Electrolyte for secondary lithium battery

Abstract

The application discloses an electrolyte for a secondary lithium battery, which comprises a first solvent, a second solvent, a first lithium salt and optionally a second lithium salt. By selecting specific electrolyte solute and solvent composition, the application can improve the interaction between the electrolyte and the lithium metal negative electrode, reduce the formation of lithium dendrites and the electrochemical reaction inside the battery, improve the ion conduction performance of the battery, improve the cycle life of the battery, and is beneficial to the commercialization of the lithium metal solid-state battery.

Description

TECHNICAL FIELD

[0001] The present application relates to an electrolyte for a secondary lithium battery, and a lithium metal battery or a lithium ion battery comprising the same. BACKGROUND

[0002] Lithium metal batteries are considered as one of the next generation battery technologies. Compared with the widely used lithium ion batteries, lithium metal batteries have higher energy density, which can store and provide more energy in the same volume or weight, which is very important for applications requiring high energy density.

[0003] One of the main challenges faced by lithium metal batteries is the interaction between the electrolyte and the lithium metal negative material, which affects the performance of the lithium metal battery. The electrolyte of the prior art usually uses 1M or lower concentration of lithium salt as solute, which causes continuous reaction between the lithium metal negative electrode and the electrolyte, resulting in low coulombic efficiency of the battery, reduced cycle number of the battery, etc. Although there are reports of using high-concentration lithium salt electrolyte, by promoting the solvation and desolvation process of lithium ions, the surface of lithium metal is more stable; but high salt content will lead to increased battery cost, increased viscosity of the electrolyte, reduced battery efficiency, and reduced charge-discharge rate.

[0004] In terms of the solvent of the electrolyte, the commonly used carbonate electrolyte is difficult to inhibit the formation of lithium metal dendrites, and has poor low-voltage stability, thermal stability and narrow working temperature range; simple ether electrolyte is prone to react with lithium metal, and is difficult to form a stable passivation film on the negative electrode surface, and has high evaporation and flammability risk and low low-temperature conductivity. In addition, the traditional ether solvent 1,3-dioxolane (DOL) or ethylene glycol dimethyl ether (DME) will have solvent co-intercalation side reactions at the positive electrode or negative electrode, and the voltage stability range is narrow.

[0005] In order to make lithium metal batteries a reliable energy storage solution, further improvement is needed in the selection and design of the electrolyte to solve the above problems of lithium metal batteries. SUMMARY

[0006] The present application aims to improve the interaction between the electrolyte and the lithium metal, to reduce the formation of lithium dendrites and the electrochemical reaction inside the battery, and to improve the performance and safety of the lithium metal battery.

[0007] The generation and accumulation of lithium dendrites can easily lead to the following problems: (1) reduced safety: if lithium ions are deposited unevenly, lithium dendrites are easily produced; (2) reduced cycle life: the continuous consumption of lithium metal will reduce the number of battery cycles, thereby reducing the service life of the battery; (3) reduced battery performance: the reaction between lithium metal and conventional electrolyte will affect the charge-discharge efficiency of the battery, resulting in a continuous decrease in the coulombic efficiency of the battery, thereby reducing the performance of the battery.

[0008] To solve the above problems, the inventors of the present application have provided a novel electrolyte formulation of multiple solutes, solvents and additives, which significantly improves the cycle number of lithium metal batteries and prolongs the service life of lithium metal batteries.

[0009] The first aspect of the present application provides an electrolyte for lithium batteries, which comprises a first solvent, a second solvent, a first lithium salt, and optionally a second lithium salt, wherein

[0010] The first solvent is one or both selected from 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME),

[0011] 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,

[0012] The first lithium salt is one or more selected from lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonyl)imide (LiBETI), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroaluminate (LiAlF6), lithium tetrafluoroborate (LiBF4), lithium fluorosulfonate (LiFSO3), lithium triflate (LiCF3SO3) and lithium perchlorate (LiClO4);

[0013] The second lithium salt is one or more selected from lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium nitrate (LiNO3) and lithium fluoride (LiF).

[0014] In some embodiments of the present application, 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.

[0015] In some embodiments of the present application, 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.

[0016] In some embodiments of the present application, 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, in terms of lithium ions.

[0017] In some embodiments of the present application, the first solvent is 1,3-dioxolane (DOL).

[0018] In some embodiments of the present application, the second solvent is perfluoroisobutyl methyl ether.

[0019] In some embodiments of the present application, 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).

[0020] In some embodiments of the present application, the second lithium salt is lithium difluoro(oxalato)borate (LiDFOB), lithium nitrate (LiNO3), or a combination thereof.

[0021] The second aspect of the present application provides an application of the electrolyte for lithium batteries according to the first aspect of the present application in a lithium metal battery or a lithium ion battery.

[0022] The third aspect of the present application provides a lithium battery, characterized in that the lithium battery comprises a positive electrode, a negative electrode, a separator, and an electrolyte for lithium batteries according to the first aspect of the present application.

[0023] In some embodiments of the present application, the lithium battery is a lithium metal battery or a lithium ion battery.

[0024] Advantages of the present application

[0025] The electrolyte of the present application has the following technical advantages:

[0026] The electrolyte of the present application can improve the interaction between the electrolyte and the lithium metal, reduce the formation of lithium dendrites and the electrochemical reaction inside the battery by adding specific chemical additives (i.e. the second lithium salt). For example, the second lithium salt and the first lithium salt can jointly form a protective solid electrolyte interface layer on the surface of the lithium metal, preventing the components in the electrolyte from directly reacting with the lithium metal.

[0027] The present application can improve the performance and safety of lithium metal batteries by adjusting the chemical composition and concentration of the solvents and solutes used in the electrolyte. By optimizing the concentration of the electrolyte, the concentration of the additives, and the electrolyte solvent, etc., the ion conduction performance of the battery can be improved, the growth of lithium dendrites can be inhibited, and the cycle life can be improved.

[0028] The present application can increase the energy density of the battery and reduce the formation of lithium metal dendrites and the reaction between the lithium metal anode and the electrolyte by using a combination of multiple lithium salts with moderate concentrations. The present application has changed the solvation effect of lithium ions by adjusting the formulation of the electrolyte, and has improved the performance of lithium metal batteries by using a double-solute electrolyte or a triple-solute electrolyte solution without increasing or only slightly increasing the lithium salt concentration of the electrolyte.

[0029] In summary, the present application provides an electrolyte that is stable to lithium metal and ternary cathodes, and can promote long cycling of the battery, solve lithium metal uniform deposition, and is resistant to high pressure. The electrolyte of the present application can promote the uniform deposition of lithium metal, thereby greatly increasing the cycle number of lithium metal batteries. By enhancing the cycle life of the battery, the lithium metal battery will be more durable and reliable, reducing the frequency of battery replacement and reducing the cost of use. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 A graph showing the cycle capacity of a battery assembled with the electrolyte of Formulation A and Formulation B at room temperature, respectively.

[0031] Figure 2 A graph showing the cycle capacity of a battery assembled with the electrolyte of Formulation B and Formulation C at room temperature, respectively.

[0032] Figure 3 A graph showing the cycle capacity of a battery assembled with the electrolyte of Formulation B, Formulation D and Formulation E at room temperature, respectively. DETAILED DESCRIPTION

[0033] The present application will be further described by specific embodiments. Unless otherwise defined, the terms used herein have the same meaning as commonly understood by one of ordinary skill in the art.

[0034] The numerical limits or ranges expressed herein include the endpoints, specifically including all values and sub-ranges within the numerical limits or ranges.

[0035] A first aspect of the present application provides an electrolyte for a lithium battery, the electrolyte for a lithium battery comprising a first solvent, a second solvent, a first lithium salt, and optionally a second lithium salt, wherein

[0036] The first solvent is one or both selected from 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME),

[0037] 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,

[0038] The first lithium salt is one or more selected from lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonyl)imide (LiBETI), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroaluminate (LiAlF6), lithium tetrafluoroborate (LiBF4), lithium fluorosulfate (LiFSO3), lithium triflate (LiCF3SO3) and lithium perchlorate (LiClO4);

[0039] The second lithium salt is one or more selected from the group consisting of lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium nitrate (LiN03), and lithium fluoride (LiF).

[0040] In the electrolyte of the present application, the ratio of DOL and DME as the first solvent can be any ratio. The properties of DOL and DME are similar, and the ratio of their use 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 preferred embodiments, the first solvent is DOL.

[0041] In the electrolyte of the present application, the second solvent is one or more selected from the group consisting of 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 found that, when using the above-mentioned polyfluoroethers instead of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE) known in the prior art as a solvent, the cycle life of a lithium metal battery can be improved.

[0042] Perfluoroisobutyl methyl ether is (CF3)2CF2OCH3, perfluoropropyl methyl ether is CF3CF2CF2OCH3, perfluoropentyl methyl ether is (CF3)2CF(OCH3)CF3, tris(2,2,2-trifluoroethyl) orthoformate is HC(O-CH2CF3)3, and bis(2,2,2-trifluoroethyl) ether is CF3CH2OCH2CF3. In some embodiments, as the second solvent, the fluorine-containing ethers such as perfluoroisobutyl methyl ether, perfluoropropyl methyl ether, perfluoropentyl methyl ether, tris(2,2,2-trifluoroethyl) orthoformate, and bis(2,2,2-trifluoroethyl) ether can be used in a mixture to adjust the physical properties of the electrolyte. In preferred embodiments, the second solvent comprises perfluoroisobutyl methyl ether, and one or more other fluorine-containing ethers, for example, a mixture of perfluoroisobutyl methyl ether and perfluoropropyl methyl ether, a mixture of perfluoroisobutyl methyl ether and perfluoropentyl methyl ether, etc. In the most preferred embodiments, the second solvent is perfluoroisobutyl methyl ether.

[0043] In the electrolyte of the present application, 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, most preferably 1.4:3. For example, in certain 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 any of the above-mentioned molar ratio ranges. It should be understood that the first solvent (or the second solvent) can be only one solvent, or a combination of multiple solvents, the molar number of which should be combined for the calculation of the molar ratio of the two solvents.

[0044] In the electrolyte of the present application, 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 certain embodiments, the concentration of the first lithium salt, in terms of lithium ions, is 1 M to 2.5 M, preferably 1.1 M to 2.2 M, more preferably 1.2 M to 1.7 M. For example, in certain embodiments, the concentration of the first lithium salt can be 1 M, 1.1 M, 1.2 M, 1.3 M, 1.4 M, 1.5 M, 1.6 M, 1.7 M, 1.8 M, 1.9 M, 2.0 M, 2.1 M, 2.2 M, etc., as well as any value within any of the above-mentioned concentration ranges. When the first lithium salt includes only one lithium salt, the concentration of the lithium salt is 1 M or more, preferably 1.2 M or more. When the first lithium salt includes another lithium salt, the concentration of the other lithium salt is 0.2 M or more, preferably 0.3 M to 1.0 M, more preferably 0.4 M to 0.6 M. For example, in certain embodiments, when the first lithium salt consists of two lithium salts, the concentration of one of the lithium salts can be 0.8 M, 0.9 M, 1 M, 1.1 M, 1.2 M, 1.3 M, 1.4 M, 1.5 M, etc., and the concentration of the other lithium salt can be 0.2 M, 0.3 M, 0.4 M, 0.5 M, 0.6 M, 0.7 M, 0.8 M, 0.9 M, 1 M, etc. In certain embodiments, the first lithium salt can also consist of more than two lithium salts. The inventors have found that the use of multiple lithium salts at a medium concentration can facilitate the formation of a solid electrolyte interface (SEI) film and the uniform deposition of lithium.

[0045] In the electrolyte of the present application, one or more of the second lithium salt can be included. The second lithium salt is preferably lithium difluoro(oxalato)borate (LiDFOB), lithium nitrate (LiNO3), or a combination thereof, and more preferably LiDFOB. In the case where the second lithium salt is included, the concentration of the second lithium salt is 0.01 M to 1 M, preferably 0.03 M to 0.8 M, and more preferably 0.3 M to 0.6 M, in terms of lithium ions. For example, in some embodiments, the concentration of the second lithium salt can be 0.01 M, 0.03 M, 0.05 M, 0.1 M, 0.15 M, 0.2 M, 0.25 M, 0.3 M, 0.4 M, 0.5 M, 0.6 M, 0.7 M, 0.8 M, 0.9 M, 1 M, and the like, as well as any numerical value within any of the above-mentioned concentration ranges. In some embodiments, the second lithium salt can also consist of two or more lithium salts. The inventors have found that even when a small amount of the second lithium salt is added to the electrolyte, the uniform deposition of lithium metal is greatly improved. Furthermore, when the second lithium salt is used in combination with a plurality of the first lithium salt, such a multi-solute scheme can greatly improve the cycle life of the battery.

[0046] It should be understood that in the prior art, in order to improve the performance of the electrolyte, it is generally necessary to greatly increase the concentration of the lithium salt. Although the concentration of the lithium salt in the electrolyte of the present application is slightly higher than that of the prior art, the inventors have found that when two or three lithium salts are used in combination, the solvation effect of lithium ions can be changed, so that the same or better effect can be achieved at a lower total concentration compared to a single-solute electrolyte.

[0047] In an exemplary preferred embodiment of the present application, the first solvent is 1,3-dioxolane (DOL), and / or

[0048] the second solvent is perfluoroisobutyl methyl ether, and / or

[0049] 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

[0050] the second lithium salt is lithium difluoro(oxalato)borate (LiDFOB).

[0051] The second aspect of the present application provides the use of the above-mentioned electrolyte for lithium batteries according to the first aspect of the present application in a lithium metal battery.

[0052] The third aspect of the present application provides a lithium battery, characterized in that the lithium battery comprises a positive electrode, a negative electrode, a separator, and an electrolyte for lithium batteries according to the first aspect of the present application.

[0053] In some embodiments of the present application, the lithium battery is a lithium metal battery. The materials for the parts of the lithium metal battery other than the electrolyte and the method for producing the same are not particularly limited, and conventional materials and methods in the art can be used.

[0054] Examples

[0055] The present application is described in detail below by way of examples, which are not intended to limit the present application. The experimental methods in the following examples are conventional methods unless otherwise specified. The reagents and the like used in the following examples are commercially available unless otherwise specified.

[0056] In each of the formulations of the following examples and comparative examples, the relevant compounds and their abbreviations are as follows, respectively

[0057] • LiFSI: lithium bis(fluorosulfonyl)imide

[0058] • LiTFSI: lithium bis(trifluoromethanesulfonyl)imide

[0059] • LiPF6: lithium hexafluorophosphate

[0060] • LiCF3SO3: lithium trifluoromethanesulfonate

[0061] • LiDFOB: lithium difluoro(oxalato)borate

[0062] • LiNO3: lithium nitrate

[0063] • DOL: 1,3-dioxolane

[0064] • Perfluoroisobutyl methyl ether (CAS # : 163702-08-7)

[0065] • TTE: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether

[0066] Comparative Example 1

[0067] This example is for illustrating the composition and the method for producing the electrolyte for lithium battery as a comparative example. The composition of the electrolyte of this comparative example is as follows, which is also referred to as Formulation A herein.

[0068] First solvent: DOL

[0069] Second solvent: TTE

[0070] Molar ratio of the first solvent and the second solvent: DOL : TTE = 1.4 : 3

[0071] First lithium salt: 1.2 M of LiFSI (final concentration, same below)

[0072] Preparation method of electrolyte: mix the first solvent DOL and the second solvent TTE according to the molar ratio, take the corresponding weight of lithium salt LiFSI and add it into the mixed solvent, stir until completely dissolved, to form formula A.

[0073] Example 1

[0074] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as formula B herein.

[0075] First solvent: DOL

[0076] Second solvent: perfluoroisobutyl methyl ether

[0077] Molar ratio of the first solvent and the second solvent: DOL: perfluoroisobutyl methyl ether = 1.4:3

[0078] First lithium salt: 1.2M of LiFSI

[0079] Preparation method of electrolyte: mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to the molar ratio, take the corresponding weight of lithium salt LiFSI and add it into the mixed solvent, stir until completely dissolved, to form formula B.

[0080] Example 2

[0081] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as formula C herein.

[0082] First solvent: DOL

[0083] Second solvent: perfluoroisobutyl methyl ether

[0084] Molar ratio of the first solvent and the second solvent: DOL: perfluoroisobutyl methyl ether = 1.4:3

[0085] First lithium salt: 1.2M of LiFSI

[0086] Second lithium salt: 0.03M of LiDFOB

[0087] Preparation method of electrolyte: mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to the molar ratio, take the corresponding weight of lithium salt LiFSI and LiDFOB and add it into the mixed solvent, stir until completely dissolved, to form formula C.

[0088] Example 3

[0089] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as formula D herein.

[0090] First solvent: DOL

[0091] Second solvent: perfluoroisobutyl methyl ether

[0092] Molar ratio of the first solvent and the second solvent: DOL : perfluoroisobutyl methyl ether = 1.4:3

[0093] First lithium salt: 1.2M of LiFSI and 1.0M of LiTFSI

[0094] Preparation method of the electrolyte: the first solvent DOL and the second solvent perfluoroisobutyl methyl ether are mixed according to the molar ratio, and the corresponding weight of lithium salt LiFSI and LiTFSI is added to the mixed solvent, stirred until completely dissolved, to form formula D.

[0095] Example 4

[0096] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as formula E herein.

[0097] First solvent: DOL

[0098] Second solvent: perfluoroisobutyl methyl ether

[0099] Molar ratio of the first solvent and the second solvent: DOL : perfluoroisobutyl methyl ether = 1.4:3

[0100] First lithium salt: 1.2M of LiFSI and 0.5M of LiTFSI

[0101] Second lithium salt: 0.5M of LiDFOB

[0102] Preparation method of the electrolyte: the first solvent DOL and the second solvent perfluoroisobutyl methyl ether are mixed according to the molar ratio, and the corresponding weight of lithium salt LiFSI, LiTFSI and LiDFOB is added to the mixed solvent, stirred until completely dissolved, to form formula E.

[0103] Example 5

[0104] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as formula F herein.

[0105] First solvent: DOL

[0106] Second solvent: perfluoroisobutyl methyl ether

[0107] Molar ratio of the first solvent and the second solvent: DOL : perfluoroisobutyl methyl ether = 1.4:3

[0108] First lithium salt: 1.2M of LiFSI and 0.5M of LiTFSI

[0109] Second lithium salt: 0.5M of LiDFOB

[0110] Preparation method of electrolyte: the first solvent DOL and the second solvent perfluoropropyl methyl ether were mixed according to the molar ratio, and the corresponding weight of lithium salt LiFSI, LiTFSI and LiDFOB was added to the mixed solvent, stirred until completely dissolved, and formula F was formed.

[0111] Example 6

[0112] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as formula G herein.

[0113] First solvent: DOL

[0114] Second solvent: bis(2,2,2-trifluoroethyl) ether

[0115] Molar ratio of first solvent and second solvent: DOL : bis(2,2,2-trifluoroethyl) ether = 1.4:3

[0116] First lithium salt: 1.2M of LiFSI and 0.5M of LiTFSI

[0117] Second lithium salt: 0.5M of LiDFOB

[0118] Preparation method of electrolyte: the first solvent DOL and the second solvent bis(2,2,2-trifluoroethyl) ether were mixed according to the molar ratio, and the corresponding weight of lithium salt LiFSI, LiTFSI and LiDFOB was added to the mixed solvent, stirred until completely dissolved, and formula G was formed.

[0119] Example 7

[0120] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as formula H herein.

[0121] First solvent: DOL

[0122] Second solvent: perfluoroisobutyl methyl ether

[0123] Molar ratio of first solvent and second solvent: DOL : perfluoroisobutyl methyl ether = 1.4:3

[0124] First lithium salt: 1.2M of LiFSI and 0.5M of LiTFSI

[0125] Second lithium salt: 0.03M of LiNO3

[0126] Preparation method of electrolyte: the first solvent DOL and the second solvent perfluoroisobutyl methyl ether were mixed according to the molar ratio, and the corresponding weight of lithium salt LiFSI, LiTFSI and LiNO3 was added into the mixed solvent, stirred until completely dissolved, to form formula H.

[0127] Example 8

[0128] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as formula I herein.

[0129] First solvent: DOL

[0130] Second solvent: perfluoroisobutyl methyl ether

[0131] Molar ratio of the first solvent and the second solvent: DOL : perfluoroisobutyl methyl ether = 1.4:3

[0132] First lithium salt: 1.2M of LiFSI and 0.5M of LiTFSI

[0133] Second lithium salt: 0.03M of LiNO3 and 0.5M of LiDFOB

[0134] Preparation method of electrolyte: the first solvent DOL and the second solvent perfluoroisobutyl methyl ether were mixed according to the molar ratio, and the corresponding weight of lithium salt LiFSI, LiTFSI, LiNO3 and LiDFOB was added into the mixed solvent, stirred until completely dissolved, to form formula I.

[0135] Example 9

[0136] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as formula J herein.

[0137] First solvent: DOL

[0138] Second solvent: perfluoroisobutyl methyl ether

[0139] Molar ratio of the first solvent and the second solvent: DOL : perfluoroisobutyl methyl ether = 1.4:3

[0140] First lithium salt: 1.2M of LiFSI and 0.3M of LiPF6

[0141] Second lithium salt: 0.5M of LiDFOB

[0142] Preparation method of electrolyte: mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to the molar ratio, take the corresponding weight of lithium salt LiFSI, LiPF6 and LiDFOB, add them into the mixed solvent, stir until completely dissolved, and form formula J.

[0143] Example 10

[0144] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as formula K herein.

[0145] First solvent: DOL

[0146] Second solvent: perfluoroisobutyl methyl ether

[0147] Molar ratio of the first solvent and the second solvent: DOL: perfluoroisobutyl methyl ether = 1.4:3

[0148] First lithium salt: 1.2M of LiFSI and 0.3M of LiCF3SO3

[0149] Second lithium salt: 0.5M of LiDFOB

[0150] Preparation method of electrolyte: mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to the molar ratio, take the corresponding weight of lithium salt LiFSI, LiCF3SO3 and LiDFOB, add them into the mixed solvent, stir until completely dissolved, and form formula K.

[0151] Example 11

[0152] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as formula L herein.

[0153] First solvent: DOL

[0154] Second solvent: perfluoroisobutyl methyl ether

[0155] Molar ratio of the first solvent and the second solvent: DOL: perfluoroisobutyl methyl ether = 2:1

[0156] First lithium salt: 1.2M of LiFSI and 0.5M of LiTFSI

[0157] Second lithium salt: 0.5M of LiDFOB

[0158] Preparation method of electrolyte: mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to the molar ratio, take the corresponding weight of lithium salt LiFSI, LiTFSI and LiDFOB, add them into the mixed solvent, stir until completely dissolved, and form formula L.

[0159] Example 12

[0160] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as Formula M herein.

[0161] First solvent: DOL

[0162] Second solvent: perfluoroisobutyl methyl ether

[0163] Molar ratio of the first solvent and the second solvent: DOL : perfluoroisobutyl methyl ether = 1:1

[0164] First lithium salt: 1.2M of LiFSI and 0.5M of LiTFSI

[0165] Second lithium salt: 0.5M of LiDFOB

[0166] 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, add them into the mixed solvent, stir until completely dissolved, and form Formula M.

[0167] Example 13

[0168] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as Formula N herein.

[0169] First solvent: DOL

[0170] Second solvent: perfluoroisobutyl methyl ether

[0171] Molar ratio of the first solvent and the second solvent: DOL : perfluoroisobutyl methyl ether = 1:1.5

[0172] First lithium salt: 1.2M of LiFSI and 0.5M of LiTFSI

[0173] Second lithium salt: 0.5M of LiDFOB

[0174] 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, add them into the mixed solvent, stir until completely dissolved, and form Formula N.

[0175] Example 14

[0176] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as Formula O herein.

[0177] First solvent: DOL

[0178] Second solvent: perfluoroisobutyl methyl ether

[0179] Molar ratio of the first solvent and the second solvent: DOL : perfluoroisobutyl methyl ether = 1:2

[0180] First lithium salt: 1.2M of LiFSI and 0.5M of LiTFSI

[0181] Second lithium salt: 0.5M of LiDFOB

[0182] Preparation method of the electrolyte: the first solvent DOL and the second solvent perfluoroisobutyl methyl ether are mixed according to the molar ratio, and the corresponding weights of lithium salts LiFSI, LiTFSI and LiDFOB are added to the mixed solvent, stirred until completely dissolved, to form formula O.

[0183] Example 15

[0184] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as formula P herein.

[0185] First solvent: DOL

[0186] Second solvent: perfluoroisobutyl methyl ether

[0187] Molar ratio of the first solvent and the second solvent: DOL : perfluoroisobutyl methyl ether = 1.4:3

[0188] First lithium salt: 0.8M of LiFSI and 0.8M of LiTFSI

[0189] Second lithium salt: 0.5M of LiDFOB

[0190] Preparation method of the electrolyte: the first solvent DOL and the second solvent perfluoroisobutyl methyl ether are mixed according to the molar ratio, and the corresponding weights of lithium salts LiFSI, LiTFSI and LiDFOB are added to the mixed solvent, stirred until completely dissolved, to form formula P.

[0191] Example 16

[0192] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as formula Q herein.

[0193] First solvent: DOL

[0194] Second solvent: perfluoroisobutyl methyl ether

[0195] Molar ratio of the first solvent and the second solvent: DOL : Perfluoroisobutyl methyl ether = 1.4:3

[0196] First lithium salt: 1M of LiFSI and 0.7M of LiTFSI

[0197] Second lithium salt: 0.5M of LiDFOB

[0198] Preparation method of the electrolyte: the first solvent DOL and the second solvent perfluoroisobutyl methyl ether were mixed according to the molar ratio, and the corresponding weights of lithium salts LiFSI, LiTFSI and LiDFOB were added to the mixed solvent, stirred until completely dissolved, to form formula Q.

[0199] Example 17

[0200] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as formula R herein.

[0201] First solvent: DOL

[0202] Second solvent: Perfluoroisobutyl methyl ether

[0203] Molar ratio of the first solvent and the second solvent: DOL : Perfluoroisobutyl methyl ether = 1.4:3

[0204] First lithium salt: 1.2M of LiFSI and 0.4M of LiTFSI

[0205] Second lithium salt: 0.6M of LiDFOB

[0206] Preparation method of the electrolyte: the first solvent DOL and the second solvent perfluoroisobutyl methyl ether were mixed according to the molar ratio, and the corresponding weights of lithium salts LiFSI, LiTFSI and LiDFOB were added to the mixed solvent, stirred until completely dissolved, to form formula R.

[0207] Example 18

[0208] This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present application. The composition of the electrolyte of this example is as follows, which is also referred to as formula S herein.

[0209] First solvent: DOL

[0210] Second solvent: Perfluoroisobutyl methyl ether

[0211] Molar ratio of the first solvent and the second solvent: DOL : Perfluoroisobutyl methyl ether = 1.4:3

[0212] First lithium salt: 1.2M of LiFSI and 0.6M of LiTFSI

[0213] Second lithium salt: 0.4M of LiDFOB

[0214] Preparation method of electrolyte: the first solvent DOL and the second solvent perfluoroisobutyl methyl ether were mixed according to the molar ratio, and the corresponding weight of lithium salt LiFSI, LiTFSI and LiDFOB was added to the mixed solvent, stirred until completely dissolved, and formula S was formed.

[0215] Test example

[0216] This example is used to illustrate the characterization method of the electrolyte for lithium battery.

[0217] First, the electrolyte of formula A-S prepared by using the above comparative example 1 and examples 1-18 was assembled into a battery respectively. The positive electrode, negative electrode and separator of each battery all used the same material, the positive electrode of the battery used ternary high-nickel material, the loading capacity was 4mAh / cm 2 ; the negative electrode used 20 microns of lithium metal; the battery separator was PP-ceramic film. For each of the above formulas A-S, 3 batteries were made respectively, and the battery test was carried out after the battery was stored for 24 hours. The test standard of 0.33C charging and 1C discharging was used to obtain and analyze the battery test results. The cycle number test of the battery was tested until the battery capacity retention rate decreased to 80% SOH (state of health). The composition and test results of all formulas are summarized in Table 1. The cycle capacity chart of some formulas is shown in Figures 1-3 .

[0218] Table 1

[0219]

[0220] Figure 1 The cycle performance data of the batteries assembled respectively using the electrolyte of formula A and formula B at room temperature is shown. It can be seen that the formula B using perfluoroisobutyl methyl ether has better effect than TTE as solvent. Specifically, the capacity of formula A decreases to below 80% SOH after the 86th cycle; the capacity of formula B decreases to below 80% SOH after the 113th cycle. In other words, the battery performance at 80% SOH, formula B can improve the cycle life by more than 20% compared with formula A.

[0221] Figure 2The cycle performance data of the batteries assembled using electrolyte formulations B and C, respectively, at room temperature is shown. As can be seen by comparison, when the second lithium salt LiDFOB is added to the electrolyte at 0.03 M, the cycle life of the battery is improved by about 30%. Specifically, formulation B has a capacity drop below 80% SOH after 113 cycles; formulation C has a capacity drop below 80% SOH after 144 cycles. This comparison shows that the additive LiDFOB helps lithium metal uniform deposition and can improve the cycle life of the battery.

[0222] Figure 3 The cycle performance data of the batteries assembled using electrolyte formulations B, D and E, respectively, at room temperature is shown. As shown, formulation D has a capacity drop below 80% SOH after 265 cycles; formulation E has a capacity drop below 80% SOH after 281 cycles. As can be seen by comparison, when the first lithium salt is a combination of LiFSI and LiTFSI and the lithium salt concentration is increased, the cycle life of the battery can be greatly improved. When the total lithium salt concentration is unchanged, the use of the second lithium salt LiDFOB to replace part of the first lithium salt LiTFSI can further improve the cycle life of the battery. In general, when three lithium salts of medium concentration are used (i.e., formulation E, LiFSI, LiTFSI and LiDFOB), lithium metal SEI formation and uniform lithium deposition can be facilitated in the solvents DOL and perfluoroisobutyl methyl ether, and the 80% SOH service life can be improved by more than 3 times compared to the electrolyte with a single solute and TTE as the solvent (formulation A).

[0223] As can be seen from the test data of other examples in Table 1, when the second solvent is selected from the fluorine-containing solvents within the scope of the present application, and a plurality of solute combinations of the first lithium salt and the second lithium salt are used, excellent battery capacity cycling effects can be achieved at a low total lithium salt concentration.

[0224] In summary, by selecting specific electrolyte solute and solvent compositions, the present application can improve the interaction between the electrolyte and the lithium metal negative electrode, reduce the formation of lithium dendrites and the electrochemical reactions inside the battery, improve the ion conduction performance of the battery, and improve the cycle life of the battery, which is conducive to the commercialization of lithium metal solid-state batteries.

[0225] The above describes exemplary embodiments of the present application through examples, but the present application is not limited thereto. Those skilled in the art will understand that the above examples are for illustrative purposes only, and the specific embodiments and examples of the present application should not be considered as limiting the scope of the present application. Changes and modifications can be made to the embodiments within the scope of the present application, and such changes and modifications should be considered as falling within the scope of the present application.

Claims

1. An electrolyte solution for a lithium battery, characterized by comprising: The electrolyte for lithium battery comprises a first solvent, a second solvent, a first lithium salt, and optionally a second lithium salt, wherein the first solvent is 1,3-dioxolane (DOL), the second solvent is one or more selected from the group consisting of perfluoroisobutyl methyl ether, perfluoropropyl methyl ether, perfluoropentyl methyl ether, and tris(2,2,2-trifluoroethoxy)methane, the first lithium salt is one or more selected from the group consisting of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI), lithium bis(pentafluoroethylsulfonyl)imide (LiBETI), lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroaluminate (LiAlF6), lithium tetrafluoroborate (LiBF4), lithium fluorosulfate (LiFSO3), lithium trifluoromethanesulfonate (LiCF3SO3), and lithium perchlorate (LiClO4); the second lithium salt is one or more selected from the group consisting of lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium nitrate (LiNO3), and lithium fluoride (LiF); the molar ratio of the first solvent to the second solvent is 1:1 to 1:3; the concentration of the first lithium salt is 1.1 M to 2.2 M in terms of lithium ions; when the second lithium salt is included, the concentration of the second lithium salt is 0.03 M to 0.8 M in terms of lithium ions.

2. The electrolyte for lithium battery according to claim 1, wherein the concentration of the first lithium salt is 1.2 M to 1.7 M in terms of lithium ions.

3. The electrolyte for lithium battery according to claim 1, wherein the second solvent is perfluoroisobutyl methyl ether.

4. The electrolyte for lithium battery according to any one of claims 1 to 3, wherein 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(trifluoromethylsulfonyl)imide (LiTFSI).

5. The electrolyte for lithium battery according to any one of claims 1 to 3, wherein the second lithium salt is lithium difluoro(oxalato)borate (LiDFOB), lithium nitrate (LiNO3), or a combination thereof.

6. Use of the electrolyte for lithium battery according to any one of claims 1 to 5 in a lithium metal battery or a lithium ion battery.

7. A lithium battery, characterized by The lithium battery comprises a positive electrode, a negative electrode, a separator, and the electrolyte for lithium battery according to any one of claims 1 to 5.

8. The lithium battery of claim 7, wherein, The lithium battery is a lithium metal battery or a lithium ion battery.

Images