Lithium-sulfur battery, preparation method thereof and electric equipment

Abstract

The lithium-sulfur battery comprises a positive pole piece, a negative pole piece and an electrolyte, the positive pole piece comprises a positive current collector, at least one side of the positive current collector is provided with a positive active material layer, the positive active material layer comprises a positive active material, and the positive active material comprises a substrate, at least part of the surface of the substrate is provided with a coating layer, the substrate comprises a sulfur-based material, and the coating layer comprises a conductive polymer; the electrolyte comprises a solvent and a fluorine-containing diluent. Therefore, the conductive polymer on the surface of the positive electrode active material can swell to absorb the lithium salt-solvent cluster, and then the lithium polysulfide can be dissolved in the lithium salt-solvent cluster in the surface conductive polymer coating layer, so that the reaction of sulfur is a solid-liquid-solid reaction, the reaction rate is increased, and the rate capability of the battery is improved; meanwhile, the probability that the lithium polysulfide shuttles back and forth to the negative electrode can be reduced, the side reaction between the lithium polysulfide and the negative electrode lithium is reduced, and the capacity and the cycle performance of the battery are improved.

Description

Technical Field

[0001] This application relates to the field of batteries, specifically to lithium-sulfur batteries and their preparation methods and electrical equipment. Background Technology

[0002] Batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, but also widely used in electric vehicles such as electric bicycles, electric motorcycles and electric cars, as well as in military equipment and aerospace and other fields.

[0003] Lithium-sulfur batteries are a type of lithium battery that uses sulfur as the positive electrode and metallic lithium as the negative electrode. Elemental sulfur is abundant on Earth and is characterized by its low price and environmental friendliness. Lithium-sulfur batteries using sulfur as the positive electrode material have high theoretical specific capacity and theoretical specific energy. However, lithium polysulfides, an intermediate product of lithium-sulfur batteries, are readily soluble in the electrolyte and can shuttle to the metallic lithium side of the negative electrode. There, they undergo side reactions with the metallic lithium, consuming it and forming non-conductive lithium sulfide coatings on the surface of the metallic lithium, leading to a decrease in capacity and cycle performance. Summary of the Invention

[0004] The first aspect of this application provides a lithium-sulfur battery, comprising: a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector, and at least one side of the positive current collector is provided with a positive active material layer. The positive active material layer includes a positive active material, which comprises: a substrate, at least a portion of the surface of the substrate having a coating layer, the substrate comprising a sulfur-based material, and the coating layer comprising a conductive polymer. The electrolyte comprises a solvent and a fluorinated diluent. Thus, the conductive polymer on the surface of the positive active material can swell and absorb lithium salt-solvent clusters, thereby allowing lithium polysulfides to dissolve in the lithium salt-solvent clusters within the conductive polymer coating layer. This makes the sulfur reaction a solid-liquid-solid reaction, increasing the reaction rate and improving the battery's rate performance. Simultaneously, it reduces the probability of lithium polysulfides shuttling to the negative electrode, decreasing side reactions between lithium polysulfides and negative electrode lithium, and improving the battery's capacity and cycle performance.

[0005] According to some embodiments of this application, the fluorinated diluent includes one or more of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. This forms a locally highly concentrated electrolyte, reducing lithium polysulfide shuttling.

[0006] According to some embodiments of this application, the solvent includes one or more of the following: dimethyl ether, 1,2-dimethoxypropane, dimethoxymethane, ethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, pentaethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, triethylene glycol diethyl ether, tetraethylene glycol diethyl ether, pentaethylene glycol diethyl ether, ethylene glycol dibutyl ether, and diethylene glycol dibutyl ether, and 1,3-dioxane. This improves the solubility of the lithium salt.

[0007] According to some embodiments of this application, the mass ratio of the fluorinated diluent to the solvent is 1.25-19. This results in a locally highly concentrated electrolyte, reducing lithium polysulfide shuttling.

[0008] According to some embodiments of this application, the fluorinated diluent accounts for 50%-95% of the total mass of the electrolyte.

[0009] According to some embodiments of this application, the solvent accounts for 5%-40% of the total mass of the electrolyte.

[0010] Therefore, by keeping the contents of solvent and fluorinated diluent within the above range, a locally highly concentrated electrolyte is formed, reducing the shuttle of lithium polysulfides.

[0011] According to some embodiments of this application, the conductive polymer includes one or more of polyaniline, polydioxyethylthiophene, and polypyrrole. This allows for the absorption of lithium salt-solvent clusters, enabling lithium polysulfides to dissolve in the lithium salt-solvent clusters within the surface conductive polymer coating layer, thereby making the sulfur reaction a solid-liquid-solid reaction and increasing the reaction rate.

[0012] According to some embodiments of this application, the thickness of the coating layer is 1 nm-20 nm. This improves the absorption effect on lithium salt-solvent clusters.

[0013] According to some embodiments of this application, the molecular weight of the conductive polymer is 5000-100000. This improves the absorption effect on lithium salt-solvent clusters.

[0014] According to some embodiments of this application, the positive electrode active material further includes a conductive layer located on at least a portion of the surface of the substrate, and the coating layer located on at least a portion of the surface of the conductive layer. This improves the electronic conductivity of the positive electrode active material.

[0015] According to some embodiments of this application, the electrolyte further includes an electrolyte salt, which includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, or lithium tetrafluorooxalate phosphate. This improves the ionic conductivity of the electrolyte.

[0016] According to some embodiments of this application, the mass percentage of the electrolyte salt is 1%-8% based on the total mass of the electrolyte. This improves the ionic conductivity of the electrolyte.

[0017] According to some embodiments of this application, the sulfur-based material includes one or more of elemental sulfur, sulfur-selenium complex, and sulfur-tellurium complex.

[0018] A second aspect of this application provides a method for preparing a lithium-sulfur battery. The method includes: mixing a conductive polymer, a sulfur-based material, and a solvent, reacting the mixture, and drying it to obtain a positive electrode active material. The positive electrode active material includes a matrix, and at least a portion of the surface of the matrix has a coating layer. The matrix includes the sulfur-based material, and the coating layer includes the conductive polymer. A slurry containing the positive electrode active material is formed on at least one side of a positive electrode current collector to obtain a positive electrode sheet. The positive electrode sheet, a negative electrode sheet, and an electrolyte are assembled into a lithium-sulfur battery. The electrolyte includes a solvent and a fluorinated diluent. This yields a lithium-sulfur battery with both excellent specific capacity and cycle performance.

[0019] According to some embodiments of this application, the method further includes: mixing the sulfur-based material and the conductive carbon material, heating under an inert gas atmosphere to form a conductive carbon layer on at least the surface of the substrate; mixing the positive electrode active material containing the conductive carbon layer, the conductive polymer, and the solvent, reacting the mixture, and drying it to form the coating layer on at least a portion of the surface of the conductive carbon layer. This improves the electronic conductivity of the positive electrode active material.

[0020] According to some embodiments of this application, the heating temperature is 120℃-200℃. This improves the coating effect of the conductive carbon.

[0021] The third aspect of this application provides an electrical device, including a lithium-sulfur battery provided in the first aspect of this application or a lithium-sulfur battery prepared by the method provided in the second aspect of this application.

[0022] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0023] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0024] Figure 1 This is a schematic diagram of the structure of the positive electrode active material prepared in Example 2 of this application.

[0025] Figure 2 This is a schematic flowchart of a method for preparing a lithium-sulfur battery according to an embodiment of this application.

[0026] Figure 3 This is a schematic diagram of a battery according to one embodiment of this application.

[0027] Figure 4 yes Figure 3 An exploded view of a lithium-sulfur battery according to one embodiment of this application is shown.

[0028] Figure 5 This is a schematic diagram of a battery module according to one embodiment of this application.

[0029] Figure 6 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0030] Figure 7 yes Figure 6 An exploded view of a battery pack according to one embodiment of this application is shown.

[0031] Figure 8 This is a schematic diagram of an electrical device using a lithium-sulfur battery as a power source according to one embodiment of this application.

[0032] Explanation of reference numerals in the attached figures:

[0033] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Lithium-sulfur battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0034] The embodiments of the technical solution of this application are described in detail below. The following embodiments are only used to illustrate the technical solution of this application more clearly, and are therefore only examples, and should not be used to limit the scope of protection of this application.

[0035] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0036] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0037] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0038] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0039] Currently, judging from market trends, battery applications are becoming increasingly widespread. Batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of battery applications, market demand is also constantly increasing.

[0040] Lithium-sulfur batteries have the advantage of high theoretical specific capacity. However, lithium polysulfides, an intermediate product, are readily soluble in the electrolyte and can shuttle to the negative electrode lithium metal side. There, they undergo side reactions with the lithium metal, consuming it and forming non-conductive lithium sulfide coatings on the lithium metal surface, leading to a decrease in capacity and cycle performance. Related technologies employ locally concentrated electrolytes to suppress lithium polysulfide shuttle. Specifically, a locally concentrated electrolyte includes lithium salt, solvent, and diluent. The introduction of the diluent reduces the total salt concentration in the electrolyte while preserving the local coordination environment of the lithium salt-solvent clusters. The lithium salt and solvent can generate strong coordination to form an electrolyte of a certain concentration, while the diluent's coordination ability with lithium ions remains at a low level. This results in very low or no solubility of the lithium salt in the diluent, thus forming a locally concentrated electrolyte.

[0041] A diluent is introduced into the locally concentrated electrolyte. Since lithium polysulfides cannot dissolve in the diluent, the shuttle movement of lithium polysulfides can be suppressed. However, in lithium-sulfur batteries containing locally concentrated electrolytes, the interaction between the positive electrode active material and the lithium salt-solvent clusters in the locally concentrated electrolyte is weak. Some lithium salt-solvent clusters are free in a position far away from the positive electrode. The sulfur in the positive electrode active material is mostly in contact with the diluent (e.g., fluorinated ethers), while the intermediate product lithium polysulfides are insoluble in most diluents (e.g., fluorinated ethers). This results in the reaction of sulfur in the positive electrode being a solid-solid reaction, which reduces the battery capacity and cycle performance.

[0042] The lithium-sulfur battery proposed in this application utilizes a conductive polymer coating layer formed on the surface of the positive electrode active material. This conductive polymer swells and absorbs a lithium salt-solvent cluster (when the lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI) and the solvent is dimethyl ethylene glycol (DME), the lithium salt-solvent cluster is Li...). + -DME-FSI - This process enriches lithium salt-solvent clusters in the conductive polymer coating layer, allowing lithium polysulfides to dissolve in the lithium salt-solvent clusters within the conductive polymer coating layer. This results in a solid-liquid-solid reaction of sulfur, leading to higher rate performance and higher specific capacity in the battery. Furthermore, the enrichment of lithium polysulfides on the surface of the positive electrode active material reduces the amount of lithium polysulfides that shuttle to the negative electrode, thereby improving the battery's cycle performance.

[0043] The lithium-sulfur battery proposed in this application can be used in electrical devices that use lithium-sulfur batteries as a power source or in various energy storage systems that use batteries as energy storage elements. Electrical devices can include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys can include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc., while spacecraft can include airplanes, rockets, space shuttles, and spacecraft, etc.

[0044] The first aspect of this application provides a lithium-sulfur battery, comprising a positive electrode, a negative electrode, and an electrolyte. The positive electrode includes a positive current collector, and at least one side of the positive current collector has a positive active material layer, the positive active material layer comprising a positive active material. (Refer to...) Figure 1 The positive electrode active material includes: a matrix, at least a portion of the surface of the matrix having a coating layer, the matrix comprising a sulfur-based material, and the coating layer comprising a conductive polymer; the electrolyte comprising a fluorinated diluent.

[0045] The lithium-sulfur battery proposed in this application features a conductive polymer on the surface of the positive electrode active material that can swell and absorb lithium salt-solvent clusters. Consequently, lithium polysulfides can dissolve in the lithium salt-solvent clusters within the conductive polymer coating layer, making the sulfur reaction a solid-liquid-solid reaction. This increases the reaction rate and improves the rate performance of the lithium-sulfur battery. Simultaneously, it reduces the probability of lithium polysulfides shuttling to the negative electrode, decreases side reactions between lithium polysulfides and negative electrode lithium, and improves the capacity and cycle performance of the lithium-sulfur battery.

[0046] In this application, the method for detecting conductive polymers in the positive electrode active material can be as follows: A positive electrode slurry containing positive electrode active material and electrolyte can be obtained by disassembling a lithium-sulfur slurry battery. The positive electrode active material and liquid electrolyte can be obtained separately by centrifugation. Infrared and Raman spectroscopy analyses are performed on the positive electrode active material. By comparing the characteristic absorption peaks of different conductive polymers, the types of conductive polymers contained in the positive electrode active material can be determined. Further analysis using transmission electron microscopy and EDS can determine the distribution and thickness of the conductive polymers in the positive electrode active material. In addition, combined chromatographic and mass spectrometric analysis of the obtained liquid electrolyte can determine the types and contents of lithium salts, ether solvents, and fluorinated diluents.

[0047] According to some embodiments of this application, the fluorinated diluent includes one or more of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. This forms a locally highly concentrated electrolyte, reducing lithium polysulfide shuttle behavior. Therefore, the aforementioned types of fluorinated diluents can reduce electrolyte viscosity, improve wetting properties, maintain the electrochemical stability of highly concentrated electrolytes, inhibit lithium dendrite formation, increase ionic conductivity, and improve the capacity and cycle performance of batteries containing them.

[0048] According to some embodiments of this application, the solvent includes one or more of the following: dimethyl ether, 1,2-dimethoxypropane, dimethoxymethane, ethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, pentaethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, triethylene glycol diethyl ether, tetraethylene glycol diethyl ether, pentaethylene glycol diethyl ether, ethylene glycol dibutyl ether, and diethylene glycol dibutyl ether, and 1,3-dioxane. This improves the solubility of the lithium salt.

[0049] According to some embodiments of this application, the mass ratio of the fluorinated diluent to the solvent is 1.25-19, for example, it can be 1.25, 3, 6, 9, 12, 15, 17, 19, etc., or it can be any range of the above values. By keeping the mass ratio of the fluorinated diluent to the solvent within the above range, a locally high-concentration electrolyte is formed, reducing the probability of lithium polysulfides shuttling to the negative electrode and undergoing side reactions with lithium metal, thereby improving the capacity and cycle performance of the lithium-sulfur battery.

[0050] According to some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the fluorinated diluent can be 50%-95%, for example, it can be 50%, 60%, 70%, 80%, 90%, 95%, etc., or it can be any range of the above values.

[0051] According to some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the solvent can be 5%-40%, for example, it can be 5%, 10%, 20%, 30%, 40%, etc., or it can be any range of the above values.

[0052] In this application, the qualitative and quantitative analysis of fluorinated diluents in the electrolyte can be performed by gas chromatography, with reference to standard GB / T 9722-2006.

[0053] According to some embodiments of this application, the conductive polymer includes one or more of polyaniline (PANi), polydioxyethylthiophene (PEDOT), and polypyrrole (PPy). This allows for the absorption of lithium salt-solvent clusters, enabling lithium polysulfides to dissolve in the lithium salt-solvent clusters within the surface conductive polymer coating layer, thereby making the sulfur reaction a solid-liquid-solid reaction and increasing the reaction rate.

[0054] According to some embodiments of this application, the thickness of the coating layer is 1nm-20nm, for example, it can be 1nm, 5nm, 10nm, 15nm, 20nm, etc., or it can be any range of the above values. This improves the absorption effect on lithium salt-solvent clusters.

[0055] In this application, the thickness of the coating layer is tested using transmission electron microscopy.

[0056] According to some embodiments of this application, the molecular weight of the conductive polymer is 5,000-100,000, for example, it can be 5,000, 10,000, 30,000, 50,000, 70,000, 90,000, 100,000, etc., or can be any range of the above values. This improves the absorption effect on lithium salt-solvent clusters.

[0057] According to some embodiments of this application, the positive electrode active material further includes a conductive layer located on at least a portion of the surface of the substrate, and the coating layer located on at least a portion of the surface of the conductive layer. This improves the electronic conductivity of the positive electrode active material.

[0058] According to some embodiments of this application, the electrolyte further includes an electrolyte salt, which includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, or lithium tetrafluorooxalate phosphate. Therefore, while improving the ionic conductivity of the electrolyte, the above-mentioned lithium salts exhibit strong stability and compatibility with the electrolyte and positive electrode active material, thereby enhancing the capacity and cycle performance of batteries containing them.

[0059] According to some embodiments of this application, based on the total mass of the electrolyte, the mass percentage of the electrolyte salt is 1%-8%, for example, it can be 1%, 3%, 5%, 7%, 8%, etc., or it can be any range of the above values. This improves the ionic conductivity of the electrolyte.

[0060] In this application, JY / T 020-1996 can be used to perform qualitative and quantitative analysis of lithium salts in electrolytes by ion chromatography.

[0061] According to some embodiments of this application, the sulfur-based material includes one or more of elemental sulfur, sulfur-selenium complex, and sulfur-tellurium complex.

[0062] Typically, a lithium-sulfur battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. Sulfur is used as the positive electrode reactant, and lithium is used as the negative electrode. During discharge, the negative electrode reaction involves lithium losing electrons to become lithium ions, while the positive electrode reaction involves sulfur reacting with lithium ions and electrons to form sulfides. The potential difference between the positive and negative electrode reactions is the discharge voltage provided by the lithium-sulfur battery. Under the influence of an applied voltage, the positive and negative electrode reactions of the lithium-sulfur battery proceed in reverse, which is the charging process.

[0063] In some embodiments of this application, the electrolyte may optionally include additives. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and may also include additives that can improve certain performance characteristics of lithium-sulfur batteries, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0064] In some embodiments of this application, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0065] In some embodiments of this application, the positive electrode active material layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0066] In some embodiments of this application, the positive electrode active material layer may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0067] In some embodiments of this application, the negative electrode sheet comprises a lithium metal alloy with the chemical formula LiR, wherein R comprises at least one of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, platinum, boron, carbon, or silicon.

[0068] In some embodiments of this application, the material of the separator may include at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0069] A second aspect of this application provides a method for preparing a lithium-sulfur battery. The method includes: mixing a conductive polymer, a sulfur-based material, and a solvent, reacting the mixture, and drying it to obtain a positive electrode active material. The positive electrode active material includes a matrix, and at least a portion of the surface of the matrix has a coating layer. The matrix includes the sulfur-based material, and the coating layer includes the conductive polymer. A slurry containing the positive electrode active material is formed on at least one side of a positive electrode current collector to obtain a positive electrode sheet. This results in a lithium-sulfur battery with both excellent specific capacity and cycle performance.

[0070] The method for preparing lithium-sulfur batteries proposed in this application is described in detail below. (Refer to...) Figure 2 The method includes:

[0071] S10: The conductive polymer, sulfur-based material, and solvent are mixed and reacted, then dried to obtain the positive electrode active material.

[0072] According to some embodiments of this application, a conductive polymer, a sulfur-based material, and a solvent are mixed and reacted, and then dried to obtain a positive electrode active material. The positive electrode active material includes a matrix, at least a portion of the surface of the matrix has a coating layer, the matrix includes the sulfur-based material, and the coating layer includes the conductive polymer.

[0073] According to some embodiments of this application, when the conductive polymer is PANi, a suspension A is obtained by mixing sulfur-based material, aniline, phytic acid aqueous solution and deionized water, and ammonium persulfate is dissolved in deionized water to obtain solution B. Solution B is added to suspension A, and the mixture is subjected to an ice bath, filtered and washed to obtain the sulfur-based material coated with PANi.

[0074] According to some embodiments of this application, when the conductive polymer is PEDOT, sulfur-based material, PEDOT, and deionized water are mixed, ground, and dried to obtain sulfur-based material coated with PEDOT.

[0075] According to some embodiments of this application, when the conductive polymer is PPy, a suspension is obtained by mixing sulfur-based material, pyrrole, and deionized water, and FeCl3 solution is added dropwise to the suspension and filtered to obtain PPy-coated sulfur-based material.

[0076] According to some embodiments of this application, the method further includes: mixing the sulfur-based material and the conductive carbon material, heating under inert gas protection to form a conductive carbon layer on at least the surface of the substrate; mixing the positive electrode active material containing the conductive carbon layer, the conductive polymer, and the solvent, reacting them, and drying to form the coating layer on at least a portion of the surface of the conductive carbon layer.

[0077] Specifically, sulfur-based materials and conductive carbon materials are mixed in a certain mass ratio and heated and kept at a constant temperature under a nitrogen atmosphere to obtain an S / C composite positive electrode active material.

[0078] According to some embodiments of this application, the heating temperature can be 120℃-200℃, for example, it can be 120℃, 140℃, 160℃, 180℃, 200℃, etc., or it can be any range of the above values.

[0079] S20: A slurry containing the positive electrode active material is formed on at least one side of the positive electrode current collector to obtain a positive electrode sheet; the positive electrode sheet, the negative electrode sheet, and the electrolyte are assembled into a lithium-sulfur battery.

[0080] In some embodiments of this application, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0081] In some embodiments of this application, the positive electrode includes a current collector and a positive electrode slurry disposed on at least one side of the current collector. The positive electrode slurry includes a positive electrode active material and the electrolyte. Therefore, the above-described battery is a lithium-sulfur slurry battery. By directly dispersing the positive electrode active material in the electrolyte, the traditional steps of coating and drying the positive electrode can be saved, reducing the cost of lithium-sulfur batteries. Furthermore, it facilitates the recycling of the positive electrode active material and can improve the capacity and cycle performance of lithium-sulfur batteries.

[0082] The third aspect of this application provides an electrical device, including a lithium-sulfur battery provided in the first aspect of this application or a lithium-sulfur battery prepared by the method provided in the second aspect of this application.

[0083] In some embodiments, the lithium-sulfur battery may include an outer packaging. This outer packaging can be used to encapsulate the aforementioned positive electrode, negative electrode, and electrolyte.

[0084] In some implementations, the outer packaging of the lithium-sulfur battery can be a hard shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging can also be a soft pack, such as a pouch. The soft pack can be made of plastic, including materials such as polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0085] This application does not impose any particular limitation on the shape of the lithium-sulfur battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 3 This is an example of a square-structured lithium-sulfur battery.

[0086] In some implementations, refer to Figure 4 The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, the bottom plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. Positive electrode sheets, negative electrode sheets, and a separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The lithium-sulfur battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0087] In some implementations, the batteries can be assembled into battery modules, and the number of batteries contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0088] Figure 5 This is battery module 4, used as an example. (See reference...) Figure 5 In battery module 4, multiple lithium-sulfur batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple lithium-sulfur batteries 5 can be fixed in place using fasteners.

[0089] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple lithium-sulfur batteries 5 are housed.

[0090] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0091] Figure 6 and Figure 7 This is battery pack 1 as an example. (See reference...) Figure 6 and Figure 7 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0092] In addition, this application also provides an electrical device, which includes the lithium-sulfur battery provided in this application. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0093] Figure 8 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the device's requirements for high power and high energy density batteries, a battery pack or battery module can be used.

[0094] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a battery as their power source.

[0095] To make the technical problems, technical solutions, and beneficial effects solved by the embodiments of this application clearer, the following will provide a more detailed description in conjunction with the embodiments and accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit this application or its applications. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0096] Example 1

[0097] 1. Preparation of electrolyte

[0098] 1 g of LiFSI (lithium bisfluorosulfonylimide) was dissolved in 5 g of DME (ethylene glycol dimethyl ether) to obtain 1 M LiFSI@DME. 6 g of 1 M LiFSI@DME was dissolved in 84 g of OFE (1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether) to obtain the electrolyte.

[0099] 2. Preparation of positive electrode slurry

[0100] Elemental sulfur powder and the above-mentioned Ketjen black conductive carbon were mixed in a mass ratio of 8:2, and then kept at 155°C for 12 hours under a nitrogen atmosphere to obtain the S / C composite positive electrode active material.

[0101] Suspension A was prepared by mixing 50 mg of S / C composite positive electrode active material, 7 μL of aniline, 14 μL of 70% phytic acid aqueous solution, and 36 mL of deionized water; solution B was prepared by dissolving 6.8 mg of ammonium persulfate in 1.2 mL of deionized water; solution B was added to suspension A and then placed in an ice bath for 5 hours, followed by filtration and washing to obtain PANi-coated S / C composite positive electrode active material.

[0102] The positive electrode slurry is formed by uniformly mixing the PANi-coated S / C composite positive electrode active material, the corresponding electrolyte, and Ketjen Black particles (conductive agent) in a mass ratio of 20:79:1.

[0103] 3. Negative electrode plate

[0104] A lithium metal sheet with a thickness of 1 mm was used as the negative electrode.

[0105] 4. Separating membrane

[0106] A glass fiber sheet with a thickness of 2 mm was used as the diaphragm.

[0107] 5. Preparation of lithium-sulfur batteries

[0108] The assembly form is a button cell: First, place the lithium metal sheet on the negative electrode shell, then cover it with a glass fiber separator, then cover it with a carbon felt as a current collector, then drop 400mg of the above positive electrode slurry onto the carbon felt, then cover it with the positive electrode shell, and finally use a button cell packaging machine to press and seal the battery to obtain a lithium slurry battery.

[0109] Example 2

[0110] The preparation method of the lithium-sulfur battery is the same as in Example 1, except that 50 mg of S / C composite positive electrode active material and 1 mg of PEDOT are mixed and ground with an appropriate amount of deionized water, and then dried to obtain PEDOT-coated S / C composite positive electrode active material.

[0111] Example 3

[0112] The preparation method of the lithium-sulfur battery is the same as in Example 1, except that 0.02g of pyrrole, 1g of S / C composite positive electrode active material and 10mL of deionized water are mixed to obtain a suspension. Then, 1.5mL of 0.5mol / L FeCl3 solution is added dropwise to the suspension. After reacting for 2 hours, the mixture is filtered and washed to obtain PPy-coated S / C composite positive electrode active material.

[0113] The preparation methods of the lithium-sulfur batteries in Examples 4-11, Comparative Example 1, and Comparative Example 2 are the same as those in Example 2, with the differences detailed in Table 1.

[0114] Table 1

[0115]

[0116] Performance testing

[0117] 1. Cyclic performance

[0118] Each lithium-sulfur battery was discharged to 1.5V at a current density of 100mA / g at room temperature, then charged to 3V, and then discharged to 1.5V again at a current density of 100mA / g. The reversible capacity was measured as C0. After repeating this charge-discharge cycle 50 times, the reversible capacity was measured as Cn. The cycle capacity retention rate was calculated as Cn / C0 × 100%.

[0119] 2.100mA / g discharge specific capacity test

[0120] Each lithium-sulfur battery was discharged to 1.5V at a current density of 100mA / g at room temperature, charged to 3V, and then discharged to 1.5V again at a current density of 100mA / g. The reversible capacity was measured as the discharge specific capacity.

[0121] 3.1000mA / g discharge specific capacity test

[0122] Each lithium-sulfur battery was discharged to 1.5V at room temperature with a current density of 1000mA / g, charged to 3V with a current density of 1000mA / g, and then discharged to 1.5V again with a current density of 1000mA / g. The reversible capacity was measured as the discharge specific capacity.

[0123] The test results of lithium-sulfur batteries in Examples 1-11, Comparative Example 1, and Comparative Example 2 are shown in Table 2.

[0124] Table 2

[0125]

[0126] As can be seen from the comparison between Examples 1-11 and Comparative Examples 1 and 2, the sodium-free secondary battery proposed in this application has a higher specific capacity and cycle capacity retention rate. This indicates that by forming a coating layer containing a conductive polymer on the surface of the positive electrode active material, the coating layer absorbs lithium salt-solvent clusters, allowing lithium polysulfides to dissolve in the coating layer formed by the conductive polymer. This makes the reaction of sulfur a solid-liquid-solid reaction, thereby improving the specific capacity of the lithium-sulfur battery. At the same time, since the lithium polysulfides are enriched on the surface of the positive electrode active material, the amount of lithium polysulfides shuttling to the negative electrode can also be reduced, thereby improving the cycle performance of the lithium-sulfur battery.

[0127] As can be seen from Examples 1-3, the three conductive polymers PANi, PEDOT, and PPy can all form a coating layer on the surface of the positive electrode active material, thereby making the sulfur reaction a solid-liquid-solid reaction, which improves the specific capacity and cycle performance of lithium-sulfur batteries.

[0128] As can be seen from Examples 4-8, based on the formation of a coating layer on the surface of the positive electrode active material, the content of solvent and fluorine-containing diluent in the electrolyte can be adjusted to obtain a lithium-sulfur battery with high specific capacity and cycle capacity retention.

[0129] As can be seen from Examples 9-11, lithium-sulfur batteries with high specific capacity and good cycle performance can be obtained by using different types of solvents, fluorinated diluents, and electrolyte salts in the electrolyte.

[0130] From the appendix Figure 1 It can be seen that the surface of the positive electrode active material in Example 2 has a coating layer.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and not to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application, and they should all be covered within the scope of the claims and specification of this application. In particular, as long as there is no structural conflict, the various technical features mentioned in the embodiments can be combined in any way. This application is not limited to the specific embodiments disclosed herein, but includes all technical solutions falling within the scope of the claims.

Claims

1. A lithium-sulfur battery, characterized in that, Includes positive electrode, negative electrode, and electrolyte: The positive electrode sheet includes a positive current collector, and a positive active material layer is disposed on at least one side of the positive current collector. The positive active material layer includes a positive active material, and the positive active material includes: a matrix, and at least a portion of the surface of the matrix has a coating layer. The matrix includes a sulfur-based material, and the coating layer includes a conductive polymer. The electrolyte includes a solvent and a fluorinated diluent.

2. The lithium-sulfur battery according to claim 1, characterized in that, The fluorinated diluent includes one or more of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether.

3. The lithium-sulfur battery according to claim 1 or 2, characterized in that, The solvent includes one or more of the following: dimethyl ether, 1,2-dimethoxypropane, dimethoxymethane, ethylene glycol dimethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, pentaethylene glycol dimethyl ether, polyethylene glycol dimethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, triethylene glycol diethyl ether, tetraethylene glycol diethyl ether, pentaethylene glycol diethyl ether, ethylene glycol dibutyl ether, diethylene glycol dibutyl ether, and 1,3-dioxopentane.

4. The lithium-sulfur battery according to claim 3, characterized in that, The mass ratio of the fluorinated diluent to the solvent is 1.25-19.

5. The lithium-sulfur battery according to claim 3 or 4, characterized in that, Based on the total mass of the electrolyte, the fluorinated diluent accounts for 50%-95% of the total mass.

6. The lithium-sulfur battery according to any one of claims 3-5, characterized in that, The solvent accounts for 5%-40% of the total mass of the electrolyte.

7. The lithium-sulfur battery according to any one of claims 1-6, characterized in that, The conductive polymer includes one or more of polyaniline, polydioxyethylthiophene, and polypyrrole.

8. The lithium-sulfur battery according to any one of claims 1-7, characterized in that, The thickness of the coating layer is 1nm-20nm.

9. The lithium-sulfur battery according to any one of claims 1-8, characterized in that, The conductive polymer has a molecular weight of 5,000-100,000.

10. The lithium-sulfur battery according to any one of claims 1-9, characterized in that, The positive electrode active material further includes a conductive layer located on at least a portion of the surface of the substrate, and the coating layer located on at least a portion of the surface of the conductive layer.

11. The lithium-sulfur battery according to any one of claims 1-10, characterized in that, The electrolyte further includes an electrolyte salt, which includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalate borate, lithium dioxalate borate, lithium difluorodioxalate phosphate, or lithium tetrafluorooxalate phosphate.

12. The lithium-sulfur battery according to claim 11, characterized in that, Based on the total mass of the electrolyte, the mass percentage of the electrolyte salt is 1%-8%.

13. The lithium-sulfur battery according to any one of claims 1-12, characterized in that, The sulfur-based material includes one or more of elemental sulfur, sulfur-selenium complex, and sulfur-tellurium complex.

14. A method for preparing a lithium-sulfur battery, characterized in that, include: A conductive polymer, a sulfur-based material, and a solvent are mixed and reacted, then dried to obtain a positive electrode active material. The positive electrode active material includes a matrix, and at least a portion of the surface of the matrix has a coating layer. The matrix includes the sulfur-based material, and the coating layer includes the conductive polymer. A slurry containing the positive electrode active material is formed on at least one side of the positive electrode current collector to obtain a positive electrode sheet; The positive electrode, negative electrode, and electrolyte are assembled into a lithium-sulfur battery, wherein the electrolyte includes a solvent and a fluorinated diluent.

15. The method according to claim 14, characterized in that, Also includes: The sulfur-based material and the conductive carbon material are mixed and heated under inert gas protection to form a conductive carbon layer on at least the surface of the substrate. The positive electrode active material containing the conductive carbon layer, the conductive polymer, and the solvent are mixed and reacted, and then dried to form the coating layer on at least a portion of the surface of the conductive carbon layer.

16. The method according to claim 15, characterized in that, The heating temperature is 120℃-200℃.

17. An electrical appliance, characterized in that, Including the lithium-sulfur battery according to any one of claims 1-13.

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