Lithium-sulfur battery electrolyte containing additive and application of lithium-sulfur battery electrolyte in lithium-sulfur battery

Abstract

The invention provides an additive-containing lithium-sulfur battery electrolyte and application thereof in a lithium-sulfur battery, and belongs to the technical field of lithium-sulfur battery electrolytes. Raw materials of the lithium-sulfur battery electrolyte containing the additive comprise a conductive lithium salt, an ether solvent and the additive, the additive is bis (trifluoromethylsulfonyl) imide zinc, and the content of the additive in the lithium-sulfur battery electrolyte is 0.5-2wt%. And assembling a positive electrode material, a negative electrode material, a diaphragm and the lithium-sulfur battery electrolyte containing the additive to obtain the lithium-sulfur battery. The lithium-sulfur battery electrolyte provided by the invention takes bis (trifluoromethylsulfonyl) imide zinc as an additive, so that the cycle performance of a lithium-sulfur battery is improved, and the dynamic process of the whole battery is promoted.

Description

Technical Field

[0001] The 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] In new energy storage systems, lithium-sulfur batteries are seen as a potential alternative to advanced lithium-ion batteries. Its characteristics are 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 substances and reduced 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 transmission performance of lithium ions. These problems will cause the loss of active substances, reduced coulombic efficiency, shortened cycle life and irreversible capacity decay in lithium-sulfur batteries, 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 main materials can be confined; or catalysts such as oxides, sulfides or nitrides are introduced into the positive electrode. These strategies can inhibit the shuttle effect of polysulfide ions to a certain extent and improve the utilization rate of active substances. However, these methods have the problem of complex synthesis routes, which will increase the manufacturing cost of the battery, and the impact on 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 provides 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 SEI (solid electrolyte interface layer) on the surface of the lithium metal anode, effectively slowing down the side reactions at the anode interface, and greatly improving the capacity, Coulomb efficiency and long-cycle stability of the lithium-sulfur battery.

[0006] To achieve the above object, 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, wherein 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 0.5-2 wt%.

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

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

[0011] Even further, the conductive lithium salt includes LiTFSI and LiNO 3 , the concentration of LiTFSI in the lithium-sulfur battery electrolyte is 1 mol / L, and the content of LiNO 3 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 the additive in the lithium-sulfur battery electrolyte refers to the mass ratio of the additive in the lithium-sulfur battery electrolyte, and the content of LiNO 3 in the lithium-sulfur battery electrolyte refers to the mass ratio of LiNO 3 in the lithium-sulfur battery electrolyte.

[0014] Another technical solution of the present invention:

[0015] The application of the lithium-sulfur battery electrolyte containing an additive in a lithium-sulfur battery.

[0016] Another technical solution of the present invention:

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

[0018] Further, 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 1-1.7 mg·cm -2 .

[0019] Even further, the preparation method of the sulfur-carbon positive electrode material is as follows:

[0020] Mix multi-walled carbon nanotubes (MWCNTs) and sulfur powder (S) in a mass ratio of 3:7, place them in a mortar and grind for 30 min to make them evenly mixed, put them in a reaction kettle and fill argon in a tube furnace, keep warm at 155 °C for 12 h to obtain S@MWCNTs, mix S@MWCNTs, SuperP conductive carbon black and binder PVDF (polyvinylidene fluoride) in a mass ratio of 7:2:1 and grind, dissolve with NMP (N-methylpyrrolidone), and then coat it on an aluminum foil current collector, dry in a vacuum oven at 60 °C for 8 h to obtain the sulfur-carbon positive electrode material.

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

[0022] Further, the dosage of the lithium-sulfur battery electrolyte containing an additive 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 undergo a complexation reaction with polysulfides, and the reaction product thereof participates in the subsequent redox reaction process to inhibit the shuttle 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 shuttle effect caused 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, this 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 shows a small polarization; on the other hand, at the negative electrode interface, zinc bis(trifluoromethylsulfonyl)imide will help generate SEI, which has a protective effect on the negative electrode and can accelerate charge transfer and improve the Coulomb efficiency.

[0026] (3) The electrolyte containing zinc bis(trifluoromethylsulfonyl)imide provided by the present invention has excellent cycle stability and a relatively high specific capacity, and has the potential for commercial application. Description of the Drawings

[0027] The drawings forming a part of the present invention are used to provide a further understanding of the present invention. The schematic embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0028] Figure 1 It is a graph of the cycle performance and Coulomb efficiency of the lithium-sulfur batteries of Example 1 and Comparative Example 1 of the present invention;

[0029] Figure 2 It is a graph of the first charge-discharge curves of the lithium-sulfur batteries of Example 1 and Comparative Example 1 of the present invention;

[0030] Figure 3 It is a Raman spectrum of the electrolyte of the lithium-sulfur battery containing additives (polysulfide + zinc bis(trifluoromethylsulfonyl)imide) prepared in Example 1 and the electrolyte of the lithium-sulfur battery without additives (polysulfide) in Comparative Example 1;

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

[0032] Figure 5 It is a comparison graph of the negative electrode morphologies of the lithium-sulfur batteries of Example 1 and Comparative Example 1 of the present invention. Detailed Description of the Invention

[0033] Now, various exemplary embodiments of the present invention will be described in detail. This detailed description should not be considered as a limitation of the present invention, but should be understood as a more detailed description of certain aspects, characteristics, and implementation schemes of the present invention.

[0034] It should be understood that the terms described in the present invention are only for describing specific embodiments and are not used to limit the present invention. Additionally, for the numerical ranges in the present invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Each intermediate value within any stated value or stated range, as well as each smaller range between any other stated value or intermediate value within the stated range, is also included in the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0035] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Although this invention only describes preferred methods and materials, any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of this invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials related to those documents. In case of conflict with any incorporated document, the content of this specification shall prevail.

[0036] Without departing from the scope or spirit of this invention, various improvements and changes can be made to the specific embodiments of the description of this invention, which are obvious to those skilled in the art. Other embodiments obtained from the description of this invention are obvious to those skilled in the art. The description and examples of this invention are merely exemplary.

[0037] Regarding the use of "comprising", "including", "having", "containing", etc. in this article, they are all open-ended terms, meaning including but not limited to.

[0038] An embodiment of this 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 - 2 wt%.

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

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

[0041] It should be noted that in the embodiment of this invention, the content of the additive in the lithium-sulfur battery electrolyte refers to the mass ratio of the additive in the lithium-sulfur battery electrolyte, and the content of LiNO 3 in the lithium-sulfur battery electrolyte refers to the mass ratio of LiNO 3 in the lithium-sulfur battery electrolyte.

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

[0043] In a glove box filled with argon (O 2 , H 2 O < 0.01 ppm), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) is added to a mixed solvent of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL), where DME:DOL (V:V) = 1:1. Then, zinc bis(trifluoromethanesulfonyl)imide and lithium nitrate (LiNO 3 ) are added. After mixing evenly, a lithium-sulfur battery electrolyte containing zinc bis(trifluoromethanesulfonyl)imide is obtained and stored in a bottle.

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

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

[0046] In a preferred embodiment of the present invention, the positive electrode material is a sulfur-carbon positive electrode material, and the sulfur loading in the sulfur-carbon positive electrode material is 1 - 1.7 mg·cm -2 , and the sulfur loading in the sulfur-carbon positive electrode material = (total mass of sulfur in the positive electrode material / positive electrode area). The change in sulfur loading 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 as follows:

[0048] Multi-walled carbon nanotubes (MWCNTs) and sulfur powder (S) are mixed at a mass ratio of 3:7, ground in a mortar for 30 min to mix evenly, placed in a reaction kettle, and argon is filled in a tubular furnace. It is kept at 155 °C for 12 h to obtain S@MWCNTs. S@MWCNTs, SuperP conductive carbon black, and a binder PVDF (polyvinylidene fluoride) are mixed and ground at a mass ratio of 7:2:1, 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 h to obtain the sulfur-carbon positive electrode material (note: the PVDF used in the embodiment is dissolved in NMP with a content of 5 wt%, and the NMP added during the subsequent mixing process is 0.05 mL per 0.1 g).

[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, the lithium-sulfur battery electrolyte containing the additive is dropped on both sides of the separator to contact the positive and negative electrode materials.

[0052] Zinc bis(trifluoromethanesulfonyl)imide, conductive lithium salt, ether solvent, battery case, separator, and lithium metal sheet involved in the present invention are all purchased from the market, and the present invention has no special restrictions on the models of the battery case, lithium metal sheet, and separator.

[0053] The technical solution of the present invention is further described below through examples.

[0054] Example 1

[0055] A lithium-sulfur battery electrolyte containing an additive, the raw materials include an additive (zinc bis(trifluoromethanesulfonyl)imide), a conductive lithium salt (LiTFSI and LiNO 3 ) and an ether solvent (DME:DOL (V:V)=1:1), and the preparation method is as follows:

[0056] In a glove box filled with argon (O 2 , H 2 O<0.01 ppm), LiTFSI is added to the ether solvent (DME:DOL (V:V)=1:1), and then zinc bis(trifluoromethanesulfonyl)imide and LiNO 3 are added. After mixing evenly, a lithium-sulfur battery electrolyte containing the additive is obtained. The content of zinc bis(trifluoromethanesulfonyl)imide in the lithium-sulfur battery electrolyte containing the additive is 1 wt%, the concentration of LiTFSI is 1.0 M, and the content of LiNO 3 is 2 wt%;

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

[0058] By controlling the coating thickness, a sulfur-carbon positive electrode material with a sulfur loading of 1.3 mg / cm 2 is prepared. The sulfur-carbon positive electrode material is cut into a circular electrode sheet with a diameter of 12 mm by a punching machine. The prepared lithium-sulfur battery electrolyte containing the additive is dropped 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 a CR2016 type stainless steel is used as the battery case. The lithium-sulfur battery is assembled in a glove box filled with argon to obtain a lithium-sulfur battery.

[0059] Example 2

[0060] A lithium-sulfur battery electrolyte containing additives, the raw materials include additives (zinc bis(trifluoromethylsulfonyl)imide), conductive lithium salts (LiTFSI and LiNO 3 ), and an ether solvent (DME:DOL (V:V)=1:1). The preparation method is as follows:

[0061] In a glove box filled with argon (O 2 , H 2 O < 0.01 ppm), add LiTFSI to the ether solvent (DME:DOL (V:V)=1:1), then add zinc bis(trifluoromethylsulfonyl)imide and LiNO 3 , and after mixing evenly, obtain a lithium-sulfur battery electrolyte containing additives. The content of zinc bis(trifluoromethylsulfonyl)imide in the lithium-sulfur battery electrolyte containing additives is 0.5 wt%, the concentration of LiTFSI is 1.0 M, and the content of LiNO 3 is 2 wt%;

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

[0063] Prepare a sulfur-carbon positive electrode material with a sulfur loading of 1.4 mg / cm 2 by controlling the coating thickness. Cut the sulfur-carbon positive electrode material into a circular electrode sheet with a diameter of 12 mm using a punching machine. Drop the prepared lithium-sulfur battery electrolyte containing additives on both sides of the separator to contact the positive and negative electrode materials. The electrolyte dosage is 20 μL / mg·S. Use Celgard 2500 with a diameter of 18 mm as the separator, a metal lithium sheet with a diameter of 15 mm as the negative electrode, and a CR2016 type stainless steel as the battery shell. Assemble the lithium-sulfur battery in a glove box filled with argon to obtain a lithium-sulfur battery.

[0064] Example 3

[0065] A lithium-sulfur battery electrolyte containing additives, the raw materials include additives (zinc bis(trifluoromethylsulfonyl)imide), conductive lithium salts (LiTFSI and LiNO 3 ), and an ether solvent (DME:DOL (V:V)=1:1). The preparation method is as follows:

[0066] In a glove box filled with argon (O 2 , H 2Add LiTFSI into an ether solvent (DME:DOL (V:V)=1:1) with O < 0.01 ppm, and then add zinc bis(trifluoromethanesulfonyl)imide and LiNO 3 , and after mixing evenly, an electrolyte for a lithium-sulfur battery containing additives is obtained. The content of zinc bis(trifluoromethanesulfonyl)imide in the electrolyte for a lithium-sulfur battery containing additives is 2 wt%, the concentration of LiTFSI is 1.0 M, and LiNO 3 The content is 2 wt%;

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

[0068] Prepare a sulfur-carbon positive electrode material with a sulfur loading of 1.2 mg / cm 2 by controlling the coating thickness. Cut the sulfur-carbon positive electrode material into circular electrode sheets with a diameter of 12 mm using a punching machine. Drop the prepared electrolyte for a lithium-sulfur battery containing additives on both sides of the separator to contact the positive and negative electrode materials. The electrolyte dosage is 20 μL / mg·S. Use Celgard 2500 with a diameter of 18 mm as the separator, use a lithium metal sheet with a diameter of 15 mm as the negative electrode, and use a CR2016 type stainless steel as the battery casing. Assemble the lithium-sulfur battery in a glove box filled with argon to obtain a lithium-sulfur battery.

[0069] Example 4

[0070] An electrolyte for a lithium-sulfur battery containing additives, the raw materials include additives (zinc bis(trifluoromethanesulfonyl)imide), conductive lithium salts (LiTFSI and LiNO 3 ), and an ether solvent (DME:DOL (V:V)=1:1). The preparation method is as follows:

[0071] In a glove box filled with argon (O 2 , H 2 O < 0.01 ppm), add LiTFSI into an ether solvent (DME:DOL (V:V)=1:1), and then add zinc bis(trifluoromethanesulfonyl)imide and LiNO 3 , and after mixing evenly, an electrolyte for a lithium-sulfur battery containing additives is obtained. The content of zinc bis(trifluoromethanesulfonyl)imide in the electrolyte for a lithium-sulfur battery containing additives is 1 wt%, the concentration of LiTFSI is 1.0 M, and LiNO 3 The content is 1 wt%;

[0072] A lithium-sulfur battery includes 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] The sulfur-carbon positive electrode material with a sulfur loading of 1.3 mg / cm is prepared by controlling the coating thickness. 2 The sulfur-carbon positive electrode material is cut into circular electrode sheets with a diameter of 12 mm using a punching machine. The prepared lithium-sulfur battery electrolyte containing an additive is dropped 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 a CR2016 type stainless steel is used as the battery case. 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 include an additive (zinc bis(trifluoromethylsulfonyl)imide), a conductive lithium salt (LiTFSI and LiNO 3 ), and an ether solvent (DME:DOL (V:V)=1:1). The preparation method is as follows:

[0076] In a glove box filled with argon (O 2 , H 2 O<0.01 ppm), LiTFSI is added to the ether solvent (DME:DOL (V:V)=1:1), and then zinc bis(trifluoromethylsulfonyl)imide and LiNO 3 are added. After mixing evenly, a lithium-sulfur battery electrolyte containing an additive is obtained. The content of zinc bis(trifluoromethylsulfonyl)imide in the lithium-sulfur battery electrolyte containing an additive is 0.5 wt%, the concentration of LiTFSI is 1.0 M, and the content of LiNO 3 is 1 wt%;

[0077] A lithium-sulfur battery includes 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] The sulfur-carbon positive electrode material with a sulfur loading of 1.4 mg / cm is prepared by controlling the coating thickness. 2For the sulfur-carbon cathode material, the sulfur-carbon cathode material was cut into circular cathode plates with a diameter of 12 mm using a punching machine. The prepared lithium-sulfur battery electrolyte containing additives was dropped on both sides of the separator to contact the positive and negative materials. The electrolyte dosage was 20 μL / mg·S. Celgard 2500 with a diameter of 18 mm was used as the separator, a metal lithium sheet with a diameter of 15 mm was used as the anode, and CR2016 type stainless steel was used as the battery case. The lithium-sulfur battery was assembled in a glove box filled with argon to obtain the lithium-sulfur battery.

[0079] Example 6

[0080] A lithium-sulfur battery electrolyte containing additives, the raw materials include additives (zinc bis(trifluoromethylsulfonyl)imide), conductive lithium salts (LiTFSI and LiNO 3 ), and ether solvents (DME:DOL(V:V)=1:1). The preparation method is as follows:

[0081] In a glove box filled with argon (O 2 , H 2 O<0.01 ppm), LiTFSI was added to the ether solvent (DME:DOL(V:V)=1:1), and then zinc bis(trifluoromethylsulfonyl)imide and LiNO 3 were added. After mixing evenly, the lithium-sulfur battery electrolyte containing additives was obtained. The content of zinc bis(trifluoromethylsulfonyl)imide in the lithium-sulfur battery electrolyte containing additives was 2 wt%, the concentration of LiTFSI was 1.0 M, and the content of LiNO 3 was 1 wt%;

[0082] A lithium-sulfur battery includes a sulfur-carbon cathode material, an anode material (lithium metal sheet), a separator (Celgard-2500), and the prepared lithium-sulfur battery electrolyte containing additives. The battery was assembled according to the following steps:

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

[0084] Comparative Example 1

[0085] A lithium-sulfur battery electrolyte, which is the same as that in Example 1, except that the raw materials do not contain an additive (zinc bis(trifluoromethanesulfonyl)imide), and the preparation method is as follows:

[0086] In a glove box filled with argon (O 2 , H 2 O < 0.01 ppm), LiTFSI was added to an ether solvent (DME:DOL (V:V) = 1:1), and then LiNO 3 was added. After mixing evenly, a lithium-sulfur battery electrolyte without an additive was obtained. The concentration of LiTFSI in the electrolyte was 1.0 M, and the content of LiNO 3 was 2 wt%;

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

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

[0089] Comparative Example 2

[0090] A lithium-sulfur battery electrolyte, which is the same as that in Example 5, except that the raw materials do not contain an additive (zinc bis(trifluoromethanesulfonyl)imide), and the preparation method is as follows:

[0091] In a glove box filled with argon (O 2 , H 2 O < 0.01 ppm), LiTFSI was added to an ether solvent (DME:DOL (V:V) = 1:1), and then LiNO 3 was added. After mixing evenly, a lithium-sulfur battery electrolyte without an additive was obtained. The concentration of LiTFSI in the electrolyte was 1.0 M, and the content of LiNO 3 was 1 wt%;

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

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

[0094] Performance Test

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

[0096] Electrochemical performance test: After the assembled battery was left standing at 25 °C for 8 h, charge-discharge cycling was carried out 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 the lithium-sulfur batteries in Examples 1-6 and Comparative Examples 1-2

[0098]

[0099]

[0100] As can be seen from Table 1, Example 1 had the highest initial discharge specific capacity, which was 1311.0 mAh / g, and the capacity retention rate was 64.57%, while the Coulombic efficiency also remained at 99.78%. At the same time, by comparing the data of each example and the comparative example, it can be seen that the addition of the additive zinc bis(trifluoromethylsulfonyl)imide can significantly improve the discharge specific capacity and Coulombic efficiency of the lithium-sulfur battery, and the addition amount in Example 1 was the most appropriate.

[0101] The cycle performance and the first-cycle charge-discharge curves of the lithium-sulfur batteries in Example 1 and Comparative Example 1 are shown in Figure 1 and Figure 2 respectively. It can be seen that the capacity decay of Example 1 was weaker and the discharge specific capacity was higher. At the same time, by comparing the charge-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 during the conversion stage of long-chain polysulfides.

[0102] The Raman spectra of the lithium-sulfur battery electrolyte (polysulfide + zinc bis(trifluoromethylsulfonyl)imide) containing additives prepared in Example 1 and the lithium-sulfur battery electrolyte (polysulfide) without additives in Comparative Example 1 are shown in Figure 3, it can be seen that this additive promotes the conversion of polysulfides. In addition, new peak positions appear after the addition of this additive, symbolizing the formation of new substances.

[0103] The comparison of the rate performance between Example 1 and Comparative Example 1 is shown in Figure 4 , from Figure 4 it can be seen that the lithium-sulfur battery containing the additive has a higher specific capacity at each rate, indicating that it can achieve fast charge and discharge in terms of charge and discharge speed, can output high power and has high efficiency in energy output and conversion, can also reduce battery loss, maintain stable performance to extend the life, and at the same time endows the battery with a wider application scenario and flexibility to adapt to different working conditions.

[0104] In order to verify the formation of the negative electrode SEI, the surface morphology of the negative electrode after 5 cycles was characterized. The negative electrode morphology characterizations of Example 1 and Comparative Example 1 are as Figure 5 shown, where the left figure is Example 1 and the right figure is Comparative Example 1. By comparison, it can be seen that SEI is indeed formed in Example 1, while no SEI is formed in Comparative Example 1. SEI can slow down the influence of polysulfides on the interface of the lithium metal negative electrode, thereby improving the Coulombic efficiency of the lithium-sulfur battery.

[0105] Generally speaking, the advantages of the present invention by adding zinc bis(trifluoromethanesulfonyl)imide to the electrolyte of the lithium-sulfur battery are as follows:

[0106] (1) This additive can undergo a complexation reaction with polysulfides, and the reaction product thereof participates in the subsequent redox reaction process to inhibit the shuttle of polysulfides. In addition, zinc ions can react on the positive electrode side to generate a large number of nanoscale catalytic active sites, 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 the lithium-sulfur battery. Without the addition of such an additive, long-chain polysulfides cannot be converted, 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, so the electrochemical performance decreases significantly.

[0107] (2) The substance formed by the co-action of this additive with S and Li participates in the formation of SEI, providing a special transmission interface for Li + . On the one hand, it can slow down the erosion of polysulfides on the negative electrode, and on the other hand, it can accelerate the lithium ion transmission, thereby improving the Coulombic efficiency of the lithium-sulfur battery.

[0108] The above reflects the bifunctionality of the present invention using zinc bis(trifluoromethanesulfonyl)imide as an additive. By acting on the positive and negative electrode interfaces of the lithium-sulfur battery and jointly transforming in multiple aspects, the performance of the lithium-sulfur battery is improved.

[0109] The above are only the preferred specific embodiments of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope 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 conductive lithium salt, ether solvent and additives. The additive is bis(trifluoromethylsulfonyl)imide zinc. The content of the additive in the lithium-sulfur battery electrolyte is 0.5-2wt%.

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. The additive-containing lithium-sulfur battery electrolyte according to claim 1, characterized in that: The conductive lithium salt includes lithium bis(trifluoromethylsulfonyl)imide and / or lithium nitrate.

4. The additive-containing lithium-sulfur battery electrolyte according to claim 1, characterized in that: The ether solvents are ethylene glycol dimethyl ether and 1,3-dioxolane.

5. The additive-containing lithium-sulfur battery electrolyte according to claim 1, characterized in that: The conductive lithium salt comprises lithium bis(trifluoromethylsulfonyl imide) and lithium nitrate, wherein the concentration of lithium bis(trifluoromethylsulfonyl imide) 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.

6. Use of the lithium-sulfur battery electrolyte containing additives according to any one of claims 1 to 5 in lithium-sulfur batteries.

7. A lithium-sulfur battery, characterized in that: The invention comprises a positive electrode material, a negative electrode material, a separator and a lithium-sulfur battery electrolyte containing additives as claimed in any one of claims 1 to 5.

8. The lithium-sulfur battery according to claim 7, 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 .

9. The lithium-sulfur battery according to claim 7, characterized in that: The negative electrode material is a lithium metal sheet.

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

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