Lithium-sulfur battery electrolyte suitable for long cycle life

Abstract

The application discloses a lithium-sulfur battery electrolyte suitable for long cycle life. The electrolyte comprises an organic solvent, a lithium salt, a lithium nitrate additive and a film-forming additive selected from one or more of o-nitrotrifluorotoluene, m-nitrotrifluorotoluene and p-nitrotrifluorotoluene. The electrolyte is applied to a lithium-sulfur battery, improves the long-term cycle stability of the lithium-sulfur battery and improves the cycle life. The preparation method and the lithium-sulfur battery also have the above beneficial effects respectively.

Description

Technical Field

[0001] This application belongs to the field of lithium-sulfur batteries, specifically relating to a lithium-sulfur battery electrolyte suitable for long cycle life. Background Technology

[0002] Lithium-sulfur batteries are an important next-generation high-energy-density rechargeable battery system and have attracted widespread attention from researchers. During charging and discharging, lithium-sulfur batteries undergo a redox process involving numerous lithium polysulfide intermediates. For example, during discharge, lithium ions generated at the lithium metal anode migrate through the electrolyte to the cathode, reacting with the active material sulfur to form lithium polysulfides and lithium sulfides (Li₂S₂). n (1≤n≤8), the above reaction is a multi-electron electrochemical reaction at the liquid-solid interface. Based on the above reaction, lithium-sulfur batteries have ultra-high specific capacity (1675mAh / g) and theoretical specific energy (2600Wh / kg), and are considered to be one of the new high-energy-density secondary battery systems that can replace traditional lithium-ion batteries.

[0003] Lithium-sulfur batteries face challenges in practical application, including low actual energy density, rapid capacity decay, and short cycle life. The primary reason for this is that soluble polysulfides generated during charging and discharging diffuse to the negative electrode, undergoing irreversible chemical reactions that corrode the lithium anode, leading to severe lithium dendrite growth and rapid anode failure. Furthermore, a "shuttle effect" occurs between the sulfur cathode and lithium anode; polysulfides diffused to the anode are further reduced to insoluble lithium sulfide, resulting in the loss of active material at the cathode, hindering lithium-ion transport, and consequently causing rapid capacity decay with cycling. Therefore, improvements are urgently needed. Summary of the Invention

[0004] This application provides a lithium-sulfur battery electrolyte suitable for long cycle life, a method for preparing the same, and a lithium-sulfur battery, aiming to solve the problem that lithium-sulfur batteries cannot simultaneously achieve high energy density and long cycle life.

[0005] In a first aspect, embodiments of this application provide a lithium-sulfur battery electrolyte suitable for long cycle life, comprising an organic solvent, a lithium salt, a lithium nitrate additive, and a film-forming additive, wherein the film-forming additive is selected from one or more of o-nitrotrifluorotoluene, m-nitrotrifluorotoluene, and p-nitrotrifluorotoluene.

[0006] According to one embodiment of this application, o-nitrotrifluorotoluene and p-nitrotrifluorotoluene each independently account for a molar concentration of 400–650 mmol / L in the organic solvent.

[0007] According to one embodiment of this application, the volume fraction of m-nitrotrifluorotoluene in the mixture formed by the organic solvent and m-nitrotrifluorotoluene is 10% to 40%.

[0008] According to one embodiment of this application, the organic solvent includes a first organic solvent selected from one or more of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether.

[0009] According to one embodiment of this application, the second organic solvent is selected from one or more of 1,3-dioxolane and 1,4-dioxane.

[0010] According to one embodiment of this application, the organic solvent includes a first organic solvent and a second organic solvent, wherein the volume ratio of the first solvent to the second solvent is 3:1.

[0011] According to an embodiment of one aspect of this application, the lithium salt is selected from one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

[0012] According to one embodiment of this application, the concentration of the lithium salt is 200–2000 mmol / L.

[0013] According to one embodiment of this application, the concentration of lithium nitrate additive is 700–1000 mmol / L.

[0014] Secondly, embodiments of this application provide a method for preparing a lithium-sulfur battery electrolyte suitable for long cycle life, comprising:

[0015] Under a protective atmosphere, lithium salt, organic solvent, lithium nitrate additive, and film-forming additive are mixed to obtain an electrolyte. The film-forming additive is selected from one or more of o-nitrotrifluorotoluene, m-nitrotrifluorotoluene, and p-nitrotrifluorotoluene.

[0016] According to one embodiment of this application, the organic solvent includes a first organic solvent and a second organic solvent, wherein the first organic solvent is selected from one or more of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether; and the second organic solvent is selected from one or more of 1,3-dioxolane and 1,4-dioxane; the method includes: mixing a lithium salt with the first solvent under argon protection to obtain a mixed solution;

[0017] The mixed solution is combined with a second solvent, lithium nitrate additive, and film-forming additive to obtain an electrolyte.

[0018] Thirdly, embodiments of this application provide a lithium-sulfur battery comprising a positive electrode, a separator, a negative electrode, and an electrolyte prepared by the first aspect or the second aspect.

[0019] This application has at least the following beneficial effects:

[0020] The lithium-sulfur battery electrolyte provided in this application, suitable for long cycle life, employs specific film-forming additives such as o-nitrotrifluorotoluene, m-nitrotrifluorotoluene, and p-nitrotrifluorotoluene. On the one hand, it can effectively promote the formation of the solid electrolyte interface film at the negative electrode, making the interface film rich in nitrogen, oxygen, fluorine, and other species, which is conducive to the uniform transport of active lithium ions, thereby promoting the uniform deposition and extraction of lithium ions. On the other hand, it can also regulate the ionic solvent structure of polysulfides, reduce the harmful irreversible chemical reactions between polysulfides and the negative electrode, thus improving the long-term cycle stability and cycle life of lithium-sulfur batteries.

[0021] The method for preparing lithium-sulfur battery electrolyte suitable for long cycle life provided in this application is simple and feasible, and the prepared lithium-sulfur battery electrolyte has low viscosity, good miscibility and high stability.

[0022] The lithium-sulfur battery provided in this application exhibits excellent cycle life and coulombic efficiency. As demonstrated in the examples, a lithium-sulfur battery constructed with a suitable lithium-sulfur battery electrolyte for long cycle life can achieve an initial energy density of 400–500 Wh / kg and 100–200 cycles with 80% capacity retention. This lithium-sulfur battery electrolyte is an electrolyte with significant research value and practical application potential. Detailed Implementation

[0023] To make the purpose, technical solution, and beneficial technical effects of this application clearer, the following detailed description is provided in conjunction with embodiments. It should be understood that the embodiments described in this specification are merely for explaining this application and are not intended to limit it.

[0024] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, every point or individual value between the endpoints of the range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value or with other lower or upper limits to form a range not explicitly stated.

[0025] In the description of this application, it should be noted that, unless otherwise stated, "above" and "below" include the stated number, and "multiple" in "one or more" means two or more.

[0026] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0027] Lithium-sulfur batteries face challenges in practical application, including low actual energy density, rapid discharge capacity decay, and short cycle life.

[0028] Research has shown that a uniform and stable solid electrolyte interfacial film formed by the reaction of electrolyte components and lithium metal at the negative electrode can prevent polysulfides from corroding lithium metal and suppress continuous side reactions between the electrolyte and lithium metal at the negative electrode. Simultaneously, the solid electrolyte film can also modulate the Li... + Deposition and removal behavior can mitigate lithium dendrite growth, thereby extending the cycle life of the battery. As a crucial component of lithium-sulfur batteries, the electrolyte is of great significance for extending the cycle life of lithium-sulfur batteries. By designing the electrolyte composition to regulate the ionic solvent structure of polysulfides and promoting the formation of a uniform and stable protective solid electrolyte interface film at the negative electrode, the cycle life of lithium-sulfur batteries can be significantly extended.

[0029] Extending the cycle life of lithium-sulfur batteries still cannot meet the needs of practical applications, especially in high-energy-density lithium-sulfur battery devices. Therefore, further research is required.

[0030] Electrolytes for lithium-sulfur batteries with long cycle life

[0031] In a first aspect, embodiments of this application provide a lithium-sulfur battery electrolyte suitable for long cycle life, comprising an organic solvent, a lithium salt, a lithium nitrate additive, and a film-forming additive, wherein the film-forming additive is selected from one or more of o-nitrotrifluorotoluene, m-nitrotrifluorotoluene, and p-nitrotrifluorotoluene.

[0032] According to the embodiments of this application, the organic solvent can be an ether-based solvent, and therefore the electrolyte of this application can be an ether-based electrolyte.

[0033] According to the embodiments of this application, film-forming additives such as o-nitrotrifluorotoluene, m-nitrotrifluorotoluene, and p-nitrotrifluorotoluene are added to the electrolyte. These additives interact with other substances, enabling the electrolyte to be used in lithium-sulfur batteries. This effectively promotes the formation of the solid electrolyte interface film at the negative electrode, which is beneficial for the uniform transport of lithium ions. At the same time, it can also regulate the ionic solvent structure of polysulfides, reduce harmful irreversible chemical reactions between polysulfides and the negative electrode, thereby improving the stability of the lithium-sulfur battery during long-term charge-discharge cycles and increasing cycle life.

[0034] According to the embodiments of this application, the presence of lithium nitrate additive in the electrolyte can effectively reduce the probability of overcharging during the charging process of lithium-sulfur batteries containing the electrolyte, which is beneficial to improving the reliability of lithium-sulfur batteries.

[0035] In some embodiments, o-nitrotrifluorotoluene and p-nitrotrifluorotoluene each independently account for a molar concentration of 400–650 mmol / L in the organic solvent.

[0036] For example, the molar concentration of o-nitrotrifluorotoluene or p-nitrotrifluorotoluene can be any value or any combination thereof from 400 mmol / L, 450 mmol / L, 500 mmol / L, 550 mmol / L, 600 mmol / L, 650 mol / L.

[0037] According to the embodiments of this application, o-nitrotrifluorotoluene and p-nitrotrifluorotoluene are added to the electrolyte, and their concentrations are within a suitable range. This can effectively promote the formation of the solid electrolyte interface film at the negative electrode, which is beneficial to the uniform transport of lithium ions. At the same time, it can also regulate the ionic solvent structure of polysulfides, reduce the harmful irreversible chemical reactions between polysulfides and the negative electrode, thereby improving the stability of the lithium-sulfur battery during long-term charge-discharge cycles.

[0038] In some embodiments, the volume fraction of m-nitrotrifluorotoluene in the mixture formed by the organic solvent and m-nitrotrifluorotoluene is 10% to 40%.

[0039] For example, the volume fraction of m-nitrotrifluorotoluene can be any value or any combination thereof from 10%, 15%, 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 35%, 40%.

[0040] According to the embodiments of this application, m-nitrotrifluorotoluene is added to the electrolyte. When its volume fraction is within a suitable range, it can effectively promote the formation of the solid electrolyte interface film at the negative electrode, which is beneficial to the uniform transport of lithium ions. At the same time, it can also regulate the ionic solvent structure of polysulfides, reduce the harmful irreversible chemical reaction between polysulfides and the negative electrode, thereby improving the stability of the lithium-sulfur battery during long-term discharge-charge cycles.

[0041] In some embodiments, the organic solvent includes a first organic solvent selected from one or more of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether.

[0042] According to embodiments of this application, the -O- group in the above-mentioned compound contains a lone pair of electrons and has a strong electron-donating ability, so it can react with Li in polysulfides that have electron-withdrawing ability. +It produces a strong coordination effect; the first organic solvent has the advantages of low viscosity, strong solubility and low cost. The addition of the first organic solvent can not only improve the conductivity of the lithium-sulfur battery electrolyte, but also accelerate the dissolution of polysulfides in the electrolyte, accelerate the conversion reaction kinetics of the positive electrode, and achieve the effect of extending the cycle life of the lithium-sulfur battery.

[0043] In some embodiments, the second organic solvent is selected from one or more of 1,3-dioxolane and 1,4-dioxane.

[0044] According to embodiments of this application, the -O- group in the above-mentioned compound contains a lone pair of electrons and has a strong electron-donating ability, so it can react with Li in polysulfides that have electron-withdrawing ability. + It produces a strong coordination effect; the second organic solvent has the advantages of low viscosity, strong solubility and low cost. The addition of the second organic solvent can not only improve the conductivity of the lithium-sulfur battery electrolyte, but also accelerate the dissolution of polysulfides in the electrolyte, accelerate the conversion reaction kinetics of the positive electrode, and achieve the effect of extending the cycle life of the lithium-sulfur battery.

[0045] In some embodiments, the organic solvent includes a first organic solvent and a second organic solvent, wherein the volume ratio of the first solvent to the second solvent is 3:1.

[0046] In some embodiments, the lithium salt is selected from one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

[0047] For example, the lithium salt in the electrolyte can be lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, or a mixture of both. The addition of these lithium salts helps the lithium-sulfur battery containing this electrolyte to maintain a certain level of active lithium ions during the initial stages of charging and discharging, thus improving the performance of the lithium-sulfur battery.

[0048] In some embodiments, the concentration of lithium salt is 200–2000 mmol / L.

[0049] For example, the concentration of lithium salt in the electrolyte can be any value or any combination thereof from 200 mmol / L, 300 mmol / L, 400 mmol / L, 500 mmol / L, 600 mmol / L, 700 mmol / L, 800 mmol / L, 900 mmol / L, 1000 mmol / L, 1500 mmol / L, 2000 mmol / L.

[0050] According to embodiments of this application, a suitable concentration of lithium salt in the electrolyte promotes the dissolution of polysulfides and the discharge / charge process of lithium-sulfur batteries. +It can not only transport substances, but also participate in the reaction between the electrodes and the electrolyte, promoting the formation of a solid electrolyte interface film, thereby improving the cycle performance of the battery.

[0051] In some embodiments, the concentration of lithium nitrate auxiliaries is 700–1000 mmol / L.

[0052] For example, the mass fraction of lithium nitrate additive in the electrolyte can be any value or any combination of values ​​from 700 mmol / L, 800 mmol / L, 900 mmol / L, or 1000 mmol / L.

[0053] According to embodiments of this application, adding an appropriate amount of lithium nitrate additive to the electrolyte can improve the coulombic efficiency of lithium-sulfur batteries and reduce the probability of overcharging of lithium-sulfur batteries to a certain extent.

[0054] Preparation method of lithium-sulfur battery electrolyte suitable for long cycle life

[0055] Secondly, embodiments of this application provide a method for preparing a lithium-sulfur battery electrolyte suitable for long cycle life, comprising:

[0056] Under a protective atmosphere, lithium salt, organic solvent, lithium nitrate additive, and film-forming additive are mixed to obtain an electrolyte. The film-forming additive is selected from one or more of o-nitrotrifluorotoluene, m-nitrotrifluorotoluene, and p-nitrotrifluorotoluene.

[0057] Understandably, to ensure the lithium salt and additives are fully dissolved, they need to be thoroughly dissolved and dispersed in an organic solvent. This can be achieved by adding the solvent at room temperature and stirring until completely dissolved, then shaking until fully miscible, thus obtaining a lithium-sulfur battery electrolyte suitable for long cycle life.

[0058] The method for preparing a lithium-sulfur battery electrolyte suitable for long cycle life according to the embodiments of this application is simple, and the prepared lithium-sulfur battery electrolyte has low viscosity, good miscibility, and stable system.

[0059] In some embodiments, the organic solvent includes a first organic solvent and a second organic solvent, wherein the first organic solvent is selected from one or more of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether; and the second organic solvent is selected from one or more of 1,3-dioxolane and 1,4-dioxane.

[0060] The method includes: mixing a lithium salt with a first solvent under argon protection to obtain a mixed solution;

[0061] The mixed solution is combined with a second solvent, lithium nitrate additive, and film-forming additive to obtain an electrolyte.

[0062] According to the embodiments of this application, by mixing lithium salt with a first solvent and then adding other components, the lithium salt can be fully dissolved, making the electrolyte more uniformly dispersed.

[0063] Lithium-sulfur batteries

[0064] Thirdly, embodiments of this application provide a lithium-sulfur battery, including a positive electrode, a separator, a negative electrode, and a lithium-sulfur battery electrolyte suitable for long cycle life according to the first aspect or an electrolyte prepared by the preparation method of the second aspect.

[0065] According to the embodiments of this application, the lithium-sulfur battery is subjected to discharge-charge cycle testing at 25°C. The energy density of the first cycle is 400-500Wh / kg, and the number of stable cycles when the cycle capacity retention rate is 80% is 100-200.

[0066] According to embodiments of this application, the positive electrode may include a current collector and a film layer located on any layer of the current collector surface. The film layer may contain elemental sulfur as an active material, carbon as a conductive agent, and a binder. The current collector may be a metal foil or a composite current collector. For example, the metal foil may be aluminum foil. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer.

[0067] In some embodiments, the negative electrode may include a lithium metal foil and a current collector, wherein the current collector may be a copper foil.

[0068] In some embodiments, the diaphragm material can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The diaphragm can be a single-layer film or a multi-layer composite film, without particular limitation.

[0069] The lithium-sulfur battery according to the embodiments of this application, since it includes the lithium-sulfur battery electrolyte in any of the embodiments of the first aspect, hinders the reaction between polysulfides and metallic lithium while ensuring the positive electrode kinetics, thereby improving the cycle life and coulombic efficiency of the lithium-sulfur battery. Therefore, the lithium-sulfur battery according to the embodiments of this application can be applied to energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as multiple fields such as power tools, military equipment, and aerospace.

[0070] Example

[0071] The following embodiments describe the disclosure of this application in more detail. These embodiments are merely illustrative, as various modifications and variations will be apparent to those skilled in the art within the scope of the disclosure of this application. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on weight, and all reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing, and the instruments used in the embodiments are commercially available.

[0072] Example 1

[0073] This embodiment provides a method for preparing a lithium-sulfur battery electrolyte suitable for long cycle life, including:

[0074] 1) In a glove box under an argon atmosphere, weigh out lithium bis(trifluoromethanesulfonyl)imide according to the stoichiometric ratio and add it to a reagent bottle. Then slowly add the first solvent, ethylene glycol dimethyl ether, and stir to fully dissolve the lithium salt in the first solvent.

[0075] 2) The second solvent was added at a volume ratio of 3:1 between the first solvent and the second solvent, followed by the film-forming additive o-nitrotrifluorotoluene, and then the lithium nitrate additive. The mixture was stirred until no solid precipitates to obtain the electrolyte. The concentration of lithium bis(trifluoromethanesulfonyl)imide lithium salt was 500 mmol / L, the concentration of o-nitrotrifluorotoluene was 500 mmol / L, and the concentration of lithium nitrate additive was 800 mmol / L.

[0076] Fabrication of a 3Ah lithium-sulfur pouch cell: The electrolyte was prepared under an argon protective atmosphere. The positive electrode used a sulfur loading of 8 mg / cm³. 2 The double-sided S / C composite positive electrode uses 75μm lithium metal as the negative electrode, and the separator uses polypropylene membrane (PP). The electrolyte mass to active material mass ratio is 2.8g / g. A lithium-sulfur soft pack with a capacity of 3Ah was produced in a dry chamber.

[0077] Comparative Example 1

[0078] The difference between this comparative example and Example 1 is that o-nitrotrifluorotoluene is not added, while the other components and preparation process remain the same as in Example 1.

[0079] Example 2: Effect of Film-Forming Additive Type

[0080] The difference between this embodiment and Example 1 is that the type of film-forming additive is changed to m-nitrotrifluorotoluene; and the volume fraction of m-nitrotrifluorotoluene is 25%, while the other components and preparation process remain the same as in Example 1.

[0081] Example 3: Effect of Film-Forming Additive Type

[0082] The difference between this embodiment and Example 1 is that the type of film-forming additive is changed to p-nitrotrifluorotoluene; the molar concentration of p-nitrotrifluorotoluene is 500 mmol / L, and the other components and preparation process are the same as in Example 1.

[0083] Example 4: Effect of film-forming additive volume fraction

[0084] The difference between this embodiment and Embodiment 2 is that the volume fraction of the film-forming additive is changed to 10%, while the other components and preparation process remain the same as in Embodiment 2.

[0085] Example 5: Effect of film-forming additive volume fraction

[0086] The difference between this embodiment and Embodiment 2 is that the volume fraction of the film-forming additive is changed to 40%, while the other components and preparation process remain the same as in Embodiment 2.

[0087] Performance testing

[0088] The prepared pouch cell was left to stand at 25°C for 12 hours, and then its performance was tested at the same temperature. The cell was subjected to constant current charge-discharge cycles at 0.05C (1C = 1000mA / g) within a voltage range of 1.7V to 2.6V. The first discharge capacity of the cell was recorded as C0, and the first discharge energy was recorded as E0.

[0089] Soft-pack battery weight measurement: Place the battery on an electronic balance until the weight stabilizes, and read the battery weight value M0.

[0090] Energy density calculation: The energy density of this pouch battery is calculated as follows: battery discharge energy E0 / battery weight M0. The test results of the examples and comparative examples are shown in the table below.

[0091] Under the above cycle test conditions, the number of cycles required for the lithium-sulfur pouch battery to retain 80% of its initial capacity is shown in the table below.

[0092]

[0093]

[0094] The experimental results above show that in Examples 1, 2, and 3, the film-forming additives o-nitrotrifluorotoluene, m-nitrotrifluorotoluene, and p-nitrotrifluorotoluene all have a significant impact on the cycle stability of the electrolyte, ensuring the long-term cycle stability of the lithium-sulfur battery. Lithium-sulfur battery electrolytes without added film-forming additives cannot achieve the long cycle life of lithium-sulfur batteries.

[0095] As can be seen from Examples 2, 4, and 5 above, the volume fraction of the film-forming additive has a significant impact on the first-cycle energy density and cycle life of the lithium-sulfur battery electrolyte. When the volume fraction of the film-forming additive is reduced to 10%, the first-cycle energy density of the battery will be increased, but the cycle life will also be reduced; while when the volume fraction is too large, the positive electrode kinetics will be impaired, and the cycle life of the battery will be controlled by the positive electrode, thus reducing the cycle life.

[0096] Example 6

[0097] This embodiment provides a method for preparing a lithium-sulfur battery electrolyte suitable for long cycle life, including:

[0098] 1) In a glove box under an argon atmosphere, weigh out lithium bis(trifluoromethanesulfonyl)imide according to the stoichiometric ratio and add it to a reagent bottle. Then slowly add the first solvent, ethylene glycol dimethyl ether, and stir to fully dissolve the lithium salt in the first solvent.

[0099] 2) Add the second solvent at a volume ratio of 3:1 (first solvent:second solvent) to 1,3-dioxolane. Then add the film-forming additives o-nitrotrifluorotoluene and p-nitrotrifluorotoluene, and then add the lithium nitrate auxiliary agent. Stir until no solid precipitates, so that the concentration of lithium salt bis(trifluoromethanesulfonyl)imide lithium is 500 mmol / L, the concentration of film-forming additives o-nitrotrifluorotoluene and p-nitrotrifluorotoluene is 500 mmol / L, and the concentration of lithium nitrate auxiliary agent is 800 mmol / L.

[0100] The electrolyte prepared using this method was applied to a 3Ah lithium-sulfur pouch cell as described in Example 1 and tested using the above method. It was found that it could achieve an initial energy density of 443Wh / kg and a cycle capacity retention of 80% for 156 cycles.

[0101] Example 7: Effect of Lithium Salt Type

[0102] This embodiment provides a method for preparing a lithium-sulfur battery electrolyte suitable for long cycle life, including:

[0103] 1) In an argon atmosphere glove box, weigh lithium bis(fluorosulfonyl)imide according to the stoichiometric ratio and add it to a reagent bottle. Then slowly add the first solvent, ethylene glycol dimethyl ether, and stir to fully dissolve the lithium salt in the first solvent.

[0104] 2) Add the second solvent at a volume ratio of 3:1 (first solvent to second solvent 1,3-dioxolane), then add the film-forming additive o-nitrotrifluorotoluene, and then add the lithium nitrate auxiliary agent. Stir until no solid precipitates, so that the concentration of lithium salt bis(fluorosulfonyl)imide lithium is 500 mmol / L, the concentration of film-forming additive o-nitrotrifluorotoluene is 500 mmol / L, and the concentration of lithium nitrate auxiliary agent is 800 mmol / L.

[0105] The electrolyte prepared using this method was applied to a 3Ah lithium-sulfur pouch cell as described in Example 1 and tested according to the above method. It was found that it could achieve an initial energy density of 431Wh / kg and a cycle capacity retention of 80% for 139 cycles.

[0106] Example 8 Effect of Lithium Salt Concentration

[0107] The difference between this embodiment and Example 1 is that the concentration of lithium salt bis(trifluoromethanesulfonyl)imide lithium is changed from 500 mmol / L to 200 mmol / L, while the other components and preparation process remain the same as in Example 1.

[0108] The electrolyte prepared using this method was applied to a 3Ah lithium-sulfur pouch cell as described in Example 1 and tested according to the above method. It was found that it could achieve an initial energy density of 441Wh / kg and a cycle capacity retention of 80% for 112 cycles.

[0109] Example 9 Effect of Lithium Salt Concentration

[0110] The difference between this embodiment and Example 1 is that the concentration of lithium salt bis(trifluoromethanesulfonyl)imide lithium is changed from 500 mmol / L to 2000 mmol / L, while the other components and preparation process remain the same as in Example 1.

[0111] The electrolyte prepared using this method was tested in a 3Ah lithium-sulfur pouch cell as described in Example 1. It was found that it could achieve an initial energy density of 426Wh / kg and a stable cycle count of 133 cycles with 80% capacity retention.

[0112] Example 10 Effect of Lithium Nitrate Additive Concentration

[0113] The difference between this embodiment and Example 1 is that the concentration of lithium nitrate auxiliaries is changed from 800 mmol / L to 700 mmol / L, while the other components and preparation process remain the same as in Example 1.

[0114] The electrolyte prepared using this method was tested in a 3Ah lithium-sulfur pouch cell as described in Example 1. It was found that it could achieve an initial energy density of 432Wh / kg and a stable cycle count of 118 cycles with 80% capacity retention.

[0115] Example 11 Effect of Lithium Nitrate Additive Concentration

[0116] The difference between this embodiment and Example 1 is that the concentration of lithium nitrate auxiliaries is changed from 800 mmol / L to 1000 mmol / L, while the other components and preparation process remain the same as in Example 1.

[0117] The electrolyte prepared using this method was tested in a 3Ah lithium-sulfur pouch cell as described in Example 1. It was found that it could achieve an initial energy density of 429Wh / kg and a stable cycle count of 136 cycles with a capacity retention of 80%.

[0118] Example 12

[0119] This embodiment provides a method for preparing a lithium-sulfur battery electrolyte suitable for long cycle life, including:

[0120] 1) In an argon atmosphere glove box, weigh out lithium salt bis(trifluoromethanesulfonyl)imide lithium according to the stoichiometric ratio and add it to a reagent bottle. Then slowly add the first solvent diethylene glycol dimethyl ether and stir to fully dissolve the lithium salt in the first solvent.

[0121] 2) Add the second solvent at a volume ratio of 3:1 (first solvent to second solvent 1,4-dioxane), then add the film-forming additive o-nitrotrifluorotoluene, and then add the lithium nitrate auxiliary agent. Stir until no solid precipitates, so that the concentration of lithium salt bis(trifluoromethanesulfonyl)imide lithium is 500 mmol / L, the concentration of film-forming additive o-nitrotrifluorotoluene is 500 mmol / L, and the concentration of lithium nitrate auxiliary agent is 800 mmol / L.

[0122] The electrolyte prepared using this method was applied to a 3Ah lithium-sulfur pouch cell as described in Example 1 and tested using the above method. It was found that it could achieve an initial energy density of 421Wh / kg and a cycle capacity retention of 80% for 129 cycles.

[0123] Based on the performance test results above, it can be seen that the lithium-sulfur battery containing the electrolyte of the examples exhibits improved stability and cycle life during discharge-charge cycles. In contrast, the lithium-sulfur battery using the electrolyte of Comparative Example 1, lacking the aforementioned film-forming additives, performs significantly worse than the lithium-sulfur battery using the electrolyte of the examples.

[0124] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in this application, and these modifications or substitutions should all be covered within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A lithium-sulfur battery electrolyte suitable for long cycle life, comprising an organic solvent, a lithium salt, a lithium nitrate additive, and a film-forming additive, wherein the film-forming additive is selected from one or more of o-nitrotrifluorotoluene, m-nitrotrifluorotoluene, and p-nitrotrifluorotoluene; When the film-forming additive includes o-nitrotrifluorotoluene and p-nitrotrifluorotoluene, the o-nitrotrifluorotoluene and p-nitrotrifluorotoluene each independently account for a molar concentration of 400~650 mmol / L in the organic solvent; When the film-forming additive includes m-nitrotrifluorotoluene, the volume fraction of m-nitrotrifluorotoluene in the mixture formed by the organic solvent and m-nitrotrifluorotoluene is 10% to 40%; The organic solvent includes a first organic solvent and a second organic solvent, wherein the first organic solvent is selected from one or more of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether; The second organic solvent is selected from one or more of 1,3-dioxolane and 1,4-dioxane; The lithium salt is selected from one or more of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

2. The electrolyte as described in claim 1, characterized in that, The organic solvent includes a first organic solvent and a second organic solvent, and the volume ratio of the first organic solvent to the second organic solvent is 3:

1.

3. The electrolyte as described in claim 1, characterized in that, The concentration of the lithium salt is 200~2000 mmol / L.

4. The electrolyte as described in claim 1, characterized in that, The concentration of the lithium nitrate additive is 700~1000 mmol / L.

5. A method for preparing an electrolyte as described in any one of claims 1 to 4, characterized in that, include: Under a protective atmosphere, lithium salt, organic solvent, lithium nitrate additive, and film-forming additive are mixed to obtain the electrolyte. The film-forming additive is selected from one or more of o-nitrotrifluorotoluene, m-nitrotrifluorotoluene, and p-nitrotrifluorotoluene.

6. The preparation method according to claim 5, characterized in that, The organic solvent includes a first organic solvent and a second organic solvent, wherein the first organic solvent is selected from one or more of ethylene glycol dimethyl ether and diethylene glycol dimethyl ether; and the second organic solvent is selected from one or more of 1,3-dioxolane and 1,4-dioxane. Under argon protection, the lithium salt is mixed with the first organic solvent to obtain a mixed solution; The mixed solution is mixed with a second organic solvent, lithium nitrate additive and film-forming additive to obtain the electrolyte.

7. A lithium-sulfur battery, characterized in that, It includes a positive electrode, a separator, a negative electrode, and a lithium-sulfur battery electrolyte suitable for long cycle life as described in any one of claims 1 to 4, or an electrolyte prepared by the preparation method described in claim 5 or 6.

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