Polymer electrolyte and preparation method and application thereof

Abstract

The invention provides a polymer electrolyte and a preparation method and application thereof, the polymer electrolyte comprises the following raw materials by mass: 8-12 parts of an alkene polymer, 4-8 parts of a sodium salt, 0.4-1.2 parts of hydrophobic gas phase SiO2, 7-30 parts of a fluorinated small molecule plasticizer, and 35-85 parts of a solvent; the polymer electrolyte disclosed by the invention adopts fluorinated small molecules with relatively weak solvation ability as a plasticizer in the electrolyte, so that the mechanical property of an electrolyte membrane is improved, and meanwhile, the fluorinated small molecules and a residual solvent with relatively strong solvation ability form a competitive coordination effect, so that the corrosion effect of sodium salt on a current collector is favorably inhibited, and the hydrophobic gas-phase SiO2 filler is beneficial to improving the corrosion resistance of the current collector. The crystallinity of a polymer matrix is reduced, and the activity of a chain segment of the polymer matrix is enhanced, so that the ionic conductivity is improved.

Description

Technical Field

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

[0002] The combination of sodium-ion batteries and new energy vehicles is one of the current hot topics in the development of battery technology and green transportation. Due to the abundant sodium resources and low cost, rechargeable sodium-ion batteries have received increasing attention in large-scale stationary energy storage. Sodium-ion batteries are suitable for vehicles with a range of less than 300 kilometers (such as urban commuter vehicles and A0-class vehicles), filling the gap between lead-acid batteries (low energy density) and lithium batteries (high cost). As a differentiated technology route, they have unique competitiveness in the cost-sensitive new energy vehicle market segment (such as shared cars and low-speed electric vehicles). However, when using liquid electrolytes, sodium batteries are subject to the risks of battery short circuit, liquid electrolyte leakage, combustion and explosion. Therefore, there is an urgent need for highly safe solid electrolytes to replace liquid electrolytes to solve the above problems. Among the various solid electrolytes, polymer solid electrolytes are considered to be the most likely to be used in commercial solid-state batteries due to their good interface compatibility, flexibility and large-scale preparation. In order to overcome the disadvantage of low ionic conductivity of polymer solid electrolytes, it is usually necessary to use organic salts with high dissociation degree (such as NaTFSI and NaFSI) and certain plasticizers to ensure their electrochemical performance, which also brings the risk of combustion when the battery short circuit causes rapid heat release. In addition, during the cycle of solid-state batteries using polymer electrolytes, the electrolyte will gradually penetrate into the interior of the positive electrode. When the voltage is higher than 3.7V, NaTFSI will seriously corrode the aluminum foil current collector, causing the battery to overcharge and fail. The fluorine element in fluorinated small molecules has high electronegativity and extremely small polarization properties. It is often used as a liquid electrolyte additive, but hydrofluoric acid (HF) will be produced during the decomposition process, causing cathode corrosion, resulting in the loss of active sodium and failure of the electrode structure. In order to obtain a good, high-safety, and long-life solid-state sodium battery, it is necessary to design an electrolyte with good flame retardant properties and electrochemical stability.

[0003] Adding fillers to polymer electrolytes is a common optimization design method. Fillers can be used to enhance their mechanical strength and ionic conductivity. However, among fillers, ordinary silicon dioxide (SiO2) has relatively low purity, may contain a large number of impurities, and has a particle size typically ranging from submicron to micron, resulting in a small specific surface area. Vapor-phase SiO2 has a three-dimensional dendritic structure on its surface, with a particle size generally ranging from 7-40nm, high purity, and a SiO2 content of no less than 99.8%. Untreated vapor-phase SiO2, also known as hydrophilic vapor-phase SiO2, contains highly reactive silanol (Si-OH) groups on its surface, which are highly polar, highly active, and hydrophilic. These silanol groups readily interact through hydrogen bonds, causing particles to aggregate and form agglomerates. Due to its hydrophilic nature, it has poor compatibility with organic solvents, requiring specialized dispersion equipment and processes for dispersion in organic systems. Furthermore, stratification and precipitation are prone to occur during the dispersion process, increasing the difficulty and cost of dispersion. It has poor compatibility with hydrophobic PVDF-HFP and is prone to poor interfacial solubility when used as a polymer electrolyte filler.

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

[0005] The purpose of the present invention is to solve the problems of poor interface stability and poor compatibility of fillers in sodium battery polymer electrolytes, and to provide a polymer electrolyte and its preparation method and application.

[0006] In order to achieve the above object, the present invention provides a polymer electrolyte, wherein the raw materials of the polymer electrolyte include the following components in parts by mass:

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

[0008] The fluorinated small molecule plasticizer includes one or more of fluoroethylene carbonate (FEC), bisfluoroethylene 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) cyclotriphosphine (PFPN) or 3,3,4,4-tetrafluorotetrahydrofuran (TFTHF).

[0009] Hydrophobic gas-phase SiO2 is made by treating untreated gas-phase SiO2 with chemical reagents, replacing the surface hydroxyl groups with corresponding groups (generally hydrophobic groups), thus becoming hydrophobic. Hydrophobic gas-phase SiO2 can be used in polymer electrolytes to improve the air stability of the electrolyte. It also has a certain ability to restrain the anions and small molecule additives of sodium salts through electrostatic adsorption and hydrogen bonding, thereby improving the stability of the positive and negative electrodes of sodium batteries. At the same time, during the preparation process, it can be evenly dispersed in various polar solvents to form a stable dispersion system, avoiding problems such as precipitation and agglomeration.

[0010] The polymer electrolyte of the present invention uses a fluorinated small molecule with a weak solvating ability as a plasticizer in the electrolyte to improve the mechanical properties of the electrolyte membrane; the fluorinated small molecule also forms a competitive coordination effect with the residual solvent with a strong solvating ability, which is beneficial to inhibit the TFSI in the sodium salt. - In addition, high-fluorine small molecules have good flame retardancy when applied to electrolytes.

[0011] The molecular structures of fluorinated small molecules FEC and EC are as follows Figure 9 As shown, due to its extremely high electronegativity and extremely small polarization characteristics, the fluorine-containing additives have lower LUMO and HOMO energy levels. This chemical property significantly improves its antioxidant performance. Fluorinated small molecules also have a high flash point, which helps to improve the flame retardancy of the electrolyte.

[0012] Hydrophobic gas-phase SiO2 exhibits a large electrostatic adsorption effect on the 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, a SEI with lower impedance and higher stability is formed on the negative electrode side, which effectively inhibits the growth of dendrites and reduces interfacial resistance, thereby improving the interfacial stability between the electrolyte and the negative electrode.

[0013] Preferably, the vinyl 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-chlorotrifluoroethylene) copolymer.

[0014] The olefinic polymer selected in the present application has a relatively high dielectric constant and mechanical properties, and has a high ability to dissociate sodium salt.

[0015] Preferably, the sodium salt includes one or more of sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium hexafluorophosphate, sodium difluorophosphate, sodium tetrafluoroborate, sodium difluorooxalatoborate, sodium bisoxalatoborate 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 the solvent is not only to dissolve the polymer to form a film, but also to remain in the electrolyte to transport ions. However, the residual solvent alone is unstable and is prone to side reactions at the interface during the electrochemical process. Therefore, the fluorinated small molecules selected in the present invention can combine with the residual solvent to form a competitive coordination effect, thereby avoiding 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) mixing an olefin polymer, a sodium salt, a hydrophobic gas-phase SiO2, and a fluorinated small molecule plasticizer with a solvent, and dispersing the mixture to obtain a high-stability electrolyte slurry;

[0020] (2) The high-stability electrolyte slurry obtained in step (1) is cast and shaped, and air-dried to remove the solvent at a temperature of 60° C. to 90° C. for 15 min to 45 min to obtain a polymer electrolyte.

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

[0022] Preferably, the casting and shaping in step (2) includes casting the high-stability electrolyte slurry on a glass plate or a polytetrafluoroethylene mold; the dew point of the ambient humidity of the casting and shaping and the forced air drying is less than -40°C.

[0023] Preferably, the forced air drying is performed under 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, and the structure of the sodium solid-state battery is a positive electrode sheet, the polymer electrolyte layer and the negative electrode stacked in sequence.

[0025] Preferably, the positive electrode plate includes an active material, a conductive agent, a binder and an additive, and 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, a metal oxide negative electrode or a negative electrode-free current collector.

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

[0029] (1) The polymer electrolyte of the present invention uses a fluorinated small molecule with a weak solvation ability as a plasticizer 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 a strong solvation ability, which is beneficial to inhibit the corrosion of the sodium salt on the current collector. In addition, the high-fluorine small molecule has good flame retardancy when applied to the electrolyte;

[0030] (2) The hydrophobic gas-phase SiO2 filler added by the present invention reduces the crystallinity of the polymer matrix and enhances the mobility of the polymer matrix chain segments, thereby improving the ionic conductivity. At the same time, the hydrophobic gas-phase SiO2 has a very small particle size, a large specific surface area, and a strong surface adsorption force. Under the action of hydrogen bonds, it can enhance thixotropy and improve the dispersion uniformity and stability of the filler in the polymer. The hydrophobic gas-phase SiO2 exhibits a large electrostatic adsorption effect on the electronegative groups in the sodium salt and the fluorinated plasticizer. This adsorption effect inhibits the interfacial side reactions and increases the interfacial stability. At the same time, a SEI with lower impedance and higher stability is formed on the negative electrode side, which effectively inhibits the growth of dendrites and reduces the interfacial resistance, thereby improving the interfacial stability between the electrolyte and the negative electrode;

[0031] (3) The sodium solid-state battery proposed in the present invention can be stably cycled for 1000 cycles at a rate of 1C at room temperature with a capacity retention rate of 77.35%. It also has excellent safety performance and has great practical prospects in new energy vehicles, which is conducive to research and practical applications.

[0032] Other beneficial effects of the present invention will be described in detail in the subsequent specific implementation section. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a physical picture of the hydrophobic gas-phase SiO2 filler used in the examples of the present invention;

[0034] Figure 2 1 is a physical picture of the high-stability polymer electrolyte slurry prepared in the examples and comparative examples of the present invention;

[0035] Figure 3 This is a physical picture of the polymer electrolyte prepared in an embodiment of the present invention;

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

[0037] Figure 5 is the ionic conductivity of the polymer electrolytes prepared in the examples and comparative examples of the present invention;

[0038] Figure 6The flame retardancy of the polymer electrolytes prepared in the examples and comparative examples of the present invention;

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

[0040] Figure 8 This is a physical picture of the corrosion of the positive electrode aluminum foil after the battery was disassembled after 100 cycles in the embodiment of the present invention and the comparative example;

[0041] Figure 9 It is the molecular structure formula of FEC and EC. DETAILED DESCRIPTION

[0042] To make the technical problems, technical solutions, and advantages to be solved by the present invention more clear, the following is a detailed description with reference to the accompanying drawings and specific embodiments. It is obvious that the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0043] In the description of the present invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," and "outer," etc., indicating orientations or positional relationships, are based on the orientations or positional relationships shown in the accompanying drawings and are intended solely to facilitate and simplify the description of the present invention. They are not intended to indicate or imply that the devices or components referred to must have, be constructed, or operate in a specific orientation, and therefore should not be construed as limitations on the present 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 the present invention, it should be noted that, unless otherwise expressly specified or limited, the terms "mounted," "connected," and "connected" should be understood broadly. For example, they may refer to a locking connection, a detachable connection, or an integral connection; they may refer to a mechanical connection or an electrical connection; they may refer to a direct connection or an indirect connection through an intermediate medium; and they may refer to internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on the specific circumstances.

[0045] In addition, 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] A polymer electrolyte raw material provided in this embodiment includes the following components:

[0048] Poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP, Mw = 400000, Sigma Merck) 1g; sodium bis(trifluoromethylsulfonyl)imide (NaTFSI, Duoduo Reagent, purity ≥ 99.5%) 0.8g; commercial hydrophobic fumed SiO2 filler (Aladdin, purity ≥ 99.8%, specific surface area 400m 2 / g, particle size 7-40nm, the actual picture of hydrophobic gas phase SiO2 filler is as follows Figure 1 0.08 g of fluoroethylene carbonate (FEC, Duoduo reagent, purity ≥99.9%, density 1.454 g / ml) 1 ml; 3 ml of N,N-dimethylformamide (DMF, Aladdin, purity ≥99.8%, density 0.948 g / ml); 1 ml of acetone (AC, Chengdu Kelon, AR, density 0.7899 g / ml);

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

[0050] (1) PVDF-HFP, NaTFSI, commercial hydrophobic gas-phase SiO2 filler, FEC, DMF and AC were placed in a serum bottle, the temperature was set to 40 ° C, the stirring speed was 800 r / min, stirring was performed for 12 h, and ultrasonic dispersion was performed for 15 min to obtain a high-stability polymer electrolyte slurry. The sedimentation of the slurry was observed. The actual picture of the high-stability polymer electrolyte slurry is shown in the figure. 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 of <-40°C, placed in a blast oven, and the solvent was removed by blast drying. The blast drying was carried out in an argon atmosphere at a baking temperature of 75°C and a baking time of 25 min to obtain a polymer electrolyte. The obtained polymer electrolyte physical image and SEM image are shown as follows: Figure 3 、 4 As shown, Figure 4 (a) is the magnification electron microscope size of 10μm. Figure 4 (b) is under the magnification electron microscope size of 20μm.

[0052] (3) The polymer electrolyte obtained in step (2) was cut into 19 mm discs, and the ionic conductivity and flame retardancy of the polymer electrolyte were tested. The ionic conductivity and flame retardancy of the obtained polymer electrolyte are shown in the figure below. Figure 5 、 6 As shown;

[0053] Ionic conductivity (σ) was measured as follows: a symmetrical stainless steel / polymer electrolyte membrane / stainless steel cell was assembled. Impedance spectroscopy (EIS) was performed using an electrochemical workstation to obtain the impedance R. Ionic conductivity data were calculated 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: the polymer electrolyte membrane is placed at a certain height above the flame and the combustion is observed for the same period of time; Figure 6 In the middle, the left picture is at a height of 1 cm from the flame, the middle picture is at a height of 0 cm from the flame, and the right picture is the combustion condition observed after a duration of 1.5 s at a height of 0 cm from the flame.

[0055] (4) A sodium metal button-type solid-state battery with a sodium vanadium phosphate (NVP) positive electrode was assembled in the order of stacking the positive electrode sheet, polymer electrolyte, and negative electrode, and the electrochemical performance of the button-type battery was tested. The electrochemical performance test method is as follows: a charge and discharge cycle test was performed at a rate of 1C in the voltage range of 2.0 to 3.8 V at room temperature to test the cycle performance of the above-mentioned battery, and the capacity retention rate (%) of the battery after 1000 cycles was calculated. The test results of this embodiment are shown in FIG. Figure 7 And Table 1. It can be stably cycled for 1000 cycles at 1C rate at room temperature with a capacity retention rate of 77.35%, and has good safety performance.

[0056] The sodium metal button solid-state battery was cycled 100 times. The button battery was disassembled after 100 cycles to observe the corrosion of the positive electrode aluminum foil. The actual corrosion situation is shown in the figure below. Figure 8 As shown, Figure 8 (a) is the positive electrode corrosion situation of Example 1, where Figure 8 (b) shows the positive electrode corrosion condition of comparative example 5.

[0057] Example 2

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

[0059] The ionic conductivity and flame retardancy of the composite solid electrolyte membrane of this embodiment, the cycle performance of the button 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 example are consistent with those of Example 1, with the only difference being that the amount of commercial hydrophobic gas-phase SiO2 filler added in step (1) is changed to 0.12 g.

[0062] The ionic conductivity and flame retardancy of the composite solid electrolyte membrane of this embodiment, the cycle performance of the button 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 example are consistent with those of Example 1, with the only difference being 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 of this embodiment, the cycle performance of the button 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 example are consistent with those of Example 1, with the only difference being 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 of this embodiment, the cycle performance of the button 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 Example 1, with the only difference being that the plasticizer in step (1) is changed from FEC to DFEC, and the addition amount is 1 ml.

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

[0072] Example 7

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

[0074] The ionic conductivity and flame retardancy of the composite solid electrolyte membrane of this embodiment, the cycle performance of the button 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, with the only difference being that the plasticizer in step (1) is changed from FEC to PFPN, and the added amount is 1 ml.

[0077] The ionic conductivity and flame retardancy of the composite solid electrolyte membrane of this embodiment, the cycle performance of the button 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, with the only difference being that the blast baking temperature in step (2) is changed to 120°C.

[0080] The composite solid-state electrolyte membrane of this comparative example was tested for ionic conductivity and flame retardancy, button cell cycling performance, and post-cycling corrosion of the positive electrode aluminum foil. The results are shown in Table 1. When the drying temperature of the electrolyte membrane is too low, excess solvent and plasticizer remain within the membrane, resulting in insufficient mechanical properties for battery applications. When the drying temperature is too high, the residual solvent and plasticizer remain too low, leading to a predominantly crystalline polymer interior and difficulty in ion migration. This results in low ionic conductivity, poor cycling stability, and flammability of the membrane when exposed to open flames.

[0081] Comparative Example 2

[0082] Compared with Example 1, most of the contents are the same, except that the blast baking time in step (2) is changed to 60 min.

[0083] The composite solid-state electrolyte membrane of this comparative example was tested for ionic conductivity and flame retardancy, as well as the cycling performance of button-type batteries and the corrosion of the positive electrode aluminum foil after cycling. The results are shown in Table 1. The baking time and temperature of the electrolyte membrane jointly affect the internal structure of the electrolyte membrane, exhibiting similar effects. Excessive baking time reduces the plasticizer content within the electrolyte membrane, resulting in poor flame retardancy.

[0084] Comparative Example 3

[0085] Compared with Example 1, most of the steps are the same except that the addition of FEC plasticizer in step (1) is removed.

[0086] The ionic conductivity and flame retardancy of the composite solid electrolyte membrane of this comparative example, the cycle performance of the button battery and the corrosion of the positive electrode aluminum foil after the cycle were tested. The ionic conductivity and flame retardancy of the polymer electrolyte obtained are shown in the figure below. Figure 5 、 6 As shown in the figure, the room temperature electrochemical performance of the prepared polymer electrolyte assembled button cell is as follows Figure 7 The results are shown in Table 1. FEC exhibits excellent flame retardancy. Removing the FEC plasticizer increases the crystalline region of the polymer electrolyte, decreases ionic conductivity, and loses its flame retardancy. Residual solvent in the electrolyte continuously reacts with lithium metal, leading to battery failure.

[0087] Comparative Example 4

[0088] Compared with Example 1, most of the steps are the same except that the amount of FEC added in step (1) is changed to 3 ml.

[0089] When the amount of plasticizer FEC added is too much, the polymer electrolyte slurry will be too thin, the polymer structure will be broken, and no film will be formed after baking, which cannot meet the requirements of practical applications.

[0090] Comparative Example 5

[0091] Compared with Example 1, most of the steps are the same except that the addition of the hydrophobic gas-phase SiO2 filler in step (1) is removed.

[0092] The ionic conductivity and flame retardancy of the composite solid electrolyte membrane of this comparative example, the cycle performance of the button battery and the corrosion of the positive electrode aluminum foil after the cycle were tested. The obtained polymer electrolyte ionic conductivity is shown in the figure below. Figure 5 The results are shown in Table 1. The sodium metal button solid-state battery was cycled 100 times. The button battery after 100 cycles was disassembled to observe the corrosion of the positive electrode aluminum foil. The actual corrosion situation is shown in the figure Figure 8 shown.

[0093] Hydrophobic fumed SiO2 fillers can reduce the crystallinity of the electrolyte and have a significant effect on TFSI - Removing the hydrophobic gas phase SiO2 filler will reduce the ionic conductivity and will not prevent TFSI during the cycle. - The corrosion of the positive electrode aluminum foil causes the positive electrode sheet to fall off from the current collector, and the battery fails due to overcharge. - Continuous participation in electrochemical reaction decomposition increases the interface impedance, destroys the electrolyte membrane structure, and causes cycle failure.

[0094] Comparative Example 6

[0095] Compared with Example 1, most of the steps are the same except that the addition of hydrophobic gas-phase SiO2 filler and FEC plasticizer in step (1) is removed. Figure 2 As shown;

[0096] The ionic conductivity and flame retardancy of the composite solid electrolyte membrane of this comparative example, the cycle performance of the button battery and the corrosion of the positive electrode aluminum foil after the cycle were tested. The obtained polymer electrolyte ionic conductivity is shown in the figure below. Figure 5 The results are shown in Table 1. Hydrophobic gas-phase SiO2 filler can reduce the crystallinity of the electrolyte and at the same time - Removing the hydrophobic gas phase SiO2 filler will reduce the ionic conductivity and will not prevent TFSI during the cycle. -The corrosion of the positive electrode aluminum foil causes the positive electrode sheet to fall off from the current collector, and the battery fails due to overcharge. - Continuous participation in electrochemical reaction decomposition increases the interface impedance, destroys the electrolyte membrane structure, and causes cycle failure.

[0097] Comparative Example 7

[0098] Compared with Example 1, most of the above are the same, except that the hydrophobic gas phase SiO2 filler in step (1) is replaced with a conventional SiO2 filler. Figure 2 As shown;

[0099] Conventional SiO2 fillers have a large specific surface area and are prone to sedimentation during the preparation of electrolyte slurry, resulting in filler agglomeration and uneven distribution in the electrolyte.

[0100] Comparative Example 8

[0101] Compared with Example 1, most of the above are the same, except that the hydrophobic gas phase SiO2 filler in step (1) is replaced by a hydrophilic gas phase SiO2 filler. Figure 2 As shown;

[0102] The hydrophilic silanol groups on the surface of the hydrophilic fumed SiO2 filler cannot be dispersed in the slurry containing PVDF-HFP and will float on the upper layer of the slurry.

[0103] Comparative Example 9

[0104] Compared with Example 1, most of the above are the same, except that the amount of commercial hydrophobic gas-phase SiO2 filler added in step (1) is changed to 0.2g. Figure 2 As shown;

[0105] The hydrophobic gas-phase SiO2 has a large specific surface area. When too much is added, the viscosity of the electrolyte slurry is too high, and it becomes a gel and sticks to the inner wall of the serum bottle, and cannot form a film.

[0106] Comparative Example 10

[0107] Compared with Example 1, most of the steps are the same except that the fluorinated small molecule plasticizer FEC in step (1) is replaced by EC having a similar structure and not containing fluorine.

[0108] EC without fluorine element is not flame retardant, and the hydrophobic gas-phase SiO2 has a weak effect on EC, which cannot inhibit the interfacial side reactions, resulting in poor electrochemical performance.

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

[0110]

[0111]

[0112] The above is a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A polymer electrolyte, characterized in that The raw materials of the polymer electrolyte include the following components in parts by mass: 8-12 parts of vinyl polymer, 4-8 parts of sodium salt, 0.4-1.2 parts of hydrophobic gas-phase SiO2, 7-30 parts of fluorinated small molecule plasticizer, and 35-85 parts of solvent; The fluorinated small molecule plasticizer includes one or more of 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.

2. The polymer electrolyte according to claim 1, wherein The vinyl 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-chlorotrifluoroethylene) copolymer.

3. The polymer electrolyte according to claim 1, wherein The sodium salt includes one or more of sodium bis(fluorosulfonyl)imide, sodium bis(trifluoromethylsulfonyl)imide, sodium hexafluorophosphate, sodium difluorophosphate, sodium tetrafluoroborate, sodium difluorooxalatoborate, sodium bisoxalatoborate or sodium perchlorate.

4. The polymer electrolyte according to claim 1, wherein 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.

5. A method for preparing a polymer electrolyte, characterized in that: The following steps are involved: (1) mixing an olefin polymer, a sodium salt, a hydrophobic gas-phase SiO2, and a fluorinated small molecule plasticizer with a solvent, and dispersing the mixture to obtain a high-stability electrolyte slurry; (2) The high-stability electrolyte slurry obtained in step (1) is cast and shaped, and air-dried to remove the solvent at a temperature of 60° C. to 90° C. for 15 min to 45 min to obtain a polymer electrolyte.

6. The preparation method according to claim 5, wherein The mixing method in step (1) is stirring, the stirring temperature is 25° C. to 45° C., and the stirring time is 6 h to 14 h; the dispersion method is ultrasonic dispersion, and the dispersion time is 15 min to 45 min.

7. The preparation method according to claim 5, wherein The casting and shaping in step (2) includes casting the high-stability electrolyte slurry on a glass plate or a polytetrafluoroethylene mold; the dew point of the ambient humidity of the casting and shaping and the forced air drying is less than -40°C.

8. The preparation method according to claim 7, wherein The forced air drying was performed under an argon atmosphere.

9. Application of a polymer electrolyte, wherein the polymer electrolyte according to any one of claims 1 to 4 or the polymer electrolyte prepared by the preparation method according to any one of claims 5 to 8 is used in a sodium solid-state battery, characterized in that: The structure of the sodium solid-state battery is a positive electrode sheet, the polymer electrolyte layer and the negative electrode stacked in sequence.

10. The use according to claim 9, characterized in that The positive electrode sheet includes an active material, a conductive agent, a binder and an additive, wherein the additive includes an ion conductor; The thickness of the polymer electrolyte layer is 20-200 μm; The negative electrode includes at least one of sodium metal, hard carbon, a metal oxide negative electrode or a negative electrode-free current collector.

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