Solid electrolyte and preparation method and application thereof

Abstract

The invention relates to the technical field of lithium batteries, and discloses a solid electrolyte and a preparation method and application thereof. The solid electrolyte is a solid polymer electrolyte modified by adding a functional filler; the functional filler is beta-cyclodextrin inclusion ionic liquid. According to the solid electrolyte provided by the invention, the beta-cyclodextrin inclusion ionic liquid functional filler is introduced into the solid polymer electrolyte, and the ionic liquid is fixed in the cavity by a rigid ring structure of beta-cyclodextrin to form the solid filler, so that the mechanical property of the electrolyte is improved, and dendritic crystals are inhibited; the host-guest inclusion structure realizes directional transmission of lithium ions, and breaks through the bottleneck of disordered transmission of the traditional polymer electrolyte; compared with the traditional solid polymer electrolyte, the solid polymer electrolyte has the advantages that the mechanical strength and toughness are obviously improved, the interface impedance is lower, the ionic conductivity is higher, and the application requirements of a lithium metal battery can be better met; the safety performance, the energy density and the service life of the lithium metal battery using the solid electrolyte are further improved.

Description

Technical Field

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

[0002] In recent years, energy storage components such as primary batteries, secondary batteries, and lithium metal batteries have developed rapidly. Primary batteries are widely used due to their advantages, such as requiring no recharging and being able to store energy for long periods without self-discharge. However, their low energy density requires frequent replacement, and they are environmentally friendly, significantly limiting their use in high-power electrical appliances. Secondary batteries, on the other hand, offer high energy density, long cycle life, and environmental friendliness. They are gradually replacing primary batteries and are widely used in a variety of applications, including digital products and electric vehicles. Currently, the most commonly used commercial lithium-ion battery among secondary batteries uses graphite as the negative electrode. Its theoretical capacity density is only 372 mAh / g and its theoretical energy density is only 390 Wh / kg. This limits the battery life of electronic products, energy storage systems, and electric vehicles, hindering the development of lithium-ion batteries. Among metals, lithium has the lowest density, the lowest standard electrode potential, and the highest theoretical specific capacity (3860 Ah / kg). Lithium metal batteries, using lithium as the negative electrode, further improve the energy density of secondary batteries and are considered a promising next-generation energy storage component to replace lithium-ion batteries.

[0003] Electrolytes, as a crucial component of lithium metal batteries, transport ions between the positive and negative electrodes. Selecting the right electrolyte is crucial for achieving batteries with high energy density, long cycle life, and good safety. However, commonly used organic liquid electrolytes suffer from toxicity, volatility, leakage, and poor thermal stability. These defects can cause rapid heating of the battery during charge and discharge, leading to fire or even explosion, posing significant safety concerns. In contrast, solid-state electrolytes not only possess superior mechanical properties and effectively inhibit lithium dendrite growth, but also exhibit low flammability and no leakage, significantly improving battery safety. Among solid-state electrolytes, solid polymer electrolytes—composite materials composed of a uniform mixture of polymers and lithium salts—have attracted widespread attention due to their excellent flexibility, processability, and interfacial compatibility. Common polymer electrolyte matrices include polyethylene oxide (PEO), polyvinylidene fluoride (PVDF), polyacrylonitrile (PAN), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polymethyl methacrylate (PMMA), and thermoplastic polyurethane (TPU).

[0004] However, in traditional polymer solid electrolytes, lithium salts lack effective dissociation sites, have insufficient dissociation degree, low free lithium ion concentration, and the crystalline region of the polymer chain hinders the continuous transport of ions, resulting in their room temperature ionic conductivity generally lower than 1×10 -4S / cm, which seriously restricts the rate performance and low-temperature adaptability of the battery, and limits the application of the battery in high-performance scenarios. The existing technology improves the ionic conductivity of solid polymer electrolytes by preparing a blended polymer matrix and adding plasticizers or high-concentration lithium salts to the electrolyte, but this will lead to a decrease in the crystallinity of the polymer matrix and disordered chain segments, significantly weakening the mechanical strength of the solid polymer electrolyte (such as tensile strength, fracture strain, etc.), making it easy to cause safety hazards due to deformation or lithium dendrite penetration; and measures to enhance mechanical properties by cross-linking or introducing rigid fillers are likely to block ion transmission channels and reduce conductivity. In addition, existing polymer solid electrolytes are more sensitive to temperature changes, and often experience problems such as dehydration, decomposition and melting at high temperatures, which reduces the reliability and life of the battery and limits the application of the battery under extreme temperature conditions. Summary of the Invention

[0005] The present invention aims to solve at least one of the above-mentioned technical problems in the prior art. To this end, one of the purposes of the present invention is to provide a solid electrolyte.

[0006] A second object of the present invention is to provide a method for preparing the solid electrolyte.

[0007] A third object of the present invention is to provide a lithium metal battery.

[0008] In order to achieve the above object, the technical solution adopted by the present invention is:

[0009] A first aspect of the present invention provides a solid electrolyte, which is a solid polymer electrolyte modified by adding a functional filler; the functional filler is a β-cyclodextrin inclusion ionic liquid.

[0010] In some embodiments of the present invention, the functional filler is prepared from the following raw materials: β-cyclodextrin, ionic liquid and water.

[0011] In some embodiments of the present invention, the ionic liquid is selected from 1-ethyl-3-methylimidazolium hexafluorophosphate ([EMIM]PF6) or 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6).

[0012] In some embodiments of the present invention, the mass ratio of the β-cyclodextrin, the ionic liquid and the water is (2-5):1:(80-120).

[0013] In some preferred embodiments of the present invention, the mass ratio of the β-cyclodextrin, the ionic liquid and the water is (3-5):1:(90-110).

[0014] In some embodiments of the present invention, the functional filler is prepared by a method comprising the following steps: mixing various preparation raw materials and removing water to obtain the functional filler.

[0015] In some embodiments of the present invention, the mixing temperature is 20-30° C. and the mixing time is 20-30 min.

[0016] In some preferred embodiments of the present invention, the mixing temperature is 20-25° C. and the mixing time is 20-25 min.

[0017] In some embodiments of the present invention, the mixing process is supplemented by stirring.

[0018] In some embodiments of the present invention, the temperature of the water removal is 50-80°C.

[0019] In some preferred embodiments of the present invention, the temperature for removing water is 60-70°C.

[0020] In some embodiments of the present invention, the water removal method includes rotary evaporation.

[0021] In some embodiments of the present invention, after the water removal, the step of drying the product at 50-70° C. for 10-12 hours is further included.

[0022] Specifically, the preparation process of functional fillers is a host-guest inclusion complex: β-cyclodextrin serves as the host, with a hydrophobic inner cavity and a hydrophilic outer surface, which can accommodate hydrophobic or partially hydrophobic molecules of matching size (such as organic cations in ionic liquids); the organic cations in ionic liquids serve as guests and are encapsulated in the cavity of β-cyclodextrin through hydrophobic interaction, van der Waals forces or hydrogen bonds, while water serves as the reaction medium, helping to dissolve β-cyclodextrin and promote the dispersion of ionic liquids, while regulating the inclusion efficiency through competitive hydrogen bonds; finally, by removing water molecules through methods such as rotary evaporation, the inclusion equilibrium can be destroyed, and the reaction can be pushed towards the direction of forming inclusion complexes, ultimately obtaining a solid inclusion material.

[0023] In some embodiments of the present invention, the solid electrolyte is prepared from the following raw materials: a functional filler, a polymer matrix, a lithium salt, and a solvent.

[0024] In some embodiments of the present invention, the mass ratio of the functional filler, the polymer matrix, the lithium salt and the solvent is 1:(3-6):(3.5-6):(14-20).

[0025] In some preferred embodiments of the present invention, the mass ratio of the functional filler, the polymer matrix, the lithium salt and the solvent is 1:(3-4.5):(4-5):(16-19).

[0026] In some embodiments of the present invention, the polymer matrix is ​​selected from at least one of polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), polychlorotrifluoroethylene (PCTFE), and polyvinylidene fluoride (PVDF).

[0027] In some embodiments of the present invention, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LIODFB), lithium bis(fluorosulfonyl)imide (LIFSI), lithium difluorophosphate (LiPO2F2), and lithium tetrafluoroborate (LiBF4).

[0028] In some embodiments of the present invention, the solvent is selected from at least one of N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), ethylene glycol dimethyl ether (DME), and dimethyl carbonate (DMC).

[0029] The basic principles of the present invention are described as follows:

[0030] 1) Ionic liquid is a room-temperature molten salt composed of organic cations and organic or inorganic anions. It has the advantages of high thermal stability, wide electrochemical window, high ionic conductivity and adjustable structure. It can be used as a functional additive to effectively make up for the low ionic conductivity of existing solid polymer electrolytes. However, the direct application of ionic liquids to solid polymer electrolytes still has the following problems: ① Poor mechanical properties: Ionic liquids are liquid (even at room temperature) and cannot provide the mechanical strength required for solid electrolytes. They cannot inhibit the penetration of lithium dendrites and have a high risk of battery short circuits. ② Poor compatibility with polymers: High concentrations of ionic liquids can easily cause polymer swelling or plasticization, destroying their structural integrity, making the electrolyte membrane prone to rupture and reducing cycle stability. ③ Poor interface contact: Liquid components can easily form an unstable interface with electrodes (such as lithium metal), exacerbating side reactions, causing the SEI film to continue to thicken and the battery capacity to decay rapidly. ④ Disordered ion migration: Ion migration in free ionic liquids is non-directional and less efficient than that in ordered structures, so that the actual conductivity may be lower than the theoretical value. Therefore, the present invention includes ionic liquids.

[0031] 2) Cyclodextrin (CD) is a cyclic oligosaccharide that can be produced by enzymatic hydrolysis of starch and can form inclusion complexes with a variety of molecules. The three most common cyclodextrins include α-CD, β-CD, and γ-CD. These are cyclic molecules composed of 6, 7, and 8 sugar units, respectively. The pore size order is α-CD < β-CD < γ-CD. α-CD has a smaller pore size and can usually only encapsulate small gas molecules such as aliphatic hydrocarbons and CO2. Although γ-CD has a larger pore size and can accommodate organic cyclic macromolecules, its production cost is relatively high. β-CD has a moderate pore size and can effectively encapsulate certain drug molecules and small aromatic compounds. It also has a low production cost, making it an ideal inclusion complex material.

[0032] 3) The guest type of the inclusion complex is related to the pore size of cyclodextrin. The size of the organic cations in ionic liquids such as [EMIM]PF6 and [BMIM]PF6 is compatible with the pore size of β-CD. The inclusion complexes they form have the following advantages: ① Solidification and mechanical enhancement: The rigid ring structure of β-CD "fixes" the ionic liquid in the cavity to form a solid filler, avoiding liquid flow, thereby improving tensile strength and inhibiting dendrites; ② Ordered ion transport channels: The inclusion complex forms a head-to-head channel structure for Li + Providing a directional transport path, thereby improving ionic conductivity; ③ Optimizing interface stability: The hydroxyl groups (-OH) on the outer surface of β-CD form hydrogen bonds with the polymer matrix (such as PVDF-HFP), improving dispersion and thus reducing interfacial impedance; ④ Inhibiting side reactions: The inclusion complex restricts direct contact between the ionic liquid and lithium metal, reducing electrolyte decomposition and extending battery cycle life;

[0033] Therefore, the present invention uses β-cyclodextrin inclusion ionic liquid as a functional filler to modify traditional solid polymer electrolytes, which actually combines the advantages of ionic liquids (high conductivity) with the rigid requirements of solid electrolytes (mechanical strength, interface stability), and ultimately achieves: ① solidification: solving the problems of liquid leakage and dendrite penetration; ② ordering: improving ion transmission efficiency; ③ stabilization: extending the battery cycle life, thereby effectively solving the defects of existing electrolytes.

[0034] The second aspect of the present invention provides a method for preparing the solid electrolyte according to the first aspect of the present invention, comprising the following steps:

[0035] S1, mixing a functional filler, a polymer matrix, a lithium salt and a solvent to obtain an electrolyte precursor solution;

[0036] S2. Forming a film of the electrolyte precursor solution on a carrier and drying the film to obtain the solid electrolyte.

[0037] In some embodiments of the present invention, in step S1, the mixing temperature is 50-70° C. and the mixing time is 10-15 hours.

[0038] In some preferred embodiments of the present invention, in step S1, the mixing temperature is 55-65° C. and the mixing time is 10-12 h.

[0039] In some embodiments of the present invention, in step S1, the mixing is performed in a water bath.

[0040] In some embodiments of the present invention, in step S1, the mixing process is supplemented by stirring.

[0041] In some embodiments of the present invention, step S1 further includes removing bubbles from the electrolyte precursor solution.

[0042] Specifically, removing bubbles can prevent the electrolyte precursor solution from having bubbles that cause the electrolyte surface to be rough, thereby preventing the interface impedance from being too high.

[0043] In some embodiments of the present invention, in step S2, the film forming temperature is 20-30°C, the humidity is 70% RH-85% RH, and the time is 2-5 hours.

[0044] In some preferred embodiments of the present invention, in step S2, the film forming temperature is 20-25°C, the humidity is 75% RH-85% RH, and the time is 2-4 hours.

[0045] In some embodiments of the present invention, in step S2, the carrier comprises a glass plate.

[0046] In some embodiments of the present invention, in step S2, the film forming method includes blade coating.

[0047] In some embodiments of the present invention, in step S2, the film thickness of the electrolyte precursor solution is 80-120 μm.

[0048] In some embodiments of the present invention, in step S2, after the electrolyte precursor solution is formed into a film, a freeze-drying step is further included.

[0049] Specifically, during the preparation of the solid electrolyte, the polymer matrix is ​​dissolved in a polar solvent to form a solution in which the polymer chains are freely stretched, providing a dispersion medium for subsequent components; the lithium salt dissociates into Li in the solvent. + , controlling the mass ratio of polymer matrix to lithium salt close to 1:1, can form high salt concentration and increase free Li +concentration; the solvent molecules interact with the β-cyclodextrin hydroxyl groups or ionic liquid anions outside the functional filler and prevent the van der Waals forces between the filler particles from aggregating, thereby dispersing the functional filler in the solvent to form a uniform and stable electrolyte precursor solution; during the film formation process, the solvent gradually evaporates, and the polymer chain forms a three-dimensional network structure with the functional filler and lithium salt. The functional filler is dispersed in the polymer chain, providing an ion transmission channel, and Li + The ionic conductivity is improved through the movement of polymer chains and the coordinated migration of filler interfaces.

[0050] A third aspect of the present invention provides a lithium metal battery, which includes the solid electrolyte described in the first aspect of the present invention.

[0051] Compared with the prior art, the present invention has the following beneficial effects:

[0052] 1) The solid electrolyte provided by the present invention incorporates a β-cyclodextrin inclusion ionic liquid as a functional filler into a solid polymer electrolyte. The rigid ring structure of β-cyclodextrin fixes the ionic liquid in the cavity, forming a solid filler, thereby improving the mechanical properties of the electrolyte and inhibiting dendrites. The β-cyclodextrin inclusion ionic liquid also achieves directional lithium ion transport through the host-guest inclusion structure, breaking through the bottleneck of disordered transport in traditional polymer electrolytes.

[0053] 2) The preparation method of the solid electrolyte provided by the present invention has simple steps, mild process conditions, and is suitable for industrial use;

[0054] 3) Compared with traditional solid polymer electrolytes, the solid electrolyte provided by the present invention has significantly improved mechanical strength and toughness, lower interfacial impedance, higher ionic conductivity, and can better meet the application requirements of lithium metal batteries; the lithium metal battery using this solid electrolyte will further improve its safety performance, energy density and service life. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 is the X-ray diffraction pattern of the functional filler in Example 1;

[0056] Figure 2 This is the infrared spectrum of the functional filler in Example 1;

[0057] Figure 3 This is a scanning electron microscope image of the functional filler in Example 1 magnified 20,000 times;

[0058] Figure 4 This is a scanning electron microscope image of the functional filler in Example 1 magnified 50,000 times;

[0059] Figure 5 This is a thermogravimetric curve of the functional filler in Example 1;

[0060] Figure 6 is the stress-strain diagram of the solid electrolyte in Example 1;

[0061] Figure 7 is the stress-strain diagram of the solid electrolyte in Comparative Example 1;

[0062] Figure 8 is the electrochemical impedance spectroscopy of the solid electrolyte in Example 1;

[0063] Figure 9 This is the electrochemical impedance spectroscopy of the solid electrolyte in Comparative Example 1. DETAILED DESCRIPTION

[0064] The present invention is further described in detail below using specific examples. Unless otherwise specified, the raw materials, reagents, and apparatus used in the examples and comparative examples are available from conventional commercial sources or by conventional methods. Unless otherwise specified, all experimental or testing methods are conventional in the art.

[0065] Example 1

[0066] This embodiment prepares a solid electrolyte, and the steps are as follows:

[0067] S11. Add 0.20 g of β-cyclodextrin and 0.05 g of ionic liquid [EMIM]PF6 to 5.00 mL of deionized water, stir at room temperature for 25 min, pour the mixed solution into a round-bottom flask, and perform rotary evaporation at 65°C to remove water until there is no liquid in the flask. Then stop the rotary evaporation and dry the evaporated solid at 60°C for 12 h to obtain a β-cyclodextrin inclusion ionic liquid functional filler.

[0068] S12, 0.300 g of polyvinylidene fluoride-hexafluoropropylene copolymer, 0.330 g of lithium bis(trifluoromethanesulfonyl imide), 0.075 g of functional filler, and 1.30 g of N,N-dimethylformamide were mixed, and the mixture was stirred in a water bath at 60° C. for 12 h. The resulting solution was placed in a glove box and vacuumed to remove bubbles, thereby obtaining an electrolyte precursor solution;

[0069] S21. Pour the electrolyte precursor solution onto a clean glass plate and apply it to a film using a 400 μm stainless steel scraper. Place the film in a constant temperature and humidity chamber at 25°C and 80% RH for 3 hours to obtain an electrolyte membrane with a thickness of approximately 100 μm.

[0070] S22. Take out the electrolyte membrane and freeze-dry it for 24 hours to obtain a solid electrolyte.

[0071] Example 2

[0072] This embodiment prepares a solid electrolyte, and the steps are as follows:

[0073] S11. Add 0.15 g of β-cyclodextrin and 0.05 g of ionic liquid [BMIM]PF6 to 4.50 mL of deionized water, stir at room temperature for 25 min, pour the mixed solution into a round-bottom flask, and perform rotary evaporation at 65°C to remove water until there is no liquid in the flask. Then stop the rotary evaporation and dry the solid obtained by rotary evaporation at 60°C for 12 h to obtain a β-cyclodextrin inclusion ionic liquid functional filler.

[0074] S12, 0.300 g of polyvinylidene fluoride, 0.300 g of lithium bis(oxaloyl)borate, 0.080 g of functional filler, and 1.50 g of N-methylpyrrolidone were mixed, and the mixture was stirred in a water bath at 60° C. for 12 h. The resulting solution was placed in a glove box and vacuumed to remove bubbles, thereby obtaining an electrolyte precursor solution;

[0075] S21. Pour the electrolyte precursor solution onto a clean glass plate and apply it to a film using a 400 μm stainless steel scraper. Place the film in a constant temperature and humidity chamber at 25°C and 80% RH for 3 hours to obtain an electrolyte membrane with a thickness of approximately 100 μm.

[0076] S22. Take out the electrolyte membrane and freeze-dry it for 24 hours to obtain a solid electrolyte.

[0077] Example 3

[0078] This embodiment prepares a solid electrolyte, and the steps are as follows:

[0079] S11. Add 0.15 g of β-cyclodextrin and 0.05 g of ionic liquid [EMIM]PF6 to 5.50 mL of deionized water, stir at room temperature for 25 min, pour the mixed solution into a round-bottom flask, and perform rotary evaporation at 65°C to remove water until there is no liquid in the flask. Then stop the rotary evaporation and dry the solid obtained by rotary evaporation at 60°C for 12 h to obtain a β-cyclodextrin inclusion ionic liquid functional filler.

[0080] S12, 0.375 g of polychlorotrifluoroethylene, 0.380 g of lithium bis(fluorosulfonyl)imide, 0.075 g of functional filler, and 1.50 g of ethylene glycol dimethyl ether were mixed, and the mixture was stirred in a water bath at 60° C. for 12 h. The resulting solution was placed in a glove box and vacuumed to remove bubbles, thereby obtaining an electrolyte precursor solution;

[0081] S21. Pour the electrolyte precursor solution onto a clean glass plate and apply it to a film using a 400 μm stainless steel scraper. Place the film in a constant temperature and humidity chamber at 25°C and 80% RH for 3 hours to obtain an electrolyte membrane with a thickness of approximately 100 μm.

[0082] S22. Take out the electrolyte membrane and freeze-dry it for 24 hours to obtain a solid electrolyte.

[0083] Comparative Example 1

[0084] This comparative example prepares a solid electrolyte in the following steps:

[0085] S12, 0.300 g of polyvinylidene fluoride-hexafluoropropylene copolymer, 0.330 g of lithium bis(trifluoromethanesulfonyl imide), 0.075 g of functional filler, and 1.30 g of N,N-dimethylformamide were mixed, and the mixture was stirred in a water bath at 60° C. for 12 h. The resulting solution was placed in a glove box and vacuumed to remove bubbles, thereby obtaining an electrolyte precursor solution;

[0086] S21. Pour the electrolyte precursor solution onto a clean glass plate and apply it to a film using a 400 μm stainless steel scraper. Place the film in a constant temperature and humidity chamber at 25°C and 80% RH for 3 hours to obtain an electrolyte membrane with a thickness of approximately 100 μm.

[0087] S22. Take out the electrolyte membrane and freeze-dry it for 24 hours to obtain a solid electrolyte.

[0088] Characterization and performance testing

[0089] 1. X-ray diffraction characterization of the functional filler β-cyclodextrin inclusion ionic liquid in Example 1 was performed to explore the inclusion of β-cyclodextrin and the ionic liquid [EMIM]PF6:

[0090] Figure 1 is the X-ray diffraction pattern of the functional filler in Example 1, Figure 1 It can be seen that the functional filler shows broad diffraction peaks at 11.65° and 17.65°, while the typical peaks of the original β-cyclodextrin (such as 12.5° and 20.8°) disappear, confirming that the ionic liquid destroys the crystal stacking mode of β-cyclodextrin, and the host-guest inclusion reaction between the cavity of β-cyclodextrin and the ionic liquid successfully occurs. β-cyclodextrin is transformed from a cage structure to a channel-type inclusion complex. The ionic liquid is embedded in the channel between β-cyclodextrin molecules, producing a head-to-head channel-type structure. This channel-type structure can provide a directional transmission path for lithium ions, which is superior to the disordered cage structure.

[0091] 2. The functional filler β-cyclodextrin inclusion ionic liquid in Example 1 was characterized by infrared spectroscopy to explore the changes in the functional groups in the functional filler:

[0092] Figure 2 is the infrared spectrum of the functional filler in Example 1, Figure 2 It can be seen that 3000cm in the spectrum -1 There is a strong and broad peak at 1150 cm, which corresponds to the stretching vibration of -OH in β-cyclodextrin. The peak becomes broadened after the inclusion reaction, indicating that the hydrogen bond network is disturbed by the ionic liquid; -1 Appears from [EMIM] +The stretching vibration peak caused by the N-N bond proves that there is an interaction between the ionic liquid and β-cyclodextrin. The ionic liquid is successfully included, and it is only a physical inclusion without chemical bond breaking.

[0093] 3. Scanning electron microscopy was performed on the functional filler β-cyclodextrin inclusion ionic liquid in Example 1 to observe the appearance of the functional filler:

[0094] Figure 3 This is a scanning electron microscope image of the functional filler in Example 1 magnified 20,000 times. Figure 4 This is a scanning electron microscope image of the functional filler in Example 1 magnified 50,000 times. Figure 3 and Figure 4 It can be seen that the functional filler prepared in Example 1 has an irregular flaky structure, porous channels are distributed on the surface, β-cyclodextrin molecules are closely arranged, and the white bright area shows that the ionic liquid fills the gap; the pore structure of the functional filler provides an additional transmission channel for lithium ions, allowing lithium ions to pass through the material more easily, thereby improving the transmission efficiency of lithium ions; the pore structure can also increase the effective specific surface area, providing more active sites for lithium ions, thereby further improving the performance of the battery.

[0095] 4. The thermogravimetric curve test of the functional filler β-cyclodextrin inclusion ionic liquid in Example 1 was performed to explore the thermal stability of the functional filler:

[0096] Figure 5 is the thermogravimetric curve of the functional filler in Example 1, Figure 5 It can be seen that the main thermal decomposition of the functional filler occurs at 250-350°C, corresponding to the decomposition of the ionic liquid and β-cyclodextrin complex, indicating that the functional filler has good thermal stability and can meet the battery operating temperature requirements (usually <80°C); the glass transition temperature (Tg) of the functional filler is lower than 100°C, indicating that the material is flexible at room temperature. The low glass transition temperature can enhance creep ability and is beneficial to the migration of lithium ions in the polymer chain segments.

[0097] 5. Mechanical properties tests were performed on the solid electrolytes in Example 1 and Comparative Example 1:

[0098] The test was carried out with reference to GB / T 1040.1-2018 "Determination of tensile properties of plastics". Specifically, the solid electrolytes in Example 1 and Comparative Example 1 were cut into rectangular film specimens with a length of 100 mm and a width of 20 mm. The specimens were placed in the two clamps of an electronic stretching machine for testing. During the test, the longitudinal axis of the specimen was aligned with the center line of the upper and lower clamps, and the tightness was appropriate to prevent the specimen from slipping and breaking in the clamps. The clamps should be lined with elastic materials such as rubber. The experimental speed was 2±0.5 m / min.

[0099] Figure 6 is the stress-strain diagram of the solid electrolyte in Example 1, Figure 7 is the stress-strain diagram of the solid electrolyte in comparative example 1, and Table 1 is the stress-strain test results of the solid electrolyte in embodiment 1 and comparative example 1. Figure 6 、 Figure 7 As shown in Table 1, the solid electrolyte prepared in Example 1 has excellent mechanical properties, and its stress increases rapidly in a lower strain range and maintains a high level in a higher strain range. Compared with the traditional solid polymer electrolyte prepared in Comparative Example 1, its mechanical strength and toughness are significantly improved, indicating that the physical crosslinking of the rigid ring structure of β-cyclodextrin and the polymer chain can improve the mechanical properties of the polymer electrolyte membrane, thereby effectively inhibiting the growth of lithium dendrites.

[0100] Table 1 Stress-strain test results of the solid electrolytes in Example 1 and Comparative Example 1

[0101] Material Example 1 Comparative Example 1 Tensile strength (MPa) 0.25 0.12 Fracture strain (%) 400 50

[0102] 6. Electrochemical impedance spectroscopy test was performed on the solid electrolytes in Example 1 and Comparative Example 1:

[0103] The solid electrolytes in Example 1 and Comparative Example 1 were respectively used to assemble lithium-ion batteries, wherein the positive electrode was a LiFePO4 electrode, and the assembly structure consisted of an anode shell, a spring, a gasket, an electrolyte membrane, a gasket, and a cathode shell. The batteries were then used for electrochemical impedance spectroscopy testing. The assembly of the lithium-ion batteries was carried out in a glove box under an argon atmosphere to avoid the influence of moisture and oxygen on the experimental results.

[0104] All batteries were pressurized to 50 N under a press and subjected to AC impedance spectroscopy testing using a CHI660E electrochemical workstation. The frequency of the AC impedance spectroscopy test was 106 Hz and the amplitude was 5 mV.

[0105] The ionic conductivity is calculated from the measured impedance value according to the following formula:

[0106] Where R is the AC impedance of the electrolyte membrane obtained from the impedance diagram, in Ω, L is the thickness of the electrolyte membrane, in cm, and S is the effective contact area between the electrolyte and the electrode, in cm 2 Considering that the membrane will become thinner under pressure when installing the battery, the actual thickness of the membrane needs to be measured after disassembling the test battery. The above tests are carried out at 25℃.

[0107] Figure 8 is the electrochemical impedance spectroscopy of the solid electrolyte in Example 1, Figure 9 is the electrochemical impedance spectrum of the solid electrolyte in comparative example 1, and Table 2 is the electrochemical impedance spectrum test results of the solid electrolyte in embodiment 1 and comparative example 1. Figure 8 、 Figure 9 As shown in Table 2, compared with the traditional solid polymer electrolyte prepared in Comparative Example 1, the solid electrolyte in Example 1 has lower interfacial impedance and higher ionic conductivity, which indicates that the addition of the functional filler β-cyclodextrin inclusion ionic liquid promotes the rapid transport of ions at the interface between the electrolyte and the electrode, ensures the electrode / electrolyte contact, and helps to achieve high-speed charging of the battery.

[0108] Table 2 Electrochemical impedance spectroscopy test results of solid electrolytes in Example 1 and Comparative Example 1

[0109] Material Example 1 Comparative Example 1 Interface impedance (Ω) 13.0 19.2 Ionic conductivity (S / cm) <![CDATA[3.82×10 -4 ]]> <![CDATA[2.59×10 -4 ]]>

Claims

1. A solid electrolyte, characterized in that The solid electrolyte is a solid polymer electrolyte modified by adding a functional filler; the functional filler is a beta-cyclodextrin inclusion ionic liquid.

2. The solid electrolyte according to claim 1, characterized in that The functional filler is prepared from the following raw materials: beta-cyclodextrin, ionic liquid and water.

3. The solid electrolyte according to claim 2, characterized in that The mass ratio of the beta-cyclodextrin, the ionic liquid and the water is (2-5):1:(80-120).

4. The solid electrolyte according to claim 2, characterized in that The functional filler is prepared by a method comprising the following steps: mixing various raw materials and removing water to obtain the functional filler.

5. The solid electrolyte according to any one of claims 1 to 4, characterized in that The solid electrolyte is prepared from the following raw materials: functional filler, polymer matrix, lithium salt and solvent.

6. The solid electrolyte according to claim 5, characterized in that The mass ratio of the functional filler, the polymer matrix, the lithium salt and the solvent is 1:(3-6):(3.5-6):(14-20).

7. The solid electrolyte according to claim 5, characterized in that The polymer matrix is ​​selected from at least one of polyvinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polychlorotrifluoroethylene, and polyvinylidene fluoride; and / or, the lithium salt is selected from at least one of lithium bis(trifluoromethanesulfonyl imide), lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(fluorosulfonyl imide), lithium difluorophosphate, and lithium tetrafluoroborate; And / or, the solvent is selected from at least one of N,N-dimethylformamide, N-methylpyrrolidone, ethylene glycol dimethyl ether, and dimethyl carbonate.

8. The method for preparing a solid electrolyte according to any one of claims 5 to 7, characterized in that: The following steps are involved: S1, mixing a functional filler, a polymer matrix, a lithium salt and a solvent to obtain an electrolyte precursor solution; S2. Forming a film of the electrolyte precursor solution on a carrier to obtain the solid electrolyte.

9. The preparation method according to claim 8, characterized in that In step S1, the mixing temperature is 50-70°C and the mixing time is 10-15h; And / or, in step S2, the film forming temperature is 20-30°C, the humidity is 70%RH-85%RH, and the time is 2-5 hours.

10. A lithium metal battery, characterized in that: The solid electrolyte comprises the solid electrolyte according to any one of claims 1 to 7.

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