Composite solid electrolyte, preparation method thereof and battery

Abstract

The invention provides a composite solid electrolyte, a preparation method thereof and a battery, the composite solid electrolyte comprises a lithium salt, polyformaldehyde, a plasticizer and an inorganic filler, and the mass ratio of the plasticizer to the polyformaldehyde is 1: 50-1: 4. When the plasticizer accounts for a relatively small amount, crystallization of polyformaldehyde cannot be effectively inhibited, and the ionic conductivity of the composite solid electrolyte is relatively low; and when the plasticizer accounts for a large amount, the mechanical property of the electrolyte is poor. Therefore, the ionic conductivity of the polyformaldehyde-based electrolyte can be improved by a proper amount of plasticizer, and meanwhile, the electrolyte keeps good mechanical properties. The room-temperature ionic conductivity of the polyformaldehyde-based composite solid electrolyte provided by the invention can reach 1.43 mS / cm.

Description

Technical Field

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

[0002] All-solid-state lithium batteries have a long history of research and development. In recent years, new inorganic solid electrolytes with high ionic conductivity are being developed. For example, Li 6.75 La3Zr 1.75 Ta 0.25 O 12 , Li 3.25 Ge 0.25 P 0.75 S4, Li 10 GeP2S 12 showed up to 8.7 × 10 -4 S / cm, 2.2 × 10 -4 S / cm, 1.2 × 10 -2 S / cm of room temperature ionic conductivity. However, the high mechanical strength of inorganic solid electrolytes makes it easy to have hard contact with the lithium metal negative electrode, resulting in a large contact resistance. The researchers then changed their direction and looked for solid electrolytes with closer interface contact with the lithium metal negative electrode. A series of polymer-based solid electrolytes have been developed and applied. Polymers are light, flexible, and have low interface contact impedance with electrodes, which can meet the use requirements of high energy density batteries. However, at room temperature, the ionic conductivity and ion migration number of polymers are very low, which easily leads to the aggregation and polarization of lithium ions, forming lithium dendrites, and easily piercing the polymer electrolyte with low mechanical strength, ultimately leading to battery short circuit failure. In addition, the voltage window of polymer solid electrolytes is generally low, which limits the improvement of battery energy density.

[0003] At this time, researchers have turned to combining the advantages of inorganic solid electrolytes and polymer electrolytes, and have developed a series of organic / inorganic composite solid electrolytes, such as PEO / LLZTO, PEC / LLZTO, and PEG / LATP. Composite solid electrolytes offer the advantages of a wide electrochemical stability window, high ionic conductivity, high mechanical strength, and a good electrode interface, effectively overcoming the disadvantages of single-component solid electrolytes. Therefore, the development of composite solid electrolytes has become a hot topic in future solid electrolyte research.

[0004] Currently, the polymer matrix in composite solid-state electrolytes still suffers from low room-temperature ionic conductivity, which limits the improvement of the ionic conductivity of composite solid-state electrolytes and hinders their large-scale application in the energy storage industry. Therefore, finding a suitable polymer matrix to improve the room-temperature ionic conductivity of composite solid-state electrolytes is an urgent problem to be solved. Summary of the Invention

[0005] The present invention provides a composite solid electrolyte, a preparation method thereof, and a battery, for improving the room temperature ionic conductivity of the composite solid electrolyte.

[0006] In a first aspect, the present application provides a composite solid electrolyte, comprising: a lithium salt, polyformaldehyde, a plasticizer, and an inorganic filler, wherein the mass ratio of the plasticizer to the polyformaldehyde is 1:50 to 1:4.

[0007] Furthermore, the stoichiometric ratio of lithium ions in the lithium salt to oxygen atoms in the polyoxymethylene is 1:30 to 1:6.

[0008] Furthermore, the plasticizer includes one or more of propylene carbonate, succinonitrile and triethylene glycol dimethyl ether.

[0009] Furthermore, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium hexafluorophosphate and lithium perchlorate.

[0010] Furthermore, the inorganic filler includes one or more of lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium titanate, lithium lanthanum titanate, lithium lanthanum titanate, lithium titanium phosphate, lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium germanium phosphosulfur, lithium phosphosulfur chloride, lithium aluminum gallium phosphate, lithium aluminum titanium phosphate, aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, zinc oxide, nickel oxide, silicon nitride, magnesium hydroxide, diatomaceous earth, zeolite, montmorillonite and kaolin.

[0011] Furthermore, the mass ratio of the inorganic filler to the polyoxymethylene is 1:10 to 1:30.

[0012] In a second aspect, the present application provides a method for preparing a composite solid electrolyte, the method being used to prepare the composite solid electrolyte according to any one of the first aspects, the method comprising the following steps:

[0013] In an inert gas atmosphere, a lithium salt, polyoxymethylene, a plasticizer, an inorganic filler, and an organic solvent are mixed, wherein the mass ratio of the plasticizer to the polyoxymethylene is 1:50 to 1:4;

[0014] The mixed liquid is poured into a mold with a polytetrafluoroethylene substrate and vacuum dried to prepare a composite solid electrolyte.

[0015] Furthermore, the organic solvent includes one or more of N-methylpyrrolidone, tetrahydrofuran, dichloromethane, acetone and dimethylformamide.

[0016] Furthermore, the mass ratio of the organic solvent to polyoxymethylene is 5:1 to 150:1.

[0017] In a third aspect, the present application provides a battery, comprising the composite solid electrolyte described in any one of the first aspects, or the composite solid electrolyte prepared by the preparation method described in any one of the second aspects.

[0018] The present application provides a composite solid electrolyte, a preparation method, and a battery. The composite solid electrolyte comprises a lithium salt, polyoxymethylene, a plasticizer, and an inorganic filler, wherein the mass ratio of the plasticizer to the polyoxymethylene is 1:50 to 1:4. The mass ratio of the plasticizer to the polyoxymethylene can affect the crystallization of the polymer. When the plasticizer content is low, the crystallization of the polyoxymethylene cannot be effectively inhibited, resulting in poor electrolyte ionic conductivity. When the plasticizer content is high, the electrolyte mechanical properties are insufficient. Therefore, an appropriate amount of plasticizer can improve the ionic conductivity of the polyoxymethylene-based electrolyte (the ionic conductivity can reach 1.43 mS / cm) while maintaining good mechanical properties. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0020] In order to solve the problem of low room temperature ionic conductivity of the polymer matrix in composite solid electrolytes, this application provides a composite solid electrolyte with polyoxymethylene as the polymer matrix. By mixing lithium salt, polyoxymethylene, plasticizer, inorganic filler, and organic solvent in a certain proportion, heating, stirring, and drying the organic solvent, a composite solid electrolyte with a conductivity of up to 1.43 mS cm -1 The ionic conductivity can be used in the preparation of secondary batteries and energy storage functional devices.

[0021] Based on this, the first aspect of the present invention provides a composite solid electrolyte, lithium salt, polyformaldehyde, plasticizer and inorganic filler, the mass ratio of plasticizer to polyformaldehyde is 1:50 to 1:4.

[0022] Exemplarily, the mass ratio of plasticizer to polyoxymethylene is 1:50, 1:45, 1:40, 1:35, 1:30, 1:25, 1:20, 1:10, 1:4, or a range consisting of any two of the above ratios.

[0023] When the plasticizer-to-POM ratio is low, the crystallization of POM cannot be effectively suppressed, resulting in low electrolyte ionic conductivity. However, when the plasticizer ratio is high, the electrolyte mechanical properties are poor. A plasticizer ratio between 1:50 and 1:4 can inhibit POM crystallization while maintaining good mechanical properties.

[0024] In some embodiments, the stoichiometric ratio of lithium ions in the lithium salt to oxygen atoms in the polyoxymethylene is 1:30 to 1:6, for example, 1:30, 1:15, 1:20, 1:15, 1:10, 1:6, or a range consisting of any two of the above ratios.

[0025] In some embodiments, the plasticizer includes one or more of propylene carbonate, succinonitrile, and triglyme.

[0026] In some embodiments, the lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium hexafluorophosphate (LiPF6), and lithium perchlorate (LiClO4).

[0027] In some embodiments, the inorganic filler includes one or more of lithium lanthanum zirconium oxide (LLZO), lithium lanthanum zirconium tantalum oxide (LLZTO), lithium lanthanum zirconium titanate, lithium lanthanum titanate, lithium lanthanum titanate, lithium titanium phosphate, lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium germanium phosphosulfur, lithium phosphosulfur chloride (LPSCl), lithium aluminum gallium phosphate, lithium aluminum titanium phosphate, aluminum oxide (Al2O3), silicon dioxide (SiO2), titanium dioxide, zirconium oxide, zinc oxide, nickel oxide, silicon nitride, magnesium hydroxide, diatomaceous earth, zeolite, montmorillonite, and kaolin.

[0028] In some embodiments, the mass ratio of the inorganic filler to the polyoxymethylene is 1:10 to 1:30, for example, 1:10, 1:15, 1:20, 1:25, 1:30, or a range consisting of any two of the above ratios.

[0029] A second aspect of the present application provides a method for preparing a composite solid electrolyte, which is used to prepare any composite solid electrolyte according to the first aspect, and comprises the following steps:

[0030] Under an inert gas atmosphere, lithium salt, polyoxymethylene, plasticizer, inorganic filler and organic solvent are mixed, and the mass ratio of plasticizer to polyoxymethylene is 1:50 to 1:4.

[0031] The mixed liquid is poured into a mold with a polytetrafluoroethylene substrate and vacuum dried to prepare a composite solid electrolyte.

[0032] In some embodiments, the organic solvent includes one or more of N-methylpyrrolidone, tetrahydrofuran, dichloromethane, acetone, and dimethylformamide.

[0033] In some embodiments, the mass ratio of the organic solvent to the polyoxymethylene is 5:1 to 150:1. For example, 5:1, 25:1, 45:1, 65:1, 85:1, 105:1, 125:1, 150:1, or a range consisting of any two of the above ratios.

[0034] In addition to the above preparation method, various raw materials can also be mixed, ball-milled and hot-pressed to prepare a composite solid electrolyte membrane.

[0035] The present application also provides a battery prepared using any of the above composite solid electrolytes, or a battery prepared using a composite solid electrolyte prepared using the above preparation method. The method for preparing a battery using a composite solid electrolyte is the same as the conventional method and will not be repeated here.

[0036] The present invention is further described below through specific examples.

[0037] Example 1-1

[0038] Polyoxymethylene (POM) 100P was dried in a vacuum oven at 80°C for 48 h. LiTFSI (Aladdin, 99.9%) was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days. LLZTO (room temperature ionic conductivity 0.6 mS / cm) and SN (Aladdin, 99%) were stored in an argon-filled glove box. 0.418 g of POM 100P, 0.400 g of LiTFSI, 0.021 g of LLZTO, 0.021 g of SN, and 4.18 g of NMP (Aladdin, 99.9%) were placed in a screw-cap bottle and magnetically stirred at 120°C at 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in vacuum at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was tested by AC impedance measurement using a stainless steel disc as a blocking electrode at a test frequency of 8 MHz to 1 Hz. According to σ = L / R·S, the ionic conductivity of the composite membrane was 1.0 mS cm -1 The mechanical strength of the electrolyte composite membrane was tested using a tensile tester. When the deformation of the electrolyte membrane reached 0.2%, the yield strength of the electrolyte membrane was read. The yield strength of the electrolyte membrane obtained in this example was 2.5 MPa.

[0039] Example 1-2

[0040] POM 100P was dried in a vacuum oven at 80°C for 48 h. LiDFOB (Aladdin, 99%) was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days. LLZTO and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.200 g LiDFOB, 0.021 g LLZTO, 0.021 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. AC impedance spectroscopy (ECI) measurements were performed using a stainless steel disc as a blocking electrode at frequencies between 8 MHz and 1 Hz. The ionic conductivity of the composite membrane was 0.97 mS cm-1, calculated using the equation σ = L / R·S. -1 .

[0041] Examples 1-3

[0042] POM 100P was dried in a vacuum oven at 80°C for 48 h. LiFSI (Aladdin, 98%) was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days. LLZTO and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.261 g LiFSI, 0.021 g LLZTO, 0.021 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. AC impedance spectroscopy (ECI) was performed on the electrolyte composite membrane using a stainless steel disc as a blocking electrode at a frequency of 8 MHz to 1 Hz. The ionic conductivity of the composite membrane was 0.56 mS cm-1, calculated using the equation σ = L / R·S. -1 .

[0043] Comparative Example 1-1

[0044] POM 100P was dried in a vacuum oven at 80°C for 48 h. Li₂CO₃ (Aladdin, 99%) was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days. LLZTO and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.052 g Li₂CO₃, 0.021 g LLZTO, 0.021 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in vacuum at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. AC impedance spectroscopy (ECI) was performed on the electrolyte composite membrane using a stainless steel disc as a blocking electrode at a frequency of 8 MHz to 1 Hz. The ionic conductivity of the composite membrane was 0.005 mS cm-1, calculated using the equation σ = L / R·S. -1 .

[0045] Example 2-1

[0046] POM 100P was dried in a vacuum oven at 80°C for 48 h; LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days; LLZTO and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.667 g LiTFSI, 0.021 g LLZTO, 0.021 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. AC impedance spectroscopy (ECI) measurements were performed using a stainless steel disc as a blocking electrode at frequencies between 8 MHz and 1 Hz. The ionic conductivity of the composite membrane was 0.79 mS cm-1, calculated using the equation σ = L / R·S. -1 .

[0047] Example 2-2

[0048] POM 100P was dried in a vacuum oven at 80°C for 48 h; LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days; LLZTO and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.267 g LiTFSI, 0.021 g LLZTO, 0.021 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. AC impedance spectroscopy (ECI) measurements were performed using a stainless steel disc as a blocking electrode at frequencies between 8 MHz and 1 Hz. The ionic conductivity of the composite membrane was 0.77 mS cm-1, calculated using the equation σ = L / R·S. -1 .

[0049] Example 2-3

[0050] POM 100P was dried in a vacuum oven at 80°C for 48 h; LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days; LLZTO and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.133 g LiTFSI, 0.021 g LLZTO, 0.021 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. AC impedance spectroscopy (ECI) measurements were performed using a stainless steel disc as a blocking electrode at frequencies between 8 MHz and 1 Hz. The ionic conductivity of the composite membrane was 0.44 mS cm-1, calculated using the equation σ = L / R·S. -1 .

[0051] Comparative Example 2-1

[0052] POM 100P was dried in a vacuum oven at 80°C for 48 h; LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days; LLZTO and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 2.000 g LiTFSI, 0.021 g LLZTO, 0.021 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. AC impedance spectroscopy (ECI) measurements were performed using a stainless steel disc as a blocking electrode at frequencies between 8 MHz and 1 Hz. The ionic conductivity of the composite membrane was 0.01 mS cm-1, as calculated using the equation σ = L / R·S. -1 .

[0053] Comparative Example 2-2

[0054] POM 100P was dried in a vacuum oven at 80°C for 48 h; LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days; LLZTO and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.080 g LiTFSI, 0.021 g LLZTO, 0.021 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance measurements using stainless steel discs as blocking electrodes at frequencies of 8 MHz to 1 Hz. According to σ = L / R·S, the ionic conductivity of the composite membrane is 0.08 mS cm -1 .

[0055] Example 3-1

[0056] POM 100P was dried in a vacuum oven at 80°C for 48 h. LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days. LLZTO and propylene carbonate (Aladdin, 99%) were stored in an argon-filled glove box. 0.418 g POM 100P, 0.400 g LiTFSI, 0.021 g LLZTO, 0.021 g propylene carbonate, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance measurements using a stainless steel disc as a blocking electrode at a frequency of 8 MHz to 1 Hz. According to σ = L / R·S, the ionic conductivity of the composite membrane is 0.83 mS cm -1 .

[0057] Example 3-2

[0058] POM 100P was dried in a vacuum oven at 80°C for 48 h. LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days. LLZTO and triglyme (Aladdin, 99%) were stored in an argon-filled glove box. 0.418 g POM 100P, 0.400 g LiTFSI, 0.021 g LLZTO, 0.021 g triglyme, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance measurements using a stainless steel disc as a blocking electrode at a frequency of 8 MHz to 1 Hz. According to σ = L / R·S, the ionic conductivity of the composite membrane is 0.8 mS cm -1 .

[0059] Comparative Example 3-1

[0060] POM 100P was dried in a vacuum oven at 80°C for 48 h. LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days. LLZTO and dioxolane (Aladdin, 99%) were stored in an argon-filled glove box. 0.418 g of POM 100P, 0.400 g of LiTFSI, 0.021 g of LLZTO, 0.021 g of dioxolane, and 4.18 g of NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance measurements using a stainless steel disc as a blocking electrode at a frequency of 8 MHz to 1 Hz. According to σ = L / R·S, the ionic conductivity of the composite membrane is 0.12 mS cm -1 .

[0061] Comparative Example 3-2

[0062] POM 100P was dried in a vacuum oven at 80°C for 48 h. LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days. LLZTO and dimethyl carbonate (Aladdin, 99%) were stored in an argon-filled glove box. 0.418 g POM 100P, 0.400 g LiTFSI, 0.021 g LLZTO, 0.021 g dimethyl carbonate, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance measurements using a stainless steel disc as a blocking electrode at a frequency of 8 MHz to 1 Hz. According to σ = L / R·S, the ionic conductivity of the composite membrane is 0.12 mS cm -1 .

[0063] Example 4-1

[0064] POM 100P was dried in a vacuum oven at 80°C for 48 h; LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days; LLZTO and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.400 g LiTFSI, 0.021 g LLZTO, 0.104 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance measurements using stainless steel discs as blocking electrodes at frequencies of 8 MHz to 1 Hz. According to σ = L / R·S, the ionic conductivity of the composite membrane is 1.43 mS cm -1 The mechanical strength of the electrolyte composite membrane was tested using a tensile tester. When the deformation of the electrolyte membrane reached 0.2%, the yield strength of the electrolyte membrane was read. The yield strength of the electrolyte membrane obtained in this example was 1.5 MPa.

[0065] Example 4-2

[0066] POM 100P was dried in a vacuum oven at 80°C for 48 h; LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days; LLZTO and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.400 g LiTFSI, 0.021 g LLZTO, 0.028 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance measurements using stainless steel discs as blocking electrodes at frequencies of 8 MHz to 1 Hz. According to σ = L / R·S, the ionic conductivity of the composite membrane is 1.21 mS cm -1 The mechanical strength of the electrolyte composite membrane was tested using a tensile tester. When the deformation of the electrolyte membrane reached 0.2%, the yield strength of the electrolyte membrane was read. The yield strength of the electrolyte membrane obtained in this example was 1.8 MPa.

[0067] Example 4-3

[0068] POM 100P was dried in a vacuum oven at 80°C for 48 h; LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days; LLZTO and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.400 g LiTFSI, 0.021 g LLZTO, 0.008 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance measurements using stainless steel discs as blocking electrodes at frequencies of 8 MHz to 1 Hz. According to σ = L / R·S, the ionic conductivity of the composite membrane is 0.48 mS cm -1 The mechanical strength of the electrolyte composite membrane was tested using a tensile tester. When the deformation of the electrolyte membrane reached 0.2 wt%, the yield strength of the electrolyte membrane was read. The yield strength of the electrolyte membrane obtained in this example was 2.8 MPa.

[0069] Comparative Example 4-1

[0070] POM 100P was dried in a vacuum oven at 80°C for 48 h; LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days; LLZTO and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.400 g LiTFSI, 0.021 g LLZTO, 0.418 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance measurements using stainless steel discs as blocking electrodes at frequencies of 8 MHz to 1 Hz. According to σ = L / R·S, the ionic conductivity of the composite membrane is 1.46 mS cm -1 The mechanical strength of the electrolyte composite membrane was tested using a tensile tester. When the deformation of the electrolyte membrane reached 0.2%, the yield strength of the electrolyte membrane was read. The yield strength of the electrolyte membrane obtained in this example was 0.1 MPa.

[0071] Comparative Example 4-2

[0072] POM 100P was dried in a vacuum oven at 80°C for 48 h; LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days; LLZTO and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.400 g LiTFSI, 0.021 g LLZTO, 0.004 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance measurements using stainless steel discs as blocking electrodes at frequencies of 8 MHz to 1 Hz. According to σ = L / R·S, the ionic conductivity of the composite membrane is 0.02 mS cm -1 The mechanical strength of the electrolyte composite membrane was tested using a tensile tester. When the deformation of the electrolyte membrane reached 0.2%, the yield strength of the electrolyte membrane was read. The yield strength of the electrolyte membrane obtained in this example was 2.8 MPa.

[0073] Example 5-1

[0074] POM 100P was dried in a vacuum oven at 80°C for 48 h. LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days. SiO2 (Aladdin, 99.9%) and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.400 g LiTFSI, 0.021 g SiO2, 0.021 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance measurements using stainless steel discs as blocking electrodes at frequencies of 8 MHz to 1 Hz. According to σ = L / R·S, the ionic conductivity of the composite membrane is 0.46 mS cm -1 .

[0075] Example 5-2

[0076] POM 100P was dried in a vacuum oven at 80°C for 48 h. LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days. Al₂O₃ (Aladdin, 99.9%) and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.400 g LiTFSI, 0.021 g Al₂O₃, 0.021 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance measurements using stainless steel discs as blocking electrodes at frequencies of 8 MHz to 1 Hz. According to σ = L / R·S, the ionic conductivity of the composite membrane is 0.47 mS cm -1 .

[0077] Example 5-3

[0078] POM 100P was dried in a vacuum oven at 80°C for 48 h. LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days. LLZO (room temperature ionic conductivity 0.5 mS / cm) and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.400 g LiTFSI, 0.021 g LLZO, 0.021 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance measurements using a stainless steel disc as a blocking electrode at a frequency of 8 MHz to 1 Hz. According to σ = L / R·S, the ionic conductivity of the composite membrane is 0.83 mScm -1 .

[0079] Example 5-4

[0080] POM 100P was dried in a vacuum oven at 80°C for 48 h. LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days. LPSCl (room temperature ionic conductivity 5 mS / cm) and SN were stored in an argon-filled glove box. 0.418 g POM 100P, 0.400 g LiTFSI, 0.021 g LPSCl, 0.021 g SN, and 4.18 g NMP were placed in a screw-cap bottle and magnetically stirred at 120°C and 300 rpm for 2.4 h. The mixture was then poured into a polytetrafluoroethylene-lined mold and dried in a vacuum oven at 80°C for 48 h to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance measurements using stainless steel discs as blocking electrodes at frequencies of 8 MHz to 1 Hz. According to σ = L / R·S, the ionic conductivity of the composite membrane is 0.87 mS cm -1 .

[0081] Example 6-1

[0082] POM 100P was dried in a vacuum oven at 80°C for 48 h; LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days; LLZTO and SN were stored in an argon-filled glove box. 0.418 g of POM 100P, 0.400 g of LiTFSI, and 0.021 g of LLZTO were ball-milled at 400 rpm for 2 h at a ball-to-material ratio of 10:1. 0.021 g of SN was added and hot-pressed at 120°C to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance spectroscopy (ACIS) measurements using a stainless steel disc as a blocking electrode at a frequency of 8 MHz to 1 Hz. The ionic conductivity of the composite membrane was 0.87 mS cm-1, calculated using the equation σ = L / R·S. -1 .

[0083] Example 6-2

[0084] POM 100P was dried in a vacuum oven at 80°C for 48 h; LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days; LLZTO and SN were stored in an argon-filled glove box. 0.418 g of POM 100P, 0.400 g of LiTFSI, and 0.042 g of LLZTO were ball-milled at 400 rpm for 2 h at a ball-to-material ratio of 10:1. 0.021 g of SN was added and hot-pressed at 120°C to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance spectroscopy (ACIS) measurements using a stainless steel disc as a blocking electrode at a frequency of 8 MHz to 1 Hz. The ionic conductivity of the composite membrane was 0.77 mS cm-1, calculated using the equation σ = L / R·S. -1 .

[0085] Example 6-3

[0086] POM 100P was dried in a vacuum oven at 80°C for 48 h; LiTFSI was dried in a vacuum oven at 120°C for 48 h and equilibrated in an argon-filled glove box for at least 14 days; LLZTO and SN were stored in an argon-filled glove box. 0.418 g of POM 100P, 0.400 g of LiTFSI, and 0.014 g of LLZTO were ball-milled at 400 rpm for 2 h at a ball-to-material ratio of 10:1. 0.021 g of SN was added and hot-pressed at 120°C to prepare a polyoxymethylene-based solid electrolyte composite membrane. The electrolyte composite membrane was cut into 16.8 mm diameter discs and subjected to AC impedance spectroscopy (ACIS) measurements using a stainless steel disc as a blocking electrode at a frequency of 8 MHz to 1 Hz. The ionic conductivity of the composite membrane was 0.69 mS cm-1, calculated using the equation σ = L / R·S. -1 .

[0087] Example 7-1

[0088] This embodiment uses the composite electrolyte membrane prepared in Example 1-1 as a solid electrolyte. The obtained electrolyte membrane has a thickness of 0.25 mm and has good flexibility. The positive electrode uses LiFePO4 powder as the active material, and is evenly mixed with Super P conductive agent and PVDF binder in a mass ratio of 80:10:10. After slurrying with NMP solvent, it is evenly coated on an aluminum foil current collector, and dried and rolled to obtain a positive electrode sheet. The negative electrode uses a metal lithium sheet with a thickness of about 50 μm. In an inert argon protection environment, the positive electrode sheet, the composite electrolyte membrane and the metal lithium sheet are stacked and assembled into a button-type 2025 battery, and the battery is heated at 60 oC for 30 minutes to enhance the interface contact between the electrode and the electrolyte. After the battery was assembled, the performance test was carried out at room temperature, showing a capacity of 157 mAh g at a rate of 0.1C. -1 The initial specific capacity is 100%, and after 100 cycles at a 1C rate, the battery capacity retention rate is 90%, showing excellent cycle stability and interface stability.

[0089] Example 7-2

[0090] This embodiment uses the composite electrolyte membrane prepared in Example 1-1. After roller pressing to a thickness of 50 μm, it is introduced as a flexible interface buffer layer between the positive electrode and the oxide electrolyte. The positive electrode uses LiFePO4 powder as the active material, which is uniformly mixed with Super P conductive agent and PVDF binder in a mass ratio of 80:10:10. After being slurried using NMP solvent, it is evenly coated on an aluminum foil current collector. After drying and roller pressing, the positive electrode sheet is obtained. The negative electrode uses a metal lithium sheet with a thickness of approximately 50 μm. The oxide electrolyte sheet uses LLZTO, which is 0.72 mm thick and has an ionic conductivity of approximately 0.6 mS cm at room temperature. -1 Under argon protection, the positive electrode sheet, composite electrolyte buffer layer, LLZTO electrolyte sheet, and metal lithium sheet were stacked and assembled into a button-type 2025 battery. The battery was kept at 60°C for 30 minutes to enhance the interfacial contact between the layers. After the battery was assembled, the performance test was carried out at room temperature, showing a capacity of 159 mAh g at a rate of 0.1C. -1 The initial specific capacity is as high as 94% after 300 cycles at a 1C rate, showing excellent cycle stability and interface stability.

[0091] Table 1 Effect of lithium salt types on the performance of polyoxymethylene-based composite solid electrolytes

[0092]

[0093] Table 2 Li + : Effect of O on the performance of polyoxymethylene-based composite solid electrolytes

[0094]

[0095] Table 3 Effect of plasticizer type on the performance of polyoxymethylene-based composite solid electrolyte

[0096]

[0097] Table 4 Effect of the mass ratio of plasticizer to polyoxymethylene on the performance of polyoxymethylene-based composite solid electrolytes

[0098]

[0099] Table 5 Effect of inorganic fillers on the performance of polyoxymethylene-based composite solid electrolytes

[0100]

[0101] Table 6 Effect of the mass ratio of inorganic filler and polyoxymethylene on the performance of polyoxymethylene-based composite solid electrolyte

[0102]

[0103] As shown in Table 1, in preparation method (a), the types of lithium salts are preferably lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium difluorooxalatoborate (LiDFOB), and the resulting ionic conductivity is higher.

[0104] As shown in Table 2, in the preparation method (a), the stoichiometric ratio of lithium salt to polyoxymethylene structural unit (-CH2O-) (Li + :0) is preferably 1:30 to 1:6. An appropriate amount of lithium salt can promote ion transport in the composite membrane, while an excessive amount of lithium salt will crystallize and aggregate, resulting in obstruction of ion transport.

[0105] As shown in Table 3, in the preparation method (a), the types of plasticizers are preferably propylene carbonate, succinonitrile, and triethylene glycol dimethyl ether.

[0106] As shown in Table 4, in preparation method (a), the mass ratio of plasticizer to polyformaldehyde is preferably 1: 50 to 1: 4. As the mass ratio of plasticizer to polyformaldehyde continues to increase, the crystallization of polyformaldehyde can be effectively suppressed, and the ionic conductivity of the electrolyte continues to improve. However, when the content of the plasticizer is too high, the mechanical properties of the electrolyte significantly decrease. Therefore, an appropriate amount of plasticizer can improve the ionic conductivity of the polyformaldehyde-based electrolyte and simultaneously keep the electrolyte in good mechanical properties.

[0107] As shown in Table 5, in preparation method (a), polyformaldehyde can be compounded with a variety of inorganic fillers to prepare a polyformaldehyde-based composite solid electrolyte.

[0108] As can be seen in Table 6, the preparation methods used in each example in Table 6 differ from those in the other examples described above. Based on the ionic conductivity data, the preparation method using organic solvent mixing is preferred. Compared to ball milling, organic solvents promote entanglement of polymer molecular chains, reduce the formation of grain boundaries within the solid electrolyte, and thus improve the ionic conductivity of the solid electrolyte.

[0109] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A composite solid electrolyte, characterized in that The composite solid electrolyte includes: lithium salt, polyformaldehyde, a plasticizer and an inorganic filler, and the mass ratio of the plasticizer to the polyformaldehyde is 1:50 to 1:

4.

2. The composite solid electrolyte according to claim 1, characterized in that The stoichiometric ratio of lithium ions in the lithium salt to oxygen atoms in the polyoxymethylene is 1:30 to 1:

6.

3. The composite solid electrolyte according to claim 1, characterized in that The plasticizer includes one or more of propylene carbonate, succinonitrile and triethylene glycol dimethyl ether.

4. The composite solid electrolyte according to any one of claims 1 to 3, characterized in that The lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium hexafluorophosphate and lithium perchlorate.

5. The composite solid electrolyte according to any one of claims 1 to 3, characterized in that The inorganic filler includes one or more of lithium lanthanum zirconium oxide, lithium lanthanum zirconium tantalum oxide, lithium lanthanum zirconium titanate, lithium lanthanum titanate, lithium lanthanum titanate, lithium titanium phosphate, lithium aluminum titanium phosphate, lithium aluminum germanium phosphate, lithium germanium phosphosulfur, lithium phosphosulfur chloride, lithium aluminum gallium phosphate, lithium aluminum titanium phosphate, aluminum oxide, silicon dioxide, titanium dioxide, zirconium oxide, zinc oxide, nickel oxide, silicon nitride, magnesium hydroxide, diatomaceous earth, zeolite, montmorillonite and kaolin.

6. The composite solid electrolyte according to any one of claims 1 to 3, characterized in that: The mass ratio of the inorganic filler to the polyoxymethylene is 1:10 to 1:

30.

7. A method for preparing a composite solid electrolyte, characterized in that: The preparation method is used to prepare the composite solid electrolyte according to any one of claims 1 to 6, and the preparation method comprises the following steps: In an inert gas atmosphere, a lithium salt, polyoxymethylene, a plasticizer, an inorganic filler, and an organic solvent are mixed, wherein the mass ratio of the plasticizer to the polyoxymethylene is 1:50 to 1:4; The mixed liquid is poured into a mold with a polytetrafluoroethylene substrate and vacuum dried to prepare a composite solid electrolyte.

8. The preparation method according to claim 7, characterized in that The organic solvent includes one or more of N-methylpyrrolidone, tetrahydrofuran, dichloromethane, acetone and dimethylformamide.

9. The preparation method according to claim 7 or 8, characterized in that The mass ratio of the organic solvent to polyoxymethylene is 5:1 to 150:

1.

10. A battery, characterized in that: The battery comprises the composite solid electrolyte according to any one of claims 1 to 6, or comprises the composite solid electrolyte prepared by the preparation method according to any one of claims 7 to 9.

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