Preparation method and application of in-situ gel polymer electrolyte for lithium-sulfur battery

Abstract

The invention discloses a preparation method and application of an in-situ gel polymer electrolyte for a lithium-sulfur battery, and relates to a preparation method and application of a polymer electrolyte. The invention aims to solve the technical problems of rapid capacity attenuation and short cycle life of the existing lithium-sulfur battery. The method comprises the following steps: dissolving a lithium salt in a monomer or a solution formed by mixing the monomer and an ionic liquid, and then adding an initiator for polymerization to obtain the in-situ gel polymer electrolyte. The electrolyte can promote the formation of stable SEI, inhibit the growth of lithium dendrites, improve the ionic conductivity and accelerate the redox rate of positive electrode polysulfide, so that the cycle life of the lithium symmetric battery exceeds 1000h. The reversible specific discharge capacity of a lithium-sulfur battery assembled by using the electrolyte is 1242.0 mAh / g within the range of 1.7-2.8 V and under 0.2 C, the specific discharge capacity after 60 cycles is 953.7 mAh / g, the average coulombic efficiency is 97.5%, and the electrolyte can be used in the field of lithium-sulfur batteries.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-sulfur batteries, and in particular relates to a preparation method and application of an in-situ gel polymer electrolyte for lithium-sulfur batteries. Background Art

[0002] Lithium-sulfur batteries (LiS) boast high theoretical specific capacity (1675 mAh / g) and theoretical energy density (2600 Wh / kg), far exceeding those of traditional lithium-ion batteries. Furthermore, the abundance of sulfur and its environmentally friendly nature make LiS batteries one of the most promising next-generation battery technologies. However, the high reactivity of lithium metal and its substrate-free deposition characteristics mean that conventional liquid LiS batteries still face safety concerns due to the growth of lithium dendrites. Furthermore, given the insulating properties of sulfur and its product, lithium sulfide, the polysulfide shuttle effect caused by the dissolution of intermediates in the electrolyte, and the slow redox kinetics and large volume changes of the cathode during charge and discharge, working LiS batteries often exhibit low active material utilization and low Coulombic efficiency, leading to critical issues such as rapid capacity decay and short cycle life. The inherent properties of solid-state electrolytes enable them to reduce the dissolution of lithium polysulfides, fundamentally inhibiting the shuttle effect and preventing battery performance degradation. However, compared with liquid electrolytes, the interface formed by solid electrolytes and electrodes has completely different properties, and the electrode / solid electrolyte interface impedance is more significant. This problem causes solid-state lithium-sulfur batteries to still face technical bottlenecks such as low capacity, poor rate performance, and short cycle life, which seriously limits the commercial application of solid-state lithium-sulfur batteries. Therefore, improving and enhancing interfacial compatibility and interfacial chemical-mechanical stability is crucial to promoting the practical application of solid-state lithium-sulfur batteries. Solid polymer electrolytes have good flexibility and elasticity and can form good interfacial contact with the positive electrode. However, solid polymer electrolytes prepared by traditional non-in situ polymerization methods still have large interfacial contact resistance; in addition, the slow redox kinetics of polysulfides on the positive electrode side result in low utilization of active materials. Summary of the Invention

[0003] This invention aims to address the technical issues of rapid capacity decay and short cycle life in existing lithium-sulfur batteries, caused by the shuttle effect and slow redox reaction kinetics at the positive electrode. It provides a method for preparing and applying an in-situ gel polymer electrolyte for lithium-sulfur batteries. The invention utilizes a Lewis acidic initiator to initiate ring-opening polymerization of the monomers, trapping the ionic liquid in the gel phase via the polymer backbone. This in-situ polymerization method improves electrode-electrolyte interfacial compatibility, and the presence of the ionic liquid accelerates the positive electrode redox kinetics, effectively enhancing the battery's electrochemical and cycling performance.

[0004] The method for preparing an in-situ gel polymer electrolyte for a lithium-sulfur battery of the present invention comprises the following steps:

[0005] S1: dissolving a lithium salt in a solution of a monomer or a mixture of a monomer and an ionic liquid to obtain a mixture under a protective atmosphere; wherein the monomer is 1,3-dioxolane, 4-methyl-1,3-dioxolane or 1,3,6-trioxocane;

[0006] S2: adding an initiator into the mixture obtained in step S1 under a protective atmosphere, and uniformly dispersing to obtain a polymer electrolyte precursor solution; wherein the initiator is lanthanum triflate, lanthanum fluoride, cerium triflate, cerium fluoride, praseodymium triflate, praseodymium fluoride, neodymium triflate, neodymium fluoride, samarium triflate, samarium fluoride, gadolinium triflate, gadolinium fluoride, dysprosium triflate, dysprosium fluoride, holmium triflate, holmium fluoride, erbium triflate, erbium fluoride, lutetium triflate, lutetium fluoride, ytterbium triflate or ytterbium fluoride;

[0007] S3: allowing the polymer electrolyte precursor solution to stand at room temperature for 12-48 h to make the monomer polymerize; or heating the polymer electrolyte precursor solution to 40-80 °C for 0.5-3 h to make the monomer polymerize; to obtain an in-situ gel polymer electrolyte for a lithium-sulfur battery.

[0008] Further, the lithium salt in step S1 is one or a combination of several of lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(fluorosulfonyl)imide (LiFSI), lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB).

[0009] Further, the concentration of the lithium salt in the mixture in step S1 is 1-3 mol / L.

[0010] Further, the ionic liquid in step S1 is one or a mixture of several of 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMIM TFSI), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (BMIM TFSI), 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium hexafluorophosphate (EMIM PF6), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF6), 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide (EMIM FSI), 1-butyl-3-methylimidazolium bis(fluorosulfonyl)imide (BMIM FSI).

[0011] Further, the volume ratio of the monomer to the ionic liquid in step S1 is 1:(0-0.5); the concentration of the initiator in the polymer electrolyte precursor solution in step S2 is 4-50 mmol / L. When the volume ratio of the monomer to the ionic liquid is 1:0, it means that no ionic liquid is added. The polymer electrolyte synthesized without adding ionic liquid is in a quasi-solid state or a gel state; when the concentration of the initiator is >10 mmol / L, the monomer conversion rate is >95%, and the electrolyte is in a quasi-solid state; when the concentration of the initiator is 4-10 mmol / L, the electrolyte is in a gel state, and the monomer conversion rate is <95%. After adding the ionic liquid, the electrolyte is in a gel state.

[0012] The application of the in-situ gel polymer electrolyte for lithium-sulfur batteries prepared by the above method is to use the in-situ gel polymer electrolyte for lithium-sulfur batteries in lithium-sulfur batteries. The lithium-sulfur battery can inhibit the shuttle effect and accelerate the positive electrode polysulfide redox reaction.

[0013] Further, the negative electrode of the lithium-sulfur battery is lithium metal; the positive electrode is sulfur-carbon composite material; and the separator is PP, PE or glass fiber.

[0014] Further, the preparation method of the lithium-sulfur battery comprises the following steps:

[0015] S1: Dissolve a lithium salt in a solution of a monomer or a mixture of the monomer and an ionic liquid to obtain a mixture under a protective atmosphere; wherein the monomer is 1,3-dioxolane, 4-methyl-1,3-dioxolane or 1,3,6-trioxocane;

[0016] S2: Add an initiator to the mixture obtained in step S1 under a protective atmosphere, wherein the initiator is lanthanum triflate, lanthanum fluoride, cerium triflate, cerium fluoride, praseodymium triflate, praseodymium fluoride, neodymium triflate, neodymium fluoride, samarium triflate, samarium fluoride, gadolinium triflate, gadolinium fluoride, dysprosium triflate, dysprosium fluoride, holmium triflate, holmium fluoride, erbium triflate, erbium fluoride, lutetium triflate, lutetium fluoride, ytterbium triflate or ytterbium fluoride; and after uniform dispersion, a polymer electrolyte precursor solution is obtained;

[0017] S3: Inject the polymer electrolyte precursor solution into a to-be-injected battery assembled with a sulfur-carbon composite positive electrode, a separator and a negative electrode, and keep it at room temperature for 12-48 h to make the monomer polymerize; or inject the polymer electrolyte precursor solution into a to-be-injected battery assembled with a sulfur-carbon composite positive electrode, a separator and a negative electrode, and then heat it to 40-80°C for 0.5-3 h to make the monomer polymerize; and complete the assembly of the lithium-sulfur battery.

[0018] The initiator with high polymerization efficiency and high lithium metal interface stability and the ionic liquid with high stability, high ion conductivity and catalytic ability are added to the monomer lithium salt solution, and after polymerization, a gel polymer electrolyte is obtained. The combination can inhibit the growth of lithium dendrites and inhibit the shuttle effect and improve the polysulfide redox rate, significantly improve the discharge capacity and cycle performance of lithium-sulfur battery.

[0019] The beneficial effects of the present application are as follows:

[0020] (1) In-situ polymerization of monomers at the electrode-electrolyte interface can form good interface contact with the lithium metal surface and sulfur carbon positive electrode particles, and improve the interface stability.

[0021] (2) The initiator can inhibit the growth of lithium dendrites and form a high modulus SEI interface, thereby improving the stability of lithium metal. The cations in the initiator on the surface of lithium metal can form a high-valence ion shielding layer at the tip of lithium dendrites, inhibit the longitudinal growth of lithium dendrites, and force lithium ions to deposit uniformly laterally. In addition, the cations in the initiator can form high modulus inorganic SEI components with F and O, further inhibiting the growth of lithium dendrites. This advantage makes the cycle life of lithium symmetrical battery exceed 1000h (0.2mA / cm 2 , 0.2mAh / cm 2 ).

[0022] (3) The initiator has high polymerization efficiency and can achieve monomer conversion rate of more than 90% with a small amount of initiator. This advantage significantly improves the lithium ion conductivity, so that the lithium ion transference number of the gel polymer electrolyte is as high as 0.65.

[0023] (4) The ionic liquid as a plasticizer can reduce the crystallinity of the polymer electrolyte and improve the conductivity of the electrolyte. On the other hand, the ionic liquid can act as a catalyst; in the imidazole cation in the ionic liquid, the C atom between the two N atoms exhibits positive charge due to the strong electron-withdrawing effect of the N atom. This positively charged C atom can interact with the electron-rich terminal S atom in polysulfide; this interaction weakens the S-S bond level, reduces the S-S bond dissociation energy and Li + desolvation energy, thereby accelerating the polysulfide conversion rate. The combined increase of polysulfide conversion rate and electrolyte conductivity improves the discharge capacity and coulombic efficiency of lithium-sulfur battery.

[0024] (5) The gel polymer electrolyte provided by the application has high average coulombic efficiency and cycle performance in a quasi-solid lithium-sulfur battery with sulfur carbon as a positive electrode and metal lithium as a negative electrode: the discharge specific capacity is 1331.3 mAh / g at 0.1C, the first cycle discharge specific capacity is 1242.0 mAh / g at 0.2C, the discharge specific capacity after 60 cycles is 953.7 mAh / g, and the average coulombic efficiency is 97.5%.

[0025] (6) The application overcomes the disadvantages of low room temperature conductivity, low lithium ion transference number, poor electrochemical stability, and poor stability to lithium of the polymer electrolyte. The application has the same battery assembly process as the traditional liquid lithium ion battery, has high practical application and popularization value, and is easy to realize mass production and commercial application of lithium-sulfur batteries. BRIEF DESCRIPTION OF DRAWINGS

[0026] Figure 1 It is a schematic diagram of the mechanism of the ring-opening polymerization of DOL initiated by lanthanum triflate in Example 1.

[0027] Figure 2 It is an optical image of the gel polymer electrolyte obtained in Example 1.

[0028] Figure 3 It is a hydrogen nuclear magnetic resonance spectrum of the electrolyte and the gel electrolyte in Example 1.

[0029] Figure 4 It is a direct current polarization curve and an alternating current impedance spectrum of the gel polymer electrolyte prepared in Example 1.

[0030] Figure 5 It is a constant current charge and discharge cycle test diagram of a lithium symmetric battery assembled based on the gel electrolyte prepared in Example 1.

[0031] Figure 6 It is a charge and discharge curve diagram of the lithium-sulfur battery assembled in Example 2 at 0.1C.

[0032] Figure 7 It is a cycle performance diagram of the lithium-sulfur battery assembled in Example 2 at 0.2C. DETAILED DESCRIPTION

[0033] The beneficial effects of the application are verified by the following examples.

[0034] Example 1: The preparation method of the in-situ gel polymer electrolyte for lithium-sulfur batteries in this example is carried out in the following steps:

[0035] S1: Under an argon atmosphere, lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) was dissolved in 2 mL of 1,3-dioxolane and stirred for 30 minutes to obtain a mixture; the concentration of lithium bis(trifluoromethylsulfonyl)imide in the mixture was 1 mol / L;

[0036] S2: Under an argon atmosphere, lanthanum triflate was added to the mixture obtained in step S1 at a concentration of 10 mmol / L, and stirred for 4 h to obtain a polymer electrolyte precursor solution;

[0037] S3: The polymer electrolyte precursor solution was kept at room temperature for 24 h to allow the monomers to polymerize, thereby obtaining an in-situ gel polymer electrolyte for lithium-sulfur batteries.

[0038] Figure 1 is a schematic diagram of the mechanism of the initiation of 1,3-dioxolane (DOL) ring-opening polymerization by lanthanum triflate in Example 1. The lanthanum cation in lanthanum triflate exhibits strong Lewis acidity and can coordinate with the lone pair of electrons on the oxygen atom of the DOL ring. This coordination interaction initiates the ring-opening polymerization of DOL.

[0039] Figure 2 is an optical image of the in-situ gel polymer electrolyte for lithium-sulfur batteries prepared in Example 1. As can be seen from Figure 2 , the in-situ gel polymer electrolyte for lithium-sulfur batteries obtained by polymerization of the precursor solution is a gel-state polymer electrolyte without fluidity.

[0040] Figure 3 is a nuclear magnetic resonance hydrogen spectrum of the mixture in step S1 in Example 1 and the in-situ gel polymer electrolyte for lithium-sulfur batteries obtained in step S3. The conversion rate of the monomer 1,3-dioxolane (DOL) was calculated to be 93.5% by integrating the nuclear magnetic resonance hydrogen spectrum.

[0041] A Li / gel electrolyte / Li battery was assembled using the gel electrolyte prepared in this Example 1, using a PP separator as a support framework. The preparation method of the Li / gel electrolyte / Li battery was as follows: the polymer electrolyte precursor solution obtained in step S2 of Example 1 was added dropwise on both sides of the separator, and a lithium symmetric battery was assembled in the order of negative electrode-lithium metal-separator-lithium metal-positive electrode. The battery was kept at room temperature for 24 h to allow the monomers to polymerize, thereby obtaining a Li / gel electrolyte / Li battery.

[0042] The lithium ion transference number of the gel polymer electrolyte prepared in this Example 1 was measured by direct current polarization method and alternating current impedance method using a CHI760e electrochemical workstation. The test process and conditions were as follows:

[0043] In the direct current polarization test, the applied polarization voltage is 10 mV, and the current-time curve is recorded. The interface impedance values of Li / gel electrolyte / Li battery before and after polarization are tested by alternating current impedance method. The alternating current impedance test is carried out at room temperature in the frequency range of 10 6 0.1 Hz, the amplitude is 5 mV, and the alternating current impedance test results are fitted by ZView software. The lithium ion transference number of the composite quasi-solid electrolyte thin film is calculated according to the formula:

[0044] t Li+ = [I ss × (ΔV - I o R o )] / [I o × (ΔV - I ss R ss )]

[0045] In the formula, I o is the initial current value, I ss is the steady-state current value, R o represents the interface impedance value in the initial state, R ss represents the interface impedance value in the steady state, and ΔV is the polarization voltage.

[0046] The lithium ion transference number test curve of the gel polymer electrolyte prepared in Example 1 is shown in Figure 4 From Figure 4 , it can be seen that the current value gradually decreases from the initial 82.5 μA, and finally maintains at the steady-state value (72.6 μA) with the increase of polarization time. The impedance fitting results before and after polarization show that the interface impedance of lithium symmetric battery in the initial state and the steady state is 109.0 Ω and 118.7 Ω respectively, and it is calculated that the gel polymer electrolyte prepared in Example 1 has a lithium ion transference number of 0.65.

[0047] The Li / gel electrolyte / Li battery is tested by NEWARE CT-4008T multi-channel battery tester under the conditions of 0.2 mA / cm 2 , 0.2 mAh / cm 2 , and the cycle performance of lithium symmetric battery is shown in Figure 5 From Figure 5 , it can be seen that the cycle life of lithium symmetric battery is more than 1000 h, which indicates that the electrolyte has good interface compatibility with lithium metal.

[0048] Example 2: The preparation method of lithium-sulfur battery in this embodiment is carried out according to the following steps:

[0049] S1: Under an argon atmosphere, lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) was dissolved in 2 mL of a mixed solvent of 1,3-dioxolane (DOL) and ionic liquid (EMIMTFSI) at a volume ratio of 9:1, and stirred for 60 minutes to obtain a mixed solution; wherein the concentration of lithium bis(trifluoromethylsulfonyl)imide in the mixed solution was 2 mol / L;

[0050] S2: Under an argon atmosphere, lanthanum triflate was added to the mixed solution obtained in step S1 at a concentration of 8 mmol / L, and stirred for 4 h to disperse uniformly to obtain a polymer electrolyte precursor solution;

[0051] S3: The sulfur-carbon positive electrode, PP separator and metal lithium were placed in the battery shell, and then the polymer electrolyte precursor solution was injected, and after the battery was packaged, it was kept at room temperature for 24 h to make the monomer polymerize, to obtain a lithium-sulfur battery based on in-situ gel polymer electrolyte.

[0052] The lithium-sulfur battery prepared in Example 2 was subjected to constant current charge and discharge cycle test by NEWARE CT-4008T multi-channel battery tester in the voltage range of 1.8~2.7V, and the test temperature was room temperature (25±2℃), to obtain the cycle performance of the lithium-sulfur battery based on in-situ gel polymer electrolyte.

[0053] Figure 6 The charge-discharge curve of the lithium-sulfur battery assembled in Example 2 at 0.1C (1C=1675mAh / g) is shown in FIG. 2. Figure 6 It can be seen that the discharge specific capacity is 1331.3 mAh / g.

[0054] Figure 7 The cycle performance graph of the lithium-sulfur battery assembled in Example 2 at 0.2C is shown in FIG. 3. Figure 7 As can be seen from FIG. 3, the lithium-sulfur battery has a first cycle discharge specific capacity of 1242.0 mAh / g at 0.2C, and a discharge specific capacity of 953.7 mAh / g after 60 cycles, with an average coulombic efficiency of 97.5%.

[0055] The present application uses lanthanide triflate and fluoride to initiate the in-situ polymerization of cyclic ether monomers inside the battery, to obtain a multifunctional polymer electrolyte layer. The electrolyte layer can promote the formation of stable SEI and inhibit the growth of lithium dendrites, so that the cycle life of lithium symmetric battery is more than 1000h. In addition, the addition of imidazole ionic liquid to the polymer electrolyte not only improves the ionic conductivity of the electrolyte, but also accelerates the redox rate of the positive electrode polysulfide, improving the charge-discharge performance of the battery. The lithium-sulfur battery prepared by the method of the present application has high discharge capacity and excellent cycle stability.

Claims

1. A method for preparing an in-situ gel polymer electrolyte for lithium-sulfur batteries, characterized in that: The method comprises the following steps: S1: Under a protective atmosphere, dissolving a lithium salt in a monomer or a mixture of a monomer and an ionic liquid to obtain a mixed solution; wherein the monomer is 1,3-dioxolane, 4-methyl-1,3-dioxolane or 1,3,6-trioxocane; S2: Under a protective atmosphere, adding an initiator to the mixed solution obtained in step S1, and uniformly dispersing the initiator to obtain a polymer electrolyte precursor solution; wherein the initiator is lanthanum trifluoromethanesulfonate, lanthanum fluoride, cerium trifluoromethanesulfonate, cerium fluoride, praseodymium trifluoromethanesulfonate, praseodymium fluoride, neodymium trifluoromethanesulfonate, neodymium fluoride, samarium trifluoromethanesulfonate, samarium fluoride, gadolinium trifluoromethanesulfonate, gadolinium fluoride, dysprosium trifluoromethanesulfonate, dysprosium fluoride, holmium trifluoromethanesulfonate, holmium fluoride, erbium trifluoromethanesulfonate, erbium fluoride, lutetium trifluoromethanesulfonate, lutetium fluoride, ytterbium trifluoromethanesulfonate, or ytterbium fluoride; S3: keeping the polymer electrolyte precursor solution at room temperature for 12 to 48 hours to allow the monomers to polymerize; or heating the polymer electrolyte precursor solution to 40 to 80° C. and keeping it for 0.5 to 3 hours to allow the monomers to polymerize; obtaining an in-situ gel polymer electrolyte for lithium-sulfur batteries.

2. The method for preparing an in-situ gel polymer electrolyte for a lithium-sulfur battery according to claim 1, characterized in that: The lithium salt in step S1 is one of lithium bis(trifluoromethylsulfonyl)imide, lithium bis(fluorosulfonyl)imide, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorooxalatoborate and lithium bis(oxalatoborate) or a combination of several thereof.

3. The method for preparing an in-situ gel polymer electrolyte for a lithium-sulfur battery according to claim 1 or 2, characterized in that: The concentration of lithium salt in the mixed solution in step S1 is 1-3 mol / L.

4. The method for preparing an in-situ gel polymer electrolyte for a lithium-sulfur battery according to claim 1 or 2, characterized in that: The ionic liquid described in step S1 is one of 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-ethyl-3-methylimidazolium bis(fluorosulfonyl)imide and 1-butyl-3-methylimidazolium bis(fluorosulfonyl)imide, or a mixture of several of them.

5. The method for preparing an in-situ gel polymer electrolyte for a lithium-sulfur battery according to claim 1 or 2, characterized in that: The volume ratio of the monomer to the ionic liquid in step S1 is 1:(0-0.5).

6. The method for preparing an in-situ gel polymer electrolyte for a lithium-sulfur battery according to claim 1 or 2, characterized in that: The concentration of the initiator in the polymer electrolyte precursor solution in step S2 is 4-50 mmol / L.

7. Application of the in-situ gel polymer electrolyte for lithium-sulfur batteries prepared by the method of claim 1, characterized in that: The application is to use the in-situ gel polymer electrolyte for lithium-sulfur batteries in lithium-sulfur batteries.

8. The use of the in-situ gel polymer electrolyte for lithium-sulfur batteries according to claim 7, characterized in that: The negative electrode of the lithium-sulfur battery is lithium metal; the positive electrode is a sulfur-carbon composite material; and the separator is PP, PE or glass fiber.

9. The use of the in-situ gel polymer electrolyte for lithium-sulfur batteries according to claim 7, characterized in that: A method for preparing a lithium-sulfur battery comprises the following steps: S1: Under a protective atmosphere, dissolving a lithium salt in a monomer or a mixture of a monomer and an ionic liquid to obtain a mixed solution; wherein the monomer is 1,3-dioxolane, 4-methyl-1,3-dioxolane or 1,3,6-trioxocane; S2: Under a protective atmosphere, adding an initiator to the mixed solution obtained in step S1, wherein the initiator is lanthanum trifluoromethanesulfonate, lanthanum fluoride, cerium trifluoromethanesulfonate, cerium fluoride, praseodymium trifluoromethanesulfonate, praseodymium fluoride, neodymium trifluoromethanesulfonate, neodymium fluoride, samarium trifluoromethanesulfonate, samarium fluoride, gadolinium trifluoromethanesulfonate, gadolinium fluoride, dysprosium trifluoromethanesulfonate, dysprosium fluoride, holmium trifluoromethanesulfonate, holmium fluoride, erbium trifluoromethanesulfonate, erbium fluoride, lutetium trifluoromethanesulfonate, lutetium fluoride, ytterbium trifluoromethanesulfonate or ytterbium fluoride; after uniform dispersion, a polymer electrolyte precursor solution is obtained; S3: Inject the polymer electrolyte precursor into the battery to be filled, which is assembled with a sulfur-carbon composite positive electrode, a separator, and a negative electrode, and keep it at room temperature for 12 to 48 hours to allow the monomer to polymerize; or inject the polymer electrolyte precursor into the battery to be filled, which is assembled with a sulfur-carbon composite positive electrode, a separator, and a negative electrode, and then heat it to 40 to 80°C and keep it for 0.5 to 3 hours to allow the monomer to polymerize; complete the assembly of the lithium-sulfur battery.

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