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

Abstract

The invention provides an electrolyte of a lithium metal battery, the lithium metal battery, a battery and an electric device, 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 1mol / L to 4mol / 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

Technical Field

[0001] This application belongs to the technical field of batteries, and particularly relates to an electrolyte for a lithium metal battery, a lithium metal battery, a battery, and an electrical device. Background Art

[0002] Lithium metal batteries have characteristics such as high capacity, and thus are widely used in electronic devices, such as mobile phones, laptops, battery cars, electric vehicles, electric airplanes, electric ships, electric toy cars, electric toy ships, electric toy airplanes, and electric tools, etc.

[0003] The electrolyte is an important component of a lithium metal battery and has a significant impact on the performance of the lithium metal battery; however, the current lithium metal battery has poor cycling performance and still needs to be further improved. Summary of the Invention

[0004] Embodiments of this application provide an electrolyte for a lithium metal battery, a lithium metal battery, a battery, and an electrical device, which can improve the cycling performance of the lithium metal battery.

[0005] An embodiment of the first aspect of this application provides an electrolyte for a lithium metal battery. The electrolyte for the lithium metal battery 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, wherein the viscosity of the electrolyte ≤ 5.5 mPa·s.

[0006] Thus, in the embodiments of this application, the molar concentration of the lithium salt in the electrolyte is relatively high, such as 1 mol / L to 4 mol / L. The lithium salt can form a solvation structure with the main solvent, and there is still a certain molar concentration of lithium salt in the later stage of cycling; moreover, since the electrolyte also includes a diluent, the viscosity of the electrolyte is relatively low, the ionic conductivity is relatively high, and it can effectively reduce the polarization growth of the lithium metal battery and improve the cycling performance of the lithium metal battery.

[0007] In some embodiments, the viscosity of the electrolyte ≤ 4 mPa·s. The relatively low viscosity of the electrolyte system is beneficial to reducing polarization and improving the cycling performance of the lithium metal battery.

[0008] In some embodiments, the ionic conductivity of the electrolyte is 2 mS / cm to 5 mS / cm; it can be selected as 3 mS / cm to 5 mS / cm. When the ionic conductivity of the electrolyte is within the above range, it is beneficial to improve the cycling performance of the lithium metal battery.

[0009] In some embodiments, the molar concentration of the lithium salt is from 2 mol / L to 3.5 mol / L. When the molar concentration of the lithium salt is within the above range, a solvation structure with a high molar concentration can be formed with the main solvent; although the lithium salt has a certain loss during the cycling of the lithium metal battery, due to the relatively high molar concentration of the lithium salt, there is still a certain concentration of the lithium salt in the later stage of the cycling of the lithium metal battery, which can reduce the polarization growth and achieve the long-term stable cycling of the lithium metal battery.

[0010] In some embodiments, the lithium salt includes at least one of a fluorinated lithium salt, lithium bis(oxalato)borate, and lithium perchlorate.

[0011] In some embodiments, the fluorinated lithium salt includes at least one of lithium fluorosulfonylimide salt, lithium fluorophosphate salt, lithium fluoroborate salt, lithium fluorophosphate oxalate salt, lithium hexafluoroarsenate salt, lithium trifluoromethanesulfonate salt, and lithium difluoro(oxalato)borate salt. Optionally, the fluorinated lithium salt includes lithium fluorosulfonylimide salt.

[0012] In some embodiments, the lithium fluorosulfonylimide salt includes at least one of lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide. Further optionally, the fluorinated lithium salt includes lithium bis(fluorosulfonyl)imide.

[0013] In some embodiments, the lithium fluorophosphate salt includes at least one of lithium hexafluorophosphate and lithium difluorophosphate.

[0014] In some embodiments, the lithium fluoroborate salt includes at least one of lithium tetrafluoroborate and lithium difluoroborate.

[0015] In some embodiments, the lithium fluorophosphate oxalate salt includes at least one of lithium difluoro(oxalato)phosphate and lithium tetrafluoro(oxalato)phosphate.

[0016] The above lithium salt and the main solvent cooperate to enable the dissolution of the lithium salt with a high molar concentration in the main solvent and form a solvation structure with a locally high molar concentration in combination with the diluent.

[0017] 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 solvation structure and there are basically no free main solvent molecules.

[0018] In some embodiments, based on the total mass of the main solvent and the diluent, the mass content of the diluent is 20% to 90%; optionally 60% to 80%; optionally 60% to 70%. When the mass content of the diluent is within the above range, the amount of substance of the diluent and the amount of substance of the lithium salt can meet the set range, and the diluent has basically no influence on the solvation structure, enabling 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 of the lithium metal battery.

[0019] 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 beneficial to the formation of a solvation 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 mole fraction. Even if the material of the main solvent is adjusted, the mass fraction of the main solvent is small, which is beneficial to increasing the mass fraction of the lithium salt.

[0020] In some embodiments, the viscosity of the main solvent ≤ 5 mPa·s. The relatively small viscosity of the main solvent results in a lower viscosity of the locally high-molar-concentration electrolyte and a higher ionic conductivity.

[0021] In some embodiments, the main solvent may include at least one of ester solvents, ether solvents, sulfone solvents, nitrile solvents, amide solvents, and siloxane solvents.

[0022] In some embodiments, the ester solvent includes at least one of methyl formate, ethyl formate, ethyl acetate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and propylene carbonate.

[0023] In some embodiments, the ether solvent includes at least one of C4 to C6 linear ethers, C3 to C10 alkoxyalkanes, C3 to C6 epoxyalkanes, and trimethoxymethane.

[0024] In some embodiments, the sulfone solvent includes at least one of dimethyl sulfoxide, dimethyl sulfone, sulfolane, cyclobutyl sulfoxide, methyl ethyl sulfone, and methyl ethyl sulfoxide.

[0025] In some embodiments, the nitrile solvent includes at least one of acetonitrile, propionitrile, butyronitrile, and malononitrile.

[0026] In some embodiments, the amide solvent includes at least one of dimethylformamide, dimethylacetamide, and diethylacetamide.

[0027] In some embodiments, the siloxane solvent includes at least one of dimethoxydimethylsilane and trimethoxymethylsilane.

[0028] In some embodiments, the relative molecular weight of the diluent is from 60 to 190; when the molecular weight of the diluent is within the above range, the diluent is liquid and is beneficial to further reducing the viscosity of the electrolyte. Moreover, since the relative molecular weight of the diluent is relatively small, at the same amount of substance, its mass fraction is relatively small, which is beneficial to increasing the mass fraction of the lithium salt in the solvation structure and increasing the molar concentration of the lithium salt.

[0029] In some embodiments, the viscosity of the diluent ≤ 5 mPa·s. The relatively small viscosity of the diluent results in a relatively low viscosity of the electrolyte and a relatively high ionic conductivity.

[0030] In some embodiments, the diluent comprises a compound represented by formula (C-I),

[0031]

[0032] In formula (C-I),

[0033] X1 and X2 each independently comprise a carbon atom, an oxygen atom or a nitrogen atom;

[0034] R1 and R2 each independently comprise 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;

[0035] R 31 and R 32 each independently comprise 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, a halogen atom or are absent, wherein,

[0036] when X1 is a carbon atom, R 31 and R 32 each independently comprise a hydrogen atom or a halogen atom;

[0037] when X1 is an oxygen atom, R 31 and R 32 are absent;

[0038] when X1 is a nitrogen atom, one of R 31 and R 32 comprises 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 is absent;

[0039] R 41 and R 42 each independently comprise 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, a halogen atom or are absent, wherein,

[0040] When X2 is a carbon atom, R 41 and R 42 each independently comprise a hydrogen atom or a halogen atom;

[0041] When X2 is an oxygen atom, R 41 and R 42 do not exist;

[0042] When X2 is a nitrogen atom, one of R 41 and R 42 comprises a hydrogen atom, a C1-C6 chain alkyl group, a cycloalkyl group, an aryl group, a C1-C6 haloalkyl group, a halocycloalkyl group, a haloaryl group or a halogen atom, and the other does not exist.

[0043] In some embodiments, the diluent comprises a compound represented by formula (C-IIa),

[0044]

[0045] In formula (C-IIa),

[0046] M1 comprises an oxygen atom, a nitrogen atom or a sulfur atom;

[0047] S 11 and S 12 each independently comprise a C1-C6 chain alkyl group, a cycloalkyl group, an aryl group, a C1-C6 haloalkyl group, a halocycloalkyl group or a haloaryl group;

[0048] S 13 comprises a C1-C6 chain alkyl group, a cycloalkyl group, an aryl group, a C1-C6 haloalkyl group, a halocycloalkyl group, a haloaryl group or does not exist, wherein,

[0049] when M1 is an oxygen atom or a sulfur atom, S 13 does not exist;

[0050] when M1 is a nitrogen atom, S 13 comprises a C1-C6 chain alkyl group, a cycloalkyl group, an aryl group, a C1-C6 haloalkyl group, a halocycloalkyl group or a haloaryl group.

[0051] In some embodiments, the diluent comprises a compound represented by formula (C-IIb),

[0052]

[0053] In formula (C-IIb),

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

[0055] S 21 and S23 each independently includes a C1-C6 alkyl group, a cycloalkyl group, an aryl group, a C1-C6 haloalkyl group, a halocycloalkyl group or a haloaryl group;

[0056] S 22 includes an alkylene group or a haloalkylene group;

[0057] S 24 includes a C1-C6 alkyl group, a cycloalkyl group, an aryl group, a C1-C6 haloalkyl group, a halocycloalkyl group, a haloaryl group or is absent, wherein,

[0058] when M 21 is an oxygen atom or a sulfur atom, S 24 is absent;

[0059] when M 21 is a nitrogen atom, S 24 includes a C1-C6 alkyl group, a C3-C6 cycloalkyl group, an aryl group, a C1-C6 haloalkyl group, a C3-C6 halocycloalkyl group or a haloaryl group.

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

[0061]

[0062] In formula (C-IIc),

[0063] M3 includes at least one of an oxygen atom, a nitrogen atom and a sulfur atom;

[0064] S 31 includes an alkylene group or a haloalkylene group;

[0065] S 32 includes a C1-C6 alkyl group, a cycloalkyl group, an aryl group, a C1-C6 haloalkyl group, a halocycloalkyl group, a haloaryl group or is absent, where

[0066] when M3 is an oxygen atom or a sulfur atom, S 32 is absent;

[0067] when M3 is a nitrogen atom, S 32 includes a C1-C6 alkyl group, a cycloalkyl group, an aryl group, a C1-C6 haloalkyl group, a halocycloalkyl group or a haloaryl group.

[0068] In some embodiments, the diluent includes a compound represented by formula (C-III),

[0069] C m H n Q y Formula (C-III),

[0070] In formula (C-III),

[0071] m is selected from any positive integer from 1 to 8;

[0072] y is selected from any integer from 0 to 10;

[0073] y / n is any value from 0.25 to 5;

[0074] Q includes a halogen atom. Optionally, the halogen atom includes at least one of a fluorine atom and a chlorine atom.

[0075] In some embodiments, the diluent includes a compound represented by formula (C-IV),

[0076]

[0077] In formula (C-IV),

[0078] T1 to T4 each independently include a C1-C6 alkyl chain, cycloalkyl, aryl, alkoxy, haloalkyl, halocycloalkyl, haloaryl, or haloalkoxy.

[0079] In some embodiments, the diluent includes a compound represented by formula (C-V),

[0080]

[0081] In formula (C-V),

[0082] A1 includes a C1-C3 alkyl, haloalkyl, or halogen atom;

[0083] A2 includes a C1-C3 alkyl, haloalkyl, alkoxy, haloalkoxy, N,N-dimethyl, N,N-diethyl, N,N-methylethyl, or morpholinyl.

[0084] The second aspect of the present application provides a lithium metal battery, including an electrolyte according to any embodiment of the first aspect of the present application.

[0085] In some embodiments, the lithium metal battery includes a negative electrode plate, and the negative electrode plate includes a negative electrode current collector.

[0086] In some embodiments, the 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.

[0087] In some embodiments, the lithium metal battery further includes a positive electrode plate, the positive electrode plate includes a positive electrode current collector and a positive electrode film layer disposed on at least one side of the positive electrode current collector and including a positive electrode active material, and the positive electrode active material includes a general formula of Li x A y Ni a Cob Mn c M (1-a-b-c) Y z A compound of 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, Ce; and Y is selected from one or more of O and F. The above compound can improve the energy density of a lithium metal battery; and when used in combination with the above electrolyte, the stability of the electrolyte on the positive electrode side is relatively high, which is beneficial to improving the cycle performance of the lithium metal battery.

[0088] The third aspect of the present application provides a battery including a lithium metal battery according to any one of the embodiments of the second aspect of the present application.

[0089] The fourth aspect of the present application provides an electrical device including a battery according to any one of the embodiments of the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0090] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments of the present application. Obviously, the following described drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the drawings.

[0091] Figure 1 is a schematic diagram of an embodiment of the lithium metal battery of the present application.

[0092] Figure 2 is Figure 1 an exploded schematic diagram of the embodiment of the lithium metal battery.

[0093] Figure 3 is a schematic diagram of an embodiment of the battery module of the present application.

[0094] Figure 4 is a schematic diagram of an embodiment of the battery pack of the present application.

[0095] Figure 5 is Figure 4 an exploded schematic diagram of the embodiment of the battery pack shown.

[0096] Figure 6 is a schematic diagram of an embodiment of an electrical device including the lithium metal battery of the present application as a power source.

[0097] The accompanying drawings are not necessarily drawn to scale.

[0098] The reference numerals in the accompanying drawings are explained as follows:

[0099] 1. Battery pack; 2. Upper box body; 3. Lower box body; 4. Battery module;

[0100] 5. Lithium metal battery; 51. Shell; 52. Electrode assembly;

[0101] 53. Cover plate;

[0102] 6. Electrical device. Detailed implementation manners

[0103] Hereinafter, embodiments of the electrolyte, lithium metal battery, battery, and electrical device of the lithium metal battery of the present application that are specifically disclosed will be described in detail with appropriate reference to the accompanying drawings. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually identical structures are omitted. This is to prevent the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the accompanying drawings and the following description are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter recited in the claims.

[0104] The "range" disclosed in the present application is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a specific range. The ranges defined in this way can include the end values or not include the end values, and can be combined arbitrarily, that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60 - 120 and 80 - 110 are listed for a specific parameter, ranges of 60 - 110 and 80 - 120 are also contemplated. In addition, if the minimum range values 1 and 2 are listed, and if the maximum range values 3, 4, and 5 are listed, then the following ranges are all contemplated: 1 - 3, 1 - 4, 1 - 5, 2 - 3, 2 - 4, and 2 - 5. In the present application, unless otherwise stated, the numerical range "a - b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0 - 5" means that all real numbers between "0 - 5" have been fully listed herein, and "0 - 5" is only an abbreviated representation of these numerical combinations. Additionally, when stating that a certain parameter is an integer ≥2, it is equivalent to disclosing that the parameter is, for example, the integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0105] If there is no special description, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0106] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form new technical solutions.

[0107] Unless otherwise specified, all steps of this application can be carried out in sequence or randomly, preferably in sequence. For example, if a method includes steps (a) and (b), it means that the method can include steps (a) and (b) carried out in sequence, or steps (b) and (a) carried out in sequence. For example, if it is mentioned that the method may further include step (c), it means that step (c) can be added to the method in any order. For example, the method can include steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0108] Throughout this specification, substituents of compounds are disclosed in groups or ranges. It is explicitly contemplated that such a description includes every individual sub-combination of the members of these groups and ranges. For example, it is explicitly contemplated that the term "C1-C8 alkyl" discloses individually C1, C2, C3, C4, C5, C6, C7, C8, C1-C8, C1-C7, C1-C6, C1-C5, C1-C4, C1-C3, C1-C2, C2-C8, C2-C7, C2-C6, C2-C5, C2-C4, C2-C3, C3-C8, C3-C7, C3-C6, C3-C5, C3-C4, C4-C8, C4-C7, C4-C6, C4-C5, C5-C8, C5-C7, C5-C6, C6-C8, C6-C7 and C7-C8 alkyl.

[0109] As other examples, it is explicitly contemplated that the integers in the range of 5-40 are disclosed individually as 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; it is explicitly contemplated that the integers in the range of 1-20 are disclosed individually as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19 and 20. Accordingly, other groups or ranges can be explicitly contemplated.

[0110] Due to its high specific capacity, lithium metal can significantly improve the energy density of a single battery cell. Therefore, lithium metal batteries have broad application prospects. A lithium metal battery includes an electrode assembly and an electrolyte. The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator. The separator is located between the positive electrode sheet and the negative electrode sheet to isolate the positive electrode sheet and the negative electrode sheet. A lithium metal battery stores and discharges energy through the stripping and deposition of lithium metal. Specifically, during the charging process of a lithium metal battery, lithium ions are removed from the positive active material of the positive electrode sheet, pass through the electrolyte and the separator, are desolvated from solvent molecules, pass through the Solid Electrolyte Interface (SEI) film, 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 discharging process of a lithium metal battery, the lithium metal on the surface of the negative electrode sheet loses electrons to the external circuit, the lithium metal forms lithium ions and is released into the electrolyte and solvated, and migrates through the electrolyte to the positive active material.

[0111] Due to the high reactivity of lithium metal, the interfacial stability between the surface of the negative electrode sheet and the electrolyte of a lithium metal battery is poor, making it easy for the electrolyte to decompose on the surface of the negative electrode sheet, deteriorating the performance of the lithium metal battery.

[0112] In related technologies, a locally high molar concentration electrolyte is used to improve the performance of lithium metal batteries. However, there is still a risk of failure of the locally high molar concentration electrolyte during the cycling process. The failure mechanism mainly stems from the following two aspects. On the one hand, the lithium salt continuously decomposes and forms a film during cycling, resulting in a continuous decrease in the lithium salt molar concentration in the electrolyte and a continuous decrease in the ionic conductivity. After reaching a certain threshold, the polarization of the lithium metal battery is too large, leading to a capacity drop. On the other hand, after the electrolyte is cycled, a by-product layer is formed by the accumulation of the SEI interfacial film components on the surface of the negative electrode sheet of the lithium metal battery, with a thickness of up to dozens of micrometers. Although a diluent is added to the electrolyte, the viscosity of the electrolyte is still relatively high, and the wettability of the electrolyte on the electrode sheet is poor, resulting in too large polarization of the lithium metal battery and triggering a capacity drop.

[0113] Based on the above failure mechanism, the embodiments of the present application improve the composition of the electrolyte. By selecting specific organic solvents and lithium salts, the lithium salt molar concentration in the electrolyte is relatively high, and a solvation structure dominated by anion coordination can be formed, and there is still a certain lithium salt molar concentration in the later stage of cycling. Moreover, 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 cycling performance of the lithium metal battery.

[0114] Electrolyte

[0115] In a first aspect, the embodiments of the present application propose an electrolyte. This electrolyte can be used in lithium metal batteries.

[0116] The electrolyte includes a main solvent, a diluent, and a lithium salt. The molar concentration of the lithium salt is from 1 mol / L to 4 mol / L. Among them, the viscosity of the electrolyte ≤ 5.5 mPa·s.

[0117] In the embodiments of the present application, the molar concentration of the lithium salt in the electrolyte is relatively high, such as from 1 mol / L to 4 mol / L. The lithium salt can form a solvation structure with the main solvent, and there is still a certain molar concentration of lithium salt in the later stage of cycling. Moreover, since the electrolyte also includes a diluent, the viscosity of the electrolyte is relatively low, the ionic conductivity is high, which can effectively reduce the polarization growth of the lithium metal battery and improve the cycling performance of the lithium metal battery.

[0118] Specifically,

[0119] As 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, and the cations, anions, and the main solvent form a solvation structure. In other words, the solvation structure includes the lithium salt and the main solvent. The structural forms of the solvation structure include contact ion pairs (one anion coordinates with one cation and the main solvent) and aggregates (one anion coordinates with two or more cations and the main solvent), etc. When the solvation structure comes into contact with the surface of the negative electrode plate of the lithium metal battery, the anion in the solvation structure preferentially decomposes and participates in the film-forming reaction rather than the main solvent, which can improve the Coulomb efficiency of the lithium metal battery.

[0120] The solubility of the lithium salt in the diluent is low, and even the lithium salt hardly dissolves in the diluent. For example, the solubility of the lithium salt in the diluent ≤ 0.1 g / 100 g. The diluent can reduce the content of the lithium salt per unit volume of the electrolyte. The diluent and the solvation structure exist in a form similar to a mixture. Both the diluent and the solvation structure can contact the positive and negative electrodes, which is beneficial to the infiltration of the electrolyte into the electrode plate and the transmission of lithium ions. Since the diluent has poor solubility and dissociation ability for the lithium salt, the diluent hardly participates in the construction of the solvation structure, so that the introduction of the diluent hardly affects the coordination structure formed by the lithium salt and the main solvent. The lithium salt forms a local high molar concentration state, providing sufficient lithium ions for the battery system during the cyclic charge and discharge process, enabling the lithium ions to migrate between the positive and negative electrodes and reducing the polarization phenomenon of the lithium metal battery. Moreover, as an inert component, the diluent can significantly reduce the viscosity of the electrolyte, making the viscosity of the electrolyte ≤ 5.5 mPa·s, improving the wettability of the electrolyte to the electrode plate, further reducing the polarization growth of the lithium metal battery, and being beneficial to improving the ionic conductivity of the electrolyte and the cycling performance of the lithium metal battery.

[0121] In the embodiments of the present application, the specific structure of the solvation structure of lithium ions in the electrolyte can be analyzed by Raman spectroscopy. For example, in an argon glove box (oxygen concentration less than 0.1 ppm, water content less than 0.1 ppm), the electrolyte is taken as a sample, a glass capillary with a diameter of 0.3 mm is used to suck it up, and both ends of the glass capillary are sealed with melted paraffin. After the paraffin solidifies, the glass capillary forms a closed space that can isolate air. Then, the glass capillary is fixed on a glass slide with tape for testing, and the test range is 100 cm -1 to 3000 cm -1 , the mode is ordinary point scanning, and the laser wavelength is selected as 785 nm to reduce the interference of fluorescence effects. In the embodiments of the present application, the specific structure of the solvation structure in the electrolyte can also be detected by nuclear magnetic resonance (NMR).

[0122] 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 ≥ 10 g / 100 g. 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.

[0123] In some embodiments, the viscosity of the electrolyte is ≤ 5.5 mPa·s; optionally, the viscosity of the electrolyte is ≤ 5.1 mPa·s; optionally, the viscosity of the electrolyte is ≤ 4 mPa·s. The relatively low viscosity of the electrolyte system is beneficial to reducing polarization and improving the cycling performance of the lithium metal battery.

[0124] For example, the viscosity of the electrolyte 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, 5.1 mPa·s, 5.2 mPa·s, 5.3 mPa·s, 5.4 mPa·s, 5.5 mPa·s or the range composed of any two of the above values.

[0125] In some embodiments, the ionic conductivity of the electrolyte is 2 mS / cm to 5 mS / cm; it can be optionally 3 mS / cm to 5 mS / cm. When the ionic conductivity of the electrolyte is within the above range, it is beneficial to improve the cycling performance of the lithium metal battery.

[0126] For example, the ionic conductivity of the electrolyte can 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 composed of any two of the above values.

[0127] [Lithium salt]

[0128] In some embodiments, the molar concentration of the lithium salt is from 1 mol / L to 4 mol / L; optionally from 1.5 mol / L to 4 mol / L; optionally from 2 mol / L to 4 mol / L; and further optionally from 2 mol / L to 3.5 mol / L. When the molar concentration of the lithium salt is within the above range, a high-molar-concentration solvation structure can be formed with the main solvent; although the lithium salt has a certain loss during the cycling of the lithium metal battery, due to the relatively high molar concentration of the lithium salt, there is still a certain concentration of the lithium salt in the later stage of the lithium metal battery cycling, which can reduce the polarization growth and achieve long-term stable cycling of the lithium metal battery. In the embodiments of the present application, the molar concentration of the lithium salt refers to the molar concentration of the lithium salt in the electrolyte.

[0129] Exemplarily, 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, 2.35 mol / L, 2.40 mol / L, 2.45 mol / L, 2.5 mol / L, 2.55 mol / L, 2.6 mol / L, 2.65 mol / L, 2.7 mol / L, 2.75 mol / L, 2.8 mol / L, 2.9 mol / L, 3 mol / L, 3.1 mol / L, 3.2 mol / L, 3.25 mol / L, 3.3 mol / L, 3.4 mol / L, 3.5 mol / L, 3.6 mol / L, 3.75 mol / L, 3.8 mol / L, 3.85 mol / L, 3.9 mol / L, 3.95 mol / L, 4 mol / L, or a range composed of any two of the above values.

[0130] In some embodiments, the lithium salt includes at least one of a fluorinated lithium salt, lithium bis(oxalato)borate (LiBOB), and lithium perchlorate.

[0131] In some embodiments, the fluorinated lithium salt includes at least one of lithium fluorosulfonimide salt, lithium fluorophosphate salt, lithium fluoroborate salt, lithium fluoroxalate phosphate salt, lithium hexafluoroarsenate (LiAsF6), lithium trifluoromethanesulfonate (LiOTF), and lithium difluoro(oxalato)borate (LiDFOB). Optionally, the fluorinated lithium salt includes lithium fluorosulfonimide salt.

[0132] In some embodiments, the lithium fluorosulfonimide salt includes at least one of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). Further optionally, the fluorinated lithium salt includes lithium bis(fluorosulfonyl)imide (LiFSI).

[0133] In some embodiments, the lithium fluorophosphate salt includes at least one of lithium hexafluorophosphate (LiPF6) and lithium difluorophosphate (LiDFP).

[0134] In some embodiments, the lithium fluoroborate salt includes at least one of lithium tetrafluoroborate (LiBF4) and lithium difluoroborate.

[0135] In some embodiments, the lithium fluoroxalate phosphate salt includes at least one of lithium difluoro(oxalato)phosphate and lithium tetrafluoro(oxalato)phosphate.

[0136] The above lithium salt and the main solvent cooperate to enable the dissolution of a high molar concentration of the lithium salt in the main solvent, and cooperate with the diluent to form a locally high molar concentration solvated structure.

[0137] 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). The above lithium salt has a relatively high solubility in the main solvent, and can preferentially decompose on the surface of the negative electrode sheet to form an SEI component rich in inorganic fluorine, which is beneficial to the long cycle of the lithium metal battery. At the same time, the above lithium salt has relatively good oxidation stability and can support cycling under high voltage.

[0138] [Main Solvent]

[0139] The lithium salt has excellent solubility in the main solvent, which is beneficial to the coordination of the lithium salt and the main solvent to form a solvated structure, and promotes the decomposition and film formation of the lithium salt on the surface of the negative electrode sheet.

[0140] In some embodiments, the molar concentration of the lithium salt in the main solvent is ≥ 4 mol / L. The main solvent has strong dissolving ability and dissociating ability for the lithium salt, resulting in a relatively high concentration of the lithium salt in the solvation structure. 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 composed of any two of the above values. In the embodiments of the present application, the molar concentration of the lithium salt in the main solvent refers to the concentration data detected when the lithium salt is dissolved in the main solvent with the main solvent as the solvent.

[0141] In some embodiments, the viscosity of the main solvent is ≤ 5 mPa·s. The viscosity of the main solvent is relatively small, resulting in a lower viscosity of the locally highly concentrated electrolyte and a higher ionic conductivity. 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 composed of any two of the above values.

[0142] 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 in a liquid state and the viscosity is not too high, which is beneficial to the formation of a solvation structure with the lithium salt. Since the relative molecular weight range of the main solvent is small, the main solvent does not occupy a higher mass content at the same molar fraction. Even if the material of the main solvent is adjusted, the mass fraction of the main solvent is small, which is beneficial to increasing the mass fraction 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 composed of any two of the above values.

[0143] In some embodiments, based on the total mass of the main solvent and the diluent in the electrolyte, 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 solvation structure, and there are basically no free main solvent molecules.

[0144] 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 composed of any two of the above values.

[0145] 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.

[0146] In some embodiments, the ester solvent includes at least one of methyl formate, ethyl formate, ethyl acetate, dimethyl carbonate, methyl ethyl carbonate, diethyl carbonate, and propylene carbonate.

[0147] 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 alkylene oxide, and trimethoxymethane. The ether solvent has good reduction resistance and is not easily decomposed; moreover, the ether solvent has excellent solubility for lithium salts, which is beneficial to increasing the molar concentration of lithium salts to construct a locally high-molar-concentration solvation structure. And since the anion in the lithium salt in this solvation structure dominates, it is beneficial for the anion to be preferentially decomposed into an inorganic SEI film; and the viscosity of the electrolyte is low and it has excellent ionic conductivity.

[0148] Exemplarily, the C4 to C6 linear ether includes at least one of diethyl ether, methyl propyl ether, propyl ether, methyl butyl ether, and ethyl propyl ether.

[0149] Exemplarily, the C3 to C10 alkoxyalkane includes at least one of a C3 to C10 dimethoxyalkane, a C3 to C10 diethoxyalkane, a C3 to C10 methoxyethoxyalkane, a C3 to C10 methoxypropoxyalkane, a C3 to C10 methoxybutoxyalkane, and a C3 to C10 ethoxypropoxyalkane.

[0150] For example, the C3 to C10 dimethoxyalkane includes 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. Optionally, the C3 to C10 dimethoxyalkane includes 1,3-dimethoxypropane (DMP).

[0151] For example, C3 to C10 diethoxyalkanes include at least one of diethoxymethane, 1,1 - diethoxyethane, and 1,2 - diethoxyethane (DME). Optionally, the C3 to C10 diethoxyalkanes include 1,2 - diethoxyethane (DME).

[0152] For example, C3 to C10 methoxyethoxyalkanes include 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.

[0153] For example, C3 to C10 methoxypropoxyalkanes include 1 - methoxy - 1 - propoxymethane.

[0154] For example, C3 to C10 methoxybutoxyalkanes include 1 - methoxy - 2 - butoxymethane.

[0155] For example, C3 to C10 ethoxypropoxyalkanes include 1 - ethoxy - 1 - propoxymethane.

[0156] For example, C3 to C6 epoxyalkanes include at least one of tetrahydrofuran, tetrahydropyran, 1,3 - dioxolane, 1,3 - dioxane, and 1,4 - dioxane.

[0157] In some embodiments, the sulfone solvents include at least one of dimethyl sulfoxide, dimethyl sulfone, sulfolane, cyclobutyl sulfoxide, methyl ethyl sulfone, and methyl ethyl sulfoxide.

[0158] In some embodiments, the nitrile solvents include at least one of acetonitrile, propionitrile, butyronitrile, and malononitrile.

[0159] In some embodiments, the amide solvents include at least one of dimethylformamide, dimethylacetamide, and diethylacetamide.

[0160] In some embodiments, the siloxane solvents include at least one of dimethoxydimethylsilane and trimethoxymethylsilane.

[0161] [Diluent]

[0162] As an inert diluent, the diluent can reduce the viscosity of the electrolyte; moreover, it has a low solubility for lithium salts and has little impact on the solvation structure in the electrolyte, enabling the solvation structure to fully play the role of preferential anion film formation.

[0163] In some embodiments, the viscosity of the diluent is ≤ 5 mPa·s; optionally ≤ 3 mPa·s. The relatively small viscosity of the diluent results in a relatively low viscosity of the electrolyte and a relatively high ionic conductivity. 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 composed of any two of the above values.

[0164] In some embodiments, the relative molecular weight of the diluent is from 60 to 190. When the molecular weight of the diluent is within the above range, the diluent is liquid and is beneficial to further reducing the viscosity of the electrolyte. Moreover, since the relative molecular weight of the diluent is relatively small, at the same amount of substance, its mass fraction is relatively small, which is beneficial to increasing the mass fraction of the lithium salt in the solvation 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 composed of any two of the above values.

[0165] When the amount of substance of the diluent and the amount of substance of the lithium salt are within a set range, the diluent has little effect on the solvation structure. When reducing the viscosity of the electrolyte system, the electrolyte still has a solvation structure, enabling the lithium salt in the solvation structure to form a film preferentially, improving the performance of the SEI film, and reducing the risk of capacity drop of the lithium-metal battery. Since the range of the relative molecular weight of the diluent is small, the diluent will not occupy a higher mass content at the same molar fraction. Even if the material of the diluent is adjusted, the mass ratio of the diluent is small, which is beneficial to increasing the mass ratio of the lithium salt. In some embodiments, based on the total mass of the main solvent and the diluent in the electrolyte, the mass content of the diluent is 20% to 90%; optionally 60% to 80%; optionally 60% to 70%. When the mass content of the diluent is within the above range, the amount of substance of the diluent and the amount of substance of the lithium salt can meet the set range, the diluent has basically no effect on the solvation structure, enabling the lithium salt to form a film preferentially in the solvation structure, improving the performance of the SEI film, and reducing the risk of capacity drop of the lithium-metal battery. 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 composed of any two of the above values.

[0166] In some embodiments, the diluent includes a compound represented by formula (C-I),

[0167]

[0168] In formula (C-I),

[0169] X1 and X2 each independently include a carbon atom, an oxygen atom or a nitrogen atom;

[0170] R1 and R2 each independently include 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; optionally, the halogen atom includes a fluorine atom or a chlorine atom;

[0171] R 31 and R 32 each independently include 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, a halogen atom or do not exist, wherein,

[0172] when X1 is a carbon atom, R 31 and R 32 each independently include a hydrogen atom or a halogen atom;

[0173] when X1 is an oxygen atom, R 31 and R 32 do not exist;

[0174] 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;

[0175] R 41 and R 42 Each independently 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, a halogen atom or does not exist, wherein,

[0176] When X2 is a carbon atom, R 41 and R 42 Each independently includes a hydrogen atom or a halogen atom;

[0177] When X2 is an oxygen atom, R 41 and R 42 Do not exist;

[0178] When X2 is a nitrogen atom, R 41 and R 42 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, and the other does not exist.

[0179] Optionally, R1 and R2 each independently include a C1-C6 linear alkyl group, a C1-C6 halogenated linear alkyl group, or a halogen atom.

[0180] Optionally, R 31 and R 32 Each independently includes a hydrogen atom, a C1-C6 linear alkyl group, a C1-C6 halogenated linear alkyl group, a halogen atom or does not exist.

[0181] Optionally, R 41 and R 42 Each independently includes a hydrogen atom, a C1-C6 linear alkyl group, a C1-C6 halogenated linear alkyl group, a halogen atom or does not exist.

[0182] In some embodiments, when both X1 and X2 are carbon atoms, the compound represented by formula (C-I) is a ketone compound.

[0183] In some embodiments, when both X1 and X2 are oxygen atoms, the compound represented by formula (C-I) is a carbonate compound.

[0184] In some embodiments, when both X1 and X2 are nitrogen atoms, the compound represented by formula (C-I) is a urea compound.

[0185] 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 (C-I) is a carboxylic acid ester compound.

[0186] 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 (C-I) is an amide compound.

[0187] 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 (C-I) is a carbamate compound.

[0188] Exemplarily, the compound represented by formula (C-I) includes at least one of the compounds represented by formula (C-I-1) to the compounds represented by formula (C-I-32).

[0189]

[0190]

[0191] In some embodiments, the diluent includes the compound represented by formula (C-IIa).

[0192]

[0193] In formula (C-IIa),

[0194] M1 includes an oxygen atom, a nitrogen atom or a sulfur atom.

[0195] S 11 and S 12 each independently includes a C1-C6 linear alkyl group, a cycloalkyl group, an aryl group, a C1-C6 halogenated linear alkyl group, a halogenated cycloalkyl group or a halogenated aryl group; optionally, S 11 and S 12 each independently includes a C1-C6 linear alkyl group, a C3-C6 cycloalkyl group, an aryl group, a C1-C6 halogenated linear alkyl group, a C3-C6 halogenated cycloalkyl group or a halogenated aryl group.

[0196] S 13 includes 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 is absent, wherein

[0197] when M1 is an oxygen atom or a sulfur atom, S 13 is absent;

[0198] when M1 is a nitrogen atom, S 13 includes a C1-C6 linear alkyl group, a C3-C6 cycloalkyl group, an aryl group, a C1-C6 halogenated linear alkyl group, a C3-C6 halogenated cycloalkyl group or a halogenated aryl group.

[0199] Optionally, S 13 independently includes C1-C6 alkyl, C3-C6 cycloalkyl, aryl, C1-C6 haloalkyl, C3-C6 halocycloalkyl, haloaryl or is absent.

[0200] Exemplarily, 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),

[0201]

[0202]

[0203] Exemplarily, 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),

[0204]

[0205] Exemplarily, 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),

[0206]

[0207] Exemplarily, the compound represented by formula (C-II) includes the compound represented by formula (C-II-68),

[0208]

[0209] In some embodiments, the diluent includes the compound represented by formula (C-IIb),

[0210]

[0211] In formula (C-IIb),

[0212] M 21 and M 22 each independently includes an oxygen atom, a nitrogen atom or a sulfur atom;

[0213] S 21 and S 23 each independently includes C1-C6 alkyl, cycloalkyl, aryl, C1-C6 haloalkyl, halocycloalkyl or haloaryl; optionally, S 21 and S 23 each independently includes C1-C6 alkyl, C3-C6 cycloalkyl, aryl, C1-C6 haloalkyl, C3-C6 halocycloalkyl or haloaryl;

[0214] S22 Comprising an alkylene or haloalkylene; optionally a C1-C4 alkylene or C1-C4 haloalkylene;

[0215] S 24 Comprising a C1-C6 alkyl, cycloalkyl, aryl, C1-C6 haloalkyl, halocycloalkyl, haloaryl or absent, wherein,

[0216] When M 21 is an oxygen atom or a sulfur atom, S 24 is absent;

[0217] When M 21 is a nitrogen atom, S 24 Comprises a C1-C6 alkyl, cycloalkyl, aryl, C1-C6 haloalkyl, halocycloalkyl or haloaryl.

[0218] Optionally, S 24 Comprises a C1-C6 alkyl, C3-C6 cycloalkyl, aryl, C1-C6 haloalkyl, C3-C6 halocycloalkyl, haloaryl or absent,

[0219] S 25 Comprises a C1-C6 alkyl, cycloalkyl, aryl, C1-C6 haloalkyl, halocycloalkyl, haloaryl or absent, wherein,

[0220] When M 22 is an oxygen atom or a sulfur atom, S 25 is absent;

[0221] When M 22 is a nitrogen atom, S 25 Comprises a C1-C6 alkyl, cycloalkyl, aryl, C1-C6 haloalkyl, halocycloalkyl or haloaryl.

[0222] Optionally, S 25 Comprises a C1-C6 alkyl, C3-C6 cycloalkyl, aryl, C1-C6 haloalkyl, C3-C6 halocycloalkyl, haloaryl or absent.

[0223] Exemplarily, 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),

[0224]

[0225] Exemplarily, 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),

[0226]

[0227]

[0228] Exemplarily, 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).

[0229]

[0230] In some embodiments, the diluent includes the compound represented by formula (C-IIc).

[0231]

[0232] In formula (C-IIc),

[0233] M3 includes at least one of an oxygen atom, a nitrogen atom, and a sulfur atom;

[0234] S 31 includes an alkylene or a haloalkylene; optionally a C1-C4 alkylene or a C1-C4 haloalkylene;

[0235] S 32 includes a C1-C6 alkyl, cycloalkyl, aryl, C1-C6 haloalkyl, halocycloalkyl, haloaryl or is absent, wherein,

[0236] When M3 is an oxygen atom or a sulfur atom, S 32 is absent;

[0237] When M3 is a nitrogen atom, S 32 includes a C1-C6 alkyl, cycloalkyl, aryl, C1-C6 haloalkyl, halocycloalkyl or haloaryl.

[0238] Exemplarily, 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).

[0239]

[0240]

[0241] Exemplarily, 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).

[0242]

[0243] Optionally, the diluent may include at least one of the compounds represented by formula (C-II-3), the compounds represented by formula (C-II-4), the compounds represented by formula (C-II-21), the compounds represented by formula (C-II-32), and the compounds represented by formula (C-II-30). The molecular weights of the above compounds are relatively low and the viscosities are small; moreover, the boiling points of the above compounds are relatively high, and the thermal stability is high at the relatively high working temperature of the lithium metal battery, which is beneficial to improving the thermal stability of the electrolyte at high temperatures.

[0244] In some embodiments, the diluent includes the compound represented by formula (C-III),

[0245] C m H n Q y Formula (C-III),

[0246] In formula (C-III),

[0247] m is selected from any positive integer from 1 to 8;

[0248] y is selected from any integer from 0 to 10;

[0249] y / n is any value from 0.25 to 5;

[0250] Q includes a halogen atom. Optionally, the halogen atom includes at least one of a fluorine atom and a chlorine atom.

[0251] Exemplarily, the compound represented by formula (C-III) may include at least one of an alkane, a halogenated alkane, an alkene, a halogenated alkene, a cycloalkane, a halogenated cycloalkane, an aromatic hydrocarbon, and a halogenated aromatic hydrocarbon; further optionally, the compound represented by formula (C-III) may include at least one of an alkane, a halogenated alkane, a halogenated alkene, a cycloalkane, an aromatic hydrocarbon, and a halogenated aromatic hydrocarbon. Exemplarily, the compound represented by formula (C-III) may include at least one of C1-C6 alkanes, C1-C6 halogenated alkanes, C2-C6 alkenes, C2-C6 halogenated alkenes, C3-C6 cycloalkanes, C3-C6 halogenated cycloalkanes, C6-C8 aromatic hydrocarbons, and C6-C8 halogenated aromatic hydrocarbons.

[0252] For example, the compound represented by formula (C-III) may include at least one of the compounds represented by formula (C-III-1) to the compounds represented by formula (C-III-10), and the compounds represented by formula (C-III-13) to the compounds represented by formula (C-III-21),

[0253]

[0254] 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).

[0255]

[0256] 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).

[0257]

[0258] 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).

[0259]

[0260] For example, the compound represented by formula (C-III) may include the compound represented by formula (C-III-33).

[0261]

[0262] In some embodiments, the diluent includes the compound represented by formula (C-IV).

[0263]

[0264] In formula (C-IV), each of T1 to T4 independently includes C1-C6 linear alkyl, cycloalkyl, aryl, alkoxy, haloalkyl, halocycloalkyl, haloaryl or haloalkoxy.

[0265] Optionally, each of T1 to T4 independently includes at least one of C1-C6 linear alkyl, C3-C6 cycloalkyl, aryl, C1-C6 alkoxy, C1-C6 haloalkyl, C3-C6 halocycloalkyl, haloaryl, C1-C6 haloalkoxy.

[0266] Exemplarily, the compound represented by formula (C-IV) includes at least one of the compound represented by formula (C-IV-1) to the compound represented by formula (C-IV-21).

[0267]

[0268] In some embodiments, the diluent includes the compound represented by formula (C-V).

[0269]

[0270] In formula (C-V),

[0271] A1 includes C1-C3 alkyl, haloalkyl or a halogen atom; optionally, A1 includes C1-C3 alkyl, C1-C3 haloalkyl or a halogen atom.

[0272] A2 includes C1-C3 alkyl, haloalkyl, alkoxy, haloalkoxy, N,N-dimethyl, N,N-diethyl, N,N-methyl-ethyl or morpholinyl; optionally, A2 includes C1-C3 alkyl, C1-C3 haloalkyl, alkoxy, haloalkoxy, N,N-dimethyl, N,N-diethyl, N,N-methyl-ethyl or morpholinyl.

[0273] Optionally, the compound represented by formula (C-V) may include at least one of sulfonamide compounds and sulfite compounds.

[0274] Exemplarily, the compound represented by formula (C-V) may include at least one of the compounds represented by formula (C-V-1) to the compounds represented by formula (C-V-17),

[0275]

[0276] Exemplarily, the compound represented by formula (C-V) may include at least one of the compounds represented by formula (C-V-18) to the compounds represented by formula (C-V-21),

[0277]

[0278] In the embodiments of the present application, the qualitative and quantitative determination of each substance or each element can be carried out by using suitable equipment and methods known to those skilled in the art. The relevant detection methods can refer to domestic and foreign detection standards, domestic and foreign enterprise standards, etc. And those skilled in the art can also adaptively change some detection steps / instrument parameters, etc. from the perspective of detection accuracy to obtain more accurate detection results. One detection method can be used for qualitative or quantitative determination, or several detection methods can be used in combination for qualitative or quantitative determination.

[0279] The types and contents of the molar concentrations of inorganic components / lithium salts in the electrolyte have meanings well-known in the art and can be detected by using equipment and methods well-known in the art. For example, reference can be made to the standard JY / T020-1996 General Rules for Ion Chromatographic Analysis Methods to qualitatively or quantitatively analyze the molar concentrations of inorganic components / lithium salts in the electrolyte by ion chromatography analysis method. In the embodiments of the present application, newly prepared electrolyte can be taken as a sample, or the battery that has been discharged (discharged to the lower cut-off voltage so that the charged state of the battery is about 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample and detected by ion chromatography analysis method.

[0280] The types and contents of the organic components in the electrolyte are of meanings well-known in the art, and can be detected by devices 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 to qualitatively and quantitatively analyze the organic components in the electrolyte by gas chromatography. In the embodiments of the present application, newly 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 charged state of the battery is about 0% SOC) can be disassembled in reverse, and the free electrolyte obtained from the battery can be taken as a sample, and ion chromatography analysis method can be used for detection.

[0281] The viscosity of the electrolyte or the viscosity of the organic solvent in the electrolyte is of meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, take the electrolyte as a sample, use a rotational viscometer, select a rotor, set the rotation speed to 12 rpm, set the rotation time to 5 min, and after the value is stable, read and record the viscosity value. After detecting the type of the organic solvent, separately take the organic solvent of this type as a sample and perform detection according to the above test method to test the viscosity value.

[0282] The ionic conductivity of the electrolyte is of meanings well-known in the art, and can be detected by devices and methods well-known in the art. For example, take the electrolyte as a sample and measure it with a conductivity meter at room temperature.

[0283] Lithium metal battery

[0284] In a second aspect, an embodiment of the present application provides a lithium metal battery, and the lithium metal battery includes the electrolyte of any one of the embodiments of the first aspect of the present application. The cycle performance of the lithium metal battery is improved.

[0285] [Negative electrode plate]

[0286] The lithium metal battery further includes a negative electrode plate. During the cyclic charge and discharge of the lithium metal battery, accompanied by the deposition and stripping of metallic lithium, the negative electrode plate cooperates with the above-mentioned electrolyte, the electrolyte has a high stability for the negative electrode plate, the oxidative decomposition of the electrolyte is alleviated, the interfacial performance between the electrolyte and the negative electrode plate is more stable, and the cycle performance of the lithium metal battery can be improved, especially the cycle life in the high voltage range is improved.

[0287] In some embodiments, the negative electrode plate may include a negative electrode current collector. During the charging process of the lithium metal battery, lithium ions can deposit on the surface of the negative electrode current collector to form a metallic lithium layer; during the discharging process of the lithium metal battery, the metallic lithium layer loses electrons to form lithium ions and migrates to the positive electrode active material.

[0288] The negative electrode current collector can be a metal foil or a composite current collector. As an example of the metal foil, copper foil can be used. The composite current collector can include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the main material of the metal material layer can include at least one of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer can include at least one of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0289] The negative electrode sheet does not exclude additional functional layers. For example, in some embodiments, the negative electrode sheet of the embodiment of the present application further includes a conductive layer (for example, composed of a conductive agent and a binder) provided on the surface of the negative electrode current collector. In some other embodiments, the negative electrode sheet of the embodiment of the present application further includes a protective layer covering the surface of the negative electrode current collector.

[0290] Optionally, the negative electrode sheet can further include a conductive layer provided on at least one side of the negative electrode current collector, and the conductive layer includes a negative electrode conductive agent. As an example, the negative electrode conductive agent can include at least one of superconducting carbon, conductive graphite, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0291] Further optionally, the conductive layer can further include a negative electrode binder. As an example, the negative electrode binder can include at least one of styrene-butadiene rubber (SBR), water-soluble unsaturated resin SR-1B, water-based acrylic resins (for example, polyacrylic acid (PAA), polymethacrylic acid (PMAA), sodium polyacrylate (PAAS)), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), and carboxymethyl chitosan (CMCS).

[0292] In some other embodiments, the negative electrode sheet can include a negative electrode current collector and a lithium metal layer provided on at least one side of the negative electrode current collector. For example, the negative electrode current collector has two opposite surfaces in its own thickness direction, and the lithium metal layer is provided on either or both of the two opposite surfaces of the negative electrode current collector. The lithium metal layer can be provided on the negative electrode current collector in the form of a lithium foil.

[0293] Optionally, in addition to lithium metal, the lithium metal layer can further include a non-lithium element capable of forming an alloy with lithium element, and the non-lithium element can include at least one of a metal element and a metalloid element. Exemplarily, the metal element can include at least one of tin (Sn) element, zinc (Zn) element, aluminum (Al) element, magnesium (Mg) element, silver (Ag) element, gold (Au) element, gallium (Ga) element, indium (In) element, and platinum (Pt) element. Exemplarily, the metalloid element can include at least one of boron (B) element, carbon (C) element, and silicon (Si) element.

[0294] The material of the negative electrode current collector has been described above and will not be elaborated here.

[0295] The negative electrode sheet does not exclude additional functional layers. For example, in some embodiments, the negative electrode sheet of the present application embodiment 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 some other embodiments, the negative electrode sheet of the present application embodiment further includes a protective layer covering the surface of the negative electrode current collector.

[0296] Optionally, the negative electrode sheet may further include a conductive layer disposed between the negative electrode current collector and the lithium metal layer. The conductive layer includes a negative electrode conductive agent, and the material of the negative electrode conductive agent has been described above and will not be elaborated here. Further optionally, the conductive layer may further include a negative electrode binder, and the material of the negative electrode binder has been described above and will not be elaborated here.

[0297] [Positive Electrode Sheet]

[0298] In some embodiments, the lithium metal battery may further include a positive electrode sheet.

[0299] 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 including a positive electrode active material. For example, the positive electrode current collector has two surfaces opposite to each other in its own thickness direction, and the positive electrode film layer is disposed on any one or both of the two opposite surfaces of the positive electrode current collector.

[0300] The positive electrode active material can adopt the positive electrode active materials known in the art for lithium metal batteries. By way of example, the positive electrode active material may include at least one of the following materials: lithium-containing transition metal oxides and lithium-containing phosphates with an olivine structure.

[0301] 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 their modified compounds, etc.

[0302] Exemplarily, the general formula of the lithium-containing transition metal oxide is: Li x A y Ni a Co b Mn c M (1-a-b-c) Y z, where 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. Optionally, y = 0. The above lithium-containing transition metal oxide can improve the energy density of the lithium metal battery; and when used in combination with the above electrolyte, the stability of the electrolyte on the positive electrode side is relatively high, which is beneficial to improving the cycling performance of the lithium metal battery.

[0303] Optionally, 0 < b < 1.

[0304] Optionally, 0 < c < 1.

[0305] Optionally, 0 < a + b + c < 1.

[0306] Optionally, 0 < a < 1; further optionally, 0.8 ≤ a < 1.

[0307] 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, 0.69, 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 composed of any two of the above values.

[0308] Specifically, the lithium-containing transition metal oxide may include lithium cobalt oxide LCO, lithium nickel oxide LNO, lithium manganese oxide LMO, LiNi 1 / 3Co 1 / 3 Mn 1 / 3 O2 (NCM333), LiNi 0.8 Co 0.1 Mn 0.1 O2 (NCM811) and LiNi0.5 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), or one or more of them.

[0309] Exemplarily, 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 , where 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, Mg; Me is selected from one or more of Mn, Fe, Co, 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, Ce; X is selected from one or more of S, Si, Cl, B, C, N; T is selected from one or more of O, F. Specifically, the olivine-type phosphate active material includes one or more of LiFePO4, LiMnPO4, LiNiPO4, and LiCoPO4.

[0310] In the embodiments of the present application, the above-mentioned cathode active materials can also be modified compounds, and the modified compounds can be doping modification and / or surface coating modification of the cathode active materials. For example, doping modification can be carried out by doping transition metal elements, and coating modification can be carried out by coating a carbon layer on the material surface.

[0311] During the charging and discharging process of a lithium metal battery, the insertion and consumption of active ions such as Li will occur, and the molar content of Li is different when the lithium metal battery is discharged to different states. In the enumeration of the positive electrode active material in the embodiments of the present application, the molar content of Li is the initial state of the material, that is, the state before feeding. When the positive electrode active material is applied to the battery system, after charge and discharge cycles, the molar content of Li may change.

[0312] In the enumeration of the positive electrode active material in the embodiments of the present application, the molar content of oxygen O is only the theoretical state value. The release of oxygen from the crystal lattice will cause the molar content of oxygen O to change. Actually, the molar content of oxygen O will show fluctuations.

[0313] In some embodiments, the positive electrode film layer may further optionally include a positive electrode conductive agent. The embodiments of the present application do not particularly limit the type of the positive electrode conductive agent. As an example, the positive electrode conductive agent includes 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, based on the total mass of the positive electrode film layer, the mass percentage content of the positive electrode conductive agent is ≤5%.

[0314] 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 the 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 fluorinated acrylate resin. In some embodiments, based on the total mass of the positive electrode film layer, the mass percentage content of the positive electrode binder is ≤5%.

[0315] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. As an example of the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal material layer formed on at least one surface of the polymer material base layer. As an example, the metal material of the metal material layer may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. As an example, the polymer material base layer may include at least one of polypropylene PP, polyethylene terephthalate PET, polybutylene terephthalate PBT, polystyrene PS, and polyethylene PE.

[0316] The positive electrode film layer is usually formed by coating a positive electrode slurry on a positive electrode current collector and then drying and cold pressing. The positive electrode slurry is usually formed by dispersing a positive electrode active material, an optional conductive agent, an optional binder, and any other components in a solvent and stirring evenly. The solvent may be N-methylpyrrolidone NMP, but is not limited thereto.

[0317] [Separator Film]

[0318] In some embodiments, the lithium metal battery may further include a separator film.

[0319] There is no particular limitation on the type of the separator film in the embodiments of the present application, and any well-known porous structure separator film with good chemical stability and mechanical stability can be selected.

[0320] In some embodiments, the material of the separator film may include at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator film may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator film is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0321] In some embodiments, the positive electrode sheet, the separator film, and the negative electrode sheet may be made into an electrode assembly through a winding process and / or a stacking process.

[0322] In some embodiments, the lithium metal battery may include an outer package. The outer package can be used to encapsulate the above-mentioned electrode assembly and electrolyte.

[0323] In some embodiments, the outer package of the lithium metal battery may be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the lithium metal battery may also be a soft package, such as a pouch soft package. The material of the soft package may be plastic, such as at least one of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0324] There is no particular limitation on the shape of the lithium metal battery in the embodiments of the present application, and it may be cylindrical, square, or any other shape. As Figure 1 shown is a lithium metal battery 5 with a square structure as an example.

[0325] In some embodiments, as Figure 2 shown, the outer package may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and side plates connected to the bottom plate, and the bottom plate and the side plates enclose to form a receiving cavity. The housing 51 has an opening communicating with 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 film may form an electrode assembly 52 through a winding process and / or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly 52. The number of the electrode assemblies 52 included in the lithium metal battery 5 may be one or more, which can be adjusted according to requirements.

[0326] The preparation method of the lithium metal battery according to 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 stacking process, the electrode assembly is placed in an outer package, dried, and then injected with an electrolyte, and after processes such as vacuum packaging, standing, formation, and shaping, a lithium metal battery is obtained.

[0327] In some embodiments of the embodiments of the present application, the lithium metal battery according to the embodiments of the present application can be assembled into a battery module, and the number of lithium metal batteries included in the battery module can be multiple, and the specific number can be adjusted according to the application and capacity of the battery module.

[0328] Figure 3 is a schematic diagram of a battery module 4 as an example. As Figure 3 shown, in the battery module 4, a plurality of lithium metal batteries 5 can be arranged in sequence along the length direction of the battery module 4. Of course, they can also be arranged in any other manner. Further, the plurality of lithium metal batteries 5 can be fixed by fasteners.

[0329] Optionally, the battery module 4 can further include a housing having an accommodation space, and a plurality of lithium metal batteries 5 are accommodated in the accommodation space.

[0330] In some embodiments, the above battery module can also be assembled into a battery pack, and the number of battery modules included in the battery pack can be adjusted according to the application and capacity of the battery pack.

[0331] Figure 4 and Figure 5 are schematic diagrams of a battery pack 1 as an example. As Figure 4 and Figure 5 shown, the battery pack 1 can include a battery box and a plurality of battery modules 4 arranged in the battery box. The battery box includes an upper box body 2 and a lower box body 3. The upper box body 2 is used to cover the lower box body 3 and form a closed space for accommodating the battery modules 4. The plurality of battery modules 4 can be arranged in the battery box in any manner.

[0332] Electrically operated device

[0333] 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 the power supply of the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, a mobile device (such as a mobile phone, laptop computer, etc.), an electric vehicle (such as a pure electric vehicle, hybrid electric vehicle, plug-in hybrid electric vehicle, electric bicycle, electric scooter, electric golf cart, electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc.

[0334] The electrical device can select a lithium metal battery, battery module, or battery pack according to its usage requirements.

[0335] Figure 6 It is a schematic diagram of an electrical device 6 as an example. The electrical device 6 is a pure electric vehicle, hybrid electric vehicle, or plug-in hybrid electric vehicle, etc. In order to meet the requirements of the electrical device 6 for high power and high energy density, a battery pack or battery module can be used.

[0336] Another example of an electrical device can be a mobile phone, tablet computer, laptop computer, etc. This electrical device usually requires a thin and light design, and a lithium metal battery can be used as the power supply.

[0337] Example

[0338] The following embodiments more specifically describe the content disclosed in the embodiments of the present application. These embodiments are only for illustrative purposes, because various modifications and changes within the scope of the content disclosed in the embodiments of the present application are obvious to those skilled in the art. Unless otherwise stated, all parts, percentages, and ratios reported in the following embodiments are based on mass, and all reagents used in the embodiments are commercially available or synthesized according to conventional methods and can be used directly without further treatment, and the instruments used in the embodiments are all commercially available.

[0339] Preparation of Lithium Metal Batteries in Embodiments and Comparative Examples

[0340] 1. Preparation of the Positive Electrode Sheet

[0341] The positive electrode sheet includes a positive electrode current collector and positive electrode film layers provided on both sides of the positive electrode current collector. The positive electrode current collector is aluminum foil, and the positive electrode film layer includes a film layer formed by uniformly coating the surface of the positive electrode current collector aluminum foil with a positive electrode paste (the solvent is N-methylpyrrolidone NMP), followed by drying and cold pressing. The positive electrode film layer includes a positive electrode active material, conductive agent acetylene black, and binder polyvinylidene fluoride (PVDF) with a weight ratio of 98:1:1.

[0342] The positive electrode active material includes a LiNi 0.8 Co 0.10 Mn 0.10 O2 (NCM811) compound.

[0343] 2. Preparation of negative electrode sheet

[0344] The negative electrode plate comprises 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.

[0345] 3. Isolation film

[0346] The isolation film is a polyethylene film layer.

[0347] 4. Preparation of electrolyte

[0348] The electrolyte includes an organic solvent and a lithium salt, and the organic solvent includes a main solvent and a diluent.

[0349] 5. Preparation of lithium metal batteries

[0350] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, so that the separator is between the positive electrode sheet and the negative electrode sheet to play an isolating role, thereby obtaining an electrode assembly; the electrode assembly is placed in an outer packaging shell, and after drying, the electrolyte is injected, and after vacuum packaging, standing, forming, shaping and other processes, a stacked lithium metal battery is obtained.

[0351] The electrolyte components of the embodiments and comparative examples are shown in Table 1.

[0352] Performance Testing

[0353] 1. Room temperature cycle performance test of lithium metal batteries

[0354] At 25° C., the lithium metal batteries prepared in the examples and comparative examples were charged and discharged at a rate of 0.2C (ie, 28 mA) and 1C (ie, 140 mA) respectively.

[0355] The cut-off voltages for charge and discharge were set to 4.3V and 2.8V respectively. The charging process adopted the constant current-constant voltage charging method. Specifically, when the 0.2C constant current charging reached the cut-off voltage of 4.3V, the 4.3V constant voltage charging was continued until the current decayed to 0.1C (i.e. 14mA). When the discharge capacity decayed to 80% of the first cycle discharge capacity, the battery life was considered to be over, and the number of cycles at this time was recorded.

[0356] Test Results

[0357] The test results are shown in Table 1.

[0358]

[0359] In Table 1, the mass content of the main solvent is calculated based on the total mass of the main solvent and the diluent.

[0360] The mass content of the diluent is calculated based on the total mass of the main solvent and the diluent.

[0361] DME represents 1,2 - diethoxyethane; DMP represents 1,3 - dimethoxypropane.

[0362] C - II - 4 represents the compound shown by formula (C - II - 4).

[0363] In Table 1, the solubility of the lithium salt in the diluent is ≤ 0.1 g / 100 g.

[0364] As can be seen from Table 1, for the electrolyte of Comparative Example 1, ethylene carbonate and ethyl methyl carbonate are used as organic solvents, and 1.0 mol / L lithium hexafluorophosphate LiPF6 is used as the lithium salt. When this electrolyte comes into contact with the lithium metal anode, ethylene carbonate and ethyl methyl carbonate decompose and form a film preferentially, which is not conducive to the cycling of the lithium metal anode and is prone to capacity drop. However, in the examples of the present application, by using a specific organic solvent system, a local high - molar - concentration electrolyte system can be formed with the lithium salt, and the lithium salt can decompose and form a film preferentially, which can significantly improve the cycling performance at room temperature.

[0365] Comparative Example 2 alone uses the diluent of the examples of the present application, and Comparative Example 3 alone uses the main solvent of the examples of the present application. Neither can achieve an electrolyte system with low viscosity and high - molar - concentration lithium salt; the cycling performance of the lithium metal battery cannot be effectively improved. However, in the examples of the present application, by selecting the materials of the organic solvent system, the main solvent in the organic solvent can form a high - molar - concentration solvation structure with the high - molar - concentration 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, reducing the viscosity of the electrolyte, thereby improving the cycling life of the lithium metal battery. From Comparative Examples 4 and 5, it can be seen that when using the same material system, if the molar concentration of the lithium salt is too low (e.g., less than 1 mol / L) or too high (e.g., greater than 4 mol / L), it is not conducive to improving the cycling life of the lithium metal battery. When the molar concentration of the lithium salt in the examples of the present application is between 1 mol / L and 4 mol / L, when it is combined with the main solvent and the diluent, the electrolyte further forms a local high - molar - concentration electrolyte system, reducing the viscosity of the electrolyte, thereby improving the cycling life of the lithium metal battery.

[0366] In Examples 1 to 3, by adjusting the material of the lithium salt, the cycling life of the lithium metal battery can still be improved; the lithium salt can be selected as lithium bis(fluorosulfonyl)imide LiFSI, which can promote the formation of an SEI film rich in inorganic substances.

[0367] Examples 1, 4 to 11. By adjusting the material of the main solvent, the cycle life of the lithium metal battery can be further improved. 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.

[0368] Examples 1, 12 to 20. By adjusting the material of the diluent, the cycle life of the lithium metal battery can be further improved. In particular, when the diluent includes at least one of the compounds represented by formula (C-II-3), the compounds represented by formula (C-II-4), the compounds represented by formula (C-II-21), the compounds represented by formula (C-II-32), and the compounds represented by formula (C-II-30), the cycle life of the lithium metal battery can be significantly improved.

[0369] Examples 1, 21 to 24. By adjusting the molar concentration of the lithium salt, the cycle life of the lithium metal battery can be further improved. 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.

[0370] Examples 1, 25 to 28. By adjusting the mass content of the main solvent and the diluent, the cycle life of the lithium metal battery can be further improved. In particular, 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.

[0371] The above is only the specific implementation manner of the present application, but the protection scope of the present application is not limited thereto. Any person skilled in the art within the technical scope disclosed in the present application can easily think of various equivalent modifications or substitutions, and these modifications or substitutions should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope 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 chain alkyl group, a cycloalkyl group, an aryl group, a C1-C6 halogenated chain alkyl group, a halogenated cycloalkyl group, a halogenated aryl group, a halogen atom or is absent, where When X1 is a carbon atom, R 31 and R 32 each independently includes 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 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, a halogen atom or is absent, wherein, 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, one of R 41 and R 42 includes a hydrogen atom, a C1-C6 chain alkyl group, a cycloalkyl group, an aryl group, a C1-C6 halogenated chain alkyl group, 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 chain, halocycloalkyl or haloaryl; S 22 comprising an alkylene or haloalkylene; S 24 including C1-C6 alkyl, cycloalkyl, aryl, C1-C6 haloalkyl, halocycloalkyl, haloaryl or 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 to C6 alkyl, cycloalkyl, aryl, C1 to 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 C1-C6 chain alkyl, cycloalkyl, aryl, C1-C6 haloalkyl, halocycloalkyl or haloaryl.

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 any positive integer selected from 1 to 8; y is any integer selected 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 C1-C3 alkyl, haloalkyl or halogen atom; A2 includes C1-C3 alkyl, haloalkyl, alkoxy, haloalkoxy, 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 sheet; The negative electrode sheet includes a negative 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, wherein the lithium metal battery further includes a positive electrode sheet, the positive electrode sheet includes 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, 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, Ce; Y is selected from one or more of O, 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.

Images