Non-aqueous electrolytes and their applications

Abstract

The application relates to a non-aqueous electrolyte, including a fluorine-containing organic lithium salt of a specific structure, a solvent and a diluent, by using a chemical formula of R 1 ‑O‑CH2‑CH2‑O‑R 2 The solvent, chemical formula is R 3 ‑O‑CH2‑CH2‑O‑R 4 The invention discloses a lithium metal secondary battery having a high coulombic efficiency and a low cost. The invention discloses a lithium metal secondary battery having a high coulombic efficiency and a low cost. The invention discloses a lithium metal secondary battery having a high coulombic efficiency and a low cost. The invention discloses a lithium metal secondary battery having a high coulombic efficiency and a low cost. The invention discloses a lithium metal secondary battery having a high coulombic efficiency and a low cost. The invention discloses a lithium metal secondary battery having a high coulombic efficiency and a low cost. The invention discloses a lithium metal secondary battery having a high coulombic efficiency and a high coulombic efficiency ...

Description

Technical Field

[0001] The present application relates to the technical field of non-aqueous electrolytes, and in particular to a non-aqueous electrolyte and its application. Background Art

[0002] As one of the most promising secondary batteries, the high energy density of lithium metal secondary batteries still faces some significant challenges in application. Liquid electrolytes for lithium metal secondary batteries struggle to overcome the instability of the lithium metal anode, which can lead to lithium dendrite growth, SEI film damage, and lithium metal electrode expansion. These issues can reduce battery coulombic efficiency, increase electrochemical impedance, reduce battery capacity and lifespan, and even puncture the battery separator, causing battery combustion and explosion.

[0003] Increasing the lithium salt concentration in the electrolyte is one of the means to inhibit the growth of lithium dendrites and improve battery performance, especially cycle life. However, excessively high lithium salt concentration may cause the conductivity of the liquid electrolyte to decrease, which is not conducive to the migration of lithium ions during the battery cycle, thereby leading to a substantial decrease in the performance of lithium metal secondary batteries. Summary of the Invention

[0004] Based on this, the purpose of this application includes providing a non-aqueous electrolyte that can better dissolve to obtain a high-concentration lithium salt electrolyte, effectively inhibiting the formation of lithium dendrites while improving the conductivity of the high-concentration non-aqueous electrolyte and increasing the cycle life of lithium metal secondary batteries.

[0005] In addition, the present application also provides a non-aqueous electrolyte, a preparation method and application in a lithium metal secondary battery.

[0006] In one aspect of the present application, a non-aqueous electrolyte is provided, comprising a fluorine-containing organic lithium salt, a solvent, and a diluent;

[0007] The chemical formula of the solvent is R 1 -O-CH2-CH2-OR 2 ;

[0008] The chemical formula of the diluent is R 3 -O-CH2-CH2-OR 4 ;

[0009] R 1 and R 2 Each independently selected from a linear alkyl group and R 1 and R 2 The difference in the number of carbon atoms is at least 1;

[0010] R 3 and R 4 All are perfluorinated straight-chain alkyl groups; R 1 and R 3With the same carbon chain structure, R 2 and R 4 Have the same carbon chain structure;

[0011] The fluorine-containing organic lithium salt is one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide and lithium bis(perfluoro-1-butanesulfonyl)imide.

[0012] In some embodiments, the volume ratio of the solvent to the diluent is not less than 6:4.

[0013] In some embodiments, the volume ratio of the solvent to the diluent is not less than 7:3.

[0014] In some embodiments, the concentration of the fluorine-containing organic lithium salt is not less than 2 mol / L.

[0015] In some embodiments, the concentration of the fluorine-containing organic lithium salt is no greater than 4 mol / L.

[0016] In some embodiments, the non-aqueous electrolyte further comprises an inorganic additive.

[0017] In some embodiments, the inorganic additive includes one or more of aluminum oxide, zirconium oxide, magnesium oxide, and barium oxide.

[0018] In some embodiments, the inorganic additive accounts for no more than 0.5% by mass of the non-aqueous electrolyte.

[0019] In some embodiments, the non-aqueous electrolyte further includes an organic additive.

[0020] In some embodiments, the organic additive includes one or more of a film-forming additive, an anti-overcharge additive, a flame retardant, and a stabilizer.

[0021] In some embodiments, the organic additive accounts for at least 0.1% by volume of the non-aqueous electrolyte.

[0022] The second aspect of the present application provides a method for preparing the non-aqueous electrolyte, characterized in that it comprises the following steps:

[0023] The fluorine-containing organic lithium salt, solvent and diluent are mixed to obtain the non-aqueous electrolyte.

[0024] The third aspect of the present application provides a lithium metal secondary battery comprising the non-aqueous electrolyte.

[0025] The fourth aspect of the present application provides an electrical device comprising the lithium metal secondary battery.

[0026] The above non-aqueous electrolyte comprises a fluorine-containing organic lithium salt of a specific structure, a solvent and a diluent, and is prepared by using a chemical formula of R 1 -O-CH2-CH2-OR 2 The solvent, chemical formula is R 3 -O-CH2-CH2-OR 4 Diluents, solvents and diluents with similar structures and strong polarity can dissolve higher amounts of lithium salts to obtain high-concentration lithium salts. Solvents and diluents can form a relatively stable coordination relationship with lithium salts, reducing obstacles to lithium ion migration, and the non-aqueous electrolyte has a higher conductivity. In addition, the non-aqueous electrolyte has good infiltration with the lithium metal negative electrode and has a high conductivity. The lithium metal secondary battery formed has a high coulombic efficiency, which helps to reduce the cost of the electrolyte, the cost of the lithium battery cell and the difficulty of the lithium battery manufacturing process. DETAILED DESCRIPTION

[0027] To facilitate understanding of the present application, the present application will be described in more detail below. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, the purpose of providing these embodiments is to provide a more thorough and comprehensive understanding of the disclosure of the present application.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are for the purpose of describing specific embodiments only and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0029] the term

[0030] Unless otherwise specified or incompatible herewith, the terms and phrases used herein shall have the following meanings:

[0031] Lithium bis(trifluoromethanesulfonyl)imide, molecular formula: C2HF6NO4S2Li, CAS number: 90076-65-6.

[0032] Lithium bis(fluorosulfonyl)imide, molecular formula: F2LiNO4S2, CAS number: 171611-11-3.

[0033] Lithium bis(perfluoro-1-butanesulfonyl)imide, molecular formula: C8F 18 LiNO4S2, CAS number: 119229-99-1.

[0034] Lithium metal secondary batteries, also known as lithium metal batteries, generally have a negative electrode comprising metallic lithium or an alloy of lithium and other metals, and a positive electrode comprising a lithium-containing metal oxide.

[0035] Lithium-ion secondary batteries, also known as lithium-ion batteries or lithium batteries, generally have a negative electrode comprising non-lithium compounds such as hard carbon, carbon microspheres, natural graphite, artificial graphite, etc., and a positive electrode comprising a lithium-containing metal oxide.

[0036] Herein, the terms "preferred," "better," "more preferred," and "suitable" are used solely to describe preferred implementations or examples and should not be construed as limiting the scope of protection of this application. If multiple "preferred" terms appear in a technical solution, each "preferred" term is considered independent unless otherwise specified and there are no contradictions or mutual constraints.

[0037] In this application, "further", "further", "particularly" and the like are used for descriptive purposes to indicate differences in content, but should not be understood as limiting the scope of protection of this application.

[0038] In this application, the technical features described in an open manner include closed technical solutions composed of the listed features, and also include open technical solutions of the listed features.

[0039] In this application, when it comes to a numerical interval (i.e., a numerical range), unless otherwise specified, the distribution of the optional numerical values ​​in the numerical interval is considered continuous and includes the two numerical endpoints (i.e., the minimum and maximum values) of the numerical interval, and each numerical value between the two numerical endpoints. Unless otherwise specified, when a numerical interval only refers to an integer in the numerical interval, including the two endpoint integers of the numerical range and each integer between the two endpoints is equivalent to directly enumerating each integer. When multiple numerical ranges are provided to describe a feature or characteristic, these numerical ranges can be merged. In other words, unless otherwise specified, the numerical range disclosed herein should be understood to include any and all subranges included therein. The "numerical value" in the numerical interval can be any quantitative value, such as a number, a percentage, a ratio, etc. "Numerical interval" allows for broadly including quantitative intervals such as percentage intervals, ratio intervals, and ratio intervals.

[0040] Unless otherwise specified, the temperature parameters in this application allow for both constant temperature treatment and temperature fluctuations within a certain temperature range. It should be understood that the constant temperature treatment allows for temperature fluctuations within the accuracy range of instrument control. Fluctuations within ranges such as ±5°C, ±4°C, ±3°C, ±2°C, and ±1°C are permitted.

[0041] The diffusion of lithium salts in the electrolyte and their ability and rate of migration under an electric field are key factors in the cycling performance of the charge-discharge process. Currently, the most widely used lithium salt, lithium hexafluorophosphate (LiPF6), has high ionic conductivity, but suffers from poor thermal stability and is susceptible to water absorption and deterioration. Newer lithium salts such as lithium tetrafluoroborate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium bis(trifluoromethylsulfonylimide), and lithium bis(fluorosulfonylimide) are more stable than LiPF6, but present challenges in terms of solvent solubility and ionic conductivity.

[0042] Liquid electrolytes used in lithium metal secondary batteries, or electrolyte systems, can be primarily categorized as ester electrolytes, ether electrolytes, and ionic liquid electrolytes. Ester electrolytes primarily include phosphate esters and carbonate esters, both of which are commonly used in lithium-ion and lithium metal batteries. While ester electrolytes exhibit excellent flame retardancy and high voltage resistance, they exhibit poor wetting properties with the lithium metal anode, resulting in low coulombic efficiency. Ether solvents, a primary component of ether electrolytes, possess advantages such as low viscosity and excellent wettability with separator and electrode materials. The primary reduction products on the lithium metal surface are ROLi (R = alkyl) and flexible oligomers, which facilitate the formation of a SEI membrane with superior mechanical properties and contribute to improved coulombic efficiency.

[0043] However, the application of ether electrolytes faces many challenges. First, lithium metal has a strong reducing property, while the oxidation potential of ether electrolytes is low, which makes it easy for violent oxidation reactions to occur on the surface of the positive electrode material. As the lithium battery cycles, the battery capacity decays rapidly. Secondly, increasing the salt concentration can help improve the problem of low oxidation potential of ether electrolytes, but high concentrations of lithium salts are not conducive to the migration of lithium ions. In addition, the composition of the electrolytes currently used is complex, and carbonate solvents, phosphate solvents, and even various additives are often used in combination, resulting in complex lithium battery electrolyte components and high costs.

[0044] According to the frontier orbital theory, organic molecules have the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO). The positive electrode material of a lithium battery has a high potential, and the HOMO is related to the easy loss of electrons and oxidation in the organic molecule. Correspondingly, a lower HOMO helps to avoid violent reactions between the electrolyte and the positive electrode. Therefore, the electrolyte of a lithium battery should have a lower HOMO energy level, that is, better oxidation resistance. The potential of the lithium metal or lithium alloy at the negative electrode of a lithium battery is low, and the electrochemical window of the electrolyte is generally higher than the potential of lithium. The LUMO is related to the ability of the organic molecule to easily obtain electrons and be reduced. Therefore, the higher the LUMO, the better the reduction resistance.

[0045] Ether solvents used in lithium battery electrolytes include tetrahydrofuran (THF), 1,3-dioxolane (DOL), 1,4-dioxane (DX), ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (G2), and triethylene glycol dimethyl ether (G3). Ether solvents have a low HOMO and a high LUMO, but cyclic ethers, as solvents for lithium batteries, generally need to be mixed with other solvents to improve the solubility and coordination stability of complex structured lithium salts. At the same time, the symmetrical structure of ethylene glycol dimethyl ether is not conducive to the diffusion of lithium ions, and the diffusion of lithium ions is closely related to the dynamics of lithium dendrite formation on the electrode surface during the cycle of lithium metal batteries, as well as the coulombic efficiency, capacity retention, and safety of the battery. The diffusion ability of lithium ions and their ability to migrate under an electric field are related to the viscosity of the solvent, the structure and concentration of the lithium salt, and the coordination relationship between the lithium salt and the solvent.

[0046] After extensive research, the present invention has found a non-aqueous electrolyte that can better overcome the above problems. The non-aqueous electrolyte includes a fluorine-containing organic lithium salt of a specific structure, a solvent and a diluent. 1 -O-CH2-CH2-OR 2 The solvent, chemical formula is R 3 -O-CH2-CH2-OR 4 The invention discloses a lithium metal secondary battery having a high coulombic efficiency and a low cost, wherein the lithium metal secondary battery has a high coulombic efficiency and a low cost, and ... high cost, and the lithium metal secondary battery has a high coulombic efficiency and a high cost, and the lithium metal secondary battery has a high coulombic efficiency and a high cost, and the lithium metal secondary battery has a high coulombic efficiency and a high cost, and the lithium metal secondary

[0047] According to one embodiment, the non-aqueous electrolyte includes a fluorine-containing organic lithium salt, a solvent and a diluent;

[0048] The chemical formula of the solvent is R 1 -O-CH2-CH2-OR 2 ;

[0049] The chemical formula of the diluent is R 3 -O-CH2-CH2-OR 4 ;

[0050] R 1 and R 2 Each independently selected from a linear alkyl group and R 1 and R 2 The difference in the number of carbon atoms is at least 1;

[0051] R 3 and R 4 All are perfluorinated straight-chain alkyl groups; R 1and R 3 With the same carbon chain structure, R 2 and R 4 Have the same carbon chain structure;

[0052] The fluorine-containing organic lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide, lithium bis(fluorosulfonyl)imide and lithium bis(perfluoro-1-butanesulfonyl)imide.

[0053] In this application, by using an ethylene glycol ether with linear alkyl side chains on both sides and an ethylene glycol ether with perfluoro linear alkyl side chains on both sides as the solvent and diluent, respectively, the solvent system has good polarity. The perfluoro linear diluent has a stronger ability to dissolve fluorinated organic lithium salts. The diluent structure facilitates better miscibility with the solvent and promotes the dissociation, diffusion, and migration of lithium ions in the fluorinated organic lithium salt under the action of an electric field.

[0054] This non-aqueous electrolyte system can dissolve high concentrations of fluorinated organic lithium salts. Furthermore, the solvent and diluent exhibit a strong synergistic relationship, forming a relatively stable coordination relationship with the lithium salt and maintaining high lithium ion mobility. Avoiding the use of binary or ternary solvents helps reduce the difficulty of lithium battery electrolyte preparation and lowers the cost of lithium battery electrolytes.

[0055] In some embodiments, R 1 and R 2 The difference in the number of carbon atoms is 2, 3, 4, 5, 6, 7, 8, 9 or 10.

[0056] In some embodiments, R 1 and R 2 The maximum number of carbon atoms in is not greater than 15, and can further be 14, 16, 12, 11, 10, 9, 8, 7, 6, 5, 4 or 3.

[0057] In some embodiments, the perfluoro linear alkyl group R 3 and R 4 It can be CF3, C2F5, (CF2)2-CF3, (CF2)3-CF3, (CF2)4-CF3, (CF2)5-CF3, (CF2)6-CF3, (CF2)7-CF3, (CF2)8-CF3, (CF2)9-CF3, (CF2) 10 -CF3, (CF2) 11 -CF3, (CF2) 12 -CF3, (CF2) 13 -CF3, (CF2) 14 -CF3 or (CF2) 15 -CF3.

[0058] In some embodiments, the volume ratio of the solvent to the diluent is not less than 6:4.

[0059] In some embodiments, the volume ratio of the solvent to the diluent is not less than 7:3. It can further be 8:2 or 9:1. The beneficial effect is that the general formula satisfies R 3 -O-CH2-CH2-OR 4 The diluent compound II consists of hydrocarbon groups at both ends R 3 and R 4 As the difference in the number of carbon atoms increases, the polarity of the diluent increases, which helps the fluorine-containing organic lithium salt to fully dissociate in the solvent and diluent to form a stable and uniform coordination.

[0060] In some embodiments, the concentration of the fluorine-containing organic lithium salt is not less than 2 mol / L.

[0061] In some embodiments, the concentration of the fluorinated organic lithium salt is no greater than 4 mol / L. It may further be 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L, 2.5 mol / L, 2.6 mol / L, 2.7 mol / L, 2.8 mol / L, 2.9 mol / L, 3 mol / L, 3.1 mol / L, 3.2 mol / L, 3.3 mol / L, 3.4 mol / L, 3.5 mol / L, 3.6 mol / L, 3.7 mol / L, 3.8 mol / L, 3.9 mol / L, or 4 mol / L. The perfluorinated saturated linear hydrocarbon group as a diluent has a low dielectric constant, avoids forming a solvated group with the lithium salt, and synergistically dissolves and ionizes the fluorinated organic lithium salt with the solvent having the same carbon chain skeleton structure, thereby helping to maintain the coordination structure between lithium ions, solvent, and fluorinated organic groups at high lithium salt concentrations.

[0062] In some embodiments, the non-aqueous electrolyte further includes an inorganic additive.

[0063] In some embodiments, the inorganic additive includes one or more of aluminum oxide, zirconium oxide, magnesium oxide, and barium oxide.

[0064] In some embodiments, the mass ratio of the inorganic additive to the non-aqueous electrolyte is no greater than 0.5%, and may further be 0.4%, 0.3%, 0.2% or 0.1%.

[0065] In some embodiments, the particle size of the inorganic additive may be 0.01 to 10 μm, further 0.05 to 7 μm, 0.1 to 5 μm, 1 to 3 μm. It may also include any one of the following particle sizes or any two of them: 0.02 μm, 0.03 μm, 0.04 μm, 0.05 μm, 0.06 μm, 0.07 μm, 0.08 μm, 0.09 μm, 0.1 μm, 0.11 μm, 0.12 μm, 0.13 μm, 0.14 μm, 0.15 μm, 0.16 μm, 0.17 μm, 0.18 μm, 0.19 μm, 0.2 μm, 0.3 μm, 0.4 μm, 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 26 μm, 27 μm, 28 μm, 29 μm, 30 μm, 31 μm, 32 μm, 33 μm, 34 μm, 35 μm, 36 μm, 37 μm, 38 μm, 39 μm, 40 μm, 41 μm, 42 μm, 43 μm, 44 μm, 45 μm, 46 μm, 47 μm, 48 μm, 49 μm, The particle size of the inorganic additive affects the degree of dispersion in the non-aqueous electrolyte and the synergistic effect with the organic component.

[0066] In some embodiments, the non-aqueous electrolyte further includes an organic additive.

[0067] In some embodiments, the organic additive includes one or more of a film-forming additive, an anti-overcharge additive, a flame retardant, and a stabilizer.

[0068] In some embodiments, the volume percentage of the organic additive in the non-aqueous electrolyte is not less than 0.1%, and can further be 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1.0%.

[0069] According to one embodiment, the method for preparing the non-aqueous electrolyte comprises the following steps:

[0070] The fluorine-containing organic lithium salt, the solvent and the diluent are mixed to obtain the non-aqueous electrolyte.

[0071] Under argon protection, temperature: 22±2℃, moisture content ≤20ppm, all components are stirred and mixed according to the formula ratio, and the electrolyte is packaged in a sealed can.

[0072] According to one embodiment of the present application, a lithium metal secondary battery includes the non-aqueous electrolyte.

[0073] In the lithium metal secondary battery of the above technical solution, on the one hand, the non-aqueous electrolyte system including ethylene glycol ether with linear alkyl side chains on both sides and ethylene glycol ether with perfluoro linear alkyl side chains on both sides as the solvent and diluent, respectively, has a high polarity, low viscosity, good wetting with the lithium metal negative electrode, the solvent and additive have strong solubility for high-concentration lithium salts, the solvent and diluent have a good synergistic relationship, can form a relatively stable coordination relationship with the lithium salt, has high conductivity, and the lithium metal secondary battery constructed has a high coulombic efficiency. On the other hand, the solubility, diffusion, and migration properties of lithium salts in the electrolyte significantly affect the battery capacity and battery life extension. The strong migration ability of lithium ions in lithium salts and the simple formulation of electrolyte solvents help reduce the cost of lithium battery cells and the difficulty of lithium battery manufacturing processes.

[0074] In addition, research shows that the cell cost of lithium metal secondary batteries mainly includes the positive electrode, negative electrode, separator, electrolyte, current collector and additives. The electrolyte accounts for about 12% of the cost of lithium battery cells, and more than 50% of the electrolyte cost is contributed by lithium salt, which means that lithium salt accounts for more than 6% of the cost of lithium battery cells. High lithium salt concentration helps improve the coulombic efficiency and safety performance of the battery, but the solvent in the electrolyte system affects the diffusion of lithium ions in high-concentration lithium salt electrolytes and the conduction under electric fields, requiring a higher lithium salt addition, further increasing the cost of lithium battery electrolytes.

[0075] According to one embodiment of the present application, an electrical device includes the lithium metal secondary battery. The electrical device can be a portable electronic device such as a handheld mobile terminal, a drone, a portable player, an electric vehicle, or an energy storage device.

[0076] The following are specific examples.

[0077] In the following embodiments, the lithium salt is selected from lithium bis(trifluoromethanesulfonyl)imide and lithium bis(fluorosulfonyl)imide. It is understood that in other embodiments, the present invention is not limited thereto, and for example, lithium bis(perfluoro-1-butanesulfonyl)imide may also be used.

[0078] Example 1

[0079] The solvent is CH3-O-CH2-CH2-O-CH2-CH3, the diluent is CF3-O-CH2-CH2-O-CF2-CF3, and the lithium salt is lithium bis(trifluoromethanesulfonyl imide). The solvent and the diluent are mixed in a ratio of 7:3. The lithium salt is added to prepare a non-aqueous electrolyte with a concentration of 2 mol / L. The measured conductivity is 8.49*10 -3 S / cm.

[0080] The conductivity test method is as follows: at a temperature of 22±2°C and a humidity of ≤-50RH%, take 20-30ml of electrolyte and test the conductivity using a conductivity tester.

[0081] Conductivity tester: Shanghai Yidian Scientific Instrument Co., Ltd. DDS307A

[0082] Example 2

[0083] The composition of Example 2 is substantially the same as that of Example 1, except that the solvent is CH3-O-CH2-CH2-O-CH2-CH2-CH3 and the diluent is CF3-O-CH2-CH2-O-CF2-CF2-CF3. The measured conductivity is 10.19*10 -3 S / cm.

[0084] Example 3

[0085] The composition of Example 3 is substantially the same as that of Example 1, except that the solvent is CH3-O-CH2-CH2-O-CH2-CH2-CH2-CH3 and the diluent is CF3-O-CH2-CH2-O-CF2-CF2-CF2-CF3. The measured conductivity is 12.28*10 - 3 S / cm.

[0086] Example 4

[0087] The composition of Example 4 is substantially the same as that of Example 1, except that the solvent is CH3-O-CH2-CH2-O-CH2-CH2-CH2-CH2-CH3 and the diluent is CF3-O-CH2-CH2-O-CF2-CF2-CF2-CF2-CF3. The measured conductivity is 12.31*10 -3 S / cm.

[0088] Example 5

[0089] The composition of Example 5 is substantially the same as that of Example 1, except that the solvent is CH3-O-CH2-CH2-O-CH2-CH2-CH2-CH2-CH2-CH3 and the diluent is CF3-O-CH2-CH2-O-CF2-CF2-CF2-CF2-CF2-CF3. The measured conductivity is 12.35*10 -3 S / cm.

[0090] It can be seen that the glycol ethers with hydrocarbon side chains on both sides and the fluorinated glycol ethers with trifluoromethyl side chains on both sides have similar structures. As the gap between the branches on both sides of the glycol ether with long side chains increases, the conductivity of the non-aqueous electrolyte with the same lithium salt concentration increases until R 2 When the number of carbon atoms is greater than 4, the conductivity does not increase significantly.

[0091] Comparative Example 1

[0092] The solvent is CH3-O-CH2-CH2-O-CH3, the diluent is CF3-O-CH2-CH2-O-CF3, and the lithium salt is lithium bis(trifluoromethanesulfonyl imide). The solvent and the diluent are mixed in a ratio of 7:3. The lithium salt is added to prepare a non-aqueous electrolyte with a concentration of 2 mol / L. The measured conductivity is 6.11*10 -3 S / cm.

[0093] Comparative Example 2

[0094] The composition of Comparative Example 2 is substantially the same as that of Example 4, except that the diluent is CF3-O-CH2-CH2-O-CF3. The measured conductivity is 3.68*10 -3 S / cm.

[0095] Comparative Example 3

[0096] The composition of Comparative Example 3 is substantially the same as that of Example 1, except that the diluent is CF3-O-CH2-CH2-O-CF2-CF2-CF2-CF2-CF3. The measured conductivity is 3.43*10 -3 S / cm.

[0097] Comparative Example 4

[0098] The composition of Comparative Example 4 is substantially the same as that of Example 4, except that the lithium salt is lithium bis(fluorosulfonyl)imide. The measured conductivity is 3.54*10 -3 S / cm.

[0099] Comparative Example 5

[0100] The composition of Comparative Example 5 is substantially the same as that of Example 4, except that the solvent is CH3-O-CH2-CH2-O-CH2-C5H9, R 1 CH3, R 2 CH2-C5H9 The measured conductivity is 3.79*10 -3 S / cm.

[0101] Comparative Example 6

[0102] The composition of Comparative Example 6 is substantially the same as that of Example 4, except that the lithium salt concentration is 3 mol / L. The measured conductivity is 12.29*10 -3 S / cm.

[0103] The types and proportions of the solvents, diluents, and lithium salts in the non-aqueous electrolytes of Examples 1 to 5 and Comparative Examples 1 to 6, and the conductivity values ​​are shown in Tables 1 to 3, respectively.

[0104] It can be seen from the relevant data in Table 1 and Table 2 that the carbon chain skeleton structures of the solvent and the diluent are consistent. When the diluent is a perfluorinated saturated straight-chain hydrocarbon group, the conductivity of the non-aqueous electrolyte is higher.

[0105] The carbon chain skeletons of the solvent and diluent in Comparative Example 1 are consistent, the number of carbon atoms at both ends of the diethyl ether end groups is the same, both being 1. When other conditions are the same, the conductivity of the electrolyte is low.

[0106] The carbon chain skeletons of the solvents and diluents in Comparative Examples 2 and 3 are quite different. The difference in the number of carbon atoms at the end groups of the diethyl ether of the solvent is 4 and 0, respectively, and the difference in the number of carbon atoms at the end groups of the diethyl ether of the diluent is 0 and 4, respectively. When other conditions are the same, the conductivity of the electrolyte is significantly lower.

[0107] The types of solvents and diluents and the ratios of the two are the same as those of Example 4, and the lithium salt concentration is 2 mol / L. The difference is that the lithium salt of Comparative Example 4 is lithium bis(fluorosulfonyl)imide, and the lithium salt of Example 4 is lithium bis(trifluoromethanesulfonyl)imide. The conductivity of Comparative Example 4 is significantly lower than that of Example 4.

[0108] The solvent of Comparative Example 5 is R 1 CH3, R 2 CH2-C5H9 The conductivity measured under the same other conditions is 3.79*10 -3 S / cm is smaller than that of Example 4.

[0109] Comparative Example 6 uses the same solvent and diluent as Example 4. The lithium salt concentration in Comparative Example 6 is 3 mol / L, and the measured conductivity is 12.29*10 -3 S / cm is the same as that of Example 4 (12.31*10 -3 S / cm is close.

[0110] Table 1

[0111]

[0112]

[0113] Table 2

[0114]

[0115] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0116] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art could make various modifications and improvements without departing from the spirit of the present application, all of which fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A non-aqueous electrolyte, characterized in that The non-aqueous electrolyte comprises a fluorine-containing organic lithium salt, a solvent and a diluent; The chemical formula of the solvent is R 1 -O-CH2-CH2-OR 2 ; The chemical formula of the diluent is R 3 -O-CH2-CH2-OR 4 ; R 1 and R 2 Each independently selected from a linear alkyl group and R 1 and R 2 The difference in the number of carbon atoms is at least 1; R 3 and R 4 All are perfluorinated straight-chain alkyl groups; R 1 and R 3 With the same carbon chain structure, R 2 and R 4 Have the same carbon chain structure; The fluorine-containing organic lithium salt includes one or more of lithium bis(trifluoromethanesulfonyl)imide and lithium bis(perfluoro-1-butanesulfonyl)imide, and the concentration of the fluorine-containing organic lithium salt is not less than 2 mol / L; The conductivity of the non-aqueous electrolyte is 8.49×10 -3 S / cm or more.

2. The non-aqueous electrolyte according to claim 1, characterized in that The volume ratio of the solvent to the diluent is not less than 6:

4.

3. The non-aqueous electrolyte according to claim 1, characterized in that The volume ratio of the solvent to the diluent is not less than 7:

3.

4. The non-aqueous electrolyte according to claim 1, wherein The concentration of the fluorine-containing organic lithium salt is no more than 4 mol / L.

5. The non-aqueous electrolyte according to claim 1, characterized in that The non-aqueous electrolyte further includes an inorganic additive.

6. The non-aqueous electrolyte according to claim 5, characterized in that The inorganic additive includes one or more of aluminum oxide, zirconium oxide, magnesium oxide and barium oxide.

7. The non-aqueous electrolyte according to claim 5 or 6, characterized in that The mass ratio of the inorganic additive to the non-aqueous electrolyte is no more than 0.5%.

8. The non-aqueous electrolyte according to claim 1, wherein The non-aqueous electrolyte further includes an organic additive.

9. The non-aqueous electrolyte according to claim 8, characterized in that The organic additives include one or more of a film-forming additive, an anti-overcharge additive, a flame retardant, and a stabilizer.

10. The non-aqueous electrolyte according to claim 8 or 9, characterized in that The volume percentage of the organic additive in the non-aqueous electrolyte is not less than 0.1%.

11. The method for preparing a non-aqueous electrolyte according to any one of claims 1 to 10, characterized in that: The following steps are involved: The fluorine-containing organic lithium salt, the solvent and the diluent are mixed to obtain the non-aqueous electrolyte.

12. A lithium metal secondary battery, characterized in that: The invention comprises at least one of the non-aqueous electrolyte according to any one of claims 1 to 10 and the non-aqueous electrolyte prepared by the preparation method according to claim 11.

13. An electrical device, characterized in that: Including the lithium metal secondary battery as claimed in claim 12.

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