Electrolyte for secondary lithium battery

Abstract

An electrolyte for a secondary lithium battery. The electrolyte comprises a first solvent, a second solvent, a first lithium salt, and an optional second lithium salt. By formulating the electrolyte from specific solutes and solvents, the interaction between the electrolyte and a lithium-metal negative electrode can be improved, the formation of lithium dendrites and internal electrochemical reactions of a battery can be reduced, the ion conduction performance of the battery can be improved, and the cycle life of the battery can be prolonged, thereby facilitating the commercialization of a lithium-metal solid-state battery.

Description

Electrolyte for secondary lithium battery Technical Field

[0001] The present invention relates to an electrolyte for a secondary lithium battery, and a lithium metal battery or a lithium ion battery containing the electrolyte. Background Art

[0002] Lithium metal batteries are considered one of the next generation of battery technologies. Compared to the currently widely used lithium-ion batteries, lithium metal batteries have higher energy density and can store and deliver more energy in the same volume or weight, making them very important for applications requiring high energy density.

[0003] One of the main challenges facing lithium metal batteries is the interaction between the electrolyte and the lithium metal anode material, which affects the performance of lithium metal batteries. Existing electrolytes typically use lithium salts at a concentration of 1M or lower as the solute. This causes a continuous reaction between the lithium metal anode and the electrolyte, leading to low coulombic efficiency and reduced battery cycle times. Although there are reports of using electrolytes with high lithium salt concentrations to promote the solvation and desolvation of lithium ions, making the lithium metal surface more stable, high salt concentrations lead to increased battery costs, increased electrolyte viscosity, decreased battery efficiency, and reduced charge and discharge rates.

[0004] Regarding electrolyte solvents, commonly used carbonate electrolytes have difficulty suppressing lithium metal dendrite formation, and they also suffer from low voltage stability, poor thermal stability, and a narrow operating temperature range. Simple ether electrolytes easily react with lithium metal, making it difficult to form a stable passivation film on the negative electrode surface. They also have high evaporation and flammability risks and low low-temperature conductivity. Furthermore, traditional ether solvents such as 1,3-dioxolane (DOL) or ethylene glycol dimethyl ether (DME) can cause solvent co-intercalation side reactions at the positive or negative electrode, and have a narrow voltage stability range.

[0005] In order to make lithium metal batteries a reliable energy storage solution, further improvements in the selection and design of electrolytes are needed to address the above-mentioned problems of lithium metal batteries.

[0006] Summary of the Invention

[0007] The present invention aims to improve the interaction between the electrolyte and lithium metal to reduce the formation of lithium dendrites and electrochemical reactions inside the battery, and to improve the performance and safety of lithium metal batteries.

[0008] The generation and accumulation of lithium dendrites can easily lead to the following problems: (1) Reduced safety: If lithium ions are unevenly deposited, it is easy to cause the generation of lithium dendrites; (2) Reduced cycle life: The continuous consumption of lithium metal will reduce the number of cycles that the battery can be cycled, thereby reducing the battery's service life; (3) Degraded battery performance: The reaction between lithium metal and conventional electrolyte will affect the battery's charge and discharge efficiency, causing the battery's coulombic efficiency to continue to decrease, thereby reducing the battery's performance.

[0009] In response to the above problems, the inventors of the present invention have conducted in-depth research and provided a new electrolyte formula with multiple solutes, solvents and additives, which significantly improves the number of cycles of lithium metal batteries and enhances the service life of lithium metal batteries.

[0010] The first aspect of the present invention provides an electrolyte for a lithium battery, wherein the electrolyte for a lithium battery comprises a first solvent, a second solvent, a first lithium salt, and optionally a second lithium salt, wherein

[0011] The first solvent is one or both selected from 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME),

[0012] The second solvent is one or more selected from perfluoroisobutyl methyl ether, perfluoropropyl methyl ether, perfluoropentyl methyl ether, tris(2,2,2-trifluoroethoxy)methane and bis(2,2,2-trifluoroethyl)ether,

[0013] The first lithium salt is one or more selected from lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonyl)imide (LiBETI), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroaluminate (LiAlF6), lithium tetrafluoroborate (LiBF4), lithium fluorosulfonate (LiFSO3), lithium trifluoromethanesulfonate (LiCF3SO3) and lithium perchlorate (LiClO4);

[0014] The second lithium salt is one or more selected from lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium nitrate (LiNO 3 ) and lithium fluoride (LiF).

[0015] In some embodiments of the present invention, the molar ratio of the first solvent to the second solvent is 2:1 to 1:5, preferably 1:1 to 1:3, more preferably 1:2 to 1:2.5, and most preferably 1.4:3.

[0016] In some embodiments of the present invention, the concentration of the first lithium salt is 1M to 2.5M, preferably 1.1M to 2.2M, and more preferably 1.2M to 1.7M, calculated as lithium ions.

[0017] In some embodiments of the present invention, when the second lithium salt is included, the concentration of the second lithium salt is 0.01M to 1M, preferably 0.03M to 0.8M, and more preferably 0.4M to 0.6M, calculated as lithium ions.

[0018] In some embodiments of the present invention, the first solvent is 1,3-dioxolane (DOL).

[0019] In some embodiments of the present invention, the second solvent is perfluoroisobutyl methyl ether.

[0020] In some embodiments of the present invention, the first lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI), or the first lithium salt is a combination of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0021] In some embodiments of the present invention, the second lithium salt is lithium difluorooxalatoborate (LiDFOB), lithium nitrate (LiNO 3 ) or a combination thereof.

[0022] The second aspect of the present invention provides use of the lithium battery electrolyte according to the first aspect of the present invention in a lithium metal battery or a lithium ion battery.

[0023] A third aspect of the present invention provides a lithium battery, characterized in that the lithium battery includes a positive electrode, a negative electrode, a separator, and an electrolyte for a lithium battery according to the first aspect of the present invention.

[0024] In some embodiments of the present invention, the lithium battery is a lithium metal battery or a lithium ion battery.

[0025] Advantageous Effects of the Invention

[0026] The electrolyte of the present invention has the following beneficial technical effects:

[0027] The electrolyte of the present invention, by adding a specific chemical additive (i.e., a second lithium salt), can improve the interaction between the electrolyte and lithium metal, reducing the formation of lithium dendrites and electrochemical reactions within the battery. For example, the second lithium salt, in conjunction with the first lithium salt, can form a protective solid electrolyte interface layer on the lithium metal surface, preventing direct reaction between components in the electrolyte and the lithium metal.

[0028] The present invention improves the performance and safety of lithium metal batteries by adjusting the chemical composition and concentration of the solvent and solute used in the electrolyte. By optimizing parameters such as electrolyte concentration, additive concentration, and electrolyte solvent, the battery's ion conductivity can be enhanced, lithium dendrite growth can be suppressed, and cycle life can be increased.

[0029] By combining multiple lithium salts at moderate concentrations, the present invention increases the battery's energy density, reduces the formation of lithium metal dendrites, and mitigates the reaction between the lithium metal anode and the electrolyte. By adjusting the electrolyte formulation, the present invention modifies the solute effect of lithium ions, employing a dual-solute or triple-solute electrolyte solution to improve the performance of lithium metal batteries without increasing, or only slightly increasing, the lithium salt concentration in the electrolyte.

[0030] In summary, the present invention provides an electrolyte that is stable for lithium metal and ternary cathodes, promotes long battery cycles, ensures uniform lithium metal deposition, and is resistant to high voltages. The electrolyte of the present invention promotes uniform lithium metal deposition, significantly increasing the number of cycles in lithium metal batteries. By extending the battery's cycle life, the lithium metal battery becomes more durable and reliable, reducing the frequency of battery replacement and lowering operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG1 shows the cycle capacity diagram of batteries assembled with electrolytes of formulation A and formulation B at room temperature.

[0032] FIG2 shows the cycle capacity diagram of batteries assembled with electrolytes of Formulation B and Formulation C at room temperature.

[0033] FIG3 shows the cycle capacity diagram of batteries assembled with electrolytes of Formulation B, Formulation D, and Formulation E at room temperature. DETAILED DESCRIPTION

[0034] The present invention will be further described below through specific embodiments. Unless otherwise defined, the terms used herein have the same meanings as those generally understood by those skilled in the art.

[0035] Numerical limits or ranges stated herein are inclusive of the endpoints and specifically include all values ​​and subranges within the numerical limits or ranges.

[0036] The first aspect of the present invention provides an electrolyte for a lithium battery, wherein the electrolyte for a lithium battery comprises a first solvent, a second solvent, a first lithium salt, and optionally a second lithium salt, wherein

[0037] The first solvent is one or both selected from 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME),

[0038] The second solvent is one or more selected from perfluoroisobutyl methyl ether, perfluoropropyl methyl ether, perfluoropentyl methyl ether, tris(2,2,2-trifluoroethoxy)methane and bis(2,2,2-trifluoroethyl)ether,

[0039] The first lithium salt is one or more selected from lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonyl)imide (LiBETI), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroaluminate (LiAlF6), lithium tetrafluoroborate (LiBF4), lithium fluorosulfonate (LiFSO3), lithium trifluoromethanesulfonate (LiCF3SO3) and lithium perchlorate (LiClO4);

[0040] The second lithium salt is one or more selected from lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalatoborate) (LiBOB), lithium nitrate (LiNO 3 ) and lithium fluoride (LiF).

[0041] In the electrolyte of the present invention, the ratio of DOL and DME as the first solvent can be any ratio. The properties of the two materials DOL and DME are relatively similar, and their usage ratio can be determined according to the physical properties (such as viscosity, etc.) required for the electrolyte. For example, in some embodiments, the volume ratio of DOL to DME can be 10:1 to 1:10, such as 5:1, 3:1, 2:1, 1:1, 1:2, 1:3, 1:5, etc. In some embodiments, the first solvent is DOL. In some embodiments, the first solvent is DME. In a preferred embodiment, the first solvent is DOL.

[0042] In the electrolyte of the present invention, the second solvent is one or more selected from perfluoroisobutyl methyl ether, perfluoropropyl methyl ether, perfluoropentyl methyl ether, tris(2,2,2-trifluoroethoxy)methane, and bis(2,2,2-trifluoroethyl)ether. The inventors have discovered that using these polyfluoroethers as solvents instead of the prior art 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) can improve the cycle life of lithium metal batteries.

[0043] Perfluoroisobutyl methyl ether is (CF3)2CFCF2OCH3, perfluoropropyl methyl ether is CF3CF2CF2OCH3, perfluoropentyl methyl ether is (CF3)2CFCF(OCH3)CF3, tris(2,2,2-trifluoroethoxy)methane (Tris(2,2,2-trifluoroethyl)orthoformate) is HC(O-CH2CF3)3, and bis(2,2,2-trifluoroethyl)ether is CF3CH2OCH2CF3. In certain embodiments, as the second solvent, fluorinated ethers such as perfluoroisobutyl methyl ether, perfluoropropyl methyl ether, perfluoropentyl methyl ether, tris(2,2,2-trifluoroethoxy)methane and bis(2,2,2-trifluoroethyl)ether can be mixed and used to adjust the physical properties of the electrolyte. In a preferred embodiment, the second solvent comprises perfluoroisobutyl methyl ether, and one or more other fluorinated ethers, such as a mixture of perfluoroisobutyl methyl ether and perfluoropropyl methyl ether, a mixture of perfluoroisobutyl methyl ether and perfluoropentyl methyl ether, etc. In a most preferred embodiment, the second solvent is perfluoroisobutyl methyl ether.

[0044] In the electrolyte of the present invention, the molar ratio of the first solvent to the second solvent is 2:1 to 1:5, preferably 1:1 to 1:3, more preferably 1:2 to 1:2.5, and most preferably 1.4:3. For example, in some embodiments, the molar ratio of the first solvent to the second solvent can be 2:1, 1.5:1, 1:1, 1:1.5, 1:2, 1:2.5, 1:3, 1:4, 1:5, etc., as well as any ratio within the above-mentioned arbitrary molar ratio range. It should be understood that the first solvent (or the second solvent) can be only one solvent or a combination of multiple solvents, and the molar numbers thereof should be combined and calculated and then used to calculate the molar ratio of the two solvents.

[0045] In the electrolyte of the present invention, the first lithium salt is preferably lithium bis(fluorosulfonyl)imide (LiFSI), more preferably a combination of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI). In some embodiments, the concentration of the first lithium salt is 1M to 2.5M, preferably 1.1M to 2.2M, and more preferably 1.2M to 1.7M, in terms of lithium ions. For example, in some embodiments, the concentration of the first lithium salt may be 1M, 1.1M, 1.2M, 1.3M, 1.4M, 1.5M, 1.6M, 1.7M, 1.8M, 1.9M, 2.0M, 2.1M, 2.2M, etc., and any value within the above arbitrary concentration range. When the first lithium salt includes only one lithium salt, its concentration is 1M or more, preferably 1.2M or more. When the first lithium salt also includes another lithium salt, the concentration of the other lithium salt is 0.2M or more, preferably 0.3M to 1.0M, and more preferably 0.4M to 0.6M. For example, in some embodiments, when the first lithium salt is composed of two lithium salts, the concentration of one of the lithium salts can be 0.8M, 0.9M, 1M, 1.1M, 1.2M, 1.3M, 1.4M, 1.5M, etc., and the concentration of the other lithium salt can be 0.2M, 0.3M, 0.4M, 0.5M, 0.6M, 0.7M, 0.8M, 0.9M, 1M, etc. In some embodiments, the first lithium salt can also be composed of more than two lithium salts. The inventors have found that when a moderate concentration of multiple lithium salts is used, the formation of a solid electrolyte interface (SEI) film and the uniform deposition of lithium can be promoted.

[0046] The electrolyte of the present invention may include one or more second lithium salts. The second lithium salt is preferably lithium difluorooxalatoborate (LiDFOB), lithium nitrate (LiNO3) or a combination thereof, more preferably LiDFOB. When the second lithium salt is included, the concentration of the second lithium salt is 0.01M to 1M, preferably 0.03M to 0.8M, and more preferably 0.3M to 0.6M, calculated as lithium ions. For example, in certain embodiments, the concentration of the second lithium salt may be 0.01M, 0.03M, 0.05M, 0.1M, 0.15M, 0.2M, 0.25M, 0.3M, 0.4M, 0.5M, 0.6M, 0.7M, 0.8M, 0.9M, 1M, etc., and any value within the above concentration range. In certain embodiments, the second lithium salt may also be composed of two or more lithium salts. The inventors have found that even when only a small amount of the second lithium salt is added to the electrolyte, the uniform deposition of lithium metal is greatly improved. In addition, when the second lithium salt is used simultaneously with multiple first lithium salts, such a multi-solute solution can greatly improve the battery cycle life.

[0047] It should be understood that in the prior art, to improve the performance of the electrolyte, it is generally necessary to significantly increase the concentration of the lithium salt. Although the lithium salt concentration in the electrolyte of the present invention is slightly higher than that of the prior art, the inventors have discovered through research that the combination of two or three lithium salts can change the solubilization effect of lithium ions, allowing the two-solute or three-solute electrolyte to achieve the same or better performance at a lower total concentration than a single-solute electrolyte.

[0048] In an exemplary preferred embodiment of the present invention, the first solvent is 1,3-dioxolane (DOL), and / or

[0049] The second solvent is perfluoroisobutyl methyl ether, and / or

[0050] The first lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI), or the first lithium salt is a combination of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and / or

[0051] The second lithium salt is lithium difluorooxalatoborate (LiDFOB).

[0052] The second aspect of the present invention provides use of the lithium battery electrolyte according to the first aspect of the present invention in a lithium metal battery.

[0053] A third aspect of the present invention provides a lithium battery, characterized in that the lithium battery includes a positive electrode, a negative electrode, a separator, and an electrolyte for a lithium battery according to the first aspect of the present invention.

[0054] In some embodiments of the present invention, the lithium battery is a lithium metal battery. There are no particular restrictions on the materials and preparation methods of other parts of the lithium metal battery except the electrolyte, and conventional materials and preparation methods in the art can be used.

[0055] Example

[0056] The present invention is described in detail below by way of examples, which are not intended to limit the present invention. The experimental methods in the following examples are conventional methods unless otherwise specified. The reagents used in the following examples are commercially available unless otherwise specified.

[0057] In the following examples and comparative examples, the relevant compounds and their abbreviations are as follows:

[0058] LiFSI: lithium bis(fluorosulfonyl)imide

[0059] LiTFSI: lithium bis(trifluoromethanesulfonyl)imide

[0060] LiPF6: lithium hexafluorophosphate

[0061] LiCF3SO3: lithium trifluoromethanesulfonate

[0062] LiDFOB: lithium difluorooxalatoborate

[0063] LiNO3: lithium nitrate

[0064] DOL: 1,3-dioxolane

[0065] Perfluoroisobutyl methyl ether (CAS#: 163702-08-7)

[0066] TTE: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether

[0067] Comparative Example 1

[0068] This example is used to illustrate the composition and preparation method of a lithium battery electrolyte as a comparative example. The composition of the electrolyte of this comparative example is as follows, also referred to as Formula A herein.

[0069] First solvent: DOL

[0070] Second solvent: TTE

[0071] The molar ratio of the first solvent to the second solvent: DOL:TTE=1.4:3

[0072] First lithium salt: 1.2M LiFSI (final concentration, the same below)

[0073] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent TTE according to a molar ratio, take the corresponding weight of lithium salt LiFSI and add it to the mixed solvent, stir until it is completely dissolved, and form formula A.

[0074] Example 1

[0075] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formulation B herein.

[0076] First solvent: DOL

[0077] Second solvent: perfluoroisobutyl methyl ether

[0078] The molar ratio of the first solvent to the second solvent is: DOL:perfluoroisobutyl methyl ether = 1.4:3

[0079] The first lithium salt: 1.2M LiFSI

[0080] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take the corresponding weight of lithium salt LiFSI and add it to the mixed solvent, stir until completely dissolved, and form formula B.

[0081] Example 2

[0082] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formulation C herein.

[0083] First solvent: DOL

[0084] Second solvent: perfluoroisobutyl methyl ether

[0085] The molar ratio of the first solvent to the second solvent is: DOL:perfluoroisobutyl methyl ether = 1.4:3

[0086] The first lithium salt: 1.2M LiFSI

[0087] Second lithium salt: 0.03M LiDFOB

[0088] Preparation method of the electrolyte: a first solvent DOL and a second solvent perfluoroisobutyl methyl ether are mixed according to a molar ratio, corresponding weights of lithium salts LiFSI and LiDFOB are added to the mixed solvents, and stirred until completely dissolved to form formula C.

[0089] Example 3

[0090] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formulation D herein.

[0091] First solvent: DOL

[0092] Second solvent: perfluoroisobutyl methyl ether

[0093] The molar ratio of the first solvent to the second solvent is: DOL:perfluoroisobutyl methyl ether = 1.4:3

[0094] First lithium salt: 1.2M LiFSI and 1.0M LiTFSI

[0095] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take the corresponding weight of lithium salts LiFSI and LiTFSI and add them to the mixed solvents, stir until completely dissolved, and form formula D.

[0096] Example 4

[0097] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formulation E herein.

[0098] First solvent: DOL

[0099] Second solvent: perfluoroisobutyl methyl ether

[0100] The molar ratio of the first solvent to the second solvent is: DOL:perfluoroisobutyl methyl ether = 1.4:3

[0101] First lithium salt: 1.2M LiFSI and 0.5M LiTFSI

[0102] Second lithium salt: 0.5M LiDFOB

[0103] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to the molar ratio, take the corresponding weight of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula E.

[0104] Example 5

[0105] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formula F herein.

[0106] First solvent: DOL

[0107] Second solvent: perfluoropropyl methyl ether

[0108] The molar ratio of the first solvent to the second solvent: DOL: perfluoropropyl methyl ether = 1.4:3

[0109] First lithium salt: 1.2M LiFSI and 0.5M LiTFSI

[0110] Second lithium salt: 0.5M LiDFOB

[0111] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoropropyl methyl ether according to the molar ratio, take the corresponding weight of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula F.

[0112] Example 6

[0113] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formulation G herein.

[0114] First solvent: DOL

[0115] Second solvent: bis(2,2,2-trifluoroethyl) ether

[0116] The molar ratio of the first solvent to the second solvent: DOL: bis(2,2,2-trifluoroethyl) ether = 1.4:3

[0117] First lithium salt: 1.2M LiFSI and 0.5M LiTFSI

[0118] Second lithium salt: 0.5M LiDFOB

[0119] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent bis(2,2,2-trifluoroethyl) ether according to the molar ratio, take the corresponding weight of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula G.

[0120] Example 7

[0121] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formula H herein.

[0122] First solvent: DOL

[0123] Second solvent: perfluoroisobutyl methyl ether

[0124] The molar ratio of the first solvent to the second solvent is: DOL:perfluoroisobutyl methyl ether = 1.4:3

[0125] First lithium salt: 1.2M LiFSI and 0.5M LiTFSI

[0126] Second lithium salt: 0.03M LiNO3

[0127] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to the molar ratio, take the corresponding weight of lithium salts LiFSI, LiTFSI and LiNO3 into the mixed solvent, and stir until completely dissolved to form formula H.

[0128] Example 8

[0129] This example is used to illustrate the composition and preparation method of the lithium battery electrolyte of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formula I herein.

[0130] First solvent: DOL

[0131] Second solvent: perfluoroisobutyl methyl ether

[0132] The molar ratio of the first solvent to the second solvent is: DOL:perfluoroisobutyl methyl ether = 1.4:3

[0133] First lithium salt: 1.2M LiFSI and 0.5M LiTFSI

[0134] Second lithium salt: 0.03M LiNO3 and 0.5M LiDFOB

[0135] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to the molar ratio, take the corresponding weight of lithium salts LiFSI, LiTFSI, LiNO3 and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula I.

[0136] Example 9

[0137] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formula J herein.

[0138] First solvent: DOL

[0139] Second solvent: perfluoroisobutyl methyl ether

[0140] The molar ratio of the first solvent to the second solvent is: DOL:perfluoroisobutyl methyl ether = 1.4:3

[0141] First lithium salt: 1.2M LiFSI and 0.3M LiPF6

[0142] Second lithium salt: 0.5M LiDFOB

[0143] Preparation method of the electrolyte: mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to the molar ratio, take the corresponding weight of lithium salts LiFSI, LiPF6 and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula J.

[0144] Example 10

[0145] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formulation K herein.

[0146] First solvent: DOL

[0147] Second solvent: perfluoroisobutyl methyl ether

[0148] The molar ratio of the first solvent to the second solvent is: DOL:perfluoroisobutyl methyl ether = 1.4:3

[0149] First lithium salt: 1.2M LiFSI and 0.3M LiCF3SO3

[0150] Second lithium salt: 0.5M LiDFOB

[0151] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to the molar ratio, take the corresponding weight of lithium salts LiFSI, LiCF3SO3 and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula K.

[0152] Example 11

[0153] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formula L herein.

[0154] First solvent: DOL

[0155] Second solvent: perfluoroisobutyl methyl ether

[0156] The molar ratio of the first solvent to the second solvent is: DOL:perfluoroisobutyl methyl ether = 2:1

[0157] First lithium salt: 1.2M LiFSI and 0.5M LiTFSI

[0158] Second lithium salt: 0.5M LiDFOB

[0159] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to the molar ratio, take the corresponding weight of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula L.

[0160] Example 12

[0161] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formulation M herein.

[0162] First solvent: DOL

[0163] Second solvent: perfluoroisobutyl methyl ether

[0164] The molar ratio of the first solvent to the second solvent is: DOL:perfluoroisobutyl methyl ether = 1:1

[0165] First lithium salt: 1.2M LiFSI and 0.5M LiTFSI

[0166] Second lithium salt: 0.5M LiDFOB

[0167] Preparation method of the electrolyte: a first solvent DOL and a second solvent perfluoroisobutyl methyl ether are mixed according to a molar ratio, corresponding weights of lithium salts LiFSI, LiTFSI and LiDFOB are added to the mixed solvents, and stirred until completely dissolved to form formula M.

[0168] Example 13

[0169] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formulation N herein.

[0170] First solvent: DOL

[0171] Second solvent: perfluoroisobutyl methyl ether

[0172] The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1:1.5

[0173] First lithium salt: 1.2M LiFSI and 0.5M LiTFSI

[0174] Second lithium salt: 0.5M LiDFOB

[0175] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take the corresponding weight of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula N.

[0176] Example 14

[0177] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formulation O herein.

[0178] First solvent: DOL

[0179] Second solvent: perfluoroisobutyl methyl ether

[0180] The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1:2

[0181] First lithium salt: 1.2M LiFSI and 0.5M LiTFSI

[0182] Second lithium salt: 0.5M LiDFOB

[0183] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to the molar ratio, take the corresponding weight of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula O.

[0184] Example 15

[0185] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formulation P herein.

[0186] First solvent: DOL

[0187] Second solvent: perfluoroisobutyl methyl ether

[0188] The molar ratio of the first solvent to the second solvent is: DOL:perfluoroisobutyl methyl ether = 1.4:3

[0189] First lithium salt: 0.8M LiFSI and 0.8M LiTFSI

[0190] Second lithium salt: 0.5M LiDFOB

[0191] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to the molar ratio, take the corresponding weight of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula P.

[0192] Example 16

[0193] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formula Q herein.

[0194] First solvent: DOL

[0195] Second solvent: perfluoroisobutyl methyl ether

[0196] The molar ratio of the first solvent to the second solvent is: DOL:perfluoroisobutyl methyl ether = 1.4:3

[0197] First lithium salt: 1M LiFSI and 0.7M LiTFSI

[0198] Second lithium salt: 0.5M LiDFOB

[0199] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take the corresponding weight of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula Q.

[0200] Example 17

[0201] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formulation R herein.

[0202] First solvent: DOL

[0203] Second solvent: perfluoroisobutyl methyl ether

[0204] The molar ratio of the first solvent to the second solvent is: DOL:perfluoroisobutyl methyl ether = 1.4:3

[0205] First lithium salt: 1.2M LiFSI and 0.4M LiTFSI

[0206] Second lithium salt: 0.6M LiDFOB

[0207] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to the molar ratio, take the corresponding weight of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula R.

[0208] Example 18

[0209] This example is used to illustrate the composition and preparation method of the electrolyte for lithium batteries of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formulation S herein.

[0210] First solvent: DOL

[0211] Second solvent: perfluoroisobutyl methyl ether

[0212] The molar ratio of the first solvent to the second solvent is: DOL:perfluoroisobutyl methyl ether = 1.4:3

[0213] First lithium salt: 1.2M LiFSI and 0.6M LiTFSI

[0214] Second lithium salt: 0.4 M LiDFOB

[0215] Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to the molar ratio, take the corresponding weight of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula S.

[0216] Test Case

[0217] This example is used to illustrate the characterization method of electrolyte for lithium batteries.

[0218] First, batteries were assembled using the electrolytes of formula AS prepared in Comparative Example 1 and Examples 1-18. The positive electrode, negative electrode, and separator of each battery were made of the same material. The positive electrode of the battery was made of ternary high nickel material with a loading capacity of 4 mAh / cm 2 ; The negative electrode uses 20 micron lithium metal; the battery separator is a PP-ceramic film. For each of the above formulas AS, three batteries were made and the batteries were tested after storage for 24 hours. The battery test results were obtained and analyzed using the test standard of 0.33C charging and 1C discharging. The battery cycle number test was tested until the battery capacity retention rate dropped to 80% SOH (state of health). The composition and test results of all formulas are summarized in Table 1. The cycle capacity diagrams of some formulas are shown in Figures 1-3.

[0219] Figure 1 shows the cycling performance data at room temperature for batteries assembled using electrolytes from Formulations A and B, respectively. This comparison shows that Formulation B, which uses perfluoroisobutyl methyl ether as a solvent, performs better than TTE. Specifically, the capacity of Formulation A drops below 80% SOH after the 86th cycle, while the capacity of Formulation B drops below 80% SOH after the 113th cycle. In other words, at 80% SOH, Formulation B improves cycle life by over 20% compared to Formulation A.

[0220] Figure 2 shows the cycling performance data at room temperature for batteries assembled using electrolytes from Formulations B and C, respectively. A comparison shows that the addition of 0.03M of the second lithium salt, LiDFOB, to the electrolyte increases the battery's cycle life by approximately 30%. Specifically, the capacity of Formulation B drops below 80% SOH after the 113th cycle, while the capacity of Formulation C drops below 80% SOH after the 144th cycle. This comparison demonstrates that the LiDFOB additive significantly aids in uniform lithium metal deposition, thereby improving the battery's cycle life.

[0221] Figure 3 shows the cycling performance data at room temperature for batteries assembled using electrolytes from Formulations B, D, and E, respectively. As shown, the capacity of Formulation D drops below 80% SOH after the 265th cycle, while the capacity of Formulation E drops below 80% SOH after the 281st cycle. A comparison shows that using a combination of LiFSI and LiTFSI as the first lithium salt and increasing the lithium salt concentration significantly improves the battery's cycle life. While maintaining the total lithium salt concentration, replacing part of the first lithium salt, LiTFSI, with the second lithium salt, LiDFOB, further improves the battery's cycle life. Overall, using a moderate concentration of the three lithium salts (i.e., Formulation E, LiFSI, LiTFSI, and LiDFOB) in the solvents DOL and perfluoroisobutyl methyl ether facilitates lithium metal SEI formation and uniform lithium deposition, resulting in a more than threefold improvement in 80% SOH service life compared to the electrolyte using a single solute and TTE as the solvent (Formulation A).

[0222] It can be seen from the test data of other embodiments in Table 1 that when the second solvent is selected from the fluorine-containing solvent within the scope of the present invention, and at the same time, through the combination of multiple solutes of the first lithium salt and the second lithium salt, an excellent battery capacity cycling effect can be achieved at a low total lithium salt concentration.

[0223] In summary, the present invention can improve the interaction between the electrolyte and the lithium metal negative electrode by selecting specific electrolyte solute and solvent composition, reduce the formation of lithium dendrites and electrochemical reactions inside the battery, improve the battery's ion conductivity performance, and increase the battery's cycle life, which is conducive to the commercialization of lithium metal solid-state batteries.

[0224] The above examples are used to describe exemplary embodiments of the present invention, but the present invention is not limited thereto. It should be understood by those skilled in the art that the above examples are for illustrative purposes only, and the specific embodiments and examples of the present invention should not be construed as limiting the scope of the present invention. The embodiments can be changed and modified within the scope of the present invention, and such changes and modifications should fall within the scope of protection of the present invention.

Claims

1. An electrolyte for a lithium battery, characterized in that: The lithium battery electrolyte comprises a first solvent, a second solvent, a first lithium salt, and optionally a second lithium salt, wherein The first solvent is one or two selected from 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME), The second solvent is one or more selected from perfluoroisobutyl methyl ether, perfluoropropyl methyl ether, perfluoropentyl methyl ether, tris(2,2,2-trifluoroethoxy)methane and bis(2,2,2-trifluoroethyl) ether, The first lithium salt is selected from one or more of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonyl)imide (LiBETI), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroaluminate (LiAlF6), lithium tetrafluoroborate (LiBF4), lithium fluorosulfonate (LiFSO3), lithium trifluoromethanesulfonate (LiCF3SO3) and lithium perchlorate (LiClO4); The second lithium salt is one or more selected from lithium difluorooxalatoborate (LiDFOB), lithium bis(oxalateborate) (LiBOB), lithium nitrate (LiNO3) and lithium fluoride (LiF).

2. The lithium battery electrolyte according to claim 1, characterized in that The molar ratio of the first solvent to the second solvent is 2:1 to 1:5, preferably 1:1 to 1:

3.

3. The lithium battery electrolyte according to claim 1 or 2, characterized in that: Calculated in terms of lithium ions, the concentration of the first lithium salt is 1M to 2.5M, preferably 1.1M to 2.2M, and more preferably 1.2M to 1.7M.

4. The lithium battery electrolyte according to any one of claims 1 to 3, characterized in that When the second lithium salt is included, the concentration of the second lithium salt is 0.01M to 1M, preferably 0.03M to 0.8M, calculated as lithium ions.

5. The lithium battery electrolyte according to any one of claims 1 to 4, characterized in that: The first solvent is 1,3-dioxolane (DOL).

6. The lithium battery electrolyte according to any one of claims 1 to 5, characterized in that: The second solvent is perfluoroisobutyl methyl ether.

7. The lithium battery electrolyte according to any one of claims 1 to 6, characterized in that The first lithium salt is lithium bis(fluorosulfonyl)imide (LiFSI), or The first lithium salt is a combination of lithium bis(fluorosulfonyl)imide (LiFSI) and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

8. The lithium battery electrolyte according to any one of claims 1 to 7, characterized in that The second lithium salt is lithium difluorooxalatoborate (LiDFOB), lithium nitrate (LiNO3) or a combination thereof.

9. Use of the lithium battery electrolyte according to any one of claims 1 to 8 in a lithium metal battery or a lithium ion battery.

10. A lithium battery, characterized in that: The lithium battery comprises a positive electrode, a negative electrode, a separator, and an electrolyte for a lithium battery according to any one of claims 1 to 8.

11. The lithium battery according to claim 10, characterized in that: The lithium battery is a lithium metal battery or a lithium ion battery.

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