A fluorinated two-dimensional inorganic nanofiller reinforced PEO-based solid-state polymer electrolyte, and a preparation method and application thereof

Abstract

The application relates to a fluorinated two-dimensional inorganic nanofiller reinforced PEO-based solid-state polymer electrolyte and a preparation method and application thereof, and comprises the following steps: S1, obtaining fluorinated two-dimensional inorganic nanofillers by treating two-dimensional inorganic materials with a mixed gas of fluorine and nitrogen; S2, dissolving polyethylene oxide and a lithium salt in a polar solvent, then adding the fluorinated two-dimensional inorganic nanofillers obtained in the step S1, mixing, and obtaining a uniform mixed polymer solution; and S3, pouring the mixed polymer solution obtained in the step S2 on a polytetrafluoroethylene mold, vacuum drying, and obtaining the PEO-based solid-state polymer electrolyte. Compared with the prior art, the preparation process is simple and easy to operate, the ionic conductivity of the polymer electrolyte based on the fluorinated two-dimensional inorganic nanofillers can be improved, the electrochemical stability window can be widened, and the interface stability between the electrolyte and a lithium metal electrode can be improved.

Description

Technical Field

[0001] This invention relates to the field of all-solid-state lithium battery technology, and in particular to a PEO-based solid polymer electrolyte reinforced with fluorinated two-dimensional inorganic nanofillers, its preparation method, and its application. Background Technology

[0002] Lithium-ion batteries, with their advantages of high operating voltage, high energy density, long cycle life, and low pollution, have become a hot topic in the research and application of rechargeable batteries for energy storage worldwide. Currently, commercially available lithium-ion batteries using liquid electrolytes face the risk of leakage and numerous side reactions; solid-state electrolytes, in contrast, are safer. Compared to solid inorganic electrolytes, solid polymer electrolytes offer advantages such as thinness, good elasticity, and excellent contact with the electrode interface. They also possess better thermal stability and mechanical strength, significantly improving the safety performance of lithium-ion batteries using lithium metal as the negative electrode. Furthermore, this makes it possible to match high-capacity positive electrodes with lithium metal negative electrodes.

[0003] Polyethylene oxide (PEO) was the first polymer electrolyte introduced into lithium-ion batteries. It is not only an excellent lithium-ion complexing agent but also forms good interfacial contact with the electrode, facilitating lithium-ion insertion / extraction and deposition. However, PEO itself has certain performance drawbacks. First, PEO is prone to crystallization at room temperature and has poor chain segment mobility, resulting in poor lithium-ion conductivity. Furthermore, PEO has a narrow electrochemical stability window, typically beginning to decompose at 3.6V. These problems severely limit the application of PEO-based solid-state polymer electrolytes in all-solid-state lithium-ion batteries.

[0004] Most current methods aim to lower the glass transition temperature of PEO, thereby enhancing the mobility of PEO segments and improving the ionic conductivity of PEO-based solid polymer electrolytes at room temperature. Meanwhile, to broaden the electrochemical stability window, PEO-based composite materials can be prepared through modification methods such as blending, crosslinking, and adding inorganic fillers.

[0005] CN 116102870 A discloses a crosslinked modified solid polymer electrolyte. This electrolyte utilizes the benzene ring structure in a phenyl crosslinking agent to enhance the mechanical strength and stability of the solid polymer electrolyte, while also improving the cycle stability of the battery. CN 116231067 A discloses a method for preparing a flame-retardant ultrathin PEO-based solid electrolyte. It uses a multifunctional HNT@TMP flame-retardant filler to provide flame-retardant properties to the electrolyte, while using ultrathin porous cellulose nanopaper (CN) as a support layer to achieve excellent mechanical properties. CN 112397780 A discloses a polymer electrolyte thin film material using two-dimensional lamellar vermiculite (VNs) as a filler and its preparation method. By adding two-dimensional fillers, the glass transition temperature of PEO is lowered, and its chain segment mobility is improved, thereby solving the problems of low room-temperature ionic conductivity and high interfacial impedance of polymer electrolytes.

[0006] While the existing technologies mentioned above have improved the ionic conductivity, battery stability, mechanical properties, and flame retardant properties of PEO-based solid polymer electrolytes to some extent, the copolymerization and crosslinking methods are complex and involve intricate composition. In comparison, adding inorganic fillers is a simpler, more effective, and practical method. However, adding ordinary inorganic fillers cannot simultaneously improve the comprehensive performance of PEO, including ionic conductivity, electrochemical stability window, and battery cycle performance. This is because ordinary inorganic fillers often only lower the glass transition temperature of PEO and increase its chain segment mobility, without significantly affecting the electrochemical stability window. Furthermore, ordinary inorganic fillers do not improve the composition and structure of the solid electrolyte interphase (SEI), thus failing to enhance battery cycle stability. Therefore, there is an urgent need to design a PEO-based solid polymer electrolyte with added special inorganic fillers that can be prepared simply and efficiently, improving ionic conductivity, widening the electrochemical stability window, and promoting the formation of a good solid electrolyte interphase (SEI), thereby improving the interfacial stability between the electrolyte and the electrode. Summary of the Invention

[0007] The purpose of this invention is to overcome the problems of complex preparation methods, minimal impact of inorganic fillers on the electrochemical stability window, lack of improvement on the composition and structure of the SEI, and inability to improve the cycle stability of the battery by providing a PEO-based solid polymer electrolyte reinforced with fluorinated two-dimensional inorganic nanofillers, as well as its preparation method and application.

[0008] The objective of this invention can be achieved through the following technical solutions:

[0009] One of the technical solutions of the present invention is to provide a method for preparing a PEO-based solid polymer electrolyte reinforced with fluorinated two-dimensional inorganic nanofillers, comprising the following steps:

[0010] S1. Fluorinated two-dimensional inorganic nanofillers are obtained by reacting two-dimensional inorganic materials with a mixture of fluorine and nitrogen gas (F2 / N2, with nitrogen as a protective gas).

[0011] S2. Dissolve polyethylene oxide and lithium salt in a polar solvent, then add the fluorinated two-dimensional inorganic nanofiller obtained in step S1, mix, and obtain a uniform mixed polymer solution.

[0012] S3. The mixed polymer solution obtained in step S2 is poured onto a polytetrafluoroethylene mold and dried under vacuum to obtain a PEO-based solid polymer electrolyte.

[0013] In some specific embodiments, in step S1, the two-dimensional inorganic material is selected from any one or more of graphene, carbon nitride, and boron nitride.

[0014] In some specific embodiments, in step S1, the concentration of fluorine (F2) in the mixed gas of fluorine and nitrogen is 10%-70%, the reaction temperature is 200-400℃, and the reaction time is 0.5-10h.

[0015] In some specific embodiments, in step S2, the lithium salt is selected from any one or more of LiPF6, LiClO4, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium di(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiDFOB), and LiNO3.

[0016] Further preferably, the lithium salt is selected from LiPF6, LiClO4, and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0017] In some specific embodiments, in step S2, the polyethylene oxide is selected from polyethylene oxide with a viscosity-average molecular weight range of 400 to 3,000,000.

[0018] More preferably, the polyethylene oxide is selected from polyethylene oxide with a viscosity-average molecular weight range of 50,000 to 2,000,000.

[0019] In some specific embodiments, in step S2, the polar solvent is selected from any one or more of acetonitrile, N-methylpyrrolidone (NMP), and N,N-dimethylformamide (DMF).

[0020] In some specific embodiments, in step S2, the amount of polyethylene oxide and lithium salt added satisfies the following: the molar ratio of lithium ions in the lithium salt to ether oxygen atoms in the polyethylene oxide is 1:(10-20).

[0021] The addition amounts of polyethylene oxide and fluorinated inorganic two-dimensional nanofillers satisfy the following: the mass ratio of polyethylene oxide to fluorinated inorganic two-dimensional nanofillers is 1:(0.005~0.2);

[0022] The amount of polyethylene oxide and polar solvent added should meet the following condition: the mass ratio of polyethylene oxide to polar solvent is 1:(20-50).

[0023] In some specific embodiments, in step S2, the mixing method is stirring, and the stirring temperature is 50-80℃.

[0024] In some specific embodiments, in step S3, the temperature for vacuum drying is 50-80°C.

[0025] The second technical solution of the present invention is to provide a PEO-based solid polymer electrolyte reinforced with fluorinated two-dimensional inorganic nanofiller, which is prepared by the preparation method described in one of the above technical solutions.

[0026] The third technical solution of the present invention is to provide an application of the PEO-based solid polymer electrolyte reinforced with fluorinated two-dimensional inorganic nanofiller as described in the second technical solution above in an all-solid-state lithium battery.

[0027] In some specific embodiments, the all-solid-state lithium battery includes a positive electrode, a PEO-based solid polymer electrolyte, and a negative electrode stacked sequentially, wherein the thickness of the PEO-based solid polymer electrolyte is 20-200 μm.

[0028] The mechanism of this invention is as follows: During the fluorination process, not only is fluorine introduced, but the etching effect of fluorine gas also generates mesopores in the two-dimensional nanomaterial, thereby increasing the specific surface area of ​​the two-dimensional material. When added to PEO to prepare a solid polymer electrolyte, the fluorine atoms in the fluorinated two-dimensional inorganic nanofiller can react with the lithium metal anode to generate LiF, participating in the formation of the solid electrolyte interphase (SEI) layer. This effectively inhibits the growth of lithium dendrites and reduces interfacial resistance, thus solving the problem of poor interfacial stability between the electrolyte and the lithium metal electrode. The addition of two-dimensional inorganic materials can disrupt the crystalline segments of PEO, enhancing its activity and thereby improving lithium-ion migration efficiency. Strengthening the porous structure of the two-dimensional inorganic material also facilitates lithium-ion transport and improves ionic conductivity. Simultaneously, fluorine atoms can increase the chemical stability of the polymer electrolyte, preventing oxidation or reduction and decomposition under high voltage, and improving the electrochemical stability window of the electrolyte. The mass ratio of polyethylene oxide to fluorinated inorganic two-dimensional nanofiller is controlled at 1:(0.005~0.2). If the content of fluorinated inorganic two-dimensional nanofiller is too low, the performance improvement is not significant. If the content of fluorinated inorganic two-dimensional nanofiller is too high, it will cause the fluorinated inorganic two-dimensional nanofiller to agglomerate, resulting in uneven dispersion of the fluorinated inorganic two-dimensional nanofiller in the electrolyte membrane. Moreover, if the content of fluorinated inorganic two-dimensional nanofiller is too high, it will greatly reduce its compatibility with PEO.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] (1) In the process of fluorination, this invention not only introduces fluorine, but also generates mesopores on the two-dimensional inorganic nanomaterial through the etching effect of fluorine gas, thereby increasing the specific surface area of ​​the two-dimensional material.

[0031] (2) This invention, by adding fluorinated two-dimensional nanofillers, to a certain extent disrupts the crystalline segments of PEO, enhancing the mobility of PEO segments, thereby improving lithium-ion migration efficiency, strengthening the porous structure of the phase, and also facilitating lithium-ion transport and improving ionic conductivity. Simultaneously, fluorine atoms can increase the chemical stability of the polymer electrolyte, preventing the electrolyte from being oxidized or reduced and decomposing under high voltage, thus improving the electrochemical stability window of the electrolyte. Furthermore, fluorine atoms can react with the lithium metal anode to generate LiF, participating in the formation of the solid electrolyte interphase (SEI) layer, effectively inhibiting the growth of lithium dendrites, reducing interfacial resistance, and thus improving the interfacial stability between the electrolyte and the lithium metal electrode. Moreover, the fluorinated two-dimensional nanofillers have a single composition and will not produce complex side reactions that affect battery performance.

[0032] (3) The preparation process of the PEO-based solid polymer electrolyte reinforced by fluorinated two-dimensional nanofiller of the present invention is simple and easy to operate. It can simultaneously improve the ionic conductivity of polymer electrolyte based on fluorinated two-dimensional inorganic nanofiller and broaden the electrochemical stability window, and enhance the interfacial stability between electrolyte and lithium metal electrode, which is beneficial to research and practical application. Attached Figure Description

[0033] Figure 1 This is a comparison of SEM images of carbon nitride before and after fluorination in Example 1 of the present invention, wherein Figure (a) is the SEM image before fluorination and Figure (b) is the SEM image after fluorination.

[0034] Figure 2 This is a graph showing the relationship between the ionic conductivity and temperature of the solid polymer electrolytes prepared in Examples 7, 8, 9 and Comparative Example 1 of this invention.

[0035] Figure 3 These are the LSV curves of the PEO-based solid polymer electrolytes prepared in Example 8 and Comparative Example 1 of this invention.

[0036] Figure 4 These are the constant current charge-discharge polarization curves of the PEO-based solid polymer electrolytes prepared in Example 8 and Comparative Example 1 of this invention.

[0037] Figure 5 This is a graph showing the cycling performance of the PEO-based solid polymer electrolyte reinforced with fluorinated two-dimensional nanofiller prepared in Example 8 of this invention in a full battery.

[0038] Figure 6 This is a physical image of the PEO-based solid polymer electrolyte reinforced with fluorinated two-dimensional nanofillers prepared in Example 1 of this invention. Detailed Implementation

[0039] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0040] Unless otherwise specified, the raw materials or processing techniques used in the following embodiments and comparative examples are all conventional commercially available raw materials or conventional processing techniques in the art.

[0041] The all-solid-state lithium batteries involved in the following embodiments and comparative examples include lithium symmetric batteries and LFP batteries (lithium iron phosphate batteries). The lithium symmetric battery consists of a lithium cathode, a PEO-based solid polymer electrolyte reinforced with fluorinated inorganic two-dimensional nanofillers, and a lithium anode. The LFP battery consists of an LFP cathode, a PEO-based solid polymer electrolyte reinforced with fluorinated inorganic two-dimensional nanofillers, and a lithium anode. There are no particular limitations on the preparation method of the all-solid-state lithium battery; any technical solution for assembling all-solid-state lithium batteries well known to those skilled in the art can be used.

[0042] In the following examples and comparative examples, the viscosity-average molecular weight of polyethylene oxide is 600,000.

[0043] Example 1:

[0044] A PEO-based solid polymer electrolyte reinforced with fluorinated inorganic two-dimensional nanofillers is prepared according to the following steps:

[0045] (1) Place 5g of carbon nitride (g-C3N4) in an F2 / N2 atmosphere with an F2 concentration of 20% and react at 200℃ for 1h to obtain mesoporous fluorinated carbon nitride (FCN) by utilizing the fluorination and etching effects of fluorine gas.

[0046] (2) At room temperature, 1.2g PEO was dissolved in 30g acetonitrile, and then 0.489g LiTFSI was added. The mixture was heated in a water bath at 60°C and stirred for 12 hours until homogeneous.

[0047] (3) Add 0.12g of carbon fluoride (FCN) to the solution in step (2) and heat in a water bath at 60°C for 12 hours until the mixture is homogeneous.

[0048] (4) Pour the mixed polymer solution from step (3) into a polytetrafluoroethylene mold, place it in a vacuum oven and dry at 60°C for 12 hours, then remove it.

[0049] (5) Cut the dried electrolyte membrane into round pieces with a diameter of 19mm, and then insert them into button cells for testing.

[0050] like Figure 1 The image shows a comparison of SEM images of carbon nitride before and after fluorination. Image a is the SEM image before fluorination, and image b is the SEM image after fluorination. Fluorinated carbon nitride produces mesopores, which increases its specific surface area.

[0051] like Figure 6 The image shows the actual electrolyte membrane prepared.

[0052] Example 2:

[0053] The two examples are largely the same as in Example 1, except that the reaction temperature in step (1) is changed to 300°C.

[0054] The specific steps are as follows:

[0055] (1) Place 5g of carbon nitride (g-C3N4) in an F2 / N2 atmosphere with an F2 concentration of 20% and react at 300℃ for 1h to obtain mesoporous fluorinated carbon nitride (FCN) by utilizing the fluorination and etching effects of fluorine gas.

[0056] (2) At room temperature, 1.2g PEO was dissolved in 30g acetonitrile, and then 0.489g LiTFSI was added. The mixture was heated in a water bath at 60°C and stirred for 12 hours until homogeneous.

[0057] (3) Add 0.12g of carbon fluoride (FCN) to the solution in step (2) and heat in a water bath at 60°C for 12 hours until the mixture is homogeneous.

[0058] (4) Pour the mixed polymer solution from step (3) into a polytetrafluoroethylene mold, place it in a vacuum oven and dry at 60°C for 12 hours, then remove it.

[0059] (5) Cut the dried electrolyte membrane into round pieces with a diameter of 19mm, and then insert them into button cells for testing.

[0060] Example 3:

[0061] The two examples are largely the same as in Example 1, except that the reaction temperature in step (1) is changed to 400°C.

[0062] The specific steps are as follows:

[0063] (1) Place 5g of carbon nitride (g-C3N4) in an F2 / N2 atmosphere with an F2 concentration of 20% and react at 400℃ for 1h to obtain mesoporous fluorinated carbon nitride (FCN) by utilizing the fluorination and etching effects of fluorine gas.

[0064] (2) At room temperature, 1.2g PEO was dissolved in 30g acetonitrile, and then 0.489g LiTFSI was added. The mixture was heated in a water bath at 60°C and stirred for 12 hours until homogeneous.

[0065] (3) Add 0.12g of carbon fluoride (FCN) to the solution in step (2) and heat in a water bath at 60°C for 12 hours until the mixture is homogeneous.

[0066] (4) Pour the mixed polymer solution from step (3) into a polytetrafluoroethylene mold, place it in a vacuum oven and dry at 60°C for 12 hours, then remove it.

[0067] (5) Cut the dried electrolyte membrane into round pieces with a diameter of 19mm, and then insert them into button cells for testing.

[0068] Example 4:

[0069] The two are largely the same as in Example 1, except that the F2 / N2 atmosphere in step (1) is adjusted to an F2 / N2 atmosphere with an F2 concentration of 10%.

[0070] The specific steps are as follows:

[0071] (1) Place 5g of carbon nitride (g-C3N4) in an F2 / N2 atmosphere with an F2 concentration of 10% and react at 200℃ for 1h to obtain mesoporous fluorinated carbon nitride (FCN) by utilizing the fluorination and etching effects of fluorine gas.

[0072] (2) At room temperature, 1.2g PEO was dissolved in 30g acetonitrile, and then 0.489g LiTFSI was added. The mixture was heated in a water bath at 60°C and stirred for 12 hours until homogeneous.

[0073] (3) Add 0.12g of carbon fluoride (FCN) to the solution in step (2) and heat in a water bath at 60°C for 12 hours until the mixture is homogeneous.

[0074] (4) Pour the mixed polymer solution from step (3) into a polytetrafluoroethylene mold, place it in a vacuum oven and dry at 60°C for 12 hours, then remove it.

[0075] (5) Cut the dried electrolyte membrane into round pieces with a diameter of 19mm, and then insert them into button cells for testing.

[0076] Example 5:

[0077] The two are largely the same as in Example 1, except that the F2 / N2 atmosphere in step (1) is adjusted to an F2 / N2 atmosphere with an F2 concentration of 30%.

[0078] The specific steps are as follows:

[0079] (1) Place 5g of carbon nitride (g-C3N4) in an F2 / N2 atmosphere with an F2 concentration of 30% and react at 200℃ for 1h to obtain mesoporous fluorinated carbon nitride (FCN) by utilizing the fluorination and etching effects of fluorine gas.

[0080] (2) At room temperature, 1.2g PEO was dissolved in 30g acetonitrile, and then 0.489g LiTFSI was added. The mixture was heated in a water bath at 60°C and stirred for 12 hours until homogeneous.

[0081] (3) Add 0.12g of carbon fluoride (FCN) to the solution in step (2) and heat in a water bath at 60°C for 12 hours until the mixture is homogeneous.

[0082] (4) Pour the mixed polymer solution from step (3) into a polytetrafluoroethylene mold, place it in a vacuum oven and dry at 60°C for 12 hours, then remove it.

[0083] (5) Cut the dried electrolyte membrane into round pieces with a diameter of 19mm, and then insert them into button cells for testing.

[0084] Example 6:

[0085] The two are largely the same as in Example 1, except that the F2 / N2 atmosphere in step (1) is adjusted to an F2 / N2 atmosphere with an F2 concentration of 50%.

[0086] The specific steps are as follows:

[0087] (1) Place 5g of carbon nitride (g-C3N4) in an F2 / N2 atmosphere with an F2 concentration of 50% and react at 200℃ for 1h to obtain mesoporous fluorinated carbon nitride (FCN) by utilizing the fluorination and etching effects of fluorine gas.

[0088] (2) At room temperature, 1.2g PEO was dissolved in 30g acetonitrile, and then 0.489g LiTFSI was added. The mixture was heated in a water bath at 60°C and stirred for 12 hours until homogeneous.

[0089] (3) Add 0.12g of carbon fluoride (FCN) to the solution in step (2) and heat in a water bath at 60°C for 12 hours until the mixture is homogeneous.

[0090] (4) Pour the mixed polymer solution from step (3) into a polytetrafluoroethylene mold, place it in a vacuum oven and dry at 60°C for 12 hours, then remove it.

[0091] (5) Cut the dried electrolyte membrane into round pieces with a diameter of 19mm, and then insert them into button cells for testing.

[0092] Example 7:

[0093] The process is largely the same as in Example 2, except that in step (1), 5g of carbon nitride (g-C3N4) is replaced with 5g of graphene. In step (3), 0.12g of fluorinated carbon nitride (FCN) is replaced with 0.012g of fluorinated graphene (FG).

[0094] The specific steps are as follows:

[0095] (1) 5g of graphene was placed in an F2 / N2 atmosphere with an F2 concentration of 20% and reacted at 300℃ for 1h to obtain fluorinated graphene (FG) by fluorination and etching with fluorine gas.

[0096] (2) At room temperature, 1.2g PEO was dissolved in 30g acetonitrile, and then 0.489g LiTFSI was added. The mixture was heated in a water bath at 60°C and stirred for 12 hours until homogeneous.

[0097] (3) Add 0.012g of fluorinated graphene (FG) to the solution in step (2) and heat in a water bath at 60°C for 12 hours until the mixture is homogeneous.

[0098] (4) Pour the mixed polymer solution from step (3) into a polytetrafluoroethylene mold, place it in a vacuum oven and dry at 60°C for 12 hours, then remove it.

[0099] (5) Cut the dried electrolyte membrane into round pieces with a diameter of 19mm, and then insert them into button cells for testing.

[0100] Tests have found that, for example Figure 2 As shown, at 60℃, the ionic conductivity of the electrolyte membrane reaches 6.09 × 10⁻⁶. -4 S / cm.

[0101] Example 8:

[0102] The majority of the results are the same as in Example 7, except that the 0.012g of fluorinated graphene (FG) in step (3) is replaced with 0.036g of fluorinated graphene (FG).

[0103] The specific steps are as follows:

[0104] (1) 5g of graphene was placed in an F2 / N2 atmosphere with an F2 concentration of 20% and reacted at 300℃ for 1h to obtain fluorinated graphene (FG) by fluorination and etching with fluorine gas.

[0105] (2) At room temperature, 1.2g PEO was dissolved in 30g acetonitrile, and then 0.489g LiTFSI was added. The mixture was heated in a water bath at 60°C and stirred for 12 hours until homogeneous.

[0106] (3) Add 0.036g of fluorinated graphene (FG) to the solution in step (2) and heat in a water bath at 60°C for 12 hours until the mixture is homogeneous.

[0107] (4) Pour the mixed polymer solution from step (3) into a polytetrafluoroethylene mold, place it in a vacuum oven and dry at 60°C for 12 hours, then remove it.

[0108] (5) Cut the dried electrolyte membrane into round pieces with a diameter of 19mm, and then insert them into button cells for testing.

[0109] Tests have found that, for example Figure 2 As shown, at 60℃, the ionic conductivity of the electrolyte membrane reaches 6.22 × 10⁻⁶. -4S / cm; such as Figure 3 As shown, the electrochemical stability window reaches 5.14V (vs. Li+ / Li); Figure 4 As shown, the lithium symmetric battery at 0.1 mA / cm 2 It can cycle stably for more than 850 hours at current density; such as Figure 5 As shown, the LEP battery at 60℃ and a charge / discharge rate of 1C has a maximum discharge specific capacity of 145.8mAh / g, and a capacity retention rate of 87.9% after 310 cycles.

[0110] Example 9:

[0111] The majority of the results are the same as in Example 7, except that the 0.012g of fluorinated graphene (FG) in step (3) is replaced with 0.12g of fluorinated graphene (FG).

[0112] The specific steps are as follows:

[0113] (1) 5g of graphene was placed in an F2 / N2 atmosphere with an F2 concentration of 20% and reacted at 300℃ for 1h to obtain fluorinated graphene (FG) by fluorination and etching with fluorine gas.

[0114] (2) At room temperature, 1.2g PEO was dissolved in 30g acetonitrile, and then 0.489g LiTFSI was added. The mixture was heated in a water bath at 60°C and stirred for 12 hours until homogeneous.

[0115] (3) Add 0.12g of fluorinated graphene (FG) to the solution in step (2) and heat in a water bath at 60°C for 12 hours until the mixture is homogeneous.

[0116] (4) Pour the mixed polymer solution from step (3) into a polytetrafluoroethylene mold, place it in a vacuum oven and dry at 60°C for 12 hours, then remove it.

[0117] (5) Cut the dried electrolyte membrane into round pieces with a diameter of 19mm, and then insert them into button cells for testing.

[0118] Tests have found that, for example Figure 2 As shown, at 60℃, the ionic conductivity of the electrolyte membrane reaches 4.18 × 10⁻⁶. -4 S / cm.

[0119] Example 10:

[0120] Compared with Example 1, most of the contents are the same, except that 5g of carbon nitride (g-C3N4) in step (1) is replaced with 5g of boron nitride, the F2 / N2 atmosphere is adjusted to an F2 / N2 atmosphere with an F2 concentration of 30%, the reaction condition of 200°C is replaced with 300°C, and 0.12g of carbon nitride fluoride (FCN) in step (3) is replaced with 0.12g of boron nitride fluoride (FBN).

[0121] The specific steps are as follows:

[0122] (1) Place 5g of boron nitride in an F2 / N2 atmosphere with an F2 concentration of 30% and react at 300℃ for 1h to obtain boron nitride fluorinated (FBN) by utilizing the fluorination and etching effects of fluorine gas.

[0123] (2) At room temperature, 1.2g PEO was dissolved in 30g acetonitrile, and then 0.489g LiTFSI was added. The mixture was heated in a water bath at 60°C and stirred for 12 hours until homogeneous.

[0124] (3) Add 0.12g of boron fluoride nitride (FBN) to the solution in step (2) and heat in a water bath at 60°C for 12 hours until the mixture is homogeneous.

[0125] (4) Pour the mixed polymer solution from step (3) into a polytetrafluoroethylene mold, place it in a vacuum oven and dry at 60°C for 12 hours, then remove it.

[0126] (5) Cut the dried electrolyte membrane into round pieces with a diameter of 19mm, and then insert them into button cells for testing.

[0127] Example 11:

[0128] Compared with Example 1, most of them are the same, except that the water bath heating temperature in step (3) is changed to 80°C.

[0129] The specific steps are as follows:

[0130] (1) Place 5g of carbon nitride (g-C3N4) in an F2 / N2 atmosphere with an F2 concentration of 20% and react at 200℃ for 1h to obtain mesoporous fluorinated carbon nitride (FCN) by utilizing the fluorination and etching effects of fluorine gas.

[0131] (2) At room temperature, 1.2g PEO was dissolved in 30g acetonitrile, and then 0.489g LiTFSI was added. The mixture was heated in a water bath at 60°C and stirred for 12 hours until homogeneous.

[0132] (3) Add 0.12g of carbon fluoride (FCN) to the solution in step (2) and heat in a water bath at 80°C for 12 hours until the mixture is homogeneous.

[0133] (4) Pour the mixed polymer solution from step (3) into a polytetrafluoroethylene mold, place it in a vacuum oven and dry at 60°C for 12 hours, then remove it.

[0134] (5) Cut the dried electrolyte membrane into round pieces with a diameter of 19mm, and then insert them into button cells for testing.

[0135] Example 12:

[0136] The majority of the steps are the same as in Example 1, except that the water bath heating time in step (3) is changed to 24 hours.

[0137] The specific steps are as follows:

[0138] (1) Place 5g of carbon nitride (g-C3N4) in an F2 / N2 atmosphere with an F2 concentration of 20% and react at 200℃ for 1h to obtain mesoporous fluorinated carbon nitride (FCN) by utilizing the fluorination and etching effects of fluorine gas.

[0139] (2) At room temperature, 1.2g PEO was dissolved in 30g acetonitrile, and then 0.489g LiTFSI was added. The mixture was heated in a water bath at 60°C and stirred for 12 hours until homogeneous.

[0140] (3) Add 0.12g of carbon fluoride (FCN) to the solution in step (2) and heat in a water bath at 60°C for 24 hours until the mixture is homogeneous.

[0141] (4) Pour the mixed polymer solution from step (3) into a polytetrafluoroethylene mold, place it in a vacuum oven and dry at 60°C for 12 hours, then remove it.

[0142] (5) Cut the dried electrolyte membrane into round pieces with a diameter of 19mm, and then insert them into button cells for testing.

[0143] Comparative Example 1:

[0144] Compared with Example 7, most of the results are the same, except that steps (1) and (3) are omitted to obtain a pure PEO solid polymer electrolyte without the addition of mesoporous fluorinated graphene (FG).

[0145] After testing, such as Figure 2 As shown, the ionic conductivity at 60℃ is only 3.17 × 10⁻⁶. -4 S / cm; such as Figure 3 As shown, the electrochemical stability window is only 4.41V; Figure 4 As shown, lithium-ion symmetric batteries have poor cycle stability.

[0146] Comparative Example 2:

[0147] The majority of the contents are the same as in Example 1, except that the F2 / N2 atmosphere is adjusted to an F2 / N2 atmosphere with an F2 concentration of 5%.

[0148] Tests showed that at low fluorine (F2) concentrations, the fluorine etching effect was not significant, resulting in carbon fluoride nitride (FCN) with low fluorine content and a specific surface area of ​​10.1 m². 2 / g, while the specific surface area of ​​fluorinated carbon nitride (FCN) obtained in Example 1 was 16.0m². 2 / g. Therefore, compared to the specific surface area of ​​ordinary carbon nitride (g-C3N4) of 8.6m², 2 / g, when the F2 concentration is low, the specific surface area of ​​the FCN obtained is only slightly improved. Therefore, it cannot effectively improve battery performance.

[0149] Comparative Example 3:

[0150] Compared with Example 8, most of them are the same, except that step (1) is omitted, that is, PEO-based solid polymer electrolyte with unfluorinated graphene as filler is obtained.

[0151] Tests showed that the lithium symmetric battery achieved a speed of 0.1 mA / cm². 2 At the specified current density, it could only cycle stably for 480 hours, while the lithium symmetric battery in Example 8 could cycle stably at 0.1 mA / cm². 2 The battery can cycle stably for over 850 hours at a given current density. This indicates that the untreated two-dimensional inorganic nanofiller has a limited effect on improving battery cycle stability.

[0152] In summary, based on the analysis of the above embodiments and comparative examples, it is evident that the pure PEO solid polymer electrolyte prepared in Comparative Example 1 exhibits low ionic conductivity, a narrow electrochemical stability window, and poor cycle stability in lithium-symmetric batteries. This invention, by introducing fluorinated inorganic two-dimensional nanofillers into PEO, can disrupt the crystalline segments of PEO, enhance its mobility, thereby improving lithium-ion migration efficiency and ionic conductivity (e.g., ...). Figure 2 The graph shows the relationship between ionic conductivity and temperature. Simultaneously, fluorine atoms can increase the chemical stability of the polymer electrolyte, preventing it from being oxidized or reduced and decomposing under high voltage, thereby improving the electrolyte's electrochemical stability window. Figure 3 The LSV curve shown is relevant here. Fluorine atoms can also react with the lithium metal anode to form LiF, which participates in the formation of the solid electrolyte interphase (SEI) layer. This effectively inhibits the growth of lithium dendrites and reduces the interfacial resistance, thus solving the problem of poor interfacial stability between the electrolyte and the lithium metal electrode (e.g., ...). Figure 4 The constant current charge-discharge polarization curves are shown. Meanwhile, the full cell using a PEO-based solid polymer electrolyte membrane reinforced with fluorinated inorganic two-dimensional nanofillers also exhibits excellent cycle performance and rate performance (e.g., Figure 5(As shown).

[0153] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for preparing a PEO-based solid polymer electrolyte reinforced with fluorinated two-dimensional inorganic nanofillers, characterized in that, Includes the following steps: S1. Fluorinated two-dimensional inorganic nanofillers are obtained by reacting two-dimensional inorganic materials with a mixed gas of fluorine and nitrogen. The concentration of fluorine in the mixed gas of fluorine and nitrogen is 10%-70%, the reaction temperature is 200-400℃, and the reaction time is 0.5-10 h. S2. Dissolve polyethylene oxide and lithium salt in a polar solvent, then add the fluorinated two-dimensional inorganic nanofiller obtained in step S1, mix, and obtain a uniform mixed polymer solution. S3. The mixed polymer solution obtained in step S2 is poured onto a polytetrafluoroethylene mold and dried under vacuum to obtain a PEO-based solid polymer electrolyte.

2. The preparation method according to claim 1, characterized in that, In step S1, the two-dimensional inorganic material is selected from any one or more of graphene, carbon nitride, and boron nitride.

3. The preparation method according to claim 1, characterized in that, In step S2, the lithium salt is selected from any one or more of LiPF6, LiClO4, LiTFSI, LiFSI, LiBOB, LiDFOB and LiNO3.

4. The preparation method according to claim 1, characterized in that, In step S2, the polar solvent is selected from any one or more of acetonitrile, N-methylpyrrolidone, and N,N-dimethylformamide.

5. The preparation method according to claim 1, characterized in that, In step S2, the amount of polyethylene oxide and lithium salt added satisfies the following condition: the molar ratio of lithium ions in the lithium salt to ether oxygen atoms in the polyethylene oxide is 1:(10~20). The addition amounts of polyethylene oxide and fluorinated inorganic two-dimensional nanofillers satisfy the following condition: the mass ratio of polyethylene oxide to fluorinated inorganic two-dimensional nanofillers is 1:(0.005~0.2). The amount of polyethylene oxide and polar solvent added should meet the following condition: the mass ratio of polyethylene oxide to polar solvent is 1:(20~50).

6. The preparation method according to claim 1, characterized in that, In step S2, the mixing method is stirring, and the stirring temperature is 50-80℃.

7. The preparation method according to claim 1, characterized in that, In step S3, the vacuum drying temperature is 50-80℃.

8. A PEO-based solid polymer electrolyte reinforced with fluorinated two-dimensional inorganic nanofillers, characterized in that, It is prepared according to any one of the preparation methods described in claims 1-7.

9. The application of a PEO-based solid polymer electrolyte reinforced with fluorinated two-dimensional inorganic nanofiller as described in claim 8 in an all-solid-state lithium battery.

Images