Electrolyte composition for lithium-sulfur battery, lithium-sulfur battery, preparation method of lithium-sulfur battery and electric device

Abstract

The invention provides an electrolyte composition for a lithium-sulfur battery, the lithium-sulfur battery, a preparation method of the lithium-sulfur battery and a power utilization device, the electrolyte composition comprises a solvent, a lithium salt and a first additive, the solvent comprises an ether solvent, the first additive comprises one or more of a carbonic ester compound, a carboxylic ester compound and a ketone compound, and the carbonic ester compound, the carboxylic ester compound and the ketone compound all have carbon positive charge centers.

Description

Electrolyte composition for lithium-sulfur battery, lithium-sulfur battery and preparation method thereof, and electrical device

[0001] The present application relates to an electrolyte composition for a lithium-sulfur battery, a lithium-sulfur battery and a preparation method thereof, and an electrical device.

[0002] In recent years, batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, as well as in power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace and other fields. With the application and promotion of batteries, the energy density of traditional lithium-ion batteries can no longer meet the demand. Lithium-sulfur batteries have attracted widespread attention due to their advantages such as high theoretical energy density, abundant reserves and low cost. However, lithium-sulfur batteries have poor cycle stability and rapid capacity decay. The above statements are only used to provide background technical information related to this application and do not necessarily constitute prior art.

[0003] Summary of the invention

[0004] The present application provides an electrolyte composition for a lithium-sulfur battery, a lithium-sulfur battery and a preparation method thereof, and an electrical device, which can improve the cycle performance of the lithium-sulfur battery.

[0005] In a first aspect, the present application provides an electrolyte composition for a lithium-sulfur battery, comprising a solvent and a first additive, wherein the solvent comprises an ether solvent, and the first additive comprises one or more of a carbonate compound, a carboxylate compound, and a ketone compound, and the carbonate compound, the carboxylate compound, and the ketone compound all have a carbon positive charge center.

[0006] When the electrolyte composition provided in the embodiments of the present application is used in a lithium-sulfur battery, it can increase the discharge specific capacity of the lithium-sulfur battery, increase the capacity retention rate of the battery, and reduce the battery impedance, so that the lithium-sulfur battery has high cycle stability and long cycle life.

[0007] In any embodiment of the present application, the carbonate compound includes one or more compounds represented by formula (I):

[0008] R 11 , R 12 Each independently represents a C1-C6 alkyl group, a C6-C18 aryl group, a C7-C18 arylalkyl group, a C2-C18 heteroaryl group, a C3-C18 heteroarylalkyl group, and a group in which the above groups are substituted with a halogen atom and / or a nitro group, and R 11 , R 12At least one of the above represents a C6-C18 aryl group, a C7-C18 arylalkyl group, a C2-C18 heteroaryl group, a C3-C18 heteroarylalkyl group, and a group in which the above groups are substituted by a halogen atom and / or a nitro group.

[0009] In any embodiment of the present application, R 11 , R 12 Each independently represents a phenyl group, a benzyl group, a phenylethyl group, a thiazolyl group, a thiazolylmethyl group, a thiazolylethyl group, and a group in which the above groups are substituted with a halogen atom and / or a nitro group.

[0010] In any embodiment of the present application, R 11 , R 12 Each independently represents one of the following groups:

[0011] In any embodiment of the present application, R 11 , R 12 At least one of represents one of the following groups:

[0012] # indicates the connection location.

[0013] In any embodiment of the present application, the carboxylate compound includes one or more compounds represented by formula (II):

[0014] R 21 represents one of cyano, 2-((diphenylmethylene)amino)methyl, C1-C6 alkyl, C2-C6 alkenyl, C6-C18 aryl, C7-C18 arylalkyl, C2-C18 heteroaryl, C3-C18 heteroarylalkyl, and the above groups substituted with at least one of halogen atoms, cyano and nitro; R 22 It represents one of C1-C6 alkyl, C2-C6 alkenyl, C6-C18 aryl, C7-C18 arylalkyl, C2-C18 heteroaryl, C3-C18 heteroarylalkyl, and groups in which the above groups are substituted with at least one of halogen atoms, cyano groups, and nitro groups.

[0015] In any embodiment of the present application, R 21 It represents one of a cyano group, a 2-((diphenylmethylene)amino)methyl group, and a C1-C6 alkyl group, a C2-C6 alkenyl group, and a phenyl group substituted with at least one of a halogen atom, a cyano group, and a nitro group.

[0016] In any embodiment of the present application, R 21 represents one of the following groups:

[0017] In any embodiment of the present application, R 21 represents one of the following groups:

[0018] # indicates the connection location.

[0019] In any embodiment of the present application, R 22 It represents one of a C1-C6 alkyl group, a C2-C6 alkenyl group, and a group in which the above groups are substituted with at least one of a halogen atom, a cyano group, and a nitro group.

[0020] In any embodiment of the present application, R 22 It represents one of a methyl group, an ethyl group, a propyl group, a tert-butyl group, a propenyl group, an allyl group, and groups in which the above groups are substituted with at least one of a halogen atom, a cyano group, and a nitro group.

[0021] In any embodiment of the present application, the ketone compound includes one or more of 1-methyl-2-pyrrolidone and the compound represented by formula (III):

[0022] R 31 , R 32 Each independently represents a C5-C18 cycloalkyl group, a C5-C18 cycloalkenyl group, a C6-C18 aryl group, a C7-C18 arylalkyl group, a C2-C18 heteroaryl group, a C3-C18 heteroarylalkyl group, and a group in which the above groups are substituted by a halogen atom and / or a nitro group.

[0023] In any embodiment of the present application, R 31 , R 32 Each independently represents a C5-C8 cycloalkyl group, a C5-C8 cycloalkenyl group, a C6-C12 aryl group, a C7-C12 arylalkyl group, and a group in which the above groups are substituted with a halogen atom and / or a nitro group.

[0024] In any embodiment of the present application, R 31 , R 32 Each independently represents one of the following groups:

[0025] In any embodiment of the present application, R 31 , R 32 At least one of represents one of the following groups:

[0026] # indicates the connection location.

[0027] In any embodiment of the present application, the first additive includes at least one of the following compounds:

[0028] In any embodiment of the present application, the first additive includes at least one of the following compounds:

[0029] The carbon positive charge center of the first additive has a lower charge density and a stronger positive charge, thereby enhancing the reaction with soluble polysulfides and increasing the reaction rate. At the same time, less positive electrode active material is consumed during the reaction, thereby better improving the cycle life of the battery.

[0030] In addition, the solid insoluble product after the reaction of the above-mentioned first additive with the soluble polysulfide has a more obvious improvement effect on the positive electrode interface and the negative electrode interface, and can also interact with the subsequent long-chain polysulfides to play a binding role; it is also beneficial to form a liquid phase conduction mechanism of a three-dimensional network structure and improve the ion conductivity; it is also beneficial to guide the growth of insoluble lithium sulfide with a three-dimensional structure, slow down the passivation of the positive electrode by the insoluble lithium sulfide with a two-dimensional structure, and improve the utilization rate of sulfur.

[0031] In any embodiment of the present application, based on the total weight of the solvent, the content of the first additive is greater than 0 and less than or equal to 10% by weight, and can be optionally 1-9% by weight. When the content of the first additive is within the above range, part of the soluble polysulfide can be fixed on the positive electrode without affecting the conversion of the soluble polysulfide to the insoluble lithium sulfide, which helps the first additive to better mitigate the shuttle effect of the soluble polysulfide and regulate the subsequent liquid-solid phase conversion and the deposition morphology of the three-dimensional insoluble lithium sulfide, thereby helping to improve the utilization rate of the positive electrode active material and improve the cycle performance of the lithium-sulfur battery; it can also make the battery have good kinetic performance.

[0032] In any embodiment of the present application, the electrolyte further includes a second additive, and the second additive includes one or more of lithium nitrate, lithium polysulfide, potassium nitrate, cesium nitrate, barium nitrate, and ammonium nitrate, and can be selected to include lithium nitrate. The second additive mainly acts on the negative electrode, which can further reduce the irreversible reaction between soluble polysulfide and lithium, improve the interface properties of the negative electrode, and enhance the stability of the negative electrode during deposition / stripping; the second additive and the first additive can also form a good synergistic effect, thereby further improving the cycle performance of the lithium-sulfur battery.

[0033] In any embodiment of the present application, based on the total weight of the solvent, the content of the second additive is greater than 0 and less than or equal to 5 weight %, and may be 1-3 weight %.

[0034] In any embodiment of the present application, the ether solvent includes 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol methyl ethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, methyl ether, ethyl ether, propyl ether, isopropyl ether, butyl ether, methyl ethyl ether, methyl propyl ether, methyl butyl ether, ethyl propyl ether, ethyl butyl ether, propyl butyl ether, dimethoxymethane, diethoxymethane, dipropoxymethane, dimethoxyethane, dimethoxypropane, diethoxyethane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-bis(1, One or more of 1,2,2-tetrafluoroethoxy)ethane, bis(2,2,2-trifluoroethyl) ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, ethyl trifluoromethyl ether, difluoromethyl-2,2,3,3,3-pentafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, perfluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, ethyl-1,2,2,2-tetrafluoroethyl ether, and bis(1,2,2,2-tetrafluoroethyl) ether.

[0035] In any embodiment of the present application, the electrolyte composition further includes a lithium salt, and the lithium salt includes lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(pentafluoroethanesulfonyl)imide, lithium (fluorosulfonyl) (trifluoromethylsulfonyl)imide, lithium bis(oxalate borate), lithium difluorooxalate borate, lithium trifluoromethanesulfonate, 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonic acid imide, lithium trifluoroacetate. , lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, and optionally lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(pentafluoroethanesulfonyl)imide, lithium (fluorosulfonyl) (trifluoromethylsulfonyl)imide, lithium bis(oxalate borate), lithium difluorooxalate borate, lithium trifluoromethanesulfonate, lithium 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonic acid imide. This helps the lithium-sulfur battery have a longer cycle life.

[0036] In any embodiment of the present application, the concentration of the lithium salt in the electrolyte composition is 0.5-4 mol / L, and can be optionally 0.8-1.5 mol / L. By adjusting the concentration of the lithium salt within the above range, it will not affect the ion conductivity of the electrolyte, nor will it affect the stability of the electrolyte to the positive and negative electrodes, thereby helping to obtain a long-life lithium-sulfur battery.

[0037] In any embodiment of the present application, the solvent further includes other solvents, and the other solvents include one or more of sulfone solvents, nitrile solvents, hydrocarbons and halogenated hydrocarbon solvents.

[0038] The second aspect of the present application provides a method for preparing a lithium-sulfur battery, comprising the following steps: mixing the electrolyte composition of the first aspect of the present application uniformly and injecting the mixture into a battery container comprising a positive electrode, a negative electrode and a separator.

[0039] In any embodiment of the present application, the positive electrode includes a positive electrode active material, and the positive electrode active material includes one or more of elemental sulfur, lithium sulfide, lithium polysulfide, sulfur-carbon composite materials, sulfur-conductive polymer composite materials, and sulfur-metal oxide composite materials.

[0040] In any embodiment of the present application, the negative electrode includes one or more of lithium element and lithium alloy.

[0041] A third aspect of the present application provides a lithium-sulfur battery prepared by the method of the second aspect of the present application.

[0042] A fourth aspect of the present application provides an electrical device, comprising the lithium-sulfur battery of the third aspect of the present application.

[0043] The electrical device of the present application includes the lithium-sulfur battery provided by the present application, and thus has at least the same advantages as the lithium-sulfur battery.

[0044] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following briefly introduces the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some implementation methods of the present application, and for ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0045] FIG. 1 is a schematic diagram of an embodiment of a lithium-sulfur battery of the present application.

[0046] FIG. 2 is an exploded schematic diagram of an embodiment of a lithium-sulfur battery of the present application.

[0047] FIG. 3 is a schematic diagram of an embodiment of a battery module of the present application.

[0048] FIG. 4 is a schematic diagram of an embodiment of a battery pack of the present application.

[0049] FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .

[0050] FIG6 is a schematic diagram of an embodiment of an electrical device including the lithium-sulfur battery of the present application as a power source.

[0051] FIG. 7 shows the reaction results of the first additive and polysulfide.

[0052] FIG8 is a morphology of the positive electrode of the lithium-sulfur battery prepared in Example 1 after discharge.

[0053] FIG9 is a morphology of the positive electrode of the lithium-sulfur battery prepared in Comparative Example 1 after discharge.

[0054] FIG10 is a charge-discharge curve diagram of the first cycle of the lithium-sulfur battery prepared in Example 1.

[0055] FIG11 is a charge-discharge curve diagram of the first cycle of the lithium-sulfur battery prepared in Comparative Example 1.

[0056] FIG12 is a cycle curve diagram of the lithium-sulfur batteries prepared in Example 1 and Comparative Example 1.

[0057] In the drawings, the drawings may not be drawn according to the actual scale. The reference numerals are explained as follows: 1 battery pack, 2 upper box, 3 lower box, 4 battery module, 5 lithium-sulfur battery, 51 housing, 52 electrode assembly, 53 cover plate.

[0058] Hereinafter, the electrolyte composition for lithium-sulfur batteries, lithium-sulfur batteries and methods for preparing the same, and embodiments of the electric device of the present application are specifically disclosed with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of substantially the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0059] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0060] If not otherwise specified, all embodiments and optional embodiments of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

[0061] Unless otherwise specified, all technical features and optional technical features of the present application may be combined with each other to form new technical solutions, and such technical solutions should be deemed to be included in the disclosure of the present application.

[0062] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0063] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0064] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0065] If not otherwise specified, in this application, the terms "first", "second", etc. are used to distinguish different objects rather than to describe a specific order or a primary-secondary relationship.

[0066] Unless otherwise specified, the terms used in this application have the commonly understood meanings that are commonly understood by those skilled in the art.

[0067] Unless otherwise specified, the values ​​of the parameters mentioned in this application can be measured by various test methods commonly used in the art, for example, they can be measured according to the test methods given in the examples of this application. Unless otherwise specified, the test temperature of the parameters is 25°C.

[0068] The term "alkyl" encompasses both straight and branched chain alkyl groups. Examples of alkyl groups include, but are not limited to, methyl, ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl, isopentyl, etc. In various embodiments, C1-C6 alkyl groups, i.e., alkyl groups, may contain 1-6 carbon atoms.

[0069] The term "alkenyl" encompasses straight-chain and branched alkenyl groups. The number of carbon-carbon double bonds in the alkenyl group may be one or more than two. Examples of alkenyl groups include, but are not limited to, vinyl, propenyl, allyl, butenyl, butadienyl, and the like. In various embodiments, a C2-C6 alkenyl group, i.e., an alkenyl group, may contain 2-6 carbon atoms.

[0070] The term "cycloalkyl" refers to a closed alicyclic ring system. The alicyclic ring may or may not contain an alkyl group. Examples of cycloalkyl groups include, but are not limited to, cyclopentyl, cyclohexyl, and the like. In various embodiments, a C5-C18 cycloalkyl group, i.e., a cycloalkyl group, may contain 5-18 carbon atoms.

[0071] The term "cycloalkenyl" refers to a closed alicyclic ring system containing a carbon-carbon double bond. The alicyclic ring may or may not contain an alkyl group. The number of carbon-carbon double bonds in the cycloalkenyl group may be 1 or more than 2. Examples of cycloalkenyl groups include, but are not limited to, cyclohexenyl, cyclopentadienyl, cyclohexadienyl, and the like. In various embodiments, a C5-C18 cycloalkenyl group, i.e., a cycloalkenyl group, may contain 5-18 carbon atoms.

[0072] The term "aryl" refers to a closed aromatic ring or ring system. The aromatic ring may or may not contain an alkyl group. Examples of aryl groups include, but are not limited to, phenyl, dimethylphenyl, trimethylphenyl, etc. In various embodiments, C6-C18 aryl, i.e., aryl, may contain 6-18 carbon atoms.

[0073] The term "arylalkyl" refers to a group where the attachment position is on an alkyl group attached to an aryl group, while the attachment position of the aryl group is on an aromatic ring. In various embodiments, the C7-C18 arylalkyl, ie, arylalkyl, may contain 7-18 carbon atoms.

[0074] The term "heteroaryl" means that one or more atoms on the ring of the aromatic group are heteroatoms other than carbon atoms. The heteroatom may include one or more of a nitrogen atom, an oxygen atom, and a sulfur atom. The number of heteroatoms may be 1 or more than 2. Examples of heteroaryl groups include, but are not limited to, thiazolyl, methylthiazolyl, isothiazolyl, pyrrolyl, furyl, oxazolyl, isoxazolyl, thienyl, imidazolyl, pyrazolyl, triazole, pyridazinyl, pyrazinyl, pyridyl, pyrimidinyl, triazinyl, etc. In various embodiments, C2-C18 heteroaryl, i.e., heteroaryl, may contain 2-18 carbon atoms.

[0075] The term "heteroarylalkyl" refers to a group in which the attachment position is located on an alkyl group attached to a heteroaryl group, while the attachment position of the heteroaryl group is located on an aromatic ring. In various embodiments, a C3-C18 heteroarylalkyl group, ie, a heteroarylalkyl group, may contain 3-18 carbon atoms.

[0076] The term "halogen atom" means a fluorine atom, a chlorine atom or a bromine atom.

[0077] In various places of this specification, the substituent of compound is disclosed with group or scope.It is clearly expected that this description includes each individual subcombination of the member of these groups and scope.For example, it is clearly expected that the term "C1-C6 alkyl" discloses C1, C2, C3, C4, C5, C6, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C6, C2-C5, C2-C4, C2-C3, C3-C6, C3-C5, C3-C4, C4-C6, C4-C5, C5-C6 alkyl individually.As other examples, it is clearly expected that the integer of 6-18 in the scope discloses 6,7,8,9,10,11,12,13,14,15,16,17 and 18 individually.Accordingly, other groups or scopes can be clearly expected.

[0078] Throughout this manual, "#" indicates a connection location when it appears.

[0079] The embodiments of the present application provide an electrolyte composition for a lithium-sulfur battery.

[0080] The electrolyte composition includes a solvent and a first additive, wherein the solvent includes an ether solvent, and the first additive includes one or more of carbonate compounds, carboxylate compounds, and ketone compounds, and the carbonate compounds, carboxylate compounds, and ketone compounds all have a carbon positive charge center.

[0081] Lithium-sulfur batteries generally refer to batteries that use sulfur and / or sulfur-containing compounds as positive electrode active materials. They have the advantages of high theoretical specific capacity and high theoretical specific energy, and therefore have attracted widespread attention. However, the commercialization process of lithium-sulfur batteries is still restricted by many factors.

[0082] For example, lithium-sulfur batteries will form soluble polysulfide intermediates during the charge and discharge process. These intermediates will inevitably react with the metal lithium negative electrode, resulting in a "shuttle effect", which will lead to the loss of positive electrode active materials, lithium loss, and rapid battery capacity decay. The shuttle effect can also cause lithium-sulfur batteries to overcharge during charging, reducing coulombic efficiency.

[0083] Soluble polysulfides will also react with the lithium in the negative electrode to corrode, exacerbating the uneven deposition of lithium, causing the growth of lithium dendrites on the negative electrode surface and serious pulverization problems during the cycle. Soluble polysulfides diffuse to the negative electrode surface, and their reduction products accumulate on the negative electrode surface, increasing the negative electrode interface impedance. The negative electrode interface ion conduction is blocked, causing the morphology of lithium metal deposition on the negative electrode surface to deteriorate, making it easy to form lithium dendrites, which not only reduces the capacity of the lithium-sulfur battery, but also reduces the reliability of the lithium-sulfur battery.

[0084] A large amount of soluble polysulfides dissolved in the electrolyte will also cause the viscosity of the electrolyte to increase and the ion conduction rate to slow down.

[0085] As a result, lithium-sulfur batteries often have problems such as poor cycle stability, rapid capacity decay, and low coulombic efficiency, and cannot meet people's demand for long cycle life.

[0086] The first additive of the electrolyte composition provided in the embodiment of the present application has a carbon positive charge center, which can undergo a nucleophilic reaction with the negatively electron-carrying soluble polysulfide produced during the electrochemical reaction of the lithium-sulfur battery. The solid insoluble product formed after the reaction covers the surface of the positive electrode active material, which can reduce the further dissolution of the positive electrode active material, reduce the shuttling effect of the polysulfide, improve the cycle stability of the lithium-sulfur battery, and reduce the capacity decay.

[0087] The solid insoluble product formed after the first additive reacts with the soluble polysulfide can also serve as a reaction site in the subsequent liquid-solid phase conversion process (i.e., the process of converting soluble polysulfide into insoluble lithium sulfide, such as Li2S2 / Li2S), guiding the growth of three-dimensional insoluble lithium sulfide and slowing down the passivation of the positive electrode by the two-dimensional insoluble lithium sulfide, thereby extending the discharge time of the positive electrode and improving the utilization rate of sulfur.

[0088] Therefore, the first additive of the electrolyte composition provided in the embodiment of the present application can reduce the dissolution of the positive electrode active material and reduce the shuttle effect of polysulfides. It can also serve as a second active site to guide the growth of insoluble lithium sulfide with a three-dimensional structure and slow down the passivation of the positive electrode by the insoluble lithium sulfide with a two-dimensional structure, thereby extending the discharge time of the positive electrode and improving the utilization rate of sulfur.

[0089] After the first additive undergoes a nucleophilic reaction with the soluble polysulfide to fix the soluble polysulfide at the positive electrode, the reaction between the soluble polysulfide and lithium can be reduced, thereby alleviating the overcharge phenomenon; it can also further reduce the corrosion on the negative electrode interface, reduce or even hinder the deposition of non-conductive insoluble lithium sulfide at the negative electrode, thereby improving the stability of the negative electrode deposition / stripping process, improving the lithium metal deposition morphology, reducing dendrite formation, and improving the coulombic efficiency of the lithium-sulfur battery; it can also reduce the negative electrode interface impedance.

[0090] After the first additive undergoes a nucleophilic reaction with the soluble polysulfide to fix the soluble polysulfide on the positive electrode, it can also reduce the dissolution of the soluble polysulfide into the electrolyte, thereby reducing the viscosity of the electrolyte and improving the ionic conductivity of the electrolyte.

[0091] In addition, the electrolyte additives of lithium-sulfur batteries used in the prior art usually act on the electrolyte or the negative electrode, while the first additive of the electrolyte composition provided in the embodiment of the present application acts directly on the positive electrode, thereby more efficiently exerting the effect of the first additive; at the same time, only a small amount of soluble polysulfide needs to be consumed during the nucleophilic reaction, that is, the subsequent continuous dissolution of soluble polysulfide can be reduced. Therefore, the first additive of the electrolyte composition provided in the embodiment of the present application can more effectively reduce the dissolution of soluble polysulfide and reduce the irreversible chemical reaction between soluble polysulfide and lithium.

[0092] When the electrolyte composition provided in the embodiments of the present application is used in a lithium-sulfur battery, it can increase the discharge specific capacity of the lithium-sulfur battery, increase the capacity retention rate of the battery, and reduce the battery impedance, so that the lithium-sulfur battery has high cycle stability and long cycle life.

[0093] In some embodiments, the carbonate compound may include one or more of the compounds represented by formula (I):

[0094] R 11 , R 12 Each independently represents a C1-C6 alkyl group, a C6-C18 aryl group, a C7-C18 arylalkyl group, a C2-C18 heteroaryl group, a C3-C18 heteroarylalkyl group, and a group in which the above groups are substituted with a halogen atom and / or a nitro group, and R 11 , R 12 At least one of the above represents a C6-C18 aryl group, a C7-C18 arylalkyl group, a C2-C18 heteroaryl group, a C3-C18 heteroarylalkyl group, and a group in which the above groups are substituted by a halogen atom and / or a nitro group.

[0095] Optionally, R 11 , R 12 Each independently represents a phenyl group, a benzyl group, a phenylethyl group, a thiazolyl group, a thiazolylmethyl group, a thiazolylethyl group, and a group in which the above groups are substituted with a halogen atom and / or a nitro group. 11 , R 12 At least one of them represents a phenyl group substituted by a fluorine atom and / or a nitro group.

[0096] Optionally, R 11 , R 12 Each independently represents one of the following groups:

[0097] Optionally, R 11 , R 12 At least one of represents one of the following groups:

[0098] R 11 , R 12 When within the above range, the carbonate compound can react with the negatively electron-carrying soluble polysulfide produced during the electrochemical reaction of the lithium-sulfur battery to undergo a nucleophilic reaction to form a solid insoluble product including alkyl (or aryl) lithium carbonate, alkyl (or aryl) lithium oxide, polysulfide carbon, etc., and cover the surface of the positive electrode active material, thereby reducing the further dissolution of the positive electrode active material, reducing the shuttle effect of the polysulfide, improving the cycle stability of the lithium-sulfur battery, and reducing the capacity decay; it can also serve as a reaction site in the subsequent liquid-solid phase conversion process (i.e., the process of converting soluble polysulfide to insoluble lithium sulfide (such as Li2S2 / Li2S)), guiding the growth of insoluble lithium sulfide with a three-dimensional structure, and slowing down the passivation of the positive electrode by the insoluble lithium sulfide with a two-dimensional structure, thereby extending the positive electrode discharge time and improving the utilization rate of sulfur.

[0099] The electron-withdrawing effect of halogen atoms, nitro groups, aromatic rings, and heteroaromatic rings can make the charge density of the carbon positive charge center of carbonate compounds lower and more positively charged, thereby enhancing the reaction with soluble polysulfides and increasing the reaction rate. At the same time, less positive electrode active materials can be consumed during the reaction, thereby better improving the cycle life of the battery.

[0100] In addition, halogen atoms (especially fluorine atoms) and nitro groups can make the solid insoluble products after the reaction of carbonate compounds with soluble polysulfides more effective in improving the positive electrode interface and the negative electrode interface; they can also interact with subsequent long-chain polysulfides to play a binding role; and they are also conducive to the formation of a three-dimensional network structure of the liquid phase conduction mechanism, thereby improving the ionic conductivity.

[0101] In some embodiments, the carboxylate compound may include one or more compounds of formula (II):

[0102] R 21 represents one of cyano (-CN), 2-((diphenylmethylene)amino)methyl, C1-C6 alkyl, C2-C6 alkenyl, C6-C18 aryl, C7-C18 arylalkyl, C2-C18 heteroaryl, C3-C18 heteroarylalkyl, and the above groups substituted with at least one of halogen atoms, cyano and nitro; R 22 It represents one of C1-C6 alkyl, C2-C6 alkenyl, C6-C18 aryl, C7-C18 arylalkyl, C2-C18 heteroaryl, C3-C18 heteroarylalkyl, and groups in which the above groups are substituted with at least one of halogen atoms, cyano groups, and nitro groups.

[0103] Optionally, R 21 It represents one of a cyano group (—CN), a 2-((diphenylmethylene)amino)methyl group, and a C1-C6 alkyl group, a C2-C6 alkenyl group, and a phenyl group substituted with at least one of a halogen atom, a cyano group, and a nitro group.

[0104] Optionally, R 21 represents one of the following groups:

[0105] Optionally, R 21 represents one of the following groups:

[0106] Optionally, R 22 It represents one of a C1-C6 alkyl group, a C2-C6 alkenyl group, and a group in which the above groups are substituted with at least one of a halogen atom, a cyano group, and a nitro group.

[0107] Optionally, R 22 It represents one of a methyl group, an ethyl group, a propyl group, a tert-butyl group, a propenyl group, an allyl group, and groups in which the above groups are substituted with at least one of a halogen atom, a cyano group, and a nitro group.

[0108] R 21 , R 22 When within the above range, the carboxylate compound can react with the negatively electron-carrying soluble polysulfide produced during the electrochemical reaction of the lithium-sulfur battery to undergo a nucleophilic reaction to form a solid insoluble product including alkyl (or aryl) carboxylic acid lithium, alkyl (or aryl) oxygen lithium, polysulfide carbon, etc., and cover the surface of the positive electrode active material, thereby reducing the further dissolution of the positive electrode active material, reducing the shuttle effect of the polysulfide, improving the cycle stability of the lithium-sulfur battery, and reducing the capacity decay; it can also serve as a reaction site in the subsequent liquid-solid phase conversion process (i.e., the process of converting soluble polysulfide to insoluble lithium sulfide (such as Li2S2 / Li2S)), guiding the growth of insoluble lithium sulfide with a three-dimensional structure, and slowing down the passivation of the positive electrode by the insoluble lithium sulfide with a two-dimensional structure, thereby extending the positive electrode discharge time and improving the utilization rate of sulfur.

[0109] The electron-withdrawing effect of halogen atoms, cyano groups, nitro groups, aromatic rings, and heteroaromatic rings can make the charge density of the carbon positive charge center of carboxylic acid ester compounds lower and more positively charged, thereby enhancing the reaction with soluble polysulfides and increasing the reaction rate. At the same time, less positive electrode active materials can be consumed during the reaction, thereby better improving the cycle life of the battery.

[0110] In addition, halogen atoms (especially fluorine atoms), cyano groups, and nitrogen atoms (such as N atoms on amino groups) can also make the solid insoluble products after the reaction of carboxylic acid ester compounds with soluble polysulfides have a more obvious improvement effect on the positive electrode interface and the negative electrode interface; they can also interact with subsequent long-chain polysulfides to play a binding role; they are also conducive to the formation of a three-dimensional network structure of the liquid phase conduction mechanism, thereby improving the ionic conductivity.

[0111] In some embodiments, the ketone compound may include 1-methyl-2-pyrrolidone, one or more of the compounds of formula (III):

[0112] R 31 , R 32 Each independently represents a C5-C18 cycloalkyl group, a C5-C18 cycloalkenyl group, a C6-C18 aryl group, a C7-C18 arylalkyl group, a C2-C18 heteroaryl group, a C3-C18 heteroarylalkyl group, and a group in which the above groups are substituted by a halogen atom and / or a nitro group.

[0113] Optionally, the ketone compound may include 1-methyl-2-pyrrolidone and the compound represented by formula (III) at the same time.

[0114] Optionally, the ketone compound may include one or more compounds represented by formula (III).

[0115] Optionally, R 31 , R 32 Each independently represents a C5-C8 cycloalkyl group, a C5-C8 cycloalkenyl group, a C6-C12 aryl group, a C7-C12 arylalkyl group, and a group in which the above groups are substituted with a halogen atom and / or a nitro group.

[0116] Optionally, R 31 , R 32 Each independently represents one of the following groups:

[0117] Optionally, R 31 , R 32 At least one of represents one of the following groups:

[0118] R 31 , R 32 When within the above range, the ketone compound can react with the negatively electron-carrying soluble polysulfide produced during the electrochemical reaction of the lithium-sulfur battery to undergo a nucleophilic reaction to form a solid insoluble product including alkyl (or aryl) lithium, alkyl (or aryl) oxygen lithium, polysulfide carbon, etc., and cover the surface of the positive electrode active material, thereby reducing the further dissolution of the positive electrode active material, reducing the shuttle effect of the polysulfide, improving the cycle stability of the lithium-sulfur battery, and reducing the capacity decay; it can also serve as a reaction site in the subsequent liquid-solid phase conversion process (i.e., the process of converting soluble polysulfide to insoluble lithium sulfide (such as Li2S2 / Li2S)), guiding the growth of insoluble lithium sulfide with a three-dimensional structure, and slowing down the passivation of the positive electrode by the insoluble lithium sulfide with a two-dimensional structure, thereby extending the positive electrode discharge time and improving the utilization rate of sulfur.

[0119] The electron-withdrawing effect of halogen atoms, nitro groups, aromatic rings, heteroaromatic rings, and carbon-carbon double bonds can make the charge density of the carbon positive charge center of ketone compounds lower and the positive charge stronger, thereby enhancing the reaction with soluble polysulfides and increasing the reaction rate. At the same time, less positive electrode active materials can be consumed during the reaction, thereby better improving the cycle life of the battery.

[0120] In addition, halogen atoms (especially fluorine atoms) and nitro groups can make the solid insoluble products after the reaction of ketone compounds with soluble polysulfides more effective in improving the positive electrode interface and the negative electrode interface; they can also interact with subsequent long-chain polysulfides to play a binding role; and they are also conducive to the formation of a three-dimensional network structure of the liquid phase conduction mechanism, thereby improving the ionic conductivity.

[0121] In some embodiments, the first additive may include at least one of the following compounds:

[0122] In some embodiments, the first additive may include at least one of the following compounds:

[0123] The carbon positive charge center of the first additive has a lower charge density and a stronger positive charge, thereby enhancing the reaction with soluble polysulfides and increasing the reaction rate. At the same time, less positive electrode active material is consumed during the reaction, thereby better improving the cycle life of the battery.

[0124] In addition, the solid insoluble product after the reaction of the above-mentioned first additive with the soluble polysulfide has a more obvious improvement effect on the positive electrode interface and the negative electrode interface, and can also interact with the subsequent long-chain polysulfides to play a binding role; it is also beneficial to form a liquid phase conduction mechanism of a three-dimensional network structure and improve the ion conductivity; it is also beneficial to guide the growth of insoluble lithium sulfide with a three-dimensional structure, slow down the passivation of the positive electrode by the insoluble lithium sulfide with a two-dimensional structure, and improve the utilization rate of sulfur.

[0125] The first additive can be purchased commercially, and when used, a molecular sieve (such as 4A molecular sieve) can be used to remove water.

[0126] In some embodiments, based on the total weight of the solvent, the content of the first additive may be greater than 0 and less than or equal to 10 wt %. When the content of the first additive is too high, more soluble polysulfides may react with the first additive to form a large amount of solid insoluble products covering the surface of the positive electrode, which may hinder subsequent ion conduction and / or electron conduction, making it difficult for lithium ions to transfer charge with the positive electrode active material, which may cause problems such as increased battery impedance, reduced utilization of active materials, and poor battery kinetic performance.

[0127] In some embodiments, based on the total weight of the solvent, the content of the first additive may be 1-9% by weight, 1-8% by weight, 1-7% by weight, 1-6% by weight, or 1-5% by weight. When the content of the first additive is within the above range, part of the soluble polysulfide can be fixed on the positive electrode without affecting the conversion of the soluble polysulfide to the insoluble lithium sulfide, which helps the first additive to better mitigate the shuttle effect of the soluble polysulfide and regulate the subsequent liquid-solid phase conversion and the deposition morphology of the three-dimensional insoluble lithium sulfide, thereby helping to improve the utilization rate of the positive electrode active material and improve the cycle performance of the lithium-sulfur battery; it can also make the battery have good kinetic performance.

[0128] The amount of each first additive can be adjusted within the above range according to the type of the first additive to better improve the cycle performance and / or kinetic performance of the lithium-sulfur battery.

[0129] In some embodiments, the electrolyte may further include a second additive, which may include lithium nitrate, lithium polysulfide (LiS x , 4≤x≤8), one or more of potassium nitrate, cesium nitrate, barium nitrate, and ammonium nitrate, which may optionally include lithium nitrate. The second additive mainly acts on the negative electrode, which can further reduce the irreversible reaction between soluble polysulfides and lithium, improve the interface properties of the negative electrode, and enhance the stability of the negative electrode during deposition / stripping; the second additive and the first additive can also form a good synergistic effect, thereby further improving the cycle performance of the lithium-sulfur battery.

[0130] In some embodiments, based on the total weight of the solvent, the content of the second additive may be greater than 0 and less than or equal to 5 wt %, and may be 1-3 wt %.

[0131] In some embodiments, the ether solvent may be a solvent known in the art that is suitable for lithium-sulfur batteries, and may include, for example, 1,3-dioxolane (DOL), 1,3-dioxane, 1,4-dioxane, ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol methyl ethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, methyl ether, ethyl ether, propyl ether, isopropyl ether, butyl ether, methyl ethyl ether, methyl propyl ether, methyl butyl ether, ethyl propyl ether, ethyl butyl ether, propyl butyl ether, dimethoxymethane, diethoxymethane, dipropoxymethane, dimethoxyethane, dimethoxypropane, diethoxyethane, 1,1,2,2-tetrafluoroethyl-2,2,3,3 -tetrafluoropropyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, bis(2,2,2-trifluoroethyl) ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, ethyl trifluoromethyl ether, difluoromethyl-2,2,3,3,3-pentafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, perfluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, ethyl-1,2,2,2-tetrafluoroethyl ether, one or more of bis(1,2,2,2-tetrafluoroethyl) ether.

[0132] In some embodiments, the electrolyte composition further includes a lithium salt. The lithium salt may include lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium (fluorosulfonyl) (trifluoromethylsulfonyl)imide (LiFTFSI), lithium bis(oxalate borate), lithium difluorooxalate borate, lithium trifluoromethanesulfonate, 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonic acid imide lithium, lithium trifluoroacetate, lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate One or more. Alternatively, the lithium salt may include one or more of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethanesulfonyl)imide (LiBETI), lithium (fluorosulfonyl) (trifluoromethylsulfonyl)imide (LiFTFSI), lithium bis(oxalate borate), lithium bis(difluorooxalate borate), lithium trifluoromethanesulfonate, and lithium 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonic acid imide, thereby helping the lithium-sulfur battery to have a longer cycle life.

[0133] In some embodiments, the concentration of the lithium salt in the electrolyte composition may be 0.5-4 mol / L, and may be 0.8-1.5 mol / L. By adjusting the concentration of the lithium salt within the above range, the ion conductivity of the electrolyte will not be affected, and the stability of the electrolyte to the positive and negative electrodes will not be affected, thereby helping to obtain a long-life lithium-sulfur battery.

[0134] In some embodiments, the solvent may further include other solvents, for example, one or more of sulfone solvents, nitrile solvents, hydrocarbons and halogenated hydrocarbon solvents, which is not limited in the embodiments of the present application.

[0135] Preparation method of lithium-sulfur battery

[0136] The present application also provides a method for preparing a lithium-sulfur battery. The method comprises the following steps: mixing the above electrolyte composition uniformly and injecting it into a battery container including a positive electrode, a negative electrode and a separator.

[0137] In some embodiments, the preparation method may further include the following steps: forming the positive electrode, the separator and the negative electrode into an electrode assembly through a winding process and / or a lamination process, and placing the electrode assembly in a battery container.

[0138] In some embodiments, the preparation method may further include the following step: sealing the battery container.

[0139] In some embodiments, the preparation method may further include the following step: performing a chemical formation treatment on the sealed battery container.

[0140] In some embodiments, the battery container may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc., or may be a soft package, such as a bag-type soft package. The material of the soft package may be an aluminum-plastic film or plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT) and polybutylene succinate (PBS).

[0141] The present application has no particular limitation on the shape of the lithium-sulfur battery, which can be cylindrical, square or any other shape. FIG1 is a square lithium-sulfur battery 5 as an example.

[0142] In some embodiments, as shown in FIG. 2 , the battery container may include a shell 51 and a cover plate 53. The shell 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening connected to the receiving cavity, and the cover plate 53 is used to cover the opening to close the receiving cavity. The positive electrode, the separator and the negative electrode may form an electrode assembly 52 through a winding process and / or a lamination process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the lithium-sulfur battery 5 may be one or more, which can be adjusted according to demand.

[0143] [positive electrode]

[0144] In some embodiments, the positive electrode may include a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector, wherein the positive electrode film layer includes a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in its thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0145] In some embodiments, the positive electrode active material may include one or more of elemental sulfur, lithium sulfide, lithium polysulfide, sulfur-carbon composites, sulfur-conductive polymer composites, and sulfur-metal oxide composites.

[0146] In some embodiments, the positive electrode film layer may further include a positive electrode conductive agent. The present application has no particular restrictions on the type of the positive electrode conductive agent. As an example, the positive electrode conductive agent includes one or more of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0147] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The present application has no particular restrictions on the type of positive electrode binder. As an example, the positive electrode binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0148] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS) and polyethylene (PE).

[0149] The positive electrode film layer can be formed by coating the positive electrode slurry on the positive electrode current collector, drying and cold pressing. The positive electrode slurry is usually formed by dispersing the positive electrode active material, optional conductive agent, optional binder and any other components in a solvent and stirring them uniformly. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0150] [negative electrode]

[0151] In some embodiments, the negative electrode may include a negative electrode current collector and a metal layer disposed on at least one surface of the negative electrode current collector, wherein the metal layer includes one or more of lithium element and lithium alloy.

[0152] In some embodiments, the negative electrode current collector may include a metal foil, a three-dimensional porous current collector, or a composite current collector. As an example of a metal foil, copper foil, copper alloy foil, nickel foil, and nickel alloy foil may be used. As an example of a three-dimensional porous current collector, copper mesh, nickel mesh, foam copper, and foam nickel may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material may include one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0153] In some embodiments, the negative electrode may include a negative electrode current collector and an ultra-thin lithium sheet or a lithium alloy sheet disposed on at least one surface of the negative electrode current collector.

[0154] In some embodiments, the negative electrode may be a lithium sheet or a lithium alloy sheet.

[0155] The lithium alloy may be an alloy formed by metallic lithium and other metallic elements or non-metallic elements. As an example, the other metallic elements in the lithium alloy may include one or more of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, and platinum, and the non-metallic elements in the lithium alloy may include one or more of boron, carbon, and silicon.

[0156] In some embodiments, the negative electrode may include only a negative electrode current collector. Alternatively, the negative electrode current collector may be a three-dimensional porous current collector, such as a copper mesh, a nickel mesh, a copper foam, a nickel foam, and the like.

[0157] [Isolation film]

[0158] In some embodiments, the separator is disposed between the positive electrode and the negative electrode, mainly to prevent internal short circuits. The present application has no particular restrictions on the type of separator, and any known porous structure membrane with good chemical stability and mechanical stability can be selected.

[0159] In some embodiments, the material of the isolation membrane may include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride, and polyimide. The isolation membrane may be a single-layer film or a multi-layer composite film. When the isolation membrane is a multi-layer composite film, the materials of each layer are the same or different.

[0160] Lithium-sulfur battery

[0161] The present application also provides a lithium-sulfur battery prepared by the above method, which has good cycle performance.

[0162] In some embodiments, the lithium-sulfur batteries provided in the embodiments of the present application can be assembled into a battery module. The number of lithium-sulfur batteries contained in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0163] FIG3 is a schematic diagram of an exemplary battery module 4. As shown in FIG3, in the battery module 4, a plurality of lithium-sulfur batteries 5 may be arranged in sequence along the length direction of the battery module 4. Of course, they may also be arranged in any other manner. Further, the plurality of lithium-sulfur batteries 5 may be fixed by fasteners.

[0164] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of lithium-sulfur batteries 5 are received in the receiving space.

[0165] In some embodiments, the battery modules described above may also be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0166] FIG4 and FIG5 are schematic diagrams of a battery pack 1 as an example. As shown in FIG4 and FIG5, the battery pack 1 may include a battery box and a plurality of battery modules 4 disposed in the battery box. The battery box includes an upper box body 2 and a lower box body 3, wherein the upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 may be arranged in the battery box in any manner.

[0167] Electrical devices

[0168] The embodiments of the present application also provide an electrical device, which includes one or more of the lithium-sulfur batteries, battery modules or battery packs provided in the embodiments of the present application. The battery, 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 can be, but is not limited to, a mobile device (such as a mobile phone, a tablet computer, a laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship and a satellite, an energy storage system, etc.

[0169] Electrical devices can choose lithium-sulfur batteries, battery modules or battery packs according to their usage requirements.

[0170] Fig. 6 is a schematic diagram of an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electric device for high power and high energy density, a battery pack or a battery module may be used.

[0171] As another example, the electric device may be a mobile phone, a tablet computer, a laptop computer, etc. The electric device is usually required to be light and thin, and a lithium-sulfur battery may be used as a power source.

[0172] Example

[0173] The following examples describe the disclosure of the present application in more detail, and these examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present application are apparent to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following examples are by weight, and all reagents used in the examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and the instruments used in the examples are commercially available.

[0174] Example 1

[0175] (1) Preparation of electrolyte

[0176] In a glove box with an argon atmosphere (H2O<0.1ppm, O2<0.1ppm), ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL) were mixed with lithium salt LiTFSI (concentration of 1.0 mol / L) in a volume ratio of 1:1, and then 3 wt% of compound 1 (the first additive, based on the weight of the solvent, the structural formula is shown in Table 1) and 2 wt% of anhydrous lithium nitrate (the second additive, based on the weight of the solvent) were added, and the mixture was thoroughly stirred to obtain an electrolyte.

[0177] (2) Preparation of positive electrode

[0178] The sulfur-carbon composite material (sulfur loading of 70%), conductive carbon black Super P, and binder PVDF were mixed in a weight ratio of 8:1:1, and an appropriate volume of N-methylpyrrolidone (NMP) was added and stirred in a mixer for 30 minutes (speed 20kr / min) to form a stable and uniform positive electrode slurry. The positive electrode slurry was coated on the surface of the positive electrode current collector aluminum foil with a scraper, and then placed in an 80°C oven for 12 hours until the NMP was completely volatilized to obtain a positive electrode.

[0179] (3) Preparation of lithium-sulfur batteries

[0180] The prepared positive electrode was punched into a circular sheet with a diameter of 10 mm and dried in an oven at 60°C for 6 h. In a glove box with an argon atmosphere (H2O < 0.1 ppm, O2 < 0.1 ppm), a metal lithium sheet was used as the negative electrode, and a Celgard2400 polypropylene microporous membrane was used as the separator, and the circular sheet was assembled into a CR 2025 lithium-sulfur button cell. The amount of electrolyte used was 18 μL / mgS.

[0181] Example 2-37

[0182] The preparation method of the lithium-sulfur battery is similar to that of Example 1, except that the composition of the electrolyte is different, for example, the type and / or weight content of the first additive is different, as shown in Table 1 and Table 2. The weight content of the first additive is based on the weight of the solvent.

[0183] Comparative Example 1

[0184] The preparation method of the lithium-sulfur battery is similar to that of Example 1, except that the composition of the electrolyte is different and the first additive is not added to the electrolyte.

[0185] Comparative Example 2

[0186] The preparation method of the lithium-sulfur battery is similar to that of Example 1, except that the composition of the electrolyte is different, and the first additive and the second additive are not added to the electrolyte.

[0187] Test Section

[0188] The prepared lithium-sulfur battery was placed in a constant temperature room at 25°C for 8 hours, and then subjected to a constant current charge and discharge cycle test on a Blue Electric Test Charge and Discharge Tester. The test conditions were constant current 0.5C charging and 0.5C discharging, a voltage window of 1.7V-2.8V, and 200 cycles.

[0189] The initial specific capacity of the lithium-sulfur battery (mAh / g) = the first cycle discharge capacity of the lithium-sulfur battery / the weight of the sulfur-carbon composite material.

[0190] The specific capacity of the lithium-sulfur battery after 200 cycles (mAh / g) = the discharge capacity of the lithium-sulfur battery after 200 cycles / the weight of the sulfur-carbon composite material.

[0191] The capacity retention rate of the lithium-sulfur battery after 200 cycles (%) = (discharge capacity of the lithium-sulfur battery after 200 cycles / first cycle discharge capacity of the lithium-sulfur battery) × 100%.

[0192] The test results are shown in Table 2.

[0193] Table 1

[0194] Table 2

[0195] The reaction result of the first additive and polysulfide is shown in Figure 7. As shown in Figure 7, the first additive and polysulfide can generate solid insoluble matter.

[0196] FIG8 is a morphological diagram of the positive electrode of the lithium-sulfur battery prepared in Example 1 after discharge. FIG9 is a morphological diagram of the positive electrode of the lithium-sulfur battery prepared in Comparative Example 1 after discharge. As shown in FIG8, when the electrolyte contains the first additive, the solid insoluble product formed after the first additive reacts with the soluble polysulfide can guide the growth of the insoluble lithium sulfide with a three-dimensional structure, slow down the passivation of the positive electrode by the insoluble lithium sulfide with a two-dimensional structure, thereby extending the discharge time of the positive electrode, improving the utilization rate of sulfur, and improving the specific capacity of the lithium-sulfur battery. As shown in FIG9, when the electrolyte does not contain the first additive, an insoluble lithium sulfide with a two-dimensional structure will be formed on the surface of the positive electrode, thereby causing large-area passivation of the positive electrode, and thus the utilization rate of sulfur is low and the specific capacity of the lithium-sulfur battery is also low.

[0197] FIG10 is a charge-discharge curve of the first cycle of the lithium-sulfur battery prepared in Example 1. FIG11 is a charge-discharge curve of the first cycle of the lithium-sulfur battery prepared in Comparative Example 1. FIG12 is a cycle curve of the lithium-sulfur batteries prepared in Example 1 and Comparative Example 1. It can be seen from the test results of FIG10 to FIG12 and Table 2 that the first additive in the electrolyte can improve the discharge specific capacity and cycle stability of the lithium-sulfur battery.

[0198] The lithium-sulfur battery prepared in Comparative Example 2 cannot be cyclically charged and discharged due to the severe shuttle effect.

[0199] It should be noted that the present application is not limited to the above-mentioned embodiments. The above-mentioned embodiments are only examples, and the embodiments having the same structure as the technical idea and the same effect as the technical solution of the present application are all included in the technical scope of the present application. In addition, without departing from the scope of the main purpose of the present application, various modifications that can be thought of by those skilled in the art to the embodiments and other methods of combining some of the constituent elements in the embodiments are also included in the scope of the present application.

Claims

An electrolyte composition for a lithium-sulfur battery, wherein: The electrolyte composition includes a solvent and a first additive, wherein the solvent includes an ether solvent, and the first additive includes one or more of a carbonate compound, a carboxylate compound, and a ketone compound, and the carbonate compound, the carboxylate compound, and the ketone compound all have a carbon positive charge center. The electrolyte composition according to claim 1, wherein The carbonate compound includes one or more of the compounds represented by formula (I): R 11 , R 12 Each independently represents a C1-C6 alkyl group, a C6-C18 aryl group, a C7-C18 arylalkyl group, a C2-C18 heteroaryl group, a C3-C18 heteroarylalkyl group, and a group in which the above groups are substituted with a halogen atom and / or a nitro group, and R 11 , R 12 At least one of represents a C6-C18 aryl group, a C7-C18 arylalkyl group, a C2-C18 heteroaryl group, a C3-C18 heteroarylalkyl group, and a group in which the above groups are substituted by a halogen atom and / or a nitro group; and / or, the carboxylate compound includes one or more of the compounds represented by formula (II): R 21 represents one of cyano, 2-((diphenylmethylene)amino)methyl, C1-C6 alkyl, C2-C6 alkenyl, C6-C18 aryl, C7-C18 arylalkyl, C2-C18 heteroaryl, C3-C18 heteroarylalkyl, and the above groups substituted with at least one of halogen atoms, cyano and nitro; R 22 represents one of C1-C6 alkyl, C2-C6 alkenyl, C6-C18 aryl, C7-C18 arylalkyl, C2-C18 heteroaryl, C3-C18 heteroarylalkyl, and groups substituted by at least one of halogen atoms, cyano groups, and nitro groups; and / or, the ketone compound includes one or more of 1-methyl-2-pyrrolidone and the compound represented by formula (III): R 31 , R 32 Each independently represents a C5-C18 cycloalkyl group, a C5-C18 cycloalkenyl group, a C6-C18 aryl group, a C7-C18 arylalkyl group, a C2-C18 heteroaryl group, a C3-C18 heteroarylalkyl group, and a group in which the above groups are substituted by a halogen atom and / or a nitro group. The electrolyte composition according to claim 2, wherein R 11 , R 12 Each independently represents a phenyl group, a benzyl group, a phenylethyl group, a thiazolyl group, a thiazolylmethyl group, a thiazolylethyl group, and a group in which the above groups are substituted with a halogen atom and / or a nitro group; optionally, R 11 , R 12 Each independently represents one of the following groups: More optionally, R 11 , R 12 At least one of represents one of the following groups: R 21 represents a cyano group, a 2-((diphenylmethylene)amino)methyl group, and a C1-C6 alkyl group, a C2-C6 alkenyl group, or a phenyl group substituted with at least one of a halogen atom, a cyano group, or a nitro group; optionally, R 21 represents one of the following groups: More optionally, R 21 represents one of the following groups: R 22 represents a C1-C6 alkyl group, a C2-C6 alkenyl group, or a group in which the above groups are substituted by at least one of a halogen atom, a cyano group, and a nitro group; optionally, R 22 represents one of methyl, ethyl, propyl, tert-butyl, propenyl, allyl, and the above groups substituted with at least one of halogen atoms, cyano groups, and nitro groups; R 31 , R 32 Each independently represents a C5-C8 cycloalkyl group, a C5-C8 cycloalkenyl group, a C6-C12 aryl group, a C7-C12 arylalkyl group, and a group in which the above groups are substituted with a halogen atom and / or a nitro group; optionally, R 31 , R 32 Each independently represents one of the following groups: More optionally, R 31 , R 32 At least one of represents one of the following groups: # indicates the connection location. The electrolyte composition according to claim 2 or 3, wherein The first additive comprises at least one of the following compounds: Optionally, the first additive includes at least one of the following compounds: The electrolyte composition according to any one of claims 1 to 4, wherein Based on the total weight of the solvent, the content of the first additive is greater than 0 and less than or equal to 10 wt %, and may be 1-9 wt %. The electrolyte composition according to any one of claims 1 to 5, wherein The electrolyte further includes a second additive, which includes one or more of lithium nitrate, lithium polysulfide, potassium nitrate, cesium nitrate, barium nitrate, and ammonium nitrate, and may optionally include lithium nitrate. The electrolyte composition according to claim 6, wherein Based on the total weight of the solvent, the content of the second additive is greater than 0 and less than or equal to 5 weight %, and may be 1-3 weight %. The electrolyte composition according to any one of claims 1 to 7, wherein The ether solvents include 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, ethylene glycol methyl ethyl ether, ethylene glycol diethyl ether, diethylene glycol diethyl ether, tetrahydrofuran, methyltetrahydrofuran, tetrahydropyran, methyl ether, ethyl ether, propyl ether, isopropyl ether, butyl ether, methyl ethyl ether, methyl propyl ether, methyl butyl ether, ethyl propyl ether, ethyl butyl ether, propyl butyl ether, dimethoxymethane, diethoxymethane, dipropoxymethane, dimethoxyethane, dimethoxypropane, diethoxyethane, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-bis(1,1,2,2- One or more of tetrafluoroethoxy)ethane, bis(2,2,2-trifluoroethyl) ether, 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether, ethyl trifluoromethyl ether, difluoromethyl-2,2,3,3,3-pentafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, difluoromethyl 2,2,3,3-tetrafluoropropyl ether, perfluoroisopropyl methyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, ethyl-1,2,2,2-tetrafluoroethyl ether, and bis(1,2,2,2-tetrafluoroethyl) ether. The electrolyte composition according to any one of claims 1 to 8, wherein The electrolyte composition further includes a lithium salt, and the lithium salt includes one or more of lithium bis(fluorosulfonyl)imide, lithium bis(trifluoromethanesulfonyl)imide, lithium bis(pentafluoroethanesulfonyl)imide, lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, lithium bis(oxalate borate), lithium difluorooxalate borate, lithium trifluoromethanesulfonate, 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonic acid imide lithium, lithium trifluoroacetate, lithium hexafluorophosphate, lithium tetrafluoroborate, and lithium perchlorate, and optionally includes The invention relates to a lithium bis(fluorosulfonyl)imide, a lithium bis(trifluoromethanesulfonyl)imide, a lithium bis(pentafluoroethanesulfonyl)imide, a lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, a lithium bis(oxalate borate), a lithium difluorooxalate borate, a lithium trifluoromethanesulfonate, and a lithium 1,1,2,2,3,3-hexafluoropropane-1,3-disulfonic acid imide; and / or the concentration of the lithium salt in the electrolyte composition is 0.5-4 mol / L, and can be optionally 0.8-1.5 mol / L. The electrolyte composition according to any one of claims 1 to 9, wherein The solvent also includes other solvents, and the other solvents include one or more of sulfone solvents, nitrile solvents, hydrocarbons and halogenated hydrocarbon solvents. A method for preparing a lithium-sulfur battery comprises the following steps: The electrolyte composition according to any one of claims 1 to 10 is mixed uniformly and then injected into a battery container including a positive electrode, a negative electrode and a separator. The preparation method according to claim 11, wherein The positive electrode includes a positive electrode active material, and the positive electrode active material includes one or more of elemental sulfur, lithium sulfide, lithium polysulfide, a sulfur-carbon composite material, a sulfur-conductive polymer composite material, and a sulfur-metal oxide composite material. The preparation method according to claim 11 or 12, wherein The negative electrode includes one or more of lithium single substance and lithium alloy. A lithium-sulfur battery prepared by the method according to any one of claims 11 to 13. An electrical device comprising a lithium-sulfur battery prepared by the method according to any one of claims 11 to 13.

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