Electrolyte for secondary lithium battery

Abstract

The invention discloses 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 selecting the specific electrolyte solute and solvent, the interaction between the electrolyte and the lithium metal negative electrode can be improved, the formation of lithium dendrites and the electrochemical reaction in the battery can be reduced, the ion conduction performance of the battery can be improved, the cycle life of the battery can be prolonged, and the commercialization of the lithium metal solid-state battery can be facilitated.

Description

Technical Field

[0001] The 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 with the currently widely used lithium-ion batteries, lithium metal batteries have higher energy density and can store and provide more energy in the same volume or weight, which is very important for applications that require high energy density.

[0003] One of the main challenges facing lithium metal batteries is the interaction between the electrolyte and the lithium metal negative electrode material, which affects the performance of lithium metal batteries. The electrolytes of the prior art usually use 1M or lower concentrations of lithium salt as the solute, which will cause the lithium metal negative electrode and the electrolyte to react continuously, resulting in low coulombic efficiency of the battery, reduced number of battery cycles and other problems. Although there are reports of using electrolytes with high concentrations of lithium salts to make the lithium metal surface more stable by promoting the solvation and desolvation process of lithium ions; however, the high concentration of salt content will lead to higher battery costs, increased viscosity of the electrolyte, decreased battery efficiency, and lower charge and discharge rates.

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

[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. Summary of the invention

[0006] The present invention aims to improve the interaction between 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.

[0007] The generation and accumulation of lithium dendrites can easily lead to the following problems: (1) Reduced safety: Uneven deposition of lithium ions can easily lead to 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 used, 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.

[0008] In response to the above problems, the inventors of the present invention, through in-depth research, have provided a new electrolyte formula with multiple solutes, solvents and additives, which significantly improves the number of cycles of lithium metal batteries and increases the service life of lithium metal batteries.

[0009] A first aspect of the present invention 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 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).

[0010] 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.

[0011] In some embodiments of the present invention, the concentration of the first lithium salt is 1M-2.5M, preferably 1.1M-2.2M, and more preferably 1.2M-1.7M, calculated as lithium ions.

[0012] In some embodiments of the present invention, when the second lithium salt is included, the concentration of the second lithium salt is 0.01M~1M, preferably 0.03M~0.8M, and more preferably 0.4M~0.6M, calculated as lithium ions.

[0013] In some embodiments of the present invention, the first solvent is 1,3-dioxolane (DOL).

[0014] In some embodiments of the present invention, the second solvent is perfluoroisobutyl methyl ether.

[0015] 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).

[0016] In some embodiments of the present invention, the second lithium salt is lithium difluorooxalatoborate (LiDFOB), lithium nitrate (LiNO 3 ) or a combination thereof.

[0017] The second aspect of the present invention provides the use of the electrolyte for lithium batteries according to the first aspect of the present invention in lithium metal batteries or lithium ion batteries.

[0018] A third aspect of the present invention provides 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 the first aspect of the present invention.

[0019] In some embodiments of the present invention, the lithium battery is a lithium metal battery or a lithium ion battery.

[0020] Advantageous Effects of the Invention The electrolyte of the present invention has the following beneficial technical effects: The electrolyte of the present invention can improve the interaction between the electrolyte and lithium metal by adding a specific chemical additive (i.e., the second lithium salt), reduce the formation of lithium dendrites and the electrochemical reaction inside the battery. For example, the second lithium salt and the first lithium salt can work together to 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.

[0021] The present invention can improve 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 the concentration of the electrolyte, the concentration of additives and the electrolyte solvent, the ion conductivity of the battery can be improved, the growth of lithium dendrites can be inhibited and the cycle life can be increased.

[0022] The present invention can increase the energy density of the battery, reduce the formation of lithium metal dendrites, and reduce the reaction between the lithium metal negative electrode and the electrolyte by combining and using a variety of lithium salts of medium concentration. The present invention changes the solubilization effect of lithium ions by adjusting the formula of the electrolyte, adopts a two-solute electrolyte or a three-solute electrolyte, and improves the performance of the lithium metal battery without increasing or only slightly increasing the lithium salt concentration of the electrolyte.

[0023] In general, the present invention provides an electrolyte that is stable to lithium metal and ternary positive electrodes, can promote long battery cycles, solve the problem of uniform lithium metal deposition, and is resistant to high pressure. The electrolyte of the present invention can promote uniform lithium metal deposition, thereby greatly increasing the number of cycles of lithium metal batteries. By increasing the cycle life of the battery, the lithium metal battery will be more durable and reliable, the frequency of battery replacement will be reduced, and the cost of use will be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The graph shows the cycle capacity of batteries assembled from electrolytes of formulation A and formulation B at room temperature.

[0025] Figure 2 The graphs show the cycle capacity of batteries assembled from electrolytes of formulation B and formulation C at room temperature.

[0026] Figure 3 The graphs show the cycle capacity of batteries assembled from electrolytes of formulation B, formulation D, and formulation E at room temperature. DETAILED DESCRIPTION

[0027] The present invention is further described below by means of specific embodiments. Unless otherwise defined, the terms used herein have the same meanings as those generally understood by those of ordinary skill in the art.

[0028] Numerical limits or ranges stated herein are inclusive of the endpoints and specifically include all values ​​and sub-ranges within the numerical limits or ranges.

[0029] A first aspect of the present invention 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 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).

[0030] 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 by the electrolyte. For example, in some embodiments, the volume ratio of DOL to DME can be 10:1~1:10, 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.

[0031] 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 found that when the above-mentioned polyfluoroethers are used 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 the lithium metal battery can be improved.

[0032] 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 (Bis(2,2,2-trifluoroethyl)ether) is CF3CH2OCH2CF3. In some 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.

[0033] 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., and 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 calculated together and then used to calculate the molar ratio of the two solvents.

[0034] 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~2.5M, preferably 1.1M~2.2M, and more preferably 1.2M~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 may 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 may 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 may also be composed of more than two lithium salts. The inventors have found that when a medium 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.

[0035] In the electrolyte of the present invention, one or more of the second lithium salts may be included. The second lithium salt is preferably lithium difluorooxalate borate (LiDFOB), lithium nitrate (LiNO3) or a combination thereof, more preferably LiDFOB. In the case of including the second lithium salt, the concentration of the second lithium salt is 0.01M~1M, preferably 0.03M~0.8M, and more preferably 0.3M~0.6M in terms of lithium ions. For example, in some 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-mentioned arbitrary concentration range. In some embodiments, the second lithium salt may also be composed of two or more lithium salts. The inventors have found through research 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.

[0036] It should be understood that in the prior art, in order to improve the performance of the electrolyte, it is usually necessary to significantly increase the concentration of the lithium salt. Although the concentration of the lithium salt in the electrolyte of the present invention is slightly higher than that of the prior art, the inventors have found through research that when two or three lithium salts are used in combination, the solubilization effect of lithium ions can be changed, so that compared with a single-solute electrolyte, a two-solute or three-solute electrolyte can achieve the same or better effect at a lower total concentration.

[0037] In an exemplary preferred embodiment of the present invention, the first solvent is 1,3-dioxolane (DOL), and / or The second solvent is perfluoroisobutyl methyl ether, and / or 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 The second lithium salt is lithium difluorooxalatoborate (LiDFOB).

[0038] The second aspect of the present invention provides the use of the lithium battery electrolyte according to the first aspect of the present invention in a lithium metal battery.

[0039] A third aspect of the present invention provides 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 the first aspect of the present invention.

[0040] In some embodiments of the present invention, the lithium battery is a lithium metal battery. There is no particular limitation 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.

[0041] Example 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.

[0042] In the following examples and comparative examples, the relevant compounds and their abbreviations are as follows: LiFSI: Lithium bis(fluorosulfonyl)imide ·LiTFSI: Lithium bis(trifluoromethanesulfonyl)imide ·LiPF6: lithium hexafluorophosphate ·LiCF3SO3: Lithium trifluoromethanesulfonate ·LiDFOB: lithium difluorooxalate borate ·LiNO3: lithium nitrate ·DOL:1,3-Dioxolane ·Perfluoroisobutyl methyl ether (CAS #: 163702-08-7) ·TTE: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether Comparative Example 1 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery as a comparative example. The composition of the electrolyte of this comparative example is as follows, also referred to as Formula A herein.

[0043] First solvent: DOL Second solvent: TTE The molar ratio of the first solvent to the second solvent: DOL:TTE = 1.4:3 First lithium salt: 1.2M LiFSI (final concentration, the same below) Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent TTE according to a molar ratio, add the corresponding weight of lithium salt LiFSI to the mixed solvent, and stir until completely dissolved to form formula A.

[0044] Example 1 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as formulation B herein.

[0045] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1.4:3 The first lithium salt: 1.2M LiFSI Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, add the corresponding weight of lithium salt LiFSI to the mixed solvent, and stir until completely dissolved to form formula B.

[0046] Example 2 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formula C herein.

[0047] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1.4:3 The first lithium salt: 1.2M LiFSI Second lithium salt: 0.03M LiDFOB Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, add corresponding weights of lithium salts LiFSI and LiDFOB to the mixed solvent, and stir until completely dissolved to form formula C.

[0048] Example 3 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formula D herein.

[0049] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1.4:3 The first lithium salt: 1.2M LiFSI and 1.0M LiTFSI Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take corresponding weights of lithium salts LiFSI and LiTFSI and add them to the mixed solvents, stir until they are completely dissolved, and form formula D.

[0050] Example 4 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formula E herein.

[0051] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1.4:3 The first lithium salt: 1.2M LiFSI and 0.5M LiTFSI Second lithium salt: 0.5M LiDFOB Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take corresponding weights of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula E.

[0052] Example 5 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formula F herein.

[0053] First solvent: DOL Second solvent: perfluoropropyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoropropyl methyl ether = 1.4:3 The first lithium salt: 1.2M LiFSI and 0.5M LiTFSI Second lithium salt: 0.5M LiDFOB Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoropropyl methyl ether according to a molar ratio, take corresponding weights of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula F.

[0054] Example 6 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formula G herein.

[0055] First solvent: DOL Second solvent: bis(2,2,2-trifluoroethyl) ether The molar ratio of the first solvent to the second solvent: DOL: bis(2,2,2-trifluoroethyl) ether = 1.4:3 The first lithium salt: 1.2M LiFSI and 0.5M LiTFSI Second lithium salt: 0.5M LiDFOB Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent bis(2,2,2-trifluoroethyl) 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 G.

[0056] Example 7 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, which is also referred to as Formula H herein.

[0057] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1.4:3 The first lithium salt: 1.2M LiFSI and 0.5M LiTFSI Second lithium salt: 0.03M LiNO3 Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take corresponding weights of lithium salts LiFSI, LiTFSI and LiNO3 and add them to the mixed solvent, stir until completely dissolved, and form formula H.

[0058] Example 8 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 I herein.

[0059] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1.4:3 The first lithium salt: 1.2M LiFSI and 0.5M LiTFSI Second lithium salt: 0.03M LiNO3 and 0.5M LiDFOB 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, LiNO3 and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula I.

[0060] Example 9 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formula J herein.

[0061] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1.4:3 First lithium salt: 1.2M LiFSI and 0.3M LiPF6 Second lithium salt: 0.5M LiDFOB Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take corresponding weights of lithium salts LiFSI, LiPF6 and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula J.

[0062] Example 10 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formula K herein.

[0063] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1.4:3 First lithium salt: 1.2M LiFSI and 0.3M LiCF3SO3 Second lithium salt: 0.5M LiDFOB Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take corresponding weights of lithium salts LiFSI, LiCF3SO3 and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula K.

[0064] Embodiment 11 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as formula L herein.

[0065] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 2:1 The first lithium salt: 1.2M LiFSI and 0.5M LiTFSI Second lithium salt: 0.5M LiDFOB Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take corresponding weights of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula L.

[0066] Example 12 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, which is also referred to as Formula M herein.

[0067] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1:1 The first lithium salt: 1.2M LiFSI and 0.5M LiTFSI Second lithium salt: 0.5M LiDFOB Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take corresponding weights of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula M.

[0068] Example 13 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, which is also referred to as Formula N herein.

[0069] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1:1.5 The first lithium salt: 1.2M LiFSI and 0.5M LiTFSI Second lithium salt: 0.5M LiDFOB Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take corresponding weights of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula N.

[0070] Embodiment 14 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as formulation O herein.

[0071] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1:2 The first lithium salt: 1.2M LiFSI and 0.5M LiTFSI Second lithium salt: 0.5M LiDFOB Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take corresponding weights of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula O.

[0072] Embodiment 15 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, which is also referred to as formulation P herein.

[0073] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1.4:3 First lithium salt: 0.8M LiFSI and 0.8M LiTFSI Second lithium salt: 0.5M LiDFOB Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take corresponding weights of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula P.

[0074] Example 16 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, which is also referred to as Formula Q herein.

[0075] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1.4:3 The first lithium salt: 1M LiFSI and 0.7M LiTFSI Second lithium salt: 0.5M LiDFOB Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take corresponding weights of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula Q.

[0076] Embodiment 17 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, also referred to as Formula R herein.

[0077] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1.4:3 First lithium salt: 1.2M LiFSI and 0.4M LiTFSI Second lithium salt: 0.6M LiDFOB Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take corresponding weights of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula R.

[0078] Embodiment 18 This example is used to illustrate the composition and preparation method of the electrolyte for lithium battery of the present invention. The composition of the electrolyte of this embodiment is as follows, which is also referred to as formulation S herein.

[0079] First solvent: DOL Second solvent: perfluoroisobutyl methyl ether The molar ratio of the first solvent to the second solvent: DOL: perfluoroisobutyl methyl ether = 1.4:3 The first lithium salt: 1.2M LiFSI and 0.6M LiTFSI Second lithium salt: 0.4M LiDFOB Preparation method of the electrolyte: Mix the first solvent DOL and the second solvent perfluoroisobutyl methyl ether according to a molar ratio, take corresponding weights of lithium salts LiFSI, LiTFSI and LiDFOB and add them to the mixed solvent, stir until completely dissolved, and form formula S.

[0080] Test Case This example is used to illustrate the characterization method of electrolyte for lithium batteries.

[0081] First, the electrolytes of formula AS prepared in the above comparative example 1 and examples 1-18 were used to assemble batteries. 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 ; 20 micron lithium metal is used for the negative electrode; the battery separator is a PP-ceramic film. For each of the above formulas AS, 3 batteries were made respectively, and the batteries were tested after being stored for 24 hours. The battery test results were obtained and analyzed using the test standards 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 diagram of some formulas is Figure 1-3 Shown in.

[0082] Table 1

[0083] Figure 1The cycle performance data of batteries assembled using electrolytes of formula A and formula B at room temperature are shown. By comparison, formula B using perfluoroisobutyl methyl ether has a better effect than TTE as a solvent. Specifically, the capacity of formula A drops below 80% SOH after the 86th cycle; the capacity of formula B drops below 80% SOH after the 113th cycle. In other words, when the battery performance is at 80% SOH, formula B can improve the cycle life by more than 20% relative to formula A.

[0084] Figure 2 The cycle performance data of batteries assembled using electrolytes of Formula B and Formula C at room temperature are shown. By comparison, when 0.03M of the second lithium salt LiDFOB is added to the electrolyte, the cycle life of the battery is increased by about 30%. Specifically, the capacity of Formula B drops below 80% SOH after the 113th cycle; the capacity of Formula C drops below 80% SOH after the 144th cycle. This comparison shows that the additive LiDFOB is of great help to the uniform deposition of lithium metal and can increase the cycle life of the battery.

[0085] Figure 3 The cycle performance data of the battery assembled with the electrolytes of formula B, formula D and formula E at room temperature are shown. As shown in the figure, the capacity of formula D drops below 80% SOH after the 265th cycle; the capacity of formula E drops below 80% SOH after the 281st cycle. By comparison, when the first lithium salt of LiFSI and LiTFSI is used and the lithium salt concentration is increased, the cycle life of the battery can be greatly improved. When the total concentration of lithium salt remains unchanged, the second lithium salt LiDFOB is used to replace part of the first lithium salt LiTFSI, which can further improve the cycle life of the battery. In general, when using three lithium salts of medium concentration (i.e., formula E, LiFSI, LiTFSI and LiDFOB), the solvent DOL and perfluoroisobutyl methyl ether can help the formation of lithium metal SEI and the uniform deposition of lithium. Compared with the electrolyte (formula A) with a single solute and TTE as a solvent, the 80% SOH service life can be improved by more than 3 times.

[0086] 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 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.

[0087] In summary, the present invention 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 conductivity of the battery, and increase the cycle life of the battery by selecting specific electrolyte solute and solvent composition, which is conducive to the commercialization of lithium metal solid-state batteries.

[0088] The exemplary embodiments of the present invention are described above by way of examples, 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 considered to limit the scope of the present invention. The embodiments can be changed and altered within the scope of the gist of the present invention, and such changes and alterations should belong to the protection scope 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: 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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