PVDF (polyvinylidene fluoride)-based solid electrolyte as well as preparation and application thereof

Abstract

The invention relates to the technical field of polymer-based solid electrolyte preparation, in particular to PVDF-based solid electrolyte as well as preparation and application thereof. The preparation method comprises the following steps: uniformly mixing a lithium bis (trifluoromethylsulfonyl) imide dispersion liquid and a PVDF / FPI composite solution, or uniformly mixing the lithium bis (trifluoromethylsulfonyl) imide dispersion liquid, an inorganic active material dispersion liquid and the PVDF / FPI composite solution; and drying to obtain the PVDF / FPI composite solid electrolyte. The PVDF-based solid electrolyte prepared by the invention has remarkable heat resistance and flame retardance, so that a solid-state lithium battery can also realize excellent electrochemical performance under the working condition of higher temperature; the mechanical strength of the solid electrolyte is obviously improved, so that the solid lithium battery can still obtain excellent cycling stability under the condition of high current density; the lithium ion battery has a hydrophilic-hydrophobic phase separation structure, a hydrophilic phase selectively enriches lithium ions, and a hydrophobic phase selectively enriches organic fluorine ions, so that the ionic conductivity is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer-based solid electrolyte preparation, and in particular to a PVDF-based solid electrolyte and its preparation and application. Background Art

[0002] Traditional liquid lithium-ion batteries can no longer meet the needs of sustainable energy storage technology due to inherent defects such as poor electrochemical stability, poor thermal conductivity and electrolyte leakage risk. Replacing organic liquid electrolytes with highly safe solid electrolytes is an inevitable trend in the development of energy storage batteries. Compared with inorganic solid electrolytes and organic polymer solid electrolytes, polymer-based composite solid electrolytes have the advantages of excellent flexibility, processability, high ionic conductivity and stable electrochemical performance, making them one of the best choices to replace flammable liquid electrolytes.

[0003] Polyvinylidene fluoride (PVDF)-based electrolytes have good chemical stability, a considerable voltage window, excellent thermal stability and conductivity. Despite this, the mechanical strength of PVDF-based electrolytes is still limited, making it difficult to suppress lithium dendrites. Polyimide (PI) has excellent mechanical properties, excellent chemical corrosion resistance, high temperature resistance and flame retardancy, and is highly designable, and is considered to be an ideal candidate material for advanced solid electrolytes. Therefore, the problem of lithium dendrites in PVDF films can be solved by optimizing the mechanical properties of PVDF by using PI to reinforce PVDF and regulating the microphase separation structure. At the same time, by optimizing the molecular structure of PI and introducing fluorine-containing groups, the ionic conductivity and interfacial wettability of the solid electrolyte can be improved, thereby improving the electrochemical performance of the battery. Summary of the invention

[0004] In order to solve the above problems, the purpose of the present invention is to provide a PVDF-based solid electrolyte and its preparation and application.

[0005] The purpose of the present invention can be achieved by the following technical solutions:

[0006] The first object of the present invention is to provide a method for preparing a PVDF-based solid electrolyte, comprising the following steps:

[0007] (S1) After dissolving 4,4'-diaminodiphenyl ether, 4,4'-(hexafluoroisopropylene) diphthalic anhydride is added in batches under an ice bath, and mixed to obtain a fluorinated polyamic acid precursor; the fluorinated polyamic acid precursor is coated on a glass plate, and after demolding, it is heated according to a temperature gradient for imidization to obtain FPI;

[0008] (S2) dissolving the FPI prepared in step (S1) and PVDF and mixing them to obtain a PVDF / FPI composite solution;

[0009] dissolving lithium bis(trifluoromethylsulfonyl)imide to obtain a lithium bis(trifluoromethylsulfonyl)imide dispersion;

[0010] Mixing the lithium bis(trifluoromethylsulfonyl)imide dispersion with the PVDF / FPI composite solution, or mixing the lithium bis(trifluoromethylsulfonyl)imide dispersion, the inorganic active material dispersion and the PVDF / FPI composite solution; drying to obtain the PVDF / FPI composite solid electrolyte;

[0011] The inorganic active material dispersion is prepared by the following method:

[0012] The inorganic active material is dissolved, ball-milled, and centrifuged. The precipitate is mixed with N-methylpyrrolidone and then ultrasonically crushed to obtain an inorganic active material dispersion.

[0013] In one embodiment of the present invention, in step (S1), 4,4'-diaminodiphenyl ether is dissolved in a solvent, and the dosage ratio of 4,4'-diaminodiphenyl ether to the solvent is 1 g: 10-30 mL; the mass ratio of 4,4'-diaminodiphenyl ether to 4,4'-(hexafluoroisopropylene) diphthalic anhydride is 1: 1-4.

[0014] Preferably, the usage ratio of 4,4'-diaminodiphenyl ether to the solvent is 1 g:16 mL; the mass ratio of 4,4'-diaminodiphenyl ether to 4,4'-(hexafluoroisopropylene) diphthalic anhydride is 1:2.25.

[0015] In one embodiment of the present invention, in step (S1), the temperature gradient conditions for heating imidization are specifically as follows:

[0016] 1) 80℃, 1h;

[0017] 2) 100°C, 1h;

[0018] 3) 120°C, 1h;

[0019] 4) 160°C, 1h;

[0020] 5) 180°C, 1h;

[0021] 6) 200℃, 1h.

[0022] In one embodiment of the present invention, in step (S2), the mass ratio of PVDF to FPI is 5:1 to 1:5;

[0023] Preferably, the mass ratio of PVDF to FPI is 3:1.

[0024] The ratio of the sum of the mass of lithium bis(trifluoromethylsulfonyl)imide, PVDF and FPI is 1 to 6:10; preferably, the ratio of the sum of the mass of lithium bis(trifluoromethylsulfonyl)imide, PVDF and FPI is 4:10;

[0025] The sum ratio of the mass of the inorganic active material, PVDF and FPI is 1:5-20; preferably, the sum ratio of the mass of the inorganic active material, PVDF and FPI is 1:10.

[0026] In one embodiment of the present invention, in step (S2), the inorganic active material is selected from Li 1.3 Al 0.3 Ti 1.7 (PO4)3(NASICON), Li 14 ZnGe4O 16 One of lithium phosphorus oxide nitrogen (LISICON), lithium lanthanum zirconium oxide (LLZO) and lithium lanthanum zirconium tantalum oxide (LLZTO);

[0027] The inorganic active material is dissolved in the solvent, and the mass ratio of the inorganic active material to the solvent is 1:5 to 1:15; the mass ratio of the inorganic active material to N-methylpyrrolidone is 1:10.

[0028] In one embodiment of the present invention, in step (S2), during the ball milling process, the rotation speed is 600 to 900 r / min and the time is 5 to 7 h;

[0029] Preferably, during the ball milling process, the rotation speed is 800 r / min.

[0030] In one embodiment of the present invention, in step (S2), the drying process is under vacuum conditions, the temperature is 50 to 70° C., and the time is 24 to 72 hours;

[0031] Preferably, during the drying process, the temperature is 60-70°C and the time is 34-38h;

[0032] Further preferably, during the drying process, the temperature is 65° C. and the time is 36 hours.

[0033] The second object of the present invention is to provide a PVDF-based solid electrolyte prepared by the above method.

[0034] The third object of the present invention is to provide a PVDF-based solid electrolyte for use in preparing a solid-state lithium battery.

[0035] A fourth object of the present invention is to provide a solid-state lithium battery, which contains the above-mentioned PVDF-based solid electrolyte.

[0036] The technical solution principle of the invention is:

[0037] Room temperature Li in inorganic solid electrolytes + High conductivity and good compatibility with lithium metal. The addition of inorganic active materials can make it interact with the polymer matrix to reduce the crystallinity of the polymer system and increase the movement of the chain.

[0038] The fluorinated group-rich PVDF / FPI composite solid electrolyte provides a negatively charged environment with a high concentration of active sites for the battery, which accelerates the Li + In addition, the introduction of trifluoromethyl (-CF3) groups is beneficial to increase the free volume of polyimide and improve the compatibility of polyimide and PVDF. The FPI-modified PVDF matrix obtains excellent heat resistance and flame retardancy.

[0039] Fluorinated polyimide FPI and PVDF phase separation to form a continuous phase network. Due to the hydrophilicity of the inorganic active material, it is selectively enriched in the FPI continuous phase, which increases the transmission speed of lithium ions and improves ion conductivity. In addition, Li+ ions are enriched in the polar FPI, and TFSI - Ions are enriched in the hydrophobic PVDF phase, forming a physically cross-linked network with high dynamic reversibility.

[0040] Compared with the prior art, the present invention has the following beneficial effects:

[0041] (1) The PVDF-based solid electrolyte prepared by the present invention has significant heat resistance and flame retardancy, enabling solid-state lithium batteries to achieve excellent electrochemical performance even under higher temperature working conditions.

[0042] (2) The PVDF-based solid electrolyte provided by the present invention significantly improves the mechanical strength of the solid electrolyte, so that the solid-state lithium battery can still achieve excellent cycle stability under high current density conditions.

[0043] (3) The PVDF-based solid electrolyte provided by the present invention has a hydrophilic and hydrophobic phase separation structure, the hydrophilic phase selectively enriches lithium ions, and the hydrophobic phase selectively enriches organic fluoride ions, thereby improving ionic conductivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 The stress-strain curves of the solid electrolytes prepared in Examples 1 to 4 and Comparative Examples 1 to 2;

[0045] Figure 2 The LSV curves of the solid electrolytes prepared in Examples 3 to 6;

[0046] Figure 3The EIS impedance graphs of the solid electrolytes prepared in Examples 3 to 6 and Comparative Examples 1 to 2;

[0047] Figure 4 This is a charge and discharge cycle test diagram of the solid electrolyte prepared in Example 5 and Comparative Examples 1-2. DETAILED DESCRIPTION

[0048] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0049] In the following examples, unless otherwise specified, all reagents used are commercially available reagents, and all detection means and methods used are conventional detection means and methods in the art.

[0050] Example 1

[0051] This embodiment provides a method for preparing a PVDF-based solid electrolyte membrane and a battery, comprising the following steps:

[0052] (S1) Preparation of FPI: 2 g of ODA was completely dissolved in 32 mL of NMP to obtain a mixed solution;

[0053] Under ice-water bath conditions, 4.5 g of 6FDA was added to the mixed solution three times, and the mixture was stirred and polymerized to obtain a fluorinated polyamic acid (FPAA) precursor;

[0054] The FPAA precursor was evenly coated onto a dry and clean glass plate, and then placed in water to remove the film. The film was then heated in sequence at a temperature gradient of 80°C / 1h+100°C / 1h+120°C / 1h+160°C / 1h+180°C / 1h+200°C / 1h for imidization to obtain FPI.

[0055] (S2) Preparation of PVDF-based solid electrolyte membrane: 2 g of the FPI prepared in step (S1) and 1 g of PVDF were mixed in 15 mL of NMP and magnetically stirred at room temperature for 1 h to obtain a PVDF / FPI composite solution;

[0056] 1.2 g LITFSI (the mass of LITFSI is 40% of the sum of the mass of PVDF and FPI) was dissolved in 5 mL NMP under stirring at room temperature to obtain a LITFSI dispersion;

[0057] The LITFSI dispersion was added to the PVDF / FPI composite solution, magnetically stirred at room temperature for 1 h, and coated with a 500 μm coating rod; then placed in a vacuum oven and dried at 60 ° C for 48 h under vacuum to remove the remaining solvent to obtain a 0.05 mm PVDF-based solid electrolyte membrane (its stress-strain curve is shown in Figure 1 The tensile properties are shown in Table 1, the ionic conductivity is shown in Table 2, and the discharge specific capacity and cycle life are shown in Table 3).

[0058] A battery is prepared based on the PVDF-based solid electrolyte membrane obtained above, as follows:

[0059] (1) Dissolve 1 g of PVDF in 15 mL of NMP to obtain a PVDF solution;

[0060] 7 g of lithium iron phosphate (LiFePO4, LFP) and 2 g of conductive carbon black were ground evenly, mixed with PVDF solution, and ball-milled at room temperature for 4 h to obtain a positive electrode slurry;

[0061] (2) Using aluminum foil as the positive electrode current collector, the positive electrode slurry prepared in step (S1) was coated on the aluminum foil (by scraping with a 25 μm coating rod to form a film), and then dried in a vacuum oven at 60° C. The aluminum foil was cut into discs with a diameter of 11 mm using a slicer as the positive electrode; and lithium discs with a diameter of 14 mm were used as the negative electrode;

[0062] (3) Assemble a standard button cell (CR 2032) in a glove box filled with argon gas for charge and discharge tests. The PVDF-based solid electrolyte membrane prepared as above is used as electrolyte and separator, and a metal lithium sheet with a thickness of 0.4 mm and a diameter of 14 mm is used as the negative electrode. The negative electrode shell, spring sheet, gasket, lithium sheet, PVDF-based solid electrolyte membrane, positive electrode sheet, and positive electrode shell are assembled in this order to obtain a battery.

[0063] Example 2

[0064] This embodiment provides a method for preparing a PVDF-based solid electrolyte membrane and a battery, comprising the following steps:

[0065] (S1) Preparation of FPI: 2 g of ODA was completely dissolved in 32 mL of NMP to obtain a mixed solution;

[0066] Under ice-water bath conditions, 4.5 g of 6FDA was added to the mixed solution three times, and the mixture was stirred and polymerized to obtain a fluorinated polyamic acid (FPAA) precursor;

[0067] The FPAA precursor was evenly coated onto a dry and clean glass plate, and then placed in water to remove the film. The film was then heated in sequence at a temperature gradient of 80°C / 1h+100°C / 1h+120°C / 1h+160°C / 1h+180°C / 1h+200°C / 1h for imidization to obtain FPI.

[0068] (S2) Preparation of PVDF-based solid electrolyte membrane: 1 g of the FPI prepared in step (S1) and 1 g of PVDF were mixed in 10 mL of NMP and magnetically stirred at room temperature for 1 h to obtain a PVDF / FPI composite solution;

[0069] 0.8 g of LITFSI (the mass of LITFSI is 40% of the sum of the mass of PVDF and FPI) was dissolved in 3.33 mL of NMP under stirring at room temperature to obtain a LITFSI dispersion;

[0070] The LITFSI dispersion was added to the PVDF / FPI composite solution, magnetically stirred at room temperature for 1 h, and coated with a 500 μm coating rod to form a film; then placed in a vacuum oven and dried at 60°C for 48 h under vacuum to remove the remaining solvent to obtain a PVDF-based solid electrolyte membrane (its stress-strain curve is shown in FIG. Figure 1 The tensile properties are shown in Table 1, the ionic conductivity is shown in Table 2, and the discharge specific capacity and cycle life are shown in Table 3).

[0071] A battery is prepared based on the PVDF-based solid electrolyte membrane obtained above, as follows:

[0072] (1) Dissolve 1 g of PVDF in 15 mL of NMP to obtain a PVDF solution;

[0073] 7 g of lithium iron phosphate (LiFePO4, LFP) and 2 g of conductive carbon black were ground evenly, mixed with PVDF solution, and ball-milled at room temperature for 4 h to obtain a positive electrode slurry;

[0074] (2) Using aluminum foil as the positive electrode current collector, the positive electrode slurry prepared in step (S1) was coated on the aluminum foil (by scraping with a 25 μm coating rod to form a film), and then dried in a vacuum oven at 60° C. The aluminum foil was cut into discs with a diameter of 11 mm using a slicer as the positive electrode; and lithium discs with a diameter of 14 mm were used as the negative electrode;

[0075] (3) Assemble a standard button cell (CR 2032) in a glove box filled with argon gas for charge and discharge tests. The PVDF-based solid electrolyte membrane prepared as above is used as electrolyte and separator, and a metal lithium sheet with a thickness of 0.4 mm and a diameter of 14 mm is used as the negative electrode. The negative electrode shell, spring sheet, gasket, lithium sheet, PVDF-based solid electrolyte membrane, positive electrode sheet, and positive electrode shell are assembled in this order to obtain a battery.

[0076] Example 3

[0077] This embodiment provides a method for preparing a PVDF-based solid electrolyte membrane and a battery, comprising the following steps:

[0078] (S1) Preparation of FPI: 2 g of ODA was completely dissolved in 32 mL of NMP to obtain a mixed solution;

[0079] Under ice-water bath conditions, 4.5 g of 6FDA was added to the mixed solution three times, and the mixture was stirred and polymerized to obtain a fluorinated polyamic acid (FPAA) precursor;

[0080] The FPAA precursor was evenly coated onto a dry and clean glass plate, and then placed in water to remove the film. The film was then heated in sequence at a temperature gradient of 80°C / 1h+100°C / 1h+120°C / 1h+160°C / 1h+180°C / 1h+200°C / 1h for imidization to obtain FPI.

[0081] (S2) Preparation of PVDF-based solid electrolyte membrane: 1 g of the FPI prepared in step (S1) and 3 g of PVDF were mixed in 20 mL of NMP and magnetically stirred at room temperature for 1 h to obtain a PVDF / FPI composite solution;

[0082] 1.6 g of LITFSI (the mass of LITFSI is 40% of the sum of the mass of PVDF and FPI) was dissolved in 6.67 mL of NMP under stirring at room temperature to obtain a LITFSI dispersion;

[0083] The LITFSI dispersion was added to the PVDF / FPI composite solution, magnetically stirred at room temperature for 1 h, and coated with a 500 μm coating rod to form a film; then placed in a vacuum oven and dried at 60°C for 48 h under vacuum to remove the remaining solvent to obtain a PVDF-based solid electrolyte membrane (its stress-strain curve is shown in FIG. Figure 1 As shown, the LSV curve is as follows Figure 2 As shown, the EIS impedance diagram is as follows Figure 3 The tensile properties are shown in Table 1, the ionic conductivity is shown in Table 2, and the discharge specific capacity and cycle life are shown in Table 3).

[0084] A battery is prepared based on the PVDF-based solid electrolyte membrane obtained above, as follows:

[0085] (1) Dissolve 1 g of PVDF in 15 mL of NMP to obtain a PVDF solution;

[0086] 7 g of lithium iron phosphate (LiFePO4, LFP) and 2 g of conductive carbon black were ground evenly, mixed with PVDF solution, and ball-milled at room temperature for 4 h to obtain a positive electrode slurry;

[0087] (2) Using aluminum foil as the positive electrode current collector, the positive electrode slurry prepared in step (S1) was coated on the aluminum foil (by scraping with a 25 μm coating rod to form a film), and then dried in a vacuum oven at 60° C. The aluminum foil was cut into discs with a diameter of 11 mm using a slicer as the positive electrode; and lithium discs with a diameter of 14 mm were used as the negative electrode;

[0088] (3) Assemble a standard button cell (CR 2032) in a glove box filled with argon gas for charge and discharge tests. The PVDF-based solid electrolyte membrane prepared as above is used as electrolyte and separator, and a metal lithium sheet with a thickness of 0.4 mm and a diameter of 14 mm is used as the negative electrode. The negative electrode shell, spring sheet, gasket, lithium sheet, PVDF-based solid electrolyte membrane, positive electrode sheet, and positive electrode shell are assembled in this order to obtain a battery.

[0089] Example 4

[0090] This embodiment provides a method for preparing a PVDF-based solid electrolyte membrane and a battery, comprising the following steps:

[0091] (S1) Preparation of FPI: 2 g of ODA was completely dissolved in 32 mL of NMP to obtain a mixed solution;

[0092] Under ice-water bath conditions, 4.5 g of 6FDA was added to the mixed solution three times, and the mixture was stirred and polymerized to obtain a fluorinated polyamic acid (FPAA) precursor;

[0093] The FPAA precursor was evenly coated onto a dry and clean glass plate, and then placed in water to remove the film. The film was then heated in sequence at a temperature gradient of 80°C / 1h+100°C / 1h+120°C / 1h+160°C / 1h+180°C / 1h+200°C / 1h for imidization to obtain FPI.

[0094] (S2) Preparation of PVDF-based solid electrolyte membrane: 1 g of the FPI prepared in step (S1) and 4 g of PVDF were mixed in 25 mL of NMP and magnetically stirred at room temperature for 1 h to obtain a PVDF / FPI composite solution;

[0095] 2.0 g of LITFSI (the mass of LITFSI is 40% of the sum of the mass of PVDF and FPI) was dissolved in 8.33 mL of NMP under stirring at room temperature to obtain a LITFSI dispersion;

[0096] The LITFSI dispersion was added to the PVDF / FPI composite solution, magnetically stirred at room temperature for 1 h, and coated with a 500 μm coating rod to form a film; then placed in a vacuum oven and dried at 60°C for 48 h under vacuum to remove the remaining solvent to obtain a PVDF-based solid electrolyte membrane (its stress-strain curve is shown in FIG. Figure 1 As shown, the LSV curve is as follows Figure 2 As shown, the EIS impedance diagram is as follows Figure 3 The tensile properties are shown in Table 1, the ionic conductivity is shown in Table 2, and the discharge specific capacity and cycle life are shown in Table 3).

[0097] A battery is prepared based on the PVDF-based solid electrolyte membrane obtained above, as follows:

[0098] (1) Dissolve 1 g of PVDF in 15 mL of NMP to obtain a PVDF solution;

[0099] 7 g of lithium iron phosphate (LiFePO4, LFP) and 2 g of conductive carbon black were ground evenly, mixed with PVDF solution, and ball-milled at room temperature for 4 h to obtain a positive electrode slurry;

[0100] (2) Using aluminum foil as the positive electrode current collector, the positive electrode slurry prepared in step (S1) was coated on the aluminum foil (by scraping with a 25 μm coating rod to form a film), and then dried in a vacuum oven at 60° C. The aluminum foil was cut into discs with a diameter of 11 mm using a slicer as the positive electrode; and lithium discs with a diameter of 14 mm were used as the negative electrode;

[0101] (3) Assemble a standard button cell (CR 2032) in a glove box filled with argon gas for charge and discharge tests. The PVDF-based solid electrolyte membrane prepared as above is used as electrolyte and separator, and a metal lithium sheet with a thickness of 0.4 mm and a diameter of 14 mm is used as the negative electrode. The negative electrode shell, spring sheet, gasket, lithium sheet, PVDF-based solid electrolyte membrane, positive electrode sheet, and positive electrode shell are assembled in this order to obtain a battery.

[0102] Example 5

[0103] This embodiment provides a method for preparing a PVDF-based solid electrolyte membrane and a battery, comprising the following steps:

[0104] (S1) Preparation of an inorganic active material dispersion: 0.4 g of lithium lanthanum zirconium tantalum oxide and isopropyl alcohol are added to a zirconium oxide ball mill to obtain a ball milled mixed solution;

[0105] Pour the ball mill mixture into a beaker, wash the ball mill with isopropanol to collect the remaining liquid, and centrifuge to obtain a precipitate;

[0106] The precipitate was added with 5 mL of NMP for ultrasonic crushing to prepare an inorganic active material dispersion;

[0107] (S2) Preparation of FPI: 2 g of ODA was completely dissolved in 32 mL of NMP to obtain a mixed solution;

[0108] Under ice-water bath conditions, 4.5 g of 6FDA was added to the mixed solution three times, and the mixture was stirred and polymerized to obtain a fluorinated polyamic acid (FPAA) precursor;

[0109] The FPAA precursor was evenly coated onto a dry and clean glass plate, and then placed in water to remove the film. The film was then heated in sequence at a temperature gradient of 80°C / 1h+100°C / 1h+120°C / 1h+160°C / 1h+180°C / 1h+200°C / 1h for imidization to obtain FPI.

[0110] (S3) Preparation of PVDF-based solid electrolyte membrane: 1 g of the FPI prepared in step (S2) and 3 g of PVDF were mixed in 20 mL of NMP and magnetically stirred at room temperature for 1 h to obtain a PVDF / FPI composite solution;

[0111] 1.6 g of LITFSI (the mass of LITFSI is 40% of the sum of the mass of PVDF and FPI) was dissolved in 6.67 mL of NMP under stirring at room temperature to obtain a LITFSI dispersion;

[0112] The LITFSI dispersion and the inorganic active material dispersion prepared in step (S1) were added to the PVDF / FPI composite solution, magnetically stirred at room temperature for 1 hour, and coated with a 500 μm coating rod to form a film; then placed in a vacuum oven, dried at 60° C. for 48 hours under vacuum to remove the remaining solvent, and a PVDF-based solid electrolyte membrane (whose LSV curve is shown in FIG. 1 ) was obtained. Figure 2 As shown, the EIS impedance diagram is as follows Figure 3 As shown in the charge and discharge cycle test diagram Figure 4 The tensile properties are shown in Table 1, the ionic conductivity is shown in Table 2, and the discharge specific capacity and cycle life are shown in Table 3).

[0113] A battery is prepared based on the PVDF-based solid electrolyte membrane obtained above, as follows:

[0114] (1) Dissolve 1 g of PVDF in 15 mL of NMP to obtain a PVDF solution;

[0115] 7 g of lithium iron phosphate (LiFePO4, LFP) and 2 g of conductive carbon black were ground evenly, mixed with PVDF solution, and ball-milled at room temperature for 4 h to obtain a positive electrode slurry;

[0116] (2) Using aluminum foil as the positive electrode current collector, the positive electrode slurry prepared in step (S1) was coated on the aluminum foil (by scraping with a 25 μm coating rod to form a film), and then dried in a vacuum oven at 60° C. The aluminum foil was cut into discs with a diameter of 11 mm using a slicer as the positive electrode; and lithium discs with a diameter of 14 mm were used as the negative electrode;

[0117] (3) Assemble a standard button cell (CR 2032) in a glove box filled with argon gas for charge and discharge tests. The PVDF-based solid electrolyte membrane prepared as above is used as electrolyte and separator, and a metal lithium sheet with a thickness of 0.4 mm and a diameter of 14 mm is used as the negative electrode. The negative electrode shell, spring sheet, gasket, lithium sheet, PVDF-based solid electrolyte membrane, positive electrode sheet, and positive electrode shell are assembled in this order to obtain a battery.

[0118] Example 6

[0119] This embodiment provides a method for preparing a PVDF-based solid electrolyte membrane and a battery, comprising the following steps:

[0120] (S1) Preparation of an inorganic active material dispersion: 0.8 g of lithium lanthanum zirconium tantalum oxide and isopropyl alcohol are added to a zirconium oxide ball mill to obtain a ball milled mixed solution;

[0121] Pour the ball mill mixture into a beaker, wash the ball mill with isopropanol to collect the remaining liquid, and centrifuge to obtain a precipitate;

[0122] The precipitate was added with 5 mL of NMP for ultrasonic crushing to prepare an inorganic active material dispersion;

[0123] (S2) Preparation of FPI: 2 g of ODA was completely dissolved in 32 mL of NMP to obtain a mixed solution;

[0124] Under ice-water bath conditions, 4.5 g of 6FDA was added to the mixed solution three times, and the mixture was stirred and polymerized to obtain a fluorinated polyamic acid (FPAA) precursor;

[0125] The FPAA precursor was evenly coated onto a dry and clean glass plate, and then placed in water to remove the film. The film was then heated in sequence at a temperature gradient of 80°C / 1h+100°C / 1h+120°C / 1h+160°C / 1h+180°C / 1h+200°C / 1h for imidization to obtain FPI.

[0126] (S3) Preparation of PVDF-based solid electrolyte membrane: 1 g of the FPI prepared in step (S2) and 3 g of PVDF were mixed in 10 mL of NMP and magnetically stirred at room temperature for 1 h to obtain a PVDF / FPI composite solution;

[0127] 1.6 g of LITFSI (the mass of LITFSI is 40% of the sum of the mass of PVDF and FPI) was dissolved in 6.67 mL of NMP under stirring at room temperature to obtain a LITFSI dispersion;

[0128] The LITFSI dispersion and the inorganic active material dispersion prepared in step (S1) were added to the PVDF / FPI composite solution, magnetically stirred at room temperature for 1 hour, and coated with a 500 μm coating rod to form a film; then placed in a vacuum oven, dried at 60° C. for 48 hours under vacuum to remove the remaining solvent, and a PVDF-based solid electrolyte membrane (whose LSV curve is shown in FIG. 1 ) was obtained. Figure 2 As shown, the EIS impedance diagram is as follows Figure 3 The tensile properties are shown in Table 1, the ionic conductivity is shown in Table 2, and the discharge specific capacity and cycle life are shown in Table 3).

[0129] A battery is prepared based on the PVDF-based solid electrolyte membrane obtained above, as follows:

[0130] (1) Dissolve 1 g of PVDF in 15 mL of NMP to obtain a PVDF solution;

[0131] 7 g of lithium iron phosphate (LiFePO4, LFP) and 2 g of conductive carbon black were ground evenly, mixed with PVDF solution, and ball-milled at room temperature for 4 h to obtain a positive electrode slurry;

[0132] (2) Using aluminum foil as the positive electrode current collector, the positive electrode slurry prepared in step (S1) was coated on the aluminum foil (by scraping with a 25 μm coating rod to form a film), and then dried in a vacuum oven at 60° C. The aluminum foil was cut into discs with a diameter of 11 mm using a slicer as the positive electrode; and lithium discs with a diameter of 14 mm were used as the negative electrode;

[0133] (3) Assemble a standard button cell (CR 2032) in a glove box filled with argon gas for charge and discharge tests. The PVDF-based solid electrolyte membrane prepared as above is used as electrolyte and separator, and a metal lithium sheet with a thickness of 0.4 mm and a diameter of 14 mm is used as the negative electrode. The negative electrode shell, spring sheet, gasket, lithium sheet, PVDF-based solid electrolyte membrane, positive electrode sheet, and positive electrode shell are assembled in this order to obtain a battery.

[0134] Comparative Example 1

[0135] This comparative example provides a method for preparing a PVDF-based solid electrolyte membrane and a battery, comprising the following steps:

[0136] (S1) Preparation of an inorganic active material dispersion: 0.1 g of lithium lanthanum zirconium tantalum oxide and isopropyl alcohol are added to a zirconium oxide ball mill and ball milled to obtain a ball milled mixed solution;

[0137] Pour the ball mill mixture into a beaker, wash the ball mill with isopropanol to collect the remaining liquid, and centrifuge to obtain a precipitate;

[0138] The precipitate was added with 1.25 mL of NMP for ultrasonic crushing to prepare an inorganic active material dispersion;

[0139] (S2) Preparation of PVDF-based solid electrolyte membrane: 1 g of PVDF was mixed in 5 mL of NMP and magnetically stirred at room temperature for 1 h to obtain a PVDF solution;

[0140] 0.4 g LITFSI (the mass of LITFSI is 40% of the mass of PVDF) was dissolved in 1.67 mL NMP under stirring at room temperature to obtain a LITFSI dispersion;

[0141] The LITFSI dispersion and the inorganic active material dispersion prepared in step (S1) were added to the PVDF / FPI composite solution, magnetically stirred at room temperature for 1 hour, and coated with a 500 μm coating rod to form a film; then placed in a vacuum oven, dried at 60° C. for 48 hours under vacuum to remove the remaining solvent, and a PVDF-based solid electrolyte membrane (whose stress-strain curve is shown in FIG. 1 ) was obtained. Figure 1 As shown, the EIS impedance diagram is as follows Figure 3 As shown in the charge and discharge cycle test diagram Figure 4 The tensile properties are shown in Table 1, the ionic conductivity is shown in Table 2, and the discharge specific capacity and cycle life are shown in Table 3)

[0142] A battery is prepared based on the PVDF-based solid electrolyte membrane obtained above, as follows:

[0143] (1) Dissolve 1 g of PVDF in 15 mL of NMP to obtain a PVDF solution;

[0144] 7 g of lithium iron phosphate (LiFePO4, LFP) and 2 g of conductive carbon black were ground evenly, mixed with PVDF solution, and ball-milled at room temperature for 4 h to obtain a positive electrode slurry;

[0145] (2) Using aluminum foil as the positive electrode current collector, the positive electrode slurry prepared in step (S1) was coated on the aluminum foil (by scraping with a 25 μm coating rod to form a film), and then dried in a vacuum oven at 60° C. The aluminum foil was cut into discs with a diameter of 11 mm using a slicer as the positive electrode; and lithium discs with a diameter of 14 mm were used as the negative electrode;

[0146] (3) Assemble a standard button cell (CR 2032) in a glove box filled with argon gas for charge and discharge tests. The PVDF-based solid electrolyte membrane prepared as above is used as electrolyte and separator, and a metal lithium sheet with a thickness of 0.4 mm and a diameter of 14 mm is used as the negative electrode. The negative electrode shell, spring sheet, gasket, lithium sheet, PVDF-based solid electrolyte membrane, positive electrode sheet, and positive electrode shell are assembled in this order to obtain a battery.

[0147] Comparative Example 2

[0148] This comparative example provides a method for preparing a solid electrolyte membrane and a battery, comprising the following steps:

[0149] (S1) Preparation of an inorganic active material dispersion: 0.3 g of lithium lanthanum zirconium tantalum oxide and isopropyl alcohol are added to a zirconium oxide ball mill to obtain a ball milled mixed solution;

[0150] Pour the ball mill mixture into a beaker, wash the ball mill with isopropanol to collect the remaining liquid, and centrifuge to obtain a precipitate;

[0151] The precipitate is added into NMP for ultrasonic crushing to prepare an inorganic active material dispersion;

[0152] (S2) Preparation of FPI: 2 g of ODA was completely dissolved in 32 mL of NMP to obtain a mixed solution;

[0153] Under ice-water bath conditions, 4.5 g of 6FDA was added to the mixed solution three times, and the mixture was stirred and polymerized to obtain a fluorinated polyamic acid (FPAA) precursor;

[0154] The FPAA precursor was evenly coated onto a dry and clean glass plate, and then placed in water to remove the film. The film was then heated in sequence at a temperature gradient of 80°C / 1h+100°C / 1h+120°C / 1h+160°C / 1h+180°C / 1h+200°C / 1h for imidization to obtain FPI.

[0155] (S3) Preparation of solid electrolyte membrane: 3 g of the FPI prepared in step (S2) was mixed in NMP and magnetically stirred at room temperature for 1 h to obtain an FPI composite solution;

[0156] 1.2 g of LITFSI was dissolved in 5 mL of NMP under stirring at room temperature to obtain a LITFSI dispersion;

[0157] The LITFSI dispersion and the inorganic active material dispersion prepared in step (S1) were added to the FPI solution, magnetically stirred at room temperature for 1 hour, and coated with a 500 μm coating rod to form a film; then placed in a vacuum oven, dried at 60° C. for 48 hours under vacuum to remove the remaining solvent, and a PVDF-based solid electrolyte membrane (whose stress-strain curve is shown in FIG. 1 ) was obtained. Figure 1 As shown, the EIS impedance diagram is as follows Figure 3 As shown in the charge and discharge cycle test diagram Figure 4 The tensile properties are shown in Table 1, the ionic conductivity is shown in Table 2, and the discharge specific capacity and cycle life are shown in Table 3).

[0158] A battery is prepared based on the PVDF-based solid electrolyte membrane obtained above, as follows:

[0159] (1) Dissolve 1 g of PVDF in 15 mL of NMP to obtain a PVDF solution;

[0160] 7 g of lithium iron phosphate (LiFePO4, LFP) and 2 g of conductive carbon black were ground evenly, mixed with PVDF solution, and ball-milled at room temperature for 4 h to obtain a positive electrode slurry;

[0161] (2) Using aluminum foil as the positive electrode current collector, the positive electrode slurry prepared in step (S1) was coated on the aluminum foil (by scraping with a 25 μm coating rod to form a film), and then dried in a vacuum oven at 60° C. The aluminum foil was cut into discs with a diameter of 11 mm using a slicer as the positive electrode; and lithium discs with a diameter of 14 mm were used as the negative electrode;

[0162] (3) Assemble a standard button cell (CR 2032) in a glove box filled with argon gas for charge and discharge tests. The PVDF-based solid electrolyte membrane prepared as above is used as electrolyte and separator, and a metal lithium sheet with a thickness of 0.4 mm and a diameter of 14 mm is used as the negative electrode. The negative electrode shell, spring sheet, gasket, lithium sheet, PVDF-based solid electrolyte membrane, positive electrode sheet, and positive electrode shell are assembled in this order to obtain a battery.

[0163] Performance Analysis:

[0164] Figure 1 It is a stress-strain curve diagram of the solid electrolyte prepared by Examples 1 to 4 and Comparative Examples 1 to 2. Table 1 is a summary table of the tensile strength and elongation at break of the solid electrolytes prepared by Examples 1 to 6 and Comparative Examples 1 to 2. It can be found from Table 1 that with the increase of FPI in the system, the tensile strength of the composite solid electrolyte gradually increases, but the corresponding elongation at break decreases accordingly. At the same time, the tensile strength of the solid electrolyte prepared by Example 3 is 9.4MPa, and the elongation at break is 25.3%. The tensile strength of Example 6 is 10.1MPa, and the elongation at break is 17.1%. The above results show that after an excessive amount of inorganic active material is added to the solid electrolyte matrix, agglomeration will occur. When the composite solid electrolyte is subjected to external forces, uneven force is caused, thereby affecting the elongation at break.

[0165] Table 1 Tensile properties of Examples 1 to 6 and Comparative Examples 1 to 2

[0166]

[0167] Figure 2 The LSV curves of the solid electrolytes prepared in Examples 3 to 6 were tested using a Li|electrolyte|SS battery, with metal lithium and stainless steel electrodes on both sides. Figure 2 It can be found that when the scan voltage reaches 4.9V (vs. Li / Li + ), no obvious oxidation current was observed in Example 5, indicating that it has a wider and more stable electrochemical window compared with other examples (Example 1, Example 4 and Example 6).

[0168] Figure 3 The EIS impedance graphs of the solid electrolytes prepared in Examples 3 to 6 and Comparative Examples 1 to 2 are shown. The SS|electrolyte|SS symmetric blocking cell is assembled, where SS is a stainless steel electrode; specifically, the electrolyte is sandwiched between a pair of stainless steel electrodes with a diameter of 15.6 mm, and the AC impedance under different conditions is measured using an electrochemical workstation. After determining the specific impedance value, it is calculated using the formula: Figure 3It can be found that with the increase of FPI in the system, the ionic conductivity of the composite solid electrolyte first increases and then decreases. Due to the phase separation of the system, the lithium cation (Li + ) and organic fluoride anions (TFSI - ) are selectively enriched in the hydrophilic microphase and the hydrophobic microphase, respectively. A long-range ordered hydrophilic nanodomain is formed, which selectively enriches lithium ions, thereby providing an efficient conductive pathway.

[0169] Table 2 is a summary table of the ionic conductivity of the solid electrolytes prepared in Examples 1 to 6 and Comparative Examples 1 to 2. It can be seen from Table 2 that the introduction of inorganic active materials is conducive to lithium ion transport; however, excessive inorganic active fillers may have agglomerated and destroyed the permeation network, resulting in a decrease in the ionic conductivity of the solid-state lithium battery.

[0170] Table 2 Summary of ionic conductivity of composite solid electrolytes of Examples 1 to 6 and Comparative Examples 1 to 2

[0171]

[0172] Figure 4 The discharge capacity and cycle life curves of the solid electrolytes prepared in Example 5, Comparative Example 1, and Comparative Example 2 show that by introducing the solid electrolyte of the present invention into the battery, the battery exhibits very excellent discharge capacity and cycle life characteristics, and still exhibits 100% cycle life after 150 cycles of 0.1C charge and discharge; and it can be seen from the cycle data that Example 5 is better than Comparative Example 1, and Comparative Example 1 is better than Comparative Example 2. Table 3 is a summary table of the discharge capacity and cycle life of the solid electrolytes prepared in Examples 1 to 6 and Comparative Examples 1 to 2. It can be found from Table 3 that the solid electrolyte prepared in Example 5 generally has better performance.

[0173] Table 3 Summary of discharge capacity and cycle life of each solid electrolyte

[0174]

[0175]

[0176] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the explanation of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for preparing a PVDF-based solid electrolyte, characterized in that: The following steps are involved: (S1) After dissolving 4,4'-diaminodiphenyl ether, 4,4'-(hexafluoroisopropylene) diphthalic anhydride is added in batches under an ice bath, and mixed to obtain a fluorinated polyamic acid precursor; the fluorinated polyamic acid precursor is coated on a glass plate, and after demolding, it is heated according to a temperature gradient for imidization to obtain FPI; (S2) dissolving the FPI prepared in step (S1) and PVDF and mixing them to obtain a PVDF / FPI composite solution; dissolving lithium bis(trifluoromethylsulfonyl)imide to obtain a lithium bis(trifluoromethylsulfonyl)imide dispersion; Mixing the lithium bis(trifluoromethylsulfonyl)imide dispersion with the PVDF / FPI composite solution, or mixing the lithium bis(trifluoromethylsulfonyl)imide dispersion, the inorganic active material dispersion and the PVDF / FPI composite solution; drying to obtain the PVDF / FPI composite solid electrolyte; The inorganic active material dispersion is prepared by the following method: The inorganic active material is dissolved, ball-milled, and centrifuged. The precipitate is mixed with N-methylpyrrolidone and then ultrasonically crushed to obtain an inorganic active material dispersion.

2. The method for preparing a PVDF-based solid electrolyte according to claim 1, characterized in that: In step (S1), 4,4'-diaminodiphenyl ether is dissolved in a solvent, and the usage ratio of 4,4'-diaminodiphenyl ether to the solvent is 1 g: 10-30 mL; the mass ratio of 4,4'-diaminodiphenyl ether to 4,4'-(hexafluoroisopropylene) diphthalic anhydride is 1: 1-4.

3. The method for preparing a PVDF-based solid electrolyte according to claim 1, characterized in that: In step (S1), the temperature gradient conditions for heating imidization are specifically as follows: 1)80℃，1h； 2)100℃，1h； 3)120℃，1h； 4)160℃，1h； 5)180℃，1h； 6)200℃，1h。 4. The method for preparing a PVDF-based solid electrolyte according to claim 1, characterized in that: In step (S2), the mass ratio of PVDF to FPI is 5:1 to 1:5; The ratio of the sum of the mass of lithium bis(trifluoromethylsulfonyl)imide, PVDF and FPI is 1 to 6:10; The ratio of the sum of the mass of the inorganic active material, the mass of PVDF and the mass of FPI is 1:5-20.

5. The method for preparing a PVDF-based solid electrolyte according to claim 1, characterized in that: In step (S2), the inorganic active material is selected from Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li 14 ZnGe4O 16 , one of lithium phosphorus oxygen nitrogen, lithium lanthanum zirconium oxygen and lithium lanthanum zirconium tantalum oxygen; The inorganic active material is dissolved in the solvent, and the mass ratio of the inorganic active material to the solvent is 1:5 to 1:15; the mass ratio of the inorganic active material to N-methylpyrrolidone is 1:

10.

6. The method for preparing a PVDF-based solid electrolyte according to claim 1, characterized in that: In step (S2), during the ball milling process, the rotation speed is 600 to 900 r / min and the time is 5 to 7 hours.

7. The method for preparing a PVDF-based solid electrolyte according to claim 1, characterized in that: In step (S2), the drying process is carried out under vacuum conditions, at a temperature of 60 to 70° C., and for a period of 34 to 38 hours.

8. A PVDF-based solid electrolyte, characterized in that: It is prepared by the method according to any one of claims 1 to 7.

9. Use of the PVDF-based solid electrolyte as claimed in claim 8 in the preparation of a solid-state lithium battery.

10. A solid-state lithium battery, characterized in that: The solid-state lithium battery contains the PVDF-based solid-state electrolyte according to claim 8.

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