Weakly solvating electrolyte for lithium-sulfur batteries and preparation and use thereof

Abstract

The present application relates to a kind of weakly solvating electrolyte suitable for long cycle lithium-sulfur battery and its preparation and application strategy, belong to lithium-sulfur battery technical application field.Intermediate product lithium polysulfide solubility in sulfur positive electrode is adjusted using weakly solvating electrolyte, and the shuttle effect of lithium polysulfide and the side reaction of lithium negative electrode are reduced, so as to improve the cycle stability of positive and negative electrode.But weakly solvating electrolyte also reduces the utilization rate of positive active material sulfur, so it needs to match high active positive catalyst, by improving the positive electrode reaction kinetics, improve the discharge specific capacity of positive electrode.Lithium-sulfur battery in the present application still shows good discharge specific capacity, better cycle performance and higher coulomb efficiency under high sulfur loading, low electrolyte and negative electrode dosage.The present application can be generally applicable to a variety of weakly solvating electrolyte and high activity catalyst system, preparation method is simple and good consistency, can provide guidance strategy for the development of long cycle high specific energy lithium-sulfur battery.

Description

Technical Field

[0001] This invention belongs to the field of new energy technology, specifically relating to a weakly solvated electrolyte suitable for long-cycle lithium-sulfur batteries and its preparation and application strategies. Background Technology

[0002] With the progress and development of human society, environmental pollution and the depletion of fossil fuels are becoming increasingly serious problems. Utilizing renewable energy sources such as solar and wind power to replace fossil fuel power generation can effectively solve these problems. However, there is a mismatch between power generation and consumption, so there is an urgent need to develop large-scale energy storage technologies to achieve efficient resource utilization. Rechargeable batteries can serve as a key carrier for energy storage and conversion. Currently, lithium-ion batteries are not only used in energy storage grids but also widely applied in portable electronic devices, electric vehicles, and other fields. However, the actual energy density of traditional lithium-ion batteries cannot exceed 400Wh / kg, which cannot meet society's demand for high-energy-density rechargeable battery energy storage. In contrast, lithium-sulfur batteries have a discharge specific capacity as high as 1675mAh / g and a theoretical energy density as high as 2600Wh / kg, and their raw material costs are low and environmentally friendly. Therefore, lithium-sulfur batteries are considered one of the most promising high-energy-density rechargeable battery systems for the future.

[0003] However, the development of lithium-sulfur batteries still faces the following problems: the sulfur cathode reaction kinetics are slow, and the utilization rate of active materials is low, resulting in actual discharge specific capacity and energy density of lithium-sulfur batteries being far lower than theoretical values. Furthermore, the intermediate product lithium polysulfides (LiPSs) generated during the charging and discharging process of the sulfur cathode are easily soluble in conventional lithium-sulfur battery ether electrolytes. Therefore, lithium polysulfides can "shuttle" to the metallic lithium anode and undergo a reduction reaction, causing self-discharge of the lithium-sulfur battery. Moreover, the side reactions between lithium polysulfides and the anode can cause lithium corrosion, electrolyte depletion, and uneven lithium dissolution and deposition, leading to dendrites and dead lithium, thus reducing lithium stripping / deposition efficiency and resulting in rapid capacity decay and short cycle life of lithium-sulfur batteries. For high-energy-density practical pouch batteries, high sulfur loading on the cathode surface, thin lithium anode, and low liquid sulfur ratio are required, which further significantly reduces cycle performance. Therefore, to improve the long-cycle performance of high-energy-density pouch lithium-sulfur batteries, it is necessary to improve the sulfur cathode conversion kinetics and reduce the shuttle effect and side reactions between lithium polysulfides and the lithium anode.

[0004] To improve cathode kinetics, various highly active catalysts for the conversion of sulfur at the cathode have been licensed and disclosed. The electrolyte, as the "blood" of lithium-sulfur batteries, is crucial. Conventional ether-based electrolytes for lithium-sulfur batteries, such as DOL and DME, cannot suppress lithium polysulfide shuttle, lithium anode side reactions, and corrosion, resulting in low capacity retention. By adjusting the electrolyte composition, the solubility of lithium polysulfides can be altered, thereby regulating the sulfur cathode reaction kinetics and the shuttle effect of the intermediate lithium polysulfide.

[0005] For example, Chinese patent CN106816634A discloses a pseudo-high-concentration lithium-sulfur battery electrolyte. This electrolyte contains lithium salt, ether solvent, and non-solvent solution. The concentration of lithium salt in the ether solvent is higher than 3.0 mol / L, and the concentration of lithium salt in the pseudo-high-concentration electrolyte is not less than 0.5 mol / L. This electrolyte can suppress the dissolution shuttle of lithium polysulfides and improve the cycle life of lithium-sulfur batteries. However, it significantly reduces the positive electrode reactivity of lithium-sulfur batteries, resulting in a severe decrease in the battery's discharge specific capacity. Furthermore, some researchers have improved the sulfur positive electrode reactivity by adding highly solvated additives, but the severe shuttle effect leads to serious side reactions, corrosion, and dendrite problems at the lithium negative electrode, significantly reducing cycle life. Therefore, there is an urgent need to propose a design strategy for lithium-sulfur batteries that can improve the cycle life of lithium-sulfur batteries while taking into account the sulfur positive electrode kinetics. Summary of the Invention

[0006] This invention designs a weakly solvated electrolyte suitable for long-cycle lithium-sulfur batteries. By adjusting the electrolyte composition and ratio, the dissolution of lithium polysulfides can be reduced, the shuttle effect can be suppressed, and the side reactions between lithium polysulfides and the lithium anode can be reduced. Simultaneously, it can alleviate corrosion and dendrite formation on the lithium anode, reducing electrolyte and lithium anode losses, thereby improving battery cycle performance. To maintain a high discharge specific capacity of the sulfur cathode, a highly active catalyst needs to be applied to the sulfur cathode to improve cathode reaction kinetics and achieve high specific energy and long-cycle lithium-sulfur batteries. The weakly solvated electrolyte preparation method of this invention is simple, reproducible, and has a strong coupling effect with the highly active single-atom catalyst sulfur cathode, resulting in lithium-sulfur batteries with high sulfur loading, low liquid sulfur ratio, and low anode usage exhibiting excellent performance. This design strategy provides design ideas and guidance for realizing practical long-cycle, high-specific-energy pouch lithium-sulfur batteries.

[0007] This invention provides a lithium-sulfur battery electrolyte, comprising: an organic solvent, a lithium salt, and additives, wherein the additives include inorganic salt additives and weakly solvated electrolyte additives.

[0008] In one specific embodiment of the present invention, the inorganic salt additive used is a metal nitrate (RNO3), selected from one or more of lithium nitrate (LiNO3), sodium nitrate (NaNO3), potassium nitrate (KNO3), cesium nitrate (CsNO3), and lanthanum nitrate (LaNO3); preferably, lithium nitrate (LiNO3) can undergo a coupling reaction with lithium polysulfides to form a dense LiN on the surface of the lithium metal anode. x O y and LiS x O y The passivation layer suppresses the side reactions of lithium polysulfide on metallic lithium.

[0009] In one specific embodiment of the present invention, the mass percentage of metal nitrate in the lithium-sulfur battery electrolyte is 0.01 wt% to 5 wt%, preferably 0.1 wt% to 3 wt%, and more preferably 2 wt%.

[0010] In one specific embodiment of the present invention, the weakly solvated electrolyte additives used are 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), hexafluoroisopropyl methyl ether (HFME), 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (TFEE), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OFE), and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether. One or more of the following: fluoroethyl ether (TFTFE), bis(2,2,2-trifluoroethyl) ether (BTFE), 1,1,2,2-tetrafluoroethyl ether (ETFE), 1-(1,1,2,2-tetrafluoroethoxy)propane, 2-methyl-1-(1,1,2,2-tetrafluoroethoxy)propane, tert-butyl-1,1,2,2-tetrafluoroethyl ether, 2,2'-thiodipropane (DIPS), and 1-methoxyhexane (HME).

[0011] In one specific embodiment of the present invention, the volume fraction of the weakly solvated electrolyte additive is 1% to 50%, preferably 10% to 30%, and more preferably 10% to 20%.

[0012] In one specific embodiment of the present invention, the organic solvent used is selected from two or more of the following: ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, ethylene carbonate, vinylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl trifluoroethyl carbonate, and fluoroethylene carbonate.

[0013] In one specific embodiment of the present invention, when the organic solvent is selected from two or more, the volume content of any one of them is not less than 10%; preferably, when there are two, the volume ratio of the two organic solvents is 1:0.1 to 10, preferably 1:0.25 to 4, and more preferably 1:1.

[0014] In one specific embodiment of the present invention, the lithium salt used is selected from at least one of LiTFSI, LiFSI, LiFTFSI, LiCF3SO3, LiN(CF3SO2)2, LiN(FSO2)2, LiPF6, LiBF4, LiBOB, LiDFOB, LiBC2O4F2, LiClO4, LiAsF6, LiBETI, LiTDI, LiTNFSI, LiDCTI, and LiB(CN)4; preferably, the lithium salt is LiTFSI.

[0015] In one specific embodiment of the present invention, the concentration of lithium salt is 0.01 mol / L to 5 mol / L, preferably 0.1 mol / L to 2 mol / L, and more preferably 1 mol / L.

[0016] This invention also provides a method for preparing a weakly solvated electrolyte suitable for long-cycle lithium-sulfur batteries, the method comprising the following steps:

[0017] (1) In an environment filled with an inert atmosphere (e.g., argon and / or nitrogen), the organic solvents are mixed in the required volume ratio;

[0018] (2) Add the weak solvation electrolyte additive to the solution obtained in step (1) according to the required volume ratio, and stir to mix evenly; the mixing time is 0.5 to 1 hour.

[0019] (3) Add lithium salt and inorganic salt additives to the solution obtained in step (2), stir to dissolve, and obtain the weak solvation electrolyte of lithium-sulfur battery; the dissolution and stirring time is 1 to 4 hours.

[0020] The present invention also applies the electrolyte to lithium-sulfur batteries, wherein the lithium-sulfur batteries use a highly active catalyst combined with sulfur as a sulfur positive electrode active material.

[0021] In one specific embodiment of the present invention, the highly active catalyst used is selected from MnO2, MoS2, carbon-supported single atoms, such as Fe-NC, Co-NC, Ni-NC, Fe / Co-NC, Fe / Ni-NC, Co-NS-C, Fe-PC, or one or more of these.

[0022] The electrolyte and application strategy of this invention, when applied to lithium-sulfur batteries with high sulfur loading and low liquid sulfur ratio, exhibit good discharge specific capacity and cycle performance.

[0023] This invention employs a weakly solvated electrolyte to adjust the solubility of lithium polysulfide, an intermediate product of the sulfur cathode, reducing the shuttle effect of lithium polysulfide and side reactions at the lithium anode, thereby improving the cycle stability of both the cathode and anode. However, the weakly solvated electrolyte also reduces the utilization rate of sulfur, the active material at the cathode. Therefore, a highly active cathode catalyst is required to enhance the cathode reaction kinetics and improve the discharge specific capacity of the cathode. Lithium-sulfur batteries assembled using the weakly solvated electrolyte and highly active sulfur cathode catalyst developed in this invention exhibit good discharge specific capacity, superior cycle performance, and high coulombic efficiency even with high sulfur loading, low electrolyte, and low anode content. This invention is universally applicable to various weakly solvated electrolyte and highly active catalyst systems, and the preparation method is simple and consistent, providing a guiding strategy for the development of long-cycle, high-energy-density lithium-sulfur batteries.

[0024] The present invention has the following advantages:

[0025] (1) The lithium-sulfur battery electrolyte provided by this invention utilizes weak solubilizing additives to reduce the dissolution of lithium polysulfides, suppress the shuttle effect, and inhibit the side reactions between lithium polysulfides and the lithium anode, thereby reducing lithium anode corrosion and electrolyte loss. Combined with a highly active catalyst sulfur cathode, it improves the cycle performance of lithium-sulfur batteries with high areal sulfur loading and low liquid sulfur ratio while maintaining a suitable discharge specific capacity of the cathode. Based on the electrolyte provided by this invention, the thickness of the thin lithium anode is 50 μm, and the high areal sulfur loading of the cathode is 4 mg / cm³. 2 The liquid sulfur ratio (E / S) is 5 μl / mg, the first-cycle discharge specific capacity is 800-1500 mAh / g, and it can cycle 100-200 times at 0.1C.

[0026] (2) The preparation method of lithium-sulfur battery electrolyte provided by the present invention has simple steps, high repeatability, and is suitable for the preparation of large batches of electrolyte. This design strategy can be applied on a large scale to practical soft-pack batteries. Attached Figure Description

[0027] Figure 1 This is a comparison chart of the cycle performance of lithium-sulfur batteries in Example 1 and Comparative Example 1;

[0028] Figure 2 This is a comparison chart of the cycle performance of lithium-sulfur batteries in Example 6 and Comparative Example 2;

[0029] Figure 3 This is a comparison chart of the cycle performance of lithium-sulfur batteries in Example 18 and Comparative Example 3;

[0030] Figure 4 This is a comparison chart of the cycle performance of lithium-sulfur batteries in Example 1 and Comparative Example 4;

[0031] Figure 5 This is a comparison chart of the charge-discharge curves of lithium-sulfur batteries in Example 1 and Comparative Example 4. Detailed Implementation

[0032] The following embodiments are further illustrations of the present invention, but are not intended to limit the scope of the invention.

[0033] Examples 1-5

[0034] (1) In a glove box filled with argon atmosphere, ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) were mixed in volume ratios as shown in Table 1.

[0035] Table 1

[0036] volume ratio Example 1 Example 2 Example 3 Example 4 Example 5 DME / DOL 1：1 1：2 2：3 1：4 1：9

[0037] (2) Add 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (TFEE) to the electrolyte at a final volume fraction of 10% and stir for 0.5 h to mix evenly.

[0038] (3) Add LiTFSI and LiNO3 to the electrolyte and stir for 4 hours to dissolve them, so that the concentration of LiTFSI is 1 mol / L and the mass concentration of LiNO3 is 2 wt%, and the electrolyte is obtained.

[0039] Examples 6-10

[0040] (1) In a glove box filled with argon atmosphere, ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) are mixed at a volume ratio of 1:1.

[0041] (2) Add 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) to the electrolyte according to the required final volume fraction and stir for 0.6 h to mix evenly. The final volume fraction is shown in Table 2.

[0042] Table 2

[0043] volume ratio Example 6 Example 7 Example 8 Example 9 Example 10 TTE 5％ 10％ 20％ 30％ 40％

[0044] (3) Add LiTFSI and LiNO3 to the electrolyte and stir for 4 hours to dissolve them, so that the lithium salt concentration is 1 mol / L and the mass concentration of LiNO3 is 2 wt%, and the electrolyte is obtained.

[0045] Examples 11-15

[0046] (1) In a glove box filled with argon atmosphere, ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) are mixed at a volume ratio of 1:1.

[0047] (2) Add 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) to the electrolyte at a final volume fraction of 20% and stir for 0.5 min to mix evenly.

[0048] (3) LiTFSI and LiNO3 were added to the electrolyte and stirred for 4 hours to dissolve. The concentration of lithium salt and the mass concentration of LiNO3 are shown in Table 3. The electrolyte was obtained.

[0049] Table 3

[0050] concentration Example 11 Example 12 Example 13 Example 14 Example 15 LiTFSI(M) 0.1 0.5 1.0 2.0 3.0 <![CDATA[LiNO3(wt%)]]> 3.0 2.0 3.0 1.0 0.5

[0051] Examples 16-20

[0052] (1) In a glove box filled with argon atmosphere, the two organic solvents were mixed at a volume ratio of 1:1. The types of organic solvents are shown in Table 4.

[0053] Table 4

[0054]

[0055] (2) After adding the weak solvation electrolyte additive to the electrolyte at the required final volume fraction, stir for 0.6 h to mix evenly. The types and volume fractions of the weak solvation electrolyte additive are shown in Table 5.

[0056] Table 5

[0057]

[0058] (3) Add lithium salt and inorganic salt additives to the electrolyte and stir for 3 hours to dissolve. The types and concentrations of lithium salt and inorganic salt additives are shown in Table 6. The electrolyte is obtained.

[0059] Table 6

[0060]

[0061] Examples 21-25

[0062] (1) Several organic solvents were mixed in volume ratio in a glove box filled with argon atmosphere. The types of organic solvents and their corresponding volumes are shown in Table 7.

[0063] Table 7

[0064]

[0065] (2) Add the weakly solvated electrolyte at a final volume fraction of 15% to the electrolyte and stir for 0.5 h to mix thoroughly. The types of weakly solvated electrolyte additives are shown in Table 8.

[0066] Table 8

[0067]

[0068] (3) Add lithium salt and inorganic salt additives to the electrolyte and stir for 3 h to dissolve. The types and concentrations of lithium salt and inorganic salt additives are shown in Table 9. The electrolyte is obtained.

[0069] Table 9

[0070]

[0071] Comparative Example 1

[0072] The electrolyte contained no (no) 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (TFEE) weak solvent electrolyte additive, otherwise it was the same as in Example 1 (composition and preparation process).

[0073] Comparative Example 2

[0074] The electrolyte contained no (no) 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) weak solvent electrolyte additives, otherwise the same as in Example 6 (composition and preparation process).

[0075] Comparative Example 3

[0076] The electrolyte contained no (no) 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TFTFE) weak solvent electrolyte additive, otherwise the same as in Example 18 (composition and preparation process).

[0077] Application examples

[0078] The lithium-sulfur battery electrolytes prepared in Examples 1-25 and Comparative Example 1 were used to assemble batteries. The battery assembly methods were the same for all of them, and the specific steps are as follows:

[0079] 1. Preparation of the positive electrode sheet: Sulfur powder and catalyst are mixed at a mass ratio of 85:15 and impregnated with sulfur at 155℃ for 12 hours to obtain sulfur composite positive electrode material. The sulfur composite positive electrode material, conductive carbon black and binder PVDF are mixed evenly at a mass ratio of 8:1:1, NMP is added to prepare a slurry, and then the slurry is coated on aluminum foil and dried to obtain a sulfur surface loading of 4 mg / cm³. 2 The sulfur composite positive electrode sheet.

[0080] The positive electrode catalysts used in the electrolytes of Examples 1-25 are shown in Table 7.

[0081] Table 10

[0082]

[0083] 2. Battery Assembly: Using the lithium-sulfur battery electrolytes prepared in Examples 1-25 and Comparative Example 1, respectively, the electrolytes were mixed with electrolytes having a diameter of [missing information]. A sulfur composite positive electrode, a thin lithium metal negative electrode (50μm thick lithium sheet), and a Celgard2000 separator are assembled into a CR2016 coin cell.

[0084] The sulfur loading on the positive electrode surface is 4 mg / cm³. 2 A lithium-sulfur battery with a liquid sulfur ratio (E / S) of 5 μl / mg.

[0085] The CR2016 coin cells assembled with the lithium-sulfur battery electrolytes in Examples 1-25 and Comparative Examples 1, 2, and 3 were charged and discharged at a rate of 0.1C between 1.8 and 2.7V.

[0086] Comparative Example 4

[0087] The positive electrode uses carbon nanotubes instead of the Fe / Co-NC catalyst used in the electrolyte of Example 1 in the above application examples, and the other usage processes are the same as those of the electrolyte of Example 1 in the above application examples.

[0088] Figure 1 , Figure 2 , Figure 3 The figures show a comparison of the cycle performance of lithium-sulfur batteries in Examples 1 and 1, 6 and 2, and 18 and 3, respectively. As can be seen from the figures, adding a weakly solvated electrolyte additive can effectively improve the cycle performance of lithium-sulfur batteries under conditions of thin lithium metal anode, high sulfur loading on the cathode surface, and low liquid sulfur ratio.

[0089] Figure 4 This is a comparison of the charge-discharge curves of lithium-sulfur batteries in Example 1 and Comparative Example 4. The figure shows that using a highly active Fe / Co-NC cathode catalyst can improve cathode kinetics. Figure 5 This is a comparison graph of the cycle performance of lithium-sulfur batteries in Example 1 and Comparative Example 4. As can be seen from the graph, using a highly active cathode catalyst can improve the cycle performance of the cathode while maintaining a suitable specific capacity of the sulfur cathode.

[0090] The lithium-sulfur battery electrolyte and sulfur cathode material prepared using Example 1 can achieve a lithium anode thickness of 50 μm and a sulfur loading of 4 mg / cm² on the cathode surface. 2 In a lithium-sulfur battery with a liquid sulfur ratio (E / S) of 5 μl / mg, the first discharge specific capacity is 1000 mAh / g, and it can cycle 200 times at 0.1C.

[0091] The lithium-sulfur battery electrolyte and sulfur cathode material prepared using Example 6 can achieve a lithium anode thickness of 50 μm and a sulfur loading of 4 mg / cm² on the cathode surface. 2 In a lithium-sulfur battery with a liquid sulfur ratio (E / S) of 5 μl / mg, the first discharge specific capacity is 1030 mAh / g, and it can cycle 140 times at 0.1C.

[0092] The lithium-sulfur battery electrolyte and sulfur cathode material prepared using Example 18 can achieve a lithium anode thickness of 50 μm and a sulfur loading of 4 mg / cm² on the cathode surface. 2 In a lithium-sulfur battery with a liquid sulfur ratio (E / S) of 5 μl / mg, the first discharge specific capacity is 900 mAh / g, and it can cycle 120 times at 0.1C.

Claims

1. A weakly solvated electrolyte for lithium-sulfur batteries, characterized in that, The lithium-sulfur battery electrolyte includes an organic solvent, a lithium salt, and additives; The additives include inorganic salt additives and weakly solvated electrolyte additives; The inorganic salt additives include metal nitrates (RNO3), selected from one or more of lithium nitrate (LiNO3), sodium nitrate (NaNO3), potassium nitrate (KNO3), cesium nitrate (CsNO3), and lanthanum nitrate (LaNO3); The weakly solubilized electrolyte additives include 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), hexafluoroisopropyl methyl ether (HFME), 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane (TFEE), 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OFE), and 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (T... One or more of the following: FTFE, bis(2,2,2-trifluoroethyl) ether (BTFE), 1,1,2,2-tetrafluoroethyl ether (ETFE), 1-(1,1,2,2-tetrafluoroethoxy)propane, 2-methyl-1-(1,1,2,2-tetrafluoroethoxy)propane, tert-butyl-1,1,2,2-tetrafluoroethyl ether, 2,2'-thiodipropane (DIPS), and 1-methoxyhexane (HME).

2. The electrolyte according to claim 1, characterized in that, The organic solvent is selected from two or more of the following: ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, 1,3-dioxolane, 1,4-dioxane, tetrahydrofuran, tetraethylene glycol dimethyl ether, ethylene carbonate, vinylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl trifluoroethyl carbonate, and fluoroethylene carbonate.

3. The electrolyte according to claim 1 or 2, characterized in that, When the organic solvent is selected from two or more, the volume content of any one of them is not less than 10%; preferably, when there are two organic solvents, the volume ratio of the two organic solvents is 1:0.1 to 10, preferably 1:0.25 to 4, and more preferably 1:

1.

4. The electrolyte according to claim 1, characterized in that, The lithium salt is selected from at least one of LiTFSI, LiFSI, LiFTFSI, LiCF3SO3, LiN(CF3SO2)2, LiN(FSO2)2, LiPF6, LiBF4, LiBOB, LiDFOB, LiBC2O4F2, LiClO4, LiAsF6, LiBETI, LiTDI, LiTNFSI, LiDCTI, and LiB(CN)4.

5. The electrolyte according to claim 1 or 4, characterized in that, The concentration of the lithium salt is 0.01 mol / L to 5 mol / L, preferably 0.1 mol / L to 2 mol / L, and more preferably 1 mol / L.

6. The electrolyte according to claim 1, characterized in that, The mass percentage of metal nitrate in the lithium-sulfur battery electrolyte is 0.01 wt% to 5 wt%, preferably 0.1 wt% to 3 wt%, and more preferably 2 wt%.

7. The electrolyte according to claim 1, characterized in that, The volume fraction of the weakly solvated electrolyte additive is 1% to 50%, preferably 10% to 30%, and more preferably 20%.

8. A method for preparing the electrolyte according to any one of claims 1 to 7, characterized in that, Includes the following steps: (1) In an environment filled with an inert atmosphere (e.g., argon and / or nitrogen), the organic solvents are mixed in the required volume ratio; (2) Add the weak solvation electrolyte additive to the solution obtained in step (1) according to the required volume ratio, and stir to mix evenly; the mixing time is 0.5 to 1 hour. (3) Add lithium salt and inorganic salt additives to the solution obtained in step (2), stir to dissolve, and obtain the weak solvation electrolyte of lithium-sulfur battery. The dissolving and stirring time is 1 to 4 hours.

9. The application of the electrolyte according to any one of claims 1 to 7 in a lithium-sulfur battery, characterized in that, The lithium-sulfur battery uses a highly active catalyst combined with sulfur as the sulfur positive electrode active material. The highly active catalyst is selected from MnO2, MoS2, carbon-supported single atoms, such as Fe-NC, Co-NC, Ni-NC, Fe / Co-NC, Fe / Ni-NC, Co-NS-C, Fe-PC, or one or more of these. The mass ratio of catalyst to sulfur is 1:1 to 9, preferably 1:1.5 to 5.6, and more preferably 1:

4.

10. The application according to claim 9, characterized in that, The electrolyte described in any one of the claims is combined with a highly active sulfur cathode catalyst and applied to thin lithium anodes (50 μm) and high-area sulfur cathodes (4 mg / cm²). 2 In lithium-sulfur batteries with low liquid sulfur ratio (E / S = 5 μL / mg), the first discharge specific capacity is 800-1500 mAh / g, and it can be stably cycled for 100-200 cycles at 0.1C, making it suitable for long-cycle lithium-sulfur batteries with high energy density.

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