Preparation method of composite solid electrolyte for lithium-ion battery

Abstract

The present invention relates to lithium-ion battery technology and aims to provide a preparation method for a composite solid electrolyte for lithium-ion batteries. The method includes: uniformly mixing polymethylhydrosiloxane, polyethylene glycol allyl methyl ether, 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide salt, and Karstedt's catalyst, reacting under heating conditions, and purifying the reaction product to obtain a liquid polymer precursor; mixing lithium carbonate, lanthanum oxide, and zirconium dioxide, then performing ball milling and calcination to obtain an inorganic ceramic material; mixing the polymer precursor, the inorganic ceramic material, a lithium salt, and Karstedt's catalyst, and stirring to prepare a composite solid electrolyte precursor; and then heating and drying to form a composite solid electrolyte. The reaction conditions of the present invention are mild and easy to operate, effectively improving the problem of low room-temperature ionic conductivity of the current polyether PEO-based solid electrolyte; effectively improving the disadvantage of high crystallinity existing in the polymer solid electrolyte; and solving the problems of poor cycle stability and short service life.

Description

Technical Field

[0001] The present invention relates to lithium-ion battery technology, and particularly to a preparation method of a composite solid electrolyte for lithium-ion batteries. Background Art

[0002] At present, lithium metal batteries have attracted much attention from researchers as a new generation of energy storage components. Most of the electrolytes used in traditional lithium-ion batteries are liquid electrolytes, which contain a large amount of organic solvents and have safety problems such as easy volatilization, easy leakage, toxicity, flammability and explosiveness, endangering personal safety. At the same time, in the research and development process of lithium metal batteries, due to the high reactivity of lithium metal, unstable deposition of lithium metal is likely to occur during the charge and discharge process, resulting in problems such as dendrite growth, causing a series of problems such as a decline in battery performance and short circuit.

[0003] Polymer solid electrolytes can improve the safety problems brought by liquid electrolytes. More and more researchers have developed polymer materials that can be used as solid electrolytes in lithium-ion batteries. However, the polymer chain segments are long and the crystallinity is high, which limits the transport of lithium ions in the crystalline region. The commonly used PEO matrix has a very low ionic conductivity at room temperature, and the polymer itself does not contain lithium ions. These all limit the development of the solid electrolyte industry. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies in the prior art and provide a preparation method of a composite solid electrolyte for lithium-ion batteries.

[0005] To solve the technical problem, the solution of the present invention is:

[0006] Provide a preparation method of a composite solid electrolyte for lithium-ion batteries, including the following steps:

[0007] (1) Prepare a polymer precursor

[0008] Mix polymethylhydrosiloxane, polyethylene glycol allyl methyl ether, 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide salt and Karstedt's catalyst evenly, and react under heating conditions, and purify the reaction product to obtain a liquid polymer precursor;

[0009] (2) Prepare an inorganic ceramic material

[0010] Mix lithium carbonate, lanthanum oxide and zirconia dioxide, and then carry out ball milling and calcination to obtain an inorganic ceramic material;

[0011] (3) Prepare a composite material

[0012] Mix the polymer precursor, inorganic ceramic material, lithium salt and Karstedt catalyst, and stir to obtain a composite solid electrolyte precursor; then heat and dry to form a composite solid electrolyte.

[0013] As a preferred embodiment of the present invention, it specifically includes the following steps:

[0014] (1) Add polymethylhydrogensiloxane and solvent into a three-necked flask, and continuously stir under argon protection and at 50 °C; dissolve poly(ethylene glycol) allyl methyl ether in the solvent, add 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide salt and Karstedt catalyst, and mix evenly, then dropwise add it into the three-necked flask under argon protection and stirring conditions; after the dropping is completed, keep heating at 50 °C for 2 h, then adjust the temperature to 70 °C - 90 °C and continue to react for 24 h to obtain a polysiloxane-polyether prepolymer solution; purify by heating and rotary evaporation to obtain a liquid polymer precursor;

[0015] Among them, the molar ratio of polymethylhydrogensiloxane to poly(ethylene glycol) allyl methyl ether is 3:1, and the mass ratio of the sum of polymethylhydrogensiloxane and poly(ethylene glycol) allyl methyl ether, 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide salt and Karstedt catalyst is 1:0.05:0.004;

[0016] (2) Ball-mill and mix lithium carbonate, lanthanum oxide and zirconia dioxide, and keep preliminary calcination at 800 °C for 6 h in a tubular furnace; grind the calcined product again and press it into a sheet, then reheat to 1000 °C and keep secondary calcination for 10 h to obtain an inorganic ceramic material;

[0017] The molar ratio of Li:La:Zr in the lithium carbonate, lanthanum oxide and zirconia dioxide is 7:3:2;

[0018] (3) Stir the polymer precursor, inorganic ceramic material, lithium salt, Karstedt catalyst and solvent at room temperature for 12 h to obtain a composite solid electrolyte precursor; then heat and dry at 80 °C for 3 h to form a composite solid electrolyte;

[0019] The mass ratio of the polymer precursor, inorganic ceramic material, lithium salt and Karstedt catalyst is 1:0.01 - 0.3:0.2:0.004.

[0020] The addition of the catalyst in step (2) is to promote the subsequent reaction of the lithium salt in the polymer. The polymer precursor obtained after stirring is a mixture that has not completely reacted and needs subsequent heating to achieve the reaction.

[0021] As a preferred embodiment of the present invention, the solvent is toluene or acetonitrile, and the solvent content is 1 - 2 times the total mass of polymethylhydrogensiloxane and poly(ethylene glycol) allyl methyl ether.

[0022] As a preferred embodiment of the present invention, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

[0023] As a preferred embodiment of the present invention, the heating rate during calcination is 5 °C / min -1 .

[0024] The present invention further provides a method for applying the solid electrolyte in the preparation of a lithium-ion battery, including:

[0025] (1) Add lithium iron phosphate, a conductive agent, and a binder into a mortar and grind and mix them evenly. After adding an appropriate amount of solvent, grind them into a slurry; evenly scrape the slurry onto a carbon-coated aluminum foil, dry it, and cut it into an appropriate shape to obtain a lithium iron phosphate positive electrode sheet.

[0026] (2) Scrape the composite solid electrolyte precursor onto the lithium iron phosphate positive electrode sheet, and then heat and dry it at 80 °C for 3 h to form a tight positive electrode / solid electrolyte layer.

[0027] (3) Using a lithium metal sheet as the negative electrode and a nickel foam as a spacer, assemble a button battery in the order of lithium iron phosphate positive electrode / solid electrolyte / lithium sheet / nickel foam.

[0028] Description of the invention principle:

[0029] 1. The present invention uses the hydrosilylation method to graft poly(ethylene glycol) allyl methyl ether and 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide onto the silicon-hydrogen bond of polymethylhydrosiloxane through an addition reaction to break the carbon-carbon double bond and prepare a polymer material with a network structure; then prepare active fillers by the high-temperature solid-phase method, and physically mix the inorganic and organic materials to improve the disadvantages of long polymer chain segments and high crystallinity, and increase the disorder of polymer chain segments.

[0030] 2. The present invention introduces a lithium-containing inorganic active filler to broaden the path channels for lithium-ion transport; by introducing lithium ions that can be transported, the number of migrating lithium ions is increased, greatly improving the electrochemical performance of the lithium-ion battery.

[0031] Compared with the prior art, the beneficial effects of the present invention are:

[0032] 1. The present invention proposes to prepare a polymer material by grafting polyether and imide ions onto polysiloxane. The reaction conditions are mild and easy to operate, and it can effectively improve the problem of low room-temperature ionic conductivity of the current polyether PEO-based solid electrolyte.

[0033] 2. The present invention introduces a lithium-containing inorganic active filler, effectively improving the disadvantage of high crystallinity existing in the polymer solid electrolyte; increasing the number of lithium ions that can be transported, and to a certain extent solving the problems of poor battery cycle stability and short service life at present.

[0034] 3. The present invention introduces a solid electrolyte into a lithium-ion battery, which can inhibit the growth of lithium dendrites and improve the safety performance of the lithium-ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a graph of the conductivity performance of the electrolytes prepared in Examples 1-5 and Comparative Example 1 of the present invention;

[0036] Figure 2 It is a scanning electron microscope image of the electrolytes prepared in Comparative Example 1 and Examples 3 and 4 of the present invention;

[0037] Figure 3 It is a cyclic voltammetry curve of the electrolytes prepared in Comparative Example 1 and Examples 2-4 of the present invention;

[0038] Figure 4 It is a graph of the lithium dendrite performance of the electrolytes prepared in Comparative Example 2 and Example 3 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0039] In the following examples, raw materials or reagents such as 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide are purchased through commercial channels and used directly without treatment unless otherwise specified.

[0040] The present invention will be further described below with reference to examples.

[0041] Example 1:

[0042] (1) Take 2 g of polymethylhydrosiloxane and 2 g of toluene, add them to a beaker, stir and mix evenly under argon protection, then pour them into a 100 mL three-necked flask, place it in an oil bath at 50 °C, continue stirring, and pass circulating cooling water; take 3.5 g of polyethylene glycol allyl methyl ether, 3.5 g of toluene, 275 mg of 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide, and 22 mg of Karstedt catalyst, add them to a beaker, stir evenly under argon protection, and then drop them into the above three-necked flask through a separatory funnel. Control the dropping rate so that the time consumed after dropping is greater than 1 h. After dropping, keep the temperature at 50 °C for 2 h, then adjust the temperature to 70 °C and react for 24 h. After heating and rotary evaporation for purification, a liquid polymer precursor is obtained;

[0043] (2) Take 5.17 g of lithium carbonate, 9.77 g of lanthanum oxide, and 4.92 g of zirconium dioxide, put them into a ball milling tank, add zirconium balls, set the rotation speed of the ball mill to 128 rmp, ball mill for 15 h, take out 5 g of powder and pour it into a corundum crucible, then place it in a tubular furnace, and under an argon atmosphere, at 5 °C / min -1After heating to 800 °C at a heating rate and maintaining the initial calcination for 6 h, the sintered block was taken out and ground into fine powder. The fine powder was compacted into a green sheet with a diameter of 19 mm using a tablet press and then put into a tube furnace again. After heating to 1000 °C, the secondary calcination was maintained for 10 h.

[0044] (3) Take 30 mg of the inorganic ceramic powder prepared in (2) and pour it into 3 g of the polymer precursor in (1). Add 0.6 g of lithium bis(trifluoromethanesulfonyl)imide and 12 mg of the Kast catalyst dissolved in 3 g of acetonitrile, and stir at room temperature for 12 h to obtain a precursor of the composite solid electrolyte material.

[0045] Preparation of the electrode sheet: Lithium iron phosphate, Super-P, and the binder polyvinylidene fluoride were added to a mortar in a mass ratio of 8:1:1, ground and mixed evenly, and an appropriate amount of the solvent NMP was added and ground into a slurry for 30 min. The slurry was evenly coated on carbon-coated aluminum foil with a doctor blade and dried overnight in an oven at 60 °C. The dried positive electrode sheet was cut into a circular electrode sheet with a diameter of 19 mm, and the preparation of the positive electrode sheet was completed.

[0046] Preparation of the electrode-electrolyte sheet: The composite solid electrolyte precursor obtained in (3) was coated on the lithium iron phosphate positive electrode sheet and dried in an oven at 80 °C for 3 h, so that the composite solid electrolyte precursor material was successfully synthesized under the action of the catalyst and tightly adhered to the electrode sheet, and a thin sheet of the electrode-electrolyte integrated body was obtained.

[0047] Assembly of the lithium-ion battery: A coin-type 2025 battery was assembled, with a metal lithium sheet as the negative electrode and nickel foam as a spacer to complete the assembly of the lithium iron phosphate positive electrode-solid electrolyte / lithium sheet / nickel foam coin-type battery.

[0048] Example 2:

[0049] (1) Take 2 g of polymethylhydrogensiloxane and 4 g of toluene, add them to a beaker, stir and mix evenly under argon protection, and then pour them into a 100 mL three-necked flask. Place it in an oil bath at 50 °C and continue to stir, and pass circulating cooling water; take 3.5 g of polyethylene glycol allyl methyl ether, 7 g of toluene, 275 mg of 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide, and 22 mg of the Kast catalyst, add them to a beaker, stir evenly under argon protection, and then add them dropwise to the above three-necked flask through a separatory funnel. Control the dropping rate so that the time consumed after dropping is greater than 1 h. After dropping, continue to keep the temperature at 50 °C for 2 h and then adjust the temperature to 90 °C and react for 24 h. After heating and rotary evaporation purification, a liquid polymer precursor was obtained;

[0050] (2) Take 5.17 g of lithium carbonate, 9.77 g of lanthanum oxide, and 4.92 g of zirconium dioxide, put them into a ball milling jar, add zirconia balls, set the rotation speed of the ball mill to 128 rmp, ball mill for 15 h, take out 5 g of the powder and pour it into a corundum crucible, then place it in a tube furnace. Under an argon atmosphere, heat it to 800 °C at a heating rate of 5 °C / min -1 and keep it for preliminary calcination for 6 h. Then take out the sintered block and grind it into fine powder. Use a tablet press to press the fine powder into a green sheet with a diameter of 19 mm, and then put it into the tube furnace again. Heat it to 1000 °C and keep it for secondary calcination for 10 h.

[0051] (3) Take 150 mg of the inorganic ceramic powder prepared in (2), pour it into the 3 g of polymer precursor in (1), add 0.6 g of lithium bis(trifluoromethanesulfonyl)imide and 12 mg of Caste catalyst dissolved in 6 g of acetonitrile, and stir at room temperature for 12 h to obtain a composite solid electrolyte material precursor.

[0052] Preparation of the electrode sheet: Add lithium iron phosphate, Super-P / binder polyvinylidene fluoride in a mass ratio of 8:1:1 to a mortar, grind and mix evenly, add an appropriate amount of solvent NMP, and grind for 30 min to form a slurry. Use a doctor blade to evenly coat the slurry on the carbon-coated aluminum foil, dry it overnight in an oven at 60 °C, and cut the dried positive electrode sheet into a circular electrode sheet with a diameter of 19 mm, thus completing the preparation of the positive electrode sheet.

[0053] Preparation of the electrode-electrolyte sheet: Coat the composite solid electrolyte precursor obtained in (3) on the lithium iron phosphate positive electrode sheet, and dry it in an oven at 80 °C for 3 h, so that the composite solid electrolyte precursor material is successfully synthesized under the action of the catalyst and closely adheres to the electrode sheet, obtaining a thin sheet of electrode-electrolyte integration.

[0054] Assembly of the lithium-ion battery: Assemble it into a coin-type 2025 battery, use a lithium metal sheet as the negative electrode, and use nickel foam as a spacer to complete the assembly of the lithium iron phosphate positive electrode-solid electrolyte / lithium sheet / nickel foam coin-type battery.

[0055] Example 3:

[0056] (1) Take 2 g of polymethylhydrosiloxane and 3 g of toluene, add them to a beaker, stir and mix evenly under argon protection, then pour them into a 100 mL three-necked flask, place it in an oil bath at 50 °C and continue stirring, and pass circulating cooling water; take 3.5 g of polyethylene glycol allyl methyl ether, 5.25 g of toluene, 275 mg of 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide, and 22 mg of Karstedt's catalyst, add them to a beaker, stir evenly under argon protection, and then drop them into the above three-necked flask through a separatory funnel, control the dropping rate so that the time consumed after dropping is greater than 1 h. After dropping, keep the temperature at 50 °C for 2 h, then adjust the temperature to 80 °C and react for 24 h. After heating, rotary evaporation and purification, a liquid polymer precursor is obtained;

[0057] (2) Take 5.17 g of lithium carbonate, 9.77 g of lanthanum oxide, and 4.92 g of zirconium dioxide, put them into a ball milling jar, add zirconium balls, set the rotation speed of the ball mill to 128 rmp and ball mill for 15 h. Take out 5 g of the powder and pour it into a corundum crucible, then place it in a tubular furnace. Under an argon atmosphere, heat it to 800 °C at a heating rate of 5 °C / min, and keep the initial calcination for 6 h. Then take out the sintered block and grind it into fine powder. Use a tablet press to press the fine powder into a disc with a diameter of 19 mm, and then put it into the tubular furnace again. Heat it to 1000 °C and keep the secondary calcination for 10 h. -1

[0058] (3) Take 300 mg of the inorganic ceramic powder prepared in (2), pour it into 3 g of the polymer precursor in (1), add 0.6 g of lithium bis(trifluoromethanesulfonyl)imide and 12 mg of Karstedt's catalyst dissolved in 4.5 g of acetonitrile, and stir at room temperature for 12 h to obtain a composite solid electrolyte material precursor.

[0059] Preparation of the electrode sheet: Add lithium iron phosphate, Super-P / binder polyvinylidene fluoride in a mass ratio of 8:1:1 to a mortar, grind and mix evenly, add an appropriate amount of solvent NMP, and grind for 30 min to form a slurry. Use a doctor blade to evenly coat the slurry on the carbon-coated aluminum foil, dry it overnight in an oven at 60 °C, and cut the dried positive electrode sheet into circular electrodes with a diameter of 19 mm, thus completing the preparation of the positive electrode sheet.

[0060] Preparation of the electrode-electrolyte sheet: Coat the composite solid electrolyte precursor obtained in (3) on the lithium iron phosphate positive electrode sheet, and dry it in an oven at 80 °C for 3 h, so that the composite solid electrolyte precursor material is successfully synthesized and tightly adhered to the electrode sheet under the action of the catalyst, obtaining a thin sheet of electrode-electrolyte integration.

[0061] Assembly of the lithium-ion battery: Assemble it into a coin-type 2025 battery, use a lithium metal sheet as the negative electrode, and use nickel foam as a spacer to complete the assembly of the lithium iron phosphate positive electrode-solid electrolyte / lithium sheet / nickel foam coin-type battery.

[0062] Example 4:

[0063] According to the preparation process of Example 3, in step (3), 600 mg of the inorganic ceramic powder prepared in (2) was taken and poured into 3 g of the polymer precursor in (1). 0.6 g of lithium bis(trifluoromethanesulfonyl)imide and 12 mg of Cast catalyst dissolved in 4.5 g of acetonitrile were added, and the mixture was stirred at room temperature for 12 h to obtain a precursor of the composite solid electrolyte material, and other steps remained unchanged.

[0064] Example 5:

[0065] According to the preparation process of Example 3, in step (3), 900 mg of the inorganic ceramic powder prepared in (2) was taken and poured into 3 g of the polymer precursor in (1). 0.6 g of lithium bis(trifluoromethanesulfonyl)imide and 12 mg of Cast catalyst dissolved in 4.5 g of acetonitrile were added, and the mixture was stirred at room temperature for 12 h to obtain a precursor of the composite solid electrolyte material, and other steps remained unchanged.

[0066] Comparative Example 1:

[0067] According to the preparation process of Example 3(1), a liquid polymer precursor was obtained. The synthesis of the inorganic material in (2) and the composite step in (3) were not carried out. 4.5 g of acetonitrile was used to dissolve 0.6 g of lithium bis(trifluoromethanesulfonyl)imide and 12 mg of Cast catalyst, and then the solution was added to 3 g of the polymer obtained in the reaction of step (1). The mixture was stirred at room temperature in a glove box for 12 h, taken out and rotary evaporated at 40 °C for 2 h, and then dried in a vacuum oven at 80 °C for 24 h on a mold to successfully crosslink the polymer with the lithium salt, obtaining a polymer solid electrolyte.

[0068] Preparation of the electrode sheet: Lithium iron phosphate, Super-P, and the binder polyvinylidene fluoride were added to a mortar in a mass ratio of 8:1:1, ground and mixed evenly, and an appropriate amount of the solvent NMP was added and ground for 30 min to form a slurry. The slurry was evenly coated on the carbon-coated aluminum foil by a doctor blade method and dried overnight in an oven at 60 °C. The dried positive electrode sheet was cut into circular electrodes with a diameter of 12 mm, thus completing the preparation of the positive electrode sheet.

[0069] Assembly of the lithium-ion battery: A coin-type 2025 battery was assembled, with a lithium metal sheet as the negative electrode and a nickel foam as a spacer to complete the assembly of the lithium iron phosphate positive electrode / solid electrolyte / lithium sheet / nickel foam coin-type battery.

[0070] Comparative Example 2:

[0071] Using a commercially available polypropylene separator (abbreviation: PP, specification: battery grade, manufacturer: Celgard) and a lithium battery electrolyte (abbreviation: LB-002; specification: battery grade, manufacturer: Duoduo Chemical Reagent Company) as a combination. Lithium iron phosphate, Super-P, and the binder polyvinylidene fluoride were added to a mortar in a mass ratio of 8:1:1 and ground and mixed evenly. An appropriate amount of solvent NMP was added and ground for 30 min to form a slurry. The slurry was evenly coated on carbon-coated aluminum foil by the doctor blade method and dried overnight in an oven at 60 °C. The dried positive electrode sheet was cut into circular electrode sheets with a diameter of 12 mm. Using a lithium metal sheet as the negative electrode and a nickel foam as a gasket, the assembly of the lithium iron phosphate positive electrode / PP separator - electrolyte / lithium sheet / nickel foam button battery was completed.

[0072] The solid electrolyte prepared in Comparative Example 1 is a polymer solid electrolyte without adding inorganic nanomaterials, and the other preparation processes are the same as those in the examples. Compared with the composite solid electrolyte prepared by adding inorganic nanomaterials in the examples, it is mainly to explore the role of inorganic nanomaterials in this system on the electrochemical performance of the battery.

[0073] Performance testing:

[0074] 1. Ion conductivity test

[0075] For the ion conductivity test, the polymer electrolyte membrane was sandwiched between two stainless steel sheets (SS) to assemble a "stainless steel / polymer electrolyte / stainless steel" symmetric blocking battery. Using a Shanghai Chenhua CHI660E electrochemical workstation, the composite solid electrolytes prepared in Examples 1-5 and the polymer solid electrolyte prepared in Comparative Example 1 were subjected to ion conductivity tests, and the curve graphs are as Figure 1 shown. The variables in Examples 1-5 are the mass ratio of the added inorganic ceramic powder. Except that the inorganic material was added in excess in Example 5, the conductivity of all composite electrolytes is higher than that of the polymer electrolyte. When the proportion of the added inorganic material is 10 wt.%, the resistance of the solid electrolyte is the lowest and the ion conductivity is the highest, and the performance is the best. This is because the inorganic ceramic itself carries lithium ions and provides new lithium ions that can migrate, and the addition of the inorganic ceramic reduces the crystallinity of the polymer to a certain extent, thereby increasing the overall ion conductivity.

[0076] 2. Scanning electron microscopy test

[0077] In Examples 3 and 4 and Comparative Example 1, the surface morphologies of the prepared solid electrolytes are as Figure 2 shown. It can be seen that Figure 2 (a) The surface of the solid electrolyte membrane (Comparative Example 1) without doping inorganic materials has many crystals, indicating that the crystallinity of this electrolyte membrane is relatively high, which is not conducive to the transmission of Li + ions, while Figure 2In (b), the surface crystallization of the electrolyte membrane (Example 3) with 10 wt.% inorganic material basically disappears, and the inorganic material and the polymer matrix are tightly combined into one body, indicating that the addition of the inorganic material can effectively destroy the crystallinity of the polymer and improve the chain segment fluidity. When the doping amount of the inorganic material increases to 20 wt.% (Example 4), Figure 2 In (c), excessive inorganic ceramic particles will agglomerate and cannot be evenly dispersed in the polymer, which will reduce the composite effect.

[0078] 3. Electrochemical window test

[0079] For the electrochemical window test, a "lithium sheet / polymer electrolyte / stainless steel" battery is assembled by sandwiching the polymer electrolyte membrane between a lithium sheet and a stainless steel sheet. Using the Shanghai Chenhua CHI660E electrochemical workstation, the solid electrolytes prepared in Examples 2-4 and Comparative Example 1 are subjected to the electrochemical window test. The curve graph is as Figure 3 shown. It can be seen from the figure that the electrochemical window of the polymer solid electrolyte in the comparative example is only 4.9 V, while the electrochemical windows of the composite solid electrolytes in Examples 2-4 are all greater than 5 V, indicating that the composite electrolyte with the added inorganic material is more stable.

[0080] 4. Battery safety test

[0081] The growth of lithium dendrites in the battery is one of the fundamental problems affecting the stability and safety of lithium-ion batteries. The ability to inhibit the growth of lithium dendrites in the electrolyte is the key to evaluating the safety of the electrolyte. The lithium dendrite test is obtained by assembling a lithium symmetric battery for constant current charge and discharge testing. The current density is set to 0.1 mA cm -2 . Figure 4 The lithium dendrite test diagrams of Example 3 and Comparative Example 2 are shown. It can be seen that the electrolyte potential of Example 3 increases slowly. After stable cycling for 380 h, the polarization voltage only increases from 0.04 V to 0.1 V and still remains in a small range. This is because the addition of the inorganic material enhances the mechanical properties of the composite solid electrolyte and reduces the side reactions inside the battery. The polarization voltage of the electrolyte in Comparative Example 2 reaches a maximum of 0.38 V, and obvious polarization phenomenon occurs after about 150 h, and short circuit occurs after 200 h. This shows that the prepared composite solid electrolyte has excellent safety compared with the traditional electrolyte.

Claims

1. A preparation method of a composite solid electrolyte for a lithium-ion battery, characterized in that, It includes the following steps: (1) Prepare a polymer precursor Mix polymethylhydrogensiloxane, poly(ethylene glycol) allyl methyl ether, 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide salt and Karstedt's catalyst evenly, and react under heating conditions. Purify the reaction product to obtain a liquid polymer precursor. Among them, the molar ratio of polymethylhydrogensiloxane to poly(ethylene glycol) allyl methyl ether is 3:1, and the mass ratio of the total of polymethylhydrogensiloxane and poly(ethylene glycol) allyl methyl ether, 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide salt and Karstedt's catalyst is 1:0.05:0.004; (2) Prepare an inorganic ceramic material Take lithium carbonate, lanthanum oxide and zirconium dioxide according to the molar ratio of Li:La:Zr of 7:3:2, mix them and then carry out ball milling and calcination to obtain an inorganic ceramic material; (3) Prepare a composite material Take the polymer precursor, inorganic ceramic material, lithium salt and Karstedt's catalyst according to the mass ratio of 1:0.01 - 0.3:0.2:0.004, mix and stir to obtain a composite solid electrolyte precursor; then heat and dry it to form a composite solid electrolyte.

2. The method according to claim 1, characterized in that Specifically, it includes the following steps: (1) Add polymethylhydrogensiloxane and a solvent into a three-necked flask, and continuously stir under argon protection and at 50 °C; dissolve poly(ethylene glycol) allyl methyl ether in the solvent, add 1-vinyl-3-butylimidazolium bis(trifluoromethanesulfonyl)imide salt and Karstedt's catalyst and mix evenly, and then dropwise add it into the three-necked flask under argon protection and stirring conditions; after the dropping is completed, keep the temperature at 50 °C and heat and react for 2 h, then adjust the temperature to 70 °C - 90 °C and continue to react for 24 h to obtain a polysiloxane-polyether prepolymer solution; purify it by heating and rotary evaporation to obtain a liquid polymer precursor; (2) Ball mill and mix lithium carbonate, lanthanum oxide and zirconium dioxide, and initially calcine it in a tubular furnace at 800 °C for 6 h; re-grind the calcined product and press it into a sheet, and then reheat it to 1000 °C and keep it for secondary calcination for 10 h to obtain an inorganic ceramic material; (3) Stir the polymer precursor, inorganic ceramic material, lithium salt, Karstedt's catalyst and solvent at room temperature for 12 h to obtain a composite solid electrolyte precursor; then heat and dry it at 80 °C for 3 h to form a composite solid electrolyte.

3. The method according to claim 2, characterized in that, The solvent is toluene or acetonitrile, and the solvent content is 1 - 2 times the total mass of polymethylhydrogensiloxane and poly(ethylene glycol) allyl methyl ether.

4. The method according to claim 2, wherein The lithium salt is lithium bis(trifluoromethanesulfonyl)imide.

5. The method according to claim 2, characterized in that The heating rate during the calcination is 5 °C min -1 .

6. The application method of the composite solid electrolyte prepared by the method according to claim 1 in the preparation of lithium-ion batteries, characterized in that, It includes: (1) Add lithium iron phosphate, a conductive agent and a binder into a mortar, grind and mix them evenly, and add an appropriate amount of solvent and then grind them into a slurry; Apply the slurry evenly on carbon-coated aluminum foil, dry it and cut it into an appropriate shape to obtain a lithium iron phosphate positive electrode sheet, (2) Apply the composite solid electrolyte precursor on the lithium iron phosphate positive electrode sheet, and then heat and dry it at 80 °C for 3 h to form a tight positive electrode / solid electrolyte layer; (3) Use a lithium metal sheet as the negative electrode, use nickel foam as a gasket, and assemble a button battery in the installation order of lithium iron phosphate positive electrode / solid electrolyte / lithium sheet / nickel foam.

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