Electrolyte solution for lithium metal batteries, and preparation method therefor and use thereof

Abstract

An electrolyte solution for lithium metal batteries. Raw materials for the preparation thereof comprise: a main salt, an auxiliary salt, a solvent, and a diluent, wherein 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 a fluoroether, a fluoroarene and a fluoroaryl ether; a molar ratio of the main salt to the auxiliary salt is 1-1000:1; a ratio of the total amount of substance of the main salt and the auxiliary salt to the amount of substance of the solvent is 1:1-9; and a molar ratio of the solvent to the diluent is 1:1-4. Also provided are a preparation method for and the use of the electrolyte solution for lithium metal batteries.

Description

Lithium metal battery electrolyte and preparation method and application thereof TECHNICAL FIELD

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

[0002] The energy density of lithium batteries has become a bottleneck restricting the further improvement of the performance of electric vehicles, unmanned aerial vehicles, smart phones and other devices. The raw materials for preparing lithium ion batteries include positive active materials and negative active materials. The current commercial and mature negative active material is graphite. However, the actual capacity of the graphite negative electrode has approached its theoretical limit, and the room for improvement is limited. Therefore, it is urgent to develop a new type of high-capacity negative electrode to improve the energy density of lithium ion batteries.

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

[0004] At present, the main idea for solving the cycle problem of the lithium metal negative electrode is to optimize the composition of the electrolyte. For example, adding appropriate additives to the electrolyte in order to form a uniform and stable SEI structure on the surface of the lithium metal during the cycle process, thereby inhibiting the formation of lithium dendrites. For another example, optimizing the type of lithium salt: lithium bisfluorosulfonylimide (LiFSI) or lithium bis(trifluoromethanesulfonyl)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 generation of lithium dendrites. However, the application of LiFSI / LiTFSI in high-voltage (>4.25 V) lithium metal batteries is still subject to its corrosion of aluminum foil at high voltage. In addition, in the button test, the corrosion of LiFSI / LiTFSI to the steel shell of the battery at high voltage also affects the judgment of the performance of the electrolyte.

[0005] In summary, the existing electrolyte still has the problems of serious corrosion, poor cycle performance and safety performance when applied to lithium metal batteries.

[0006] SUMMARY

[0007] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application provides a lithium metal battery electrolyte which can effectively avoid the corrosion of the electrolyte to the current collector and the steel shell, and can also significantly improve the cycle performance of the lithium metal battery.

[0008] The present application also provides a preparation method of the above-mentioned lithium metal battery electrolyte.

[0009] The application also provides an application of the above lithium metal battery electrolyte.

[0010] According to the embodiments of the first aspect of the application, a lithium metal battery electrolyte is provided, and the raw materials for preparing the lithium metal battery electrolyte include:

[0011] a main salt, an auxiliary salt, a solvent, and a diluent;

[0012] The main salt includes at least one of LiFSI (lithium bisfluorosulfonylimide, CAS: 171611-11-3) and LiTFSI (lithium bis(trifluoromethanesulfonyl)imide, CAS: 90076-65-6);

[0013] The auxiliary salt includes at least one of LiDFOB (lithium difluoro(oxalato)borate, CAS: 409071-16-5) and LiBF4 (lithium tetrafluoroborate, CAS: 14283-07-9);

[0014] The diluent includes at least one of a fluorinated ether, a fluorinated aromatic hydrocarbon, and a fluorinated aromatic ether;

[0015] The molar ratio of the main salt and the auxiliary salt is 1-1000:1;

[0016] The ratio of the sum of the amounts of substances of the main salt and the auxiliary salt to the amount of substance of the solvent is 1:1-9;

[0017] The molar ratio of the solvent and the diluent is 1:1-4;

[0018] The main salt and the auxiliary salt are insoluble in the diluent.

[0019] The lithium metal battery electrolyte according to the embodiments of the application has at least the following beneficial effects:

[0020] The application uses LiDFOB or LiBF4 as an auxiliary salt, and keeps the obtained lithium metal battery electrolyte in a local high concentration state (a mixture formed by dissolving the main salt and the auxiliary salt in the solvent, dispersed in the diluent) by adding an inert diluent. Through the combination of the above two means, the problem of corrosion of aluminum foil / steel shell of the lithium metal battery electrolyte with LiFSI / LiTFSI as the main salt at high voltage is solved. The lithium metal battery using the above lithium metal battery electrolyte can be stably cycled at a voltage of 4.6V. The reasons are as follows: the auxiliary salt strategy alone can only guarantee the stability of the positive electrode side, and DFOB - / BF4 - FSI -The instability of the electrolyte can lead to poor overall battery cycle performance; a single local high-concentration strategy is unlikely to completely suppress the corrosive effect of lithium metal battery electrolyte on aluminum foil / steel casing, resulting in overcharging. However, when both are used in combination, thanks to the squeezing effect of the diluent on the solvated structure, FSI... - and DFOB - / BF4 - They will both appear in the first solvation shell. Due to the differences in their volume effect and electron-donating ability, DFOB - / BF4 - Position in the first solvation shell structure relative to FSI - Further inward, therefore FSI - It will precede DFOB - / BF4 - It reacts with lithium metal to form SEI, which reduces DFOB. - / BF4 - The possibility of uneven SEI. On the positive side, DFOB... - / BF4 - Al precipitation 3+ / Fe 3+ The ability remains unaffected, and the diluent's pull on the solvent further enhances the DFOB's performance. - / BF4 - Therefore, the combined effect of the two strategies can compensate for each other's weaknesses without affecting their respective strengths, thus producing a 1+1>2 effect.

[0021] Besides the synergistic effects between strategies, there are also significant synergistic effects between the amounts of raw materials used in preparation. Specifically: the main salt provides lithium ions and forms the SEI film; the auxiliary salt provides lithium ions and inhibits the corrosion of other components by the lithium metal battery electrolyte. If there is too little auxiliary salt, the corrosion of aluminum foil by the resulting lithium metal battery electrolyte cannot be inhibited; if there is too much auxiliary salt, the lithium metal electrolyte cannot form a stable SEI, resulting in poor stability of the lithium metal battery. The molar ratio of total salt (main salt + auxiliary salt) to solvent determines the ratio of solvent to anion in the first solvation shell structure, i.e., lithium salt dissolves only in the solvent and forms a local high concentration within the solvent's presence. If the total salt concentration is too high, the local high concentration is unstable, leading to easy salt precipitation; if the total salt concentration is too low, there are a large number of solvent molecules in the solvation shell structure, leading to the formation of unstable SEI and CEI. The molar ratio of solvent to diluent determines the true concentration of the resulting lithium metal battery electrolyte, significantly affecting the solubility of lithium salts (main 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 will result in a higher total concentration of the solution, leading to increased viscosity and reduced stability.

[0022] In summary, compared with the application of auxiliary salt strategy or local high concentration strategy alone, the scheme provided in the application can significantly improve the application range of the obtained lithium metal battery electrolyte, so that the lithium metal battery can be stably cycled at a high voltage of 4.6 V for more than 300 cycles.

[0023] According to some embodiments of the application, the molar ratio of the main salt and the auxiliary salt is 3-20:1, for example, specifically about 4:1, 5:1, 10:1 or about 15:1.

[0024] According to some embodiments of the application, the solvent includes at least one of an ether solvent and a carbonate solvent.

[0025] According to some embodiments of the application, the ether solvent includes at least one of DME (dimethyl ether glycol, CAS: 110-71-4), DEGDME (diethylene glycol dimethyl ether, CAS: 111-96-6), DEE (diethylene glycol diethyl ether, CAS: 16484-86-9) and THF (tetrahydrofuran, CAS: 109-99-9).

[0026] According to some embodiments of the application, 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 (methyl ethyl carbonate, CAS: 623-53-0) and PC (propylene carbonate, CAS: 108-32-7).

[0027] According to some embodiments of the application, the ratio of the sum of the amounts of substances of the main salt and the auxiliary salt to the amount of substance of the solvent is 1:1.5-6.5, for example, specifically about 1:2, 1:3, 1:4, 1:4.5, 1:5 or about 1:6.

[0028] According to some embodiments of the application, the DN value of the diluent is ≤10.

[0029] According to some embodiments of the application, the DN value of the diluent is between 1 and 10 (including the end point value). Within the above range, the lithium metal battery electrolyte does not appear to be stratified, and does not dissolve the main salt or the auxiliary salt, which is more helpful to form a local high concentration of lithium metal battery electrolyte.

[0030] According to some embodiments of the present application, the fluorinated ether 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).

[0031] According to some embodiments of the present application, the fluorine atom substitution number in the fluorinated ether is ≥ 6, for example, specifically can be 7 or 8.

[0032] According to some embodiments of the present application, the fluorinated aromatic hydrocarbon includes 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).

[0033] According to some embodiments of the present application, the fluorinated aromatic ether includes DFEB (2,3-difluoro phenyl ethyl ether, CAS: 121219-07-6).

[0034] The antioxidant 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 also relates to the stability of the solvent molecules at high voltage. By selecting a suitable diluent, the present application can significantly improve the capacity and high voltage stability of the lithium metal battery.

[0035] According to some embodiments of the present application, the diluent is TTE. As a polyfluoro ether, TTE has better high voltage stability than fluorinated aromatic hydrocarbons and fluorinated aromatic ethers. Moreover, compared with other fluorinated ethers such as BTFE, TTE has stronger hydrogen bonding 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 positive electrode at high voltage, and is more conducive to the capacity of the high voltage lithium metal battery.

[0036] According to some embodiments of the present application, the diluent is a mixture of DFEB and FB. The molar ratio of the DFEB and FB is 1.5-2.5:1, for example, specifically can be about 2:1.

[0037] Within the above molar ratio range, the mixture of DFEB and FB 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 overcharge and current collector corrosion.

[0038] According to some embodiments of the present application, the molar ratio of the solvent and the diluent is 1:1.5-3.5, for example, specifically can be about 1:2, 1:2.5, 1:2.8, 1:3 or about 1:3.2.

[0039] According to some embodiments of the present application, the preparation raw materials of 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 the industry common sense, and the present application does not make strict restrictions, and the addition of the auxiliary additives does not affect the synergistic effect between the main salt, the auxiliary salt, the solvent and the diluent.

[0040] According to the embodiments of the second aspect of the present application, a preparation method of a lithium metal battery electrolyte is provided, and the preparation method comprises mixing the preparation raw materials of the lithium metal battery electrolyte.

[0041] Since the preparation method adopts all the technical solutions of the lithium metal battery electrolyte of the above-mentioned embodiments, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments.

[0042] According to some embodiments of the present application, the preparation method is carried out under the condition of isolating water and oxygen, for example, can be carried out in a dry glove box filled with argon. In this way, the lithium metal battery electrolyte can be prevented from absorbing moisture, and the influence of moisture on the components such as lithium salt can be avoided.

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

[0044] According to some embodiments of the present application, the preparation method comprises dissolving the main salt in the solvent, dissolving the auxiliary salt in the obtained mixture, and finally mixing the obtained mixture with the diluent.

[0045] 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.

[0046] According to the embodiments of the third aspect of the present application, a lithium metal battery is provided, and the preparation raw materials of the lithium metal battery include the lithium metal battery electrolyte.

[0047] Since the lithium metal battery adopts all the technical solutions of the lithium metal battery electrolyte of the above-mentioned embodiments, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments.

[0048] According to some embodiments of the present application, the lithium metal battery comprises a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and an electrolyte infiltrating the above-mentioned components.

[0049] The electrolyte is the lithium metal battery electrolyte provided in the first aspect of the application.

[0050] The negative electrode is a lithium metal negative electrode.

[0051] According to some embodiments of the application, the positive electrode comprises a positive electrode current collector and a positive electrode coating layer covering the surface of the positive electrode current collector.

[0052] According to some embodiments of the application, the positive electrode current collector comprises an aluminum foil.

[0053] According to some embodiments of the application, the raw materials for preparing the positive electrode coating layer comprise a positive electrode active material.

[0054] According to some embodiments of the application, the positive electrode active material comprises at least one of a polyanion material, a layered material and a spinel material.

[0055] The polyanion material comprises at least one of lithium iron phosphate, lithium manganese phosphate and lithium manganese iron phosphate.

[0056] The layered material has a general formula of LiMO2, wherein M comprises at least one of nickel, cobalt and manganese.

[0057] In the layered material, M further comprises a doping element; the doping element comprises at least one of aluminum, zirconium, magnesium, titanium, boron and fluorine.

[0058] The layered material comprises at least one of undoped lithium cobaltate, lithium nickelate, lithium nickel cobaltate, lithium cobalt manganeseate and lithium nickel cobalt manganeseate. The proportion of transition metals in the layered material can be adjusted according to actual requirements.

[0059] The spinel material comprises lithium manganate (spinel phase).

[0060] According to some embodiments of the application, the lithium metal battery comprises at least one of a button cell, a soft pack battery, a cylindrical battery and a steel shell battery.

[0061] According to the embodiments of the fourth aspect of the application, the application of the lithium metal battery or the lithium metal battery electrolyte in the field of power batteries, the field of 3C small household appliances and the field of energy storage batteries is provided.

[0062] Since the application adopts all the technical solutions of the lithium metal battery or the lithium metal battery electrolyte of the above-mentioned embodiments, it at least has all the beneficial effects brought by the technical solutions of the above-mentioned embodiments.

[0063] Unless otherwise specified, "about" in the present application actually means that the allowed error is within ±2%, for example, about 100 actually means 100±2%*100.

[0064] Unless otherwise indicated herein, "between" is inclusive of the numbers, e.g., "between 2 and 3" includes the endpoints 2 and 3.

[0065] Other features and advantages of the present application will be set forth in the description that follows, and in part will be apparent from the description, or can be learned by practice of the application. DETAILED DESCRIPTION

[0066] The concept and the technical effects of the present application will be described in detail below in conjunction with the embodiments. Obviously, the described embodiments are only a part of the embodiments of the present application, and other embodiments obtained by those skilled in the art based on the embodiments of the present application without creative effort fall within the protection scope of the present application.

[0067] In the description of the present application, the description of the terms "one embodiment", "some embodiments", "exemplary embodiment", "example", "specific example" 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 application. In the present specification, the exemplary description of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0068] Embodiment 1

[0069] In this example, a lithium metal battery electrolyte is prepared, and the specific method is as follows:

[0070] In a glove box filled with dry argon, all the raw materials are mixed according to the reagents described in Table 1 and the corresponding molar ratio.

[0071] Embodiments 2 to 18 and Comparative Examples 1 to 13 each prepare a lithium metal battery electrolyte, and the specific difference from Embodiment 1 is that:

[0072] The reagent selection or the amount of some of the raw materials is different. The specific difference is shown in Table 1.

[0073] Table 1: Composition of raw materials for preparation (in molar ratio)

[0074] The ratio between the amounts in Table 1 actually represents the molar ratio between each raw material. The CAS of HPT is 110-54-3; the CAS of bis(2,2,2 trifluoroethyl) ether is 333-36-8. LiBFSI represents lithium fluorosulfonylimide trifluoroborate.

[0075] Application Example

[0076] This example provides a lithium metal battery (full battery), which comprises a positive electrode, a negative electrode, a separator arranged between the positive electrode and the negative electrode, and an electrolyte infiltrating the positive electrode, the negative electrode and the separator; wherein,

[0077] The positive electrode is composed of an aluminum foil and a positive electrode coating layer coated on the surface of the aluminum foil, and the positive electrode coating layer comprises a positive electrode active material with a material of lithium cobalt oxide (purchased from Xiamen Tungsten New Energy, model XW123, nominal specific capacity 190 mAh / g); the areal capacity density of the positive electrode coating layer is 2.3 mAh / cm 2 ;

[0078] The negative electrode is a lithium foil with a thickness of 20 μm;

[0079] The electrolyte is the lithium metal battery electrolyte obtained in the examples or comparative examples.

[0080] Test Example

[0081] In the first aspect of this example, the state of the lithium metal battery electrolyte obtained in the examples and comparative examples is tested by visual inspection to see if it is clear, if crystals are precipitated, etc.

[0082] In the second aspect of this example, the cycle performance and overcharge of the lithium metal battery obtained in the application example are tested. Specifically:

[0083] The test conditions for cycle performance are: cycle voltage 3-4.6V, charged to 4.6V at 0.5C, CV to 0.025C, discharged to 3V at 1C (set current 1.32A); temperature 25℃. Record the cycle number of each group, and calculate the capacity retention rate at 300 cycles (if the battery is running normally).

[0084] If any of the following conditions occurs, it means that the lithium metal battery is overcharged: 1. The charging voltage cannot reach 4.6V, and continues to charge below 4.6V. 2. The current cannot be reduced to 0.025C in the CV stage. 3. The charging capacity continuously exceeds the rated (1.32 Ah) capacity by more than 10% in multiple cycles, or exceeds the rated capacity by more than 20% in a single cycle.

[0085] The test results of the above are shown in Table 2.

[0086] Table 2 Appearance and performance of lithium metal battery electrolyte obtained in examples and comparative examples

[0087] From Comparative Examples 1-3, 8-9, it can be seen that the molar ratio of the solvent and the lithium salt (main salt + auxiliary salt) and the molar ratio of the diluent and the solvent are kept unchanged, the proportion of the main salt and the auxiliary salt is adjusted, and with the increase of the proportion of the main salt, the cycle performance of the lithium metal battery appears a trend of first increasing and then decreasing, and the cycle performance reaches a peak when the molar ratio of the main salt and the auxiliary salt is about 5.

[0088] From Comparative Examples 1, 4-5, 10-11, it can be seen that the molar ratio of the main salt and the auxiliary salt and the molar ratio of the diluent and the solvent are kept unchanged, the molar ratio of the solvent and the lithium salt is adjusted, and with the increase of the concentration of the lithium salt in the solvent, the cycle performance of the lithium metal battery appears a trend of first increasing and then decreasing, which may be due to that the local high-concentration structure cannot well play the performance due to too low concentration, the lithium ion conduction of the lithium metal battery electrolyte is limited, and if the concentration is too high, the solubility of the lithium salt in the solvent is limited, and the lithium ion cannot be well ionized. In Example 10, the turbidity indicates that a lithium metal battery electrolyte with uniform texture can still be formed, but the solubility critical point of the lithium salt has been reached.

[0089] From Comparative Examples 1, 6-7, 12-13, it can be seen that the molar ratio of the diluent and the solvent is adjusted while other conditions are kept unchanged, and within the range provided in the present application, the ratio has a relatively small effect on the performance of the lithium metal battery, but still appears a significant trend of first increasing and then decreasing. The specific reason is that the adjustment of the ratio of the diluent and the solvent will more affect the viscosity of the obtained lithium metal battery electrolyte, and then affect its electrochemical performance. It should be noted that when the viscosity is too high, a similar turbidity phenomenon will still occur.

[0090] From Comparative Examples 1, 14-16, it can be seen that compared with other kinds of diluents, using TTE as the diluent can better construct a local high concentration and better play the overall performance of the obtained lithium metal battery electrolyte.

[0091] From Comparative Examples 15-17, it can be seen that among the diluents used in the present application, there is a significant synergistic effect between FB and DFEB, and after the cooperation of the two, a result significantly better than using FB or DFEB alone can be obtained.

[0092] From Comparative Examples 1 and Comparative Examples 1-4, it can be seen that if one or two of the raw materials for preparing the lithium metal battery electrolyte are missing, the apparent performance of the obtained lithium metal battery electrolyte may not be affected, but the cycle performance will be affected, and the overcharge phenomenon occurring during the cycle process is also a safety hazard.

[0093] From the comparison of Example 1 and Comparative Examples 5-9, it can be seen that if the proportion of the raw materials used in the preparation of the lithium metal battery electrolyte is not within the range claimed in the present application, the comprehensive performance of the obtained lithium metal battery electrolyte will be significantly affected. For example, in Comparative Example 6, the content of the solvent is too low, and in Comparative Example 8, the content of the diluent is too high, which will affect the solubility of the lithium salt to some extent, resulting in a non-uniform texture of the lithium metal battery electrolyte, which cannot be used for electrochemical tests. In Comparative Examples 5, 7 and 9, although a lithium metal battery electrolyte with uniform texture is obtained, its cycle performance is significantly reduced, and overcharging and other safety hazards are prone to occur during the charging and discharging process.

[0094] From the comparison of Example 1 and Comparative Examples 10-13, it can be seen that in the lithium metal battery electrolyte provided in the present application, there is a synergistic effect between the main salt and the auxiliary salt, and there is also a significant synergistic effect between the diluent and other components. If the type of auxiliary salt is adjusted or the type of diluent is adjusted, the performance of the lithium metal battery electrolyte will be significantly reduced; and even the problem of the lithium metal battery electrolyte not working will occur.

[0095] In summary, within the scope provided in the present application, the lithium metal battery electrolyte prepared has a uniform texture, and due to the synergistic effect between the various parameters and conditions, it performs well in the lithium metal battery cycle test, and basically does not have safety problems such as overcharging (overcharging is usually accompanied by current collector corrosion) within the test range. Due to the above technical progress, lithium metal batteries including the above lithium metal battery electrolyte are expected to be widely used in the fields of power batteries, 3C small household appliances and energy storage batteries.

[0096] The above describes the embodiments of the present application in detail in combination with the table, but the present application is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the protection of the present application. In addition, the embodiments of the present application 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: a main salt, an auxiliary salt, a solvent, and a 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 a fluoroether, a fluoroarene, and a fluoroaromatic ether; a molar ratio of the main salt to the auxiliary salt is 1-1000:1; a ratio of a sum of amounts of substances of the main salt and the auxiliary salt to an amount of substance of the solvent is 1:1-9; a molar ratio of the solvent to the diluent is 1:1-4; the main salt and the auxiliary salt are insoluble in the diluent.

2. The lithium metal battery electrolyte of claim 1, wherein, the solvent includes at least one of an ether solvent and a carbonate solvent.

3. The lithium metal battery electrolyte of claim 2, wherein, 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 of claim 1, wherein, a DN value of the diluent is between 1 and 10; preferably, the fluoroether includes at least one of TTE, BTFE, and TFE; preferably, the fluoroarene includes at least one of FB, TFB, mFT, and TFMB; preferably, the fluoroaromatic ether includes DFEB.

5. The lithium metal battery electrolyte of any one of claims 1 to 4, wherein, a molar ratio of the main salt to the auxiliary salt is 3-20:

1.

6. The lithium metal battery electrolyte of any one of claims 1 to 4, wherein, a ratio of a sum of amounts of substances of the main salt and the auxiliary salt to an amount of substance of the solvent is 1:1.5-6.

5.

7. The lithium metal battery electrolyte of any one of claims 1 to 4, wherein, a molar ratio of the solvent to the diluent is 1:1.5-3.

5.

8. A method of preparing a lithium metal battery electrolyte as claimed in any one of claims 1 to 7, characterized in that, the preparation method includes 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 according to any one of claims 1 to 7.

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

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