Lithium-sulfur battery, electrolyte and electric equipment

Abstract

The invention discloses a lithium-sulfur battery, an electrolyte and electric equipment, and belongs to the field of secondary batteries, the lithium-sulfur battery comprises a positive pole piece, the electrolyte and a negative pole piece, the positive pole piece comprises a positive active material, the positive active material comprises sulfur and conductive carbon containing doped elements, and the conductive carbon contains a positive electrode and a negative electrode. The doping elements comprise one or more of an N element, a B element or a P element; the electrolyte comprises a lithium salt, a solvent and a diluent. The lithium-sulfur battery provided by the invention has excellent specific capacity and cycle performance.

Description

Technical Field

[0001] This application belongs to the field of secondary batteries, specifically relating to a lithium-sulfur battery, an electrolyte, and an electrical device. Background Technology

[0002] Secondary batteries are widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[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, reaching 1675 mAh / g and 2600 Wh / kg, respectively. 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. They undergo side reactions with the metallic lithium, consuming it and forming non-conductive lithium sulfide that coats the surface of the metallic lithium, leading to a decrease in capacity and cycle performance. Summary of the Invention

[0004] In view of the technical problems existing in the background art, this application provides a lithium-sulfur battery, which aims to improve the capacity and cycle performance of lithium-sulfur batteries.

[0005] To achieve the above objectives, the first aspect of this application proposes a lithium-sulfur battery, the lithium-sulfur battery comprising a positive electrode, an electrolyte, and a negative electrode, the positive electrode comprising a positive electrode active material comprising sulfur and conductive carbon containing doped elements, the doping elements comprising at least one of N, B, or P elements; the electrolyte comprising a lithium salt, a solvent, and a diluent.

[0006] This application includes at least the following beneficial effects: In the lithium-sulfur battery of this application, the electrolyte uses a diluent, which, in conjunction with conductive carbon containing doped elements, can improve the capacity and cycle performance of the lithium-sulfur battery.

[0007] In some embodiments, the doping element includes at least two of nitrogen (N), boron (B), or phosphorus (P). This can improve the capacity and cycle performance of lithium-sulfur batteries.

[0008] In some embodiments, the mass percentage of the dopant element is 0.3%-3% based on the total mass of the conductive carbon containing the dopant element. This can improve the capacity and cycle performance of the lithium-sulfur battery.

[0009] In some embodiments, the mass ratio of the doped conductive carbon to the sulfur is (1:9) to (5:5). This can improve the capacity and cycle performance of lithium-sulfur batteries.

[0010] In some embodiments, the lithium salt has a molar concentration of 0.1 mol / L to 5 mol / L in both the lithium salt and the solvent. This can improve the capacity and cycle performance of lithium-sulfur batteries.

[0011] In some embodiments, the lithium salt 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 can improve the capacity and cycle performance of lithium-sulfur batteries.

[0012] In some embodiments, the solvent includes one or more of 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, 1,3-dioxane, or dimethyl ether. This can improve the capacity and cycle performance of lithium-sulfur batteries.

[0013] In some embodiments, the diluent includes fluoroether diluents. This can improve the capacity and cycle performance of lithium-sulfur batteries.

[0014] In some embodiments, the fluorinated ether diluent includes one or more of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, or 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. This can improve the capacity and cycle performance of lithium-sulfur batteries.

[0015] In some embodiments, the sum of the volumes of the solvent and lithium salt : the volume of the diluent = (1:99) - (20:80). This can improve the capacity and cycle performance of lithium-sulfur batteries.

[0016] In some embodiments, 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 including the positive electrode active material and the electrolyte. This can improve the capacity and cycle performance of the lithium-sulfur battery.

[0017] In some embodiments, the mass ratio of the components in the positive electrode slurry is: positive electrode active material: electrolyte: conductive agent = (10-50): (50-90): (0.5-10). This can improve the capacity and cycle performance of lithium-sulfur batteries.

[0018] In a second aspect, this application proposes a method for preparing a lithium-sulfur battery, comprising: assembling a positive electrode, an electrolyte, and a negative electrode to obtain a lithium-sulfur battery, wherein the positive electrode comprises a positive electrode active material, the positive electrode active material comprises sulfur and conductive carbon containing a doped element, the doping element comprising at least one selected from nitrogen (N), boron (B), or phosphorus (P); and the electrolyte comprises a lithium salt, a solvent, and a diluent. Therefore, the method for preparing a lithium-sulfur battery proposed in this application, using a diluent in the electrolyte and in conjunction with conductive carbon containing a doped element, can improve the capacity and cycle performance of the lithium-sulfur battery.

[0019] In some embodiments, the positive electrode active material is prepared by the following method: mixing conductive carbon with at least one of an N source, a B source, or a P source, and calcining under inert gas protection to obtain conductive carbon containing doped elements; mixing the conductive carbon containing doped elements with sulfur, and heating under inert gas protection to obtain the positive electrode active material. This can improve the capacity and cycle performance of lithium-sulfur batteries.

[0020] In some embodiments, at least one of the following conditions is met: the calcination temperature is 700°C-1200°C; the heating temperature is 120°C-200°C. This can improve the capacity and cycle performance of lithium-sulfur batteries.

[0021] In a third aspect of this application, an electrical device is proposed, including the lithium-sulfur battery described in the first 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 a battery according to one embodiment of this application.

[0025] Figure 2 yes Figure 1 An exploded view of a battery according to one embodiment of this application is shown.

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

[0027] Figure 4This is a schematic diagram of a battery pack according to one embodiment of this application.

[0028] Figure 5 yes Figure 4 An exploded view of a battery pack according to one embodiment of this application is shown.

[0029] Figure 6 This is a schematic diagram of an electrical device in which a battery is used as a power source according to one embodiment of this application.

[0030] Figure 7 This is an internal state diagram of the lithium-sulfur battery of Comparative Example 1 and Example 1 of this application.

[0031] Explanation of reference numerals in the attached figures:

[0032] 1. Battery cell; 11. Housing; 12. Electrode assembly; 13. Cover plate; 2. Battery module; 3. Battery pack; 31. Upper casing; 32. Lower casing. Detailed Implementation

[0033] 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.

[0034] 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.

[0035] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[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, the application of rechargeable batteries is becoming increasingly widespread. Rechargeable 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, among other fields.

[0040] Lithium-sulfur batteries are lithium-ion batteries where the positive electrode is sulfur and the negative electrode is metallic lithium. Elemental sulfur is abundant on Earth and is inexpensive and environmentally friendly. Lithium-sulfur batteries using sulfur as the positive electrode material have high theoretical specific capacity and theoretical specific energy, reaching 1675 mAh / g and 2600 Wh / kg, respectively. 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. They undergo side reactions with the metallic lithium, consuming it and forming non-conductive lithium sulfide covering the surface of the metallic lithium, leading to a decrease in capacity and cycle performance. On the other hand, the dense, non-conductive lithium sulfide generated during battery discharge reduces the contact between sulfur positive electrode particles, disrupting the conductive network and also causing a decrease in capacity and cycle performance.

[0041] To address the shuttling problem of lithium polysulfides, existing technologies use locally high-concentration electrolytes or electrolytes that do not readily dissolve lithium polysulfides to suppress their shuttling. While high-concentration electrolytes do not contain diluents, they have a higher viscosity, and lithium polysulfides are not easily dissolved in them. This inevitably leads to an increase in electrolyte viscosity and a decrease in conductivity, affecting the battery's rate and cycle performance.

[0042] In locally concentrated electrolytes, the introduction of diluents reduces the total salt concentration while preserving the local coordination environment of high-concentration salt-solvent clusters. Lithium salts have very low or no solubility in the diluents used, allowing them to mix with the soluble salt solvents in the concentrated electrolyte to form a clear, homogeneous solution, preventing phase separation. Furthermore, the diluents have low viscosity, reducing the overall viscosity of the electrolyte. The diluents also do not dissolve lithium polysulfides, preventing them from shuttling to the negative electrode. However, in lithium-sulfur batteries containing locally concentrated electrolytes, the interaction between the positive electrode and the lithium salt-solvent clusters in the locally concentrated electrolyte is weak. Some lithium salt-solvent clusters remain free away from the positive electrode, and the components in contact with sulfur in the positive electrode are mostly diluents (e.g., fluorinated ethers). Since the intermediate lithium polysulfide is insoluble in most diluents (e.g., fluorinated ethers), the reaction of sulfur in the positive electrode is a solid-solid reaction, resulting in poor battery capacity and cycle performance.

[0043] In the lithium-sulfur battery of this application embodiment, a diluent is used in the electrolyte, along with conductive carbon containing doped elements as the positive electrode active material. This conductive carbon contains N, B, or P elements, and reacts with a lithium salt-solvent cluster in the electrolyte (for example, if the lithium salt is LiFSI and the solvent is DME, the lithium salt-solvent cluster is Li...). + -DME-FSI -The strong interaction forces cause most of the lithium salt-solvent clusters to accumulate on the surface of the positive electrode active material particles. Furthermore, lithium polysulfides can dissolve in the lithium salt-solvent clusters on the surface of the positive electrode active material, making the sulfur reaction a solid-liquid-solid reaction. This results in high rate performance and high specific capacity for the battery. In addition, because lithium polysulfides can dissolve in the lithium salt-solvent clusters, most of them are enriched on the surface of the positive electrode active material, reducing the probability of them shuttling to the negative electrode. The presence of the diluent also hinders the shuttle movement of lithium polysulfides to some extent, thus improving the battery's cycle stability. In summary, the lithium-sulfur battery proposed in this application exhibits excellent capacity and cycle performance.

[0044] The lithium-sulfur battery disclosed in this application can be used in electrical devices that use batteries as a power source or in various energy storage systems that use batteries as energy storage elements. Electrical devices may include, but are not limited to, mobile phones, tablets, laptops, electric toys, power tools, electric vehicles, electric cars, ships, spacecraft, etc. Electric toys may include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Spacecraft may include airplanes, rockets, space shuttles, and spacecraft, etc.

[0045] The first aspect of this application discloses a lithium-sulfur battery, which includes a positive electrode, an electrolyte, and a negative electrode. The positive electrode includes a positive active material, which includes sulfur and conductive carbon containing doped elements, wherein the doped elements include one or more of N, B, or P elements. The electrolyte includes a lithium salt, a solvent, and a diluent.

[0046] In the lithium-sulfur battery of this application embodiment, a diluent is used in the electrolyte, along with conductive carbon containing doped elements in the positive electrode active material. The conductive carbon containing N, B, or P elements has a strong interaction with the lithium salt-solvent clusters in the electrolyte, resulting in the lithium salt-solvent clusters being largely enriched on the surface of the positive electrode active material particles. Furthermore, lithium polysulfides can dissolve in the lithium salt-solvent cluster portion on the surface of the positive electrode active material, making the sulfur reaction in the positive electrode a solid-liquid-solid reaction. This results in high rate performance and high specific capacity. In addition, because most of the lithium polysulfides are dissolved in the lithium salt-solvent clusters and enriched on the surface of the positive electrode active material, the probability of them shuttling to the negative electrode is low. The presence of the diluent also hinders the shuttle movement of lithium polysulfides to a certain extent, thus improving the battery's cycle stability. In summary, the lithium-sulfur battery proposed in this application has excellent capacity and cycle performance.

[0047] Understandably, an electrolyte comprises 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. 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, resulting in very low or no solubility of the lithium salt in the diluent. The diluent can be miscible with the lithium salt and solvent to form a clear, homogeneous solution, avoiding phase separation. Furthermore, the diluent has a low viscosity to reduce the overall viscosity of the electrolyte.

[0048] It is understandable that sulfur and conductive carbon containing doped elements in positive electrode active materials can be determined using the following methods:

[0049] For lithium-sulfur slurry batteries, the positive electrode active material and electrolyte components can be separated by centrifugation. After washing the positive electrode active material with water to remove lithium sulfide or lithium polysulfide, the sulfur components are washed with carbon disulfide to obtain a conductive carbon substrate. The amount of doped elements in the conductive carbon substrate can be quantitatively tested by inductively coupled plasma (ICP-AES).

[0050] Understandably, JY / T 020-1996 can be used to perform qualitative and quantitative analysis of lithium salts in electrolytes via ion chromatography. Similarly, GB / T 9722-2006 can be used to perform qualitative and quantitative analysis of solvents and diluents in electrolytes via gas chromatography.

[0051] In some embodiments of this application, the doping element includes at least two of N, B, or P elements. Doping conductive carbon with at least two elements can further enrich the lithium salt-solvent clusters on the surface of the positive electrode active material particles, reducing lithium polysulfide shuttle, and improving the battery's rate performance, specific capacity, and cycle performance.

[0052] In some embodiments of this application, the mass percentage of the dopant element, based on the total mass of the conductive carbon containing the dopant element, is 0.3%-3%. For example, it could be 0.3%-2.9%, 0.4%-2.8%, 0.5%-2.5%, 0.8%-2.3%, 1%-2%, 1.5%-2%, etc. Controlling the dopant element content within these ranges allows the positive electrode to fully utilize its interaction with the lithium salt-solvent cluster, resulting in the lithium salt-solvent cluster being largely enriched on the surface of the positive electrode active material particles, without affecting the conductivity of the conductive carbon or the capacity of the positive electrode, thereby further improving the capacity and cycle performance of the lithium-sulfur battery.

[0053] It is understood that "the mass percentage of the doped element based on the total mass of the conductive carbon containing the doped element" is a well-known definition in the art and can be determined using methods known in the art, such as the following methods:

[0054] The amount of doped elements in a conductive carbon substrate can be quantitatively measured using inductively coupled plasma (ICP-AES).

[0055] In some embodiments of this application, the mass ratio of the doped conductive carbon to the sulfur is (1:9)-(5:5). For example, it can be 1:9, 2:8, 3:7, 4:6, 5:5, etc. Controlling the mass ratio of the doped conductive carbon to the sulfur within the above range allows the positive electrode to fully exert its interaction with the lithium salt-solvent cluster, resulting in the lithium salt-solvent cluster being mostly enriched on the surface of the positive electrode active material particles, without affecting the conductivity of the conductive carbon and the capacity of the positive electrode, thereby further improving the capacity and cycle performance of the lithium-sulfur battery.

[0056] In addition, the addition of conductive carbon can improve the conductivity of the positive electrode, and the conductive carbon can also adsorb lithium polysulfides to a certain extent, reducing their migration to the negative electrode. It also helps to buffer volume expansion, improve sulfur utilization and sulfur loading, and promote the conversion reaction of polysulfides, thereby significantly improving the cycle performance of lithium-sulfur batteries.

[0057] It is understood that "the mass ratio of the conductive carbon containing the doped element to the sulfur" is a definition known in the art and can be determined using methods known in the art, such as the following methods:

[0058] For lithium-sulfur slurry batteries, the positive electrode active material and electrolyte components can be separated by centrifugation. The total sulfur content of the positive electrode active material can be obtained by inductively coupled plasma (ICP-AES) testing. After washing the positive electrode active material with water to remove lithium sulfide or lithium polysulfide, the sulfur components can be removed by washing with carbon disulfide to obtain the mass of the conductive carbon substrate. The mass ratio of the conductive carbon containing doped elements to the sulfur can be obtained from the total sulfur content and the mass of the conductive carbon substrate.

[0059] In some embodiments of this application, the molar concentration of the lithium salt in the lithium salt and the solvent is 0.1 mol / L-5 mol / L. For example, the molar concentration of the lithium salt in the lithium salt and solvent can be 0.1 mol / L-4.9 mol / L, 0.5 mol / L-4.5 mol / L, 1 mol / L-4 mol / L, 1.5 mol / L-3.5 mol / L, 2 mol / L-3 mol / L, etc. Controlling the molar concentration of the lithium salt in the solvent within the above range can increase the ionic conductivity of the electrolyte and improve the capacity and cycle performance of the battery containing it.

[0060] It is understood that "the molar concentration of lithium salt in lithium salt and solvent" is a well-known definition in the art and can be determined using methods well-known in the art, such as the following methods:

[0061] For qualitative and quantitative analysis of lithium salts in electrolytes, refer to JY / T 020-1996 using ion chromatography. For qualitative and quantitative analysis of solvents and diluents in electrolytes, refer to standard GB / T 9722-2006 using gas chromatography.

[0062] In some embodiments of this application, the lithium salt 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. The above-mentioned lithium salts exhibit high stability and compatibility with electrolytes and positive electrode active materials, thereby improving the capacity and cycle performance of batteries containing them.

[0063] In some embodiments of this application, the solvent includes one or more of the following: 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, 1,3-dioxane, or dimethyl ether. These ether solvents are compatible with lithium metal anodes and sulfur-containing cathodes, exhibit strong stability, and can improve the capacity and cycle performance of batteries containing them.

[0064] In some embodiments of this application, the diluent includes fluorinated ether diluents. Fluorinated ether diluents can reduce the viscosity of the electrolyte, improve wettability, maintain the electrochemical stability of high-concentration electrolytes, inhibit lithium dendrite formation, improve ionic conductivity, and prevent lithium polysulfides from migrating to the negative electrode, thereby improving the capacity and cycle performance of batteries containing them.

[0065] It is understandable that fluorinated ether diluents refer to organic compounds containing fluorine and ether groups.

[0066] In some embodiments of this application, the fluorinated ether diluent includes one or more of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, or 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether. The above diluents can reduce the viscosity of the electrolyte, improve the wetting performance, maintain the electrochemical stability of high-concentration electrolytes, inhibit the formation of lithium dendrites, improve ionic conductivity, and enhance the capacity and cycle performance of batteries containing them.

[0067] This is understandable. You can refer to standard GB / T 9722-2006 for qualitative and quantitative analysis of diluents in electrolytes using gas chromatography.

[0068] In some embodiments of this application, the sum of the volumes of the solvent and lithium salt: the volume of the diluent = (1:99) - (20:80). For example, it can be 1:99, 5:95, 10:90, 15:85, 20:80, etc. Specifically, by controlling the ratio of solvent to diluent within the above range, the lithium salt can dissolve in the solvent but not in the diluent, so that the lithium salt-solvent clusters are mostly enriched on the surface of the positive electrode active material particles, reducing the shuttling of lithium polysulfides, improving the rate performance, specific capacity, and cycle performance of the battery.

[0069] It can be understood that the sum of the volumes of the solvent and the lithium salt refers to the volume of the solution formed by the solvent and the lithium salt.

[0070] It is understood that "the sum of the volumes of the solvent and the lithium salt: the volume of the diluent" is a definition known in the art and can be determined using methods known in the art, for example, the following methods can be used for determination:

[0071] For qualitative and quantitative analysis of lithium salts in electrolytes, refer to JY / T 020-1996 using ion chromatography. For qualitative and quantitative analysis of solvents and diluents in electrolytes, refer to standard GB / T 9722-2006 using gas chromatography.

[0072] 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-mentioned 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.

[0073] In some embodiments of this application, the mass ratio of each component in the positive electrode slurry is: positive electrode active material: electrolyte: conductive agent = (10-50):(50-90):(0.5-10). For example, the mass ratio of the three can be 10:89:1, 30:60:10, 50:49.5:0.5, etc. The addition of the conductive agent can improve the conductivity of the positive electrode side. Controlling the mass ratio of each component in the positive electrode slurry within the above range can further improve the conductivity of the positive electrode sheet, reduce the migration of lithium polysulfides to the negative electrode, and also help buffer volume expansion, improve sulfur utilization and sulfur loading, and promote the conversion reaction of polysulfides, thereby significantly improving the cycle performance of lithium-sulfur batteries.

[0074] 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.

[0075] [Electrolytes]

[0076] This application does not impose specific restrictions on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be liquid, gel, or completely solid.

[0077] In some embodiments of this application, the electrolyte is an electrolyte solution. The electrolyte solution includes a lithium salt and a solvent.

[0078] In some embodiments of this application, the solvent and the first solvent may also independently include ester solvents, which may include at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, or diethyl sulfone.

[0079] 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 battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0080] [Negative electrode plate]

[0081] 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.

[0082] [Positive electrode plate]

[0083] In some embodiments of this application, the positive electrode includes a positive current collector, which 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 can 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.).

[0084] In some embodiments of this application, the positive electrode active material forms a positive electrode active material layer on the positive electrode current collector.

[0085] 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.

[0086] 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.

[0087] 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.

[0088] This application does not impose any particular restrictions on the type of separator membrane; any known porous separator membrane with good chemical and mechanical stability can be selected.

[0089] 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.

[0090] In a second aspect of this application, a method for preparing the lithium-sulfur battery described in the first aspect is proposed, comprising:

[0091] By assembling the positive electrode, electrolyte, and negative electrode, a lithium-sulfur battery is obtained.

[0092] The positive electrode sheet includes a positive electrode active material, which includes sulfur and conductive carbon containing doped elements, wherein the doped elements include at least one of N, B or P elements.

[0093] The electrolyte includes a lithium salt, a solvent, and a diluent.

[0094] Therefore, the lithium-sulfur battery prepared in this application uses a diluent in the electrolyte, combined with conductive carbon containing doped elements in the positive electrode active material. The conductive carbon containing N, B, or P elements has a strong interaction with the lithium salt-solvent clusters in the electrolyte, resulting in the lithium salt-solvent clusters being mostly enriched on the surface of the positive electrode active material particles. Furthermore, lithium polysulfides can dissolve in the lithium salt-solvent clusters on the surface of the positive electrode active material, making the sulfur reaction in the positive electrode a solid-liquid-solid reaction. This results in high rate performance and high specific capacity. In addition, because most of the lithium polysulfides are dissolved in the lithium salt-solvent clusters and enriched on the surface of the positive electrode active material, the probability of them shuttling to the negative electrode is low. The diluent also hinders the shuttle movement of lithium polysulfides to a certain extent, thus improving the battery's cycle stability. In summary, the lithium-sulfur battery proposed in this application has excellent capacity and cycle performance.

[0095] In some embodiments of this application, the positive electrode active material is prepared by the following method:

[0096] S1: Mix conductive carbon with at least one of N source, B source or P source, and calcine under inert gas protection to obtain conductive carbon containing doped elements.

[0097] In some embodiments of this application, the N source, B source, or P source may include N-containing organic compounds, B-containing organic compounds, and P-containing organic compounds, respectively. For example, the N source may include triphenylamine, melamine, or urea; the B source may include triphenylboron, boric acid, or boron oxide; and the P source may include triphenylphosphine, phosphoric acid, or phosphorus pentoxide. Taking a dopant element including N and the N source including triphenylamine as an example, calcination at high temperature converts the carbon in the N source into conductive carbon, and the N atoms are connected to the conductive carbon through CN bonds.

[0098] In some embodiments of this application, the calcination temperature is 700℃-1200℃. For example, the calcination temperature can be 700℃-1190℃, 800℃-1100℃, 900℃-1000℃, etc. Controlling the calcination temperature within the above range is beneficial to obtaining conductive carbon with uniformly dispersed doped elements, so that most of the lithium salt-solvent clusters are enriched on the surface of the positive electrode active material particles, further improving the capacity and cycle performance of lithium-sulfur batteries.

[0099] S2: The conductive carbon containing doped elements is mixed with sulfur and heated under inert gas protection to obtain a positive electrode active material.

[0100] In some embodiments of this application, the heating temperature is 120℃-200℃. For example, the heating temperature can be 120℃-199℃, 130℃-190℃, 140℃-180℃, 150℃-170℃, etc. Controlling the heating temperature within the above range is beneficial for the uniform mixing of conductive carbon containing doped elements and sulfur, so that most of the lithium salt-solvent clusters are enriched on the surface of the positive electrode active material particles, further improving the capacity and cycle performance of lithium-sulfur batteries.

[0101] In some embodiments of this application, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly by a winding process or a stacking process.

[0102] In some embodiments of this application, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the aforementioned electrode assembly and electrolyte.

[0103] The batteries of this application include battery cells, battery modules, and battery packs. The battery cells, battery modules, and battery packs of this application will be described below with appropriate reference to the accompanying drawings.

[0104] In some embodiments of this application, the outer packaging of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0105] It is understood that the lithium-sulfur battery mentioned above in this application is a single battery cell.

[0106] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 Here is a square-structured battery cell 1 as an example.

[0107] In some embodiments of this application, reference is made to Figure 2 The outer packaging may include a housing 11 and a cover plate 13. The housing 11 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 11 has an opening communicating with the receiving cavity, and the cover plate 13 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator can be formed into an electrode assembly 12 by a winding process or a stacking process. The electrode assembly 12 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 12. The number of electrode assemblies 12 contained in a single battery cell 1 can be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0108] In some embodiments of this application, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0109] Figure 3 This is battery module 2 as an example. (See reference...) Figure 3 In battery module 2, multiple battery cells 1 can be arranged sequentially along the length of battery module 2. Of course, they can also be arranged in any other way. Furthermore, these multiple battery cells 1 can be fixed in place using fasteners.

[0110] Optionally, the battery module 2 may also include a housing with a receiving space in which multiple battery cells 1 are received.

[0111] In some embodiments of this application, the battery modules described above can also be assembled into a battery pack. The number of battery modules contained in the battery pack can be one or more, and the specific number can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0112] Figure 4 and Figure 5 This is battery pack 3 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 3 may include a battery box and multiple battery modules 2 disposed within the battery box. The battery box includes an upper box 31 and a lower box 32, with the upper box 31 covering the lower box 32 to form a closed space for accommodating the battery modules 2. The multiple battery modules 2 can be arranged in any manner within the battery box.

[0113] In addition, this application also provides an electrical device, which includes the lithium-sulfur battery provided in the first aspect of this application. The battery cell, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. 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.

[0114] As the electrical equipment, battery cells, battery modules, or battery packs can be selected according to their usage requirements.

[0115] Figure 6This 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.

[0116] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0117] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0118] Example 1

[0119] 1. Electrolyte

[0120] 0.1 mol of LiFSI (lithium bisfluorosulfonylimide) was dissolved in 100 mL of DME (ethylene glycol dimethyl ether) to obtain 1 M LiFSI@DME. 5 mL of 1 M LiFSI@DME was dissolved in 95 mL of OFE (1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether) to obtain the electrolyte.

[0121] 2. Positive electrode plate

[0122] Preparation of positive electrode active materials:

[0123] Triphenylamine and Ketjen black were mixed at a mass ratio of 1:1 and calcined at 1000°C for 6 hours under a nitrogen atmosphere to obtain N-doped Ketjen black conductive carbon.

[0124] The above-mentioned N-doped Ketjen black conductive carbon and elemental sulfur powder were mixed in a mass ratio of 2:8, and then kept at 155°C for 12 hours under a nitrogen atmosphere to obtain the S / C composite positive electrode active material.

[0125] The positive electrode is a slurry-like positive electrode slurry. The method for preparing the positive electrode slurry is to mix the S / C composite positive electrode active material, the corresponding electrolyte, and Ketjen black particles (conductive agent) in a mass ratio of 20:79:1 to form a positive electrode slurry.

[0126] 3. Negative electrode plate

[0127] A lithium metal sheet with a thickness of 1 mm was used as the negative electrode.

[0128] 4. Separating membrane

[0129] A glass fiber sheet with a thickness of 2 mm was used as the diaphragm.

[0130] 5. Preparation of lithium-sulfur batteries

[0131] 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.

[0132] Example 2

[0133] Preparation of positive electrode active materials:

[0134] Triphenylboron and Ketjen black were mixed in a mass ratio of 1:1 and calcined at 1000°C for 6 hours under a nitrogen atmosphere to obtain B-doped Ketjen black conductive carbon.

[0135] The remaining preparation methods are the same as in Example 1.

[0136] Example 3

[0137] Preparation of positive electrode active materials:

[0138] Triphenylphosphine and Ketjen black were mixed at a mass ratio of 1:1 and calcined at 1000°C for 6 hours under a nitrogen atmosphere to obtain P-doped Ketjen black conductive carbon.

[0139] The remaining preparation methods are the same as in Example 1.

[0140] Example 4

[0141] Preparation of positive electrode active materials:

[0142] Triphenylphosphine, triphenylamine, and Ketjen black were mixed in a mass ratio of 1:1:2 and calcined at 1000°C for 6 hours under a nitrogen atmosphere to obtain N and P co-doped Ketjen black conductive carbon.

[0143] The remaining preparation methods are the same as in Example 1.

[0144] Example 5

[0145] Preparation of positive electrode active materials:

[0146] Triphenylphosphine, triphenylamine, triphenylboron and Ketjen black were mixed in a mass ratio of 1:1:1:3 and calcined at 1000°C for 6 hours under a nitrogen atmosphere to obtain N, P and B co-doped Ketjen black conductive carbon.

[0147] The remaining preparation methods are the same as in Example 1.

[0148] Example 6

[0149] Preparation of positive electrode active materials:

[0150] Triphenylamine and Ketjen black were mixed at a mass ratio of 1:3 and then calcined at 1000°C for 6 hours under a nitrogen atmosphere to obtain N-doped Ketjen black conductive carbon.

[0151] The remaining preparation methods are the same as in Example 1.

[0152] Example 7

[0153] Preparation of positive electrode active materials:

[0154] Triphenylamine and Ketjen black were mixed at a mass ratio of 2:1 and then calcined at 1000°C for 6 hours under a nitrogen atmosphere to obtain N-doped Ketjen black conductive carbon.

[0155] The remaining preparation methods are the same as in Example 1.

[0156] The preparation methods of lithium-sulfur batteries in Examples 8-14 and Comparative Examples 1-2 are the same as those in Example 1, except that the battery preparation process is different. Specifically, Comparative Example 1 uses conductive carbon directly without any doped elements, and Comparative Example 2 does not use a diluent in its electrolyte, as shown in Table 1.

[0157] Table 1

[0158]

[0159] The cycle performance and discharge specific capacity of the lithium-sulfur batteries of Examples 1-14 and Comparative Examples 1-4 were characterized, and the characterization results are shown in Table 2.

[0160] 1. Cycle Performance Test: 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. This charge-discharge cycle was repeated 50 times, and the reversible capacity was measured as Cn. The cycle capacity retention rate was calculated as Cn / C0 × 100%.

[0161] 2. 100mA / g discharge specific capacity test: 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.

[0162] 3. 1000mA / g Discharge Specific Capacity Test: 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. The results are shown in Table 2.

[0163] Table 2

[0164]

[0165] The internal state diagrams of the lithium-sulfur batteries in Comparative Example 1 and Example 1 of this application are shown below. Figure 7 As shown in the figure, it can be seen that in Comparative Example 1, the conductive carbon of the positive electrode active material does not contain doping elements, and the Li in the positive electrode sheet and electrolyte is... + -DME-FSI - Some forces are weak, and some Li + -DME-FSI - The sulfur in the positive electrode is mostly in contact with the diluent fluorinated ether, which is located far away from the positive electrode. The intermediate product lithium polysulfide is insoluble in fluorinated ether, resulting in a solid-solid reaction of sulfur in the positive electrode, which leads to poor battery capacity and cycle performance.

[0166] In Example 1, the conductive carbon containing doped elements reacts with the lithium salt-solvent cluster Li in the electrolyte. + -DME-FSI - The force is strong, making Li + -DME-FSI - Most of them are enriched on the surface of the positive electrode active material particles, and lithium polysulfides can dissolve in the Li on the surface of the positive electrode active material. + -DME-FSI - Partially, this results in a solid-liquid-solid reaction of sulfur in the positive electrode, leading to higher rate performance and higher specific capacity in the battery; furthermore, because lithium polysulfides can dissolve in Li... + -DME-FSI - In this process, most lithium polysulfides are concentrated on the surface of the positive electrode active material, and the probability of them shuttling to the negative electrode is low. The presence of diluents also hinders the shuttling of lithium polysulfides to a certain extent, thus the cycle stability of the battery is also good.

[0167] As can be seen from Table 2, in Examples 1-14 of this application, the lithium-sulfur battery uses a diluent in the electrolyte and conductive carbon containing doped elements, which can improve the capacity and cycle performance of the lithium-sulfur battery. In addition, the specific capacity of the lithium-sulfur battery at a current of 1000 mA / g is also excellent, indicating that the rate performance of the lithium-sulfur battery in this application embodiment is also excellent.

[0168] Compared to Example 1, the conductive carbon in the positive electrode active material of Comparative Example 1 is not doped with any elements, and its capacity and cycle performance are significantly lower than those of Example 1, especially the discharge specific capacity of 100mA / g and 1000mA / g. This is because the reaction of sulfur is a solid-solid reaction, which affects its capacity. In Comparative Example 2, the electrolyte does not contain a diluent. Although the discharge specific capacity of the lithium-sulfur battery is still acceptable, the cycle performance is significantly reduced. This is because the lack of diluent has a limited blocking effect on the shuttle of lithium polysulfides, resulting in poor cycle performance of the battery.

[0169] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A lithium-sulfur battery, characterized in that, The lithium-sulfur battery includes a positive electrode, an electrolyte, and a negative electrode. The positive electrode sheet includes a positive electrode active material, which includes sulfur and conductive carbon containing doped elements, wherein the doped elements include one or more of N, B, or P elements. The electrolyte includes a lithium salt, a solvent, and a diluent.

2. The lithium-sulfur battery according to claim 1, characterized in that, The doping element includes at least two of N, B, or P elements.

3. The lithium-sulfur battery according to claim 1 or 2, characterized in that, Based on the total mass of the conductive carbon containing the doped elements, the mass percentage of the doped elements is 0.3%-3%.

4. The lithium-sulfur battery according to any one of claims 1-3, characterized in that, The mass ratio of the conductive carbon containing the doped element to the sulfur is (1:9)-(5:5).

5. The lithium-sulfur battery according to any one of claims 1-4, characterized in that, In the lithium salt and the solvent, the molar concentration of the lithium salt is 0.1 mol / L to 5 mol / L.

6. The lithium-sulfur battery according to any one of claims 1-5, characterized in that, The lithium salt 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.

7. The lithium-sulfur battery according to any one of claims 1-6, characterized in that, The solvent includes one or more of 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, 1,3-dioxopentane, or dimethyl ether.

8. The lithium-sulfur battery according to any one of claims 1-7, characterized in that, The diluent includes fluoroether diluents.

9. The lithium-sulfur battery according to claim 8, characterized in that, The fluoroether diluents include one or more of 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, or 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether.

10. The lithium-sulfur battery according to any one of claims 1-9, characterized in that, The sum of the volumes of the solvent and lithium salt: the volume of the diluent = (1:99) - (20:80).

11. The lithium-sulfur battery according to any one of claims 1-10, characterized in that, 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 including the positive electrode active material and the electrolyte.

12. The lithium-sulfur battery according to claim 11, characterized in that, In the positive electrode slurry, the mass ratio of each component is: positive electrode active material: electrolyte: conductive agent = (10-50): (50-90): (0.5-10).

13. A method for preparing a lithium-sulfur battery, characterized in that, include: By assembling the positive electrode, electrolyte, and negative electrode, a lithium-sulfur battery is obtained. The positive electrode sheet includes a positive electrode active material, which includes sulfur and conductive carbon containing doped elements, wherein the doped elements include at least one of N, B or P elements. The electrolyte includes a lithium salt, a solvent, and a diluent.

14. The method according to claim 13, characterized in that, The positive electrode active material is prepared by the following method: Conductive carbon is mixed with at least one of N, B or P sources and calcined under inert gas protection to obtain conductive carbon containing doped elements. The conductive carbon containing doped elements is mixed with sulfur and heated under inert gas protection to obtain a positive electrode active material.

15. The method according to claim 14, characterized in that, At least one of the following conditions must be met: The calcination temperature is 700℃-1200℃; The heating temperature is 120℃-200℃.

16. An electrical appliance, characterized in that, The lithium-sulfur battery includes any one of claims 1-12.

Images