Electrolytes, lithium metal batteries and electrical devices

Abstract

This application provides an electrolyte, a lithium metal battery, and an electrical device. The electrolyte comprises a first solvent, which contains anions and cations. The cations include at least one structure shown in Formula I, Formula II, Formula III, and Formula IV, wherein R1, R6, and R... 11 R 16 Each independently contains C 1‑3 Alkylene or C 1‑3 Fluorinated alkylene groups, R2, R7, R 12 R 22 Each independently contains C 1‑5 Alkyl or C 1‑5 Fluoroalkyl groups, R3, R4, R8, R9, R 13 R 14 R 18 R 19 Each independently contains C 1‑3 Phenylene, R5, R 10 R 15 R 20 R 21 R 22 Each independently contains C 1‑3 Alkyl groups, R1 and R2 contain at least one fluorine atom, R6 and R7 contain at least one fluorine atom, R 11 and R 12 It contains at least one fluorine atom, R 16 and R 17 It contains at least one fluorine atom, and the anion includes at least one of tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate, trifluoromethanesulfonate, bis(trifluoromethanesulfonyl)imide, bis(fluorosulfonyl)imide, difluorophosphate, dioxaloateborate, difluorooxaloateborate, difluorodioxaloateborate, difluorodioxaloate phosphate, and tetrafluorooxaloate phosphate.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and more particularly to an electrolyte, a lithium metal battery, and an electrical device. Background Technology

[0002] Currently, the energy density of battery materials used in commercially available lithium-ion batteries has essentially reached its theoretical limit, necessitating the development of novel electrode materials to improve energy density. Among these, lithium metal anodes, with a theoretical energy density of 3860 mAh / g and a low electrode potential (-3.04 V), have attracted widespread attention from researchers and have yielded a series of application results, such as lithium metal batteries.

[0003] However, the thermodynamic instability between the lithium metal anode and the electrolyte can cause spontaneous reactions. The volume changes of lithium during deposition / stripping can damage the SEI film, and the rupture and repair of the SEI film continuously consume active lithium and electrolyte. These problems lead to a rapid decline in battery cycle capacity. Furthermore, lithium dendrites, when they grow to a certain extent, can puncture the separator, causing a short circuit. The large amount of heat released during a short circuit can potentially lead to combustion or even an explosion. Therefore, the safety of lithium metal batteries urgently needs further improvement. Summary of the Invention

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide an electrolyte, a lithium metal battery and an electrical device for improving the number of cycles at room temperature of lithium metal batteries and improving the cycle performance and safety performance of lithium metal batteries.

[0005] A first aspect of this application provides an electrolyte comprising a first solvent, the first solvent comprising anions and cations, wherein the cations comprise at least one structure represented by formulas I, II, III, and IV.

[0006]

[0007] Among them, R1, R6, R 11 R 16 Each independently contains C 1-3 Alkylene or C 1-3 Fluorinated alkylene groups, R2, R7, R 12 R 22 Each independently contains C 1-5 Alkyl or C 1-5 Fluoroalkyl groups, R3, R4, R8, R9, R 13 R 14 R 18 R 19 Each independently contains C 1-3 Phenylene, R5, R 10 R15 R 20 R 21 R 22 Each independently contains C 1-3 Alkyl groups, R1 and R2 contain at least one fluorine atom, R6 and R7 contain at least one fluorine atom, R 11 and R 12 It contains at least one fluorine atom, R 16 and R 17 It contains at least one fluorine atom.

[0008] The anion comprises at least one of tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate, trifluoromethanesulfonate, bis(trifluoromethanesulfonyl)imide, bis(fluorosulfonyl)imide, difluorophosphate, dioxaloateborate, difluorooxaloateborate, difluorodioxaloateborate, difluorodioxaloate phosphate, and tetrafluorooxaloate phosphate.

[0009] First, the primary solvent in the electrolyte is an ionic liquid, which possesses properties such as non-volatility and flame retardancy. Adding this primary solvent ionic liquid to the electrolyte can improve its flame retardancy and enhance the safety of the lithium metal battery. Second, functional modifications are made to both ends of the cation structure of the primary solvent ionic liquid. On one hand, the presence of an ether functional group at one end of the cation of the primary solvent ionic liquid can increase the ionic conductivity of the ionic liquid, reduce the viscosity of the electrolyte, and improve the migration speed of lithium ions, thereby improving the kinetic performance of the system. Simultaneously, fluorine substitution of the ether functional group lowers the HOMO (highest occupied molecular orbital) energy level, thus enhancing the antioxidant properties of the ionic liquid and the electrolyte. Furthermore, due to the high bond energy of the CF bond, the stability of the cation is improved, and the ionic liquid containing the ether functional group has excellent compatibility with the lithium metal anode, improving the compatibility between the electrolyte and the lithium metal anode, thereby improving the cycle stability of the battery. On the other hand, the other end of the cation of the first solvent ionic liquid contains an unsaturated ketone group structure, which has good film-forming properties and can form a high-toughness SEI film mainly composed of organic components on the surface of the lithium metal battery anode, reducing the possibility of SEI film breakage during battery cycling, thereby improving the cycle stability of the battery.

[0010] In summary, by using the electrolyte described above, the safety of lithium metal batteries can be guaranteed while further improving the cycle stability of the batteries, thus achieving a long lifespan for lithium metal batteries.

[0011] In any embodiment, the number of carbon atoms in R1 and R2 is not always 1, and the number of carbon atoms in R6 and R7 is not always 1. 11 and R 12 The number of carbon atoms is not both 1, the R16 and R 17 The number of carbon atoms is not always 1.

[0012] The fact that the number of carbon atoms in the groups at both ends of the oxygen atom in the fluoroether structure is different (1) can improve the stability of the fluoroether structure. This allows the fluoroether structure to improve the conductivity and oxidation resistance of the first solvent ionic liquid and electrolyte, thereby improving the cycle performance of the battery and extending its cycle life.

[0013] In any implementation, R1, R6, R 11 R 16 Each independently contains the following groups:

[0014]

[0015] Where * represents R1, R6, R 11 R 16 The connection sites of nitrogen atoms in the structures shown in Formulas I, II, III, and IV. Representing R1, R6, R 11 R 16 The connection sites with oxygen atoms in the structures shown in Formulas I, II, III, and IV.

[0016] R1, R6, R 11 R 16 The carbon atoms that undergo fluorine substitution are not directly bonded to oxygen atoms, which weakens the interaction between fluorine and oxygen atoms. This facilitates the interaction between oxygen atoms in the fluorinated ether structure and lithium ions, resulting in a more stable solvation structure between lithium ions and the first solvent ionic liquid. This also allows the unsaturated ketone structure in the ionic liquid to reach the negative electrode surface along with the solvation structure and undergo a film-forming reaction, generating a highly tough SEI film layer, improving the cycle stability and performance of the battery.

[0017] In any implementation, R2, R7, R 12 R 22 Each independently contains the following groups:

[0018]

[0019] in, Representatives R2, R7, R 12 R 22 The connection sites with oxygen atoms in the structures shown in Formulas I, II, III, and IV.

[0020] R2, R7, R 12 R 22The carbon atom that is substituted with fluorine is not directly bonded to the oxygen atom, which weakens the interaction between the fluorine atom and the oxygen atom. This is beneficial for the interaction between the oxygen atom in the fluorinated ether structure and the lithium ion, making the lithium ion and the first solvent ionic liquid form a more stable solvation structure. This is conducive to the unsaturated ketone structure in the ionic liquid reaching the negative electrode surface along with the solvation structure to form a film reaction, generating a high-toughness SEI film layer, improving the cycle stability of the battery, and improving the cycle performance of the battery.

[0021] In any embodiment, the cation includes at least one of the following structures:

[0022]

[0023]

[0024] In any embodiment, the electrolyte further includes a second solvent, wherein the volume ratio of the first solvent to the second solvent is 0.1-1, preferably 0.5-0.85.

[0025] The inclusion of a second solvent in the electrolyte further enhances its conductivity. Simultaneously, the solvation structure formed by the second solvent and lithium ions facilitates the reaction of anions in the lithium salt on the negative electrode surface, generating a highly dense SEI film primarily composed of inorganic components. This highly dense, inorganic-based SEI film, combined with the cationic structure of the first solvent ionic liquid to form a highly resilient, organic-based SEI film, works synergistically to improve the stability of the lithium metal negative electrode and enhance the battery's cycle performance.

[0026] In any embodiment, the electrolyte further includes a lithium salt, wherein the molar concentration of the lithium salt in the electrolyte is 0.5 mol / L-4 mol / L, and optionally 0.8 mol / L-2.2 mol / L.

[0027] The appropriate molar concentration of lithium salt gives the electrolyte excellent conductivity, while ensuring that a sufficient number of lithium salt anions participate in the formation of a high-density SEI film mainly composed of inorganic components, thereby comprehensively improving the cycle performance of the battery.

[0028] In any embodiment, the second solvent comprises at least one of fluorinated aromatic compounds, aromatic compounds, ester compounds, ether compounds, sulfone compounds, and nitrile compounds, and may be selected as ethylene carbonate, methyl ethyl carbonate, fluoroethylene carbonate, difluoroethylene carbonate, diethyl carbonate, methyl trifluoroethyl carbonate, dimethyl carbonate, benzene, toluene, p-xylene, m-xylene, o-xylene, fluorobenzene, p-difluorobenzene, m-difluorobenzene, o-difluorobenzene, trifluorotoluene, trifluoromethoxybenzene, decafluoropentane, perfluoropentanone, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-bis(1,1,2)-(tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether), etc. One or more of the following: (2-tetrafluoroethoxy)ethane, bis(2,2,2-trifluoroethyl) ether, 1,1,2,3,3,3-hexafluoropropylethyl ether, 1,2,2-tetrafluoroethyl ether, ethyl trifluoromethyl ether, difluoromethyl-2,2,3,3,3-pentafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, difluoromethyl-2,2,3,3-tetrafluoropropyl ether, perfluoroisopropylmethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, ethyl-2,2,2-tetrafluoroethyl ether, and bis(1,1,2,2-tetrafluoroethyl) ether.

[0029] In any embodiment, the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoroacetate, lithium tetraphenylborate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)imide, lithium difluorooxalate borate, lithium difluorooxalate borate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide, and may be selected as lithium hexafluorophosphate.

[0030] A second aspect of this application provides a lithium metal battery, including the electrolyte described in the first aspect.

[0031] A third aspect of this application provides an electrical device including the lithium metal battery described in the second aspect. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of lithium metal according to one embodiment of this application;

[0033] Figure 2 yes Figure 1 An exploded view of lithium metal according to an embodiment of this application is shown;

[0034] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0035] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0036] Figure 5 yes Figure 4An exploded view of a battery pack according to an embodiment of this application is shown;

[0037] Figure 6 This is a schematic diagram of an electrical device using a lithium metal battery as a power source according to an embodiment of this application.

[0038] Figure label:

[0039] 1 Battery pack; 2 Upper housing; 3 Lower housing; 4 Battery module; 5 Lithium metal battery; 51 Casing; 52 Electrode assembly; 53 Cover plate. Detailed Implementation

[0040] The following detailed description, with appropriate reference to the accompanying drawings, specifically discloses embodiments of the electrolyte, lithium metal battery, and power application device of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided for the purpose of enabling those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0041] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0042] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0043] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0044] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0045] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0046] Current non-aqueous electrolytes in lithium metal batteries are highly flammable, posing a safety hazard. Ionic liquids, with their advantages of being non-volatile and non-flammable, are gaining attention. However, traditional ionic liquids have high viscosity and high ionic conductivity, which can affect lithium-ion transport performance, causing uneven lithium-ion deposition on the electrode surface and leading to lithium dendrite formation, potentially resulting in "dead lithium," which is detrimental to battery cycle performance and safety. Furthermore, during battery cycling, the volume change of lithium can damage the SEI film, allowing exposed lithium metal to continue reacting with the electrolyte, negatively impacting battery cycle performance as well.

[0047] Electrolyte

[0048] Based on this, this application provides an electrolyte comprising a first solvent, the first solvent comprising anions and cations, wherein the cations comprise at least one structure shown in Formula I, Formula II, Formula III, and Formula IV.

[0049]

[0050] Among them, R1, R6, R 11 R 16 Each independently contains C 1-3 Alkylene or C 1-3 Fluorinated alkylene groups, R2, R7, R 12 R 22 Each independently contains C 1-5 Alkyl or C 1-5 Fluoroalkyl groups, R3, R4, R8, R9, R 13 R 14 R 18 R 19 Each independently contains C 1-3 Phenylene, R5, R 10 R 15 R 20R 21 R 22 Each independently contains C 1-3 Alkyl groups, R1 and R2 contain at least one fluorine atom, R6 and R7 contain at least one fluorine atom, R 11 and R 12 It contains at least one fluorine atom, R 16 and R 17 It contains at least one fluorine atom.

[0051] The anion comprises at least one of tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate, trifluoromethanesulfonate, bis(trifluoromethanesulfonyl)imide, bis(fluorosulfonyl)imide, difluorophosphate, dioxaloateborate, difluorooxaloateborate, difluorodioxaloateborate, difluorodioxaloate phosphate, and tetrafluorooxaloate phosphate.

[0052] In this article, the term "electrolyte" refers to a liquid electrolyte, which is the carrier for ion transport in lithium metal batteries.

[0053] In this paper, the term "ionic liquid" refers to a fluid composed entirely of anions and cations at or below 100°C. Ionic liquids possess advantages such as near-non-volatility, non-flammability, thermodynamic stability, a wide operating temperature range, and a wide electrochemical window.

[0054] In this article, the term "C" 1-3 "Alkylene" refers to a divalent branched or unbranched saturated hydrocarbon chain. C 1-3 Examples of alkylene groups include, but are not limited to: -CH2-, -CH2CH2-, -CH2CH2CH2-, -CH(CH3)CH2-, and -CH2CH(CH3)-.

[0055] In this article, the term "C" 1-3 "Fluoroalkylene" refers to C 1-3 At least one hydrogen atom in the alkylene group is replaced by a fluorine atom. C 1-3 Examples of fluoroalkylene groups include, but are not limited to: -CHF-, -CF2-, -CH2CHF-, -CH2CF2CH2-, -CF(CH3)CH2-, and -CF2CH(CH3)-.

[0056] In this article, the term "C" 1-5 "Alkyl" is a monovalent branched or unbranched saturated hydrocarbon chain with 1, 2, 3, 4, or 5 carbon atoms. C 1-5 Examples of alkyl groups include, but are not limited to: methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, tert-butyl, and n-pentyl.

[0057] In this article, the term "C" 1-5 "Fluoroalkyl" refers to C 1-5At least one hydrogen atom in the alkyl group is replaced by a fluorine atom. C 1-5 Examples of fluoroalkylene groups include, but are not limited to: -CF3, -CH2CH2F, -CH2CF2CF3, -CF(CH3)CH3, -CF2CH(CH3)CF3.

[0058] In some implementations, R1 contains fluorine atoms.

[0059] In some implementations, R2 contains fluorine atoms.

[0060] In some implementations, R6 contains fluorine atoms.

[0061] In some implementations, R7 contains fluorine atoms.

[0062] In some implementations, R 11 It contains fluorine atoms.

[0063] In some implementations, R 12 It contains fluorine atoms.

[0064] In some implementations, R 16 It contains fluorine atoms.

[0065] In some implementations, R 17 It contains fluorine atoms.

[0066] In this paper, the term "fluoroether structure" refers to a structure that simultaneously contains an ether bond and a fluorine atom.

[0067] In this paper, the term "structure containing unsaturated ketone groups" refers to a structure that contains both unsaturated double bonds and ketone groups.

[0068] In this paper, the term "solventized structure" refers to the aggregate formed by the solvent molecules in the electrolyte, which bind to cations much more strongly than anions. When lithium salts dissolve in a solvent, the solvent will aggregate around the lithium ions.

[0069] First, the first solvent is an ionic liquid. Ionic liquids possess properties such as non-volatility and flame retardancy. Adding an ionic liquid as the first solvent to the electrolyte can improve the flame retardancy of the electrolyte and enhance the safety of the lithium metal battery. Second, functional modifications are made to both ends of the cation structure of the first solvent ionic liquid. On one hand, the presence of an ether functional group at one end of the cation of the ionic liquid can increase the ionic conductivity of the ionic liquid, reduce the viscosity of the electrolyte, increase the ionic conductivity of the electrolyte, improve the migration speed of lithium ions, and improve the kinetic performance of the system. At the same time, the substitution of fluorine atoms for the ether functional group also lowers the HOMO (highest occupied molecular orbital) energy level, thereby improving the antioxidant properties of the ionic liquid and the electrolyte. Furthermore, due to the high bond energy of the CF bond, the stability of the cation is improved, and the ionic liquid containing ether functional groups exhibits excellent compatibility with the lithium metal anode, enhancing the compatibility between the electrolyte and the lithium metal anode, thereby improving the cycle stability of the battery. On the other hand, the other end of the cation of the first solvent ionic liquid contains an unsaturated ketone group structure, which has good film-forming properties and can form a high-toughness SEI film mainly composed of organic components on the surface of the lithium metal battery anode, reducing the possibility of SEI film breakage during battery cycling, thereby improving the cycle stability of the battery. At the same time, the anions of the first solvent ionic liquid can generate a high-density SEI film mainly composed of inorganic components on the anode surface, which, together with the high-toughness SEI film mainly composed of organic components formed by the cation structure, forms a stable SEI film.

[0070] Compared to the physical blending modification method of fluorinated ether compounds with basic ionic liquids, chemically modifying the fluorinated ether structure into the ionic liquid results in more stable chemical modification, more significant improvement in electrolyte viscosity and conductivity, and improved system kinetic performance. Furthermore, chemically modifying the fluorinated ether structure into the first solvent ionic liquid can further improve the compatibility between the first solvent ionic liquid and the lithium metal anode, thereby enhancing the compatibility between the electrolyte and the lithium metal anode and improving the system's cycle stability.

[0071] In existing technologies, film-forming additives containing unsaturated ketone structures are physically blended with a base ionic liquid. During the initial reaction of the film-forming additive with the lithium metal anode, the additive is completely consumed, forming an SEI film. However, subsequent lithium deposition / stripping on the anode during cycling destroys the initially formed SEI film, preventing the film-forming additive from continuing to function and participate in SEI film formation. To overcome these problems, this application chemically modifies and incorporates the unsaturated ketone structure into the first solvent ionic liquid. The unsaturated ketone structure on the ionic liquid participates in the formation of the lithium ion solvation structure, continuously migrating with the lithium ions to the lithium metal anode. This forms a highly tough SEI film, primarily composed of organic components, on the lithium anode surface. This allows the lithium anode SEI film to be continuously repaired during cycling, thereby achieving a longer cycle life for the lithium anode.

[0072] Compared to chemically modifying ionic liquids using unsaturated bonds, chemically modifying the first solvent ionic liquid using a structure containing both unsaturated bonds and ketone groups allows the oxygen atoms on the ketone groups to exhibit nucleophilicity, enabling them to interact with lithium ions to a certain extent and thus improve ionic conductivity.

[0073] In summary, by using an electrolyte containing a first solvent ionic liquid, the cycle stability of lithium metal batteries can be further improved while ensuring their safety, thus achieving a long lifespan for lithium metal batteries.

[0074] In some embodiments, the number of carbon atoms in R1 and R2 is not simultaneously 1, and the number of carbon atoms in R6 and R7 is not simultaneously 1. 11 and R 12 The number of carbon atoms is not both 1; the R 16 and R 17 The number of carbon atoms is not always 1.

[0075] In some embodiments, R1 comprises a methylene or a fluoromethylene group, and R2 comprises C. 2-5 Alkyl or C 2-5 Fluorinated alkyl groups.

[0076] In some implementations, R1 includes C 2-3 Alkylene or C 2-3 Fluoroalkylene, R2 contains C 1-5 Alkyl or C 1-5 Fluorinated alkyl groups.

[0077] In some embodiments, R6 comprises a methylene or a fluoromethylene group, and R7 comprises C. 2-5 Alkyl or C 2-5 Fluorinated alkyl groups.

[0078] In some implementations, R6 includes C 2-3 Alkylene or C 2-3 Fluoroalkylene, R7 contains C 1-5 Alkyl or C 1-5 Fluorinated alkyl groups.

[0079] In some implementations, R 11 Contains methylene or fluoromethylene, R 12 Includes C 2-5 Alkyl or C 2-5 Fluorinated alkyl groups.

[0080] In some implementations, R 11 Includes C 2-3 Alkylene or C 2-3 Fluoroalkylene, R 12 Includes C 1-5 Alkyl or C 1-5 Fluorinated alkyl groups.

[0081] In some implementations, R 16 Contains methylene or fluoromethylene, R 17 Includes C 2-5 Alkyl or C 2-5 Fluorinated alkyl groups.

[0082] In some implementations, R 16 Includes C 2-3 Alkylene or C 2-3 Fluoroalkylene, R 17 Includes C 1-5 Alkyl or C 1-5 Fluorinated alkyl groups.

[0083] The fact that the number of carbon atoms in the groups at both ends of the oxygen atom in the fluoroether structure is different (each has 1 atom) can improve the stability of the fluoroether structure. This allows the fluoroether structure to improve the conductivity and antioxidant properties of the first solvent ionic liquid, thereby improving the conductivity and antioxidant properties of the electrolyte, enhancing the cycle performance of the battery, and extending the cycle life of the battery.

[0084] In some implementations, R1, R6, R 11 R 16 Each independently contains the following groups:

[0085]

[0086] Where * represents R1, R6, R 11 R 16 The connection sites of nitrogen atoms in the structures shown in Formulas I, II, III, and IV. Representing R1, R6, R 11 R16 The connection sites with oxygen atoms in the structures shown in Formulas I, II, III, and IV.

[0087] R1, R6, R 11 R 16 The carbon atoms that undergo fluorine substitution are not directly bonded to oxygen atoms, which weakens the interaction between fluorine and oxygen atoms. This facilitates the interaction between oxygen atoms in the fluorinated ether structure and lithium ions, resulting in a more stable solvation structure between lithium ions and the first solvent ionic liquid. This also allows the unsaturated ketone structure in the ionic liquid to reach the negative electrode surface along with the solvation structure and undergo a film-forming reaction, generating a highly tough SEI film layer, improving the cycle stability and performance of the battery.

[0088] In some implementations, R2, R7, R 12 R 22 Each independently contains the following groups:

[0089]

[0090] in, Representatives R2, R7, R 12 R 22 The connection sites with oxygen atoms in the structures shown in Formulas I, II, III, and IV.

[0091] R2, R7, R 12 R 22 The carbon atom that is substituted with fluorine is not directly bonded to the oxygen atom, which weakens the interaction between the fluorine atom and the oxygen atom. This is beneficial for the interaction between the oxygen atom in the fluorinated ether structure and the lithium ion, making the lithium ion and the first solvent ionic liquid form a more stable solvation structure. This is conducive to the unsaturated ketone structure in the ionic liquid reaching the negative electrode surface along with the solvation structure to form a film reaction, generating a high-toughness SEI film layer, improving the cycle stability of the battery, and improving the cycle performance of the battery.

[0092] In some embodiments, the cation includes at least one of the following structures:

[0093]

[0094]

[0095] In some embodiments, the cation includes at least one of the following structures:

[0096]

[0097] The cation structures of Formula II-1, Formula II-2 and Formula II-3 described above have a reduction potential lower than that of lithium ions, exhibiting excellent reduction resistance and improving the cycle stability of the battery.

[0098] In some embodiments, the electrolyte further includes a second solvent, wherein the volume ratio of the first solvent to the second solvent is 0.1-1.

[0099] In some embodiments, the volume ratio of the first solvent to the second solvent can be selected as 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1 or any value therebetween.

[0100] The inclusion of a second solvent in the electrolyte further enhances its conductivity. Simultaneously, the solvation structure formed by the second solvent and lithium ions facilitates the reaction of anions in the lithium salt on the negative electrode surface, generating a highly dense SEI film primarily composed of inorganic components. This highly dense, inorganic-based SEI film, combined with the highly resilient, organic-based SEI film formed by the cationic structure of the ionic liquid, improves the stability of the lithium metal negative electrode and enhances the battery's cycle performance.

[0101] In some embodiments, the volume ratio of the first solvent to the second solvent is 0.5-0.85.

[0102] In some embodiments, the volume ratio of the first solvent to the second solvent can be selected as 0.5, 0.6, 0.7, 0.8, 0.85, or any value between them.

[0103] When the volume ratio of the first solvent to the second solvent is within a suitable range, the cycle performance of the battery can be further improved and the cycle life of the battery can be extended.

[0104] In some embodiments, the second solvent includes at least one of fluorinated aromatic compounds, aromatic compounds, ester compounds, ether compounds, sulfone compounds, and nitrile compounds.

[0105] In this paper, the term "fluorinated aromatic compound" refers to a compound having a benzene ring structure and including at least one fluorine atom substituent.

[0106] In this article, the term "aromatic compound" refers to a compound having a benzene ring structure.

[0107] In this text, the term "ester" refers to compounds that contain an ester group, including straight-chain esters and cyclic esters.

[0108] In this article, the term "ether compound" refers to a compound in which two hydrocarbon groups are linked together by an oxygen atom.

[0109] In this paper, the term "sulfone compounds" refers to a class of compounds characterized by having a sulfonyl group and usually being linked to two carbon atoms by means of sulfur.

[0110] In this article, the term "nitrile compound" refers to a compound in which carbon atoms containing hydrocarbon and cyano groups are linked together.

[0111] In some embodiments, the second solvent includes ethylene carbonate, methyl ethyl carbonate, fluoroethylene carbonate, difluoroethylene carbonate, diethyl carbonate, methyl trifluoroethyl carbonate, dimethyl carbonate, benzene, toluene, p-xylene, m-xylene, o-xylene, fluorobenzene, p-difluorobenzene, m-difluorobenzene, o-difluorobenzene, trifluorotoluene, trifluoromethoxybenzene, decafluoropentane, perfluoropentanone, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, and bis(2,2,2-trifluoroethyl) ether. One or more of the following: 1,1,2,3,3,3-hexafluoropropyl ethyl ether, 1,2,2-tetrafluoroethyl ether, ethyl trifluoromethyl ether, difluoromethyl-2,2,3,3,3-pentafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, difluoromethyl-2,2,3,3-tetrafluoropropyl ether, perfluoroisopropylmethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, ethyl-2,2,2-tetrafluoroethyl ether, and bis(1,1,2,2-tetrafluoroethyl) ether.

[0112] In some embodiments, the electrolyte further includes a lithium salt, wherein the molar concentration of the lithium salt in the electrolyte is 0.5 mol / L to 4 mol / L. In some embodiments, the molar concentration of the lithium salt in the electrolyte may be selected from 0.5 mol / L, 1 mol / L, 2 mol / L, 3 mol / L, 4 mol / L, or any value between these values.

[0113] In some embodiments, the molar concentration of the lithium salt in the electrolyte is 0.8 mol / L to 2.2 mol / L. In some embodiments, the molar concentration of the lithium salt in the electrolyte can be selected from 0.8 mol / L, 1 mol / L, 1.2 mol / L, 1.4 mol / L, 1.6 mol / L, 1.8 mol / L, 2.0 mol / L, 2.2 mol / L, or any value between these values.

[0114] The appropriate molar concentration of lithium salt gives the electrolyte excellent conductivity, while ensuring that a sufficient number of lithium salt anions participate in the formation of a high-density SEI film mainly composed of inorganic components, thereby comprehensively improving the cycle performance of the battery.

[0115] In some embodiments, the lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoroacetate, lithium tetraphenylborate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)borate, lithium difluorooxalateborate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0116] In some embodiments, the lithium salt includes lithium hexafluorophosphate.

[0117] Lithium hexafluorophosphate exhibits excellent cycle stability in lithium metal battery systems, thereby improving battery cycle performance.

[0118] The electrolyte proposed in this application can be prepared by the following method:

[0119] At room temperature, lithium salt is added to the first solvent in a stirred mixing tank and stirred thoroughly to dissolve, thus obtaining an electrolyte.

[0120] In some embodiments, at room temperature, the first solvent and the second solvent are mixed evenly in a stirred mixing tank, and then the lithium salt is added and stirred thoroughly to dissolve, thereby obtaining an electrolyte.

[0121] In some embodiments, a lithium metal battery is provided, including the electrolyte described in some embodiments.

[0122] In some embodiments, a lithium metal battery includes a positive electrode, a negative electrode, a separator, and an electrolyte as described in any embodiment.

[0123] [Positive electrode plate]

[0124] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including a positive electrode active material.

[0125] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0126] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0127] In some embodiments, the positive electrode active material may be a known battery positive electrode active material. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM523), LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM211), LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM811), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05 At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0128] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene (HFP)-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0129] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0130] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0131] [Negative electrode plate]

[0132] The negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector, the negative electrode film layer including a negative electrode active material.

[0133] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0134] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0135] In some implementations, the negative electrode active material is elemental lithium metal.

[0136] In some embodiments, the negative electrode active material can be an alloy of metallic lithium with other metallic or non-metallic elements. The metallic elements include any one or more of tin (Sn), zinc (Zn), aluminum (Al), magnesium (Mg), silver (Ag), gold (Au), gallium (Ga), indium (In), and phosphorus (Pt). The metalloid elements include one or more of boron (B), carbon (C), and silicon (Si).

[0137] In some implementations, the negative electrode sheet can be prepared by rolling the upper negative electrode active material onto the negative electrode current collector, and then cutting it to obtain the negative electrode sheet.

[0138] [Isolation membrane]

[0139] In some embodiments, the lithium metal battery also includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0140] In some embodiments, the material of the separator can be selected from at least one of polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and natural fibers. The separator can be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0141] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0142] In some embodiments, the lithium metal battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0143] In some implementations, the outer packaging of the lithium metal battery can be a rigid shell, such as a hard plastic shell, aluminum shell, or steel shell. The outer packaging of the lithium metal battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0144] This application does not impose any particular limitation on the shape of the lithium metal battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 This is an example of a square-structured lithium metal battery 5.

[0145] In some implementations, refer to Figure 2 The outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. A positive electrode sheet, a negative electrode sheet, and a separator can be formed into an electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The lithium metal battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0146] In some implementations, lithium metal batteries can be assembled into battery modules, and the number of lithium metal batteries contained in a battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0147] Figure 3This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple lithium metal batteries 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple lithium metal batteries 5 can be fixed in place using fasteners.

[0148] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of lithium metal batteries 5 are received.

[0149] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0150] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0151] In addition, this application also provides an electrical device, which includes at least one of the lithium metal battery, battery module, or battery pack provided in this application. The lithium metal battery, battery module, or battery pack can be used as a power source for the electrical device, or as an energy storage unit for the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0152] As the electrical device, a lithium metal battery, battery module, or battery pack can be selected according to its usage requirements.

[0153] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of the lithium metal battery in this device, a battery pack or battery module can be used.

[0154] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use lithium metal batteries as their power source.

[0155] Example

[0156] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially. In the following embodiments, only the case of lithium metal batteries is shown, but this application is not limited to this.

[0157] I. Preparation Method

[0158] Example 1

[0159] 1) Preparation of electrolyte

[0160] In an argon atmosphere glove box with a water content of <10ppm, 4ml of the first solvent and 6ml of the second solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether were thoroughly mixed to form a mixed solution. 20mmol of lithium difluorosulfonylimide was added to the mixed solution and stirred to obtain the electrolyte of Example 1. The molar concentration of lithium salt in the electrolyte was 2mol / L. The cation of the first solvent was as shown in Formula I-1, and the anion of the first solvent was hexafluorophosphate.

[0161]

[0162] 2) Preparation of positive electrode sheet

[0163] LiNi, the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2, polyvinylidene fluoride (PVDF) binder, and acetylene black conductive agent are mixed uniformly in N-methylpyrrolidone (NMP) solvent at a mass ratio of 98%:1%:1% to prepare a positive electrode slurry. The positive electrode slurry is then mixed at a concentration of 25 mg / cm³. 2 The load is evenly coated on both sides of the positive current collector aluminum foil, dried at room temperature, transferred to an oven for further drying, and then cut into 40mm*50mm rectangles as positive electrode sheets.

[0164] 3) Preparation of negative electrode sheet

[0165] A 50μm thick lithium foil is rolled onto a 12μm thick copper foil and then cut into a 41mm*51mm rectangle to serve as the negative electrode.

[0166] 4) Separating membrane

[0167] Polyethylene film (PE diaphragm) is used as the separation membrane.

[0168] 5) Battery manufacturing

[0169] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide isolation. The electrolyte is then added to assemble a lithium metal battery.

[0170] Examples 2-8

[0171] The difference between Examples 2-8 and Example 1 lies in the adjustment of the structure of the first solvent. The cation structures of the first solvent in Examples 2-8 are shown below in sequence.

[0172]

[0173]

[0174] In Examples 2-8, the anions of the first solvent are, in order, difluorooxalate borate, bis(trifluoromethylsulfonyl)imide, bis(fluorosulfonyl)imide, bis(fluorosulfonyl)imide, bis(fluorosulfonyl)imide, bis(fluorosulfonyl)imide, and bis(fluorosulfonyl)imide.

[0175] Examples 9-12

[0176] The difference between Examples 9-12 and Example 4 is that the volume ratio of the first solvent to the second solvent was adjusted. See Table 1 for specific parameters.

[0177] Comparative Examples 1-8

[0178] The difference between Comparative Examples 1-8 and Example 4 is that the electrolyte formulation was adjusted. The specific electrolyte formulations are shown below:

[0179] Comparative Example 1: In an argon atmosphere glove box with a water content of <10ppm, 4ml of ethylene glycol dimethyl ether and 6ml of the second solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether were thoroughly mixed to form a mixed solution. 20mmol of lithium difluorosulfonylimide was added to the solution and stirred to obtain the electrolyte of Comparative Example 1, wherein the molar concentration of lithium salt in the electrolyte was 2mol / L.

[0180] Comparative Example 2: In an argon atmosphere glove box with a water content of <10ppm, 4ml of the first solvent and 6ml of the second solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether were thoroughly mixed to form a mixed solution. 20mmol of lithium difluorosulfonylimide was added to the mixed solution and stirred to obtain the electrolyte of Comparative Example 2. The molar concentration of lithium salt in the electrolyte was 2mol / L. The cation of the first solvent of Comparative Example 2 is shown in Formula VI-1, and the anion is difluorosulfonylimide.

[0181]

[0182] Comparative Example 3: In an argon atmosphere glove box with a water content of <10ppm, 4ml of the first solvent and 6ml of the second solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether were thoroughly mixed to form a mixed solution. 20mmol of lithium difluorosulfonylimide was added to the mixed solution and stirred to obtain the electrolyte of Comparative Example 3. The molar concentration of lithium salt in the electrolyte was 2mol / L. The cation of the first solvent of Comparative Example 3 is shown in Formula VI-2, and the anion is difluorosulfonylimide.

[0183]

[0184] Comparative Example 4: In an argon atmosphere glove box with a water content of <10ppm, 4ml of the first solvent, 4ml of 2,2,2-trifluoroethyl ethyl ether, 4ml of vinylene carbonate, and 6ml of the second solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether were thoroughly mixed to form a mixed solution. 36mmol of lithium difluorosulfonylimide was added to the solution, and the mixture was stirred to obtain the electrolyte of Comparative Example 4. The molar concentration of lithium salt in the electrolyte was 2mol / L. The cation of the first solvent of Comparative Example 4 was as shown in Formula VI-1 above, and the anion was difluorosulfonylimide.

[0185] Comparative Example 5: In an argon atmosphere glove box with a water content of <10ppm, 4ml of the first solvent and 6ml of the second solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether were thoroughly mixed to form a mixed solution. 20mmol of lithium difluorosulfonylimide was added to the mixed solution and stirred to obtain the electrolyte of Comparative Example 5. The molar concentration of lithium salt in the electrolyte was 2mol / L. The cation of the first solvent of Comparative Example 5 is shown in Formula VI-3, and the anion is difluorosulfonylimide.

[0186]

[0187] Comparative Example 6: In an argon atmosphere glove box with a water content of <10ppm, 4ml of the first solvent, 4ml of vinylene carbonate, and 6ml of the second solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether were thoroughly mixed to form a mixed solution. 28mmol of lithium difluorosulfonylimide was added to the solution, and the mixture was stirred to obtain the electrolyte of Comparative Example 6. The molar concentration of lithium salt in the electrolyte was 2mol / L. The cation of the first solvent of Comparative Example 6 was as shown in Formula VI-3 above, and the anion was difluorosulfonylimide.

[0188] Comparative Example 7: In an argon atmosphere glove box with a water content of <10ppm, 4ml of the first solvent and 6ml of the second solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether were thoroughly mixed to form a mixed solution. 20mmol of lithium difluorosulfonylimide was added to the mixed solution and stirred to obtain the electrolyte of Comparative Example 7. The molar concentration of lithium salt in the electrolyte was 2mol / L. The cation of the first solvent of Comparative Example 7 is shown in Formula VI-4, and the anion is difluorosulfonylimide.

[0189]

[0190] Comparative Example 8: In an argon atmosphere glove box with a water content of <10ppm, 4ml of the first solvent, 4ml of 2,2,2-trifluoroethyl ethyl ether, and 6ml of the second solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether were thoroughly mixed to form a mixed solution. 28mmol of lithium difluorosulfonyl imide was added to the solution, and the mixture was stirred to obtain the electrolyte of Comparative Example 8. The molar concentration of lithium salt in the electrolyte was 2mol / L. The cation of the first solvent in Comparative Example 8 was as shown in Formula VI-4 above, and the anion was difluorosulfonyl imide.

[0191] Comparative Example 9: In an argon atmosphere glove box with a water content of <10ppm, 4ml of the first solvent and 6ml of the second solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether were thoroughly mixed to form a mixed solution. 20mmol of lithium difluorosulfonylimide was added to the mixed solution and stirred to obtain the electrolyte of Comparative Example 9. The molar concentration of lithium salt in the electrolyte was 2mol / L. The cation of the first solvent of Comparative Example 9 is shown in Formula VI-5 below, and the anion is difluorosulfonylimide.

[0192]

[0193] II. Testing Methods

[0194] 1) Room temperature cycle performance of lithium metal batteries

[0195] The lithium metal battery was placed in a constant temperature chamber at 25℃±2℃ and left to stand for 2 hours. The cycling process was as follows: charged at a constant current of 0.2C to 4.3V, then charged at a constant voltage of 4.3V to 0.05C and left to stand for 5 minutes, and then discharged at 1C to 2.8V. This is one charge-discharge cycle. The charge-discharge capacity of the lithium metal battery in the first cycle was recorded. With the capacity of the first discharge as 100%, the charge-discharge cycle was repeated. The number of cycles in which the capacity retention rate of the lithium metal battery dropped to 80% was recorded. Ten lithium metal batteries were taken from each group, and the average number of cycles in which the capacity retention rate of the lithium metal battery dropped to 80% was calculated as the number of cycles for each group.

[0196] III. Test Results

[0197] The test results of the above embodiments and comparative examples are shown in Table 1.

[0198] Table 1

[0199]

[0200] Based on the above results, it can be seen that the electrolyte in Examples 1-12 includes a first solvent, which contains cations and anions, and the cations include

[0201] Any one of the following, wherein the anion includes any one of hexafluorophosphate, difluorosulfonylimide, difluorooxalateborate, and bis(trifluoromethylsulfonylimide).

[0202] As can be seen from the comparison between Examples 1-12 and Comparative Example 1, compared with the electrolytes containing ethylene glycol dimethyl ether solvent in the prior art, the electrolyte of this application containing a first solvent ionic liquid can effectively improve the number of battery cycles at room temperature and extend the battery's cycle life. As can be seen from Examples 1-8 and Comparative Example 2, compared with electrolytes containing unmodified ionic liquids, i.e., containing the cations shown in Formula VI-1,

[0203] Using the electrolyte of this application can increase the number of battery cycles at room temperature and extend the battery's cycle life. A comparison of Examples 1-8 with Comparative Example 3 shows that, compared to the electrolyte containing the cationic structure of Formula VI-2,

[0204] Using the electrolyte of this application can increase the number of battery cycles at room temperature and extend the battery's cycle life. A comparison of Examples 1-8 with Comparative Example 4 shows that, compared to the electrolyte containing the cationic structure of Formula VI-1 and 2,2,2-trifluoroethyl ethyl ether and vinylene carbonate, using the ionic liquid of this application can increase the number of battery cycles at room temperature and extend the battery's cycle life. A comparison of Examples 1-8 with Comparative Example 5 shows that the electrolyte containing the cationic structure of Formula VI-3...

[0205] Using the electrolyte of this application can increase the number of battery cycles at room temperature and extend the battery's cycle life. A comparison of Examples 1-8 with Comparative Example 6 shows that, compared to the electrolyte containing the cationic structure of Formula VI-3 and the vinylene carbonate electrolyte, using the electrolyte of this application can increase the number of battery cycles at room temperature and extend the battery's cycle life. A comparison of Examples 1-8 with Comparative Example 7 shows that, compared to the electrolyte containing the cationic structure of Formula VI-4,

[0206] The electrolyte of this application can improve the number of battery cycles at room temperature and extend the battery's cycle life. A comparison of Examples 1-8 with Comparative Example 8 shows that, compared to the electrolyte containing the cationic structure of Formula VI-4 and 2,2,2-trifluoroethyl ethyl ether, the electrolyte of this application can improve the number of battery cycles at room temperature and extend the battery's cycle life. A comparison of Examples 1-8 with Comparative Example 9 shows that, compared to the electrolyte containing the cationic structure of Formula VI-5,

[0207] Using the electrolyte of this application can increase the number of battery cycles at room temperature and extend the battery's cycle life.

[0208] As can be seen from the comparison between Examples 4-6, 8 and Example 7, compared with the first solvent ionic liquid where the number of carbon atoms of R6 and R7 in the cationic structure is simultaneously 1, i.e. the cationic structure shown in Formula II-4, controlling the number of carbon atoms of R6 and R7 in the cationic structure of the first solvent ionic liquid to not simultaneously be 1, i.e. the cationic structures shown in Formula II-1, Formula II-2, Formula II-3 and Formula II-5, can further improve the number of cycles at room temperature of the battery and further improve the cycle stability of the battery.

[0209] A comparison of Examples 4-6 and Examples 7-8 shows that, compared to the first solvent ionic liquid in Examples 7-8, R7 in the cationic structure is... That is, the cationic structures shown in Formula II-4 and Formula II-5, while R7 in the first solvent ionic liquid cationic structure in Examples 4-6 is The cation structures shown in Formula II-1, Formula II-2 and Formula II-3 can further increase the number of cycles at room temperature and further extend the cycle life of the battery.

[0210] As shown in Examples 1-12, the electrolyte comprises a first solvent ionic liquid and a second solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, wherein the volume ratio of the first solvent ionic liquid to the second solvent is 0.1-1. This results in a high number of cycles at room temperature and excellent cycle performance. A comparison of Examples 4, 10-11 with Examples 9, 12 shows that a volume ratio of the first solvent ionic liquid to the second solvent 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether of 0.5-0.85 can further improve the number of cycles at room temperature and enhance the cycle performance of the battery.

[0211] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. An electrolyte, characterized in that, The first solvent comprises anion and cation, wherein the cation comprises at least one structure shown in Formula I, Formula II, Formula III, or Formula IV. Formula I Formula II Formula III Formula IV Among them, R1, R6, R 11 R 16 Each independently contains C 1-3 Alkylene or C 1-3 Fluorinated alkylene groups, R2, R7, R 12 R 22 Each independently contains C 1-5 Alkyl or C 1-5 Fluoroalkyl groups, R3, R4, R8, R9, R 13 R 14 R 18 R 19 Each independently contains C 1-3 Phenylene, R5, R 10 R 15 R 20 R 21 R 22 Each independently contains C 1-3 Alkyl groups, R1 and R2 contain at least one fluorine atom, R6 and R7 contain at least one fluorine atom, R 11 and R 12 It contains at least one fluorine atom, R 16 and R 17 It contains at least one fluorine atom. The anion comprises at least one of tetrafluoroborate, hexafluorophosphate, hexafluoroarsenate, trifluoromethanesulfonate, bis(trifluoromethanesulfonyl)imide, bis(fluorosulfonyl)imide, difluorophosphate, dioxaloateborate, difluorooxaloateborate, difluorodioxaloateborate, difluorodioxaloate phosphate, and tetrafluorooxaloate phosphate.

2. The electrolyte according to claim 1, characterized in that, The number of carbon atoms in R1 and R2 is not both 1, and the number of carbon atoms in R6 and R7 is not both 1. 11 and R 12 The number of carbon atoms is not both 1, the R 16 and R 17 The number of carbon atoms is not always 1.

3. The electrolyte according to claim 1, characterized in that, The R1, R6, R 11 R 16 Each independently contains the following groups: ， Where * represents R1, R6, R 11 R 16 The connection sites of nitrogen atoms in the structures shown in Formulas I, II, III, and IV. Representing R1, R6, R 11 R 16 The connection sites with oxygen atoms in the structures shown in Formulas I, II, III, and IV.

4. The electrolyte according to claim 1, characterized in that, The R2, R7, R 12 R 22 Each independently contains the following groups: ， in, Representatives R2, R7, R 12 R 22 The connection sites with oxygen atoms in the structures shown in Formulas I, II, III, and IV.

5. The electrolyte according to claim 1, characterized in that, The cation includes at least one of the following structures. Formula I-1 Formula I-2 Formula I-3 Formula II-1 Formula II-2 Formula II-3 Formula III-1 Formula III-2 Formula III-3 Formula IV-1, Formula IV-2, Formula IV-3.

6. The electrolyte according to any one of claims 1 to 5, characterized in that, The electrolyte further includes a second solvent, and the volume ratio of the first solvent to the second solvent is 0.1-1.

7. The electrolyte according to any one of claims 1 to 5, characterized in that, The electrolyte further includes a second solvent, wherein the volume ratio of the first solvent to the second solvent is 0.5-0.

85.

8. The electrolyte according to any one of claims 1 to 5, characterized in that, The electrolyte also includes a lithium salt, wherein the molar concentration of the lithium salt in the electrolyte is 0.5 mol / L to 4 mol / L.

9. The electrolyte according to any one of claims 1 to 5, characterized in that, The electrolyte also includes a lithium salt, wherein the molar concentration of the lithium salt in the electrolyte is 0.8 mol / L to 2.2 mol / L.

10. The electrolyte according to claim 6, characterized in that, The second solvent includes at least one of aromatic compounds, ester compounds, ether compounds, sulfone compounds, and nitrile compounds.

11. The electrolyte according to claim 6, characterized in that, The second solvent includes fluorinated aromatic compounds.

12. The electrolyte according to claim 6, characterized in that, The second solvent includes ethylene carbonate, methyl ethyl carbonate, fluoroethylene carbonate, difluoroethylene carbonate, diethyl carbonate, methyl trifluoroethyl carbonate, dimethyl carbonate, benzene, toluene, p-xylene, m-xylene, o-xylene, fluorobenzene, p-difluorobenzene, m-difluorobenzene, o-difluorobenzene, trifluorotoluene, trifluoromethoxybenzene, perfluoropentanone, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,2-bis(1,1,2,2-tetrafluoroethoxy)ethane, bis(2,2, One or more of the following: 2-trifluoroethyl ether, 1,1,2,3,3,3-hexafluoropropylethyl ether, ethyl trifluoromethyl ether, difluoromethyl-2,2,3,3,3-pentafluoropropyl ether, heptafluoropropyl-1,2,2,2-tetrafluoroethyl ether, difluoromethyl-2,2,3,3-tetrafluoropropyl ether, perfluoroisopropylmethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, ethyl-1,1,2,2-tetrafluoroethyl ether, and bis(1,1,2,2-tetrafluoroethyl) ether.

13. The electrolyte according to claim 8, characterized in that, The lithium salt includes one or more of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium trifluoroacetate, lithium tetraphenylborate, lithium trifluoromethanesulfonate, lithium bis(fluorosulfonyl)borate, lithium difluorooxalateborate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

14. The electrolyte according to claim 8, characterized in that, The lithium salt is lithium hexafluorophosphate.

15. A lithium metal battery, characterized in that, The electrolyte includes any one of claims 1 to 14.

16. An electrical appliance, characterized in that, Including the lithium metal battery of claim 15.

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