Low-temperature solid-state electrolyte based on MOF self-assembly and low-temperature small molecule coordination and preparation method

Abstract

The application belongs to the technical field of batteries, and discloses a low-temperature solid electrolyte based on MOF self-assembly and low-temperature small molecule cooperation and a preparation method thereof.The preparation method comprises the following steps: first, in-situ growth of AHF-5 MOF on a glass fiber substrate by a high-temperature spraying method to obtain a modified diaphragm M; then, the diaphragm M is placed in a polymer precursor solution into which a low-temperature small molecule is introduced, and a low-temperature solid electrolyte with MOF self-assembly and low-temperature small molecule cooperation is formed by in-situ thermal polymerization.The application improves the problem that the ion conductivity of a traditional lithium ion battery is poor and the cycle performance of the battery is significantly reduced under a low-temperature environment, improves the ion transmission efficiency under a low-temperature condition, promotes uniform transmission of lithium ions at an electrolyte interface, and improves the compatibility of an electrode and an electrolyte interface.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a low-temperature solid electrolyte based on MOF self-assembly and low-temperature small molecule synergy, and its preparation method. Background Technology

[0002] Lithium-ion batteries, with their outstanding energy density and cycle life, have become an important choice for next-generation energy storage systems. However, in low-temperature environments, the ion conductivity of traditional lithium-ion batteries decreases significantly, leading to a severe decline in their cycle performance. This greatly limits the practical use of batteries in cold climates or special environments. The root cause is that the viscosity of the liquid electrolyte increases and the interfacial impedance rises at low temperatures, resulting in a deterioration in ion conductivity and consequently affecting the overall battery performance. Therefore, researchers have devoted considerable time to the research of lithium battery electrolytes, developing novel electrolyte systems that maintain high ion conductivity and stable interfacial transport characteristics at low temperatures.

[0003] To address the aforementioned challenges, solid-state electrolytes (SSEs) demonstrate significant application potential. Compared to traditional liquid systems, SSEs are less affected by temperature fluctuations, fundamentally avoiding ion transport obstacles caused by electrolyte solidification, sudden viscosity increases, or solvation-induced structural changes. However, existing SSE materials generally exhibit low ionic conductivity at low temperatures, and poor solid-solid interface contact with electrodes also limits their full performance. For example, the flame-retardant gel-like symmetrical electrolyte membrane and its preparation method described in patent CN202411022354.6 show low cycle stability, discharge specific capacity, and capacity retention in batteries assembled from this membrane at room temperature (25 °C). This indicates that the electrolyte has low ionic conductivity at room temperature, and whether it can achieve rapid and stable ion transport at low temperatures requires further investigation.

[0004] Therefore, how to construct efficient ion transport channels inside solid electrolytes through material design and preparation process innovation, and achieve rapid and stable ion conduction in low-temperature environments, remains the core challenge facing this field. Summary of the Invention

[0005] The purpose of this invention is to provide a low-temperature solid electrolyte based on MOF self-assembly and low-temperature small molecule synergy and its preparation method, so as to solve the technical problems of low cycle stability, discharge specific capacity and capacity retention at room temperature (25 °C) in the above-mentioned prior art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] The preparation method of low-temperature solid electrolyte based on MOF self-assembly and low-temperature small molecule synergy includes the following steps:

[0008] S1. Preparation of MOF self-assembled modified diaphragm: AHF-5MOF material was grown in situ on a glass fiber substrate by high-temperature spraying to obtain modified diaphragm M;

[0009] S2. Preparation of polymer-based electrolyte: In a glove box, measure the volume ratio of polyethylene glycol diacrylate (PEGDA) monomer, electrolyte fluoroethylene carbonate (FEC), and ethylene glycol dimethyl ether (DME) in a glass bottle, then add lithium salt to the glass bottle, and finally add the initiator azobisisobutyronitrile (AIBN). Place the bottle on a stirrer and stir to form a polymer electrolyte.

[0010] S3. Introduction of low-temperature small molecules: In a glove box, measure ethyl acetate (EA) and ethylene carbonate (EC) in a volume ratio of 1:1, add them to the polymer electrolyte obtained in step S2, and stir for 30 min to form a low-temperature polymer electrolyte.

[0011] S4. Preparation of low-temperature solid electrolyte: In a glove box, a high-temperature resistant glass plate is placed on a heating plate, the modified diaphragm M prepared in step S1 is placed on the glass plate, the low-temperature polymer electrolyte obtained in step S3 is dropped onto the modified diaphragm, and the polymer is heated to crosslink and solidify, thus obtaining a low-temperature solid electrolyte.

[0012] Further, in step S1, the thickness of the glass fiber substrate is 260~620 μm; the number of self-assembled layers of AHF-5MOF on the glass fiber substrate is 0~20 layers.

[0013] Further, in step S2, the lithium salt is selected from one of LiPF6, LiTFSI, and LiBF4, and the concentration of the lithium salt in the electrolyte is 1~2 mol / L; the amount of azobisisobutyronitrile added as the initiator is 2 mg / mL, and the stirring time is 5-30 min.

[0014] Furthermore, steps S2 to S4 are carried out in a glove box protected by argon gas, and the oxygen level in the glove box is not higher than 0.01 ppm.

[0015] Furthermore, in step S4, the heating temperature is 50~80 ℃ and the heating time is 20~60 min.

[0016] Furthermore, in step S4, the diameter of the modified diaphragm M is 18-20 mm, and the capacity of the added low-temperature polymer electrolyte ranges from 60-120 μL / diaphragm.

[0017] Low-temperature solid electrolytes based on MOF self-assembly and low-temperature small molecule synergy are prepared using any of the above preparation methods.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] 1. This invention constructs an ordered three-dimensional ion transport framework through the ordered self-assembly of MOFs on a glass fiber substrate, providing continuous channels for rapid lithium-ion migration. Simultaneously, a polymer electrolyte containing low-temperature small molecules of ethyl acetate (EA) and ethylene carbonate (EC) is introduced. This low-temperature small molecule system maintains molecular activity at low temperatures, synergistically forming a rigid-flexible conduction network with the MOF framework, significantly reducing the ion transport activation energy and maintaining high ionic conductivity at low temperatures. The dimethyl ethylene glycol (DME) and ethyl acetate (EA) added to the precursor solution are low-melting-point, low-viscosity solvents with excellent low-temperature performance. They can lower the freezing point of the electrolyte and improve its ionic conductivity at low temperatures. Fluoroethylene carbonate (FEC) and ethylene carbonate (EC) are added to the precursor solution. The former preferentially undergoes a reduction reaction on the electrode surface in the electrolyte, forming a LiF-rich solid electrolyte interphase (SEI) film. The latter has a high dielectric constant and good film-forming properties. It can form a stable CEI film on the positive electrode surface, protecting the positive electrode material from electrolyte corrosion.

[0020] 2. This invention provides polymer electrolytes containing three different lithium salts: LiPF6, LiTFSI, and LiBF4. By comparing the effects of different lithium salts on the performance of low-temperature solid electrolytes, the optimal system can be selected according to actual application requirements. LiPF6 provides high ionic conductivity, LiTFSI enhances interfacial stability, and LiBF4 improves low-temperature performance, offering diverse options for system optimization.

[0021] 3. The low-temperature solid electrolyte prepared in this invention, based on MOF self-assembly and the synergistic effect of low-temperature small molecules, achieves an ionic conductivity of (σ) at 0 °C. Li + =1.220×10 -3 S cm -1 LSE1), (σ Li + =1.175×10 -3 S cm -1 LSE2), (σ Li + =1.171×10 -3 S cm -1 The lithium battery assembled (LSE3) has an initial charge / discharge capacity of 145.96 mAhg after 100 cycles at a 1C rated capacitance. -1 (LSE1), 150.26 mAhg -1 (LSE2), 145.30 mAhg -1(LSE3), with a Coulomb efficiency close to 99%. Attached Figure Description

[0022] Figure 1 This is a comparison of the XRD patterns of the modified diaphragm M, the AHF-5 MOF standard curve, and the blank glass fiber substrate GF in Example 1 of this invention;

[0023] Figure 2 This is a graph showing the ionic conductivity of lithium-ion batteries assembled with different low-temperature solid electrolytes according to Example 1 of the present invention at 25 °C and 0 °C.

[0024] Figure 3 This is a cycling diagram of lithium-ion batteries assembled with different low-temperature solid electrolytes based on Example 1 of the present invention at a current density of 1 C. Detailed Implementation

[0025] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0026] Example 1

[0027] This invention relates to a method for preparing a low-temperature solid electrolyte based on the synergistic effect of MOF self-assembly and low-temperature small molecules. The specific steps are as follows:

[0028] S1: Preparation of MOF self-assembled modified membrane (same as patent application number CN202411022354.6)

[0029] Zinc nitrate hexahydrate (Zn(NO3)2·6H2O) was dissolved in deionized water (H2O) and stirred for 1-2 hours to disperse it into a colorless and transparent solution A with a concentration of 0.05 mol / L. Then, 5-aminotetrazolium (CH3N5) and pyromellitic acid (C10H6O8) in a molar ratio of 2:1 were weighed and dissolved in deionized water (H2O). The pH was adjusted to 6-7 with diluted tetramethylammonium hydroxide solution, and the mixture was stirred for 1-2 hours to disperse it into a colorless and transparent solution B with a concentration of 0.075 mol / L. Glass fibers were cut into 18 mm diameter circles, appropriate for the size of a button battery casing. The glass fibers were placed on a 170°C heating plate, with the spray gun 10-15 cm away from the fibers. 1 mL of solution A was evenly sprayed onto the fibers using the spray gun. After standing for 10 seconds, the solution was washed with ethanol. Then, 2 mL of solution B was evenly sprayed onto the fibers using the spray gun. After standing for 10 seconds, the solution was washed with ethanol. After spraying 10 coats, composite glass fiber C is obtained.

[0030] At room temperature, C was soaked in deionized water (H2O) for 1 hour, then removed and soaked in ethanol for 12 hours. After removal, it was dried in an oven at 120℃ to obtain the modified diaphragm D (AHF-5@GF) loaded with carboxylic acid and tetrazolium MOF material.

[0031] S2: Preparation of polymer-based electrolyte

[0032] In a glove box, measure three portions of polyethylene glycol diacrylate (PEGDA) monomer, fluoroethylene carbonate (FEC) electrolyte, and dimethyl ethylene glycol (DME) in a volume ratio of 2:3:3 into three glass bottles. Then, add LiPF6 (1 mol / L), LiTFSI (1 mol / L), and LiBF4 (1 mol / L) to the three glass bottles respectively. Finally, add azobisisobutyronitrile (AIBN, 2 mg / mL) initiator to each bottle, and stir on a stirrer for 5-10 min to form polymer electrolytes PE1, PE2, and PE3 respectively.

[0033] S3: Introduction of low-temperature small molecules

[0034] In a glove box, measure out 3 portions of ethyl acetate (EA) and ethylene carbonate (EC) in a volume ratio of 1:1, and add them to the polymer electrolytes PE1, PE2 and PE3 obtained in step S2, respectively. Stir for 30 min to form low-temperature polymer electrolytes LE1, LE2 and LE3, respectively.

[0035] S4: Preparation of Low-Temperature Solid Electrolytes

[0036] In a glove box, a high-temperature resistant glass plate was first placed on a heating plate, and then the three modified diaphragms M prepared in step S1 were neatly placed on the glass plate. Next, using a pipette, 100 μL of the low-temperature polymer electrolytes LE1, LE2, and LE3 obtained in step S3 were transferred and slowly added dropwise onto the three modified diaphragms M (18 mm in diameter). Finally, the power was turned on to start heating, with the heating plate temperature set to 60 °C and the heating time set to 30 min. The resulting low-temperature solid electrolytes LSE1, LSE2, and LSE3 were obtained based on MOF self-assembly and the synergistic effect of low-temperature small molecules.

[0037] Example 2

[0038] This invention relates to a method for preparing a low-temperature solid electrolyte based on the synergistic effect of MOF self-assembly and low-temperature small molecules. See [link to relevant documentation]. Figure 1 The specific steps are as follows:

[0039] S1: Preparation of MOF self-assembled modified membrane (same as Example 1).

[0040] S2: Preparation of polymer-based electrolyte

[0041] In a glove box, measure three portions of polyethylene glycol diacrylate (PEGDA) monomer, fluoroethylene carbonate (FEC) electrolyte, and dimethyl ethylene glycol (DME) in a volume ratio of 2:3:3 into three glass bottles. Then, add LiPF6 (1.5 mol / L), LiTFSI (1.5 mol / L), and LiBF4 (1.5 mol / L) to the three glass bottles respectively. Finally, add azobisisobutyronitrile (AIBN, 2 mg / mL) initiator to each bottle, and stir on a stirrer for 5-10 min to form polymer electrolytes PE1, PE2, and PE3 respectively.

[0042] S3: Introduction of low-temperature small molecules

[0043] In a glove box, measure out 3 portions of ethyl acetate (EA) and ethylene carbonate (EC) in a volume ratio of 1:1, and add them to the polymer electrolytes PE1, PE2 and PE3 obtained in step S2, respectively. Stir for 30 min to form low-temperature polymer electrolytes LE1, LE2 and LE3, respectively.

[0044] S4: Preparation of Low-Temperature Solid Electrolytes

[0045] In a glove box, a high-temperature resistant glass plate was first placed on a heating plate, and then the three modified diaphragms M prepared in step S1 were neatly placed on the glass plate. Next, using a pipette, 120 μL of the low-temperature polymer electrolytes LE1, LE2, and LE3 obtained in step S3 were transferred and slowly added dropwise onto the three modified diaphragms M (18 mm in diameter). Finally, the power was turned on to start heating, with the heating plate temperature set to 60 °C and the heating time set to 40 min. The resulting low-temperature solid electrolytes LSE1, LSE2, and LSE3 were obtained based on MOF self-assembly and the synergistic effect of low-temperature small molecules.

[0046] Example 3

[0047] This invention relates to a method for preparing a low-temperature solid electrolyte based on the synergistic effect of MOF self-assembly and low-temperature small molecules. See [link to relevant documentation]. Figure 1 The specific steps are as follows:

[0048] S1: Preparation of MOF self-assembled modified membrane (same as Example 1).

[0049] S2: Preparation of polymer-based electrolyte

[0050] In a glove box, measure three portions of polyethylene glycol diacrylate (PEGDA) monomer, fluoroethylene carbonate (FEC) electrolyte, and dimethyl ethylene glycol (DME) in a volume ratio of 2:3:3 into three glass bottles. Then, add LiPF6 (2 mol / L), LiTFSI (2 mol / L), and LiBF4 (2 mol / L) to the three glass bottles respectively. Finally, add azobisisobutyronitrile (AIBN, 2 mg / mL) initiator to each bottle, and stir on a stirrer for 5-10 min to form polymer electrolytes PE1, PE2, and PE3 respectively.

[0051] S3: Introduction of low-temperature small molecules

[0052] In a glove box, measure out 3 portions of ethyl acetate (EA) and ethylene carbonate (EC) in a volume ratio of 1:1, and add them to the polymer electrolytes PE1, PE2 and PE3 obtained in step S2, respectively. Stir for 30 min to form low-temperature polymer electrolytes LE1, LE2 and LE3, respectively.

[0053] S4: Preparation of Low-Temperature Solid Electrolytes

[0054] In a glove box, a high-temperature resistant glass plate was first placed on a heating plate, and then the three modified diaphragms M prepared in step S1 were neatly placed on the glass plate. Next, using a pipette, 120 μL of the low-temperature polymer electrolytes LE1, LE2, and LE3 obtained in step S3 were transferred and slowly added dropwise onto the three modified diaphragms M (19 mm in diameter). Finally, the power was turned on to start heating, with the heating plate temperature set to 50 °C and the heating time set to 60 min. The resulting low-temperature solid electrolytes LSE1, LSE2, and LSE3 were obtained based on MOF self-assembly and the synergistic effect of low-temperature small molecules.

[0055] Example 4

[0056] This invention relates to a method for preparing a low-temperature solid electrolyte based on the synergistic effect of MOF self-assembly and low-temperature small molecules. See [link to relevant documentation]. Figure 1 The specific steps are as follows:

[0057] S1: Preparation of MOF self-assembled modified membrane (same as Example 1).

[0058] S2: Preparation of polymer-based electrolyte

[0059] In a glove box, measure three portions of polyethylene glycol diacrylate (PEGDA) monomer, fluoroethylene carbonate (FEC) electrolyte, and dimethyl ethylene glycol (DME) in a volume ratio of 2:3:3 into three glass bottles. Then, add LiPF6 (1 mol / L), LiTFSI (1 mol / L), and LiBF4 (1 mol / L) to the three glass bottles respectively. Finally, add azobisisobutyronitrile (AIBN, 2 mg / mL) initiator to each bottle, and stir on a stirrer for 5-10 min to form polymer electrolytes PE1, PE2, and PE3 respectively.

[0060] S3: Introduction of low-temperature small molecules

[0061] In a glove box, measure out 3 portions of ethyl acetate (EA) and ethylene carbonate (EC) in a volume ratio of 2:1, and add them to the polymer electrolytes PE1, PE2 and PE3 obtained in step S2, respectively. Stir for 30 min to form low-temperature polymer electrolytes LE1, LE2 and LE3, respectively.

[0062] S4: Preparation of Low-Temperature Solid Electrolytes

[0063] In a glove box, a high-temperature resistant glass plate was first placed on a heating plate, and then the three modified diaphragms M prepared in step S1 were neatly placed on the glass plate. Next, using a pipette, 80 μL of the low-temperature polymer electrolytes LE1, LE2, and LE3 obtained in step S3 were transferred and slowly added dropwise onto the three modified diaphragms M (19 mm in diameter). Finally, the power was turned on to start heating, with the heating plate temperature set to 70 °C and the heating time set to 20 min. The resulting low-temperature solid electrolytes LSE1, LSE2, and LSE3 were obtained based on MOF self-assembly and the synergistic effect of low-temperature small molecules.

[0064] Example 5

[0065] This invention relates to a method for preparing a low-temperature solid electrolyte based on the synergistic effect of MOF self-assembly and low-temperature small molecules. See [link to relevant documentation]. Figure 1 The specific steps are as follows:

[0066] S1: Preparation of MOF self-assembled modified membrane (same as Example 1).

[0067] S2: Preparation of polymer-based electrolyte

[0068] In a glove box, measure three portions of polyethylene glycol diacrylate (PEGDA) monomer, fluoroethylene carbonate (FEC) electrolyte, and dimethyl ethylene glycol (DME) in a volume ratio of 2:3:3 into three glass bottles. Then, add LiPF6 (1 mol / L), LiTFSI (1 mol / L), and LiBF4 (1 mol / L) to the three glass bottles respectively. Finally, add azobisisobutyronitrile (AIBN, 2 mg / mL) initiator to each bottle, and stir on a stirrer for 5-10 min to form polymer electrolytes PE1, PE2, and PE3 respectively.

[0069] S3: Introduction of low-temperature small molecules

[0070] In a glove box, measure out 3 portions of ethyl acetate (EA) and ethylene carbonate (EC) in a volume ratio of 1:2, and add them to the polymer electrolytes PE1, PE2 and PE3 obtained in step S2, respectively. Stir for 30 min to form low-temperature polymer electrolytes LE1, LE2 and LE3, respectively.

[0071] S4: Preparation of Low-Temperature Solid Electrolytes

[0072] In a glove box, a high-temperature resistant glass plate was first placed on a heating plate, and then the three modified diaphragms M prepared in step S1 were neatly placed on the glass plate. Next, using a pipette, 60 μL of the low-temperature polymer electrolytes LE1, LE2, and LE3 obtained in step S3 were transferred and slowly added dropwise onto the three modified diaphragms M (20 mm in diameter). Finally, the power was turned on to start heating, with the heating plate temperature set to 70 °C and the heating time set to 30 min. The resulting low-temperature solid electrolytes LSE1, LSE2, and LSE3 were obtained based on MOF self-assembly and the synergistic effect of low-temperature small molecules.

[0073] Example 6

[0074] This invention relates to a method for preparing a low-temperature solid electrolyte based on the synergistic effect of MOF self-assembly and low-temperature small molecules. The specific steps are as follows:

[0075] S1: Preparation of MOF self-assembled modified membrane (same as Example 1).

[0076] S2: Preparation of polymer-based electrolyte

[0077] In a glove box, measure three portions of polyethylene glycol diacrylate (PEGDA) monomer, fluoroethylene carbonate (FEC) electrolyte, and dimethyl ethylene glycol (DME) in a volume ratio of 2:3:3 into three glass bottles. Then, add LiPF6 (1 mol / L), LiTFSI (1 mol / L), and LiBF4 (1 mol / L) to the three glass bottles respectively. Finally, add azobisisobutyronitrile (AIBN, 2 mg / mL) initiator to each bottle, and stir on a stirrer for 5-10 min to form polymer electrolytes PE1, PE2, and PE3 respectively.

[0078] S3: Introduction of low-temperature small molecules

[0079] In a glove box, measure out 3 portions of ethyl acetate (EA) and ethylene carbonate (EC) in a volume ratio of 1:0, and add them to the polymer electrolytes PE1, PE2 and PE3 obtained in step S2, respectively. Stir for 30 min to form low-temperature polymer electrolytes LE1, LE2 and LE3, respectively.

[0080] S4: Preparation of Low-Temperature Solid Electrolytes

[0081] In a glove box, a high-temperature resistant glass plate was first placed on a heating plate, and then the three modified diaphragms M prepared in step S1 were neatly placed on the glass plate. Next, using a pipette, 100 μL of the low-temperature polymer electrolytes LE1, LE2, and LE3 obtained in step S3 were transferred and slowly added dropwise onto the three modified diaphragms M (20 mm in diameter). Finally, the power was turned on to start heating, with the heating plate temperature set to 80 °C and the heating time set to 20 min. The resulting low-temperature solid electrolytes LSE1, LSE2, and LSE3 were obtained based on MOF self-assembly and the synergistic effect of low-temperature small molecules.

[0082] Example 1 above is the best embodiment. The following are the experimental data of the product prepared in Example 1:

[0083] like Figure 1 As shown, Figure 1 The M curve in the figure is obtained by XRD testing of the modified diaphragm M prepared in this invention; the simulated curve is the standard curve of AHF-5 MOF; and the GF curve is an XRD curve obtained by X-ray diffraction of a blank glass fiber substrate. From the comparison of the three XRD curves above, it can be seen that AHF-5 MOF was successfully grown in situ on glass fiber, that is, the modified diaphragm M loaded with AHF-5 MOF material was successfully prepared.

[0084] like Figure 2As shown in the figure, the lithium-ion battery assembled in Example 1 of the present invention exhibits ionic conductivity at different temperatures. The low-temperature solid electrolyte, based on MOF self-assembly and the synergistic effect of low-temperature small molecules, achieves an ionic conductivity of 1.220 × 10⁻⁶ at 0 °C. -3 S cm -1 (LSE1), 1.175×10 -3 S cm -1 (LSE2), 1.171×10 -3 S cm -1 (LSE3).

[0085] like Figure 3 The figure shows the cycling diagram of the assembled lithium-ion battery in Embodiment 1 of the present invention at a current density of 1 C. The assembled lithium battery has an initial charge-discharge capacity of 145.96 mAhg at the rated capacitance of 1 C. -1 (LSE1), 150.26 mAhg -1 (LSE2), 145.30 mAhg -1 (LSE3), with a Coulomb efficiency close to 99%.

[0086] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for preparing a low-temperature solid electrolyte based on MOF self-assembly and low-temperature small molecule synergy, characterized in that, Includes the following steps: S1. Preparation of MOF self-assembled modified diaphragm: AHF-5MOF material was grown in situ on a glass fiber substrate by high-temperature spraying to obtain modified diaphragm M; S2. Preparation of polymer-based electrolyte: In a glove box, measure the volume ratio of polyethylene glycol diacrylate (PEGDA) monomer, electrolyte fluoroethylene carbonate (FEC), and ethylene glycol dimethyl ether (DME) in a glass bottle, then add lithium salt to the glass bottle, and finally add the initiator azobisisobutyronitrile (AIBN). Place the bottle on a stirrer and stir to form a polymer electrolyte. S3. Introduction of low-temperature small molecules: In a glove box, measure ethyl acetate (EA) and ethylene carbonate (EC) in a volume ratio of 1:1, add them to the polymer electrolyte obtained in step S2, and stir for 30 min to form a low-temperature polymer electrolyte. S4. Preparation of low-temperature solid electrolyte: In a glove box, a high-temperature resistant glass plate is placed on a heating plate, the modified diaphragm M prepared in step S1 is placed on the glass plate, the low-temperature polymer electrolyte obtained in step S3 is dropped onto the modified diaphragm, and the polymer is heated to crosslink and solidify, thus obtaining a low-temperature solid electrolyte.

2. The preparation method according to claim 1, characterized in that: In step S1, the thickness of the glass fiber substrate is 260~620 μm; the number of self-assembled layers of AHF-5MOF on the glass fiber substrate is 1~20 layers.

3. The preparation method according to claim 1, characterized in that: In step S2, the lithium salt is selected from one of LiPF6, LiTFSI, and LiBF4, and the concentration of the lithium salt in the electrolyte is 1~2 mol / L; the amount of azobisisobutyronitrile (AIBN) initiator added is 2 mg / mL, and the stirring time is 5-30 min.

4. The preparation method according to claim 1, characterized in that: Steps S2 to S4 are carried out in a glove box protected by argon gas, and the oxygen level in the water of the glove box is not higher than 0.01 ppm.

5. The preparation method according to claim 1, characterized in that: In step S4, the heating temperature is 50~80 ℃ and the heating time is 20~60 min.

6. The preparation method according to claim 1, characterized in that: In step S4, the diameter of the modified diaphragm M is 18-20 mm, and the capacity of the added low-temperature polymer electrolyte ranges from 60-120 μL / diaphragm.

7. A low-temperature solid electrolyte based on MOF self-assembly and low-temperature small molecule synergy, characterized in that, It is prepared by the preparation method described in any one of claims 1-6.

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