A polymer electrolyte, its preparation method and application

Abstract

This invention provides a polymer electrolyte, its preparation method, and its application. The raw materials of the polymer electrolyte, by mass, include the following components: 8-12 parts of an olefin polymer, 4-8 parts of a sodium salt, 0.4-1.2 parts of hydrophobic fumed silica (SiO2), 7-30 parts of a fluorinated small-molecule plasticizer, and 35-85 parts of a solvent. The polymer electrolyte of this invention uses a fluorinated small-molecule plasticizer with weak solvation ability as the plasticizer in the electrolyte, which improves the mechanical properties of the electrolyte membrane. Simultaneously, it forms a competitive coordination effect with the residual solvent with strong solvation ability, which is beneficial for inhibiting the corrosion effect of sodium salt on the current collector. The hydrophobic fumed silica filler reduces the crystallinity of the polymer matrix and enhances the mobility of the polymer matrix segments, thereby improving the ionic conductivity.

Description

Technical Field

[0001] This invention relates to the field of electric vehicle battery technology, and in particular to a polymer electrolyte, its preparation method, and its application. Background Technology

[0002] The integration of sodium-ion batteries with new energy vehicles is currently a hot topic in battery technology development and green transportation. Due to the abundance and low cost of sodium resources, rechargeable sodium-ion batteries are attracting increasing attention for large-scale stationary energy storage. Sodium-ion batteries are suitable for vehicles with a range of less than 300 kilometers (such as urban commuter cars and A0-class cars), filling the gap between lead-acid batteries (low energy density) and lithium batteries (high cost). As a differentiated technology, it possesses unique competitiveness in cost-sensitive new energy vehicle segments (such as shared cars and low-speed electric vehicles). However, when using liquid electrolytes, sodium batteries pose risks of short circuits, leakage, combustion, and explosion. Therefore, there is an urgent need for highly safe solid-state electrolytes to replace liquid electrolytes and solve these problems. Among various solid-state electrolytes, polymer solid-state electrolytes are considered the most likely to be applied to commercial solid-state batteries due to their good interfacial compatibility, flexibility, and large-scale production capabilities. To overcome the low ionic conductivity of polymer solid electrolytes, highly dissociable organic salts (such as NaTFSI and NaFSI) and certain plasticizers are typically used to ensure their electrochemical performance. However, this also poses a risk of combustion during rapid exothermic short circuits. Furthermore, in solid-state batteries using polymer electrolytes, the electrolyte gradually permeates into the positive electrode during cycling. When the voltage exceeds 3.7V, NaTFSI severely corrodes the aluminum foil current collector, causing overcharge failure. Fluorine, a small fluoride molecule, has high electronegativity and very low polarization, and is commonly used as an additive in liquid electrolytes. However, its decomposition produces hydrofluoric acid (HF), causing cathode corrosion, resulting in the loss of active sodium and electrode structural failure. To obtain a high-safety, long-life solid-state sodium battery, an electrolyte with good flame retardant properties and electrochemical stability must be designed.

[0003] Adding fillers to polymer electrolytes is a common optimization design method. Fillers can enhance their mechanical strength and ionic conductivity. However, among fillers, ordinary silica (SiO2) has relatively low purity and may contain many impurities. Its particle size is usually in the submicron to micron range, resulting in a small specific surface area. Gas-phase SiO2, on the other hand, has a three-dimensional dendritic structure on its surface, with a particle size generally between 7-40 nm. It has high purity, with a SiO2 content of not less than 99.8%. Untreated gas-phase SiO2, also known as hydrophilic gas-phase SiO2, contains highly active silanol groups (Si-OH) on its surface. It is highly polar, has high surface activity, and is hydrophilic. These silanol groups easily interact through hydrogen bonds, leading to particle aggregation and the formation of agglomerates. Due to its hydrophilicity, it has poor compatibility with organic solvents. Dispersion in organic systems requires special dispersion equipment and processes, and the dispersion process is prone to stratification and precipitation, increasing the difficulty and cost of dispersion. It has poor compatibility with hydrophobic PVDF-HFP, and is prone to interfacial compatibility problems when used as a polymer electrolyte filler.

[0004] Therefore, a comprehensive approach is still needed to improve the electrochemical performance and intrinsic safety characteristics of polymer electrolytes used in sodium-ion batteries. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of poor interfacial stability and poor filler compatibility of polymer electrolytes in sodium batteries, and to provide a polymer electrolyte, its preparation method and application.

[0006] To achieve the above objectives, the present invention provides a polymer electrolyte, wherein the raw materials of the polymer electrolyte comprise the following components by mass:

[0007] 8-12 parts of olefin polymer, 4-8 parts of sodium salt, 0.4-1.2 parts of hydrophobic fumed SiO2, 7-30 parts of fluorinated small molecule plasticizer, and 35-85 parts of solvent;

[0008] The fluorinated small molecule plasticizers include one or more of the following: fluoroethylene carbonate (FEC), difluoroethylene carbonate (DFEC), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OTE), 2H,3H-decafluoropentane (HFC), 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE), hexafluoroisopropyl methyl ether (HFME), ethoxy(pentafluoro)cyclotriphosphorus benzene (PFPN), or 3,3,4,4-tetrafluorotetrahydrofuran (TFTHF).

[0009] Hydrophobic fumed SiO2 is produced by chemically treating untreated fumed SiO2, replacing its surface hydroxyl groups with corresponding groups (usually hydrophobic groups), thus acquiring hydrophobicity. When applied to polymer electrolytes, hydrophobic fumed SiO2 can improve the electrolyte's air stability and, through electrostatic adsorption and hydrogen bonding, restrain sodium salt anions and small molecule additives, thereby enhancing the stability of the positive and negative electrodes in sodium batteries. Simultaneously, it can be uniformly dispersed in various polar solvents during preparation, forming a stable dispersion system and avoiding problems such as precipitation and agglomeration.

[0010] The polymer electrolyte of this invention uses fluorinated small molecules with weak solvation ability as plasticizers in the electrolyte to improve the mechanical properties of the electrolyte membrane; at the same time, the fluorinated small molecules form a competitive coordination effect with the residual solvent with strong solvation ability, which is beneficial to suppressing TFSI in sodium salt. - It has a corrosive effect on current collectors, and high-fluorine small molecules have good flame retardancy when applied to electrolytes.

[0011] The molecular structural formulas of fluorinated small molecules FEC and EC are as follows: Figure 9 As shown, fluorine, with its extremely high electronegativity and minimal polarization, enables additives containing fluorine to have low LUMO and HOMO energy levels. This chemical property significantly enhances their antioxidant properties. Fluorinated small molecules also have a high flash point, which helps to improve the flame retardancy of the electrolyte.

[0012] Hydrophobic vapor-phase SiO2 exhibits a significant electrostatic adsorption effect on electronegative groups in sodium salts and fluorinated small molecule plasticizers. This adsorption effect inhibits interfacial side reactions and increases interfacial stability. At the same time, it forms an SEI with lower impedance and higher stability on the negative electrode side, effectively inhibiting dendrite growth, reducing interfacial resistance, and thus improving the interfacial stability between the electrolyte and the negative electrode.

[0013] Preferably, the olefin polymer includes one or more of polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymer, poly(vinylidene fluoride-trifluoroethylene) copolymer, poly(vinylidene fluoride-tetrafluoroethylene) copolymer, or poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) copolymer.

[0014] The olefin polymers selected in this application have high dielectric constants and mechanical properties, and high ability to dissociate sodium salts.

[0015] Preferably, the sodium salt comprises one or more of sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium hexafluorophosphate, sodium difluorophosphate, sodium tetrafluoroborate, sodium difluorooxalate borate, sodium bis(oxalate borate), or sodium perchlorate.

[0016] Preferably, the solvent includes one or more of tetrahydrofuran, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, acetone, or 2,2,2-trifluoro-N,N-dimethylacetamide.

[0017] The main function of solvents is not only to dissolve polymers to form films, but also to remain in electrolytes to transport ions. However, simple residual solvents are unstable and are prone to side reactions at the interface during electrochemical processes. Therefore, the fluorinated small molecules selected in this invention can combine with residual solvents to form a competitive coordination effect and avoid side reactions.

[0018] Under the same technical concept, the present invention also provides a method for preparing a polymer electrolyte, comprising the following steps:

[0019] (1) Mix and disperse olefin polymers, sodium salts, hydrophobic gaseous SiO2 and fluorinated small molecule plasticizers with solvents to obtain a highly stable electrolyte slurry;

[0020] (2) The high-stability electrolyte slurry obtained in step (1) is cast and shaped, and then dried by blowing air to remove the solvent. The temperature is 60℃~90℃ and the time is 15min~45min to obtain the polymer electrolyte.

[0021] Preferably, the mixing method in step (1) is stirring, the stirring temperature is 25℃~45℃, and the stirring time is 6h~14h; the dispersion method is ultrasonic dispersion, and the dispersion time is 15min~45min.

[0022] Preferably, the casting and shaping in step (2) includes casting the high-stability electrolyte slurry onto a glass plate or a polytetrafluoroethylene mold; the casting and shaping takes place in an environment with a dew point of less than -40°C during forced-air drying.

[0023] Preferably, the blower drying is carried out in an argon atmosphere.

[0024] Under the same technical concept, the present invention also provides an application of a polymer electrolyte, wherein the polymer electrolyte or the polymer electrolyte prepared by the preparation method is used in a sodium solid-state battery, wherein the structure of the sodium solid-state battery is a positive electrode, the polymer electrolyte layer and the negative electrode stacked sequentially.

[0025] Preferably, the positive electrode sheet includes an active material, a conductive agent, a binder, and an additive, wherein the additive includes an ion conductor;

[0026] The thickness of the polymer electrolyte layer is 20-200 μm;

[0027] The negative electrode includes at least one of sodium metal, hard carbon, metal oxide negative electrode, or current collector without negative electrode.

[0028] The above-described solution of the present invention has the following beneficial effects:

[0029] (1) The polymer electrolyte of the present invention uses fluorinated small molecules with weak solvation ability as plasticizers in the electrolyte to improve the mechanical properties of the electrolyte membrane. At the same time, it forms a competitive coordination effect with the residual solvent with strong solvation ability, which is beneficial to suppress the corrosion effect of sodium salt on the current collector. In addition, the application of high fluorine small molecules in the electrolyte has good flame retardancy.

[0030] (2) The hydrophobic vapor-phase SiO2 filler added in this invention reduces the crystallinity of the polymer matrix and enhances the mobility of polymer matrix segments, thereby improving ionic conductivity. Simultaneously, the hydrophobic vapor-phase SiO2 has a very small particle size, a large specific surface area, and strong surface adsorption. Under hydrogen bonding, it can enhance thixotropy, improving the uniformity and stability of the filler dispersion in the polymer. The hydrophobic vapor-phase SiO2 exhibits a significant electrostatic adsorption effect on the electronegative groups in sodium salts and fluorinated plasticizers. This adsorption effect inhibits interfacial side reactions, increases interfacial stability, and simultaneously forms an SEI with lower impedance and higher stability on the negative electrode side, effectively inhibiting dendrite growth, reducing interfacial resistance, and thus improving the interfacial stability between the electrolyte and the negative electrode.

[0031] (3) The sodium solid-state battery proposed in this invention can stably cycle 1000 times at 1C rate at room temperature with a capacity retention rate of 77.35% and has excellent safety performance. It has great potential for practical application in new energy vehicles and is conducive to research and practical application.

[0032] Other beneficial effects of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0033] Figure 1 This is a physical image of the hydrophobic vapor phase SiO2 packing material used in the embodiments of the present invention;

[0034] Figure 2 These are physical images of the highly stable polymer electrolyte slurry prepared in the embodiments and comparative examples of this invention;

[0035] Figure 3 This is a photograph of the polymer electrolyte obtained in the embodiments of the present invention;

[0036] Figure 4 Here is a SEM image of the polymer electrolyte prepared in the embodiments of the present invention;

[0037] Figure 5 This refers to the ionic conductivity of the polymer electrolyte prepared in the embodiments and comparative examples of the present invention;

[0038] Figure 6This refers to the flame retardancy of the polymer electrolytes prepared in the embodiments and comparative examples of the present invention;

[0039] Figure 7 The room temperature electrochemical performance of the polymer electrolyte assembled coin cells prepared in the embodiments and comparative examples of this invention;

[0040] Figure 8 These are actual images showing the corrosion of the positive electrode aluminum foil after the battery was disassembled after 100 cycles in the embodiments and comparative examples of this invention.

[0041] Figure 9 These are the molecular structural formulas of FEC and EC. Detailed Implementation

[0042] To make the technical problems, solutions, and advantages of this invention clearer, a detailed description will be provided below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0043] In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0044] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a locking connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0045] Furthermore, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0046] Example 1

[0047] The polymer electrolyte raw material provided in this embodiment includes the following components:

[0048] 1 g of poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP, Mw = 400,000, Sigma-Aldrich); 0.8 g of sodium bis(trifluoromethanesulfonyl)imide (NaTFSI, Dodo reagent, purity ≥ 99.5%); and 0.8 g of commercial hydrophobic vapor phase SiO2 filler (Aladdin, purity ≥ 99.8%, specific surface area 400 μm). 2 / g, particle size 7-40nm, hydrophobic vapor phase SiO2 filler material physical image as shown below Figure 1 (As shown) 0.08g; fluoroethylene carbonate (FEC, Duoduo reagent, purity ≥99.9%, density 1.454g / ml) 1ml; N,N-dimethylformamide (DMF, Aladdin, purity ≥99.8%, density 0.948g / ml) 3ml; acetone (AC, Chengdu Kelon, AR, density 0.7899g / ml) 1ml;

[0049] This embodiment provides a method for preparing a polymer electrolyte, comprising the following steps:

[0050] (1) PVDF-HFP, NaTFSI, commercial hydrophobic vapor phase SiO2 filler, FEC, DMF, and AC were placed in a serum bottle. The temperature was set at 40℃, the stirring speed at 800 r / min, and the mixture was stirred for 12 h. Then, it was ultrasonically dispersed for 15 min to obtain a high-stability polymer electrolyte slurry. The sedimentation of the slurry was observed. The actual image of the high-stability polymer electrolyte slurry is shown below. Figure 2 As shown;

[0051] (2) The high-stability electrolyte slurry obtained in step (1) was poured onto a glass plate in a dry environment with a humidity dew point < -40℃, and then placed in a forced-air drying oven to remove the solvent by forced-air drying. The forced-air drying was carried out in an argon atmosphere at a baking temperature of 75℃ for 25 minutes to obtain the polymer electrolyte. The physical image and SEM image of the obtained polymer electrolyte are shown below. Figure 3 , 4 As shown, where Figure 4 (a) under a 10 μm magnifying electron microscope. Figure 4 (b) is under a 20 μm magnifying electron microscope.

[0052] (3) Cut the polymer electrolyte obtained in step (2) into 19mm round pieces, and test the ionic conductivity and flame retardancy of the polymer electrolyte. The resulting graphs of the ionic conductivity and flame retardancy of the polymer electrolyte are shown in the figure. Figure 5 , 6 As shown;

[0053] The ionic conductivity (σ) test method is as follows: Assemble a stainless steel / polymer electrolyte membrane / stainless steel symmetrical cell. Obtain the impedance R by AC impedance spectroscopy using an electrochemical workstation. Calculate the ionic conductivity data using the formula σ = L / RS, where L is the thickness of the solid electrolyte, R is the measured impedance, and S is the area of ​​the stainless steel sheet.

[0054] The flame retardancy test method is as follows: place the polymer electrolyte membrane at a certain height above the flame for the same period of time and observe the combustion. Figure 6 In the image, the left image shows a distance of 1 cm from the flame, the middle image shows a distance of 0 cm from the flame, and the right image shows the combustion observed after 1.5 seconds at a distance of 0 cm from the flame.

[0055] (4) A sodium metal coin cell solid-state battery with a sodium vanadium phosphate (NVP) positive electrode was assembled in the stacking order of positive electrode, polymer electrolyte, and negative electrode, and the electrochemical performance of the coin cell battery was tested. The electrochemical performance testing method is as follows: Charge-discharge cycle tests were conducted at room temperature within a voltage range of 2.0–3.8V using a 1C rate to test the cycle performance of the battery, and the capacity retention rate (%) of the battery after 1000 cycles was statistically analyzed. The test results of this embodiment are as follows: Figure 7 See Table 1. It exhibits stable cycling performance of 77.35% at 1C rate for 1000 cycles at room temperature, with excellent safety performance.

[0056] A sodium metal coin cell solid-state battery was cycled 100 times. The battery was then disassembled after the 100 cycles, and the corrosion of the positive electrode aluminum foil was observed. The actual corrosion condition is shown in the image below. Figure 8 As shown, where Figure 8 (a) shows the corrosion of the positive electrode in Example 1, where Figure 8 (b) shows the corrosion of the positive electrode in Comparative Example 5.

[0057] Example 2

[0058] The rest of the contents of this embodiment are consistent with those of embodiment 1, except that the amount of commercial hydrophobic gas phase SiO2 filler added in step (1) is changed to 0.04g.

[0059] The ionic conductivity and flame retardancy of the composite solid electrolyte membrane in this embodiment, the cycle performance of the coin cell, and the corrosion of the positive electrode aluminum foil after cycling were tested. The results are shown in Table 1.

[0060] Example 3

[0061] The rest of the contents of this embodiment are consistent with those of embodiment 1, except that the amount of commercial hydrophobic gas phase SiO2 filler added in step (1) is changed to 0.12g.

[0062] The ionic conductivity and flame retardancy of the composite solid electrolyte membrane in this embodiment, the cycle performance of the coin cell, and the corrosion of the positive electrode aluminum foil after cycling were tested. The results are shown in Table 1.

[0063] Example 4

[0064] The rest of the contents of this embodiment are consistent with those of embodiment 1, except that the amount of FEC added in step (1) is changed to 0.5 ml.

[0065] The ionic conductivity and flame retardancy of the composite solid electrolyte membrane in this embodiment, the cycle performance of the coin cell, and the corrosion of the positive electrode aluminum foil after cycling were tested. The results are shown in Table 1.

[0066] Example 5

[0067] The rest of the contents of this embodiment are the same as those of embodiment 1, except that the amount of FEC added in step (1) is changed to 2 ml.

[0068] The ionic conductivity and flame retardancy of the composite solid electrolyte membrane in this embodiment, the cycle performance of the coin cell, and the corrosion of the positive electrode aluminum foil after cycling were tested. The results are shown in Table 1.

[0069] Example 6

[0070] The rest of the contents of this embodiment are consistent with those of embodiment 1, except that the plasticizer in step (1) is changed from FEC to DFEC and the amount added is 1ml.

[0071] The ionic conductivity and flame retardancy of the composite solid electrolyte membrane in this embodiment, the cycle performance of the coin cell, and the corrosion of the positive electrode aluminum foil after cycling were tested. The resulting polymer electrolyte ionic conductivity graph is shown in the figure below. Figure 5 As shown in Table 1, the results are as follows.

[0072] Example 7

[0073] The rest of the contents of this embodiment are consistent with those of embodiment 1, except that the plasticizer in step (1) is changed from FEC to TTE and the amount added is 1ml.

[0074] The ionic conductivity and flame retardancy of the composite solid electrolyte membrane in this embodiment, the cycle performance of the coin cell, and the corrosion of the positive electrode aluminum foil after cycling were tested. The results are shown in Table 1.

[0075] Example 8

[0076] The rest of the contents of this embodiment are consistent with those of embodiment 1, except that the plasticizer in step (1) is changed from FEC to PFPN and the amount added is 1ml.

[0077] The ionic conductivity and flame retardancy of the composite solid electrolyte membrane in this embodiment, the cycle performance of the coin cell, and the corrosion of the positive electrode aluminum foil after cycling were tested. The results are shown in Table 1.

[0078] Comparative Example 1

[0079] The rest of the contents of this embodiment are consistent with those of embodiment 1, except that the temperature of the forced-air baking in step (2) is changed to 120°C.

[0080] The ionic conductivity, flame retardancy, coin cell cycle performance, and post-cycle corrosion of the positive electrode aluminum foil of this comparative composite solid electrolyte membrane were tested, and the results are shown in Table 1. When the drying temperature of the electrolyte membrane is too low, there is too much residual solvent and plasticizer inside the electrolyte membrane, and the mechanical properties of the polymer electrolyte do not meet the requirements for battery applications. When the drying temperature of the electrolyte membrane is too high, the residual solvent and plasticizer inside the electrolyte membrane are too low, the polymer interior is mainly composed of crystalline regions, ion migration is difficult, resulting in low ionic conductivity, poor cycle stability, and the electrolyte membrane is flammable when exposed to open flame.

[0081] Comparative Example 2

[0082] The majority of the process is the same as in Example 1, except that the blowing time in step (2) is changed to 60 minutes.

[0083] The ionic conductivity and flame retardancy, coin cell cycle performance, and corrosion of the positive electrode aluminum foil after cycling of this comparative composite solid electrolyte membrane were tested, and the results are shown in Table 1. The baking time and baking temperature of the electrolyte membrane both affect its internal structure, showing similar effects. Excessive baking time reduces the plasticizer content inside the electrolyte membrane, resulting in poor flame retardancy.

[0084] Comparative Example 3

[0085] It is largely the same as Example 1, except that the addition of FEC plasticizer in step (1) is removed.

[0086] The ionic conductivity and flame retardancy of the comparative composite solid electrolyte membrane, the cycle performance of the coin cell, and the corrosion of the positive electrode aluminum foil after cycling were tested. The resulting graphs of polymer electrolyte ionic conductivity and flame retardancy are shown in the figure. Figure 5 , 6 As shown, the room temperature electrochemical performance of the polymer electrolyte assembled coin cell is as follows: Figure 7 As shown in Table 1, the results indicate that FEC exhibits excellent flame retardant properties. Removing the FEC plasticizer increases the crystalline regions of the polymer electrolyte, reduces ionic conductivity, and eliminates its flame-retardant effect. Residual solvents in the electrolyte undergo continuous side reactions with lithium metal, leading to battery failure.

[0087] Comparative Example 4

[0088] The two methods are largely the same as in Example 1, except that the amount of FEC added in step (1) is changed to 3 ml.

[0089] Excessive addition of FEC plasticizer can lead to an overly thin polymer electrolyte slurry, causing polymer structure rupture and failure to form a film after baking. This results in unsatisfactory performance in practical applications.

[0090] Comparative Example 5

[0091] Compared with Example 1, most of them are the same, except that the hydrophobic gaseous SiO2 filler added in step (1) is removed.

[0092] The ionic conductivity and flame retardancy of this comparative composite solid electrolyte membrane, the coin cell cycle performance, and the corrosion of the positive electrode aluminum foil after cycling were tested. The resulting polymer electrolyte ionic conductivity graph is shown in the figure below. Figure 5 As shown in Table 1, the results were obtained by cycling the sodium metal coin cell solid-state battery 100 times. The coin cell was then disassembled after 100 cycles, and the corrosion of the positive electrode aluminum foil was observed. Images of the corrosion are shown below. Figure 8 As shown.

[0093] Hydrophobic vapor-phase SiO2 fillers can reduce the crystallinity of electrolytes and simultaneously improve the performance of TFSI. - FEC has an adsorption effect. Removing the hydrophobic gaseous SiO2 filler will reduce the ionic conductivity and will not prevent TFSI from forming during the cycle. - Corrosion of the positive electrode aluminum foil causes the positive electrode plate to detach from the current collector, leading to overcharge failure of the battery. Furthermore, FEC and TFSI... - Continuous participation in electrochemical decomposition increases interfacial impedance, damages the electrolyte membrane structure, and leads to cycle failure.

[0094] Comparative Example 6

[0095] The process is largely the same as in Example 1, except that the addition of hydrophobic vapor-phase SiO2 filler and FEC plasticizer in step (1) is removed. A physical image of the high-stability polymer electrolyte slurry is shown below. Figure 2 As shown;

[0096] The ionic conductivity and flame retardancy of this comparative composite solid electrolyte membrane, the coin cell cycle performance, and the corrosion of the positive electrode aluminum foil after cycling were tested. The resulting polymer electrolyte ionic conductivity graph is shown in the figure below. Figure 5 As shown in Table 1, the results indicate that hydrophobic vapor-phase SiO2 filler can reduce the crystallinity of the electrolyte and simultaneously improve the TFSI... - FEC has an adsorption effect. Removing the hydrophobic gaseous SiO2 filler will reduce the ionic conductivity and will not prevent TFSI from forming during the cycle. -Corrosion of the positive electrode aluminum foil causes the positive electrode plate to detach from the current collector, leading to overcharge failure of the battery. Furthermore, FEC and TFSI... - Continuous participation in electrochemical decomposition increases interfacial impedance, damages the electrolyte membrane structure, and leads to cycle failure.

[0097] Comparative Example 7

[0098] Compared to Example 1, most aspects are the same, except that the hydrophobic vapor-phase SiO2 filler in step (1) is replaced with conventional SiO2 filler. A physical image of the high-stability polymer electrolyte slurry is shown below. Figure 2 As shown;

[0099] Conventional SiO2 fillers have a large specific surface area, which makes them prone to sedimentation during the preparation of electrolyte slurries, leading to filler agglomeration and uneven distribution in the electrolyte.

[0100] Comparative Example 8

[0101] Compared to Example 1, most aspects are the same, except that the hydrophobic vapor-phase SiO2 filler in step (1) is replaced with a hydrophilic vapor-phase SiO2 filler. A physical image of the high-stability polymer electrolyte slurry is shown below. Figure 2 As shown;

[0102] The hydrophilic silanol groups on the surface of the hydrophilic vapor phase SiO2 filler cannot disperse in the slurry containing PVDF-HFP and will float on the top layer of the slurry.

[0103] Comparative Example 9

[0104] Compared to Example 1, most aspects are the same, except that the amount of commercial hydrophobic vapor-phase SiO2 filler added in step (1) is changed to 0.2 g. A physical image of the high-stability polymer electrolyte slurry is shown below. Figure 2 As shown;

[0105] Hydrophobic vapor phase SiO2 has a large specific surface area. When the amount added is too large, the viscosity of the electrolyte slurry becomes too high, and it forms a gel that sticks to the inner wall of the serum bottle, making it impossible to form a film.

[0106] Comparative Example 10

[0107] Compared with Example 1, most of them are the same, except that the fluorinated small molecule plasticizer FEC in step (1) is replaced with EC which has a similar structure but does not contain fluorine.

[0108] Electrochemicals without fluorine do not have flame retardancy. The hydrophobic gaseous SiO2 has a weak effect on the electrochemicals and cannot suppress interfacial side reactions, resulting in poor electrochemical performance.

[0109] Table 1: Performance test results of the examples and comparative examples

[0110]

[0111]

[0112] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A polymer electrolyte, characterized in that, The raw materials for the polymer electrolyte, by mass, include the following components: 8-12 parts of olefin polymer, 4-8 parts of sodium salt, 0.4-1.2 parts of hydrophobic fumed SiO2, 7-30 parts of fluorinated small molecule plasticizer, and 35-85 parts of solvent; The fluorinated small molecule plasticizers include one or more of the following: fluoroethylene carbonate, difluoroethylene carbonate, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, 2H,3H-decafluoropentane, 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether, hexafluoroisopropyl methyl ether, ethoxy(pentafluoro)cyclotriphosphine, or 3,3,4,4-tetrafluorotetrahydrofuran. The solvent includes one or more of tetrahydrofuran, N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide, acetone, or 2,2,2-trifluoro-N,N-dimethylacetamide.

2. The polymer electrolyte as described in claim 1, characterized in that, The olefin polymers include one or more of polyvinylidene fluoride, poly(vinylidene fluoride-hexafluoropropylene) copolymer, poly(vinylidene fluoride-trifluoroethylene) copolymer, poly(vinylidene fluoride-tetrafluoroethylene) copolymer, or poly(vinylidene fluoride-trifluoroethylene-trifluorochloroethylene) copolymer.

3. The polymer electrolyte according to claim 1, characterized in that, The sodium salt includes one or more of sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium hexafluorophosphate, sodium difluorophosphate, sodium tetrafluoroborate, sodium difluorooxalate borate, sodium dioxalate borate, or sodium perchlorate.

4. A method for preparing a polymer electrolyte as described in any one of claims 1-3, characterized in that, Includes the following steps: (1) Mix and disperse olefin polymers, sodium salts, hydrophobic gaseous SiO2 and fluorinated small molecule plasticizers with solvents to obtain a highly stable electrolyte slurry; (2) The high-stability electrolyte slurry obtained in step (1) is cast and shaped, and then dried by blowing air to remove the solvent. The temperature is 60℃~90℃ and the time is 15min~45min to obtain the polymer electrolyte.

5. The preparation method according to claim 4, characterized in that, The mixing method in step (1) is stirring, the stirring temperature is 25℃~45℃, and the time is 6h~14h; the dispersion method is ultrasonic dispersion, and the dispersion time is 15min~45min.

6. The preparation method according to claim 4, characterized in that, The casting and shaping in step (2) includes casting the high-stability electrolyte slurry onto a glass plate or a polytetrafluoroethylene mold; the casting and shaping takes place in an environment with a dew point of less than -40°C during forced-air drying.

7. The preparation method according to claim 6, characterized in that, The blower drying is carried out under an argon atmosphere.

8. An application of a polymer electrolyte, wherein the polymer electrolyte as described in any one of claims 1-3 or the polymer electrolyte prepared by the preparation method as described in any one of claims 4-7 is used in a sodium solid-state battery, characterized in that, The sodium solid-state battery has a structure consisting of a positive electrode, a polymer electrolyte layer, and a negative electrode stacked sequentially.

9. The application as described in claim 8, characterized in that, The positive electrode sheet includes an active material, a conductive agent, a binder, and additives, wherein the additives include ion conductors; The thickness of the polymer electrolyte layer is 20-200 μm; The negative electrode includes at least one of sodium metal, hard carbon, metal oxide negative electrode, or a current collector without a negative electrode.

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