Preparation method of polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery

Abstract

The invention belongs to the technical field of lithium battery materials, and particularly relates to a preparation method of a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery, and the preparation method comprises the steps of preparing a composite solid electrolyte membrane and assembling the battery. Polyvinylidene fluoride hexafluoropropylene, lithium salt and nitrogen-methyl pyrrolidone are used as raw materials, and the plasticizer and the dendritic mesoporous nano silicon dioxide are added to prepare the composite solid electrolyte membrane, so that more conductive channels are provided for migration of lithium ions, and the electric capacity of the electrolyte is improved; according to the preparation method, the interface compatibility between the PVDF-HFP and the dendritic mesoporous nano silicon dioxide is improved, the electrochemical performance is improved, the crystallinity of the PVDF-HFP is reduced, and short circuit and explosion caused by the fact that dendritic crystals pierce the diaphragm are avoided; the invention solves the potential safety hazards caused by the traditional liquid electrolyte, such as leakage, combustion, explosion and the like, and has the advantages of simple preparation method and low cost, and is suitable for industrial large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery materials, and particularly relates to a preparation method of a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery. Background Art

[0002] Under the dual challenges of current global energy depletion and environmental crisis, optimizing the energy structure and exploring emerging renewable energy have become top priorities. Lithium-ion batteries, with their excellent energy density, long cycle life, and high discharge voltage, are leading the innovation trend in the new energy field. Currently, lithium-ion batteries generally use organic liquid electrolytes, which can effectively wet the electrodes and provide high ion transport efficiency. However, lithium-ion batteries using liquid electrolytes face multiple potential safety risks such as electrolyte leakage, volatilization, fire, and even explosion. In contrast, solid-state lithium batteries exhibit excellent safety performance due to their solid electrolytes. Polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), as a material with high mechanical strength and good electrochemical stability, has become an ideal material for solid electrolyte membranes.

[0003] It is very difficult for the mechanical properties of PVDF-HFP-based polymer electrolyte membranes to exceed those of diaphragms, and it is also very difficult to manufacture large-area polymer-based electrolyte films without any defects (such as voids). The existence of these defects may lead to problems such as internal short circuits in the battery. The high-rate charge and discharge performance and low-temperature performance of the battery are poor. The room-temperature ionic conductivity of the electrolyte is several times or even more than ten times smaller than that of the liquid electrolyte. In addition, the poor interfacial compatibility between the electrolyte and the electrode is also the direct reason for the poor high-rate charge and discharge performance and low-temperature performance of the battery. Therefore, there is an urgent need to develop a solid-state lithium battery that solves the above problems. Summary of the Invention

[0004] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a preparation method of a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery.

[0005] The purpose of the present invention is achieved through the following technical solutions: A preparation method of a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery, which includes the following steps: S1. Prepare a composite solid electrolyte membrane: Mix polyvinylidene fluoride-hexafluoropropylene (PVDF-HFP), a plasticizer, and a lithium salt, then add N-methylpyrrolidone (NMP), and stir at a temperature of 40 - 70 °C for 10 - 14 h until the polymer is fully dissolved. Then add a dendritic mesoporous nano-silica solution and mix evenly. The obtained slurry is coated, dried, and cut to obtain a PVDF-HFP / dendritic mesoporous nano-silica composite solid electrolyte membrane (PHS); among them, the preferred coating thickness is 40 - 1000 μm; Among them, the preparation method of the dendritic mesoporous nano-silica is as follows: (1) Preparation of organosilicon nanoparticles: At room temperature, ammonia water and a template are dissolved in a mixed solution of ethanol and deionized water to obtain an ammonia precursor solution, and stirred at a temperature of 30-60°C for 0.5-4 h; the organosilicon source is added in two portions while maintaining the temperature, and each addition is followed by continuous stirring for 1-48 h. After the stirring is completed, the mixture is centrifuged to obtain the product, benzene-bridged organosilicon nanoparticles; (2) Hydrothermal reaction: The benzene-bridged organosilicon nanoparticles are dispersed in water, and the dispersion is loaded into a hydrothermal reaction kettle with a polytetrafluoroethylene inner liner for reaction. The temperature of the reaction is 100-180°C, and the reaction time is 1-5 h. The reaction product is post-treated to obtain dendritic mesoporous nano-silica; S2. Assembling the battery: Assemble the composite solid electrolyte membrane prepared in step S1 in a lithium-ion battery to prepare a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery.

[0006] As a preferred technical solution, the plasticizer is at least one of malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile or sebaconitrile.

[0007] As a preferred technical solution, the lithium salt is LiPF 6 , LiTFSI, LiFSI, LiBOB, LiDFOB, LiBF 4 , LiClO 4 or LiAsF 6 Any one of them.

[0008] As a preferred technical solution, the weight ratio of polyvinylidene fluoride hexafluoropropylene, plasticizer, lithium salt and N-methylpyrrolidone is 1-15:1:2.5-20:15-50; the addition amount of dendritic mesoporous nano-silica is 0.1-8.0% of the total weight of the solute; As a preferred technical solution, in step (1), the template is at least one of cetyltrimethylammonium bromide, sodium dodecyl sulfate, cetyltrimethylammonium chloride, polyethylene glycol, polyoxyethylene ether, carbon nanotubes, carbon spheres or polystyrene-b-polyethylene oxide; the organosilicon source is one or two of methoxytrimethylsilane, trimethylsilane, chloromethyltrimethylsilane, triethoxysilylethylene, dimethyloxysilane, silane coupling agent, organosilicon resin, tetraethyl orthosilicate, 1,4-bis(triethoxysilyl)benzene or bis(trimethylsilyl)methane.

[0009] More preferably, the mass-volume ratio of the template to ammonia water is 0.1 - 2.5 g:0.1 - 10 mL, the volume ratio of ammonia water, ethanol and deionized water is 1:10 - 60:15 - 150, and the volume ratio of ammonia water to the organosilicon source is 1:0.1 - 2.5; the mass-volume ratio of the benzene-bridged organosilicon nanoparticles to water is 0.1 - 1 mg:1 - 10 mL.

[0010] As a preferred technical solution, the specific operation of the post-treatment in step (2) is: after cooling the reaction product for 24 h, washing it with ultrasonic water and ethanol, centrifuging and separating the mixed solution by a centrifuge, dispersing the centrifuged product in a mixed solution of ethanol and hydrochloric acid, where the volume ratio of ethanol to hydrochloric acid is 1 - 50 mL:1 - 20 μL, stirring at 20 - 80 °C and 100 - 1000 rpm for 1 - 24 h, repeating 1 - 5 times, then washing with ultrasonic water and freeze-drying by a freeze dryer to obtain dendritic mesoporous nano-silica.

[0011] As a preferred technical solution, the positive electrode sheet of the lithium-ion battery in step S2 is prepared by the following method: adding polyvinylidene fluoride and a plasticizer to N-methylpyrrolidone and stirring overnight to obtain a transparent solution, grinding and mixing lithium iron phosphate and acetylene black evenly in a mortar, then adding the transparent liquid to the mortar and continuing to grind until the slurry becomes black, bright and viscous, coating the ground slurry on an aluminum foil, drying in an oven at 40 - 80 °C for 10 - 48 h, and cutting into circular pieces with a cutter.

[0012] As a preferred technical solution, the plasticizer is at least one of malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaonitrile or sebaconitrile; the weight ratio of lithium iron phosphate, polyvinylidene fluoride, acetylene black and the plasticizer is 7 - 10:0.1 - 2:0.1 - 2:0.1 - 2; the volume ratio of N-methylpyrrolidone to the mass of lithium iron phosphate is 1 - 12 mL:1 - 5 g.

[0013] As a preferred technical solution, the lithium-ion battery in step S2 is assembled in the order of positive electrode case, positive electrode sheet, solid electrolyte membrane, negative electrode, stainless steel sheet, spring piece, negative electrode case, and the assembled battery is placed on a battery sealing machine and pressurized to 450 - 650 kg·cm -2 .

[0014] In the present invention, the negative electrode selects a metallic lithium sheet with a diameter of 15.6 mm and a thickness of 0.6 mm, and the metallic lithium sheet is passivated. The passivation treatment can be: dropping a dimethyl sulfoxide solution of phytic acid onto the metallic lithium sheet for reaction, then washing with tetrahydrofuran (THF) and drying; or uniformly dropping a poly(diallyldimethylammonium)-bis(trifluoromethanesulfonylimide) solution onto the surface of the metallic lithium sheet and then drying; or soaking the metallic lithium sheet with fluoroethylene carbonate.

[0015] In the present invention: 1. Using PVDF-HFP (polyvinylidene fluoride-hexafluoropropylene) as the solid electrolyte substrate has the following advantages: (1) Long cycle life and strong stability: Compared with liquid electrolytes, solid electrolytes have a more stable interaction with electrode materials and better lithium stability. Due to the high electronegativity of fluorine, introducing fluorinated groups into polymers can improve the electrochemical window of polymer solid electrolytes. And fluorine can react with lithium ions in the electrolyte to form LiF, thereby forming a SEI passivation layer to promote the uniform transport and deposition of lithium ions, so as to improve the cycle stability of the battery. And HFP, as an ion-conducting plasticizer, can copolymerize with PVDF to increase the amorphous phase region of the polymer and improve the ion conductivity.

[0016] (2) Good conductivity and high energy density: PVDF has a high dielectric constant, and strong polar groups (-C-F-) will promote the dissolution of lithium salts, thus forming a high concentration of carriers, so it has a strong affinity for electrolytes; a large lithium ion transference number is beneficial to reducing the polarization phenomenon caused by concentration difference during charge and discharge, so that the battery has a higher energy density.

[0017] (3) Reducing the growth of lithium dendrites and high safety: The unique pore structure of PVDF-HFP can provide an additional Li ＋ migration path and can promote the uniform deposition of Li ＋ during charge and discharge, reducing the excessive growth of lithium dendrites and avoiding safety problems such as combustion and explosion that may be caused by the contact between the positive and negative electrodes of the battery.

[0018] (4) Low cost: PVDF has excellent flexibility, is easy to process and form, can be applied to batteries of various shapes, has a simple processing technology, and is easy to achieve large-scale production.

[0019] 2. Using dendritic mesoporous nano-silica as the filler has the following advantages: Nano-silica is divided into solid silica, mesoporous silica, hollow mesoporous silica and dendritic mesoporous silica. Among them, dendritic mesoporous silica is a material with a special three-dimensional center-radiating pore structure and hierarchical pore structure, which has a large specific surface area, a large pore volume and a narrow pore size distribution. And hollow mesoporous silica nanoparticles are simple core-shell structures, with an empty core in the center and a mesoporous shell layer on the outside. Different from the structure of dendritic mesoporous silica, dendritic mesoporous silica is a combination of a mesoporous inner layer and a dendritic outer layer.

[0020] In the present invention, the mechanism of action of dendritic mesoporous silica is as follows: The plasticizer can reduce the crystallinity of PVDF-HFP, improve the flexibility of the molecular chains, and establish a three-dimensional network structure to enhance the lithium ion conductivity. However, it will reduce the mechanical properties of PVDF-HFP. On this basis, we add dendritic mesoporous silica, which can significantly improve the mechanical properties of PVDF-HFP. The uniform dispersion of dendritic mesoporous silica can open up the aggregated and entangled PVDF-HFP molecular chains and further reduce its crystallinity to improve the flexibility of the molecular chains. The diameter of lithium ions is about 0.1 nanometer, and the size of dendritic mesoporous silica is about 200 nanometers. Its developed three-dimensional central radial pore channels and hierarchical pore structure provide more channels for the transport of lithium ions. The abundant Lewis acid centers of dendritic mesoporous silica can effectively fix bis(fluorosulfonyl)imide anions (TFSI-), thereby promoting the release of more highly free lithium ions, further increasing the concentration of free lithium ions in the electrolyte, directly enhancing the ionic conductivity of the electrolyte, and contributing to the improvement of battery performance. The immobilized TFSI⁻ may form a space charge layer on the material surface, generating an interfacial electric field that triggers the hopping transport of lithium ions under the action of the electric field, further promoting the migration of lithium ions.

[0021] 3. Environmentally friendly: Most of the materials used in solid-state batteries will not cause pollution to the environment, demonstrating environmental friendliness.

[0022] 4. Simple process and low cost: The processing technology of polymer solid electrolytes is simple and easy to achieve large-scale production.

[0023] The present invention has the following advantages: (1) Using dendritic mesoporous silica nanoparticles as inorganic fillers to prepare PHS provides more conductive channels for the migration of lithium ions. With the characteristic of high specific surface area, it can increase the capacitance of the electrolyte.

[0024] (2) Through a unique surface modification technology, the present invention improves the interfacial compatibility between PVDF-HFP and silica nanoparticles, ensures the seamless bonding of the electrolyte with the positive and negative electrode materials, reduces the interfacial resistance, improves the electrochemical performance, and enhances the interfacial compatibility.

[0025] (3) By regulating the micro-pore structure of PHS, a hierarchical ion transport channel can be established, which helps to increase the ionic conductivity and effectively inhibit the growth of lithium dendrites.

[0026] (4) The addition of dendritic mesoporous silica not only provides additional ion transport paths, but also, by using a special composite process, increases the mechanical toughness of the composite material. Even under extreme charge-discharge conditions, the integrity of the structure can be maintained, significantly extending the cycle life of the battery and enhancing the mechanical properties. The present invention also discloses a new method for preparing dendritic mesoporous silica.

[0027] (5) The PHS should have a wide electrochemical stability window, enabling the battery to operate stably within a wider voltage range to adapt to different types of electrode materials, thus broadening the electrochemical stability window. Description of the Drawings

[0028] Figure 1 Scanning electron microscope images of different materials of the present invention, where (a) is PVDF-HFP, (b) is PVDF-HFP / plasticizer, (c-d) are dendritic mesoporous nano-silica, and (e-f) are PHS.

[0029] Figure 2 It is a thermogravimetric curve of PHS.

[0030] Figure 3 It is an EIS diagram of stainless steel sheet|PHS|stainless steel sheet in the temperature range of 30 - 80 °C.

[0031] Figure 4 It is the charge and discharge curves of LFP|PHS|Li battery at different rates.

[0032] Figure 5 It is the cycle performance of LFP|PHS|Li battery at 0.5 C rate. Specific Embodiments

[0033] The following further describes the present invention in conjunction with the drawings and embodiments. The protection scope of the present invention is not limited to the following: Embodiment 1: A method for preparing a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery, which includes the following steps: S1. Prepare a composite solid electrolyte membrane: S11. The method for preparing dendritic mesoporous nano-silica is as follows: (1) Preparation of organosilicon nanoparticles: At room temperature, ammonia water and the template cetyltrimethylammonium bromide salt are dissolved in a mixed solution of ethanol and deionized water to obtain an ammonia precursor solution, which is stirred at 30 °C for 4 h; at this temperature, the organosilicon source methoxymethyltrimethoxysilane is added in two portions. After the first addition, stirring is continued for 1 h, and after the second addition, stirring is continued for 48 h. After the stirring is completed, the mixture is centrifuged to obtain the product phenyl-bridged organosilicon nanoparticles; the mass-volume ratio of the template to ammonia water is 0.1 g:3 mL, the volume ratio of ammonia water, ethanol to deionized water is 1:10:15, and the volume ratio of ammonia water to the organosilicon source is 1:0.1.

[0034] (2) Hydrothermal reaction: The phenyl-bridged organosilicon nanoparticles are dispersed in water, and the mass-volume ratio of the phenyl-bridged organosilicon nanoparticles to water is 0.1 mg:1 mL. The dispersion is loaded into a polytetrafluoroethylene-lined hydrothermal reaction kettle for reaction. The reaction temperature is 100 °C, and the reaction time is 5 h. After the reaction product is cooled for 24 h, it is washed with ultrasonic water and ethanol, and then the mixed solution is centrifuged by a centrifuge. The centrifuged product is dispersed in a mixed solution of ethanol and hydrochloric acid, where the volume ratio of ethanol to hydrochloric acid is 30 mL:10 μL, and it is stirred at 20 °C and 100 rpm for 24 h, and this is repeated once. After ultrasonic water washing, it is freeze-dried by a freeze dryer to obtain dendritic mesoporous nano-silica.

[0035] S12. Polyvinylidene fluoride-hexafluoropropylene, the plasticizer malononitrile, and the lithium salt LiTFSI are mixed and then added to N-methylpyrrolidone, and stirred at 40 °C for 14 h until the polymer is fully dissolved. Then the dendritic mesoporous nano-silica solution is added and mixed evenly. The obtained slurry is transferred to a glass plate for coating, drying, and cutting. The coating thickness is 40 μm, and PHS is prepared. Among them, the weight ratio of polyvinylidene fluoride-hexafluoropropylene, the plasticizer, the lithium salt, and N-methylpyrrolidone is 1:1:2.5:15; the addition amount of dendritic mesoporous nano-silica is 0.1% of the total solute weight; S2. Battery assembly: S21. The positive electrode sheet is prepared by the following method: Lithium iron phosphate (LFP) and acetylene black are ground in an agate mortar to make the two powders evenly mixed. Polyvinylidene fluoride and the plasticizer (malononitrile) are added to N-methylpyrrolidone (NMP) and stirred overnight to obtain a transparent solution. The transparent liquid is added to the mortar and mixed with LFP and acetylene black, and grinding is continued until the slurry becomes a black, shiny, and viscous slurry. The slurry is coated on an aluminum foil and dried in an oven at 40 °C for 48 h, and then cut into 12 mm diameter circular pieces with a cutter. Among them, the weight ratio of lithium iron phosphate, polyvinylidene fluoride, acetylene black, and the plasticizer is 7:0.1:0.1:0.1, and the volume ratio of N-methylpyrrolidone to the mass of lithium iron phosphate is 1 mL:1 g.

[0036] S22. The negative electrode uses a lithium metal sheet with a diameter of 15.6 mm and a thickness of 0.6 mm. The dimethyl sulfoxide solution of phytic acid is dropped onto the lithium metal sheet and reacted for 3 h, then washed with tetrahydrofuran (THF) and dried.

[0037] S23. The lithium-ion battery is assembled in the order of the positive electrode case, the positive electrode sheet, the solid electrolyte membrane, the negative electrode, the stainless steel sheet, the spring piece, and the negative electrode case. The assembled battery is placed on a battery sealing machine and pressurized to 450 kg·cm -2 .

[0038] Example 2: A preparation method of a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery, which includes the following steps: S1. Prepare a composite solid electrolyte membrane: S11. The preparation method of dendritic mesoporous nano-silica is as follows: (1) Prepare organosilicon nanoparticles: At room temperature, ammonia water and a template (sodium dodecyl sulfate and cetyltrimethylammonium bromide, with a weight ratio of 1:1) are dissolved in a mixed solution of ethanol and deionized water to obtain an ammonia precursor solution, which is stirred at a temperature of 60 °C for 4 h; while maintaining the temperature, the organosilicon source is added in two portions, and each portion is continuously stirred for 48 h after addition. After the stirring ends, the mixed solution is centrifuged to obtain the product, benzene-bridged organosilicon nanoparticles; the mass-volume ratio of the template to ammonia water is 2.5 g:10 mL, the volume ratio of ammonia water, ethanol, and deionized water is 1:60:150, and the volume ratio of ammonia water to the organosilicon source is 1:1.5.

[0039] (2) Hydrothermal reaction: The benzene-bridged organosilicon nanoparticles are dispersed in water. The mass-volume ratio of the benzene-bridged organosilicon nanoparticles to water is 1 mg:10 mL. The dispersion is loaded into a hydrothermal reaction kettle with a polytetrafluoroethylene inner liner for reaction. The temperature of the reaction is 180 °C, and the reaction time is 1 h. After the reaction product is cooled for 24 h, it is washed by ultrasonic wave with water and ethanol, and then the mixed solution is centrifuged by a centrifuge. The centrifuged product is dispersed in a mixed solution of ethanol and hydrochloric acid, where the volume ratio of ethanol to hydrochloric acid is 50 mL:20 μL. It is stirred at 80 °C and 1000 rpm for 1 h, and repeated 5 times. After ultrasonic washing with water again, it is freeze-dried by a freeze dryer to obtain dendritic mesoporous nano-silica.

[0040] S12. Mix poly(vinylidene fluoride - hexafluoropropylene), plasticizers (succinonitrile and glutaronitrile, with a volume ratio of 2:1), and lithium salt LiFSI, then add them to N - methyl - 2 - pyrrolidone. Stir at 70 °C for 10 h until the polymer is fully dissolved. Then add the dendritic mesoporous nano - silica solution and mix evenly. Transfer the obtained slurry to a glass plate for coating, drying, and cutting. The thickness of the coating is 1000 μm to obtain PHS. Among them, the weight ratio of poly(vinylidene fluoride - hexafluoropropylene), plasticizer, lithium salt, and N - methyl - 2 - pyrrolidone is 15:1:20:50; the addition amount of dendritic mesoporous nano - silica is 8.0% of the total weight of the solute; S2. Assemble the battery: S21. The positive electrode sheet is prepared by the following method: Lithium iron phosphate (LFP) and acetylene black are ground in an agate mortar to make the two powders evenly mixed. Add poly(vinylidene fluoride) and plasticizers (glutaronitrile and adiponitrile, with a volume ratio of 2:1) to N - methyl - 2 - pyrrolidone (NMP) and stir overnight to obtain a transparent solution. Add the transparent liquid to the mortar and mix with LFP and acetylene black, and continue grinding until the slurry becomes a black, shiny, and viscous slurry. Coat the slurry on aluminum foil and dry it in an oven at 80 °C for 10 h, and then cut it into circular pieces with a diameter of 12 mm using a cutting machine. Among them, the weight ratio of lithium iron phosphate, poly(vinylidene fluoride), acetylene black, and plasticizer is 10:2:2:2, and the addition amount of N - methyl - 2 - pyrrolidone is 12 mL:5 g in terms of the volume - to - mass ratio of N - methyl - 2 - pyrrolidone to lithium iron phosphate.

[0041] S22. Select a metallic lithium sheet with a diameter of 15.6 mm and a thickness of 0.6 mm as the negative electrode, and soak the metallic lithium sheet in fluoroethylene carbonate for 5 h for passivation treatment.

[0042] S23. Assemble the lithium - ion battery in the order of positive electrode shell, positive electrode sheet, solid electrolyte membrane, negative electrode, stainless - steel sheet, spring piece, and negative electrode shell. Place the assembled battery on a battery sealing machine and apply pressure to 650 kg·cm -2 .

[0043] Example 3: A preparation method of a poly(vinylidene fluoride - hexafluoropropylene) - based solid - state lithium battery, which includes the following steps: S1. Prepare a composite solid electrolyte membrane: S11. The preparation method of dendritic mesoporous nano - silica is: (4) Preparation of organosilicon nanoparticles: At room temperature, ammonia water and a template (cetyltrimethylammonium bromide, sodium dodecyl sulfate, and polystyrene-b-polyoxyethylene, with a weight ratio of 3:2:1) are dissolved in a mixed solution of ethanol and deionized water to obtain an ammonia precursor solution, which is stirred at 40 °C for 1 h; at the same temperature, an organosilicon source (tetraethyl orthosilicate and bis(trimethylsilyl)methane, with a weight ratio of 1:2) is added in two portions, and the mixture is stirred for 12 h each time after addition. After stirring, the mixture is centrifuged to obtain the product, benzene-bridged organosilicon nanoparticles; the mass-volume ratio of the template to ammonia water is 1 g:0.1 mL, the volume ratio of ammonia water, ethanol, and deionized water is 1:38:100, and the volume ratio of ammonia water to the organosilicon source is 1:0.1.

[0044] (2) Hydrothermal reaction: The benzene-bridged organosilicon nanoparticles are dispersed in water, with a mass-volume ratio of the benzene-bridged organosilicon nanoparticles to water of 0.4 mg:5 mL. The dispersion is loaded into a hydrothermal reaction kettle with a polytetrafluoroethylene inner liner for reaction. The reaction temperature is 130 °C, and the reaction time is 2 h. After the reaction product is cooled for 24 h, it is washed with ultrasonic water and ethanol, and then the mixed solution is centrifuged and separated by a centrifuge. The centrifuged product is dispersed in a mixed solution of ethanol and hydrochloric acid, where the volume ratio of ethanol to hydrochloric acid is 1 mL:1 μL. The mixture is stirred at 40 °C and 500 rpm for 10 h, and this process is repeated 3 times. After ultrasonic water washing, it is freeze-dried by a freeze dryer to obtain dendritic mesoporous nano-silica.

[0045] S12. Polyvinylidene fluoride-hexafluoropropylene, a plasticizer (succinonitrile, glutaronitrile, and adiponitrile, with a volume ratio of 2:2:1), and a lithium salt (LiPO 2 F 2 ) are mixed and then added with N-methylpyrrolidone. The mixture is stirred at 52 °C for 12 h until the polymer is fully dissolved. Then, a dendritic mesoporous nano-silica solution is added and mixed evenly. The resulting slurry is transferred onto a glass plate for coating, drying, and cutting. The coating thickness is 450 μm to prepare PHS. Among them, the weight ratio of polyvinylidene fluoride-hexafluoropropylene, the plasticizer, the lithium salt, and N-methylpyrrolidone is 5:1:7:20; the addition amount of dendritic mesoporous nano-silica is 3 wt% of the total solute weight; S2. Assembling the battery: S21. The positive electrode sheet is prepared by the following method: Lithium iron phosphate (LFP) and acetylene black are ground in an agate mortar to make the two powders evenly mixed. Polyvinylidene fluoride and plasticizers (adiponitrile, pimelonitrile, and suberonitrile, with a volume ratio of 1:2:3) are added to N-methylpyrrolidone (NMP) and stirred overnight to obtain a transparent solution. The transparent liquid is added to the mortar and mixed with LFP and acetylene black, and grinding is continued until the slurry becomes a black, shiny, and viscous slurry. The slurry is coated on an aluminum foil and dried in an oven at 70 °C for 22 h, and then cut into 12-mm-diameter circular pieces with a cutting machine. Among them, the weight ratio of the lithium iron phosphate, polyvinylidene fluoride, acetylene black, and plasticizer is 7.5:1.4:1:1, and the addition amount of N-methylpyrrolidone is a volume-to-mass ratio of 4 mL:4 g with respect to the lithium iron phosphate; S22. The negative electrode uses a metallic lithium sheet with a diameter of 15.6 mm and a thickness of 0.6 mm, and a poly(diallyldimethylammonium)-bis(trifluoromethanesulfonylimide) solution is evenly dropped on the surface of the metallic lithium sheet and dried at 50 °C.

[0046] S23. The lithium-ion battery is assembled in the order of the positive electrode case, positive electrode sheet, solid electrolyte membrane, negative electrode, stainless steel sheet, spring piece, and negative electrode case. The assembled battery is placed on a battery sealing machine and pressurized to 500 kg·cm -2 .

[0047] Example 4: A preparation method of a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery, which includes the following steps: S1. Prepare a composite solid electrolyte membrane: S11. The preparation method of dendritic mesoporous nano-silica is as follows: (1) Prepare organosilica nanoparticles: At room temperature, ammonia water and templates (cetyltrimethylammonium bromide, sodium dodecyl sulfate, cetyltrimethylammonium bromide, and polystyrene microspheres, with a weight ratio of 1:1:1:2) are dissolved in a mixed solution of ethanol and deionized water to obtain an ammonia precursor solution, and stirred at a temperature of 50 °C for 3.5 h; the organosilica source is added in two portions while maintaining the temperature, and stirring is continued for 40 h each time after addition. After the stirring is completed, the mixture is centrifuged to obtain the product phenyl-bridged organosilica nanoparticles; among them, the mass-to-volume ratio of the template to ammonia water is 0.4 g:8 mL, the volume ratio of ammonia water, ethanol, and deionized water is 1:10:15, and the volume ratio of ammonia water to the organosilica source is 1:2.4.

[0048] (2) Hydrothermal reaction: The benzene-bridged organosilica nanoparticles were dispersed in water, and the mass-volume ratio of the benzene-bridged organosilica nanoparticles to water was 0.8 mg: 8 mL. The dispersion was loaded into a hydrothermal reaction kettle with a polytetrafluoroethylene inner liner for reaction. The reaction temperature was 170 °C, and the reaction time was 4 h. After the reaction product was cooled for 24 h, it was washed with ultrasonic water and ethanol, and then the mixed solution was centrifuged and separated by a centrifuge. The centrifuged product was dispersed in a mixed solution of ethanol and hydrochloric acid, where the volume ratio of ethanol to hydrochloric acid was 40 mL: 17 μL, and stirred at 50 °C and 800 rpm for 20 h, repeated 4 times. After ultrasonic water washing, it was freeze-dried by a freeze dryer to obtain dendritic mesoporous nano-silica.

[0049] S12. Polyvinylidene fluoride hexafluoropropylene, plasticizers (adiponitrile, suberonitrile, azelaonitrile, and sebaconitrile, volume ratio 1: 2: 2: 1), and lithium salt LiDFOB were mixed and then added to N-methylpyrrolidone, and stirred at 60 °C for 13.5 h until the polymer was fully dissolved. Then dendritic mesoporous nano-silica solution was added and mixed evenly. The obtained slurry was transferred onto a glass plate for coating, drying, and cutting. The coating thickness was 200 μm to prepare PHS; wherein, the weight ratio of polyvinylidene fluoride hexafluoropropylene, plasticizer, lithium salt, and N-methylpyrrolidone was 14: 1: 4: 35; the addition amount of dendritic mesoporous nano-silica was 4% of the total solute weight.

[0050] S2. Battery assembly: S21. The positive electrode sheet was prepared by the following method: Lithium iron phosphate (LFP) and acetylene black were ground in an agate mortar to make the two powders evenly mixed. Polyvinylidene fluoride and plasticizers (adiponitrile, suberonitrile, azelaonitrile, and sebaconitrile, volume ratio 1: 1: 2: 2) were added to N-methylpyrrolidone (NMP) and stirred overnight to obtain a transparent solution. The transparent liquid was added to the mortar and mixed with LFP and acetylene black, and grinding was continued until the slurry became a black, shiny, and viscous slurry. The slurry was coated on an aluminum foil and dried in an oven at 75 °C for 40 h, and then cut into 12 mm diameter circular pieces with a cutter. Among them, the weight ratio of lithium iron phosphate, polyvinylidene fluoride, acetylene black, and plasticizer was 9: 1.8: 1.5: 1, and the volume ratio of N-methylpyrrolidone to the mass of lithium iron phosphate was 7 ml: 3 g.

[0051] S22. The negative electrode was a metallic lithium sheet with a diameter of 15.6 mm and a thickness of 0.6 mm, and the metallic lithium sheet was soaked in fluoroethylene carbonate for 5 h for passivation treatment.

[0052] S23. The lithium-ion battery was assembled in the order of positive electrode shell, positive electrode sheet, solid electrolyte membrane, negative electrode, stainless steel sheet, spring piece, and negative electrode shell. The assembled battery was placed on a battery sealing machine and pressurized to 600 kg·cm -2 .

[0053] The beneficial effects of the present invention are illustrated by the following experiments: Experimental Example 1: Preparation of PHS Step (1): At room temperature, dissolve 2 g of CTAB and 7 mL of ammonia water in a flat-bottom flask containing an H 2 O (120 mL) / ethanol (80 mL) solution, and vigorously stir in an oil bath at 35°C for 1 h. While maintaining the temperature, quickly add a mixture of TEOS (2 mL) / BTSB (1.5 mL) to the solution and stir for 24 hours. Then reintroduce the mixture of TEOS (2 mL) / BTSB (1.5 mL) into the system and stir while maintaining the temperature for 24 hours.

[0054] Step (2): Place the mixed solution in a centrifuge and centrifuge at a speed of 10000 rpm for 10 min to obtain the separated product, solid silica nanoparticles, which are washed ultrasonically with water multiple times.

[0055] Step (3): Disperse the solid silica nanoparticles synthesized in the above step in a flat-bottom flask containing deionized water for the following synthesis. Place the flask in an ultrasonic cleaner and use the ultrasonic cleaner to completely disperse the benzene-bridged organosilica nanoparticles until no precipitation occurs after the flat-bottom flask is left standing for a period of time. Pour the dispersion in the flask into a hydrothermal reaction kettle with a polytetrafluoroethylene inner lining. Place the hydrothermal reaction kettle with the polytetrafluoroethylene inner lining in an electrothermal constant temperature forced air drying oven, set the drying oven temperature to 130°C, and after the temperature reaches, keep the temperature for 5 h and then turn off the power of the drying oven. After the drying oven has cooled completely for 24 h, take out the reaction kettle.

[0056] Step (4): Place the mixed solution in a centrifuge and centrifuge at a speed of 10000 rpm for 10 min. After obtaining the separated product, perform 1 ultrasonic water wash and 2 ethanol washes to obtain silica.

[0057] Step (5): Disperse the silica in a flat-bottom flask containing a magnetic stirrer, ethanol, and HCl solution (Vethanol = 30 mL, VHCI = 10 μL), and stir at a speed of 500 rpm at 60°C for 12 h.

[0058] Step (6): Finally, perform one ultrasonic water wash and centrifuge the product at a speed of 10000 rpm for 10 min. After freeze-drying by a freeze dryer, dendritic mesoporous silica nanoparticles are obtained.

[0059] Step (7): Polyvinylidene fluoride - hexafluoropropylene (PVDF - HFP), succinonitrile (SCN), and lithium salt (LiTFSI) are mixed in a mass ratio of 8:1.5:2. Then, 7 mL of N - methyl - 2 - pyrrolidone (NMP) is added. The mixture is placed on a magnetic stirrer and magnetically stirred at 60 °C (580 rpm) for 12 hours until the polymer is fully dissolved.

[0060] Step (8): 3% of dendritic mesoporous nano - silica based on the total weight of the solute is added. An ultrasonic cleaner is used to uniformly disperse the dendritic mesoporous nano - silica in the polymer matrix. The solution is coated on a glass plate with a thickness of 300 μm, then dried and cut into pieces. The diameter of the PHS disc is 19 mm and it is placed in a glove box filled with argon for 24 h for standby.

[0061] Experimental Example 2: Preparation of PHS: Step (1): Synthesize dendritic mesoporous nano - silica by the method in Experimental Example 1.

[0062] Step (2): Polyvinylidene fluoride hexafluoropropylene (PVDF - HFP), succinonitrile (SCN), and lithium salt (LiTFSl) are mixed in a mass ratio of 8:1.5:2. Then, 7 mL of N - methyl - 2 - pyrrolidone (NMP) is added. The mixture is placed on a magnetic stirrer and magnetically stirred at 60 °C (580 rpm) for 12 hours until the polymer is fully dissolved.

[0063] Step (3): 0.5% of dendritic mesoporous nano - silica based on the total weight of the solute is added. An ultrasonic cleaner is used to uniformly mix the dendritic mesoporous nano - silica in the polymer matrix. The solution is coated on a glass plate with a thickness of 800 μm, then dried and cut into pieces. The diameter of the PHS disc is 19 mm and it is placed in a glove box filled with argon for 24 h for standby.

[0064] Experimental Example 3: Preparation of PHS: Step (1): Synthesize dendritic mesoporous nano - silica by the method in Experimental Example 1.

[0065] Step (2): Polyvinylidene fluoride hexafluoropropylene (PVDF - HFP), succinonitrile (SCN), and lithium salt (LiTFSl) are mixed in a mass ratio of 8:1.5:2. Then, 7 mL of N - methyl - 2 - pyrrolidone (NMP) is added. The mixture is placed on a magnetic stirrer and magnetically stirred at 60 °C (580 rpm) for 12 hours until the polymer is fully dissolved.

[0066] Step (3): Add dendritic mesoporous nano-silica with a total weight of 4% of the solute, and use an ultrasonic cleaner to uniformly mix the dendritic mesoporous nano-silica in the polymer matrix. Coat the solution on a glass plate with a thickness of 800 μm, then dry and cut the film. The diameter of the PHS wafer is 19 mm, and it is placed in a glove box filled with argon for 24 h for standby.

[0067] Experimental Example 4: Preparation of PHS: Step (1): Synthesize dendritic mesoporous nano-silica by the method in Experimental Example 1.

[0068] Step (2): Mix polyvinylidene fluoride hexafluoropropylene (PVDF-HFP), succinonitrile (SCN), and lithium salt (LiTFSl) in a mass ratio of 8:1.5:2, then add 7 mL of N-methylpyrrolidone (NMP), place it on a magnetic stirrer, and magnetically stir at 60 °C (580 rpm) for 12 hours until the polymer is fully dissolved.

[0069] Step (3): Add dendritic mesoporous nano-silica with a total weight of 8.0% of the solute, and use an ultrasonic cleaner to uniformly mix the dendritic mesoporous nano-silica in the polymer matrix. Coat the solution on a glass plate with a thickness of 800 μm, then dry and cut the film. The diameter of the PHS wafer is 19 mm, and it is placed in a glove box filled with argon for 24 h for standby.

[0070] Experimental Example 5: Preparation of PHS: Step (1): Mix polyvinylidene fluoride hexafluoropropylene (PVDF-HFP), succinonitrile (SCN), and lithium salt (LiTFSI) in a mass ratio of 8:1.5:2, then add 7 mL of N-methylpyrrolidone (NMP), place it on a magnetic stirrer, and magnetically stir at 60 °C (580 rpm) for 12 hours until the polymer is fully dissolved.

[0071] Step (2): Do not add dendritic mesoporous nano-silica. Coat the solution on a glass plate with a thickness of 800 μm, then dry and cut the film. The diameter of the PHS wafer is 19 mm, and it is placed in a glove box filled with argon for 24 h for standby.

[0072] Experimental Example 6: Preparation method of lithium iron phosphate cathode material: Weigh lithium iron phosphate, acetylene black, polyvinylidene fluoride and succinonitrile with a mass ratio of 8:1.5:1:0.5. Grind lithium iron phosphate (LFP) and acetylene black in an agate mortar to evenly mix the two powders. Add polyvinylidene fluoride and succinonitrile to N-methylpyrrolidone (NMP) and stir overnight to obtain a transparent solution. The volume ratio of N-methylpyrrolidone to the mass of lithium iron phosphate is 6 mL:3 g. Add the transparent liquid to the mortar and mix it with LFP and acetylene black, and continue grinding until the slurry becomes a black, shiny and viscous slurry. Coat the slurry on the aluminum foil and place it in a drying oven at 70 °C for 24 h, and then cut it into 12-mm-diameter circular pieces with a cutting machine.

[0073] Experimental Example 7: Assembly of a solid-state lithium battery: Assemble the PHS prepared in Experimental Examples 1-5 and the lithium iron phosphate material positive electrode prepared in Experimental Example 6 into a battery. The assembly of the battery needs to be carried out in a glove box filled with argon. For the assembly of a button battery, assemble it in the order of positive electrode case, positive electrode sheet, solid electrolyte membrane, negative electrode, stainless steel sheet, shrapnel, and negative electrode case. The positive electrode sheet is the prepared lithium iron phosphate positive electrode, and the negative electrode is a metallic lithium sheet with a diameter of 15.6 mm and a thickness of 0.4 mm. Place the assembled battery on a battery sealing machine and apply pressure to 600 kg·cm -2 Take it out. After standing for 4 h, perform electrochemical tests on it using an electrochemical workstation and a BlueTEC test system. The nominal specific capacity of lithium iron phosphate is 170 mAh·g -1 and the working voltage is 2.5-3.8 V. Among them, the negative electrode is a metallic lithium sheet with a diameter of 15.6 mm and a thickness of 0.6 mm. Drop a dimethyl sulfoxide solution of phytic acid onto the metallic lithium sheet and react for 3 h, then wash it with tetrahydrofuran (THF) and dry it.

[0074] I: Physical characterization of materials: 1. Electron microscope analysis: Perform scanning electron microscope (SEM) analysis on PVDF-HFP, PVDF-HFP / plasticizer and PHS (Experimental Example 3), and perform transmission electron microscope analysis on dendritic mesoporous nano-silica. The results are as Figure 1As shown, where Figure (a) is PVDF-HFP and Figure (b) is PVDF-HFP / plasticizer. SEM data shows that pure PVDF-HFP has a higher crystallinity, a dense surface, and fewer continuous pores (Figure (a)). In contrast, a porous interconnected network structure with uniform pore distribution and uniform pore size is observed in PVDF-HFP / plasticizer, and no agglomeration is observed on the electrolyte surface. The results show that SCN improves the three-dimensional network structure of PVDF-HFP by reducing its crystallinity. Figures (c-d) are transmission electron microscope (TEM) images of dendritic mesoporous silica. Figure c shows that the synthesized dendritic mesoporous silica is of uniform size, evenly dispersed, and without agglomeration. Figure d shows that the diameter of the dendritic mesoporous silica is about 170 nm, the outer dendritic structure is developed about 50 nm, and the inner layer is a mesoporous structure about 75 nm. Figures (e-f) are scanning electron microscope images of PHS. The dendritic mesoporous silica is evenly dispersed in PHS, further reducing the crystallinity of PVDF-HFP, making the porosity of PHS higher, and increasing the lithium-ion transport channels (Figure (e)). Figure (f) shows a three-dimensional network interconnection of spherical structures with a diameter of about 8 µm, and dendritic mesoporous silica with a diameter of about 170 nm is distributed in the three-dimensional network structure, indicating the successful construction of a three-dimensional transport channel conducive to lithium-ion transfer. The well-connected pores in PHS provide sufficient space for ion conduction, and the dendritic mesoporous silica further increases the specific surface area, forming a continuous channel conducive to lithium-ion transport.

[0075] 2. Thermogravimetric analysis PHS was tested at a heating rate of 10 °C min -1 in a nitrogen environment in the temperature range of 30 - 800 °C to obtain thermogravimetric analysis (TG) and differential thermogravimetric analysis (DTG) data. The experimental results are as Figure 2 shown. The TGA data shows that when the temperature is higher than 284 °C, PSH loses 95% of its weight, indicating that PHS (Experimental Example 3) has sufficient thermal stability below 284 °C.

[0076] II. Electrochemical performance test: 1. Ion conductivity test The electrochemical performance test includes electrochemical impedance spectroscopy (EIS) test and charge-discharge cycle test. Using a CHI 760E electrochemical workstation, in the temperature range of 30 - 80 °C and a frequency range of 10 6 -10 2 Hz, EIS data of stainless steel sheet|PHS|stainless steel sheet was obtained with a perturbation of 10 mV. Figure 3The ionic conductivity of PHS (Experimental Example 3) at different temperatures is given: as the temperature rises, the ionic conductivity gradually increases, and at 80 °C, the ionic conductivity reaches 4.5×10 -4 S cm -1 .

[0077] 2. Rate performance test of solid-state lithium batteries: The battery configured with LFP|PHS|Li (passivated) was subjected to charge and discharge tests on a LANHE CT3001A blue battery test system. The test conditions included current rates of 0.1C, 0.2C, 0.5C, and 1C, as Figure 4 shown. The results show that the solid-state battery assembled with PHS (Experimental Example 3) has an initial discharge capacity of up to 169.2 mAh·g at a rate of 0.1 C -1 , which is 99% of the theoretical value. As the current density increases, the battery can still provide high capacities of 167.2, 151.1, and 146.5 mAh·g at current densities of 0.2, 0.5, and 1C -1 .

[0078] 3. Charge and discharge cycle performance test of solid-state lithium batteries PHS prepared in Experimental Examples 1-5 was assembled into batteries, and the first-cycle discharge specific capacity and capacity retention rate after 200 cycles were tested when the charge and discharge current density of the solid-state lithium battery was 0.5 C. The experimental results are shown in Table 1: Table 1: Performance parameters of solid-state lithium batteries in Experimental Examples 1-5 when the charge and discharge current density is 0.5 C Experimental Example <![CDATA[Initial discharge specific capacity (mAh·g -1 ).]]> Capacity Retention Rate after 200 Cycles 1 161.2 97.8% 2 151.3 94.5% 3 159.6 97.2% 4 157.4 96.3% 5 149.5 93.7% The battery configured with LFP|PHS|Li (passivated) (Experimental Example 3) was subjected to 200 charge and discharge cycle tests at a current density of 0.5 C at room temperature. The experimental results are as Figure 5 shown. The results show that the maximum discharge capacity of the battery is 159.6 mAh·g when the charge and discharge current density is 0.5 C -1 , and the capacity retention rate after 200 cycles is 97.2%. In addition, the solid-state battery also shows a stable Coulombic efficiency close to 100% during the cycling process.

[0079] In summary, the method of the present invention has the following advantages: 1. Solve the problem of liquid electrolytes: Solve the safety hazards brought by traditional liquid electrolytes, such as leakage, combustion, and explosion.

[0080] 2. Enhance thermal stability: The combination of the PVDF-HFP polymer matrix and the inorganic inert filler dendritic mesoporous nano-silica improves the thermal stability of the electrolyte, effectively inhibits the decomposition of lithium salts at high temperatures, and reduces the combustion risk.

[0081] 3. Suppressing the growth of lithium dendrites: The addition of dendritic mesoporous nano-silica enhances the mechanical strength of the electrolyte, helps to inhibit the formation of lithium dendrites, and avoids short circuits and explosions caused by dendrite piercing of the separator.

[0082] 4. Improving interface compatibility: By optimizing the material composition, the surface morphology of the electrolyte membrane is improved, the compatibility between PHS and the positive and negative electrode materials is enhanced, and the interface stability between the solid electrolyte and the lithium metal negative electrode is improved, making the ion insertion and extraction on the surface of the lithium metal negative electrode more uniform.

[0083] 5. Enhancing electrochemical performance: The three-dimensional network structure formed by PHS and the large specific surface area of dendritic mesoporous nano-silica provide more channels for the transport of lithium ions, promoting the improvement of ionic conductivity. Moreover, it also has a wide electrochemical stability window and is suitable for high-energy density battery systems.

[0084] 6. Reducing the crystallinity of PVDF-HFP: Through the introduction of plasticizers and dendritic mesoporous nano-silica fillers, the PVDF-HFP system undergoes a series of complex microstructure evolution processes. The combined action of the physical barrier effect and the change of the local environment not only significantly inhibits the ordered arrangement of molecular chains but also induces the formation of amorphous regions, effectively reducing the crystallinity.

[0085] As mentioned above, it is only the preferred specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art within the technical scope disclosed by the present invention, according to the technical solution of the present invention and its inventive concept, makes equivalent substitutions or changes, which are all covered by the protection scope of the present invention.

Claims

1. A method for preparing a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery, characterized in that: It includes the following steps: S1. Preparation of composite solid electrolyte membrane: The polyvinylidene fluoride-hexafluoropropylene, plasticizer and lithium salt are mixed, and then nitrogen-methyl pyrrolidone is added, and the mixture is stirred at a temperature of 40 to 70° C. for 10 to 14 hours until the polymer is fully dissolved, and then a dendritic mesoporous nano-silica solution is added and mixed evenly, and the obtained slurry is coated, dried and cut into pieces to obtain a PVDF-HFP / dendritic mesoporous nano-silica composite solid electrolyte membrane; Wherein, the preparation method of the dendritic mesoporous nano-silica is: (1) Preparation of organosilicon nanoparticles: dissolving ammonia water and a template in a mixed solution of ethanol and deionized water at room temperature to obtain an ammonia precursor solution, and stirring the solution at a temperature of 30 to 60° C. for 0.5 to 4 hours; adding an organosilicon source twice while maintaining the temperature, and stirring the solution continuously for 1 to 48 hours each time after adding the organosilicon source; after stirring, centrifuging the mixture to obtain the product benzene-bridged organosilicon nanoparticles; (2) hydrothermal reaction: dispersing the benzene-bridged organosilicon nanoparticles with water, and placing the dispersion into a polytetrafluoroethylene-lined hydrothermal reactor for reaction at a temperature of 100 to 180° C. for 1 to 5 hours. The reaction product is post-treated to obtain dendritic mesoporous nano-silica; S2. Assembling a battery: Assembling the composite solid electrolyte membrane prepared in step S1 in a lithium-ion battery to prepare a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery.

2. The method for preparing a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery according to claim 1, characterized in that: The plasticizer is at least one of malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile or sebacononitrile.

3. The method for preparing a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery according to claim 1, characterized in that: The lithium salt is any one of LiPF6, LiTFSI, LiFSI, LiBOB, LiDFOB, LiBF4, LiClO4 or LiAsF6.

4. The method for preparing a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery according to claim 1, characterized in that: The weight ratio of the polyvinylidene fluoride hexafluoropropylene, the plasticizer, the lithium salt and the nitrogen-methyl pyrrolidone is 1-15:1:2.5-20:15-50; the added amount of the dendritic mesoporous nano-silica is 0.1-8.0% of the total weight of the solute.

5. The method for preparing a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery according to claim 1, characterized in that: The template in step (1) is at least one of hexadecyltrimethylammonium bromide, sodium dodecyl sulfate, hexadecyltrimethylammonium bromide chloride, polyethylene glycol, polyoxyethylene ether, carbon nanotubes, carbon spheres or polystyrene-b-polyoxyethylene; the organosilicon source is one or two of methoxytrimethylsilane, trimethylsilane, chloromethyltrimethylsilane, triethoxysilylethylene, dimethyloxysilane, silane coupling agent, organosilicon resin, tetraethyl orthosilicate, 1,4-bis(triethoxysilyl)benzene or bistrimethylsilane.

6. The method for preparing a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery according to claim 1, characterized in that: The mass volume ratio of the template to ammonia water is 0.1-2.5 g:0.1-10 mL, the volume ratio of ammonia water, ethanol and deionized water is 1:10-60:15-150, the volume ratio of ammonia water to the organosilicon source is 1:0.1-2.5; the mass volume ratio of the benzene-bridged organosilicon nanoparticles to water is 0.1-1 mg:1-10 mL.

7. The method for preparing a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery according to claim 1, characterized in that: The specific operation of the post-treatment in step (2) is as follows: cooling the reaction product for 24 hours, washing it with ultrasonic water and ethanol, centrifuging the mixed solution by centrifuge, dispersing the centrifuged product in a mixed solution of ethanol and hydrochloric acid, wherein the volume ratio of ethanol to hydrochloric acid is 1-50 mL:1-20 μl, stirring at 20-80° C. and 100-1000 rpm for 1-24 hours, repeating 1-5 times, and then washing it with ultrasonic water, and freeze-drying it in a freeze dryer to obtain dendritic mesoporous nano-silica.

8. The method for preparing a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery according to claim 1, characterized in that: The positive electrode sheet of the lithium-ion battery described in step S2 is prepared by the following method: polyvinylidene fluoride and a plasticizer are added to nitrogen-methyl pyrrolidone and stirred overnight to obtain a transparent solution, and lithium iron phosphate and acetylene black are ground and mixed evenly in a grinding mortar, and then the transparent liquid is added to the grinding mortar and continued to be ground until the slurry becomes black and viscous, and the ground slurry is coated on aluminum foil, placed in a drying oven at 40 to 80° C. for 10 to 48 hours, and cut into discs with a cutting machine.

9. The method for preparing a polyvinylidene fluoride-hexafluoropropylene-based solid-state lithium battery according to claim 8, characterized in that: The plasticizer is at least one of malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile or sebaconitrile; the weight ratio of the lithium iron phosphate, polyvinylidene fluoride, acetylene black and plasticizer is 7-10:0.1-2:0.1-2:0.1-2; the mass ratio of the volume of nitrogen-methylpyrrolidone to the lithium iron phosphate is 1-12mL:1-5g.

10. The method for preparing a polyvinylidene fluoride-hexafluoropropylene based solid-state lithium battery according to claim 1, characterized in that: The lithium-ion battery in step S2 is assembled in the order of positive electrode shell, positive electrode sheet, solid electrolyte membrane, negative electrode, stainless steel sheet, spring sheet, and negative electrode shell. The assembled battery is placed on a battery sealing machine and pressurized to 450-650 kg·cm -2 .

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