flask, placed in an ultrasonic oscillator at a water temperature of 50°C, dissolved with 100 mL of anhydrous ethanol, and then 25 g of magnesium borate whiskers dried at 120°C for 4 h were added. The mixture was stirred electrically and ultrasonically for 1 h. Subsequently, it was filtered, washed, and dried at 90°C for 6 h to obtain the modified magnesium borate material. The amount of anhydrous ethanol used was 3 to 5 times that of the Mg2B2O5 whiskers.

[0069] Aluminum borate and magnesium carbonate trihydrate were modified in the same manner as above for comparison.

[0070] Lithium salt (LiTFSI): Shanghai McLean Biochemical Technology Co., Ltd.

[0071] PE membrane, Hefei New Energy Materials Co., Ltd., porosity ≥ 65%, pore size > 100 nm.

[0072] Methyl methacrylate and triethylene glycol diacrylate were of analytical grade and were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd.

[0073] Example 1

[0074] A solid electrolyte composite diaphragm comprises: first, mixing a first monomer and a second monomer in a solvent to obtain a monomer slurry; then, mixing activated Mg2B2O5 whiskers and a lithium salt to obtain a filler slurry; and finally, mixing the two slurries and adding a photoinitiator to obtain a solid electrolyte precursor slurry. The electrolyte precursor slurry is coated on the surface of a diaphragm substrate, and the polymer is further cross-linked by UV irradiation and dried to obtain a composite diaphragm coated with a Mg2B2O5-doped solid electrolyte coating. The specific preparation steps are as follows:

[0075] Step 1: Preparation of electrolyte precursor slurry:

[0076] (1) Preparation of monomer slurry

[0077] Under nitrogen protection, using dichloromethane as solvent, methyl methacrylate and triethylene glycol diacrylate in a mass ratio of 3:7, i.e., 30 g of methyl methacrylate and 70 g of triethylene glycol diacrylate, were added into a reaction vessel and stirred at room temperature for 10 to 30 minutes to obtain a uniformly mixed monomer slurry;

[0078] (2) Preparation of filler slurry

[0079] In the dark, 10% (10 g) of Mg2B2O5 whiskers modified with a borate coupling agent, 7.5% (0.75 g) of PETMP, and 2% (0.015 g) of 2,2-dimethoxy-2-phenylacetophenone were added to a dichloromethane solvent system, and then sealed and sonicated under UV light with a light source energy of 25 mW for 3 minutes;

[0080] Subsequently, a lithium salt / acetonitrile solution formed by 15% (15 g) of LiTFSI was added to the above-mentioned activated Mg2B2O5 whisker reaction system, and ultrasonic treatment was continued for 5 minutes to obtain a filler slurry; the solid content of the lithium salt / acetonitrile solution was 50%;

[0081] (3) Preparation of solid electrolyte precursor slurry

[0082] In a dark place, the monomer slurry obtained in step (1) and the filler slurry obtained in step (2) were mixed, and the solid content of the slurry was controlled to be 40%±. After mixing evenly, 3 g of 2,2-dimethoxy-2-phenylacetophenone was added and ultrasonic treatment was continued until the mixture was uniform.

[0083] Step 2: Preparation of composite diaphragm coated with solid electrolyte coating

[0084] The solid electrolyte precursor slurry was coated on one side of the diaphragm substrate with a thickness of 5 μm and irradiated with UV light, where the energy of the first light source was 20 mW / cm 2 The light curing wavelength is a mercury lamp with a wavelength of 365nm, a machine speed of 2m / min, and a length of 1m; the energy of the second light source is 25mW / cm 2 , the light curing wavelength is a mercury lamp with a light source of 365nm, the machine speed is 1.2m / min, and the length is 3m; after the completion of UV-induced cross-linking, the composite membrane is placed in a drying oven at 85°C for 2 to 4 hours to remove the solvent;

[0085] The other side of the substrate is coated according to the above operation to obtain a solid electrolyte composite diaphragm.

[0086] Example 2

[0087] The mass ratio of methyl methacrylate to triethylene glycol diacrylate in step (1) of Example 1 was adjusted to 2:8, and the remaining steps remained unchanged.

[0088] Example 3

[0089] The mass ratio of methyl methacrylate to triethylene glycol diacrylate in step (1) of Example 1 was adjusted to 1:9, and the remaining steps remained unchanged.

[0090] Example 4

[0091] The amount of LiTFSI in step (2) of Example 2 was adjusted to 10%, and the remaining steps remained unchanged.

[0092] Example 5

[0093] The amount of LiTFSI in step (2) of Example 2 was adjusted to 20%, and the remaining steps remained unchanged.

[0094] Example 6

[0095] The amount of modified magnesium borate whiskers in step (2) of Example 2 was adjusted to 5%, and the other steps remained unchanged.

[0096] Example 7

[0097] The amount of modified magnesium borate whiskers in step (2) of Example 2 was adjusted to 15%, and the other steps remained unchanged.

[0098] Example 8

[0099] Step (2) of step 1 in Example 2 was adjusted to modify aluminum borate whiskers, and the other steps remained unchanged.

[0100] Example 9

[0101] The modified magnesium carbonate trihydrate whiskers were used in step (2) of step 1 of Example 2, and the other steps remained unchanged.

[0102] Comparative Example 1

[0103] The mass ratio of methyl methacrylate to triethylene glycol diacrylate in step (1) of Example 1 was adjusted to 0:10, and the remaining steps remained unchanged.

[0104] Comparative Example 2

[0105] The modified magnesium borate in step (2) of step 1 of Example 2 was adjusted to not undergo activation treatment, i.e., the amount of PETMP used was 0 g, and the remaining steps remained unchanged.

[0106] Comparative Example 3

[0107] The adjustment in step (2) of Example 2 is to use unmodified magnesium borate, i.e., Mg2B2O5 whiskers without any treatment, and the other steps remain unchanged.

[0108] Comparative Example 4

[0109] In step 1 (2), no modified magnesium borate is added, i.e., 0 g of Mg2B2O5 whiskers modified by borate coupling agent is used, and the remaining steps are consistent with those in Example 2.

[0110] Comparative Example 5

[0111] 3 g of 2,2-dimethoxy-2-phenylacetophenone was added to the monomer slurry (1) in step 1, and the mixture was irradiated with UV light of 25 mW in the dark and ultrasonically treated for 5 minutes until the mixture was uniform. In step 3, 2,2-dimethoxy-2-phenylacetophenone was not added, and the remaining steps were consistent with Example 2.

[0112] Comparative Example 6

[0113] The amount of LiTFSI in step (2) of Example 2 was adjusted to 0%, and the remaining steps remained unchanged.

[0114] Comparative Example 7

[0115] The inorganic salt whiskers in step 1 (2) of Example 2 were adjusted to borate coupling agent-modified magnesium borate whiskers with a diameter of 1.0 to 2.0 μm and a length of 2.0 to 40.0 μm, and the other steps remained unchanged.

[0116] Comparative Example 8

[0117] PE diaphragm without any coating treatment.

[0118] The diaphragms prepared in Examples 1 to 9 and Comparative Examples 1 to 8 were cut into A4 size sheets and tested for various properties. The test items are as follows:

[0119] (1) Tensile strength & elongation at break: According to GB / T 36363-2018, the longitudinal and transverse tensile strength and elongation at break of the diaphragm were tested using a Xieqiang CTM universal testing machine. Five samples were tested in each direction and the average value was calculated.

[0120] (2) Puncture strength: According to GB / T 36363-2018, the puncture strength of the diaphragm was tested using a Xieqiang CTM universal testing machine. Five samples were tested and the average value was calculated.

[0121] (3) Ionic conductivity: The ionic conductivity of each composite membrane was tested with reference to the relevant ionic conductivity test method in GB / T 36363-2018;

[0122] (4) Peel strength: The test was conducted according to the method in the national standard "GB / T 2792-2014 Peel strength of adhesive tapes", and the instrument used was the Xieqiang CTM universal material testing machine.

[0123] The test results of the samples of Examples 1 to 9 and Comparative Examples 1 to 8 are shown in Table 1.

[0124] Table 1 Test results of samples of Examples 1 to 9 and Comparative Examples 1 to 8

[0125]

[0126] From the comparison of the data of Examples 1 to 9 and Comparative Example 8 in Table 1, it can be found that the solid electrolyte composite diaphragm modified by the activated magnesium borate whiskers, aluminum borate whiskers and magnesium carbonate whiskers doped coating of the present invention has high ionic conductivity and better mechanical properties.

[0127] Among them, Examples 1 to 3 and Comparative Examples 1 and 5 are based on the control of different ratios of polymerizable monomers and the comparative investigation of whether UV polymerization is completed before coating or after coating. From the relevant data, it can be seen that the addition of a certain proportion of monofunctional monomers can, on the one hand, avoid the problems of excessively long polyfunctional monomer polymerization chains and excessive brittleness of the composite material. It gives the composite separator good flexibility and elongation at break, ensuring that the separator is not easily broken during battery charging and discharging, making the separator easier to handle during processing such as winding and lamination. On the other hand, the polyfunctional monomer acts as a crosslinking agent, containing two polymerizable functional groups, which promotes polymer crosslinking. After the subsequent UV-induced polymerization, a highly crosslinked network structure is formed, which improves the mechanical properties of the composite material and enhances the puncture and coating peel strength. Completing the coating work before monomer polymerization at this time has a low molecular weight, low viscosity, high fluidity, and is easy to apply. In addition, some monomers and fillers can better penetrate into the pores of the substrate, and the final completion of UV-induced polymerization allows the coating to adhere firmly to the substrate (the coating peel strength is better), and the electrolyte material enters the substrate to improve the overall conductivity of the separator.

[0128] Comparison of the data of Example 2, Example 8, and Example 9 with Comparative Examples 2 to 4 shows that the addition of activated Mg2B2O5 whiskers can improve ionic conductivity, which is more significant than that of aluminum borate and magnesium carbonate. At the same time, after the activation treatment, the Mg2B2O5 whiskers are more beneficial to the improvement of ionic conductivity, which means that a part of the polymer is cross-linked with the Mg2B2O5 whiskers, and the interaction between the polymer phase and the inorganic phase can better play the role of promoting the dissociation of lithium salts, fixing anionic groups and transmitting 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 a path for the transmission of lithium ions. Therefore, when compared with unactivated or unmodified Mg2B2O5 whiskers, the Li + The increase in migration number and ion conductivity may be due to the further expansion of ion channels.

[0129] In addition, by comparing the data of Example 2 with Examples 4 to 7 and Comparative Examples 5, 6, and 7, it was found that the addition of a certain amount of activated Mg2B2O5 whiskers and lithium salts significantly improved the ionic conductivity. At the same time, the introduction of fibrous whisker materials significantly helped to improve the overall mechanical strength of the material. This may be because the doping of whisker materials with a certain aspect ratio structure in the polymer system enables them to be evenly and orderly combined with the coating, thereby improving its tensile strength and puncture strength and other properties.

[0130] In summary, the solid electrolyte composite membrane disclosed in the present invention has relatively excellent mechanical strength and ion conductivity.

Claims

1. A solid electrolyte composite membrane comprising a membrane substrate and a coating covering the surface of the substrate, wherein the coating is obtained by coating an electrolyte precursor slurry onto the surface of the membrane substrate, undergoing UV light-induced crosslinking, and drying, characterized in that: The electrolyte precursor slurry includes a monomer slurry, a filler slurry and a photoinitiator; the monomer slurry is a first monomer including at least one photocurable reaction group and a second monomer including at least two photocurable reaction groups; the filler slurry includes activated inorganic salt whiskers and lithium salt; the activated inorganic salt whiskers are modified inorganic salt whiskers obtained by first treating with a borate coupling agent and then reacting with a branched compound for activation; the branched compound is one or more of pentaerythritol triacrylate, pentaerythritol tetraacrylate and pentaerythritol tetra(3-mercaptopropionic acid); the first monomer is methyl acrylate One or more of methyl acrylate, 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 used in a mass ratio of 3 to 1:7 to 9; the photoinitiator is one or more of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexyl phenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone.

2. A solid electrolyte composite membrane according to claim 1, 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.

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

4. A solid electrolyte composite diaphragm according to claim 3, 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.

5. A solid electrolyte composite membrane according to claim 4, 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.

6. A solid electrolyte composite membrane according to claim 5, 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, PP, or PET diaphragm with a porosity of ≥65% and a pore size of >85 nm.

7. The method for preparing a solid electrolyte composite membrane according to any one of claims 1 to 6, 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, add the first monomer and the second monomer in a mass ratio of 3-1:7-9 into a reaction vessel and stir 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 based on the total amount of polymer monomers, 5-10% of branched compound based on the weight of modified inorganic salt whiskers, and 2% of photoinitiator based on the weight of branched compound in a dichloromethane solvent system, then seal and ultrasonicate under ultraviolet light for 1-5 minutes; Finally, a lithium salt / acetonitrile solution containing 10-20% of lithium salt based on the total amount of polymer monomers is added to 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, the monomer slurry obtained in step (1) and the filler slurry obtained in step (2) are mixed, and the solid content of the slurry is controlled to be 30-50%. After mixing, 2-6% of a photoinitiator based on the total amount of monomers is added; The photoinitiator in step (2) or (3) of step 1 is one or more of 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, and 2,2-dimethoxy-2-phenylacetophenone; Step 2: Preparation of a composite diaphragm coated with a 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 cross-linking and dried to obtain a composite diaphragm coated with an inorganic salt-doped solid electrolyte coating.

8. The method for preparing a solid electrolyte composite membrane according to claim 7, 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 with 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 1-2 hours, filtering it, washing it, and drying it to obtain the result; wherein, by weight, the amount of the coupling agent to the inorganic salt whiskers is 0.8-1.2:40-60; the amount of anhydrous 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.

9. The method for preparing a solid electrolyte composite membrane according to claim 8, 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 20mW / cm 2 The light curing wavelength is a mercury lamp with a wavelength of 365nm, a machine speed of 2m / min, and a length of 1m; the energy of the second light source is 25mW / cm 2 The light curing wavelength is a mercury lamp with a light source of 365nm, the machine speed is 1.2m / min, and the length is 3m; after completing the UV-induced cross-linking, the composite membrane is placed in a drying oven at 85°C for 2 to 4 hours to remove the solvent and allow the coating to adhere to the surface of the membrane substrate to obtain a solid electrolyte composite membrane.

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