Electrolyte of lithium metal battery, lithium metal battery, battery, and electrical apparatus

Abstract

An electrolyte of a lithium metal battery, a lithium metal battery, a battery, and an electrical apparatus. The electrolyte of the lithium metal battery comprises a main solvent, a diluent, and a lithium salt; the molar concentration of the lithium salt is 1 mol / L to 4 mol / L, and the viscosity of the electrolyte is less than or equal to 5.5 mPa⋅s. The cycle performance of the lithium metal battery can be improved.

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. 202410020226.1, filed on January 5, 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] 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 still needs to be further improved.

[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 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, wherein the electrolyte for the lithium metal battery includes a main solvent, a diluent, and a lithium salt, wherein the molar concentration of the lithium salt is 1 mol / L to 4 mol / L, wherein the viscosity of the electrolyte is ≤5.5 mPa·s.

[0009] Therefore, in the embodiment of the present application, the molar concentration of the lithium salt in the electrolyte is relatively high, for example, 1 mol / L to 4 mol / L, and the lithium salt can form a solvated structure with the main solvent, and still has a certain molar concentration of lithium salt in the later stage of the cycle; and because the electrolyte also includes a diluent, the viscosity of the electrolyte is relatively low and the ionic conductivity is high, which can effectively reduce the polarization growth of the lithium metal battery and improve the cycle performance of the lithium metal battery.

[0010] In some embodiments, the viscosity of the electrolyte is ≤4 mPa·s. A relatively low viscosity of the electrolyte system is beneficial for reducing polarization and improving the cycle performance of the lithium metal battery.

[0011] In some embodiments, the ionic conductivity of the electrolyte is 2 mS / cm to 5 mS / cm, and optionally 3 mS / cm to 5 mS / cm. When the ionic conductivity of the electrolyte is within the above range, the cycling performance of the lithium metal battery is improved.

[0012] In some embodiments, the molar concentration of the lithium salt is 2 mol / L to 3.5 mol / L. When the molar concentration of the lithium salt is within the above range, it can form a high-molar concentration solvate structure with the main solvent. Although the lithium salt has a certain loss during the cycle of the lithium metal battery, due to the relatively high molar concentration of the lithium salt, a certain concentration of lithium salt is still present in the late stage of the lithium metal battery cycle, which can reduce polarization growth and achieve long-term stable cycling of the lithium metal battery.

[0013] In some embodiments, the lithium salt includes at least one of a fluorine-containing lithium salt, lithium bis(oxalatoborate), and lithium perchlorate.

[0014] In some embodiments, the fluorine-containing lithium salt includes at least one of a fluorine-containing lithium sulfonyl imide salt, a fluorine-containing lithium phosphate salt, a fluorine-containing lithium borate salt, a fluorine-containing lithium oxalate phosphate salt, a lithium hexafluoroarsenate salt, a lithium trifluoromethanesulfonate salt, and a lithium difluorooxalate borate salt. Alternatively, the fluorine-containing lithium salt includes a fluorine-containing lithium sulfonyl imide salt.

[0015] In some embodiments, the fluorine-containing lithium sulfonyl imide salt comprises at least one of lithium bis(fluorosulfonyl imide) and lithium bis(trifluoromethanesulfonyl imide). Further optionally, the fluorine-containing lithium salt comprises lithium bis(fluorosulfonyl imide).

[0016] In some embodiments, the fluorine-containing lithium phosphate salt includes at least one of lithium hexafluorophosphate and lithium difluorophosphate.

[0017] In some embodiments, the fluorine-containing lithium borate salt includes at least one of lithium tetrafluoroborate and lithium difluoroborate.

[0018] In some embodiments, the fluorine-containing lithium oxalate phosphate salt includes at least one of difluoro lithium oxalate phosphate salt and tetrafluoro lithium oxalate phosphate.

[0019] The lithium salt and the main solvent are combined to achieve the dissolution of the lithium salt with a high molar concentration in the main solvent, and form a solvated structure with a local high molar concentration in combination with the diluent.

[0020] In some embodiments, based on the total mass of the main solvent and the diluent, the mass content of the main solvent is 10% to 80%; optionally 20% to 40%; optionally 30% to 40%; when the mass content of the main solvent is within the above range, the solvent molecules of the main solvent can participate in the construction of the solvated structure, and there are basically no free main solvent molecules.

[0021] In some embodiments, the mass content of the diluent is 20% to 90% based on the total mass of the main solvent and the diluent; optionally, 60% to 80%; or optionally, 60% to 70%. When the mass content of the diluent is within the above range, the amount of the diluent and the amount of the lithium salt can meet the set range, and the diluent has substantially no effect on the solvated structure, allowing the lithium salt to preferentially form a film in the solvated structure, improving the performance of the SEI film, and reducing the risk of capacity drop in the lithium metal battery.

[0022] In some embodiments, the relative molecular weight of the main solvent is between 40 and 150, and optionally between 40 and 125. When the relative molecular weight of the main solvent is within this range, the main solvent is liquid and its viscosity is not excessively high, which facilitates the formation of a solvated structure with the lithium salt. Due to the relatively small relative molecular weight range of the main solvent, the main solvent does not occupy a higher mass fraction at the same mole fraction. Even if the material of the main solvent is adjusted, the mass fraction of the main solvent remains small, which facilitates increasing the mass fraction of the lithium salt.

[0023] In some embodiments, the viscosity of the main solvent is ≤5 mPa·s. The relatively low viscosity of the main solvent results in a low viscosity of the locally high molar concentration electrolyte and a high ionic conductivity.

[0024] In some embodiments, the main solvent may include at least one of an ester solvent, an ether solvent, a sulfone solvent, a nitrile solvent, an amide solvent, and a siloxane solvent.

[0025] In some embodiments, the ester solvent includes at least one of methyl formate, ethyl formate, ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate.

[0026] In some embodiments, the ether solvent includes at least one of C4 to C6 linear ethers, C3 to C10 alkoxyalkanes, C3 to C6 alkylene oxides, and trimethoxymethane.

[0027] In some embodiments, the sulfone solvent includes at least one of dimethyl sulfoxide, dimethyl sulfone, sulfolane, sulfolane oxide, methyl ethyl sulfone, and methyl ethyl sulfoxide.

[0028] In some embodiments, the nitrile solvent includes at least one of acetonitrile, propionitrile, butyronitrile, and malononitrile.

[0029] In some embodiments, the amide solvent includes at least one of dimethylformamide, dimethylacetamide, and diethylacetamide.

[0030] In some embodiments, the siloxane-based solvent includes at least one of dimethoxydimethylsilane and trimethoxymethylsilane.

[0031] In some embodiments, the diluent has a relative molecular weight of 60 to 190. When the diluent's molecular weight is within this range, the diluent is liquid and further reduces the viscosity of the electrolyte. Furthermore, because the diluent has a relatively small relative molecular weight, its mass fraction is relatively small for the same amount of substance, which helps increase the mass fraction of the lithium salt in the solvated structure and thus the molar concentration of the lithium salt.

[0032] In some embodiments, the viscosity of the diluent is ≤5 mPa·s. The relatively low viscosity of the diluent results in a relatively low viscosity of the electrolyte and a relatively high ion conductivity.

[0033] In some embodiments, the diluent comprises a compound of formula (CI),

[0034] In formula (CI),

[0035] X1 and X2 each independently include a carbon atom, an oxygen atom or a nitrogen atom;

[0036] R1 and R2 each independently include a C1 to C6 alkyl group, a cycloalkyl group, an aryl group, a C1 to C6 halogenated alkyl group, a halogenated cycloalkyl group, a halogenated aryl group or a halogen atom;

[0037] R 31 and R 32 Each independently includes a hydrogen atom, a C1 to C6 chain alkyl group, a cycloalkyl group, an aryl group, a C1 to C6 halogenated chain alkyl group, a halogenated cycloalkyl group, a halogenated aryl group, a halogen atom or does not exist, wherein,

[0038] When X1 is a carbon atom, R 31 and R 32 each independently comprises a hydrogen atom or a halogen atom;

[0039] When X1 is an oxygen atom, R 31 and R 32 does not exist;

[0040] When X1 is a nitrogen atom, R 31 and R 32 One of them includes a hydrogen atom, a C1 to C6 alkyl group, a cycloalkyl group, an aryl group, a C1 to C6 halogenated alkyl group, a halogenated cycloalkyl group, a halogenated aryl group or a halogen atom; the other one does not exist;

[0041] R 41 and R 42 Each independently includes a hydrogen atom, a C1 to C6 chain alkyl group, a cycloalkyl group, an aryl group, a C1 to C6 halogenated chain alkyl group, a halogenated cycloalkyl group, a halogenated aryl group, a halogen atom or does not exist, wherein,

[0042] When X2 is a carbon atom, R 41 and R42 each independently comprises a hydrogen atom or a halogen atom;

[0043] When X2 is an oxygen atom, R 41 and R 42 does not exist;

[0044] When X2 is a nitrogen atom, R 41 and R 42 One of them includes a hydrogen atom, a C1 to C6 alkyl group, a cycloalkyl group, an aryl group, a C1 to C6 halogenated alkyl group, a halogenated cycloalkyl group, a halogenated aryl group or a halogen atom, and the other one does not exist.

[0045] In some embodiments, the diluent comprises a compound represented by formula (C-IIa),

[0046] In formula (C-IIa),

[0047] M1 includes an oxygen atom, a nitrogen atom or a sulfur atom;

[0048] S 11 and S 12 Each independently includes C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl or halogenated aryl;

[0049] S 13 including C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl, halogenated aryl or not present, wherein,

[0050] When M1 is an oxygen atom or a sulfur atom, S 13 does not exist;

[0051] When M1 is a nitrogen atom, S 13 These include C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl or halogenated aryl.

[0052] In some embodiments, the diluent comprises a compound represented by formula (C-IIb),

[0053] In formula (C-IIb),

[0054] M 21 and M 22 each independently comprises an oxygen atom, a nitrogen atom or a sulfur atom;

[0055] S 21 and S 23 Each independently includes C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl or halogenated aryl;

[0056] S 22 including alkylene or haloalkylene;

[0057] S 24 including C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl, halogenated aryl or not present, wherein,

[0058] When M 21 When S is an oxygen atom or a sulfur atom, 24 does not exist;

[0059] When M 21 When S is a nitrogen atom, 24 These include C1 to C6 alkyl, C3 to C6 cycloalkyl, aryl, C1 to C6 halogenated alkyl, C3 to C6 halogenated cycloalkyl or halogenated aryl.

[0060] In some embodiments, the diluent comprises a compound represented by formula (C-IIc),

[0061] In formula (C-IIc),

[0062] M3 includes at least one of an oxygen atom, a nitrogen atom, and a sulfur atom;

[0063] S 31 including alkylene or haloalkylene;

[0064] S 32 including C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl, halogenated aryl or not present, wherein,

[0065] When M3 is an oxygen atom or a sulfur atom, S 32 does not exist;

[0066] When M3 is a nitrogen atom, S 32 These include C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl or halogenated aryl.

[0067] In some embodiments, the diluent includes a compound represented by formula (C-III), m H n Q y Formula (C-III),

[0068] In formula (C-III),

[0069] m is selected from any positive integer from 1 to 8;

[0070] y is selected from any integer from 0 to 10;

[0071] y / n is any value between 0.25 and 5;

[0072] Q includes a halogen atom, and optionally, the halogen atom includes at least one of a fluorine atom and a chlorine atom.

[0073] In some embodiments, the diluent comprises a compound represented by formula (C-IV),

[0074] In formula (C-IV),

[0075] T1 to T4 each independently include a C1 to C6 alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, a halogenated alkyl group, a halogenated cycloalkyl group, a halogenated aryl group or a halogenated alkoxy group.

[0076] In some embodiments, the diluent comprises a compound of formula (CV),

[0077] In formula (CV),

[0078] A1 includes C1 to C3 alkyl, haloalkyl or halogen atom;

[0079] A2 includes C1 to C3 alkyl, halogenated alkyl, alkoxy, halogenated alkoxy, N,N-dimethyl, N,N-diethyl, N,N-methylethyl or morpholinyl.

[0080] A second aspect of the present application provides a lithium metal battery, comprising an electrolyte according to any embodiment of the first aspect of the present application.

[0081] In some embodiments, a lithium metal battery includes a negative electrode sheet including a negative electrode current collector.

[0082] In some embodiments, a lithium metal battery includes a negative electrode plate; 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.

[0083] 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) Y zCompounds, 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 Y is selected from one or more of O and F. The above-mentioned compounds can improve the energy density of lithium metal batteries; and when used in combination with the above-mentioned electrolyte, the electrolyte has relatively high stability on the positive electrode side, which is beneficial to improving the cycle performance of lithium metal batteries.

[0084] 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.

[0085] 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

[0086] 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.

[0087] FIG1 is a schematic diagram of an embodiment of a lithium metal battery of the present application.

[0088] FIG. 2 is an exploded schematic diagram of an embodiment of the lithium metal battery of FIG. 1 .

[0089] FIG3 is a schematic diagram of an embodiment of a battery module of the present application.

[0090] FIG4 is a schematic diagram of an embodiment of a battery pack of the present application.

[0091] FIG. 5 is an exploded schematic diagram of the embodiment of the battery pack shown in FIG. 4 .

[0092] 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.

[0093] The drawings are not necessarily drawn to scale.

[0094] The following are the descriptions of the reference numerals:

[0095] 1. Battery pack; 2. Upper box; 3. Lower box; 4. Battery module;

[0096] 5. lithium metal battery; 51. housing; 52. electrode assembly;

[0097] 53. Cover plate;

[0098] 6. Electrical equipment. DETAILED DESCRIPTION

[0099] 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.

[0100] " 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.

[0101] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0102] 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.

[0103] 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.

[0104] In various places of this specification, the substituent of compound is disclosed with group or scope.It is clearly expected that this description comprises each individual subcombination of the member of these groups and scope.For example, it is clearly expected that the term "C1-C8 alkyl" discloses 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 individually.

[0105] 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.

[0106] Due to its high specific capacity, lithium metal can significantly improve the energy density of battery cells, so lithium metal batteries have broad application prospects. Lithium metal batteries include electrode assemblies and electrolytes. The electrode assemblies include positive electrode sheets, negative electrode sheets and separators. The separators are located between the positive electrode sheets and the negative electrode sheets to isolate the positive electrode sheets from the negative electrode sheets. Lithium metal batteries achieve energy storage and discharge through the stripping and deposition of lithium metal. Specifically, during the charging process of lithium metal batteries, 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 molar concentration difference in the external circuit; during the discharge process of lithium metal batteries, 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 solvated, and migrates through the electrolyte to the positive active material.

[0107] Due to the high reactivity of lithium metal, the interface stability between the negative electrode surface and the electrolyte of the lithium metal battery is poor, which makes the electrolyte easily decompose on the negative electrode surface, deteriorating the performance of the lithium metal battery.

[0108] In the related art, local high molar concentration electrolytes are used to improve the performance of lithium metal batteries. However, local high molar concentration electrolytes still have the risk of failure during the cycle. The failure mechanism mainly comes from the following two aspects. On the one hand, lithium salts continue to decompose into films during the cycle, resulting in a continuous decrease in the molar concentration of lithium salts in the electrolyte and a continuous decrease in the ion conductivity. After reaching a certain threshold, the lithium metal battery is polarized too much, resulting in a capacity drop. On the other hand, after the electrolyte circulates, the SEI interface film components on the surface of the negative electrode of the lithium metal battery accumulate to form a by-product layer with a thickness of up to tens of microns. Although diluents are added to the electrolyte, the viscosity of the electrolyte is still relatively large, and the wettability of the electrolyte to the electrode is poor, resulting in excessive polarization of the lithium metal battery and a capacity drop.

[0109] Based on the above failure mechanism, the embodiment of the present application improves the composition of the electrolyte. By selecting specific organic solvents and lithium salts, the molar concentration of lithium salt in the electrolyte is relatively high, and a solvation structure dominated by anion coordination can be formed, which still has a certain molar concentration of lithium salt in the later stage of the cycle; and the viscosity of the electrolyte is relatively low and the ionic conductivity is high, which can effectively reduce the polarization of the lithium metal battery and improve the cycle performance of the lithium metal battery.

[0110] electrolyte

[0111] In a first aspect, embodiments of the present application provide an electrolyte that can be used in lithium metal batteries.

[0112] The electrolyte includes a main solvent, a diluent and a lithium salt, the molar concentration of the lithium salt is 1 mol / L to 4 mol / L, and the viscosity of the electrolyte is ≤5.5 mPa·s.

[0113] In the embodiment of the present application, the molar concentration of lithium salt in the electrolyte is relatively high, for example, 1 mol / L to 4 mol / L. The lithium salt can form a solvated structure with the main solvent, and still has a certain molar concentration of lithium salt in the later stage of the cycle; and because the electrolyte also includes a diluent, the viscosity of the electrolyte is relatively low and the ionic conductivity is high, which can effectively reduce the polarization growth of the lithium metal battery and improve the cycle performance of the lithium metal battery.

[0114] Specifically,

[0115] The main solvent is the main solvent in the electrolyte. The lithium salt has a high solubility in the main solvent. The lithium salt is dissociated into cations and anions. The cations, anions and main solvent form a solvated structure. In other words, the solvated structure includes the lithium salt and the main solvent. The structural forms of the solvated structure include contact ion pairs (one anion coordinated with one cation and the main solvent) and aggregates (one anion coordinated with two or more cations and the main solvent). When the solvated structure comes into contact with the surface of the negative electrode of a lithium metal battery, the anions in the solvated structure decompose before the main solvent and participate in the film formation reaction, which can improve the coulombic efficiency of the lithium metal battery.

[0116] The solubility of lithium salt in diluent is low, and lithium salt basically does not dissolve in diluent, for example, the solubility of lithium salt in diluent is ≤0.1g / 100g; diluent can reduce the content of lithium salt in unit volume of electrolyte; diluent and solvation structure exist in the form of a similar mixture, and both diluent and solvation structure can contact with the positive and negative electrodes, which is beneficial to the electrolyte infiltration of the electrodes and the transmission of lithium ions; due to the poor solubility and dissociation ability of diluent for lithium salt, diluent basically does not participate in the construction of solvation structure, so that the introduction of diluent has basically no effect on the coordination structure formed by lithium salt and main solvent, and lithium salt forms a local high molar concentration state, providing sufficient lithium ions for the battery system during the cyclic charge and discharge process, so that lithium ions can migrate between the positive and negative electrodes, reducing the polarization phenomenon of lithium metal batteries. Moreover, as an inert component, the diluent can significantly reduce the viscosity of the electrolyte, making the viscosity of the electrolyte ≤5.5mPa·s, improving the wettability of the electrolyte to the electrode, further reducing the polarization growth of the lithium metal battery, and helping to improve the ionic conductivity of the electrolyte and the cycle performance of the lithium metal battery.

[0117] In the embodiment of the present application, the specific structure of the solvated structure containing lithium ions in the electrolyte can be analyzed by Raman spectroscopy. For example, in an argon glove box (oxygen concentration is less than 0.1 ppm, water content is less than 0.1 ppm), the electrolyte is taken as a sample, and a glass capillary with a diameter of 0.3 mm is used to absorb the sample and the two ends of the glass capillary are sealed with melted paraffin. After the paraffin solidifies, the glass capillary becomes a closed space that can isolate the air; the glass capillary is then fixed to a glass slide with tape for testing, and the test range is 100 cm -1 Up to 3000cm -1 The mode is normal scanning, and the laser wavelength is 785 nm to reduce the interference of fluorescence effect. In the embodiment of the present application, the specific structure of the solvated structure in the electrolyte can also be detected by nuclear magnetic resonance (NMR).

[0118] Optionally, the main solvent is used as the solute and the diluent is used as the solvent for testing. The solubility of the main solvent in the diluent is ≥10g / 100g, the solubility of the main solvent in the diluent is relatively high, and the two can even be miscible. After the diluent is introduced into the electrolyte, since the main solvent participates in the construction of the solvation structure, the diluent and the solvation structure can exist in a form similar to a mixture.

[0119] In some embodiments, the viscosity of the electrolyte is ≤5.5 mPa·s; alternatively, the viscosity of the electrolyte is ≤5.1 mPa·s; alternatively, the viscosity of the electrolyte is ≤4 mPa·s. A relatively low viscosity of the electrolyte system helps reduce polarization and improve the cycling performance of lithium metal batteries.

[0120] For example, the viscosity of the electrolyte can be 0.1mPa·s, 0.2mPa·s, 0.3mPa·s, 0.5mPa·s, 0.6mPa·s, 0.8mPa·s, 1mPa·s, 1.2mPa·s, 1.5mPa·s, 1.6mPa·s, 1.8mPa·s, 2mPa·s, 2.2mPa·s, 2.5mPa·s, 2.8mPa·s, 3mPa·s, 3.2mPa·s, 3.5mPa·s, 3.8mPa·s, 4mPa·s, 4.2mPa·s, 4.5mPa·s, 4.8mPa·s, 5mPa·s, 5.1mPa·s, 5.2mPa·s, 5.3mPa·s, 5.4mPa·s, 5.5mPa·s or a range consisting of any two of the above values.

[0121] In some embodiments, the ionic conductivity of the electrolyte is 2 mS / cm to 5 mS / cm, and optionally 3 mS / cm to 5 mS / cm. When the ionic conductivity of the electrolyte is within the above range, the cycling performance of the lithium metal battery is improved.

[0122] For example, the ionic conductivity of the electrolyte may be 2 mS / cm, 2.5 mS / cm, 3 mS / cm, 3.5 mS / cm, 4 mS / cm, 4.5 mS / cm, 5 mS / cm, or a range consisting of any two of the above values.

[0123] [Lithium salt]

[0124] In some embodiments, the molar concentration of the lithium salt is 1 mol / L to 4 mol / L; optionally 1.5 mol / L to 4 mol / L; optionally 2 mol / L to 4 mol / L; further optionally 2 mol / L to 3.5 mol / L. When the molar concentration of the lithium salt is within the above range, it can form a high molar concentration solvation structure with the main solvent; although the lithium salt has a certain loss during the cycle of the lithium metal battery, due to the relatively high molar concentration of the lithium salt, in the later stage of the lithium metal battery cycle, there is still a certain concentration of lithium salt, which can reduce the polarization growth and achieve long-term stable circulation of the lithium metal battery. In the embodiment of the present application, the molar concentration of the lithium salt refers to the molar concentration of the lithium salt in the electrolyte.

[0125] Illustratively, the molar concentration of the lithium salt can be 1 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.25 mol / L, 1.3 mol / L, 1.35 mol / L, 1.4 mol / L, 1.45 mol / L, 1.5 mol / L, 1.55 mol / L, 1.6 mol / L, 1.65 mol / L, 1.7 mol / L, 1.75 mol / L, 1.8 mol / L, 1.85 mol / L, 1.9 mol / L, 1.95 mol / L, 2 mol / L, 2.1 mol / L, 2.15 mol / L, 2.20 mol / L, 2.25 mol / L, 2.30 mol / L, L, 2.35mol / L, 2.40mol / L, 2.45mol / L, 2.5mol / L, 2.55mol / L, 2.6mol / L, 2.65mol / L, 2.7mol / L, 2.75mol / L, 2.8mol / L, 2.9mol / L, 3mol / L, 3.1mol / L, 3.2mol / L, 3.25mol / L, 3.3mol / L, 3.4mol / L, 3.5mol / L, 3.6mol / L, 3.75mol / L, 3.8mol / L, 3.85mol / L, 3.9mol / L, 3.95mol / L, 4mol / L or a range consisting of any two of the above values.

[0126] In some embodiments, the lithium salt includes at least one of a fluorine-containing lithium salt, lithium bis(oxalatoborate) (LiBOB), and lithium perchlorate.

[0127] In some embodiments, the fluorine-containing lithium salt includes at least one of a fluorine-containing lithium sulfonyl imide salt, a fluorine-containing lithium phosphate salt, a fluorine-containing lithium borate salt, a fluorine-containing lithium oxalate phosphate salt, a lithium hexafluoroarsenate salt (LiAsF6), a lithium trifluoromethanesulfonate salt (LiOTF), and a lithium difluorooxalate borate salt (LiDFOB). Alternatively, the fluorine-containing lithium salt includes a fluorine-containing lithium sulfonyl imide salt.

[0128] In some embodiments, the fluorine-containing lithium sulfonyl imide salt includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Further optionally, the fluorine-containing lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI).

[0129] In some embodiments, the fluorine-containing lithium phosphate salt includes at least one of lithium hexafluorophosphate (LiPF6) and lithium difluorophosphate (LiDFP).

[0130] In some embodiments, the fluorine-containing lithium borate salt includes at least one of lithium tetrafluoroborate (LiBF 4 ) and lithium difluoroborate.

[0131] In some embodiments, the fluorine-containing lithium oxalate phosphate salt includes at least one of difluoro lithium oxalate phosphate salt and tetrafluoro lithium oxalate phosphate.

[0132] The lithium salt and the main solvent are combined to achieve the dissolution of the lithium salt with a high molar concentration in the main solvent, and form a solvated structure with a local high molar concentration in combination with the diluent.

[0133] Optionally, the lithium salt may include at least one of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI); further optionally, the lithium salt may include lithium bis(fluorosulfonyl)imide (LiFSI). These lithium salts have relatively high solubility in the main solvent and can decompose on the surface of the negative electrode sheet in preference to organic solvents to form an inorganic fluorine-rich SEI component, which is beneficial for the long cycle life of lithium metal batteries. Furthermore, these lithium salts have relatively good oxidative stability and can support cycling under high voltage.

[0134] [Main solvent]

[0135] Lithium salts have excellent solubility in the main solvent, which is conducive to the coordination of lithium salts and the main solvent to form a solvation structure and promote the decomposition of lithium salts into a film on the surface of the negative electrode.

[0136] In some embodiments, the molar concentration of the lithium salt in the main solvent is ≥4 mol / L. The main solvent has a strong solubility and dissociation ability for the lithium salt, so that the concentration of the lithium salt in the solvated structure is relatively high. For example, the molar concentration of the lithium salt in the main solvent is 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L, 6 mol / L, 6.5 mol / L, 7 mol / L, 7.5 mol / L, 8 mol / L or a range consisting of any two of the above values. In an embodiment of the present application, the molar concentration of the lithium salt in the main solvent refers to the concentration data detected when the main solvent is used as the solvent and the lithium salt is dissolved in the main solvent as a solute.

[0137] In some embodiments, the viscosity of the main solvent is ≤5 mPa·s. The viscosity of the main solvent is relatively small, so that the viscosity of the local high molar concentration electrolyte is low and the ionic conductivity is high. For example, the viscosity of the main solvent can be 0.1 mPa·s, 0.2 mPa·s, 0.3 mPa·s, 0.5 mPa·s, 0.6 mPa·s, 0.8 mPa·s, 1 mPa·s, 1.2 mPa·s, 1.5 mPa·s, 1.6 mPa·s, 1.8 mPa·s, 2 mPa·s, 2.2 mPa·s, 2.5 mPa·s, 2.8 mPa·s, 3 mPa·s, 3.2 mPa·s, 3.5 mPa·s, 3.8 mPa·s, 4 mPa·s, 4.2 mPa·s, 4.5 mPa·s, 4.8 mPa·s, 5 mPa·s or a range consisting of any two of the above values.

[0138] In some embodiments, the relative molecular weight of the main solvent is 40 to 150; optionally 40 to 125. When the relative molecular weight of the main solvent is within the above range, the main solvent is liquid and the viscosity is not too high, which is conducive to forming a solvated structure with the lithium salt. Since the relative molecular weight range of the main solvent is small, the main solvent will not occupy a higher mass content at the same molar fraction. Even if the material of the main solvent is adjusted, the mass proportion of the main solvent is small, which is conducive to increasing the mass proportion of the lithium salt. For example, the relative molecular weight of the main solvent is 40, 42, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150 or a range consisting of any two of the above values.

[0139] In some embodiments, the mass content of the main solvent is 10% to 80% based on the total mass of the main solvent and diluent in the electrolyte; alternatively, 20% to 40%; alternatively, 30% to 40%. When the mass content of the main solvent is within the above range, the solvent molecules of the main solvent can participate in the construction of the solvated structure, and there are substantially no free main solvent molecules.

[0140] For example, the mass content of the main solvent can be 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80% or a range consisting of any two of the above values.

[0141] In some embodiments, the main solvent may include at least one of an ester solvent, an ether solvent, a sulfone solvent, a nitrile solvent, an amide solvent, and a siloxane solvent.

[0142] In some embodiments, the ester solvent includes at least one of methyl formate, ethyl formate, ethyl acetate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and propylene carbonate.

[0143] In some embodiments, the ether solvent includes at least one of a C4 to C6 linear ether, a C3 to C10 alkoxyalkane, a C3 to C6 epoxyalkane, and trimethoxymethane. Ether solvents have good reduction resistance and are not prone to decomposition. They also have excellent solubility for lithium salts, which helps increase the molar concentration of the lithium salt and construct a solvation structure with a locally high molar concentration. Furthermore, because the anions in the lithium salt dominate the solvation structure, the anions are preferentially decomposed into an inorganic SEI film. Furthermore, the electrolyte solution has a low viscosity and excellent ionic conductivity.

[0144] Illustratively, the C4 to C6 linear ether includes at least one of ethyl ether, methyl propyl ether, propyl ether, methyl butyl ether and ethyl propyl ether.

[0145] Illustratively, the C3 to C10 alkoxyalkane includes at least one of C3 to C10 dimethoxyalkane, C3 to C10 diethoxyalkane, C3 to C10 methoxyethoxyalkane, C3 to C10 methoxypropoxyalkane, C3 to C10 methoxybutoxyalkane, and C3 to C10 ethoxypropoxyalkane.

[0146] For example, the C3 to C10 dimethoxyalkanes include at least one of dimethoxymethane, 1,1-dimethoxyethane, 1,1-dimethoxypropane, 2,2-dimethoxypropane, 1,1-dimethoxy-n-butane, 2,2-dimethoxy-n-butane, 1,1-dimethoxyisobutane, 1,2-dimethoxyethane, 1,3-dimethoxypropane (DMP), 1,2-dimethoxypropane, 1,4-dimethoxy-n-butane, 1,3-dimethoxy-n-butane, 1,2-dimethoxy-n-butane, 1,2-dimethoxyisobutane, and 1,3-dimethoxyisobutane. Alternatively, the C3 to C10 dimethoxyalkanes include 1,3-dimethoxypropane (DMP).

[0147] For example, the C3 to C10 diethoxyalkane includes at least one of diethoxymethane, 1,1-diethoxyethane, and 1,2-diethoxyethane (DME). Alternatively, the C3 to C10 diethoxyalkane includes 1,2-diethoxyethane (DME).

[0148] For example, the C3 to C10 methoxyethoxyalkane includes at least one of 1-methoxy-1-ethoxymethane, 1-methoxy-1-ethoxyethane, 1-methoxy-1-ethoxypropane, 1-methoxy-2-ethoxyethane, 1-methoxy-2-ethoxypropane, and 1-methoxy-3-ethoxypropane.

[0149] For example, the C3 to C10 methoxypropoxyalkanes include 1-methoxy-1-propoxymethane.

[0150] For example, the C3 to C10 methoxybutoxyalkanes include 1-methoxy-2-butoxymethane.

[0151] For example, the C3 to C10 ethoxypropoxyalkanes include 1-ethoxy-1-propoxymethane.

[0152] For example, the C3 to C6 alkylene oxide includes at least one of tetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 1,3-dioxane, and 1-4-dioxane.

[0153] In some embodiments, the sulfone solvent includes at least one of dimethyl sulfoxide, dimethyl sulfone, sulfolane, sulfolane oxide, methyl ethyl sulfone, and methyl ethyl sulfoxide.

[0154] In some embodiments, the nitrile solvent includes at least one of acetonitrile, propionitrile, butyronitrile, and malononitrile.

[0155] In some embodiments, the amide solvent includes at least one of dimethylformamide, dimethylacetamide, and diethylacetamide.

[0156] In some embodiments, the siloxane-based solvent includes at least one of dimethoxydimethylsilane and trimethoxymethylsilane.

[0157] [Thinner]

[0158] As an inert diluent, the diluent can reduce the viscosity of the electrolyte; and its solubility in lithium salts is low, so it has little effect on the solvated structure in the electrolyte, so that the solvated structure can fully play the role of anion preferential film formation.

[0159] In some embodiments, the viscosity of the diluent is ≤5 mPa·s; optionally ≤3 mPa·s. The viscosity of the diluent is relatively small, so that the viscosity of the electrolyte is low and the ionic conductivity is relatively high. For example, the viscosity of the diluent can be 0.1 mPa·s, 0.2 mPa·s, 0.3 mPa·s, 0.5 mPa·s, 0.6 mPa·s, 0.8 mPa·s, 1 mPa·s, 1.2 mPa·s, 1.5 mPa·s, 1.6 mPa·s, 1.8 mPa·s, 2 mPa·s, 2.2 mPa·s, 2.5 mPa·s, 2.8 mPa·s, 3 mPa·s, 3.2 mPa·s, 3.5 mPa·s, 3.8 mPa·s, 4 mPa·s, 4.2 mPa·s, 4.5 mPa·s, 4.8 mPa·s, 5 mPa·s, or a range consisting of any two of the above values.

[0160] In some embodiments, the relative molecular weight of the diluent is 60 to 190. When the molecular weight of the diluent is within the above range, the diluent is in liquid form and is beneficial for further reducing the viscosity of the electrolyte. Moreover, since the relative molecular weight of the diluent is relatively small, its mass share is relatively small under the same amount of substance, which is beneficial for increasing the mass share of the lithium salt in the solvated structure and increasing the molar concentration of the lithium salt. For example, the relative molecular weight of the diluent is 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125, 130, 135, 140, 145, 150, 155, 160, 165, 170, 175, 180, 185, 190 or a range consisting of any two of the above values.

[0161] When the amount of the diluent and the amount of the lithium salt are within a set range, the diluent has minimal impact on the solvation structure. Even when the viscosity of the electrolyte system is reduced, the electrolyte still has the solvation structure, allowing the lithium salt in the solvation structure to preferentially form a film, improving the performance of the SEI film and reducing the risk of capacity drop in lithium metal batteries. Because the diluent's relative molecular weight range is small, the diluent does not occupy a higher mass fraction at the same mole fraction. Even if the diluent's material is adjusted, the diluent's mass fraction remains small, which helps increase the mass fraction of the lithium salt. In some embodiments, based on the total mass of the main solvent and diluent in the electrolyte, the mass fraction of the diluent is 20% to 90%; optionally 60% to 80%; or optionally 60% to 70%. When the diluent's mass fraction is within the above range, the amount of the diluent and the amount of the lithium salt meet the set range. The diluent has essentially no impact on the solvation structure, allowing the lithium salt to preferentially form a film in the solvation structure, improving the performance of the SEI film and reducing the risk of capacity drop in lithium metal batteries. For example, the mass content of the diluent can be 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or a range consisting of any two of the above values.

[0162] In some embodiments, the diluent comprises a compound of formula (CI),

[0163] In formula (CI),

[0164] X1 and X2 each independently include a carbon atom, an oxygen atom or a nitrogen atom;

[0165] R1 and R2 each independently include a C1 to C6 alkyl group, a cycloalkyl group, an aryl group, a C1 to C6 halogenated alkyl group, a halogenated cycloalkyl group, a halogenated aryl group or a halogen atom; optionally, the halogen atom includes a fluorine atom or a chlorine atom;

[0166] R 31 and R 32 Each independently includes a hydrogen atom, a C1 to C6 chain alkyl group, a cycloalkyl group, an aryl group, a C1 to C6 halogenated chain alkyl group, a halogenated cycloalkyl group, a halogenated aryl group, a halogen atom or does not exist, wherein,

[0167] When X1 is a carbon atom, R 31 and R 32 each independently comprises a hydrogen atom or a halogen atom;

[0168] When X1 is an oxygen atom, R 31 and R 32 does not exist;

[0169] When X1 is a nitrogen atom, R 31and R 32 One of them includes a hydrogen atom, a C1 to C6 alkyl group, a cycloalkyl group, an aryl group, a C1 to C6 halogenated alkyl group, a halogenated cycloalkyl group, a halogenated aryl group or a halogen atom; the other one does not exist;

[0170] R 41 and R 42 Each independently includes a hydrogen atom, a C1 to C6 chain alkyl group, a cycloalkyl group, an aryl group, a C1 to C6 halogenated chain alkyl group, a halogenated cycloalkyl group, a halogenated aryl group, a halogen atom or does not exist, wherein,

[0171] When X2 is a carbon atom, R 41 and R 42 each independently comprises a hydrogen atom or a halogen atom;

[0172] When X2 is an oxygen atom, R 41 and R 42 does not exist;

[0173] When X2 is a nitrogen atom, R 41 and R 42 One of them includes a hydrogen atom, a C1 to C6 alkyl group, a cycloalkyl group, an aryl group, a C1 to C6 halogenated alkyl group, a halogenated cycloalkyl group, a halogenated aryl group or a halogen atom, and the other one does not exist.

[0174] Alternatively, R1 and R2 each independently include a C1 to C6 alkyl group, a C1 to C6 halogenated alkyl group, or a halogen atom.

[0175] Optionally, R 31 and R 32 Each independently includes a hydrogen atom, a C1 to C6 alkyl group, a C1 to C6 halogenated alkyl group, a halogen atom, or is absent.

[0176] Optionally, R 41 and R 42 Each independently includes a hydrogen atom, a C1 to C6 alkyl group, a C1 to C6 halogenated alkyl group, a halogen atom, or is absent.

[0177] In some embodiments, when X1 and X2 are both carbon atoms, the compound represented by formula (CI) is a ketone compound.

[0178] In some embodiments, when X1 and X2 are both oxygen atoms, the compound represented by formula (CI) is a carbonate compound.

[0179] In some embodiments, when X1 and X2 are both nitrogen atoms, the compound represented by formula (CI) is a urea compound.

[0180] In some embodiments, when one of X1 and X2 is a carbon atom and the other is an oxygen atom, the compound represented by formula (CI) is a carboxylate compound.

[0181] In some embodiments, when one of X1 and X2 is a carbon atom and the other is a nitrogen atom, the compound represented by formula (CI) is an amide compound.

[0182] In some embodiments, when one of X1 and X2 is an oxygen atom and the other is a nitrogen atom, the compound represented by formula (CI) is a carbamate compound.

[0183] Illustratively, the compound represented by formula (CI) includes at least one of the compounds represented by formula (CI-1) to the compounds represented by formula (CI-32),

[0184] In some embodiments, the diluent comprises a compound represented by formula (C-IIa),

[0185] In formula (C-IIa),

[0186] M1 includes an oxygen atom, a nitrogen atom or a sulfur atom;

[0187] S 11 and S 12 Each independently includes C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl or halogenated aryl; optionally, S 11 and S 12 Each independently includes C1 to C6 alkyl, C3 to C6 cycloalkyl, aryl, C1 to C6 halogenated alkyl, C3 to C6 halogenated cycloalkyl or halogenated aryl;

[0188] S 13 including C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl, halogenated aryl or not present, wherein,

[0189] When M1 is an oxygen atom or a sulfur atom, S 13 does not exist;

[0190] When M1 is a nitrogen atom, S 13 These include C1 to C6 alkyl, C3 to C6 cycloalkyl, aryl, C1 to C6 halogenated alkyl, C3 to C6 halogenated cycloalkyl or halogenated aryl.

[0191] Optionally, S 13 It includes C1 to C6 alkyl, C3 to C6 cycloalkyl, aryl, C1 to C6 halogenated alkyl, C3 to C6 halogenated cycloalkyl, halogenated aryl or does not exist.

[0192] Illustratively, the compound represented by formula (C-II) includes at least one of the compounds represented by formula (C-II-1) to formula (C-II-12),

[0193] Illustratively, the compound represented by formula (C-II) includes at least one of the compounds represented by formula (C-II-31) to formula (C-II-34),

[0194] Illustratively, the compound represented by formula (C-II) includes at least one of the compounds represented by formula (C-II-39) to formula (C-II-42),

[0195] Illustratively, the compound represented by formula (C-II) includes the compound represented by formula (C-II-68),

[0196] In some embodiments, the diluent comprises a compound represented by formula (C-IIb),

[0197] In formula (C-IIb),

[0198] M 21 and M 22 each independently comprises an oxygen atom, a nitrogen atom or a sulfur atom;

[0199] S 21 and S 23 Each independently includes C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl or halogenated aryl; optionally, S 21 and S 23 Each independently includes C1 to C6 alkyl, C3 to C6 cycloalkyl, aryl, C1 to C6 halogenated alkyl, C3 to C6 halogenated cycloalkyl or halogenated aryl;

[0200] S 22 Including alkylene or halogenated alkylene; optionally C1 to C4 alkylene or C1 to C4 halogenated alkylene;

[0201] S 24 including C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl, halogenated aryl or not present, wherein,

[0202] When M 21 When S is an oxygen atom or a sulfur atom, 24 does not exist;

[0203] When M 21When S is a nitrogen atom, 24 These include C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl or halogenated aryl.

[0204] Optionally, S 24 including C1 to C6 alkyl, C3 to C6 cycloalkyl, aryl, C1 to C6 halogenated alkyl, C3 to C6 halogenated cycloalkyl, halogenated aryl, or not present,

[0205] S 25 including C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl, halogenated aryl or not present, wherein,

[0206] When M 22 When S is an oxygen atom or a sulfur atom, 25 does not exist;

[0207] When M 22 When S is a nitrogen atom, 25 These include C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl or halogenated aryl.

[0208] Optionally, S 25 It includes C1 to C6 alkyl, C3 to C6 cycloalkyl, aryl, C1 to C6 halogenated alkyl, C3 to C6 halogenated cycloalkyl, halogenated aryl or does not exist.

[0209] Illustratively, the compound represented by formula (C-II) includes at least one of the compounds represented by formula (C-II-13) to formula (C-II-30),

[0210] Illustratively, the compound represented by formula (C-II) includes at least one of the compounds represented by formula (C-II-69) to formula (C-II-74),

[0211] Illustratively, the compound represented by formula (C-II) includes at least one of the compounds represented by formula (C-II-75) to formula (C-II-77),

[0212] In some embodiments, the diluent comprises a compound represented by formula (C-IIc),

[0213] In formula (C-IIc),

[0214] M3 includes at least one of an oxygen atom, a nitrogen atom, and a sulfur atom;

[0215] S 31Including alkylene or halogenated alkylene; optionally C1 to C4 alkylene or C1 to C4 halogenated alkylene;

[0216] S 32 including C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl, halogenated aryl or not present, wherein,

[0217] When M3 is an oxygen atom or a sulfur atom, S 32 does not exist;

[0218] When M3 is a nitrogen atom, S 32 These include C1 to C6 alkyl, cycloalkyl, aryl, C1 to C6 halogenated alkyl, halogenated cycloalkyl or halogenated aryl.

[0219] Illustratively, the compound represented by formula (C-II) includes at least one of the compounds represented by formula (C-II-43) to formula (C-II-67),

[0220] Illustratively, the compound represented by formula (C-II) includes at least one of the compounds represented by formula (C-II-78) to formula (C-II-85),

[0221] Optionally, the diluent may include at least one of the compound represented by formula (C-II-3), the compound represented by formula (C-II-4), the compound represented by formula (C-II-21), the compound represented by formula (C-II-32), and the compound represented by formula (C-II-30). The above compounds have relatively low molecular weights and low viscosities; moreover, the above compounds have relatively high boiling points and high thermal stability at the relatively high operating temperatures of lithium metal batteries, which is beneficial to improving the thermal stability of the electrolyte at high temperatures.

[0222] In some embodiments, the diluent includes a compound represented by formula (C-III), m H n Q y Formula (C-III),

[0223] In formula (C-III),

[0224] m is selected from any positive integer from 1 to 8;

[0225] y is selected from any integer from 0 to 10;

[0226] y / n is any value between 0.25 and 5;

[0227] Q includes a halogen atom, and optionally, the halogen atom includes at least one of a fluorine atom and a chlorine atom.

[0228] Illustratively, the compound represented by formula (C-III) may include at least one of alkanes, halogenated alkanes, olefins, halogenated olefins, cycloalkanes, halogenated cycloalkanes, aromatic hydrocarbons, and halogenated aromatic hydrocarbons; further optionally, the compound represented by formula (C-III) may include at least one of alkanes, halogenated alkanes, halogenated olefins, cycloalkanes, aromatic hydrocarbons, and halogenated aromatic hydrocarbons. Illustratively, the compound represented by formula (C-III) may include at least one of C1 to C6 alkanes, C1 to C6 halogenated alkanes, C2 to C6 olefins, C2 to C6 halogenated olefins, C3 to C6 cycloalkanes, C3 to C6 halogenated cycloalkanes, C6 to C8 aromatic hydrocarbons, and C6 to C8 halogenated aromatic hydrocarbons.

[0229] For example, the compound represented by formula (C-III) may include at least one of the compound represented by formula (C-III-1) to the compound represented by formula (C-III-10), the compound represented by formula (C-III-13) to the compound represented by formula (C-III-21),

[0230] For example, the compound represented by formula (C-III) may include at least one of the compound represented by formula (C-III-11) and the compound represented by formula (C-III-12).

[0231] For example, the compound represented by formula (C-III) may include at least one of the compound represented by formula (C-III-22) and the compound represented by formula (C-III-33),

[0232] For example, the compound represented by formula (C-III) may include at least one of the compound represented by formula (C-III-30) and the compound represented by formula (C-III-32).

[0233] For example, the compound represented by formula (C-III) may include the compound represented by formula (C-III-33),

[0234] In some embodiments, the diluent comprises a compound represented by formula (C-IV),

[0235] In formula (C-IV), T1 to T4 each independently include a C1 to C6 alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, a halogenated alkyl group, a halogenated cycloalkyl group, a halogenated aryl group or a halogenated alkoxy group.

[0236] Optionally, T1 to T4 each independently include at least one of C1 to C6 chain alkyl, C3 to C6 cycloalkyl, aryl, C1 to C6 alkoxy, C1 to C6 halogenated chain alkyl, C3 to C6 halogenated cycloalkyl, halogenated aryl, and C1 to C6 halogenated alkoxy.

[0237] Illustratively, the compound represented by formula (C-IV) includes at least one of the compounds represented by formula (C-IV-1) to the compounds represented by formula (C-IV-21),

[0238] In some embodiments, the diluent comprises a compound of formula (CV),

[0239] In formula (CV),

[0240] A1 includes a C1 to C3 alkyl group, a halogenated alkyl group or a halogen atom; alternatively, A1 includes a C1 to C3 alkyl group, a C1 to C3 halogenated alkyl group or a halogen atom.

[0241] A2 includes C1 to C3 alkyl, haloalkyl, alkoxy, haloalkoxy, N,N-dimethyl, N,N-diethyl, N,N-methylethyl or morpholino; alternatively, A2 includes C1 to C3 alkyl, C1 to C3 haloalkyl, alkoxy, haloalkoxy, N,N-dimethyl, N,N-diethyl, N,N-methylethyl or morpholino.

[0242] Optionally, the compound represented by formula (CV) may include at least one of a sulfonamide compound and a sulfite compound.

[0243] Illustratively, the compound represented by formula (CV) may include at least one of the compounds represented by formula (CV-1) to the compounds represented by formula (CV-17),

[0244] Illustratively, the compound represented by formula (CV) may include at least one of the compounds represented by formula (CV-18) to the compounds represented by formula (CV-21),

[0245] 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.

[0246] The types and contents of the molar concentrations of inorganic components / lithium salts 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 molar concentrations in the electrolyte can be qualitatively or quantitatively analyzed by ion chromatography analysis according to the 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 an ion chromatography analysis method.

[0247] 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.

[0248] The viscosity of the electrolyte or the viscosity of the organic solvent in the electrolyte is well known in the art and can be measured using equipment and methods known in the art. For example, a sample of the electrolyte is measured using a rotational viscometer with a rotor set to 12 rpm for 5 minutes. After the value stabilizes, the viscosity is recorded. After determining the type of organic solvent, a separate sample of that type of organic solvent is taken and tested using the aforementioned test method to determine the viscosity.

[0249] The ionic conductivity of the electrolyte is well known in the art and can be detected using equipment and methods known in the art, for example, by using the electrolyte as a sample and measuring it using a conductivity meter at room temperature.

[0250] lithium metal batteries

[0251] In a second aspect, an embodiment of the present application provides a lithium metal battery, wherein the lithium metal battery comprises the electrolyte of any embodiment of the first aspect of the present application, and the cycle performance of the lithium metal battery is improved.

[0252] [Negative electrode]

[0253] Lithium metal batteries also include negative electrodes. During the charge and discharge cycles of lithium metal batteries, the deposition and stripping of metallic lithium accompanies the negative electrode. The electrolyte provides greater stability to the negative electrode, alleviating the oxidative decomposition of the electrolyte. This creates a more stable interface between the electrolyte and the negative electrode, improving the battery's cycling performance, particularly its cycle life at high voltages.

[0254] 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.

[0255] The negative electrode current collector may be a metal foil or a composite current collector. Copper foil may be used as an example of a metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. For example, the primary material of the metal layer may include at least one of copper, a copper alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. For example, the polymer base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0256] 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.

[0257] 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.

[0258] 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.

[0259] 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.

[0260] Optionally, in addition to lithium metal, the lithium metal layer may also include a non-lithium element capable of forming an alloy with the lithium element. The non-lithium element may include at least one of a metal element and a metalloid element. For example, 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). For example, the metalloid element may include at least one of boron (B), carbon (C), and silicon (Si).

[0261] The material of the negative electrode current collector is as described above and will not be repeated here.

[0262] 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.

[0263] 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.

[0264] [Positive electrode]

[0265] In some embodiments, the lithium metal battery may further include a positive electrode sheet.

[0266] 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.

[0267] The positive electrode active material may be a positive electrode active material known in the art for lithium metal batteries. As an example, the positive electrode active material may include at least one of the following materials: a lithium-containing transition metal oxide and a lithium-containing phosphate with an olivine structure.

[0268] In some embodiments, the lithium-containing transition metal oxide may include at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and modified compounds thereof.

[0269] For example, the general formula of lithium-containing transition metal oxide is: Li x A y Ni a Co b Mn c M (1-a-b-c) Y 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 Y is selected from one or more of O and F. Optionally, y = 0. The above-mentioned lithium-containing transition metal oxide can improve the energy density of lithium metal batteries; and when used in combination with the above-mentioned electrolyte, the electrolyte has relatively high stability on the positive electrode side, which is beneficial for improving the cycle performance of lithium metal batteries.

[0270] Optionally, 0<b<1.

[0271] Optionally, 0<c<1.

[0272] Optionally, 0<a+b+c<1.

[0273] Optionally, 0<a<1; further optionally, 0.8≤a<1.

[0274] 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.

[0275] Specifically, lithium-containing transition metal oxides 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 O2(NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2(NCM 211 ), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM 622 ), LiNi 0.96 Co 0.02 Mn 0.02 O2(Ni 96 ), lithium nickel cobalt aluminum oxide (such as LiNi 0.80 Co 0.15 Al 0.05 O2) in one or more.

[0276] 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.

[0277] 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.

[0278] 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.

[0279] 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.

[0280] 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 the 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 percentage of the positive electrode conductive agent based on the total mass of the positive electrode film layer is ≤5%.

[0281] 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 percentage of the positive electrode binder is ≤5%.

[0282] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. Aluminum foil may be used as an example of a metal foil. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base layer. For example, the metal material of the metal layer may include at least one of aluminum, an aluminum alloy, nickel, a nickel alloy, titanium, a titanium alloy, silver, and a silver alloy. For example, the polymer base layer may include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0283] The positive electrode film layer 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 may be, but is not limited to, N-methylpyrrolidone (NMP).

[0284] [Isolation film]

[0285] In some embodiments, the lithium metal battery may further include a separator.

[0286] 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.

[0287] 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.

[0288] 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.

[0289] In some embodiments, the lithium metal battery may include an outer packaging that can be used to encapsulate the electrode assembly and the electrolyte.

[0290] 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.

[0291] 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.

[0292] 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.

[0293] 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.

[0294] 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.

[0295] 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.

[0296] 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.

[0297] 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.

[0298] 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.

[0299] Electrical devices

[0300] 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.

[0301] Electrical devices can choose lithium metal batteries, battery modules or battery packs according to their usage requirements.

[0302] FIG6 is a schematic diagram of an exemplary electric device 6. The electric device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the electric device 6, a battery pack or battery module may be used.

[0303] As another example, an electric device may be a mobile phone, a tablet computer, a laptop computer, etc. Such an electric device is usually required to be lightweight and thin, and may use a lithium metal battery as a power source.

[0304] Example

[0305] 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 parts, percentages, and ratios reported in the following examples are by mass, 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.

[0306] Preparation of Lithium Metal Batteries in Examples and Comparative Examples

[0307] 1. Preparation of positive electrode sheet

[0308] The positive electrode sheet includes a positive electrode current collector and a positive electrode film layer arranged on both sides of the positive electrode current collector. The positive electrode current collector is aluminum foil. The positive electrode film layer includes a positive electrode slurry (the solvent is N-methylpyrrolidone NMP) uniformly coated on the surface of the positive electrode current collector aluminum foil, and a film layer formed after drying and cold pressing. The positive electrode film layer includes a positive electrode active material, a conductive agent acetylene black, and a binder polyvinylidene fluoride (PVDF) in a weight ratio of 98:1:1.

[0309] The positive electrode active material includes a molecular formula of LiNi 0.8 Co 0.10 Mn 0.10 Compound of O2(NCM811).

[0310] 2. Preparation of negative electrode sheet

[0311] 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.

[0312] 3. Isolation film

[0313] The isolation film is a polyethylene film layer.

[0314] 4. Preparation of electrolyte

[0315] The electrolyte includes an organic solvent and a lithium salt, and the organic solvent includes a main solvent and a diluent.

[0316] 5. Preparation of lithium metal batteries

[0317] The positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator placed between the positive electrode sheet and the negative electrode sheet to serve as an isolation to obtain an electrode assembly; the electrode assembly is placed in an outer packaging shell, dried, and then injected with electrolyte, and after vacuum packaging, standing, forming, shaping and other processes, a laminated lithium metal battery is obtained.

[0318] The electrolyte compositions of the examples and comparative examples are shown in Table 1.

[0319] Performance Testing

[0320] 1. Room temperature cycle performance test of lithium metal batteries

[0321] At 25° C., the lithium metal batteries prepared in the examples and comparative examples were subjected to charge-discharge cycles at a rate of 0.2 C (ie, 28 mA) for charging and 1 C for discharging (ie, 140 mA).

[0322] The charge and discharge cutoff voltages were set at 4.3V and 2.8V, respectively. A constant current-constant voltage method was used for charging. Specifically, after a 0.2C constant current charge reached a cutoff voltage of 4.3V, a 4.3V constant voltage charge was applied until the current decayed to 0.1C (14mA). The battery life was considered complete when the discharge capacity decayed to 80% of the initial discharge capacity, and the number of cycles at that point was recorded.

[0323] Test results

[0324] The test results are shown in Table 1.

[0325] Table 1

[0326] In Table 1, the mass content of the main solvent is calculated based on the total mass of the main solvent and the diluent.

[0327] The mass content of the diluent is calculated based on the total mass of the main solvent and the diluent.

[0328] DME stands for 1,2-diethoxyethane; DMP stands for 1,3-dimethoxypropane.

[0329] C-II-4 represents a compound represented by formula (C-II-4).

[0330] In Table 1, the solubility of lithium salt in the diluent is ≤0.1 g / 100 g.

[0331] As shown in Table 1, the electrolyte in Comparative Example 1 uses ethylene carbonate and ethyl methyl carbonate as organic solvents and 1.0 mol / L lithium hexafluorophosphate (LiPF6) as the lithium salt. When this electrolyte comes into contact with a lithium metal anode, the ethylene carbonate and ethyl methyl carbonate preferentially decompose to form a film, which is detrimental to the circulation of the lithium metal anode and easily causes a capacity drop. However, the present embodiment utilizes a specific organic solvent system that forms a locally high molar concentration electrolyte system with the lithium salt, allowing the lithium salt to preferentially decompose into a film, significantly improving the cycling performance at room temperature.

[0332] Comparative Example 2 uses the diluent of the embodiment of the present application alone, and Comparative Example 3 uses the main solvent of the embodiment of the present application alone, and both cannot achieve an electrolyte system with low viscosity and high molar concentration of lithium salt; it is impossible to effectively improve the cycle performance of the lithium metal battery. The embodiment of the present application selects the material of the organic solvent system so that the main solvent in the organic solvent can form a high molar concentration solvation structure with the high molar concentration of the lithium salt, and the diluent can play the role of a diluent, so that the electrolyte further forms a local high molar concentration electrolyte system, reduces the viscosity of the electrolyte, and thus improves the cycle life of the lithium metal battery. It can be seen from Comparative Examples 4 and 5 that when the same material system is used, the molar concentration of the lithium salt is too low (for example, less than 1 mol / L) or too high (for example, greater than 4 mol / L), which is not conducive to improving the cycle life of the lithium metal battery. When the molar concentration of the lithium salt in the embodiment of the present application is between 1 mol / L and 4 mol / L, it cooperates with the main solvent and the diluent so that the electrolyte further forms a local high molar concentration electrolyte system, reduces the viscosity of the electrolyte, and thus improves the cycle life of the lithium metal battery.

[0333] In Examples 1 to 3, the cycle life of lithium metal batteries can still be improved by adjusting the material of the lithium salt. The lithium salt can be selected as lithium bis(fluorosulfonyl)imide (LiFSI), which can promote the formation of an inorganic-rich SEI film.

[0334] In Examples 1 and 4 to 11, the cycle life of the lithium metal battery can be further improved by adjusting the material of the main solvent; in particular, when the main solvent includes at least one of DME and DMP, the cycle life of the lithium metal battery can be significantly improved.

[0335] In Examples 1 and 12 to 20, the cycle life of the lithium metal battery can be further improved by adjusting the material of the diluent; in particular, when the diluent includes at least one of the compound represented by formula (C-II-3), the compound represented by formula (C-II-4), the compound represented by formula (C-II-21), the compound represented by formula (C-II-32), and the compound represented by formula (C-II-30), the cycle life of the lithium metal battery can be significantly improved.

[0336] In Examples 1 and 21 to 24, the cycle life of the lithium metal battery can be further improved by adjusting the molar concentration of the lithium salt; in particular, when the molar concentration of the lithium salt is 1.5 mol / L to 4 mol / L, further optionally 2 mol / L to 4 mol / L, and further optionally 2 mol / L to 3.5 mol / L, the cycle life of the lithium metal battery can be significantly improved.

[0337] In Example 1 and Examples 25 to 28, the cycle life of the lithium metal battery can be further improved by adjusting the mass content of the main solvent and the diluent; especially when the content of the main solvent is 20% to 80%; optionally 30% to 40%, the cycle life of the lithium metal battery can be significantly improved.

[0338] 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 main solvent, a diluent, and a lithium salt, wherein the molar concentration of the lithium salt is from 1 mol / L to 4 mol / L, and wherein, The viscosity of the electrolyte is ≤5.5 mPa·s.

2. The electrolyte according to claim 1, wherein, The viscosity of the electrolyte is ≤4 mPa·s; and / or The ionic conductivity of the electrolyte is 2 mS / cm to 5 mS / cm.

3. The electrolyte according to claim 1 or 2, wherein The molar concentration of the lithium salt is 2 mol / L to 3.5 mol / L.

4. The electrolyte according to any one of claims 1 to 3, wherein, The lithium salt includes at least one of a fluorinated lithium salt, lithium bis(oxalato)borate, and lithium perchlorate.

5. The electrolyte according to any one of claims 1 to 4, wherein, The fluorinated lithium salt includes at least one of a lithium fluorosulfonylimide salt, a lithium fluorophosphate salt, a lithium fluoroborate salt, a lithium fluorophosphate oxalate salt, a lithium hexafluoroarsenate salt, a lithium trifluoromethanesulfonate salt, and a lithium difluoro(oxalato)borate salt.

6. The electrolyte according to any one of claims 1 to 5, wherein, The lithium fluorosulfonylimide salt includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

7. The electrolyte according to any one of claims 1 to 6, wherein, Based on the total mass of the main solvent and the diluent, the mass content of the main solvent is 10% to 80%; or Based on the total mass of the main solvent and the diluent, the mass content of the diluent is 20% to 90%.

8. The electrolyte according to claim 7, wherein, The mass content of the main solvent is 20% to 40%.

9. The electrolyte according to any one of claims 1 to 8, wherein The relative molecular weight of the main solvent is 40 to 150; and / or the viscosity of the main solvent is ≤5 mPa·s.

10. The electrolyte according to any one of claims 1 to 9, wherein The main solvent includes at least one of an ester solvent, an ether solvent, a sulfone solvent, a nitrile solvent, an amide solvent, and a siloxane solvent.

11. The electrolyte according to claim 10, wherein, The ether solvent includes at least one of a C4 to C6 linear ether, a C3 to C10 alkoxyalkane, a C3 to C6 epoxyalkane, and trimethoxymethane.

12. The electrolyte according to any one of claims 1 to 11, wherein The relative molecular weight of the diluent is 60 to 190; and / or the viscosity of the diluent is ≤5 mPa·s.

13. The electrolyte according to any one of claims 1 to 12, wherein, The diluent includes a compound represented by formula (C-I), In formula (C-I), X1 and X2 each independently include a carbon atom, an oxygen atom, or a nitrogen atom; R1 and R2 each independently include a C1 to C6 chain alkyl group, a cycloalkyl group, an aryl group, a C1 to C6 halogenated chain alkyl group, a halogenated cycloalkyl group, a halogenated aryl group, or a halogen atom; R 31 and R 32 each independently includes a hydrogen atom, a C1-C6 linear alkyl group, a cycloalkyl group, an aryl group, a C1-C6 haloalkyl group, a halocycloalkyl group, a haloaryl group, a halogen atom or is absent, provided that When X1 is a carbon atom, R 31 and R 32 each independently comprises a hydrogen atom or a halogen atom; When X1 is an oxygen atom, R 31 and R 32 do not exist; When X1 is a nitrogen atom, R 31 and R 32 One of them includes a hydrogen atom, a C1-C6 linear alkyl group, a cycloalkyl group, an aryl group, a C1-C6 halogenated linear alkyl group, a halogenated cycloalkyl group, a halogenated aryl group or a halogen atom; the other does not exist; R 41 and R 42 each independently comprises a hydrogen atom, a C1-C6 linear alkyl group, a cycloalkyl group, an aryl group, a C1-C6 haloalkyl group, a halocycloalkyl group, a haloaryl group, a halogen atom or is absent, provided that, When X2 is a carbon atom, R 41 and R 42 each independently include a hydrogen atom or a halogen atom; When X2 is an oxygen atom, R 41 and R 42 do not exist; When X2 is a nitrogen atom, R 41 and R 42 one of which includes a hydrogen atom, a C1-C6 alkyl chain, a cycloalkyl group, an aryl group, a C1-C6 halogenated alkyl chain, a halogenated cycloalkyl group, a halogenated aryl group or a halogen atom, and the other does not exist.

14. The electrolyte according to any one of claims 1 to 13, wherein, The diluent includes a compound represented by formula (C-IIa), In formula (C-IIa), M1 includes an oxygen atom, a nitrogen atom, or a sulfur atom; S 11 and S 12 each independently includes a C1-C6 alkyl chain, cycloalkyl, aryl, C1-C6 haloalkyl, halocycloalkyl or haloaryl; S 13 including C1-C6 alkyl, cycloalkyl, aryl, C1-C6 haloalkyl, halocycloalkyl, haloaryl or absent, wherein, When M1 is an oxygen atom or a sulfur atom, S 13 does not exist; When M1 is a nitrogen atom, S 13 includes a C1-C6 linear alkyl group, a cycloalkyl group, an aryl group, a C1-C6 haloalkyl group, a halocycloalkyl group or a haloaryl group.

15. The electrolyte according to any one of claims 1 to 14, wherein The diluent includes a compound represented by formula (C-IIb), In formula (C-IIb), M 21 and M 22 each independently includes an oxygen atom, a nitrogen atom, or a sulfur atom; S 21 and S 23 each independently includes a C1-C6 alkyl chain, cycloalkyl, aryl, C1-C6 haloalkyl, halocycloalkyl or haloaryl; S 22 comprising an alkylene or haloalkylene; S 24 which includes a C1-C6 alkyl chain, cycloalkyl group, aryl group, C1-C6 haloalkyl group, halocycloalkyl group, haloaryl group or is absent, wherein, When M 21 is an oxygen atom or a sulfur atom, S 24 does not exist; When M 21 is a nitrogen atom, S 24 includes a C1-C6 linear alkyl group, a C3-C6 cycloalkyl group, an aryl group, a C1-C6 haloalkyl group, a C3-C6 halocycloalkyl group or a haloaryl group.

16. The electrolyte according to any one of claims 1 to 15, wherein, The diluent includes a compound represented by formula (C-IIc), In formula (C-IIc), M3 includes at least one of an oxygen atom, a nitrogen atom, and a sulfur atom; S 31 comprising an alkylene or haloalkylene; S 32 including C1-C6 alkyl, cycloalkyl, aryl, C1-C6 haloalkyl, halocycloalkyl, haloaryl or absent, wherein, When M3 is an oxygen atom or a sulfur atom, S 32 does not exist; When M3 is a nitrogen atom, S 32 includes a C1-C6 linear alkyl group, a cycloalkyl group, an aryl group, a C1-C6 haloalkyl group, a halocycloalkyl group or a haloaryl group.

17. The electrolyte according to any one of claims 1 to 16, wherein The diluent includes a compound represented by formula (C-III), C m H n Q y Formula (C-III) In formula (C-III), m is selected from any positive integer from 1 to 8; y is selected from any integer from 0 to 10; y / n is any value from 0.25 to 5; Q includes a halogen atom.

18. The electrolyte according to any one of claims 1 to 17, wherein, The diluent includes a compound represented by formula (C-IV), In formula (C-IV), T1 to T4 each independently include a C1 to C6 chain alkyl group, a cycloalkyl group, an aryl group, an alkoxy group, a halogenated chain alkyl group, a halogenated cycloalkyl group, a halogenated aryl group, or a halogenated alkoxy group.

19. The electrolyte according to any one of claims 1 to 18, wherein, The diluent includes a compound represented by formula (C-V), In formula (C-V), A1 includes a C1 to C3 alkyl group, a halogenated alkyl group, or a halogen atom; A2 includes a C1 to C3 alkyl group, a halogenated alkyl group, an alkoxy group, a halogenated alkoxy group, N,N-dimethyl, N,N-diethyl, N,N-methylethyl, or morpholinyl.

20. A lithium metal battery, comprising the electrolyte according to any one of claims 1 to 19.

21. The lithium metal battery according to claim 20, wherein, The lithium metal battery includes a negative electrode plate; The negative electrode plate includes a negative electrode current collector; or The negative electrode sheet includes a negative current collector and a lithium metal layer provided on at least one side of the negative current collector.

22. The lithium metal battery according to claim 20 or 21, further comprising a positive electrode sheet, the positive electrode sheet including a positive current collector and a positive electrode film layer provided on at least one side of the positive current collector and including a positive electrode active material. The positive electrode active material includes a compound with the general formula Li x A y Ni a Co b Mn c M (1-a-b-c) Y 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; Y is selected from one or more of O and F.

23. A battery, comprising the lithium metal battery according to any one of claims 20 to 22.

24. An electrical device, comprising the battery according to claim 23.

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