A solid electrolyte separator with a wide temperature range, its preparation method and application

Abstract

The present invention discloses a solid electrolyte separator with a wide temperature range, its preparation method and application, belonging to the field of material chemistry. First, the present invention uses an electrospinning device to prepare a silica nanofiber precursor membrane, and obtains a pure silica nanofiber membrane SNF through high-temperature calcination; then disperses cellulose fibers into a PVDF-HFP solution containing an electrolyte salt; casts the solution onto the SNF membrane to form a double-network structure solid electrolyte PH / SNF-CNF; finally, uses magnetron sputtering to sputter AlF3 on the negative electrode side of the composite electrolyte to obtain a PH / SNF-CNF / AlF3 composite solid electrolyte separator. The obtained PH / SNF-CNF / AlF3 composite solid electrolyte separator of the present invention significantly improves the energy density of metal ion batteries and has excellent long-term cycle stability.

Description

Technical Field

[0001] The present invention relates to a solid electrolyte diaphragm with a wide temperature range, a preparation method thereof and an application, belonging to the field of material chemistry. Background Art

[0002] The booming development of electronic and electric vehicles has stimulated the demand for rechargeable batteries. Liquid electrolytes have safety risks such as flammable organic solvents and electrolyte leakage, and cannot meet the application requirements of batteries under high-temperature conditions such as space shuttles. Solid electrolytes are one of the most promising development strategies for metal-ion batteries because of their significant safety and high energy density advantages.

[0003] Solid electrolytes are generally divided into two categories: inorganic solid electrolytes and solid polymer electrolytes. Inorganic solid electrolytes have thermal stability and high ionic conductivity, but due to their brittleness and rigidity, the interfacial contact with electrodes is poor. In addition, harsh manufacturing conditions result in poor processing performance and high production costs, further limiting their practical applications. Solid polymer electrolytes stand out because of their excellent flexibility and easy manufacturability, and generally can adapt to volume expansion during cycling to achieve good electrolyte / electrode compatibility. However, solid polymer electrolytes generally have problems such as low ionic conductivity, low ion transference number, and poor thermal stability, which limit the application of secondary batteries under extreme conditions. Polymers, such as poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP), have low crystallinity and glass transition temperature and have broad application prospects under low-temperature conditions, but their thermal stability is not ideal and still cannot meet the needs of rapid ion transport. In addition, uneven deposition of ions on the metal negative electrode of metal-ion batteries during cycling will lead to the formation of dendrites, destroying their cycle stability. Summary of the Invention

[0004] Aiming at the deficiencies of existing solid electrolytes and their preparation technologies, the present invention provides a 3D network structure poly(vinylidene fluoride-hexafluoropropylene) (PVDF-HFP) / silica (SiO2) ceramic nanofiber-cellulose nanofiber (CNF) / aluminum fluoride (AlF3) composite solid electrolyte PH / SNF-CNF / AlF3 that can be mass-produced. The composite electrolyte broadens the application temperature range of solid-state batteries and improves the cycle stability of the batteries.

[0005] The first object of the present invention is to provide a preparation method of a PH / SNF-CNF / AlF3 functional composite solid electrolyte diaphragm, and the method includes the following steps:

[0006] (1) Prepare a silica nanofiber membrane:

[0007] PVA is dissolved in water to form solution A; tetraethyl orthosilicate (TEOS) is mixed with water, acid is added, and the mixture is mixed to obtain a hydrolyzate B; solution A is added dropwise to solution B, and the mixture is mixed and stirred to obtain a spinning solution C; the spinning solution C is electrospinned to obtain a nanofiber membrane; the obtained nanofiber membrane is calcined in a muffle furnace to obtain a flexible silica nanofiber membrane, which is referred to as a SNF membrane;

[0008] (2) Preparation of polyvinylidene fluoride-hexafluoropropylene / silica ceramic nanofiber-cellulose nanofiber (PH / SNF-CNF) solid electrolyte:

[0009] First, PVDF-HFP is dissolved in a mixed solution of DMF and acetone, and CNF is added after mixing to obtain a mixed solution D; then, an electrolyte salt is added to the mixed solution D in a glove box, and after sufficient mixing, a mixed solution E is formed; the mixed solution E is uniformly cast onto the SNF membrane, dried, and a PH / SNF-CNF solid electrolyte is obtained, which is stored in a glove box for later use;

[0010] (3) Preparation of PH / SNF-CNF / AlF3 composite solid electrolyte membrane:

[0011] The AlF3 target material was radio frequency sputtered onto the surface of the PH / SNF-CNF electrolyte by a high vacuum magnetron sputtering device to obtain a PH / SNF-CNF / AlF3 composite solid electrolyte membrane.

[0012] In one embodiment of the present invention, in step (1), the concentration of PVA in solution A is 8 wt%-15 wt%.

[0013] In one embodiment of the present invention, in step (1), PVA is dissolved in water, heated to 50-80° C., and stirred to form solution A.

[0014] In one embodiment of the present invention, in step (1), the mass ratio of TEOS to H2O in the hydrolyzate B is 1.0-1.5:1.

[0015] In one embodiment of the present invention, in step (1), the concentration of TEOS in the hydrolyzate B is 4-5 mol / L.

[0016] In one embodiment of the present invention, in step (1), the acid is oxalic acid or phosphoric acid.

[0017] In one embodiment of the present invention, in the hydrolyzate B of step (1), Si and H in the acid + The molar ratio is 1:0.05~0.10.

[0018] In one embodiment of the present invention, in step (1), the mass ratio of solution A to solution B in the spinning solution C is 1:1 to 3.

[0019] In one embodiment of the present invention, the width of the nanofiber membrane obtained by electrospinning is 0.5 - 1.0 m.

[0020] In one embodiment of the present invention, in step (1), the calcination temperature is 600 - 900 °C, the heating rate is 2 - 5 °C / min, and the holding time is 3 - 6 h.

[0021] In one embodiment of the present invention, in step (2), the concentration of PVDF - HFP in the relative mixed solution is 7 wt% - 10 wt%.

[0022] In one embodiment of the present invention, in step (2), the mass ratio of DMF to acetone in the mixed solution is 7:1 to 3.

[0023] In one embodiment of the present invention, in step (2), the content of CNF in the mixed solution is 5 wt% - 10 wt%.

[0024] In one embodiment of the present invention, in step (2), the electrolyte salt is an electrolyte salt for a metal ion battery; specifically, any one or more of the following can be selected: lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium hexafluorophosphate (LiPF6), sodium hexafluorophosphate (NaPF6), sodium perchlorate (NaClO4).

[0025] In one embodiment of the present invention, in step (2), the drying can specifically be vacuum drying; the drying temperature is 40 - 70 °C, and the drying time is 10 - 24 h.

[0026] In one embodiment of the present invention, in step (3), the PH / SNF - CNF electrolyte and the AlF3 target are placed in the vacuum chamber of a high - vacuum magnetron sputtering device. After reaching a certain base vacuum degree, high - purity argon is introduced, and sputtering is carried out using a radio - frequency source at a certain gas pressure and power, and AlF3 is uniformly deposited on the surface of the PH / SNF - CNF electrolyte to obtain a PH / SNF - CNF / AlF3 composite solid electrolyte.

[0027] In one embodiment of the present invention, in step (3), the sample width of the high - vacuum magnetron sputtering device is 0.2 - 1.0 m.

[0028] In one embodiment of the present invention, in step (3), the base vacuum degree of the high - vacuum magnetron sputtering device is 6.4 - 8.8×10 -4 Pa, and the working pressure is 0.6 - 3 Pa.

[0029] In one embodiment of the present invention, in step (3), the sputtering power of radio frequency sputtering is 20-80 W, and the sputtering time is 20-40 min.

[0030] In one embodiment of the present invention, the thickness of the AlF3 coating layer after sputtering is 20-100 nm.

[0031] The second object of the present invention is to provide a PH / SNF-CNF / AlF3 composite solid electrolyte separator based on the above method.

[0032] In the PH / SNF-CNF / AlF3 composite solid electrolyte of the present invention, the SNF-CNF double network structure serves as the skeleton of the solid electrolyte, improving the mechanical stability of the electrolyte. The low glass transition temperature of the PVDF-HFP polymer matrix enables the electrolyte to maintain good flexibility under low-temperature conditions. SNF improves the thermal stability of the solid electrolyte, provides a continuous migration path for ions at the same time, improves the ionic conductivity and ion transference number of the composite electrolyte, and broadens the high-temperature application range of the solid electrolyte. Metal ions can migrate in a hopping manner along polar groups such as hydroxyl groups in CNF, further improving the ion transference number of the composite solid electrolyte. The deposition of Lewis acidic AlF3 on the negative electrode side of the electrolyte forms a stable interface layer, which can inhibit the formation of metal anode dendrites.

[0033] The third object of the present invention is to provide an alkali metal ion battery comprising the above PH / SNF-CNF / AlF3 composite solid electrolyte separator.

[0034] The fourth object of the present invention is to provide the application of the above PH / SNF-CNF / AlF3 composite solid electrolyte separator in the field of metal ion batteries.

[0035] Compared with the prior art, the beneficial effects achieved by the present invention are as follows:

[0036] 1) The preparation method of the silica ceramic nanofiber membrane in the present invention can achieve large-scale production. The 3D network structure of SNF provides a continuous path for ion transport, which is beneficial to improving the ionic conductivity of the solid electrolyte. SNF improves the thermal stability of the electrolyte and can be applied to high-temperature environments such as space shuttles. The low glass transition temperature of PVDF-HFP enables it to maintain good flexibility at low temperatures and ensures a wide application temperature range of the composite electrolyte separator.

[0037] 2) In the present invention, on the one hand, the hydroxyl polar groups on the CNF in the solid electrolyte separator can generate a strong hydrogen bond binding force with the F groups on the PVDF-HFP, improving the mechanical properties of the solid electrolyte. On the other hand, metal cations can complex with the hydroxyl groups on the CNF, providing jumping sites for the migration of ions, facilitating the dissociation of electrolyte salts, and increasing the ion transference number of the solid electrolyte.

[0038] 3) The magnetron sputtering modification method in the present invention avoids the use of binders, solves the problem of thickness increase, and ensures the high energy density of the battery. At the same time, the Lewis acidic sites in AlF3 can regulate the deposition of alkali metal ions, form a stable interfacial layer on the electrolyte surface, inhibit the growth of negative electrode dendrites, and ensure the long-term cycle stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following briefly introduces the drawings required for use in the description of the embodiments or the prior art; obviously, the drawings in the following description are some embodiments of the present invention, and those of ordinary skill in the art can also obtain other drawings based on these drawings without creative efforts.

[0040] Figure 1 Schematic diagram of the large-scale electrospinning preparation of silica ceramic nanofiber membranes in the embodiments and comparative examples of the present invention.

[0041] Figure 2 SEM image of the silica ceramic nanofiber membrane in Example 1 of the present invention.

[0042] Figure 3 SEM image of the composite electrolyte separator in Example 1 of the present invention.

[0043] Figure 4 Na plating / stripping cycle performance of the prepared solid electrolyte separator in a sodium ion battery in Example 1 of the present invention.

[0044] Figure 5 Na plating / stripping cycle performance of the solid electrolyte separator prepared in Comparative Example 1 of the present invention in a sodium ion battery. DETAILED DESCRIPTION OF THE INVENTION

[0045] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0046] Embodiment 1:

[0047] Step 1: Preparation of silica nanofiber membrane

[0048] A certain amount of PVA powder was added to deionized water, heated and stirred at 75°C to prepare 8wt% solution A. A certain amount of tetraethyl orthosilicate was added to deionized water, the mass ratio of TEOS to H2O was 1.4:1, and oxalic acid (molar ratio Si:H + =1:0.08) to prepare solution B. Solution A (1 part by mass) was added dropwise to solution B (1 part by mass) and stirred overnight to obtain solution C. Solution C was spun into a nanofiber membrane SNF membrane using a multi-needle electrospinning control device. Subsequently, the nanofiber membrane was calcined at 600°C, a heating rate of 2°C / min, and a holding time of 3h to remove PVA.

[0049] Step 2: Preparation of polyvinylidene fluoride-hexafluoropropylene / silica ceramic nanofiber-cellulose nanofiber (PH / SNF-CNF) solid electrolyte

[0050] Take a certain amount of PVDF-HFP and dissolve it in a mixed solution of DMF and acetone (7:2w / w), prepare an 8wt% solution under heating and stirring conditions, and then add 8wt% CNF according to the weight of the solution. Then, after ultrasonic treatment of the mixed solution, add 4.7wt% NaPF6 to the above solution in a glove box and stir. After thorough mixing, the solution is uniformly cast onto the SNF membrane and vacuum dried at 60°C for 12h to obtain the PH / SNF-CNF solid electrolyte.

[0051] Step 3: Preparation of PH / SNF-CNF / AlF3 solid electrolyte membrane

[0052] The PH / SNF-CNF electrolyte and AlF3 target were placed in the vacuum chamber of a high vacuum magnetron sputtering device to reach 6.4×10 -4 After the background vacuum reached Pa, high-purity argon was introduced, and RF sputtering was performed for 30 min at a pressure of 0.8 Pa and a power of 30 W. The thickness of the AlF3 coating was 50 nm, and PH / SNF-CNF / AlF3 solid electrolyte was obtained.

[0053] Step 4: Punch the PH / SNF-CNF / AlF3 solid electrolyte prepared in the previous step into a disc with a diameter of 18 mm and place it in the glove box for later use.

[0054] Embodiment 2:

[0055] Step 1: Preparation of silica nanofiber membrane

[0056] A certain amount of PVA powder was added to deionized water, heated and stirred at 50°C to prepare a 12wt% solution A. A certain amount of tetraethyl orthosilicate was added to deionized water, with a mass ratio of TEOS to H2O of 1:1, and oxalic acid (molar ratio Si:H + =1:0.05) to prepare solution B. Solution A (1 part by mass) was added dropwise to solution B (2 parts by mass) and stirred overnight to obtain solution C. Solution C was spun into a nanofiber membrane using a multi-needle electrospinning control device. Subsequently, the nanofiber membrane was calcined at 700°C, a heating rate of 2°C / min, and a holding time of 3h to remove PVA.

[0057] Step 2: Preparation of polyvinylidene fluoride-hexafluoropropylene / silica ceramic nanofiber (PH / SNF) solid electrolyte

[0058] A certain amount of PVDF-HFP was dissolved in a mixed solution of DMF and acetone (7:2w / w), and a 9% solution was prepared under heating and stirring conditions, and then 6wt% CNF was added according to the weight of the solution. Then, after ultrasonic treatment of the mixed solution, 4.5wt% NaPF6 was added and stirred in the environment of a glove box. After thorough mixing, the PVDF-HFP solution containing electrolyte salt and CNF was uniformly cast onto the SNF membrane and vacuum dried at 60°C for 12h.

[0059] Step 3: Preparation of PH / SNF-CNF / AlF3 solid electrolyte membrane

[0060] The PH / SNF-CNF electrolyte and AlF3 target were placed in the vacuum chamber of a high vacuum magnetron sputtering device to reach 6.4×10 -4 After the background vacuum reached 0.8 Pa, high-purity argon gas was introduced, and the AlF3 coating was sputtered by radio frequency source at a pressure of 0.8 Pa and a power of 40 W for 20 min. The thickness of the AlF3 coating was 60 nm.

[0061] Step 4: Punch the PH / SNF-CNF / AlF3 solid electrolyte prepared in the previous step into a disc with a diameter of 18 mm and place it in the glove box for later use.

[0062] Embodiment 3:

[0063] Step 1: Preparation of silica nanofiber membrane

[0064] A certain amount of PVA powder was added to deionized water, and under the condition of 80 °C, it was heated and stirred to prepare solution A with a concentration of 15 wt%. A certain amount of tetraethyl orthosilicate was added to deionized water, and the mass ratio of TEOS to H2O was 1.5:1. Then oxalic acid (molar ratio Si:H + = 1:0.10) was added to prepare solution B. Solution A (1 part by mass) was added dropwise to solution B (3 parts by mass), and after stirring overnight, solution C was obtained. The solution C was electrospun into a nanofiber membrane with a width of 1 m using a multi-needle electrospinning control device. Subsequently, the nanofiber membrane was calcined at 700 °C with a heating rate of 2 °C / min and a holding time of 3 h to remove PVA.

[0065] Step 2: Preparation of polyvinylidene fluoride-hexafluoropropylene / silica ceramic nanofiber (PH / SNF) solid electrolyte

[0066] A certain amount of PVDF-HFP was dissolved in a mixed solution of DMF and acetone (7:2 w / w), and a 10% solution was prepared under the condition of heating and stirring. Then, according to the weight of the solution, 5 wt% of CNF was added. Then the mixed solution was ultrasonically treated, and 4.2 wt% of NaPF6 was added and stirred in the glove box environment. After thorough mixing, the PVDF-HFP solution containing the electrolyte salt and CNF was evenly cast onto the SNF membrane and vacuum dried at 70 °C for 24 h.

[0067] Step 3: Preparation of PH / SNF-CNF / AlF3 solid electrolyte separator

[0068] The PH / SNF-CNF electrolyte and the AlF3 target were placed in the vacuum chamber of a high-vacuum magnetron sputtering device. After reaching a background vacuum of 6.4×10 -4 Pa, high-purity argon was introduced, and radio frequency source sputtering was carried out at a gas pressure of 0.8 Pa and a power of 50 W for 30 min. The thickness of the AlF3 coating was 100 nm.

[0069] Step 4: The PH / SNF-CNF / AlF3 solid electrolyte prepared in the previous step was punched into a disc with a diameter of 18 mm and stored in the glove box for later use.

[0070] Comparative Example 1:

[0071] A certain amount of PVDF-HFP was dissolved in a mixed solution of DMF and acetone (7:2w / w), and a 10wt% solution was prepared under heating and stirring conditions. After ultrasonic treatment of the mixed solution, 4.7wt% NaPF6 was added to the above solution in a glove box and stirred. After thorough mixing, the solution was evenly poured onto a polytetrafluoroethylene plate and vacuum dried at 60°C for 12h to obtain a PH solid electrolyte.

[0072] The electrolyte membrane was removed and punched into a disc with a diameter of 18 mm and placed in a glove box for later use.

[0073] Comparative Example 2:

[0074] The first step: same as in Example 1.

[0075] Step 2: Preparation of polyvinylidene fluoride-hexafluoropropylene / silica ceramic nanofiber (PH / SNF) solid electrolyte

[0076] A certain amount of PVDF-HFP was dissolved in a mixed solution of DMF and acetone (7:2w / w), and an 8% solution was prepared under heating and stirring. After ultrasonic treatment of the mixed solution, 4.7wt% NaPF6 was added to the above solution in a glove box and stirred. After thorough mixing, the solution was uniformly cast onto the SNF membrane and vacuum dried at 60°C for 12h to obtain the PH / SNF solid electrolyte.

[0077] Step 3: Punch the PH / SNF solid electrolyte prepared in the previous step into a disc with a diameter of 18 mm and place it in the glove box for later use.

[0078] Comparative Example 3:

[0079] The first step: same as in Example 1.

[0080] Step 2: Preparation of polyvinylidene fluoride-hexafluoropropylene / silica ceramic nanofiber-cellulose nanofiber (PH / SNF-CNF) solid electrolyte

[0081] Take a certain amount of PVDF-HFP and dissolve it in a mixed solution of DMF and acetone (7:2w / w), prepare an 8% solution under heating and stirring conditions, and then add 8wt% CNF according to the weight of the solution. Then, after ultrasonic treatment of the mixed solution, add 4.7wt% NaPF6 to the above solution in a glove box and stir. After thorough mixing, the solution is uniformly cast onto the SNF membrane and vacuum dried at 60°C for 12h to obtain the PH / SNF-CNF solid electrolyte.

[0082] Step 3: Punch the PH / SNF-CNF solid electrolyte prepared in the previous step into a disc with a diameter of 18 mm and place it in the glove box for later use.

[0083] Comparative Example 4:

[0084] Compared with Example 1, the silica nanofiber membrane was changed to silica nanoparticles (SNP).

[0085] Step 1: Prepare a polyvinylidene fluoride - hexafluoropropylene / silica ceramic nanoparticle - cellulose nanofiber (PH / SNP - CNF) solid electrolyte

[0086] Take a certain amount of PVDF - HFP and dissolve it in a mixed solution of DMF and acetone (7:2 w / w). Prepare an 8 wt% solution under heating and stirring conditions, and then add 8 wt% of SNP and 8 wt% of CNF according to the weight of the solution. Then, after ultrasonic treatment of the mixed solution, add 4.7 wt% of NaPF6 to the above - mentioned solution and stir in a glove box. After sufficient mixing, pour the solution evenly onto the SNF membrane and vacuum - dry it at 60 °C for 12 h to obtain the PH / SNP - CNF solid electrolyte.

[0087] Step 2: Prepare a PH / SNP - CNF / AlF3 solid electrolyte

[0088] Place the PH / SNP - CNF electrolyte and the AlF3 target in the vacuum chamber of a high - vacuum magnetron sputtering device. After reaching a background vacuum of 6.4×10 -4 Pa, introduce high - purity argon gas. Under a gas pressure of 0.8 Pa and a power of 30 W, sputter with a radio - frequency source for 30 min. The thickness of the AlF3 coating is 50 nm to obtain the PH / SNP - CNF / AlF3 solid electrolyte.

[0089] Step 3: Punch the prepared PH / SNP - CNF / AlF3 solid electrolyte into a disc with a diameter of 18 mm and place it in a glove box for standby.

[0090] Comparative Example 5:

[0091] Mix AlF3 and polyvinylidene fluoride (PVDF) in a mass ratio of 8:2 and grind them evenly, then drop N - methylpyrrolidone (NMP) to form a slurry. Scrape the slurry onto one side of the PH / SNF - CNF, and the coating thickness is 20 μm.

[0092] Step 4: Punch the prepared PH / SNF - CNF / AlF3 solid electrolyte into a disc with a diameter of 18 mm and place it in a glove box for standby.

[0093] Testing method:

[0094] The 3D network structure polyvinylidene fluoride - hexafluoropropylene (PVDF - HFP) / silica (SiO2) ceramic nanofiber - cellulose nanofiber (CNF) / aluminum fluoride (AlF3) composite solid electrolyte PH / SNF - CNF / AlF3 membrane prepared in Examples 1, 2, and 3 was used as the separator of a lithium - sulfur battery, and the PVDF - HFP solid electrolyte in Comparative Example 1, the PH / SNF electrolyte in Comparative Example 2, and the PH / SNF - CNF electrolyte in Comparative Example 3 were used as the electrolytes of sodium - ion batteries, and they were assembled according to the assembly method of coin - type sodium - ion batteries.

[0095] An electrochemical workstation was used to test the ionic conductivity and interfacial impedance, and the parameter settings are as follows

[0096] Ionic conductivity test: The parameter settings are as follows: high frequency 10 6 Hz, low frequency 1 Hz, amplitude 0.01 V;

[0097] Interfacial impedance test: The parameter settings are as follows: high frequency 10 6 Hz, low frequency 100 Hz, amplitude 0.02 V.

[0098] A battery test system was used to test the cycle performance and rate performance, and the parameter settings are as follows:

[0099] Electroplating / stripping performance test:

[0100] At a current density of 0.1 mA cm -1 A constant - current electroplating / stripping test was carried out on the Na / / electrolyte / / Na symmetric battery.

[0101] Constant - current charge - discharge performance test:

[0102] Charge and discharge were carried out at 0.2 C: the discharge voltage was up to 2.5 V, the charge voltage was up to 4 V, and the number of cycles was 1000.

[0103] Figure 1 This is a schematic diagram of the precursor membrane of the silica nanofiber membrane prepared by multi - needle electrospinning in the present invention, and its output is about 30 times that of ordinary electrospinning. Figure 2 This is the SEM image of the pure silica nanofiber membrane prepared in Example 1 of the present invention, which has a three - dimensional network structure and serves as the skeleton of the electrolyte to ensure the mechanical stability and high - temperature stability of the electrolyte. Figure 3 This is the cross - sectional view of the composite solid electrolyte prepared in Example 1 of the present invention. The thickness of the composite electrolyte is about 42 microns, which is much smaller than the thickness of the glass fiber separator used in sodium - ion batteries. The magnetron sputtering interface modification technology in the present invention avoids the problem of increasing electrolyte thickness and ensures the energy density and volume density of the battery.

[0104] Figure 4 and5 They are the plating / stripping performances of the symmetric batteries assembled with the electrolytes prepared in Example 1 and Comparative Example 1 of the present invention respectively. It can be seen from the figure that the PH / SNF-CNF / AlF3 electrolyte can still maintain the voltage stability after 260 hours of cycling, while the voltage of the PVDF-HFP electrolyte in Comparative Example 1 fluctuates greatly and the polarization phenomenon is obvious, indicating that the PH / SNF-CNF / AlF3 composite solid electrolyte has good cycle stability.

[0105] The test results of the electrochemical performances of the electrolyte diaphragms prepared in Examples 1-3 and Comparative Examples 1-3 of the present invention are shown in Table 1 below. It can be seen that the PH / SNF-CNF / AlF3 electrolyte prepared in the present invention has a relatively high ionic conductivity. The ionic conductivity of the electrolyte in Example 1 at 0 °C reaches 0.171 mS / cm, which is much higher than that of the comparative examples. It indicates that the ceramic nanofibers and cellulose nanofibers in the composite electrolyte can promote the migration of ions. The interfacial impedance of Examples 1, 2, and 3 is much smaller than that of the comparative examples, indicating that magnetron sputtering of AlF3 can improve the interfacial compatibility.

[0106] The constant current charge-discharge and cycle performances of Examples 1-3 and Comparative Examples 1-3 in Table 1 further illustrate that the PH / SNF-CNF / AlF3 composite solid electrolyte diaphragm helps to improve the energy density and long-term cycle stability of metal ion batteries.

[0107] Table 1 Test data of the electrochemical performances of the electrolyte diaphragms prepared in Examples 1-3 and Comparative Examples 1-3

[0108]

[0109] Comparative Example 6

[0110] (1) Exploring the influence of the concentration of tetraethyl orthosilicate in step (1):

[0111] In the first step, referring to Example 1, only the amount of tetraethyl orthosilicate in solution B was changed (as shown in Table 2), and the others remained unchanged, and the corresponding SNF fiber membranes were prepared. The results are shown in Table 2.

[0112] Table 2

[0113] <![CDATA[TEOS:H2O(w / w)]]> Fiber morphology 1.4:1 (Example 1) The fiber thickness is uniform 0.5:1 The structure of the fiber collapses after calcination and cannot form a film 2:1 Unable to form fibers

[0114] (2) Exploring the influence of the PVA concentration in step (1):

[0115] In the first step, referring to Example 1, only the concentration of PVA in solution A was changed (as shown in Table 3), and the others remained unchanged, and the corresponding SNF fiber membranes were prepared. The results are shown in Table 3.

[0116] Table 3

[0117] PVA concentration (wt%) Fiber morphology 8 (Example 1) The fiber morphology has good uniformity 12 The fiber is well formed 15 The fiber has beads 4 Unable to form fibers

[0118] It can be seen that too high or too low concentrations of tetraethyl orthosilicate and PVA will affect the morphology of the fibers and thus affect the performance of the electrolyte. If the concentration of tetraethyl orthosilicate is too high or the concentration of PVA is too low, fiber formation cannot occur during the spinning process. In the case of fiber membrane structure collapse or beaded formation, the ionic conductivity of the electrolyte will decrease and the cycling performance will deteriorate.

Claims

1. A preparation method of a PH / SNF-CNF / AlF3 composite electrolyte membrane used as an electrolyte for a sodium-ion battery, characterized in that, The steps include: (1) Preparation of silica nanofiber membrane: PVA is dissolved in water to form solution A; tetraethyl orthosilicate is mixed with water, acid is added, and the mixture is mixed to obtain hydrolyzate B; solution A is added dropwise to solution B, and the mixture is mixed and stirred to obtain spinning solution C; the spinning solution C is used to prepare a nanofiber membrane by electrospinning; the prepared nanofiber membrane is calcined in a muffle furnace to obtain a flexible silica nanofiber membrane, which is referred to as a SNF membrane; (2) Preparation of PH / SNF-CNF solid electrolyte: First, PVDF-HFP was dissolved in a mixed solution of DMF and acetone, and CNF was added after mixing to obtain a mixed solution D; then, electrolyte salt sodium hexafluorophosphate was added to the mixed solution D in a glove box, and after thorough mixing, a mixed solution E was formed; the mixed solution E was uniformly cast onto the SNF membrane and dried to obtain a PH / SNF-CNF solid electrolyte; (3) Preparation of PH / SNF-CNF / AlF3 composite electrolyte membrane: The AlF3 target was radio frequency sputtered onto the surface of the PH / SNF-CNF electrolyte by a high vacuum magnetron sputtering device to obtain a PH / SNF-CNF / AlF3 composite electrolyte membrane; The PVA concentration in solution A is 8wt%-15wt%; The mass ratio of TEOS to H2O in the hydrolyzate B is 1.0-1.5:

1.

2. The method according to claim 1, characterized in that, In the hydrolyzate B described in step (1), the molar ratio of Si to H in the acid + is 1:0.05 to 0.

10.

3. The method according to claim 1, wherein In step (1), the mass ratio of solution A to solution B in the spinning solution C is 1:1-3.

4. The method according to claim 1, wherein In step (2), the content of CNF in the mixed solution is 5wt% to 10wt%.

5. The method according to any one of claims 1-4, characterized in that, In step (3), the background vacuum degree of the high-vacuum magnetron sputtering equipment is 6.4 - 8.8×10 -4 Pa, the working pressure is 0.6 - 3 Pa; the sputtering power of radio frequency sputtering is 20 - 80 W, and the sputtering time is 20 - 40 min.

6. A PH / SNF-CNF / AlF3 composite electrolyte membrane prepared by the method according to any one of claims 1 to 5.

7. A sodium ion battery using the PH / SNF-CNF / AlF3 composite electrolyte membrane according to claim 6.

8. Application of the PH / SNF-CNF / AlF3 composite electrolyte membrane according to claim 6 in the field of sodium ion batteries.

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