Core-shell structure polyimide flame-retardant base film, preparation method thereof and application thereof in in-situ solid-state battery

Abstract

The application provides a core-shell structure polyimide (PI) flame-retardant base film, a preparation method thereof and application thereof in in-situ solid-state batteries. The preparation method mainly comprises the following steps: dissolving polyamide acid (PAA) in an organic solvent to serve as a spinning solution of a shell layer; dissolving the polyamide acid in an organic solvent and adding high-temperature-resistant flame retardants and a silane coupling agent to serve as a spinning solution of a core layer, wherein the flame retardants are preferably high-temperature-resistant melamine polyphosphate (MPP) and magnesium hydroxide (Mg(OH)2). A light yellow non-woven fabric film is obtained through coaxial electrospinning, and then the non-woven fabric film is calcined in an air atmosphere at 250-340 DEG C to obtain a core-shell structure polyimide flame-retardant base film, which is a PI non-woven fabric composite film. The prepared PI composite film has a flame-retardant function, the flame retardants are in the core layer, and the electrochemical performance of the battery is not affected. Furthermore, since the PI has radiation resistance, the flame-retardant base film can be applied to chemical power systems such as gamma-ray in-situ solid-state lithium ion batteries.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium batteries, and particularly relates to a flame-retardant base film for improving the safety of a solid-state battery as well as a preparation method and application thereof. BACKGROUND

[0002] Current commercial lithium ion batteries (LIBs) cannot meet the production needs of people. Although the traditional liquid electrolyte has high ionic conductivity, it has the disadvantages of flammability and the like due to the use of an organic solvent, and has safety problems in the use process. Solidifying the liquid battery into a solid-state battery can not only maintain high conductivity, but also improve the electrochemical window, reduce the liquid leakage bulging of the battery, and uniform the current density and inhibit the growth of lithium dendrites through stress. The prior art discloses a method for preparing a solid-state battery by irradiation and the like. However, the solidified electrolyte of the current integrated solid-state battery still has the risk of combustion. Therefore, it is necessary to further improve it to improve the flame-retardant performance of the solid-state battery and thus improve the safety performance of the battery. SUMMARY

[0003] In view of the above problems, in order to improve the flame-retardant performance of the in-situ solidified battery and thus improve the safety performance of the battery, the application provides a core-shell structure polyimide flame-retardant base film, a preparation method thereof and application thereof in an in-situ solid-state battery.

[0004] One of the technical solutions adopted by the application to solve the technical problems is:

[0005] A core-shell structure polyimide flame-retardant base film is prepared from a composite fiber, wherein the composite fiber comprises a core layer and a shell layer coated outside the core layer; the core layer is prepared from polyimide, a high-temperature resistant flame retardant and a high-temperature resistant silane coupling agent; the shell layer is prepared from polyimide; the high-temperature resistant flame retardant comprises at least one of melamine polyphosphate (MPP) or magnesium hydroxide (Mg(OH)2); and the high-temperature resistant silane coupling agent is preferably a siloxane containing an imide structure, such as the following formula:

[0006]

[0007] wherein R is an alkyl group such as methyl, ethyl or n-butyl.

[0008] Preferably, the thickness of the core layer is 30 nm to 500 nm.

[0009] Preferably, the thickness of the shell layer is 30 nm to 1 μm.

[0010] The second technical solution adopted by the application to solve the technical problems is:

[0011] A preparation method of a core-shell structure polyimide flame-retardant base film, comprising the following steps: dissolving polyamide acid (PAA) in an organic solvent as a shell layer spinning solution; dissolving polyamide acid in an organic solvent, adding a high-temperature-resistant flame retardant and a silane coupling agent as a core layer spinning solution, the high-temperature-resistant flame retardant is preferably a high-temperature-resistant flame retardant such as melamine polyphosphate (MPP) and magnesium hydroxide (Mg(OH)2); and the core-shell structure polyimide flame-retardant base film is prepared by coaxial electrospinning of the shell layer spinning solution and the core layer spinning solution, and a light yellow non-woven fabric film is prepared, which is baked in a vacuum oven at 75-85 DEG C for 22-25 hours, and then calcined in an air atmosphere at 250-340 DEG C to obtain the flame-retardant base film, which is a polyimide (PI) non-woven fabric flame-retardant base film.

[0012] Preferably, the organic solvent used in the core layer spinning solution and the shell layer spinning solution is selected from one or more of N,N-dimethylformamide (DMF), N-methylpyrrolidone, acetone, dimethyl sulfoxide (DMSO), dichloromethane and trichloromethane; and the percentage of the organic solvent in the core layer spinning solution and the shell layer spinning solution is 0-95wt% and not 0.

[0013] Preferably, the concentration of polyamide acid in the shell layer spinning solution is 20wt%-30wt%.

[0014] Preferably, the concentration of polyamide acid in the core layer spinning solution is 15wt%-25wt%, and the concentration of the flame retardant is 1.5wt%-3wt%.

[0015] Preferably, the high-temperature-resistant silane coupling agent preferably contains an imide structure, such as the following structure, and the content is 0-50wt% and not 0 of the core layer spinning solution, and is preferably 1wt%-2wt%.

[0016]

[0017] wherein R is methyl, ethyl, n-butyl and the like alkyl.

[0018] The third technical solution adopted by the present application to solve the technical problems is:

[0019] The application of a core-shell structure polyimide flame-retardant base film in an in-situ solid-state battery.

[0020] The present application provides a core-shell structure polyimide flame-retardant base film, which can be applied to a gamma-ray in-situ solid-state lithium ion battery and other chemical power systems. The polyimide non-woven fabric is a radiation-resistant porous base film and can be used as a separator for a lithium ion battery. Figure 1 , polyamide acid (PAA) is dehydrated to form polyimide (PI); and Figure 2The temperature of the dehydration can be completed at 250 DEG C or above, and decomposition occurs at 490 DEG C or above. Therefore, a flame retardant with appropriate thermal stability and a decomposition temperature higher than the temperature at which PAA is dehydrated to generate PI is selected to be wrapped in the core layer of the non-woven fabric fiber, so that the flame retardant can retard the flame in the case of thermal runaway and can prevent the flame retardant from entering the electrolyte in the normal working condition to affect the performance of the battery. Melamine polyphosphate (MPP) is an environmentally friendly halogen-free flame retardant with very high thermal stability, and the decomposition temperature is greater than or equal to 360 DEG C. MPP has excellent thermal stability and is the preferred core layer flame retardant of the present application. Magnesium hydroxide (Mg(OH)2) is a flame retardant containing crystal water with a Td greater than or equal to 380 DEG C. In addition, the addition of a silane coupling agent can enhance the dispersibility and stability of the flame retardant and prevent agglomeration.

[0021] The fourth technical solution adopted by the present application to solve its technical problems is:

[0022] A kind of in situ solid-state battery, the in situ solid-state battery includes the core-shell structure polyimide flame retardant base film described above.

[0023] The fifth technical solution adopted by the present application to solve its technical problems is:

[0024] A preparation method of an in situ solid-state battery, in particular, a preparation method of an in situ cured lithium battery with gamma-ray flame retardant function. The electrolyte and the polymerizable monomer are mixed uniformly to obtain a mixed solution. The mixed solution is injected in situ into the core-shell structure polyimide flame retardant base film between the positive and negative electrodes, and gamma-ray irradiation is performed by Co60 or the like to generate a solidified battery.

[0025] Preferably, the electrolyte comprises an aprotic organic solvent and a lithium salt. The aprotic organic solvent includes at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, propylene carbonate, methyl ethyl carbonate, 1,3-dioxolane, dimethyl ether, N-methyl pyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, acetone, tetrahydrofuran, acetonitrile, etc. The lithium salt includes one or more of LiTFSI, LiClO4, LiPF6, LiCl, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, LiBF4, AMPSLi, STFSILi, etc. The concentration of the lithium salt in the electrolyte is 0.001-20 M. The electrolyte can also be a commercially available product.

[0026] Preferably, the polymerizable monomer is at least one of a vinyl, propenyl double bond functional group or an epoxy functional group monomer, including at least one of an acrylate, acrylonitrile, methoxy acrylate, polyethylene glycol diacrylate (PEGDA), acrylamide, 2-acrylamido-2-methylpropane sulfonic acid, glycidyl methacrylate, ethylene carbonate, propylene carbonate, oxirane, acrylic acid, styrene, fluoride, phosphine, siloxane, acetate.

[0027] Preferably, the mixed solution further comprises a cross-linking agent, such as polyethylene glycol diacrylate, divinylbenzene, N,N-methylene bisacrylamide, diisocyanate, tetraethyl orthosilicate, etc.

[0028] Preferably, in the in-situ solid-state battery, the positive electrode active material comprises at least one of lithium cobaltate, lithium iron phosphate, lithium manganate, lithium nickelate, lithium nickel manganate, lithium nickel cobalt manganate, lithium nickel cobalt aluminum, and lithium-rich manganese-based material; and the negative electrode active material is metal lithium, graphite, silicon, metal oxide, metal sulfide, etc.

[0029] Preferably, the irradiation dose of the gamma rays is 5-900 KGy.

[0030] Unless otherwise specified, the devices, reagents, processes, parameters, etc. involved in the present application are conventional devices, reagents, processes, parameters, etc. and will not be described in the examples.

[0031] All ranges listed in the present application include all point values within the range.

[0032] In the present application, unless otherwise specified, % is mass percentage, and the ratio is mass ratio.

[0033] Compared with the background art, the technical solution has the following advantages:

[0034] 1. Compared with the scheme of adding a flame-retardant additive to an electrolyte and adding a filler to an electrolyte membrane, the present application uses a polyimide flame-retardant base film with a core-shell structure, which can increase the amount of flame retardant and enhance the flame-retardant effect.

[0035] 2. The core-shell structure of the polyimide flame-retardant base film of the present application encloses the flame-retardant component in the core layer, and cooperates with the cured electrolyte, which can avoid the flame retardant from entering the electrolyte under normal working conditions, affecting the cycle and performance of the battery, and can play a flame-retardant effect in thermal runaway. BRIEF DESCRIPTION OF DRAWINGS

[0036] Figure 1 is a schematic diagram of the reaction of polyamic acid (PAA) dehydration to form polyimide (PI).

[0037] Figure 2 is a thermogravimetric (TG) and differential thermogravimetric (DTG) diagram of polyamic acid.

[0038] Figure 3 Schematic diagram of core-shell structure polyimide flame-retardant base film prepared for the embodiment of the present application.

[0039] Figure 4 Cycle curve of the battery with the flame retardant in the core layer and the shell layer respectively in Example 4. DETAILED DESCRIPTION

[0040] The present application will be further described below in conjunction with the drawings and examples.

[0041] Example 1

[0042] 1) Dissolve polyamide acid (PAA) in DMF to form a 25% shell layer spinning solution; dissolve polyamide acid in DMF to form a 15% solution, and then add thereto melamine polyphosphate (MPP) at a final concentration of 1.5% and a high-temperature-resistant silane coupling agent with the following structure at a final concentration of 1% as a core layer spinning solution. The shell layer spinning solution and the core layer spinning solution are subjected to coaxial electrospinning to obtain a light yellow non-woven fabric film, which is baked in a vacuum oven at 80°C for 24 h. Then, the non-woven fabric film is calcined in an air atmosphere at 270°C to obtain a polyimide (PI) non-woven fabric flame-retardant base film.

[0043]

[0044] 2) Mix 301 electrolyte and polyethylene glycol diacrylate (PEGDA) uniformly at a ratio of 20:1 to obtain a mixed solution;

[0045] 3) Take the 2016 battery shell positive electrode, and sequentially add a lithium iron phosphate positive electrode sheet, the flame-retardant base film prepared in step 1), the mixed solution in step 2), and a lithium metal negative electrode to package the battery. The battery is irradiated with γ rays by Co60 to generate a solidified battery.

[0046] Example 2

[0047] 1) Dissolve polyamide acid (PAA) in DMF to form a 25% shell layer spinning solution; dissolve polyamide acid in acetone to form a 25% solution, and then add thereto melamine polyphosphate (MPP) at a final concentration of 2% and a high-temperature-resistant silane coupling agent with the following structure at a final concentration of 2% as a core layer spinning solution. The shell layer spinning solution and the core layer spinning solution are subjected to coaxial electrospinning to obtain a light yellow non-woven fabric film, which is baked in a vacuum oven at 80°C for 24 h. Then, the non-woven fabric film is calcined in an air atmosphere at 270°C to obtain a polyimide (PI) non-woven fabric flame-retardant base film.

[0048]

[0049] 2) Mix 301 electrolyte and polyethylene glycol diacrylate (PEGDA) uniformly at a ratio of 20:1 to obtain a mixed solution;

[0050] 3) Take the 2016 battery shell positive electrode, sequentially add the NCM622 positive electrode sheet, the flame-retardant base film prepared in step 1), the mixed solution in step 2), and the lithium metal negative electrode, and package the battery. Irradiate the battery with γ-rays by Co60 to generate a solidified battery.

[0051] Example 3

[0052] 1) Dissolve polyamide acid (PAA) in DMF to form a 25% shell layer spinning solution; dissolve polyamide acid in acetone to form a 25% solution, and then add a high-temperature-resistant silane coupling agent with a final concentration of 3% Mg(OH)2 and a final concentration of 1% of the following structure as a core layer spinning solution. Coaxial electrospinning is performed with the shell layer spinning solution and the core layer spinning solution to obtain a light yellow non-woven fabric film, which is baked in a vacuum oven at 80°C for 24 hours. Then calcine in an air atmosphere at 270°C to obtain a polyimide (PI) non-woven fabric flame-retardant base film.

[0053]

[0054] 2) Mix 301 electrolyte and polyethylene glycol diacrylate (PEGDA) uniformly at a ratio of 20:1 to obtain a mixed solution;

[0055] 3) Take the 2016 battery shell positive electrode, sequentially add the lithium cobaltate positive electrode sheet, the flame-retardant base film prepared in step 1), the mixed solution in step 2), and the graphite negative electrode, and package the battery. Irradiate the battery with γ-rays by Co60 to generate a solidified battery.

[0056] Example 4

[0057] Dissolve polyamide acid (PAA) in DMF to form a 25% shell layer spinning solution; dissolve polyamide acid in acetone to form a 25% solution, and then add a high-temperature-resistant silane coupling agent with a final concentration of 3% Mg(OH)2 and a final concentration of 1% of the following structure as a core layer spinning solution. Coaxial electrospinning is performed with the shell layer spinning solution and the core layer spinning solution to obtain a light yellow non-woven fabric film, which is baked in a vacuum oven at 80°C for 24 hours. Then calcine in an air atmosphere at 270°C to obtain a polyimide (PI) non-woven fabric flame-retardant base film. Replace the positions of the above-mentioned core layer spinning solution and shell layer spinning solution to obtain a polyimide (PI) non-woven fabric flame-retardant base film with the flame retardant in the shell layer by coaxial electrospinning as a comparison.

[0058]

[0059] 2) Mix 301 electrolyte and polyethylene glycol diacrylate (PEGDA) uniformly at a ratio of 20:1 to obtain a mixed solution;

[0060] 3) Take the positive electrode of the 2016 battery shell, and sequentially add the lithium iron phosphate positive electrode sheet, the two fire-retardant base films prepared in step 1), the mixed solution in step 2), and the lithium metal negative electrode, and package the battery. Two kinds of solidified batteries are generated by irradiating γ-rays with Co60.

[0061] The room temperature 0.5C cycle performance of the battery prepared by the fire-retardant base film of the polyimide non-woven fabric with the fire retardant in the core layer and the battery prepared by the fire-retardant base film of the polyimide non-woven fabric with the fire retardant in the shell layer as a comparison are as shown in Figure 4

[0062] The above description is only a preferred embodiment of the present application, and therefore cannot limit the scope of the present application. Equivalent changes and modifications made in accordance with the scope of the present application and the content of the specification should still be within the scope of the present application.​

Claims

1. A method for preparing a core-shell structured polyimide flame retardant base film, characterized by: The fire-retardant base film is made of composite fibers, the composite fibers comprising a core layer and a shell layer coated outside the core layer; the core layer is made of polyimide, a fire retardant and a silane coupling agent; the shell layer is made of polyimide; the fire retardant comprises at least one of melamine polyphosphate or magnesium hydroxide; the silane coupling agent has a structural formula as shown in the following formula: or , wherein R is methyl, ethyl or n-butyl; dissolving polyamide acid in an organic solvent as a shell spinning solution; dissolving polyamide acid in an organic solvent, adding the flame retardant and the silane coupling agent as a core spinning solution; preparing the composite fiber by coaxial electrospinning of the shell spinning solution and the core spinning solution and film forming, treating at 75-85°C for 22-25h, and then calcining in air atmosphere at 250-340°C to obtain the flame-retardant base film.

2. The method of claim 1, wherein the method is characterized by: The organic solvent is at least one of N,N-dimethylformamide, N-methylpyrrolidone, acetone, dimethyl sulfoxide, dichloromethane or trichloromethane; the content of the organic solvent in the shell spinning solution is not more than 95 wt%; the content of the organic solvent in the core spinning solution is not more than 95 wt%.

3. The method of claim 1, wherein the method is characterized by: The content of the silane coupling agent in the core spinning solution is not more than 50 wt%.

4. Use of the core-shell structure polyimide flame-retardant base film prepared by the method of claim 1 in an in-situ solid-state battery.

5. An in situ solid state battery, characterized by: The in-situ solid-state battery comprises the core-shell structure polyimide flame-retardant base film prepared by the method of claim 1.

6. A method of making an in situ solid state battery as claimed in claim 5, characterized by: Mixing an electrolyte solution comprising an aprotic organic solvent and a lithium salt uniformly with a polymerizable monomer to obtain a mixed solution; injecting the mixed solution in-situ onto the core-shell structure polyimide flame-retardant base film between the positive and negative electrodes, and irradiating to generate a solidified battery.

7. The method of claim 6, wherein: The aprotic organic solvent comprises at least one of ethylene carbonate, dimethyl carbonate, diethyl carbonate, propylene carbonate, methyl ethyl carbonate, 1,3-dioxolane, dimethyl ether, N-methylpyrrolidone, dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetamide, acetone, tetrahydrofuran or acetonitrile; the lithium salt comprises at least one of LiTFSI, LiClO4, LiPF6, LiCl, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, LiBF4, AMPSLi or STFSILi; the concentration of the lithium salt in the electrolyte solution is 0.001-20 M.

8. The method of claim 6, wherein: The polymerizable monomer comprises at least one of acrylate, acrylonitrile, methoxy acrylate, polyethylene glycol diacrylate, acrylamide, 2-acrylamide-2-methylpropane sulfonic acid, glycidyl methacrylate, ethylene carbonate, propylene carbonate, oxirane, acrylic acid, styrene, fluoride, phosphine, siloxane or acetate.

9. The method of claim 6, wherein: The irradiation is gamma ray irradiation, and the irradiation dose is 5-900 KGy.

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