Lithium metal battery electrolyte and preparation method and application thereof

Abstract

The invention discloses a lithium metal battery electrolyte and a preparation method and application thereof, and belongs to the technical field of new energy materials. The lithium metal battery electrolyte provided by the invention is prepared from the following raw materials: main salt, auxiliary salt, a solvent and a diluent, the main salt comprises at least one of LiFSI and LiTFSI; the auxiliary salt comprises at least one of LiDFOB and LiBF4; the diluent comprises at least one of fluoro-ether, fluoro-aromatic hydrocarbon and fluoro-aromatic ether; the molar ratio of the main salt to the auxiliary salt is (1-1000): 1; the ratio of the sum of the amount of substance of the main salt and the auxiliary salt to the amount of substance of the solvent is 1: (1-9); the molar ratio of the solvent to the diluent is 1: (1-4). According to the lithium metal battery electrolyte provided by the invention, corrosion of the electrolyte to a current collector, a steel shell and the like can be effectively avoided, and the cycle performance of the lithium metal battery can be remarkably improved. The invention also provides a preparation method and application of the lithium metal battery electrolyte.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy materials, and in particular to a lithium metal battery electrolyte and a preparation method and application thereof. Background Art

[0002] The energy density of lithium batteries has become a bottleneck that limits the further improvement of the performance of electric vehicles, drones, smartphones and other devices. The raw materials for preparing lithium-ion batteries include positive electrode active materials and negative electrode active materials. At present, the commercially available and mature negative electrode active material is graphite. However, the actual capacity of graphite negative electrodes is close to its theoretical limit, and there is limited room for improvement. Therefore, it is urgent to develop new high-capacity negative electrodes to improve the energy density of lithium-ion batteries.

[0003] The theoretical specific capacity of lithium metal anode is as high as 3860mA / h, the electrochemical potential is -3.04V, and the theoretical energy density is extremely high, which can significantly improve the overall energy density of lithium batteries. However, the cycle stability and safety issues of lithium metal anode in use have seriously limited its further application.

[0004] At present, the main idea for the cycling problem of lithium metal negative electrodes is to optimize the composition of the electrolyte. For example, adding suitable additives to the electrolyte, in order to form a uniform and stable SEI structure on the surface of lithium metal during the cycle, thereby inhibiting the formation of lithium dendrites. For another example, optimizing the type of lithium salt: lithium bis(fluorosulfonyl)imide (LiFSI) or lithium bis(trifluorosulfonyl)imide (LiTFSI) as the main salt, so that a thin and uniform inorganic SEI film can be formed on the surface of the lithium metal negative electrode, effectively reducing the consumption of active lithium and inhibiting the formation of lithium dendrites. However, the application of LiFSI / LiTFSI in high-voltage (>4.25V) lithium metal batteries is still subject to its corrosion to aluminum foil under high voltage. In addition, in the buckle test, the corrosion of LiFSI / LiTFSI on the battery steel shell under high voltage also affects the judgment of the electrolyte performance.

[0005] In summary, when existing electrolytes are used in lithium metal batteries, there are still problems such as severe corrosion, poor cycle performance and safety performance. Summary of the invention

[0006] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a lithium metal battery electrolyte that can effectively prevent the electrolyte from corroding the current collector and the steel shell, and can also significantly improve the cycle performance of the lithium metal battery.

[0007] The present invention also provides a method for preparing the lithium metal battery electrolyte.

[0008] The present invention also provides application of the above lithium metal battery electrolyte.

[0009] According to an embodiment of the first aspect of the present invention, a lithium metal battery electrolyte is provided, and the raw materials for preparing the lithium metal battery electrolyte include:

[0010] Main salt, auxiliary salt, solvent and diluent;

[0011] The main salt includes at least one of LiFSI (lithium bis(fluorosulfonyl)imide, CAS: 171611-11-3) and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, CAS: 90076-65-6);

[0012] The auxiliary salt includes at least one of LiDFOB (lithium difluorooxalatoborate, CAS: 409071-16-5) and LiBF4 (lithium tetrafluoroborate, CAS: 14283-07-9);

[0013] The diluent includes at least one of fluorinated ethers, fluorinated aromatic hydrocarbons and fluorinated aromatic ethers;

[0014] The molar ratio of the main salt to the auxiliary salt is 1 to 1000:1;

[0015] The ratio of the sum of the amounts of the main salt and the auxiliary salt to the amount of the solvent is 1:1 to 9;

[0016] The molar ratio of the solvent to the diluent is 1:1 to 4;

[0017] The main salt and the auxiliary salt are insoluble in the diluent.

[0018] The lithium metal battery electrolyte according to the embodiment of the present invention has at least the following beneficial effects:

[0019] The present invention uses LiDFOB or LiBF4 as auxiliary salt, and maintains the obtained lithium metal battery electrolyte in a locally high concentration state by adding an inert diluent (the main salt and the auxiliary salt are dissolved in the solvent, and the formed mixture is dispersed in the diluent). By combining the above two means, the problem of corrosion of aluminum foil / steel shell under high voltage by lithium metal battery electrolyte with LiFSI / LiTFSI as the main salt is solved. Lithium metal batteries using the above lithium metal battery electrolyte can be stably cycled at a voltage of 4.6V. The reasons are as follows: A single auxiliary salt strategy can often only guarantee stability on the positive electrode side, while DFOB - / BF4 - Compared with FSI for lithium metal - The instability of the battery will lead to poor overall cycle performance. The local high concentration strategy alone is difficult to completely suppress the corrosion of lithium metal battery electrolyte on aluminum foil / steel shell, resulting in overcharge of the battery. When the two are used in combination, thanks to the squeezing effect of the diluent on the solvated structure, FSI - and DFOB- / BF4 - will appear in the first solvation shell at the same time. Due to the difference in volume effect and electron donating ability between the two, DFOB - / BF4 - Position in the first solvation shell structure relative to FSI - Further inward, so FSI - Will precede DFOB - / BF4 - Reacts with lithium metal to form SEI, reducing DFOB - / BF4 - The possibility of uneven SEI. On the positive electrode side, DFOB - / BF4 - Precipitation Al 3+ / Fe 3+ The ability of the diluent to pull the solvent is not affected, and the DFOB is further improved by the diluent's pulling effect on the solvent. - / BF4 - Therefore, the two strategies work together to fill in the other's shortcomings without affecting their respective advantages, thus producing a 1+1>2 effect.

[0020] In addition to the synergistic effect between the strategies, there is also a significant synergistic effect between the amounts of raw materials used in the preparation. Specifically: the role of the main salt is to provide lithium ions and form a SEI film at the same time; the role of the auxiliary salt is to provide lithium ions and inhibit the corrosion of the lithium metal battery electrolyte to other components at the same time; if the auxiliary salt is too little, the corrosion of the aluminum foil by the obtained lithium metal battery electrolyte cannot be inhibited, and if the auxiliary salt is too much, the lithium metal electrolyte cannot form a stable SEI, and the stability of the lithium metal battery is poor. The molar ratio of the total salt (main salt + auxiliary salt) to the solvent determines the ratio of the solvent to the anion in the first solvation shell structure, that is, the lithium salt is only dissolved in the solvent and forms a local high concentration within the range of the solvent; if the total salt concentration is too high, the local high concentration is unstable and the salt is easy to precipitate. If the total salt concentration is too low, there are a large number of solvent molecules in the solvation shell structure, resulting in the formation of unstable SEI and CEI. The molar ratio of solvent to diluent determines the actual concentration of the resulting lithium metal battery electrolyte, significantly affecting the solubility of lithium salts (main salts and auxiliary salts) and the stability of the positive and negative electrodes of the lithium metal battery electrolyte. Too much diluent can easily cause lithium salt precipitation, while too little diluent can result in a high total solution concentration, increased viscosity, and reduced stability.

[0021] In summary, compared with the application of auxiliary salt strategy or local high concentration strategy alone, the solution provided by the present invention can significantly improve the application range of the obtained lithium metal battery electrolyte, so that the lithium metal battery can be stably cycled for more than 300 weeks at a high voltage of 4.6V.

[0022] According to some embodiments of the present invention, the molar ratio of the main salt to the auxiliary salt is 3 to 20:1, for example, about 4:1, 5:1, 10:1 or about 15:1.

[0023] According to some embodiments of the present invention, the solvent includes at least one of an ether solvent and a carbonate solvent.

[0024] According to some embodiments of the present invention, the ether solvent includes at least one of DME (ethylene glycol dimethyl ether, CAS: 110-71-4), DEGDME (diethylene glycol dimethyl ether, CAS: 111-96-6), DEE (ethylene glycol diethyl ether, CAS: 16484-86-9) and THF (tetrahydrofuran, CAS: 109-99-9).

[0025] According to some embodiments of the present invention, the carbonate solvent includes at least one of EC (ethylene carbonate, CAS: 96-49-1), DMC (dimethyl carbonate, CAS: 616-38-6), DEC (diethyl carbonate, CAS: 105-58-8), EMC (ethyl methyl carbonate, CAS: 623-53-0) and PC (propylene carbonate, CAS: 108-32-7).

[0026] According to some embodiments of the present invention, the ratio of the sum of the amounts of the main salt and the auxiliary salt to the amount of the solvent is 1:1.5 to 6.5, for example, about 1:2, 1:3, 1:4, 1:4.5, 1:5 or about 1:6.

[0027] According to some embodiments of the present invention, the DN value of the diluent is ≤10.

[0028] According to some embodiments of the present invention, the DN value of the diluent is between 1 and 10 (including the endpoint value). Within the above range, the lithium metal battery electrolyte will not be stratified, and will not dissolve the main salt or auxiliary salt, which is more conducive to forming a locally high-concentration lithium metal battery electrolyte.

[0029] According to some embodiments of the present invention, the fluoroether includes at least one of TTE (1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, CAS: 16627-68-2), BTFE (bis(2,2,2-trifluoroethyl) ether, CAS: 333-36-8) and TFE (1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, CAS: 406-78-0).

[0030] According to some embodiments of the present invention, in the fluoroether, the number of fluorine atoms substituted is ≥ 6, for example, 7 or 8.

[0031] According to some embodiments of the present invention, the fluorinated aromatic hydrocarbons include at least one of FB (fluorobenzene, CAS: 462-06-6), TFB (trifluorobenzene, CAS: 372-38-3, CAS: 367-23-7, CAS: 1489-53-8), mFT (3-fluorotoluene, CAS: 352-70-5) and TFMB (trifluoromethoxybenzene, CAS: 456-55-3).

[0032] According to some embodiments of the present invention, the fluorinated aromatic ether includes DFEB (2,3-difluorophenethyl ether, CAS: 121219-07-6).

[0033] The anti-oxidation property of the diluent also affects the capacity of the lithium metal battery at high voltage. At the same time, the interaction between the diluent and the solvent is also related to the stability of the solvent molecules at high voltage. The present invention can significantly improve the capacity and high-voltage stability of the lithium metal battery by selecting a suitable diluent.

[0034] According to some embodiments of the present invention, the diluent is selected from TTE. As a polyfluorinated ether, TTE has better high voltage stability than fluorinated aromatics and fluorinated aromatic ethers. In addition, compared with other fluorinated ethers such as BTFE, TTE has stronger hydrogen bond strength with the solvent, which can pull the solvent molecules to the outside of the solvation shell, inhibit the decomposition of the solvent molecules on the surface of the high-voltage positive electrode, and is more conducive to the capacity of the high-voltage lithium metal battery.

[0035] According to some embodiments of the present invention, the diluent is selected from a mixture of DFEB and FB, wherein the molar ratio of DFEB to FB is 1.5 to 2.5:1, for example, specifically about 2:1.

[0036] The mixture of DFEB and FB within the above-mentioned dosage ratio has a significant synergistic compounding effect, which can further optimize the solvation structure of the lithium metal battery electrolyte, improve the cycle performance of the lithium metal battery, and avoid the problems of overcharging and current collector corrosion.

[0037] According to some embodiments of the present invention, the molar ratio of the solvent to the diluent is 1:1.5 to 3.5, for example, about 1:2, 1:2.5, 1:2.8, 1:3 or about 1:3.2.

[0038] According to some embodiments of the present invention, the raw materials for preparing the lithium metal battery electrolyte further include auxiliary additives. In actual production, the type and amount of the auxiliary additives can be determined according to industry common sense, and the present invention does not impose strict restrictions, and the addition of the auxiliary additives does not affect the synergistic relationship between the main salt, auxiliary salt, solvent and diluent.

[0039] According to an embodiment of the second aspect of the present invention, a method for preparing a lithium metal battery electrolyte is provided, the preparation method comprising mixing raw materials for preparing the lithium metal battery electrolyte.

[0040] Since the preparation method adopts all the technical solutions of the lithium metal battery electrolyte of the above embodiment, it at least has all the beneficial effects brought by the technical solutions of the above embodiment.

[0041] According to some embodiments of the present invention, the preparation method is carried out under conditions of isolating water and oxygen. For example, it can be carried out in a dry glove box filled with argon. This can prevent the lithium metal battery electrolyte from absorbing moisture and the influence of moisture on components such as lithium salts.

[0042] According to some embodiments of the present invention, the preparation method comprises dissolving the lithium salt and the auxiliary salt in the solvent, and then mixing the resulting mixture with the diluent.

[0043] According to some embodiments of the present invention, the preparation method comprises first dissolving the main salt in the solvent, then dissolving the auxiliary salt in the obtained mixture, and finally mixing the obtained mixture with the diluent.

[0044] By limiting the addition ratio of the above-mentioned preparation raw materials, the preparation efficiency and uniformity of the lithium metal battery electrolyte can be significantly improved.

[0045] According to an embodiment of the third aspect of the present invention, a lithium metal battery is provided, wherein raw materials for preparing the lithium metal battery include the lithium metal battery electrolyte.

[0046] Since the lithium metal battery adopts all the technical solutions of the lithium metal battery electrolyte of the above embodiment, it has at least all the beneficial effects brought by the technical solutions of the above embodiment.

[0047] According to some embodiments of the present invention, the lithium metal battery includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte that soaks the above components;

[0048] The electrolyte is the lithium metal battery electrolyte provided by the first aspect of the present invention;

[0049] The negative electrode is a lithium metal negative electrode.

[0050] According to some embodiments of the present invention, the positive electrode includes a positive electrode current collector and a positive electrode coating covering a surface of the positive electrode current collector.

[0051] According to some embodiments of the present invention, the positive electrode current collector includes aluminum foil.

[0052] According to some embodiments of the present invention, the raw material for preparing the positive electrode coating includes a positive electrode active material.

[0053] According to some embodiments of the present invention, the positive electrode active material includes at least one of a polyanion material, a layered material, and a spinel material.

[0054] The polyanion material includes at least one of lithium iron phosphate, lithium manganese phosphate, and lithium manganese iron phosphate.

[0055] The general formula of the layered material is LiMO2, wherein M comprises at least one of nickel, cobalt and manganese.

[0056] In the layered material, M also includes a doping element; the doping element includes at least one of aluminum, zirconium, magnesium, titanium, boron, and fluorine.

[0057] The layered material includes at least one of undoped lithium cobalt oxide, lithium nickel oxide, lithium nickel cobalt oxide, lithium cobalt manganese oxide and lithium nickel cobalt manganese oxide. The proportion of transition metals in the layered material can be adjusted according to actual needs.

[0058] The spinel material includes lithium manganate (spinel phase).

[0059] According to some embodiments of the present invention, the lithium metal battery includes at least one of a button cell, a soft pack cell, a cylindrical cell and a steel case cell.

[0060] According to an embodiment of the fourth aspect of the present invention, there is provided an application of the lithium metal battery or lithium metal battery electrolyte in the fields of power batteries, 3C small household appliances and energy storage batteries.

[0061] Since the application adopts all the technical solutions of the lithium metal battery or lithium metal battery electrolyte of the above-mentioned embodiment, it has at least all the beneficial effects brought by the technical solutions of the above-mentioned embodiment.

[0062] If there is no special explanation, the actual meaning of “about” in the present invention is that the error is allowed to be within the range of ±2%, for example, about 100 is actually 100±2%×100.

[0063] Unless otherwise specified, “between” in the present invention includes the number itself, for example, “between 2 and 3” includes the endpoint values ​​2 and 3.

[0064] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the present invention. DETAILED DESCRIPTION

[0065] The following will be combined with the embodiments to clearly and completely describe the concept of the present invention and the technical effects produced, so as to fully understand the purpose, characteristics and effects of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0066] In the description of the present invention, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner.

[0067] Example 1

[0068] In this example, a lithium metal battery electrolyte was prepared by the following method:

[0069] In a glove box filled with dry argon, all the preparation raw materials were mixed according to the reagents and corresponding molar ratios described in Table 1.

[0070] Examples 2 to 17 and Comparative Examples 1 to 13 respectively prepared a lithium metal battery electrolyte, which differed from Example 1 in that:

[0071] The reagent selection or dosage of some preparation materials are different. The specific differences are shown in Table 1.

[0072] Table 1 Preparation raw material composition of the embodiment and comparative example (by molar ratio)

[0073]

[0074]

[0075] The ratios between the amounts in Table 1 actually represent the molar ratios between the raw materials. The CAS of HPT is 110-54-3; the CAS of bis(2,2,2-trifluoroethyl) ether is 333-36-8. LiBFSI represents lithium trifluoroborate fluorosulfonyl imide.

[0076] Application Examples

[0077] This example provides a lithium metal battery (full battery), which includes a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte that soaks the positive electrode, the negative electrode and the separator; wherein,

[0078] The positive electrode is composed of an aluminum foil and a positive electrode coating covering the surface of the aluminum foil. The positive electrode coating includes a positive electrode active material made of lithium cobalt oxide (purchased from Xiamen Tungsten New Energy, model XW123, with a nominal gram specific capacity of 190 mAh / g); the surface capacity density of the positive electrode coating is 2.3 mAh / cm 2 ;

[0079] The negative electrode is a 20 μm thick lithium foil;

[0080] The electrolyte is the lithium metal battery electrolyte obtained in the examples or comparative examples.

[0081] Test Case

[0082] This example tests the first aspect by visually testing the state of the lithium metal battery electrolyte obtained in the embodiments and application examples to see whether it is clear, whether crystals are precipitated, etc.

[0083] The second aspect of this example tests the cycle performance and overcharge of the lithium metal battery obtained in the application example. Specifically,

[0084] The test conditions for cycle performance are: cycle voltage 3-4.6V, charge to 4.6V at 0.5C, CV to 0.025C, discharge to 3V at 1C (set current 1.32A); temperature 25°C. Record the number of cycles for each group and calculate the capacity retention rate for 300 weeks (if the battery operates normally).

[0085] The following situations indicate that the lithium metal battery is overcharged: 1. The charging voltage cannot reach 4.6V and is continuously charged below 4.6V. 2. The current cannot be reduced to 0.025C during the CV stage. 3. The charging capacity exceeds the rated capacity (1.32Ah) by more than 10% for multiple cycles, or exceeds the rated capacity by more than 20% in a single cycle.

[0086] The test results of the above items are shown in Table 2.

[0087] Table 2 Appearance and performance of lithium metal battery electrolytes obtained in embodiments and application examples

[0088]

[0089]

[0090] By comparing Examples 1 to 3 and 8 to 9, it can be seen that by keeping the molar ratio of the solvent to the lithium salt (main salt + auxiliary salt), and the molar ratio of the diluent to the solvent unchanged, and adjusting the ratio of the main salt to the auxiliary salt, it is found that with the increase of the main salt ratio, the cycle performance of the lithium metal battery shows a trend of first increasing and then decreasing, and the cycle performance reaches a peak when the molar ratio of the main salt to the auxiliary salt is around 5.

[0091] By comparing Examples 1, 4-5, and 10-11, it can be seen that by maintaining the molar ratio of the main salt to the auxiliary salt, as well as the molar ratio of the diluent to the solvent, and adjusting the molar ratio of the solvent to the lithium salt, it is found that with the increase in the concentration of the lithium salt in the solvent, the cycle performance of the lithium metal battery shows a trend of first increasing and then decreasing; this may be due to the fact that the concentration is too low, the local high-concentration structure cannot perform well, and the lithium metal battery electrolyte has limited conductivity to lithium ions. If the concentration is too high, the dissolution of the lithium salt in the solvent is limited, and the lithium ions cannot be ionized well. The turbidity in Example 10 indicates that a lithium metal battery electrolyte with a uniform texture can still be formed, but the solubility critical point of the lithium salt has been reached.

[0092] By comparing Examples 1, 6-7, and 12-13, it can be seen that by keeping other conditions unchanged and adjusting the molar ratio of the diluent to the solvent, it is found that within the range provided by the present invention, the ratio has a relatively small effect on the performance of the lithium metal battery, but there is still a significant trend of first increasing and then decreasing. The specific reason is that the adjustment of the ratio of the diluent to the solvent will more affect the viscosity of the resulting lithium metal battery electrolyte, and then the viscosity affects its electrochemical properties. It should be noted that when the viscosity is too high, a similar turbidity phenomenon will still occur.

[0093] By comparing Examples 1 and 14 to 16, it can be seen that, compared with other types of diluents, using TTE as a diluent can better construct a local high concentration and better exert the overall performance of the obtained lithium metal battery electrolyte.

[0094] Comparison of Examples 15 to 17 shows that, among the diluents used in the present invention, there is a significant synergistic effect between FB and DFEB, and the combination of the two can achieve results significantly better than those of FB and DFEB.

[0095] By comparing Example 1 with Comparative Examples 1 to 4, it can be seen that if one or two of the raw materials for preparing the lithium metal battery electrolyte are missing, it may not affect the apparent performance of the obtained lithium metal battery electrolyte, but it will definitely affect its cycle performance. The overcharging phenomenon that occurs during the cycle will also be a safety hazard.

[0096] Comparing Example 1 with Comparative Examples 5 to 9, it can be seen that if the usage ratio of the raw materials for preparing the lithium metal battery electrolyte is not within the range required by the present invention, it will significantly affect the comprehensive performance of the obtained lithium metal battery electrolyte. For example, in Comparative Example 6, the content of the solvent is too little, and in Comparative Example 8, the content of the diluent is too much, which affects the solubility of the lithium salt to a certain extent, and the obtained lithium metal battery electrolyte has an uneven texture and cannot be used for electrochemical tests. In Comparative Examples 5, 7, and 9, although a lithium metal battery electrolyte with a uniform texture is obtained, its cycle performance is significantly reduced, and safety hazards such as overcharging are prone to occur during the charging and discharging process.

[0097] By comparing Example 1 with Comparative Examples 10 to 13, it can be seen that in the lithium metal battery electrolyte provided by the present invention, there is a synergistic effect between the main salt and the auxiliary salt, and there is also a significant synergistic effect between the type of diluent and other components. If the type of auxiliary salt or the type of diluent is adjusted, the performance of the lithium metal battery electrolyte will be significantly reduced; even the problem of the lithium metal battery electrolyte not being able to work will occur.

[0098] In summary, within the scope provided by the present invention, the prepared lithium metal battery electrolyte has a uniform texture, and due to the synergistic effect between various parameters and conditions, it performs well in the lithium metal battery cycle test, and basically does not have safety problems such as overcharging within the test range (overcharging is usually accompanied by current collector corrosion). It is precisely because of the above-mentioned technological advances that lithium metal batteries including the above-mentioned lithium metal battery electrolyte are expected to be widely used in the fields of power batteries, 3C small household appliances and energy storage batteries.

[0099] The above is a detailed description of the embodiments of the present invention in conjunction with the table, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge of ordinary technicians in the relevant technical field without departing from the purpose of the present invention. In addition, the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

Claims

1. A lithium metal battery electrolyte, characterized in that: The raw materials for preparing the lithium metal battery electrolyte include: Main salt, auxiliary salt, solvent and diluent; The main salt includes at least one of LiFSI and LiTFSI; The auxiliary salt includes at least one of LiDFOB and LiBF4; The diluent includes at least one of fluorinated ethers, fluorinated aromatic hydrocarbons and fluorinated aromatic ethers; The molar ratio of the main salt to the auxiliary salt is 1 to 1000:1; The ratio of the sum of the amounts of the main salt and the auxiliary salt to the amount of the solvent is 1:1 to 9; The molar ratio of the solvent to the diluent is 1:1 to 4; The main salt and the auxiliary salt are insoluble in the diluent.

2. The lithium metal battery electrolyte according to claim 1, characterized in that The solvent includes at least one of an ether solvent and a carbonate solvent.

3. The lithium metal battery electrolyte according to claim 2, characterized in that The ether solvent includes at least one of DME, DEGDME, DEE and THF; and / or the carbonate solvent includes at least one of EC, DMC, DEC, EMC and PC.

4. The lithium metal battery electrolyte according to claim 1, characterized in that The DN value of the diluent is between 1 and 10; preferably, the fluoroether includes at least one of TTE, BTFE and TFE; preferably, the fluoroaromatic hydrocarbon includes at least one of FB, TFB, mFT and TFMB; preferably, the fluoroaromatic ether includes DFEB.

5. The lithium metal battery electrolyte according to any one of claims 1 to 4, characterized in that: The molar ratio of the main salt to the auxiliary salt is 3 to 20:

1.

6. The lithium metal battery electrolyte according to any one of claims 1 to 4, characterized in that: The ratio of the sum of the amounts of the main salt and the auxiliary salt to the amount of the solvent is 1:1.5 to 6.

5.

7. The lithium metal battery electrolyte according to any one of claims 1 to 4, characterized in that The molar ratio of the solvent to the diluent is 1:1.5 to 3.

5.

8. A method for preparing a lithium metal battery electrolyte according to any one of claims 1 to 7, characterized in that: The preparation method comprises mixing the raw materials for preparing the lithium metal battery electrolyte.

9. A lithium metal battery, characterized in that: The raw materials for preparing the lithium metal battery include the lithium metal battery electrolyte as described in any one of claims 1 to 7.

10. Use of the lithium metal battery as claimed in claim 9, or the lithium metal battery electrolyte as claimed in any one of claims 1 to 7 in the fields of power batteries, 3C small household appliances and energy storage batteries.

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