Phosphorus-nitrogen synergistic flame-retardant solid-state polymer electrolyte, preparation method and application thereof

Abstract

The application discloses a phosphorus-nitrogen synergistic flame-retardant solid-state polymer electrolyte and a preparation method and application thereof, and belongs to the technical field of lithium batteries. The application realizes synergistic optimization of the flame-retardant function and the ion transmission capacity by in-situ compounding of bisphenol B derivatives and polyethylene oxide and combining a controllable electrospinning process, and constructs a fiber network structure with the properties of flame retardancy, high ionic conductivity and mechanical stability, thereby providing a new path for development of high-safety solid-state batteries.

Description

Technical Field

[0001] This invention relates to the field of lithium battery technology, specifically to a phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte, its preparation method, and its application. Background Technology

[0002] In recent years, the application of lithium-ion batteries in new energy vehicles, energy storage systems, and other fields has continued to expand, demonstrating their significant advantages in high energy density and cycle performance. However, the use of flammable organic solvents (such as carbonates) in traditional liquid electrolyte systems has resulted in a persistently high risk of battery thermal runaway, seriously threatening the safety of end products. Especially under conditions of high temperature, overcharging, or mechanical abuse, combustion or even explosion caused by electrolyte leakage has become a core bottleneck restricting the development of high-energy-density batteries.

[0003] Currently, commercially available lithium-ion batteries mainly use a polyolefin membrane-liquid electrolyte system. Although safety can be improved by adding phosphate ester flame retardants (such as TPP), these small molecule additives are prone to side reactions with the electrodes, leading to increased interfacial impedance and reduced cycle life. Solid polymer electrolytes (such as polyethylene oxide systems) are considered an ideal alternative due to their solvent-free nature, but they still have two major drawbacks: first, insufficient intrinsic flame retardancy, as thermal decomposition of polymer segments at high temperatures may still trigger combustion; second, the challenge of balancing mechanical strength and ionic conductivity, where high cross-linking can improve mechanical properties but severely limits lithium-ion migration rates.

[0004] In existing technologies, the main strategy for improving the flame retardancy of solid electrolytes is to add composite inorganic flame-retardant fillers (such as layered double hydroxides). However, filler agglomeration can disrupt the uniformity of the electrolyte film and result in poor interfacial compatibility with the polymer matrix. In addition, electrolyte films prepared by traditional solution casting methods suffer from defects such as low porosity and limited ion transport channels.

[0005] In view of the problems existing in the current technology, there is an urgent need to develop a new flame-retardant solid polymer electrolyte. Summary of the Invention

[0006] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and provide a phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte, its preparation method and application. By in-situ composite of bisphenol B derivatives and polyethylene oxide, combined with a controllable electrospinning process, a fiber network structure with flame retardancy, high ionic conductivity and mechanical stability is constructed, thereby achieving synergistic optimization of flame retardant function and ion transport capability, and providing a new path for the development of high-safety solid-state batteries.

[0007] The technical solution of this invention is as follows:

[0008] In a first aspect, the present invention provides a method for preparing a phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte, comprising the following steps:

[0009] S1: Mix dried bisphenol B with aluminum trichloride to obtain mixture A. React mixture A with phosphorus oxychloride under nitrogen protection to obtain intermediate product B.

[0010] S2: Mix aniline, pyridine, anhydrous aluminum trichloride, and tetrahydrofuran to obtain solution C;

[0011] S3: Add intermediate product B to solution C under nitrogen protection to carry out the reaction. After filtering, washing, precipitating and drying the reaction product, product D is obtained.

[0012] S4: Mix product D with polyethylene oxide (PEO) in a solvent to obtain solution E;

[0013] S5: Add lithium bis(trifluoromethanesulfonylimide) to solution E and obtain a phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte by electrospinning.

[0014] Preferably, the specific process of step S1 is as follows: Bisphenol B is dried at 60-80℃ for 2 hours, and then mixed with aluminum trichloride to obtain mixture A; mixture A is reacted with phosphorus oxychloride at 100-115℃ for 2.5-3.5 hours under nitrogen protection; after the reaction is completed, residual phosphorus oxychloride in the mixture is removed by vacuum distillation to obtain intermediate product B.

[0015] Preferably, in step S1, the mass ratio of bisphenol B, aluminum trichloride and phosphorus oxychloride is (20-25):(0.1-0.2):(75-80).

[0016] Preferably, the specific process of step S2 is as follows: aniline, pyridine, anhydrous aluminum trichloride, and tetrahydrofuran are thoroughly mixed under stirring and heated to 55-70°C to obtain solution C.

[0017] Preferably, in step S2, the mass-to-volume ratio of aniline, pyridine, anhydrous aluminum trichloride, and tetrahydrofuran is (35-40) g: (40-45) g: (0.1-0.2) g: 150 mL.

[0018] Preferably, the specific process of step S3 is as follows: the intermediate product B is dispersed in a solvent and added to solution C multiple times under nitrogen protection, and the reaction is carried out for 2-4 hours; after the reaction, the reaction solution is filtered to remove byproducts, washed multiple times with ethanol solution and NaOH solution, and washed with deionized water until neutral. After the product is completely precipitated, it is filtered and the solid phase is dried to obtain product D.

[0019] Preferably, in step S3, the mass ratio of intermediate product B to aniline is 25:(35-40).

[0020] Preferably, in step S4, the mass-to-volume ratio of product D to polyethylene oxide and solvent is 1 g:(8-30) g:(30-100) mL; in step S5, lithium bis(trifluoromethanesulfonylimide) is 3-20 wt.% of polyethylene oxide; in step S5, the electrospinning parameters are set as follows: pushing speed 0.1-0.2 mm / min, pushing distance 30-45 mm, positive high voltage 10-30 kV, negative high voltage 3-10 kV, temperature 30-40℃, humidity 30%RH, needle-to-roll distance 10-15 mm, and roller speed 140 r / min.

[0021] Secondly, the present invention provides a phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte, which is prepared by the above-described method for preparing phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte.

[0022] Thirdly, the present invention provides the application of the above-mentioned phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte, comprising the following steps:

[0023] (1) Lithium iron phosphate (LFP), carbon black and polyvinylidene fluoride in a mass ratio of (7-8):(1-2):1 are dispersed by N-methylpyrrolidone, ground evenly and then coated onto aluminum foil with a scraper and dried to obtain lithium iron phosphate electrode sheet.

[0024] (2) A lithium battery was prepared by using a lithium metal sheet as the negative electrode, a lithium iron phosphate sheet as the positive electrode, and a phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte as the polymer flame-retardant electrolyte.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] 1. This invention proposes a method for preparing a phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte. Bisphenol B is reacted with phosphorus oxychloride under the catalysis of aluminum trichloride to obtain an intermediate product. This intermediate product is dispersed in a solvent and then reacted with aniline under the catalysis of aluminum trichloride and pyridine to synthesize a product containing a nitrogen-phosphorus flame-retardant system. This product is then compounded with polyethylene oxide in a solvent to obtain the final product PEO / BPB'. The phosphorus-nitrogen synergistic flame-retardant system introduced in this invention significantly enhances the thermal stability of the electrolyte. Simultaneously, the solid electrolyte is prepared using an electrospinning process, and the synergistic effect of molecular structure design and electrospinning constructs a fiber network structure that combines flame retardancy, high ionic conductivity, and mechanical stability. This invention solves the problem of the difficulty in simultaneously achieving flame retardancy and ion conductivity in traditional solid electrolytes, achieving synergistic optimization of flame retardant function and ion transport capability at the molecular design level, providing a new path for high-safety lithium-ion batteries.

[0027] 2. This invention uses economical and practical PEO as the main component, and synthesizes PEO / BPB' through organic modification to prepare a polymer electrolyte PEO / BPB' with excellent flame retardant effect. The organic modification technology not only eliminates the free radicals released by PEO combustion in PEO / BPB', thus exerting a flame retardant effect at high temperatures, but also demonstrates a significant effect. Furthermore, under thermal runaway conditions, PEO / BPB' can effectively improve the safety performance of the polymer electrolyte and control the combustion reaction of flammable materials through the synergistic effect of nitrogen and phosphorus elements. Simultaneously, it promotes the chain movement of the polymer electrolyte matrix and enhances electron transfer and ion transport by using C=O functional groups as lithium ion migration sites. It also improves the mechanical properties of the polymer by forming hydrogen bonds through its own functional groups, inhibiting the growth of lithium dendrites. Moreover, through the synergistic effect of molecular structure design and electrospinning, the formed three-dimensional fiber network structure effectively improves ion transport efficiency and mechanical strength, thereby improving the cycle performance of lithium batteries. Attached Figure Description

[0028] Figure 1 This is a SEM image of PEO / BPB' in Embodiment 1 of the present invention.

[0029] Figure 2 This is the stretch curve of PEO / BPB' in Embodiment 1 of the present invention.

[0030] Figure 3 This is the stretching curve of PEO in Comparative Example 1 of this invention.

[0031] Figure 4 This is a comparison of the limiting oxygen index of PEO / BPB' and PEO in Embodiment 1 and Comparative Example 1 of the present invention.

[0032] Figure 5 This is the coulombic efficiency diagram of the Li|PEO / BPB'|LFP half-cell of Embodiment 1 of the present invention.

[0033] Figure 6 This is a cycle performance diagram of the Li|PEO / BPB'|LFP half-cell of Embodiment 1 of the present invention.

[0034] Figure 7 This is the coulombic efficiency diagram of the Li|PEO|LFP half-cell of Comparative Example 1 of this invention.

[0035] Figure 8 This is a cycle performance diagram of the Li|PEO|LFP half-cell of Comparative Example 1 of this invention. Detailed Implementation

[0036] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of this invention will be clearly and completely described below in conjunction with the embodiments of this invention.

[0037] Example 1

[0038] The preparation method of the phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte in this embodiment includes the following steps:

[0039] S1: Bbisphenol B was dried in an oven at 80°C for 2 hours. 22 g of dry bisphenol B and 0.14 g of aluminum trichloride were added to a 250 mL three-necked culture flask and mixed thoroughly to obtain mixture A. Mixture A was reacted with 76 g of phosphorus oxychloride at 110°C for 3 hours under nitrogen protection. After the reaction was completed, the residual phosphorus oxychloride in the mixture was removed by vacuum distillation to obtain intermediate product B.

[0040] S2: Add 39g aniline, 40g pyridine, 0.14g anhydrous aluminum trichloride, and 150mL tetrahydrofuran to a 1000mL three-necked flask, mix thoroughly with stirring, and heat to 60℃ to obtain solution C;

[0041] S3: Add 25g of intermediate product B to solution C in a three-necked flask in three portions under nitrogen protection, and react for 4h. After the reaction, filter the reaction solution to remove the byproduct triethylamine hydrochloride, wash three times with ethanol solution and 500mL of 1wt.% NaOH solution, and wash with deionized water until neutral. After the product is completely precipitated, filter and dry the solid phase to obtain product D.

[0042] S4: Mix 1g of product D with 10g of PEO in 30mL of DMF until homogeneous to obtain solution E;

[0043] S5: Add 0.3g of lithium bis(trifluoromethanesulfonyl)imide to solution E, inject into a syringe, connect to the positive terminal of a high-voltage power supply, and connect the negative terminal to the roller. Obtain the phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte PEO / BPB' solidified into fibers at the roller through an electrospinning process (its SEM is shown in Figure 1). Figure 1 (As shown); the parameters for electrospinning are set as follows: push speed 0.1 mm / min, push distance 30 mm, positive high voltage 10 kV, negative high voltage 3 kV, temperature 35℃, humidity 30%RH, needle-to-roll distance 15 mm, and roller speed 140 r / min.

[0044] The obtained PEO / BPB' is prepared into a disc with a diameter of 18 mm and used as the electrolyte in the assembly of lithium-ion batteries, including the following steps:

[0045] (1) Preparation of positive electrode sheet: Lithium iron phosphate, carbon black and PVDF in a mass ratio of 8:1:1 are dispersed with N-methylpyrrolidone, ground evenly and then coated on aluminum foil with a scraper and dried to obtain lithium iron phosphate electrode sheet.

[0046] (2) Preparation of lithium half-cell: Using lithium metal sheet as negative electrode, lithium iron phosphate sheet as positive electrode, and PEO / BPB' as polymer electrolyte, 2032 coin cell was prepared.

[0047] The cycle performance and coulombic efficiency of the Li|PEO / BPB'|LFP half-cell assembled in this embodiment are as follows: Figure 5-6 As shown.

[0048] Example 2

[0049] The preparation method of the phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte in this embodiment includes the following steps:

[0050] S1: Bbisphenol B was dried in an oven at 70°C for 2 hours. 23 g of dry bisphenol B and 0.15 g of aluminum trichloride were added to a 250 mL three-necked culture flask and mixed thoroughly to obtain mixture A. Mixture A was reacted with 77 g of phosphorus oxychloride at 100°C for 3.5 hours under nitrogen protection. After the reaction was completed, the residual phosphorus oxychloride in the mixture was removed by vacuum distillation to obtain intermediate product B.

[0051] S2: Add 40g aniline, 40g pyridine, 0.16g anhydrous aluminum trichloride, and 150mL tetrahydrofuran to a 1000mL three-necked flask, mix thoroughly with stirring, and heat to 70℃ to obtain solution C;

[0052] S3: Add 25g of intermediate product B to solution C in a three-necked flask in three portions under nitrogen protection, and react for 3h. After the reaction, filter the reaction solution to remove the byproduct triethylamine hydrochloride, wash three times with ethanol solution and 500mL of 1wt.% NaOH solution, and wash with deionized water until neutral. After the product is completely precipitated, filter and dry the solid phase to obtain product D.

[0053] S4: Mix 1g of product D with 8g of PEO in 30mL of DMF until homogeneous to obtain solution E;

[0054] S5: Add 0.3g of lithium bis(trifluoromethanesulfonylimide) to solution E, inject it into a syringe, connect the positive terminal of the high-voltage power supply, and connect the negative terminal to the roller. Obtain the phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte PEO / BPB' solidified into a fibrous form at the roller through electrospinning. The electrospinning parameters are set as follows: push speed 0.2mm / min, push distance 45mm, positive high voltage 30kV, negative high voltage 10kV, temperature 40℃, humidity 30%RH, needle-to-roll distance 11mm, and roller speed 140r / min.

[0055] The obtained PEO / BPB' is prepared into a disc with a diameter of 18 mm and used as the electrolyte in the assembly of lithium-ion batteries, including the following steps:

[0056] (1) Preparation of positive electrode sheet: Lithium iron phosphate, carbon black and PVDF in a mass ratio of 7:2:1 are dispersed with N-methylpyrrolidone, ground evenly and then coated on aluminum foil with a scraper and dried to obtain lithium iron phosphate electrode sheet.

[0057] (2) Preparation of lithium half-cell: Using lithium metal sheet as negative electrode, lithium iron phosphate sheet as positive electrode, and PEO / BPB' as polymer electrolyte, 2032 coin cell was prepared.

[0058] Example 3

[0059] The preparation method of the phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte in this embodiment includes the following steps:

[0060] S1: Bbisphenol B was dried in an oven at 60°C for 2 hours. 22 g of dry bisphenol B and 0.14 g of aluminum trichloride were added to a 250 mL three-necked culture flask and mixed thoroughly to obtain mixture A. Mixture A was reacted with 76 g of phosphorus oxychloride at 115°C for 2.5 hours under nitrogen protection. After the reaction was completed, residual phosphorus oxychloride in the mixture was removed by vacuum distillation to obtain intermediate product B.

[0061] S2: Add 35g aniline, 45g pyridine, 0.2g anhydrous aluminum trichloride, and 150mL tetrahydrofuran to a 1000mL three-necked flask, mix thoroughly with stirring, and heat to 55℃ to obtain solution C;

[0062] S3: Add 25g of intermediate product B to solution C in a three-necked flask in three portions under nitrogen protection, and react for 2 hours. After the reaction, filter the reaction solution to remove the byproduct triethylamine hydrochloride, wash three times with ethanol solution and 500mL of 1wt.% NaOH solution, and wash with deionized water until neutral. After the product is completely precipitated, filter and dry the solid phase to obtain product D.

[0063] S4: Mix 1g of product D with 12g of PEO in 30mL of DMF until homogeneous to obtain solution E;

[0064] S5: Add 2.4g of lithium bis(trifluoromethanesulfonylimide) to solution E, inject it into a syringe, connect the positive terminal of the high-voltage power supply, and connect the negative terminal to the roller. Obtain the phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte PEO / BPB' solidified into a fibrous form at the roller through electrospinning. The electrospinning parameters are set as follows: push speed 0.1mm / min, push distance 30mm, positive high voltage 10kV, negative high voltage 3kV, temperature 35℃, humidity 30%RH, needle-to-roll distance 15mm, and roller speed 140r / min.

[0065] The obtained PEO / BPB' is prepared into a disc with a diameter of 18 mm and used as the electrolyte in the assembly of lithium-ion batteries, including the following steps:

[0066] (1) Preparation of positive electrode sheet: Lithium iron phosphate, carbon black and PVDF in a mass ratio of 8:1:1 are dispersed with N-methylpyrrolidone, ground evenly and then coated on aluminum foil with a scraper and dried to obtain lithium iron phosphate electrode sheet.

[0067] (2) Preparation of lithium half-cell: Using lithium metal sheet as negative electrode, lithium iron phosphate sheet as positive electrode, and PEO / BPB' as polymer electrolyte, 2032 coin cell was prepared.

[0068] Comparative Example 1

[0069] The difference from Example 1 is that PEO film is prepared by electrospinning instead of PEO / BPB' in Example 1.

[0070] Tensile tests were performed on the PEO / BPB' and PEO films prepared in Example 1 and Comparative Example 1, and the tensile curves were obtained as follows: Figure 2-3 As shown, the maximum tensile force that the PEO electrolyte membrane can withstand is approximately 14 MPa, corresponding to an elongation of 14%; however, the PEO / BPB' electrolyte exhibits superior mechanical properties, corresponding to a maximum tensile force of approximately 42 MPa and an elongation of approximately 50%. Limiting oxygen index tests were performed on the PEO / BPB' and PEO membranes prepared in Example 1 and Comparative Example 1, and the limiting oxygen indices were obtained as follows: Figure 4 As shown, the concentrations are 29% and 15% respectively, indicating that the PEO / BPB' electrolyte meets the non-flammable standard. Therefore, by modifying bisphenol B, the designed PEO / BPB' electrolyte increases the electrolyte strength and mechanical properties through the introduced benzene ring, and achieves flame retardant effects through carbon layer formation and the introduction of nitrogen and phosphorus elements, making the electrolyte non-flammable and providing higher safety.

[0071] The cycle performance and coulombic efficiency of the Li|PEO|LFP half-cell assembled in Comparative Example 1 are as follows: Figure 7-8 As shown.

[0072] By comparing Example 1 and Comparative Example 1, it can be found that the phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte PEO / BPB' of the present invention has a certain effect on improving the cycle stability and coulombic efficiency of lithium batteries. This is because the present invention modifies the PEO electrolyte with bisphenol B, increasing ion transport sites, avoiding side reactions, and improving the battery coulombic efficiency. In addition, compared with PEO, the prepared PEO / BPB' electrolyte has better chemical and electrochemical stability, thus greatly benefiting the improvement of battery stability.

Claims

1. A method for preparing a phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte, characterized in that, Includes the following steps: S1: Mix dried bisphenol B with aluminum trichloride to obtain mixture A. React mixture A with phosphorus oxychloride under nitrogen protection to obtain intermediate product B. The mass ratio of bisphenol B, aluminum trichloride and phosphorus oxychloride is (20-25):(0.1-0.2):(75-80). S2: Mix aniline, pyridine, anhydrous aluminum trichloride, and tetrahydrofuran to obtain solution C; S3: Add intermediate product B to solution C under nitrogen protection to carry out the reaction. After filtering, washing, precipitating and drying the reaction product, product D is obtained. S4: Mix product D with polyethylene oxide in a solvent to obtain solution E; S5: Add lithium bis(trifluoromethanesulfonylimide) to solution E and obtain a phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte by electrospinning.

2. The preparation method of the phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte as described in claim 1, characterized in that, The specific process of step S1 is as follows: Bisphenol B is dried at 60-80℃ for 2 hours, and then mixed with aluminum trichloride to obtain mixture A; mixture A is reacted with phosphorus oxychloride at 100-115℃ for 2.5-3.5 hours under nitrogen protection; after the reaction is completed, the residual phosphorus oxychloride in the mixture is removed by vacuum distillation to obtain intermediate product B.

3. The preparation method of the phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte as described in claim 1, characterized in that, The specific process of step S2 is as follows: Aniline, pyridine, anhydrous aluminum trichloride, and tetrahydrofuran are thoroughly mixed under stirring and heated to 55-70℃ to obtain solution C.

4. The method for preparing the phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte as described in claim 1 or 3, characterized in that, In step S2, the mass-to-volume ratio of aniline, pyridine, anhydrous aluminum trichloride, and tetrahydrofuran is (35-40)g:(40-45)g:(0.1-0.2)g:150mL.

5. The preparation method of the phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte as described in claim 1, characterized in that, The specific process of step S3 is as follows: Disperse intermediate product B in a solvent, add it to solution C multiple times under nitrogen protection, and react for 2-4 hours; after the reaction, filter the reaction solution to remove byproducts, wash it multiple times with ethanol solution and NaOH solution, and wash it with deionized water until neutral. After the product is completely precipitated, filter and dry the solid phase to obtain product D.

6. The method for preparing the phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte as described in claim 1 or 5, characterized in that, In step S3, the mass ratio of intermediate product B to aniline is 25:(35-40).

7. The preparation method of the phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte as described in claim 1, characterized in that, In step S4, the mass-to-volume ratio of product D to polyethylene oxide and solvent is 1g:(8-30)g:(30-100)mL; in step S5, lithium bis(trifluoromethanesulfonylimide) is 3-20wt.% of polyethylene oxide; in step S5, the electrospinning parameters are set as follows: pushing speed 0.1-0.2mm / min, pushing distance 30-45mm, positive high voltage 10-30kV, negative high voltage 3-10kV, temperature 30-40℃, humidity 30%RH, needle-to-roll distance 10-15mm, and roller speed 140r / min.

8. A phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte, characterized in that, It was prepared by the method for preparing phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte as described in any one of claims 1-7.

9. The application of the phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte as described in claim 8, characterized in that, Includes the following steps: (1) Disperse lithium iron phosphate, carbon black and polyvinylidene fluoride in a mass ratio of (7-8):(1-2):1 using N-methylpyrrolidone, grind them evenly, and then coat them onto aluminum foil with a scraper and dry them to obtain lithium iron phosphate electrode sheets. (2) A lithium battery was prepared by using a lithium metal sheet as the negative electrode, a lithium iron phosphate sheet as the positive electrode, and a phosphorus-nitrogen synergistic flame-retardant solid polymer electrolyte as the polymer flame-retardant electrolyte.

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