A lithium-sulfur battery electrolyte containing additives and its application in lithium-sulfur batteries

Abstract

The present invention proposes an additive-containing lithium-sulfur battery electrolyte and its application in a lithium-sulfur battery, belonging to the technical field of lithium-sulfur battery electrolytes. The additive-containing lithium-sulfur battery electrolyte of the present invention comprises raw materials for a conductive lithium salt, an ether solvent, and an additive, wherein the additive is zinc bis(trifluoromethylsulfonyl)imide, and the content of the additive in the lithium-sulfur battery electrolyte is 0.5 to 2 wt%. A positive electrode material, a negative electrode material, a separator, and the additive-containing lithium-sulfur battery electrolyte are assembled to obtain a lithium-sulfur battery. The lithium-sulfur battery electrolyte provided by the present invention uses zinc bis(trifluoromethylsulfonyl)imide as an additive, improves the cycle performance of the lithium-sulfur battery, and promotes the kinetic process of the entire battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-sulfur battery electrolytes, and in particular relates to a lithium-sulfur battery electrolyte containing an additive and application thereof in a lithium-sulfur battery. Background Art

[0002] Among new energy storage systems, lithium-sulfur batteries are seen as a potential alternative to advanced lithium-ion batteries. Their characteristics lie in the coupling of a high-capacity sulfur cathode (theoretical specific capacity of 1675mAh·g-1) and a lithium metal anode (theoretical specific capacity of 3860mAh·g-1). The combination of sulfur cathode and lithium metal anode can provide lithium-sulfur batteries with extremely high theoretical energy density (2600Wh·kg-1 and 2800Wh·L-1, respectively). In addition, elemental sulfur has the advantages of low price, abundant resources, and environmental friendliness, which makes the lithium-sulfur battery system extremely commercially valuable and is recognized as one of the most promising next-generation battery systems.

[0003] Although lithium-sulfur batteries have shown significant advantages in energy density and cost, they still face many difficult problems. On the one hand, under the action of concentration gradient, lithium polysulfides (LiPSs) with high solubility will diffuse from the positive electrode to the electrolyte, thereby triggering a "shuttle effect", resulting in the loss of active materials and a decrease in coulombic efficiency. On the other hand, the presence of polysulfides will intensify the side reactions at the lithium negative electrode interface, leading to the consumption of metallic lithium and a negative impact on the transport performance of lithium ions. These problems will cause the loss of active materials in lithium-sulfur batteries, reduce coulombic efficiency, shorten cycle life and irreversible capacity decay, ultimately leading to a decline in battery performance.

[0004] In response to the above problems, current research progress is mainly focused on the field of positive electrode materials. By modifying the structure of sulfur positive electrode materials, such as synthesizing binary metal sulfides, organic sulfides, sulfur / metal oxide composites, sulfur / carbon composites, sulfur / polymer composites, etc., polysulfides or sulfur-based materials can be confined; or catalysts such as oxides, sulfides or nitrides can be introduced into the positive electrode. These strategies can, to a certain extent, suppress the shuttle effect of polysulfide ions and improve the utilization rate of active materials. However, these methods have the problem of complex synthesis routes, which will increase the manufacturing cost of the battery, and the influence of the negative electrode interface is rarely considered during the research process, which has hindered the practical application of lithium-sulfur batteries. Summary of the Invention

[0005] To solve the above technical problems, the present invention proposes a lithium-sulfur battery electrolyte containing an additive and its application in a lithium-sulfur battery. The additive can nano-catalyze the conversion of polysulfides, improve the utilization rate of sulfur, and at the same time form a layer of SEI (solid electrolyte interface layer) on the surface of the lithium metal negative electrode, effectively slowing down the side reactions at the negative electrode interface, and greatly improving the capacity, coulombic efficiency and long-cycle stability of the lithium-sulfur battery.

[0006] To achieve the above objectives, the present invention provides the following technical solutions:

[0007] One of the technical solutions of the present invention:

[0008] A lithium-sulfur battery electrolyte containing an additive. The raw materials of the lithium-sulfur battery electrolyte include a conductive lithium salt, an ether solvent and an additive. The additive is zinc bis(trifluoromethylsulfonyl)imide. The content of the additive in the lithium-sulfur battery electrolyte is 0.5-2 wt%.

[0009] Furthermore, the content of the additive in the lithium-sulfur battery electrolyte is 1 wt%.

[0010] Furthermore, the conductive lithium salt includes lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and / or lithium nitrate (LiNO3); and the ether solvent includes ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL).

[0011] Furthermore, the conductive lithium salt includes LiTFSI and LiNO3, the concentration of LiTFSI in the lithium-sulfur battery electrolyte is 1 mol / L, and the content of LiNO3 in the lithium-sulfur battery electrolyte is 1-2 wt%;

[0012] The volume ratio of DME to DOL in the ether solvent is 1:1.

[0013] It should be noted that the content of additives in lithium-sulfur battery electrolyte refers to the mass proportion of additives in lithium-sulfur battery electrolyte, and the content of LiNO3 in lithium-sulfur battery electrolyte refers to the mass proportion of LiNO3 in lithium-sulfur battery electrolyte.

[0014] The second technical solution of the present invention:

[0015] Application of the additive-containing lithium-sulfur battery electrolyte in lithium-sulfur batteries.

[0016] The third technical solution of the present invention:

[0017] A lithium-sulfur battery comprises a positive electrode material, a negative electrode material, a separator and the lithium-sulfur battery electrolyte containing the additive.

[0018] Furthermore, the cathode material is a sulfur-carbon cathode material, and the loading amount of sulfur in the sulfur-carbon cathode material is 1 to 1.7 mg·cm -2 .

[0019] Furthermore, the preparation method of the sulfur-carbon positive electrode material is:

[0020] Multi-walled carbon nanotubes (MWCNTs) and sulfur powder (S) are mixed in a mass ratio of 3:7, placed in a mortar and ground for 30 minutes to mix them evenly, placed in a reactor and filled with argon in a tube furnace, and kept warm at 155°C for 12 hours to obtain S@MWCNTs. S@MWCNTs, SuperP conductive carbon black and binder PVDF (polyvinylidene fluoride) are mixed and ground in a mass ratio of 7:2:1, and dissolved in NMP (N-methylpyrrolidone), and then coated on an aluminum foil current collector and dried in a vacuum oven at 60°C for 8 hours to obtain the sulfur-carbon positive electrode material.

[0021] Furthermore, the negative electrode material is a lithium metal sheet, and the separator is Celgard-2500.

[0022] Furthermore, the dosage of the additive-containing lithium-sulfur battery electrolyte is 20 μL / mg·S.

[0023] Compared with the prior art, the present invention has the following advantages and technical effects:

[0024] (1) The lithium-sulfur battery electrolyte provided by the present invention uses zinc bis(trifluoromethylsulfonyl)imide as an additive, which can react with polysulfides to form a complex. The reaction product of the two participates in the subsequent redox reaction process to inhibit the shuttling of polysulfides. In addition, zinc ions can react on the positive electrode side to generate a large number of nano-scale catalytic active sites, regulate the conversion path of polysulfides, and inhibit the shuttling effect brought by long-chain polysulfides, thereby significantly improving the discharge capacity and cycle stability of the lithium-sulfur battery, improving the cycle performance of the lithium-sulfur battery, and promoting the kinetic process of the entire battery.

[0025] (2) The zinc bis(trifluoromethylsulfonyl)imide contained in the lithium-sulfur battery electrolyte provided by the present invention is bifunctional. On the one hand, the additive can react with polysulfides and form a large number of active catalytic sites, which is beneficial to the regulation of the conversion of long-chain polysulfides, can improve the discharge capacity, and show smaller polarization; on the other hand, the zinc bis(trifluoromethylsulfonyl)imide will help form SEI at the negative electrode interface, have a protective effect on the negative electrode, and can accelerate charge transfer and improve coulombic efficiency.

[0026] (3) The electrolyte containing zinc bis(trifluoromethylsulfonyl)imide provided by the present invention has excellent cycle stability and high specific capacity, and has potential for commercial application. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0028] Figure 1 1 is a graph showing the cycle performance and coulombic efficiency of the lithium-sulfur battery of Example 1 of the present invention and Comparative Example 1;

[0029] Figure 2 The first cycle charge and discharge curves of the lithium-sulfur battery of Example 1 of the present invention and Comparative Example 1 are shown;

[0030] Figure 3 Raman spectra of the additive-containing lithium-sulfur battery electrolyte (polysulfide + zinc bis(trifluoromethylsulfonyl)imide) prepared in Example 1 and the additive-free lithium-sulfur battery electrolyte (polysulfide) in Comparative Example 1;

[0031] Figure 4 1 is a rate performance diagram of the lithium-sulfur battery of Example 1 of the present invention and Comparative Example 1;

[0032] Figure 5 1 is a comparison diagram of the negative electrode morphology of the lithium-sulfur battery of Example 1 of the present invention and Comparative Example 1. DETAILED DESCRIPTION

[0033] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0034] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each smaller range between any intermediate value within a stated value or stated range and any other stated value or intermediate value within the stated range is also encompassed by the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0035] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0036] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0037] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0038] An embodiment of the present invention provides a lithium-sulfur battery electrolyte containing an additive. The raw materials of the lithium-sulfur battery electrolyte include a conductive lithium salt, an ether solvent and an additive. The additive is zinc bis(trifluoromethylsulfonyl)imide, and the content of the additive in the lithium-sulfur battery electrolyte is 0.5 to 2 wt%.

[0039] In a preferred embodiment of the present invention, the content of the additive in the lithium-sulfur battery electrolyte is 1 wt%.

[0040] In a preferred embodiment of the present invention, the conductive lithium salt includes lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) and / or lithium nitrate (LiNO3); the ether solvent is ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL); more preferably, the conductive lithium salt includes LiTFSI and LiNO3, the concentration of LiTFSI in the lithium-sulfur battery electrolyte is 1 mol / L, and the content of LiNO3 in the lithium-sulfur battery electrolyte is 1-2 wt%; the volume ratio of DME and DOL in the ether solvent is 1:1.

[0041] It should be noted that, in the embodiments of the present invention, the content of the additive in the lithium-sulfur battery electrolyte refers to the mass proportion of the additive in the lithium-sulfur battery electrolyte, and the content of LiNO3 in the lithium-sulfur battery electrolyte refers to the mass proportion of LiNO3 in the lithium-sulfur battery electrolyte.

[0042] In a preferred embodiment of the present invention, the method for preparing the additive-containing lithium-sulfur battery electrolyte comprises the following steps:

[0043] In an argon-filled glove box (O2, H2O <0.01ppm), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) was added to a mixed solvent of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL), wherein DME:DOL (V:V) = 1:1, and then bis(trifluoromethylsulfonyl)imide zinc and lithium nitrate (LiNO3) were added. After mixing evenly, a lithium-sulfur battery electrolyte containing bis(trifluoromethylsulfonyl)imide zinc was obtained, which was stored in a bottle.

[0044] The additive-containing lithium-sulfur battery electrolyte obtained in the embodiment of the present invention is mainly used in lithium-sulfur batteries.

[0045] An embodiment of the present invention provides a lithium-sulfur battery, comprising a positive electrode material, a negative electrode material, a separator, and the lithium-sulfur battery electrolyte containing the additive.

[0046] In a preferred embodiment of the present invention, the cathode material is a sulfur-carbon cathode material, and the sulfur loading amount in the sulfur-carbon cathode material is 1 to 1.7 mg·cm -2 The sulfur loading amount in the sulfur-carbon positive electrode material = (total mass of sulfur in the positive electrode material / positive electrode area), and the change of the sulfur loading amount is achieved by controlling the coating thickness during the preparation process.

[0047] In a preferred embodiment of the present invention, the preparation method of the sulfur-carbon positive electrode material is:

[0048] Multi-walled carbon nanotubes (MWCNTs) and sulfur powder (S) were mixed in a mass ratio of 3:7, placed in a mortar and ground for 30 minutes to mix them evenly, placed in a reactor and filled with argon in a tube furnace, and kept warm at 155°C for 12 hours to obtain S@MWCNTs. S@MWCNTs, SuperP conductive carbon black and binder PVDF (polyvinylidene fluoride) were mixed and ground in a mass ratio of 7:2:1, and dissolved with NMP (N-methylpyrrolidone). Then, they were coated on an aluminum foil current collector and dried in a vacuum oven at 60°C for 8 hours to obtain the sulfur-carbon positive electrode material (Note: the PVDF used in the embodiment was dissolved in NMP with a content of 5wt%, and 0.05mL of NMP was added for every 0.1g in the subsequent mixing process).

[0049] In a preferred embodiment of the present invention, the negative electrode material is a lithium metal sheet, and the separator is Celgard-2500.

[0050] In a preferred embodiment of the present invention, the dosage of the lithium-sulfur battery electrolyte containing the additive is 20 μL / mg·S.

[0051] In a preferred embodiment of the present invention, a lithium-sulfur battery electrolyte containing additives is dripped onto both sides of the separator to contact the positive and negative electrode materials.

[0052] The bis(trifluoromethylsulfonyl)imide zinc, conductive lithium salt, ether solvent, battery shell, diaphragm, and lithium metal sheet involved in the present invention are all purchased from the market. The present invention has no special restrictions on the models of the battery shell, lithium metal sheet, and diaphragm.

[0053] The technical solution of the present invention is further illustrated by the following examples.

[0054] Example 1

[0055] A lithium-sulfur battery electrolyte containing an additive, wherein the raw materials include an additive (zinc bis(trifluoromethylsulfonyl)imide), a conductive lithium salt (LiTFSI and LiNO3) and an ether solvent (DME:DOL (V:V)=1:1), and the preparation method is as follows:

[0056] In an argon-filled glove box (O2, H2O <0.01ppm), LiTFSI was added to an ether solvent (DME:DOL (V:V) = 1:1), and then bis(trifluoromethylsulfonyl)imide zinc and LiNO3 were added and mixed uniformly to obtain an additive-containing lithium-sulfur battery electrolyte. The additive-containing lithium-sulfur battery electrolyte had a bis(trifluoromethylsulfonyl)imide zinc content of 1wt%, a LiTFSI concentration of 1.0M, and a LiNO3 content of 2wt%.

[0057] A lithium-sulfur battery comprises a sulfur-carbon positive electrode material, a negative electrode material (lithium metal sheet), a separator (Celgard-2500) and a prepared lithium-sulfur battery electrolyte containing an additive. The battery is assembled according to the following steps:

[0058] By controlling the coating thickness, the sulfur loading capacity was 1.3 mg / cm 2 The sulfur-carbon positive electrode material is cut into circular electrode sheets with a diameter of 12 mm using a sheet punching machine, and the prepared lithium-sulfur battery electrolyte containing additives is dripped on both sides of the separator to contact the positive and negative electrode materials. The electrolyte dosage is 20 μL / mg·S. Celgard 2500 with a diameter of 18 mm is used as the separator, a metal lithium sheet with a diameter of 15 mm is used as the negative electrode, and CR2016 stainless steel is used as the battery casing. The lithium-sulfur battery is assembled in an argon-filled glove box to obtain a lithium-sulfur battery.

[0059] Example 2

[0060] A lithium-sulfur battery electrolyte containing an additive, the raw materials including the additive (bis(trifluoromethylsulfonyl)imide zinc), a conductive lithium salt (LiTFSI and LiNO3), and an ether solvent (DME:DOL (V:V)=1:1), is prepared as follows:

[0061] In an argon-filled glove box (O2, H2O <0.01ppm), LiTFSI was added to an ether solvent (DME:DOL (V:V) = 1:1), and then bis(trifluoromethylsulfonyl)imide zinc and LiNO3 were added and mixed uniformly to obtain an additive-containing lithium-sulfur battery electrolyte. The additive-containing lithium-sulfur battery electrolyte had a bis(trifluoromethylsulfonyl)imide zinc content of 0.5wt%, a LiTFSI concentration of 1.0M, and a LiNO3 content of 2wt%.

[0062] A lithium-sulfur battery comprises a sulfur-carbon positive electrode material, a negative electrode material (lithium metal sheet), a separator (Celgard-2500) and a prepared lithium-sulfur battery electrolyte containing an additive. The battery is assembled according to the following steps:

[0063] By controlling the coating thickness, the sulfur loading capacity was 1.4 mg / cm 2 The sulfur-carbon positive electrode material is cut into circular electrode sheets with a diameter of 12 mm using a sheet punching machine, and the prepared lithium-sulfur battery electrolyte containing additives is dripped on both sides of the diaphragm to contact the positive and electrode materials. The electrolyte dosage is 20 μL / mg·S. Celgard 2500 with a diameter of 18 mm is used as a diaphragm, a metal lithium sheet with a diameter of 15 mm is used as a negative electrode, and CR2016 stainless steel is used as a battery casing. The lithium-sulfur battery is assembled in a glove box filled with argon to obtain a lithium-sulfur battery.

[0064] Example 3

[0065] A lithium-sulfur battery electrolyte containing an additive, the raw materials including the additive (bis(trifluoromethylsulfonyl)imide zinc), a conductive lithium salt (LiTFSI and LiNO3), and an ether solvent (DME:DOL (V:V)=1:1), is prepared as follows:

[0066] In an argon-filled glove box (O2, H2O <0.01ppm), LiTFSI was added to an ether solvent (DME:DOL (V:V) = 1:1), and then bis(trifluoromethylsulfonyl)imide zinc and LiNO3 were added and mixed uniformly to obtain an additive-containing lithium-sulfur battery electrolyte. The additive-containing lithium-sulfur battery electrolyte had a bis(trifluoromethylsulfonyl)imide zinc content of 2wt%, a LiTFSI concentration of 1.0M, and a LiNO3 content of 2wt%.

[0067] A lithium-sulfur battery comprises a sulfur-carbon positive electrode material, a negative electrode material (lithium metal sheet), a separator (Celgard-2500) and a prepared lithium-sulfur battery electrolyte containing an additive. The battery is assembled according to the following steps:

[0068] By controlling the coating thickness, the sulfur loading capacity was 1.2 mg / cm 2 The sulfur-carbon positive electrode material is cut into circular electrode sheets with a diameter of 12 mm using a sheet punching machine, and the prepared lithium-sulfur battery electrolyte containing additives is dripped on both sides of the diaphragm to contact the positive and electrode materials. The electrolyte dosage is 20 μL / mg·S. Celgard 2500 with a diameter of 18 mm is used as a diaphragm, a metal lithium sheet with a diameter of 15 mm is used as a negative electrode, and CR2016 stainless steel is used as a battery casing. The lithium-sulfur battery is assembled in a glove box filled with argon to obtain a lithium-sulfur battery.

[0069] Example 4

[0070] A lithium-sulfur battery electrolyte containing an additive, the raw materials including the additive (bis(trifluoromethylsulfonyl)imide zinc), a conductive lithium salt (LiTFSI and LiNO3), and an ether solvent (DME:DOL (V:V)=1:1), is prepared as follows:

[0071] In an argon-filled glove box (O2, H2O <0.01ppm), LiTFSI was added to an ether solvent (DME:DOL (V:V) = 1:1), and then bis(trifluoromethylsulfonyl)imide zinc and LiNO3 were added and mixed uniformly to obtain an additive-containing lithium-sulfur battery electrolyte. The additive-containing lithium-sulfur battery electrolyte had a bis(trifluoromethylsulfonyl)imide zinc content of 1wt%, a LiTFSI concentration of 1.0M, and a LiNO3 content of 1wt%;

[0072] A lithium-sulfur battery comprises a sulfur-carbon positive electrode material, a negative electrode material (lithium metal sheet), a separator (Celgard-2500) and a prepared lithium-sulfur battery electrolyte containing an additive. The battery is assembled according to the following steps:

[0073] By controlling the coating thickness, the sulfur loading capacity was 1.3 mg / cm 2 The sulfur-carbon positive electrode material is cut into circular electrode sheets with a diameter of 12 mm using a sheet punching machine, and the prepared lithium-sulfur battery electrolyte containing additives is dripped on both sides of the diaphragm to contact the positive and electrode materials. The electrolyte dosage is 20 μL / mg·S. Celgard 2500 with a diameter of 18 mm is used as a diaphragm, a metal lithium sheet with a diameter of 15 mm is used as a negative electrode, and CR2016 stainless steel is used as a battery casing. The lithium-sulfur battery is assembled in a glove box filled with argon to obtain a lithium-sulfur battery.

[0074] Example 5

[0075] A lithium-sulfur battery electrolyte containing an additive, the raw materials including the additive (bis(trifluoromethylsulfonyl)imide zinc), a conductive lithium salt (LiTFSI and LiNO3), and an ether solvent (DME:DOL (V:V)=1:1), is prepared as follows:

[0076] In an argon-filled glove box (O2, H2O <0.01ppm), LiTFSI was added to an ether solvent (DME:DOL (V:V) = 1:1), and then bis(trifluoromethylsulfonyl)imide zinc and LiNO3 were added and mixed uniformly to obtain an additive-containing lithium-sulfur battery electrolyte. The additive-containing lithium-sulfur battery electrolyte had a bis(trifluoromethylsulfonyl)imide zinc content of 0.5wt%, a LiTFSI concentration of 1.0M, and a LiNO3 content of 1wt%;

[0077] A lithium-sulfur battery comprises a sulfur-carbon positive electrode material, a negative electrode material (lithium metal sheet), a separator (Celgard-2500) and a prepared lithium-sulfur battery electrolyte containing an additive. The battery is assembled according to the following steps:

[0078] By controlling the coating thickness, the sulfur loading capacity was 1.4 mg / cm 2 The sulfur-carbon positive electrode material is cut into circular electrode sheets with a diameter of 12 mm using a sheet punching machine, and the prepared lithium-sulfur battery electrolyte containing additives is dripped on both sides of the diaphragm to contact the positive and electrode materials. The electrolyte dosage is 20 μL / mg·S. Celgard 2500 with a diameter of 18 mm is used as a diaphragm, a metal lithium sheet with a diameter of 15 mm is used as a negative electrode, and CR2016 stainless steel is used as a battery casing. The lithium-sulfur battery is assembled in a glove box filled with argon to obtain a lithium-sulfur battery.

[0079] Example 6

[0080] A lithium-sulfur battery electrolyte containing an additive, the raw materials including the additive (bis(trifluoromethylsulfonyl)imide zinc), a conductive lithium salt (LiTFSI and LiNO3), and an ether solvent (DME:DOL (V:V)=1:1), is prepared as follows:

[0081] In an argon-filled glove box (O2, H2O <0.01ppm), LiTFSI was added to an ether solvent (DME:DOL (V:V) = 1:1), and then bis(trifluoromethylsulfonyl)imide zinc and LiNO3 were added and mixed uniformly to obtain an additive-containing lithium-sulfur battery electrolyte. The additive-containing lithium-sulfur battery electrolyte had a bis(trifluoromethylsulfonyl)imide zinc content of 2wt%, a LiTFSI concentration of 1.0M, and a LiNO3 content of 1wt%;

[0082] A lithium-sulfur battery comprises a sulfur-carbon positive electrode material, a negative electrode material (lithium metal sheet), a separator (Celgard-2500) and a prepared lithium-sulfur battery electrolyte containing an additive. The battery is assembled according to the following steps:

[0083] By controlling the coating thickness, the sulfur loading capacity was 1.2 mg / cm 2The sulfur-carbon positive electrode material is cut into circular electrode sheets with a diameter of 12 mm using a sheet punching machine, and the prepared lithium-sulfur battery electrolyte containing additives is dripped on both sides of the diaphragm to contact the positive and electrode materials. The electrolyte dosage is 20 μL / mg·S. Celgard 2500 with a diameter of 18 mm is used as a diaphragm, a metal lithium sheet with a diameter of 15 mm is used as a negative electrode, and CR2016 stainless steel is used as a battery casing. The lithium-sulfur battery is assembled in a glove box filled with argon to obtain a lithium-sulfur battery.

[0084] Comparative Example 1

[0085] A lithium-sulfur battery electrolyte, similar to Example 1, except that the raw materials do not contain the additive (zinc bis(trifluoromethylsulfonyl)imide), is prepared as follows:

[0086] In an argon-filled glove box (O2, H2O <0.01ppm), LiTFSI was added to an ether solvent (DME:DOL (V:V) = 1:1), and then LiNO3 was added and mixed to obtain an additive-free lithium-sulfur battery electrolyte. The LiTFSI concentration in the electrolyte was 1.0M and the LiNO3 content was 2wt%;

[0087] A lithium-sulfur battery comprises a sulfur-carbon positive electrode material, a negative electrode material (lithium metal sheet), a separator (Celgard-2500) and the prepared lithium-sulfur battery electrolyte. The battery is assembled according to the following steps:

[0088] By controlling the coating thickness, the sulfur loading capacity was 1.3 mg / cm 2 The sulfur-carbon positive electrode material is cut into circular electrode sheets with a diameter of 12 mm using a sheet punching machine, and the above-mentioned lithium-sulfur battery electrolyte is dripped on both sides of the separator to contact the positive and electrode materials. The electrolyte dosage is 20 μL / mg·S. A Celgard 2500 with a diameter of 18 mm is used as a separator, a metal lithium sheet with a diameter of 15 mm is used as a negative electrode, and a CR2016 stainless steel is used as a battery casing. The lithium-sulfur battery is assembled in an argon-filled glove box to obtain a lithium-sulfur battery.

[0089] Comparative Example 2

[0090] A lithium-sulfur battery electrolyte, similar to Example 5, except that the raw materials do not contain the additive (zinc bis(trifluoromethylsulfonyl)imide), is prepared as follows:

[0091] In an argon-filled glove box (O2, H2O <0.01ppm), LiTFSI was added to an ether solvent (DME:DOL (V:V) = 1:1), and then LiNO3 was added and mixed to obtain an additive-free lithium-sulfur battery electrolyte. The LiTFSI concentration in the electrolyte was 1.0M and the LiNO3 content was 1wt%;

[0092] A lithium-sulfur battery comprises a sulfur-carbon positive electrode material, a negative electrode material (lithium metal sheet), a separator (Celgard-2500) and the prepared lithium-sulfur battery electrolyte. The battery is assembled according to the following steps:

[0093] By controlling the coating thickness, the sulfur loading capacity was 1.4 mg / cm 2 The sulfur-carbon positive electrode material is cut into circular electrode sheets with a diameter of 12 mm using a sheet punching machine, and the above-mentioned lithium-sulfur battery electrolyte is dripped on both sides of the separator to contact the positive and electrode materials. The electrolyte dosage is 20 μL / mg·S. A Celgard 2500 with a diameter of 18 mm is used as a separator, a metal lithium sheet with a diameter of 15 mm is used as a negative electrode, and a CR2016 stainless steel is used as a battery casing. The lithium-sulfur battery is assembled in an argon-filled glove box to obtain a lithium-sulfur battery.

[0094] Performance Testing

[0095] The electrochemical performance of the lithium-sulfur batteries of Examples 1 to 6 and Comparative Examples 1 to 2 was verified:

[0096] Electrochemical performance test: After the assembled battery was left to stand at 25°C for 8 hours, it was charged and discharged at a rate of 0.5C between 1.7V and 2.8V. The specific capacity, capacity retention rate and average coulombic efficiency after 100 cycles are shown in Table 1.

[0097] Electrochemical performance test results of lithium-sulfur batteries of Examples 1 to 6 and Comparative Examples 1 to 2

[0098]

[0099]

[0100] As can be seen from Table 1, Example 1 has the highest initial discharge capacity of 1311.0 mAh / g, with a capacity retention rate of 64.57%, and a coulombic efficiency of 99.78%. At the same time, a comparison of the data of each embodiment and the comparative example shows that the addition of the additive zinc bis(trifluoromethylsulfonyl)imide can significantly improve the discharge capacity and coulombic efficiency of the lithium-sulfur battery, and the addition amount of Example 1 is the most suitable.

[0101] The cycle performance and first cycle charge and discharge curves of the lithium-sulfur battery in Example 1 and Comparative Example 1 are shown in FIG. Figure 1 and Figure 2 It can be seen that the capacity decay of Example 1 is weaker and the discharge specific capacity is higher. At the same time, by comparing the charge and discharge curves, it can be seen that the addition of zinc bis(trifluoromethylsulfonyl)imide can effectively reduce the polarization of the battery and bring more discharge capacity in the long-chain polysulfide conversion stage.

[0102] The Raman spectra of the additive-containing lithium-sulfur battery electrolyte (polysulfide + bis(trifluoromethylsulfonyl)imide zinc) prepared in Example 1 and the additive-free lithium-sulfur battery electrolyte (polysulfide) in Comparative Example 1 are shown in FIG. Figure 3 It can be seen that the additive promotes the conversion of polysulfides. In addition, new peaks appear after the addition of the additive, indicating the generation of new substances.

[0103] The rate performance comparison between Example 1 and Comparative Example 1 is shown in Figure 4 ,Depend on Figure 4 It can be seen that the lithium-sulfur battery containing additives has a higher specific capacity at each rate, which means that it can achieve fast charging and discharging speed, high power output and high efficiency in energy output and conversion, and can also reduce battery loss, maintain stable performance to extend life, and at the same time give the battery a wider range of application scenarios and the flexibility to adapt to different working conditions.

[0104] In order to verify the formation of negative electrode SEI, the morphology of the negative electrode surface after 5 cycles was characterized. The morphology of the negative electrode of Example 1 and Comparative Example 1 is as follows: Figure 5 As shown, the left figure is Example 1 and the right figure is Comparative Example 1. By comparison, it can be seen that Example 1 does form SEI, while Comparative Example 1 does not. SEI can mitigate the impact of polysulfides on the lithium metal negative electrode interface, thereby improving the coulombic efficiency of lithium-sulfur batteries.

[0105] In general, the present invention has the following advantages by adding bis(trifluoromethylsulfonyl)imide zinc to the electrolyte of the lithium-sulfur battery:

[0106] (1) The additive can react with polysulfides to form a complex. The reaction products of the two participate in the subsequent redox reaction process to inhibit the shuttling of polysulfides. In addition, zinc ions can react on the positive electrode side to generate a large number of nano-scale catalytic active sites, which regulate the conversion path of polysulfides and inhibit the shuttle effect brought by long-chain polysulfides, thereby significantly improving the discharge capacity and cycle stability of lithium-sulfur batteries. Without the addition of such additives, long-chain polysulfides cannot be converted and exist in the positive and negative electrodes of the battery. The shuttle effect is aggravated, which has a negative impact on both the positive and negative electrodes, and the electrochemical performance is significantly reduced.

[0107] (2) The substance formed by the interaction of the additive with S and Li participates in the formation of SEI, which is Li + It provides a special transmission interface, which can slow down the corrosion of polysulfides on the negative electrode on the one hand, and accelerate the transmission of lithium ions on the other hand, thereby improving the coulombic efficiency of lithium-sulfur batteries.

[0108] The above demonstrates that the dual functionality of the present invention using bis(trifluoromethylsulfonyl)imide zinc as an additive can improve the performance of lithium-sulfur batteries by acting at the positive and negative electrode interfaces of the lithium-sulfur battery and jointly transforming multiple aspects.

[0109] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A lithium-sulfur battery electrolyte containing an additive, characterized in that: The raw materials of the lithium-sulfur battery electrolyte include a conductive lithium salt, an ether solvent and an additive, wherein the additive is zinc bis(trifluoromethylsulfonyl)imide, and the content of the additive in the lithium-sulfur battery electrolyte is 0.5 to 2 wt%; The ether solvents are ethylene glycol dimethyl ether and 1,3-dioxolane; The conductive lithium salt includes lithium bis(trifluoromethylsulfonylimide) and lithium nitrate, the concentration of lithium bis(trifluoromethylsulfonylimide) in the lithium-sulfur battery electrolyte is 1 mol / L, and the content of lithium nitrate in the lithium-sulfur battery electrolyte is 1-2 wt%; The volume ratio of ethylene glycol dimethyl ether to 1,3-dioxolane in the ether solvent is 1:

1.

2. The additive-containing lithium-sulfur battery electrolyte according to claim 1, characterized in that: The content of the additive in the lithium-sulfur battery electrolyte is 1 wt%.

3. Use of the additive-containing lithium-sulfur battery electrolyte according to any one of claims 1 to 2 in a lithium-sulfur battery.

4. A lithium-sulfur battery, characterized in that: The invention comprises a positive electrode material, a negative electrode material, a separator and the lithium-sulfur battery electrolyte containing the additive according to any one of claims 1 to 2.

5. The lithium-sulfur battery according to claim 4, characterized in that The positive electrode material is a sulfur-carbon positive electrode material, and the loading amount of sulfur in the sulfur-carbon positive electrode material is 1 to 1.7 mg·cm -2 .

6. The lithium-sulfur battery according to claim 4, characterized in that The negative electrode material is a lithium metal sheet.

7. The lithium-sulfur battery according to claim 4, characterized in that The dosage of the additive-containing lithium-sulfur battery electrolyte is 20 μL / mg·S.

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