Electrolyte of lithium metal battery, lithium metal battery, battery and electric device

Abstract

The present application provides an electrolyte of a lithium metal battery, a lithium metal battery, a battery and an electric device. The electrolyte of a lithium metal battery comprises a lithium salt, a cyclic sulfone solvent and a diluent, wherein the diluent comprises at least one of a fluoroether compound and an aromatic compound. The present application can reduce gas production in lithium metal batteries, and improve the cycle performance of lithium metal batteries.

Description

Lithium metal battery electrolyte, lithium metal battery, battery and electrical device

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to Chinese patent application No. 202410269873.6, filed on March 8, 2024, entitled “Electrolyte for lithium metal battery, lithium metal battery, battery and electrical device,” the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present application belongs to the field of battery technology, and in particular relates to an electrolyte for a lithium metal battery, a lithium metal battery, a battery, and an electrical device. Background Art

[0004] Lithium metal batteries have high capacity and other characteristics, so they are widely used in electronic devices such as mobile phones, laptops, electric vehicles, electric airplanes, electric boats, electric toy cars, electric toy boats, electric toy airplanes and power tools, etc.

[0005] The electrolyte is an important component of lithium metal batteries and has a significant impact on the performance of lithium metal batteries. However, the current cycle performance of lithium metal batteries is poor and gas production is serious.

[0006] Summary of the Invention

[0007] The embodiments of the present application provide an electrolyte for a lithium metal battery, a lithium metal battery, a battery, and an electrical device, which can reduce the gas production of the lithium metal battery and improve the cycle performance of the lithium metal battery.

[0008] An embodiment of the first aspect of the present application provides an electrolyte for a lithium metal battery, the electrolyte comprising a lithium salt, a cyclic sulfone solvent and a diluent, wherein the diluent comprises at least one of a fluoroether compound and an aromatic compound.

[0009] Therefore, the cyclic sulfone solvent of the embodiment of the present application can form a solvation structure with the anions and lithium ions in the lithium salt, which helps to form a stable and uniform solid electrolyte interface (SEI) film, can induce uniform deposition of lithium metal, reduce the risk of lithium dendrite growth, and improve the cycle performance of the lithium metal battery; and the diluent makes the viscosity of the electrolyte relatively small, which is conducive to reducing polarization and further improving the cycle performance of the lithium metal battery; in addition, the electrolyte is not easy to produce gas, which can reduce the gas production of the lithium metal battery and improve the gas production resistance.

[0010] In some embodiments, the cyclic sulfone solvent includes a compound represented by formula (I),

[0011] In formula (I), R1, R2, R3, and R4 each independently comprise a hydrogen atom, a fluorine atom, or a C1 to C5 fluoroalkyl group. The cyclic sulfone solvents have relatively strong solubility and dissociation ability for lithium salts, allowing the lithium ions in the lithium salts to form a solvated structure. Furthermore, the cyclic sulfone solvents have high structural stability and are not susceptible to decomposition.

[0012] In some embodiments, R1 and R4 comprise different groups; and / or R2 and R3 comprise different groups. Asymmetric cyclic sulfone solvents have better stability on the negative electrode side, which can further improve the cycle performance of lithium metal batteries.

[0013] In some embodiments, at least one of R1, R2, R3, and R4 includes a fluorine atom or a C1 to C5 fluoroalkyl group. This structure can further reduce the viscosity and polarization of the electrolyte and improve the cycle performance of the lithium metal battery.

[0014] In some embodiments, the cyclic sulfone solvent includes at least one of the compounds represented by formula (I1) to the compounds represented by formula (I20),

[0015] In some embodiments, the fluoroether compound includes a compound represented by formula (A), M1-O-M2 formula (A),

[0016] In formula (A), M1 and M2 each independently comprise a C2 to C5 alkyl group or a C2 to C5 fluoroalkyl group, wherein at least one of M1 and M2 comprises a C2 to C5 fluoroalkyl group. The relatively small volume of the diluent can reduce the viscosity of the electrolyte system, thereby reducing polarization and improving the cycling performance of the lithium metal battery.

[0017] In some embodiments, M1 and M2 each independently comprise a C2 to C5 linear alkyl group or a C2 to C5 fluorinated linear alkyl group, wherein at least one of M1 and M2 comprises a C2 to C5 fluorinated linear alkyl group. Alkyl groups with linear structures are more conducive to reducing the viscosity of the electrolyte system and polarization, thereby improving the cycling performance of lithium metal batteries.

[0018] In some embodiments, the fluoroether compound includes at least one of the compounds represented by formula (A1) to the compounds represented by formula (A9),

[0019] In some embodiments, the aromatic compound includes at least one of benzene, anisole, phenethyl ether, furan, and thiophene. These compounds have relatively small molecular volumes, minimally impacting lithium ion transport, facilitating lithium ion transport within the solvated structure and reducing polarization. Furthermore, these compounds have high boiling points and are less susceptible to decomposition at the normal operating temperature of lithium metal batteries, further enhancing the stability of the solvent system in the electrolyte, improving high-temperature cycling performance, and improving gas generation resistance.

[0020] In some embodiments, based on the total molar amount of the electrolyte, the ratio of the molar content of the cyclic sulfone solvent to the molar content of the lithium salt is greater than 1:1 and less than or equal to 3:1. When the ratio of the molar content of the cyclic sulfone solvent to the molar content of the lithium salt is within the above range, the cyclic sulfone solvent can form a solvation structure with the lithium salt, and can further improve the cycling performance of the lithium metal battery.

[0021] In some embodiments, the ratio of the molar content of the cyclic sulfone solvent to the molar content of the lithium salt is 1.2:1 to 3:1.

[0022] In some embodiments, the ratio of the molar content of the cyclic sulfone solvent to the molar content of the lithium salt is 1.2:1 to 2.5:1.

[0023] In some embodiments, based on the total molar amount of the electrolyte, the ratio of the molar content of the diluent to the molar content of the lithium salt is 1:1 to 5:1. When the ratio of the molar content of the diluent to the molar content of the lithium salt is within the above range, the viscosity of the electrolyte is relatively lower, the lithium salt content is moderate, and the cycle performance of the lithium metal battery can be further improved.

[0024] In some embodiments, the lithium salt includes a first lithium salt, and the first lithium salt includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide. When the first lithium salt is used in combination with the above-mentioned organic solvent, the first lithium salt has a relatively high solubility in the organic solvent and can be dissociated by the organic solvent, which is conducive to forming a solvated structure.

[0025] In some embodiments, the lithium salt further includes a second lithium salt, which includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium dioxalatoborate, lithium difluorodioxalatophosphate and lithium tetrafluorooxalatophosphate; the second lithium salt and the first lithium salt are combined to further improve the cycle performance of the lithium metal battery.

[0026] In some embodiments, based on the total molar amount of the electrolyte, the ratio of the molar content of the second lithium salt to the molar content of the first lithium salt is 0.05:1 to 0.20:1.

[0027] An embodiment of the second aspect of the present application provides a lithium metal battery, which includes the electrolyte of any embodiment of the first aspect of the present application.

[0028] In some embodiments, a lithium metal battery includes a negative electrode sheet including a negative electrode current collector.

[0029] In some embodiments, a lithium metal battery includes a negative electrode plate, wherein the negative electrode plate includes a negative electrode current collector and a lithium metal layer disposed on at least one side of the negative electrode current collector.

[0030] In some embodiments, the lithium metal layer includes lithium metal element or lithium metal alloy, and the lithium metal alloy includes non-lithium elements and lithium elements, and the non-lithium elements include at least one of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, platinum, boron, carbon, and silicon.

[0031] In some embodiments, the lithium metal battery further comprises a positive electrode sheet, the positive electrode sheet comprising a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector and comprising a positive electrode active material, the positive electrode active material comprising a general formula of Li x A y Ni a Co b Mn c M (1-a-b-c) Q z A compound, wherein 0<x≤2.1, 0≤y≤2.1, and 0.9≤x+y≤2.1; 0<a<1, 0<b<1, 0<c<1, and 0.1≤a+b+c≤1; 1.8≤z≤3.5; A includes at least one of Na, K, and Mg; M includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; Q includes at least one of O and F; the above-mentioned layered structure positive electrode active material has a relatively high specific capacity, which is beneficial to improving the energy density of the lithium metal battery; and when the above-mentioned positive electrode active material and the electrolyte are used in combination, the stability of the interface between the electrolyte and the positive electrode sheet is high, which is beneficial to improving the cycle performance of the lithium metal battery.

[0032] A third aspect of the present application provides a battery, comprising a lithium metal battery according to any embodiment of the second aspect of the present application.

[0033] A fourth aspect of the present application provides an electrical device comprising a battery according to any embodiment of the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments of the present application. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on the drawings without creative work.

[0035] FIG1 is a schematic diagram of an embodiment of a lithium metal battery of the present application.

[0036] FIG. 2 is an exploded schematic diagram of an embodiment of the lithium metal battery of FIG. 1 .

[0037] FIG3 is a schematic diagram of an embodiment of a battery module of the present application.

[0038] FIG4 is a schematic diagram of an embodiment of a battery pack of the present application.

[0039] FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .

[0040] FIG6 is a schematic diagram of an embodiment of an electric device including the lithium metal battery of the present application as a power source.

[0041] The drawings are not necessarily drawn to scale.

[0042] The following are the descriptions of the reference numerals:

[0043] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module;

[0044] 5. lithium metal battery; 51. housing; 52. electrode assembly;

[0045] 53. Cover plate;

[0046] 6. Electrical equipment. DETAILED DESCRIPTION

[0047] Below, the embodiments of the lithium metal battery electrolyte, lithium metal battery, battery and electrical device of the present application are described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there may be cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structures are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate understanding by those skilled in the art. In addition, the drawings and the following description 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.

[0048] " range " disclosed in the present application is limited in the form of lower limit and upper limit, and 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 special range. The scope limited in this way can be to include end value or not include end value, and can be arbitrarily combined, that is, any lower limit can form a range with any upper limit combination. For example, if the scope of 60-120 and 80-110 is listed for specific parameters, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range value 1 and 2 are listed, and if the maximum range value 3,4 and 5 are listed, then the following range can all be expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this 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 all real numbers. For example, a numerical range of "0-5" indicates that all real numbers between "0-5" are listed herein, and "0-5" is simply an abbreviation for these numerical combinations. Furthermore, when a parameter is expressed as an integer ≥ 2, this 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.

[0049] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0050] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0051] Unless otherwise specified, all steps of the present application may be performed sequentially or randomly, preferably sequentially. For example, a method includes steps (a) and (b), which indicates that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, a method may further include step (c), which 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 may include steps (a), (c), and (b), or may include steps (c), (a), and (b), etc.

[0052] The term "alkyl" encompasses both straight and branched chain alkyl groups. For example, the alkyl group can be a C5-C500 alkyl group, a C20-C400 alkyl group, a C1-C50 alkyl group, a C1-C40 alkyl group, a C1-C30 alkyl group, a C1-C20 alkyl group, a C1-C12 alkyl group, a C1-C10 alkyl group, a C1-C6 alkyl group, a C1-C5 alkyl group, a C2-C5 alkyl group. In some embodiments, the alkyl group includes a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, a sec-butyl group, a tert-butyl group, a cyclobutyl group, a pentyl group, an isopentyl group, a neopentyl group, a tert-pentyl group, a cyclopentyl group, a hexyl group, a cyclohexyl group, a heptyl group, a cycloheptyl group, an octyl group, a cyclooctyl group, a nonyl group, and a decyl group. In addition, the alkyl group can be optionally substituted. The term "haloalkyl" refers to an alkyl group in which some or all of the hydrogen atoms are replaced by halogen atoms, and the term "halogen atom" refers to a fluorine atom, a chlorine atom, a bromine atom, an iodine atom, and the like.

[0053] The term "hydrogen" refers to 1H (protium, H), 2H (deuterium, D), or 3H (tritium, T). In various embodiments, "hydrogen" may be 1H (protium, H).

[0054] At various places in this specification, substituents of compounds are disclosed in groups or ranges. It is expressly intended that such description includes every individual subcombination of the members of these groups and ranges. For example, the term "C1-C8 alkyl" is specifically intended to disclose individually C1, C2, C3, C4, C5, C6, C7, C8, C1-C8, C1-C7, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C8, C2-C7, C2-C6, C2-C5, C2-C4, C2-C3, C3-C8, C3-C7, C3-C6, C3-C5, C3-C4, C4-C8, C4-C7, C4-C6, C4-C5, C5-C8, C5-C7, C5-C6, C6-C8, C6-C7, and C7-C8 alkyl.

[0055] As further examples, the integers in the range of 5-40 are specifically contemplated as individually disclosing 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, and 40; the integers in the range of 1-20 are specifically contemplated as individually disclosing 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, and 20. Additional groups or ranges are expressly contemplated accordingly.

[0056] A lithium metal battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is located between the positive electrode sheet and the negative electrode sheet to isolate the positive electrode sheet from the negative electrode sheet. Lithium metal batteries achieve energy storage and discharge through the stripping and deposition of lithium metal. Specifically, during the charging process of a lithium metal battery, lithium ions are released from the positive active material of the positive electrode sheet, pass through the separator through the electrolyte, desolvate from the solvent molecules, pass through the solid electrolyte interface (SEI) membrane, and are deposited and reduced to lithium metal on the surface of the negative electrode sheet, thereby generating a current concentration difference in the external circuit. During the discharge process of a lithium metal battery, the lithium metal on the surface of the negative electrode sheet loses electrons to the external circuit, and the lithium metal forms lithium ions that are released into the electrolyte and, after solvation, migrate through the electrolyte to the positive active material.

[0057] Due to the high reactivity of lithium metal and the high risk of dendrite formation, the reliability of lithium metal batteries is affected. To improve the reliability of lithium metal batteries, the lithium salt concentration of the electrolyte is usually increased in related technologies. However, as the lithium salt concentration increases, the viscosity of the electrolyte system increases, polarization intensifies, and this may lead to poor cycling performance of the lithium metal battery. Moreover, during the cyclic charge and discharge process of the lithium metal battery, the organic solvent in the electrolyte may decompose and produce gas, causing the lithium metal battery to swell or even explode and fail, which to a certain extent affects the reliability of the lithium metal battery and results in insignificant improvements in the reliability of the lithium metal battery.

[0058] In view of the above problems, the embodiments of the present application improve the composition of the electrolyte. By selecting specific organic solvents, diluents and lithium salts, the organic solvent can form a solvation structure with the anions and lithium ions in the lithium salt, which helps to form a stable and uniform SEI film, can induce uniform deposition of lithium metal, reduce the risk of lithium dendrite growth, and improve the cycle performance of lithium metal batteries; and the diluent makes the viscosity of the electrolyte relatively small, which is conducive to reducing polarization and further improving the cycle performance of lithium metal batteries; in addition, the electrolyte is not easy to produce gas, which can reduce the gas production of lithium metal batteries and improve gas production resistance. The technical solution of this application is described in detail below.

[0059] electrolyte

[0060] In a first aspect, an embodiment of the present application provides an electrolyte.

[0061] The electrolyte includes lithium salt, cyclic sulfone solvent and diluent, and the diluent includes at least one of fluoroether compound and aromatic compound.

[0062] When the organic solvent includes a cyclic sulfone solvent, the solubility and dissociation ability of the lithium salt are relatively strong, and the lithium ions in the lithium salt can form a solvated structure. Specifically, the lithium salt is dissociated into lithium ions and anions by the organic solvent. The lithium ions can coordinate with the solvent molecules and with a large number of anions, forming contact ion pairs and cation-anion aggregates, thereby forming a solvated structure. This solvated structure facilitates the anions to participate in the reaction on the surface of the negative electrode before the organic solvent to form an inorganic-rich SEI film. The SEI film is stable and has a uniform thickness, which is conducive to inducing uniform deposition of lithium metal, reducing the risk of lithium dendrite growth, improving the reliability of the lithium metal battery, and enhancing the cycling performance of the lithium metal battery.

[0063] Compared with chain sulfone solvents, cyclic sulfone solvents have excellent oxidation resistance. During the charge and discharge cycle of lithium metal batteries, cyclic sulfone solvents have better stability on the positive electrode side of the lithium metal battery and are not easy to decompose. On the negative electrode side of the lithium metal battery, due to the preferential film formation of anions, cyclic sulfone solvents have higher stability on the negative electrode side, that is, the interface stability between the electrolyte and the negative electrode is higher, and cyclic sulfone solvents are not easy to decompose. Even if the cyclic sulfone solvent decomposes, due to its cyclic structure, it decomposes into a chain structure and is not easy to produce gas, thereby reducing the gas production in the lithium metal battery system and improving the gas production resistance.

[0064] The electrolyte also includes a diluent, which includes a fluoroether compound and an aromatic compound. The combination of a cyclic sulfone solvent and a diluent can reduce the viscosity of the electrolyte, reduce polarization, and further improve the cycle performance of the lithium metal battery. In particular, the molecular volume of the diluent is relatively small, which has little effect on the transmission of lithium ions, and can further improve the polarization phenomenon and improve the cycle performance of the lithium metal battery. Furthermore, when the boiling point of the diluent is relatively high, the saturated vapor pressure of the electrolyte can be reduced, further improving the stability of the electrolyte at high temperatures, thereby improving the high-temperature cycle performance of the lithium metal battery.

[0065] The electrolyte of the embodiment of the present application can improve the cycle performance of the lithium metal battery and have a relatively low gas production by using the above-mentioned cyclic sulfone solvent and diluent in combination.

[0066] [Cyclic sulfone solvents]

[0067] The cyclic sulfone solvents include compounds represented by formula (I),

[0068] In formula (I), R1, R2, R3 and R4 each independently include a hydrogen atom, a fluorine atom or a C1 to C5 fluoroalkyl group.

[0069] The cyclic sulfone solvents have relatively strong solubility and dissociation ability for lithium salts, and the lithium ions in the lithium salts can form a solvated structure; and the cyclic sulfone solvents have high structural stability and are not easily decomposed.

[0070] The C1 to C5 alkyl group may be methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, n-pentyl, isopentyl, etc. At least one hydrogen atom in the C1 to C5 alkyl group may be substituted with a fluorine atom.

[0071] In some embodiments, the cyclic sulfone solvent may include an asymmetric cyclic sulfone solvent. An asymmetric cyclic sulfone solvent refers to a solvent in which the groups in the symmetrical positions on the ring structure are different, for example, R1 and R4 include different groups, in which case, R2 and R3 may include the same group, of course, R2 and R3 may include different groups; or, for example, R2 and R3 include different groups, in which case, R1 and R4 may include the same group.

[0072] Asymmetric cyclic sulfone solvents have a relatively low melting point and low viscosity, which can reduce electrolyte viscosity and polarization, thereby improving the cycling performance of lithium metal batteries. Even if cyclic sulfone solvents undergo ring opening on the negative electrode side, the side chain of asymmetric cyclic sulfone solvents contains electron-donating groups, which has little impact on the negative electrode. In other words, asymmetric cyclic sulfone solvents have better stability on the negative electrode side, which can further improve the cycling performance of lithium metal batteries.

[0073] In some embodiments, the cyclic sulfone solvent may include a fluorinated cyclic sulfone solvent. Fluorinated cyclic sulfone solvents have a relatively low melting point and low viscosity, which can reduce electrolyte viscosity and polarization, thereby improving the cycling performance of lithium metal batteries. For example, at least one of R1, R2, R3, and R4 includes at least one of a fluorine atom and a C1 to C5 fluorinated alkyl group.

[0074] In some embodiments, the cyclic sulfone solvent may include an asymmetric fluorinated cyclic sulfone solvent. This structure can further reduce the viscosity and polarization of the electrolyte and improve the cycle performance of the lithium metal battery.

[0075] Illustratively, the compound represented by formula (I) includes at least one of the compounds represented by formula (I1) to the compounds represented by formula (I20),

[0076] Optionally, the compound represented by formula (I) includes at least one of the compounds represented by formula (I2) to the compounds represented by formula (I9). Such compounds are asymmetric cyclic sulfone compounds that can further reduce the viscosity and polarization of the electrolyte and improve the cycle performance of lithium metal batteries.

[0077] Optionally, the compound represented by formula (I) includes at least one of the compounds represented by formula (I11) to the compounds represented by formula (I20). Such compounds are fluorinated cyclic sulfone compounds that can further reduce the viscosity and polarization of the electrolyte and improve the cycle performance of lithium metal batteries.

[0078] In some embodiments, based on the total molar amount of the electrolyte, the ratio of the molar content of the cyclic sulfone solvent to the molar content of the lithium salt is greater than 1:1 and less than or equal to 3:1; optionally, 1.2:1 to 3:1; or optionally, 1.2:1 to 2.5:1. When the ratio of the molar content of the cyclic sulfone solvent to the molar content of the lithium salt is within the above range, the cyclic sulfone solvent can form a solvation structure with the lithium salt, and can further improve the cycling performance of the lithium metal battery.

[0079] Illustratively, the ratio of the molar content of the cyclic sulfone solvent to the molar content of the lithium salt can be 1.1:1, 1.2:1, 1.3:1, 1.5:1, 1.6:1, 1.8:1, 2.0:1, 2.2:1, 2.5:1, 2.6:1, 2.8:1, 3:1, or a range consisting of any two of the above values.

[0080] [Thinner]

[0081] The diluent includes at least one of a fluoroether compound and an aromatic compound. The volume of the diluent is relatively small, which can reduce the viscosity of the electrolyte system, and is beneficial to reducing polarization and improving the cycle performance of the lithium metal battery.

[0082] In some embodiments, the fluoroether compound includes a compound represented by formula (A), M1-O-M2 formula (A),

[0083] In formula (A), M1 and M2 each independently include a C2 to C5 alkyl group or a C2 to C5 fluoroalkyl group, wherein at least one of M1 and M2 includes a C2 to C5 fluoroalkyl group. Alternatively, M1 and M2 each independently include at least one of a C2 to C3 alkyl group and a C2 to C3 fluoroalkyl group, wherein at least one of M1 and M2 includes a C2 to C3 fluoroalkyl group.

[0084] The alkyl group may be a linear alkyl group or a branched alkyl group. For example, a C2 to C5 alkyl group may include a C2 to C5 linear alkyl group or a C2 to C5 branched alkyl group, and may optionally be a C2 to C5 linear alkyl group. For example, a C2 to C5 fluoroalkyl group may include a C2 to C5 linear fluoroalkyl group or a C2 to C5 branched fluoroalkyl group, and may optionally be a C2 to C5 linear fluoroalkyl group. At least one hydrogen atom in the alkyl group may be replaced by a fluorine atom. Alkyl groups with a linear structure are more conducive to reducing the viscosity of the electrolyte system, reducing polarization, and improving the cycle performance of lithium metal batteries.

[0085] Specifically, M1 and M2 each independently include a C2 to C5 linear alkyl group or a C2 to C5 fluorinated linear alkyl group, wherein at least one of M1 and M2 each includes a C2 to C5 fluorinated linear alkyl group.

[0086] Optionally, M1 and M2 each independently include at least one of a C2 to C3 linear alkyl group and a C2 to C3 fluorinated linear alkyl group, wherein at least one of M1 and M2 each includes a C2 to C3 fluorinated linear alkyl group.

[0087] Illustratively, the compound represented by formula (A) includes at least one of the compounds represented by formula (A1) to the compounds represented by formula (A9),

[0088] Optionally, the compound represented by formula (A) includes the compound represented by formula (A6). The molecular volume of the above-mentioned compound is relatively small, which has little effect on the transmission of lithium ions, is conducive to the transmission of lithium ions in the solvated structure, and reduces polarization. In addition, the above-mentioned compound has a high boiling point and is not easily decomposed at the relatively high operating temperature of the lithium metal battery. It can further improve the stability of the solvent system in the electrolyte, improve high-temperature cycle performance and gas production resistance.

[0089] In some embodiments, the aromatic compound includes at least one of benzene, anisole, phenethyl ether, furan, and thiophene. Optionally, the aromatic compound may include benzene. The molecular volume of the above-mentioned compound is relatively small, which has little effect on the transmission of lithium ions, is conducive to the transmission of lithium ions in the solvated structure, and reduces polarization. In addition, the above-mentioned compound has a high boiling point and is not easily decomposed at the normal operating temperature of the lithium metal battery. It can further improve the stability of the solvent system in the electrolyte, improve high-temperature cycle performance and gas production resistance.

[0090] In some embodiments, based on the total molar amount of the electrolyte, the ratio of the molar content of the diluent to the molar content of the lithium salt is 1:1 to 5:1. When the ratio of the molar content of the diluent to the molar content of the lithium salt is within the above range, the viscosity of the electrolyte is relatively lower, the lithium salt content is moderate, and the cycle performance of the lithium metal battery can be further improved.

[0091] Illustratively, the ratio of the molar content of the diluent to the molar content of the lithium salt can be 1:1, 1.2:1, 1.3:1, 1.5:1, 1.6:1, 1.8:1, 2.0:1, 2.2:1, 2.5:1, 2.6:1, 2.8:1, 3:1, 3.2:1, 3.5:1, 3.8:1, 4:1, 4.2:1, 4.5:1, 4.8:1, 5:1 or a range consisting of any two of the above values.

[0092] [Lithium salt]

[0093] The concentration of lithium salt in the cyclic sulfone solvent is 3 mol / L to 8 mol / L, and can be optionally 3 mol / L to 6 mol / L. The relatively high concentration of lithium salt can enable the cyclic sulfone solvent in the electrolyte to form a high-concentration solvation structure, thereby improving the high-voltage tolerance of the electrolyte. The anions in the solvation structure preferentially participate in the film-forming reaction to form an inorganic-rich SEI film, which is beneficial to improving the uniformity of the SEI film. In other words, the solvation structure includes anions, cations and cyclic sulfone solvents in the lithium salt, and the concentration of lithium salt in the solvation structure is 3 mol / L to 8 mol / L.

[0094] In some embodiments, the lithium salt includes a first lithium salt, and the first lithium salt includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethylsulfonyl)imide (LiTFSI). When the first lithium salt is used in combination with the organic solvent, the first lithium salt has relatively high solubility in the organic solvent and can be dissociated by the organic solvent, which is conducive to forming a solvated structure.

[0095] In some embodiments, the ratio of the molar content of the cyclic sulfone solvent to the molar content of the first lithium salt is 1:1 to 3:1; optionally 1.2:1 to 3:1; or optionally 1.2:1 to 2.5:1. When the ratio of the molar content of the cyclic sulfone solvent to the molar content of the first lithium salt is within the above range, the cyclic sulfone solvent can form a solvation structure with the first lithium salt, and can further improve the cycling performance of the lithium metal battery.

[0096] Illustratively, the ratio of the molar content of the cyclic sulfone solvent to the molar content of the first lithium salt can be 1:1, 1.2:1, 1.3:1, 1.5:1, 1.6:1, 1.8:1, 2.0:1, 2.2:1, 2.5:1, 2.6:1, 2.8:1, 3:1, 3.2:1, 3.5:1, 3.6:1, 3.8:1, 4:1, or a range consisting of any two of the above values.

[0097] In some embodiments, in addition to the first lithium salt, the lithium salt may further include a second lithium salt, the second lithium salt including at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium difluorooxalatoborate (LiDFOB), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiOTf), lithium bis(oxalatoborate) (LiBOB), lithium difluorobis(oxalatophosphate) (LiDFBOP), and lithium tetrafluorooxalatophosphate (LiOTFP). The second lithium salt, in combination with the first lithium salt, can further enhance the cycling performance of the lithium metal battery. The second lithium salt may not solvate with the cyclic sulfone solvent; however, the second lithium salt may also solvate with the cyclic sulfone solvent.

[0098] The anions in the second lithium salt, such as LiDFOB, can preferentially participate in the formation of the SEI film as a solvent. The second lithium salt can even participate in the film-forming reaction preferentially over the anions in the first lithium salt, further reducing the risk of solvent decomposition and further improving the cycle performance of the lithium metal battery.

[0099] The second lithium salt, such as LiBF4, is more difficult to dissociate and can provide more lithium ions to the electrolyte, which is beneficial to reduce polarization and improve the cycle performance of lithium metal batteries.

[0100] In some embodiments, based on the total molar amount of the electrolyte, the ratio of the molar content of the second lithium salt to the molar content of the first lithium salt is 0.05:1 to 0.20:1. For example, the ratio of the molar content of the second lithium salt to the molar content of the first lithium salt is 0.05:1, 0.06:1, 0.08:1, 0.10:1, 0.12:1, 0.15:1, 0.18:1, 0.20:1, or a range consisting of any two of the foregoing values.

[0101] The qualitative and quantitative determinations of each substance or element in the embodiments of the present application can be performed using appropriate equipment and methods known to those skilled in the art. The relevant detection methods can refer to domestic and international testing standards, domestic and international enterprise standards, etc., and those skilled in the art can also adapt certain detection steps / instrument parameters, etc., based on the accuracy of the detection, to obtain more accurate detection results. A single detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0102] The types and contents of inorganic components / lithium salt concentrations in the electrolyte are well known in the art and can be detected using equipment and methods well known in the art. For example, the inorganic components / lithium salt concentrations in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography analysis according to standard JY / T020-1996 "General Rules for Ion Chromatography Analysis Methods". In the embodiments of the present application, a freshly prepared electrolyte can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cut-off voltage so that the battery's state of charge is approximately 0%) can be reversely disassembled, and the free electrolyte obtained from the battery can be used as a sample for detection using ion chromatography analysis.

[0103] The types and contents of organic components in the electrolyte are well known in the art and can be detected using equipment and methods well known in the art. For example, reference can be made to GB / T9722-2006 "General Rules for Gas Chromatography of Chemical Reagents" for qualitative and quantitative analysis of organic components in the electrolyte by gas chromatography. In the embodiments of the present application, a freshly prepared electrolyte can be taken as a sample, or a battery that has been fully discharged (discharged to the lower cutoff voltage so that the battery's state of charge is approximately 0%) can be reversely disassembled, and the free electrolyte obtained from the battery can be used as a sample for detection using ion chromatography.

[0104] lithium metal batteries

[0105] In a second aspect, embodiments of the present application provide a lithium metal battery, comprising the electrolyte of any embodiment of the first aspect of the present application, wherein the cycle performance and gas generation resistance of the lithium metal battery can be improved.

[0106] [Negative electrode]

[0107] Lithium metal batteries also include negative electrodes. During the charge and discharge cycles of lithium metal batteries, the deposition and stripping of metallic lithium occurs. The combination of the negative electrode and the aforementioned electrolyte significantly improves the uniformity of lithium metal deposition and the interfacial properties of the negative electrode. Furthermore, the electrolyte has low viscosity and polarization, which reduces gas production, further enhancing the cycling performance and gassing resistance of lithium metal batteries.

[0108] In some embodiments, the negative electrode plate may include a negative electrode current collector. During the charging process of a lithium metal battery, lithium ions can be deposited on the surface of the negative electrode current collector to form a lithium metal layer. During the discharge process of the lithium metal battery, the lithium metal layer loses electrons to form lithium ions, which migrate to the positive electrode active material.

[0109] The negative electrode current collector may be a metal foil or a composite current collector. As an example of a metal foil, copper 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 main material of the metal material layer may include at least one of copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0110] The negative electrode plate does not exclude additional functional layers. For example, in some embodiments, the negative electrode plate of the embodiments of the present application further includes a conductive layer (e.g., composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode plate of the embodiments of the present application further includes a protective layer covering the surface of the negative electrode current collector.

[0111] Optionally, the negative electrode plate may further include a conductive layer disposed on at least one side of the negative electrode current collector, wherein the conductive layer includes a negative electrode conductive agent. As an example, the negative electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0112] Optionally, the conductive layer may further include a negative electrode binder. For example, the negative electrode binder may include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resin (e.g., polyacrylic acid PAA, polymethacrylic acid PMAA, sodium polyacrylate PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0113] In other embodiments, the negative electrode plate may include a negative electrode current collector and a lithium metal layer disposed on at least one side of the negative electrode current collector. For example, the negative electrode current collector may have two opposing surfaces along its thickness, and the lithium metal layer may be disposed on either or both of the two opposing surfaces of the negative electrode current collector. The lithium metal layer may be disposed on the negative electrode current collector in the form of lithium foil.

[0114] Optionally, in addition to lithium metal, the lithium metal layer may also include an alloy of lithium and non-lithium elements, and the non-lithium element may include at least one of a metal element and a metalloid element. Exemplarily, the metal element may include at least one of tin (Sn), zinc (Zn), aluminum (Al), magnesium (Mg), silver (Ag), gold (Au), gallium (Ga), indium (In), and platinum (Pt). Exemplarily, the metalloid element may include at least one of boron (B), carbon (C), and silicon (Si).

[0115] The material of the negative electrode current collector is as described above and will not be repeated here.

[0116] The negative electrode plate does not exclude additional functional layers. For example, in some embodiments, the negative electrode plate of the embodiments of the present application further includes a conductive layer (e.g., composed of a conductive agent and a binder) disposed on the surface of the negative electrode current collector. In other embodiments, the negative electrode plate of the embodiments of the present application further includes a protective layer covering the surface of the negative electrode current collector.

[0117] Optionally, the negative electrode plate may further include a conductive layer disposed between the negative electrode current collector and the lithium metal layer. The conductive layer may include a negative electrode conductive agent. The material of the negative electrode conductive agent is as described above and will not be further described here. Further, the conductive layer may further include a negative electrode binder. The material of the negative electrode binder is as described above and will not be further described here.

[0118] [Positive electrode]

[0119] In some embodiments, the lithium metal battery may further include a positive electrode sheet.

[0120] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer disposed on at least one surface of the positive electrode current collector and comprising a positive electrode active material. For example, the positive electrode current collector may have two opposing surfaces in its thickness direction, and the positive electrode film layer may be disposed on either or both of the two opposing surfaces of the positive electrode current collector.

[0121] The positive electrode active material may be a positive electrode active material for lithium metal batteries known in the art. As an example, the positive electrode active material may include at least one of the following materials: a layered positive electrode active material (e.g., ternary, lithium nickelate / sodium, lithium cobaltate / sodium, lithium manganate / sodium, lithium-rich / sodium layered, and rock salt phase layered materials), an olivine-type phosphate active material, a spinel-structured positive electrode active material (e.g., spinel lithium manganate, spinel lithium nickel manganate, lithium-rich spinel lithium manganate, and lithium nickel manganate, etc.).

[0122] For example, the general formula of the layered structure positive electrode active material is: Li x A y Ni aCo b Mn c M (1-a-b-c) Q z , wherein 0 < x ≤ 2.1, 0 ≤ y ≤ 2.1, and 0.9 ≤ x + y ≤ 2.1; 0 ≤ a ≤ 1, 0 ≤ b ≤ 1, 0 ≤ c ≤ 1, and 0.1 ≤ a + b + c ≤ 1; 1.8 ≤ z ≤ 3.5; A is selected from one or more of Na, K, and Mg; M is selected from one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; and Q is selected from one or more of O and F. Optionally, y = 0. Optionally, 0 < a < 1; further optionally, 0.8 ≤ a < 1. The above-mentioned layered structure positive electrode active material has a relatively high specific capacity, which is beneficial to improving the energy density of lithium metal batteries; and when the above-mentioned positive electrode active material and electrolyte are used in combination, the stability of the interface between the electrolyte and the positive electrode sheet is relatively high, which is beneficial to improving the cycle performance of lithium metal batteries.

[0123] a can be 0.01, 0.02, 0.05, 0.08, 0.10, 0.12, 0.15, 0.18, 0.20, 0.22, 0.25, 0.28, 0.30, 0.32, 0.35, 0.38, 0.40, 0.42, 0.45, 0.48, 0.50, 0.52, 0.55, 0.58, 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 0.91, 0.99, 0.91, 0.91 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, 0.86, 0.87, 0.88, 0.89, 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1 or a range consisting of any two of the above values.

[0124] Optionally, 0<b<1.

[0125] Optionally, 0<c<1.

[0126] Optionally, 0.1≤a+b+c<1.

[0127] z can be 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, or a range consisting of any two of the above values.

[0128] Specifically, the layered structure positive electrode active material may include lithium cobalt oxide LCO, lithium nickel oxide LNO, lithium manganese oxide LMO, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333),LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811) and LiNi 0.5 Co 0.2 Mn 0.3 One or more of O2 (NCM523).

[0129] For example, the general formula of the olivine-type phosphate active material is: Li x A y Me a Q b P 1-c X c T z , wherein 0≤x≤1.3, 0≤y≤1.3, and 0.9≤x+y≤1.3; 0.9≤a≤1.5, 0≤b≤0.5, and 0.9≤a+b≤1.5; 0≤c≤0.5; 3≤z≤5; A is selected from one or more of Na, K, and Mg; Me is selected from one or more of Mn, Fe, Co, and Ni; Q is selected from one or more of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; X is selected from one or more of S, Si, Cl, B, C, and N; and T is selected from one or more of O and F. Specifically, the olivine-type phosphate active material includes one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0130] For example, the general formula of the positive electrode active material of the spinel structure is: Li x A y Mn a R 2-a U z , wherein 0≤x≤2, 0≤y≤1, and 0.9≤x+y≤2; 0.5≤a≤2; 3≤z≤5; A is selected from one or more of Na, K, and Mg; R is selected from one or more of Ni, Co, B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; and U is selected from one or more of O and F. Specifically, the positive active materials of the spinel structure include LiMn2O4, LiNi 0.5Mn 1.5 O4、LiCr 0.3 Mn 1.7 O4、Li 1.1 Al 0.1 Mn 1.9 O4, Li2Mn2O4 and Li 1.5 One or more of Mn2O4.

[0131] In the embodiments of the present application, each of the above-mentioned positive electrode active materials may also be a modified compound, and the modified compound may be a doping modification and / or surface coating modification of the positive electrode active material. For example, the doping modification may be performed by doping with a transition metal element, or the coating modification may be performed by coating a carbon layer on the surface of the material.

[0132] The charge and discharge process of lithium metal batteries is accompanied by the deintercalation and consumption of active ions such as Li. The molar content of Li in lithium metal batteries varies at different discharge states. The molar content of Li in the examples of positive electrode active materials in the embodiments of this application refers to the initial state of the material, i.e., the state before the material is added. When the positive electrode active material is used in a battery system, the molar content of Li may change after charge and discharge cycles.

[0133] In the examples of the positive electrode active materials in the embodiments of the present application, the molar content of oxygen O is only a theoretical value. Lattice oxygen release will cause the molar content of oxygen O to change. In practice, the molar content of oxygen O will fluctuate.

[0134] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. The present embodiments do not particularly limit the type of positive electrode conductive agent. By way of example, the positive electrode conductive agent may include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. In some embodiments, the mass content of the positive electrode conductive agent is ≤5% based on the total mass of the positive electrode film layer.

[0135] In some embodiments, the positive electrode film layer may further optionally include a positive electrode binder. The embodiments of the present application do not particularly limit the type of positive electrode binder. As an example, the positive electrode binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin. In some embodiments, based on the total mass of the positive electrode film layer, the mass content of the positive electrode binder is ≤5%.

[0136] 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 of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0137] The positive electrode film is typically formed by coating a positive electrode slurry onto a positive electrode current collector, drying it, and cold pressing it. The positive electrode slurry is typically formed by dispersing the positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring them uniformly. The solvent can be, but is not limited to, N-methylpyrrolidone (NMP).

[0138] [Isolation film]

[0139] In some embodiments, the lithium metal battery may further include a separator.

[0140] The embodiments of the present application have no particular limitation on the type of isolation membrane, and any known isolation membrane with a porous structure having good chemical stability and mechanical stability can be selected.

[0141] In some embodiments, the material of the separator may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and 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.

[0142] In some embodiments, the positive electrode sheet, the separator, and the negative electrode sheet may be formed into an electrode assembly through a winding process and / or a lamination process.

[0143] In some embodiments, the lithium metal battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0144] In some embodiments, the outer packaging of the lithium metal battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer packaging of the lithium metal battery can also be a soft package, such as a pouch-type soft package. The material of the soft package can be plastic, such as at least one of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0145] The embodiment of the present application has no particular limitation on the shape of the lithium metal battery, which can be cylindrical, square or any other shape. FIG1 shows a lithium metal battery 5 with a square structure as an example.

[0146] In some embodiments, as shown in FIG2 , the outer packaging 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 sheet, the negative electrode sheet and the separator may be formed into 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 impregnated in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in the lithium metal battery 5 may be one or more, which can be adjusted according to demand.

[0147] The preparation method of the lithium metal battery of the embodiments of the present application is well known. In some embodiments, a positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte can be assembled to form a lithium metal battery. As an example, the positive electrode sheet, the separator, and the negative electrode sheet can be formed into an electrode assembly through a winding process and / or a lamination process. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte. The lithium metal battery is obtained through vacuum packaging, static standing, chemical formation, and shaping processes.

[0148] In some embodiments of the present application, the lithium metal batteries according to the present application can be assembled into a battery module. The number of lithium metal 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.

[0149] Figure 3 is a schematic diagram of an exemplary battery module 4. As shown in Figure 3 , within the battery module 4, multiple lithium metal batteries 5 may be arranged sequentially along the length of the battery module 4. Of course, any other arrangement is also possible. Furthermore, the multiple lithium metal batteries 5 may be secured using fasteners.

[0150] Optionally, the battery module 4 may further include a housing having a receiving space, and the plurality of lithium metal batteries 5 are received in the receiving space.

[0151] 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.

[0152] Figures 4 and 5 are schematic diagrams of an exemplary battery pack 1. As shown in Figures 4 and 5, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box comprises an upper case 2 and a lower case 3. The upper case 2 covers the lower case 3 and forms an enclosed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0153] Electrical devices

[0154] A third aspect of the embodiments of the present application provides an electrical device, which includes at least one of the lithium metal battery, battery module, or battery pack of the embodiments of the present application. The lithium metal 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 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, a satellite, an energy storage system, etc.

[0155] Electrical devices can choose lithium metal batteries, battery modules or battery packs according to their usage requirements.

[0156] Figure 6 is a schematic diagram of an exemplary electrical device 6. This device 6 can be a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of this device 6, a battery pack or battery module can be used. Another exemplary electrical device can be a mobile phone, tablet computer, or laptop computer. These devices are typically required to be lightweight and thin, and lithium metal batteries can be used as a power source.

[0157] Example

[0158] The following examples describe the disclosure of the present invention in more detail. These examples are intended for illustrative purposes only, as various modifications and variations within the scope of the disclosure of the present invention will be apparent to those skilled in the art. Unless otherwise stated, all reagents used in the following examples are commercially available or synthesized according to conventional methods and can be used directly without further processing, and all instruments used in the examples are commercially available.

[0159] Example 1

[0160] 1. Preparation of positive electrode sheet

[0161] The positive electrode slurry is prepared by mixing the positive electrode active material, the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) in a weight ratio of 98:1:1; the positive electrode active material includes the molecular formula LiNi 0.8Co 0.10 Mn 0.10 Compounds of O2(NCM811);

[0162] The positive electrode slurry is placed on both sides of the positive electrode current collector aluminum foil, and is dried and cold pressed to form a positive electrode film layer.

[0163] 2. Preparation of negative electrode sheet

[0164] 50 μm lithium foil was rolled onto both sides of 8 μm negative electrode current collector copper foil to prepare a negative electrode sheet.

[0165] The negative electrode plate includes a negative electrode current collector and a lithium foil arranged on the negative electrode current collector, and the negative electrode current collector is a copper foil.

[0166] 3. Isolation film

[0167] The isolation film is a polyethylene film layer.

[0168] 4. Preparation of electrolyte

[0169] The electrolyte includes an organic solvent, a lithium salt, and a diluent. The organic solvent includes a cyclic sulfone solvent. The injection amount of the electrolyte is 2.1 g / Ah.

[0170] 5. Preparation of lithium metal batteries

[0171] The above-mentioned positive electrode sheet, separator, and negative electrode sheet are stacked in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, thereby obtaining an electrode assembly; the electrode assembly is placed in an outer packaging shell, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a laminated lithium metal battery is obtained, and the rated capacity of the battery is 1.4Ah.

[0172] Example 2-1 to Example 2-8

[0173] A lithium metal battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the types of organic solvents were adjusted in Examples 2-1 to 2-8.

[0174] Comparative Example 1

[0175] A lithium metal battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the types of organic solvent and diluent were adjusted in Comparative Example 1.

[0176] Comparative Example 2

[0177] A lithium metal battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the type of organic solvent was adjusted in Comparative Example 2.

[0178] Comparative Example 3

[0179] A lithium metal battery was prepared using a method similar to that of Example 1. Unlike Example 1, the types of organic solvent and diluent were adjusted in Comparative Example 3.

[0180] Comparative Example 4

[0181] A lithium metal battery was prepared using a method similar to that of Example 1. Unlike Example 1, the types of organic solvent and diluent were adjusted in Comparative Example 3.

[0182] The electrolyte parameters in the examples and comparative examples are detailed in Table 1.

[0183] Performance Testing

[0184] 1. Room temperature cycle performance test of lithium metal batteries

[0185] The lithium metal batteries prepared in the comparative example and the example were subjected to charge and discharge cycles at a rate of 0.2C at 25°C. The charge and discharge cutoff voltages were set at 4.3V and 2.8V, respectively. The battery life was considered to have expired when the discharge capacity decayed to 80% of the initial discharge capacity, and the number of cycles of the lithium metal batteries was counted.

[0186] 2. High temperature cycle performance test of lithium metal batteries

[0187] The lithium metal batteries prepared in the comparative example and the example were subjected to charge and discharge cycles at 60°C using a 0.2C rate. The charge and discharge cutoff voltages were set at 4.3V and 2.8V, respectively. The battery life was considered to have expired when the discharge capacity decayed to 80% of the initial discharge capacity, and the number of cycles of the lithium metal batteries was counted.

[0188] 3. Gas production test of lithium metal batteries

[0189] The gas production of the lithium metal battery was tested by the silicone oil drainage method. The lithium metal batteries prepared in the above embodiments and comparative examples were placed in a container filled with silicone oil and placed in a 60°C oven for 8 hours. After the system stabilized, the initial scale V1 (mL) of the silicone oil was read. The charge and discharge cycle was performed at a rate of 0.2C, and the cut-off voltages of charge and discharge were set to 4.3V and 2.8V, respectively. After 50 cycles, the silicone oil scale V2 (mL) was read, and the gas production was (V2-V1) / 1.4.

[0190] Test results

[0191] The test results are shown in Table 1.

[0192] Table 1

[0193] In Table 1, BDE represents di-(2,2-difluoroethyl) ether, and TTE represents 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0194] The molar ratio of the cyclic sulfone solvent to the lithium salt refers to the ratio of the molar content of the cyclic sulfone solvent to the molar content of the lithium salt.

[0195] The molar ratio of the diluent to the lithium salt refers to the ratio of the molar content of the diluent to the molar content of the lithium salt.

[0196] In Table 1, formula (M) represents the compound represented by formula (M), for example, formula (I2) represents the compound represented by formula (I2).

[0197] As can be seen from Table 1, the organic solvents in Comparative Examples 1 and 2 include dimethyl sulfone, which has a non-cyclic structure. Dimethyl sulfone may decompose and produce gas during the cycle of the lithium metal battery, resulting in a poor cycle life of the lithium metal battery.

[0198] Comparative Examples 3 and 4 do not contain a diluent and only include the compound represented by formula (I1) or the compound represented by formula (I13). Although the gas production is small, the organic solvent and the lithium salt form a high-concentration electrolyte system, and the electrolyte viscosity is high, which may aggravate polarization and make the cycle life of the lithium metal battery unable to be significantly improved. For example, the lithium metal battery in Comparative Example 3 cannot even work normally at 25°C.

[0199] Compared to Comparative Examples 1 to 4, the present examples utilize a cyclic sulfone solvent and a diluent, allowing the cyclic sulfone solvent to form a high-concentration electrolyte system containing a solvation structure with the lithium salt. The diluent, as an inert substance, acts as a diluent, reducing the viscosity of the electrolyte and minimizing polarization, thereby significantly improving the cycle life of the lithium metal battery. Furthermore, because the anions in the solvation structure form a film prior to the solvent, the solvent is less likely to decompose, further reducing gas production and improving cycle performance.

[0200] Example 3-1 to Example 3-6

[0201] A lithium metal battery was prepared using a method similar to that of Example 1. Unlike Example 1, the type of diluent was adjusted in Examples 3-1 to 3-6.

[0202] Example 4-1 and Example 4-2

[0203] A lithium metal battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the molar ratio of the diluent to the lithium salt was adjusted in Examples 4-1 and 4-2.

[0204] Example 5-1 to Example 5-4

[0205] A lithium metal battery was prepared using a method similar to that of Example 1. The difference from Example 1 was that the molar ratio of the cyclic sulfone solvent to the lithium salt was adjusted in Examples 5-1 to 5-5.

[0206] The test results of the above embodiment are shown in Table 2.

[0207] Table 2

[0208] In Table 2, BZ represents benzene, and BTFE represents bis(2,2,2-trifluoroethyl)ether.

[0209] As can be seen from Table 2,

[0210] In Example 1 and Example 3-1 to Example 3-6, by selecting the material of the diluent, especially selecting a solvent with a small molecular volume, the resistance to lithium ion transmission can be reduced, thereby further improving the cycle performance.

[0211] In Example 1, Example 4-1 and Example 4-2, by adjusting the molar ratio of the diluent to the lithium salt, the resistance to lithium ion transmission can be further improved, thereby further improving the cycle performance.

[0212] In Example 1 and Example 5-1 to Example 5-4, by adjusting the molar ratio of the cyclic sulfone solvent and the lithium salt, the resistance to lithium ion transmission can be further improved, thereby further improving the cycle performance.

[0213] Example 6-1 to Example 6-7

[0214] A lithium metal battery was prepared using a method similar to that of Example 1. Unlike Example 1, the type and content of the lithium salt were adjusted in Examples 6-1 and 6-7.

[0215] The test results of the above embodiment are shown in Table 3.

[0216] Table 3

[0217] In Table 3, the molar ratio of the second lithium salt to the first lithium salt refers to the ratio of the molar content of the second lithium salt to the molar content of the first lithium salt.

[0218] As can be seen from Table 3, the embodiments of the present application are applicable to high-concentration lithium salt systems, and can effectively improve the cycle performance of lithium metal batteries under high-concentration lithium salt systems.

[0219] By selecting a lithium salt system, Examples 6-1 to 6-7 of the present application can further improve the cycle performance of lithium metal batteries by adjusting the material and content of the lithium salt.

[0220] The above description is merely a specific embodiment of the present application, but the scope of protection of the present application is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present application, and such modifications or substitutions should be included in the scope of protection of the present application. Therefore, the scope of protection of the present application should be based on the scope of protection of the claims.

Claims

1. An electrolyte for a lithium metal battery, comprising a lithium salt, a cyclic sulfone solvent and a diluent, wherein the diluent comprises at least one of a fluoroether compound and an aromatic compound.

2. The electrolyte according to claim 1, wherein The cyclic sulfone solvent includes a compound represented by formula (I), In formula (I), R1, R2, R3 and R4 each independently include a hydrogen atom, a fluorine atom or a C1 to C5 fluoroalkyl group.

3. The electrolyte according to claim 2, wherein R1 and R4 include different groups; and / or R2 and R3 include different groups.

4. The electrolyte according to claim 2 or 3, wherein At least one of R1, R2, R3, and R4 includes a fluorine atom or a C1 to C5 fluoroalkyl group.

5. The electrolyte according to any one of claims 2 to 4, wherein The cyclic sulfone solvent includes at least one of the compounds represented by formula (I1) to the compounds represented by formula (I20), 6. The electrolyte according to any one of claims 1 to 5, wherein The fluoroether compounds include compounds represented by formula (A), M1-O-M2 formula (A), In formula (A), M1 and M2 each independently include a C2 to C5 alkyl group or a C2 to C5 fluoroalkyl group, wherein at least one of each of M1 and M2 includes a C2 to C5 fluoroalkyl group.

7. The electrolyte according to claim 6, wherein M1 and M2 each independently include C2 to C5 linear alkyl or C2 to C5 fluorinated linear alkyl, wherein, At least one of each of M1 and M2 includes a C2 to C5 fluorinated linear alkyl group.

8. The electrolyte according to claim 6 or 7, wherein The fluoroether compound includes at least one of the compounds represented by formula (A1) to the compounds represented by formula (A9), 9. The electrolyte according to any one of claims 1 to 8, wherein The aromatic compound includes at least one of benzene, anisole, phenetole, furan and thiophene.

10. The electrolyte according to any one of claims 1 to 9, wherein Based on the total molar amount of the electrolyte, the ratio of the molar content of the cyclic sulfone solvent to the molar content of the lithium salt is greater than 1:1 and less than or equal to 3:

1.

11. The electrolyte according to claim 10, wherein The ratio of the molar content of the cyclic sulfone solvent to the molar content of the lithium salt is 1.2:1 to 3:

1.

12. The electrolyte according to claim 11, wherein The ratio of the molar content of the cyclic sulfone solvent to the molar content of the lithium salt is 1.2:1 to 2.5:

1.

13. The electrolyte according to any one of claims 1 to 12, wherein Based on the total molar amount of the electrolyte, the ratio of the molar content of the diluent to the molar content of the lithium salt is 1:1 to 5:

1.

14. The electrolyte according to any one of claims 1 to 13, wherein The lithium salt includes a first lithium salt including at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethylsulfonyl)imide.

15. The electrolyte according to claim 14, wherein The lithium salt further includes a second lithium salt, which includes at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium difluorophosphate, lithium difluorooxalatoborate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoromethanesulfonate, lithium dioxalatoborate, lithium difluorodioxalatophosphate, and lithium tetrafluorooxalatophosphate.

16. The electrolyte according to claim 14 or 15, wherein Based on the total molar amount of the electrolyte, a ratio of the molar content of the second lithium salt to the molar content of the first lithium salt is 0.05:1 to 0.20:

1.

17. A lithium metal battery comprising the electrolyte according to any one of claims 1 to 16.

18. The lithium metal battery according to claim 17, wherein The lithium metal battery includes a negative electrode plate; The negative electrode plate includes a negative electrode current collector; or The negative electrode plate includes a negative electrode current collector and a lithium metal layer disposed on at least one side of the negative electrode current collector.

19. The lithium metal battery according to claim 18, wherein The lithium metal layer includes lithium metal element or lithium metal alloy, the lithium metal alloy includes non-lithium elements and lithium elements, and the non-lithium elements include at least one of tin, zinc, aluminum, magnesium, silver, gold, gallium, indium, platinum, boron, carbon, and silicon.

20. The lithium metal battery according to any one of claims 17 to 19, further comprising a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode film layer provided on at least one side of the positive electrode current collector and comprising a positive electrode active material. The positive electrode active material includes a general formula of Li x A y Ni a Co b Mn c M (1-a-b-c) Q z A compound wherein 0<x≤2.1, 0≤y≤2.1, and 0.9≤x+y≤2.1; 0<a<1, 0<b<1, 0<c<1, and 0.1≤a+b+c≤1; 1.8≤z≤3.5; A includes at least one of Na, K, and Mg; M includes at least one of B, Mg, Al, Si, P, S, Ca, Sc, Ti, V, Cr, Fe, Cu, Zn, Sr, Y, Zr, Nb, Mo, Cd, Sn, Sb, Te, Ba, Ta, W, Yb, La, and Ce; Q includes at least one of O and F.

21. A battery comprising the lithium metal battery according to any one of claims 17 to 20.

22. An electrical device comprising the battery according to claim 21.