Perfluorinated electrolyte and high-voltage incombustible lithium metal battery

Abstract

The invention belongs to the technical field of lithium metal batteries, and particularly relates to a perfluorinated electrolyte and a high-voltage incombustible lithium metal battery. The perfluorinated electrolyte comprises the following components: a perfluorinated organic solvent and a lithium salt, the perfluorinated organic solvent comprises fluorinated chain ester, a fluorinated annular film-forming agent and a fluorinated diluent. The electrolyte provided by the invention can synchronously realize dual protection on the positive electrode and the negative electrode of the lithium metal battery, and enhances the compatibility with the lithium metal negative electrode; and the electrolyte has good flame retardant property, so that the safety of the secondary battery is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and more particularly relates to a perfluorinated electrolyte and a high-voltage non-flammable lithium metal battery. Background Art

[0002] Lithium metal batteries (LMBs) are regarded as a promising electrochemical energy storage technology due to their high energy density potential. However, interfacial problems between the lithium metal anode and the electrolyte, such as continuous electrolyte decomposition and unstable solid electrolyte interface (SEI) formation, as well as safety hazards and low Coulombic efficiency (CE) caused by lithium dendrite growth, limit their practical application. To address these problems, researchers have explored various strategies, among which electrolyte engineering has become a key research direction. By designing new electrolyte systems, the interfacial stability of the lithium metal anode can be improved, the growth of lithium dendrites can be inhibited, and the overall performance of the battery can be improved. Ester electrolytes are compatible with high-voltage cathode materials (>4.5V) due to their excellent antioxidant properties, which is crucial for improving the energy density of lithium metal batteries. However, they have obvious shortcomings in interfacial stability with the lithium metal anode.

[0003] Currently, the main strategy to address the compatibility of esters with lithium metal anodes is to form a stable SEI, which is derived from anion-rich lithium ion solvation structure, such as highly concentrated electrolytes (HCEs), locally highly concentrated electrolytes (LHCEs) and weakly solvating electrolytes (WSEs). However, HCEs require high salt concentrations, resulting in high viscosity and low wettability. Suitable diluents and weakly solvating solvents are the key points of LHCEs and WSEs systems, respectively, leading to high complexity in electrolyte design. Therefore, it is necessary to develop an effective, convenient and safe high-voltage electrolyte. Summary of the Invention

[0004] The purpose of the present invention is to provide a perfluorinated electrolyte and a high-voltage non-flammable lithium metal battery, specifically a perfluorinated ester-based electrolyte, which significantly improves the compatibility between the ester electrolyte and the negative electrode material in the lithium metal battery by precisely controlling the solvation structure. It can not only effectively inhibit the continuous decomposition of the electrolyte under high voltage conditions, but also ensure the structural stability of the positive electrode material and the overall cycle performance of the battery, thereby solving the problems existing in the above-mentioned prior art.

[0005] To achieve the above object, the present invention provides the following solutions:

[0006] One of the technical solutions of the present invention is to provide a perfluoroester-based electrolyte, the components of which include a perfluoroorganic solvent and a lithium salt;

[0007] The perfluorinated organic solvent includes a fluorinated chain ester, a fluorinated cyclic film-forming agent and a fluorinated diluent.

[0008] Furthermore, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

[0009] Furthermore, the fluorinated chain ester includes at least one of bis(2-fluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) carbonate, methyl trifluoroethyl carbonate and ethyl trifluoroethyl carbonate, preferably bis(2-fluoroethyl) carbonate.

[0010] Furthermore, the fluorinated cyclic film-forming agent includes at least one of fluoroethylene carbonate, difluoroethylene carbonate and 3,3,3-trifluoropropylene carbonate, preferably fluoroethylene carbonate.

[0011] Furthermore, the fluorinated diluent includes at least one of fluorobenzene, 1,2-difluorobenzene and 1,3,5-trifluorobenzene, preferably fluorobenzene.

[0012] Furthermore, the volume ratio of the fluorinated chain ester, the fluorinated cyclic film-forming agent and the fluorinated diluent in the perfluorinated organic solvent is 6-8:1-2:1-2.

[0013] Furthermore, the concentration of lithium salt in the perfluoroester-based electrolyte is 0.5-1 mol / L.

[0014] The perfluoroester-based electrolyte provided by the present invention uses a fluorinated film-forming agent and a fluorinated diluent as co-additives. When the film-forming agent and the diluent are present at the same time, the fluorinated film-forming agent can form an excellent passivation film at the electrode interface, thereby blocking direct contact between the lithium metal negative electrode / positive electrode and the electrolyte, inhibiting the continuous decomposition of the electrolyte on the electrode surface, and ensuring electrode stability. The fluorinated chain ester is used as the main solvent to reduce the viscosity of the electrolyte and improve the conductivity. The fluorine in the diluent forms an intermolecular force with other solvents (the fluorine in the fluorinated diluent forms intermolecular hydrogen bonds with the hydrogen between the fluorinated chain ester and the fluorinated cyclic ester), so that more The anions enter the solvation shell and form a solvation structure rich in anions, which is more conducive to forming a dense and tough film on the electrode interface, thereby avoiding the problem of fragmentation / reorganization of the protective film during the deposition / stripping process due to insufficient film-forming strength of the film-forming agent on the electrode surface, further blocking the continuous decomposition of the solvent and anions, inhibiting the decomposition of the electrolyte, and improving the cycle stability of the electrolyte; the present invention promotes the mutual promotion of the film-forming agent and the diluent to improve the oxidation resistance of the electrolyte and the cycle stability of the electrode. The obtained electrolyte is used in lithium metal batteries, which can improve the cycle stability under high pressure.

[0015] The second technical solution of the present invention is to provide an application of the above-mentioned perfluoroester-based electrolyte in a lithium metal battery.

[0016] The perfluoroester-based electrolyte provided by the present invention is a perfluoro high-voltage non-flammable electrolyte and can be used for the preparation of high-voltage lithium metal batteries.

[0017] The third technical solution of the present invention: provides a lithium metal battery, wherein the electrolyte of the lithium metal battery is the above-mentioned perfluoroester-based electrolyte.

[0018] The fourth technical solution of the present invention: provides a method for improving the flame retardant performance of a lithium metal battery, wherein the electrolyte of the lithium metal battery uses the above-mentioned perfluoroester-based electrolyte.

[0019] The lithium metal battery prepared by using the perfluoroester-based electrolyte provided by the present invention has excellent flame retardant properties and is a non-flammable lithium metal battery.

[0020] The present invention discloses the following technical effects:

[0021] The perfluoroester-based electrolyte provided by the present invention comprises a perfluoroorganic solvent and a lithium salt as its components; the perfluoroorganic solvent comprises a fluorinated chain ester, a fluorinated cyclic film-forming agent, and a fluorinated diluent. The electrolyte uses the diluent and the film-forming agent as common additives. When used in lithium metal batteries, it can achieve excellent cycle performance at a cutoff voltage of 4.6V and has broad application prospects.

[0022] The perfluoroester-based electrolyte provided by the present invention uses less lithium salt, has low cost, is free of secondary pollution, and significantly improves the long-cycle performance of lithium metal batteries under high voltage.

[0023] The perfluoroester-based electrolyte provided by the present invention can simultaneously achieve dual protection for the positive and negative electrodes of lithium metal batteries, enhancing compatibility with the lithium metal negative electrode; and the electrolyte has excellent flame retardant properties, thereby effectively improving the safety of secondary batteries.

[0024] The lithium metal battery electrolyte of the present invention significantly improves the antioxidant performance of the electrolyte through reasonable optimization of perfluorinated solvents and lithium salts; and significantly improves the cycle life of the lithium metal battery under high voltage conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings, which constitute part of the present invention, are provided to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are provided to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0026] Figure 1 These are the linear sweep voltammetry test results of the Li||SS batteries prepared in Examples 1-2 and Comparative Example 1.

[0027] Figure 2 Comparison of the coulombic efficiency of the Li||Cu batteries prepared in Example 1 and Comparative Example 1.

[0028] Figure 3This is a long cycle performance diagram of the Li||LiCoO2 battery prepared in Examples 1-2 and Comparative Example 1.

[0029] Figure 4 The voltage curves of the Li||Li batteries prepared in Example 1 and Comparative Example 1 are shown.

[0030] Figure 5 The charge and discharge performance of the Li||LiCoO2 batteries prepared in Example 1 and Comparative Example 1, where a is Comparative Example 1 and b is Example 1.

[0031] Figure 6 Li||LiNi prepared in Example 2 0.8 Co 0.1 Mn 0.1 Stable cycle test results of O2 batteries.

[0032] Figure 7 The flame retardant performance comparison between Example 1 and Comparative Example 1 is shown in FIG. 1 , wherein a is Comparative Example 1 and b is Example 1. DETAILED DESCRIPTION

[0033] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0034] It should be understood that the terms described herein are intended only to describe particular embodiments and are not intended to limit the present invention. In addition, for numerical ranges herein, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. The intermediate value within any stated value or stated range, and each smaller range between any other stated value or intermediate value within the stated range, is also encompassed within the present invention. The upper and lower limits of these smaller ranges may be independently included or excluded within the scope.

[0035] Unless otherwise indicated, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art. Although only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may also be used in the practice or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of any conflict with any incorporated document, the contents of this specification shall prevail.

[0036] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments described herein without departing from the scope or spirit of the invention. Other embodiments will be apparent to those skilled in the art from the description of the invention. The description and examples are intended to be illustrative only.

[0037] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0038] In some specific embodiments, the present invention provides a perfluoroester-based electrolyte comprising a perfluoroorganic solvent and a lithium salt;

[0039] The perfluorinated organic solvent includes a fluorinated chain ester, a fluorinated cyclic film-forming agent and a fluorinated diluent.

[0040] In some specific embodiments, the lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide, and lithium bis(trifluoromethanesulfonyl)imide.

[0041] In some specific embodiments, the fluorinated chain ester includes at least one of bis(2-fluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) carbonate, methyl trifluoroethyl carbonate and ethyl trifluoroethyl carbonate, preferably bis(2-fluoroethyl) carbonate.

[0042] In some specific embodiments, the fluorinated cyclic film-forming agent includes at least one of fluoroethylene carbonate, bisfluoroethylene carbonate and 3,3,3-trifluoropropylene carbonate, preferably fluoroethylene carbonate.

[0043] In some specific embodiments, the fluorinated diluent includes at least one of fluorobenzene, 1,2-difluorobenzene and 1,3,5-trifluorobenzene, preferably fluorobenzene.

[0044] In some specific embodiments, the volume ratio of the fluorinated chain ester, the fluorinated cyclic film-forming agent, and the fluorinated diluent in the perfluorinated organic solvent is 6-8:1-2:1-2.

[0045] In some specific embodiments, the concentration of the lithium salt in the perfluoroester-based electrolyte is 0.5-1 mol / L.

[0046] In some specific embodiments, the present invention provides a use of the above-mentioned perfluoroester-based electrolyte in a lithium metal battery.

[0047] Among them, the positive electrode active material in the lithium metal battery is high-voltage lithium cobalt oxide, lithium manganese oxide or ternary nickel cobalt manganese.

[0048] In some specific embodiments, the present invention provides a lithium metal battery, wherein the electrolyte of the lithium metal battery is the above-mentioned perfluoroester-based electrolyte.

[0049] The lithium metal battery provided by the present invention is in the form of a button battery or a pouch-type soft-pack battery.

[0050] In some specific embodiments, a button battery includes a negative electrode, a positive electrode, an electrolyte, a spring, a gasket, and a separator;

[0051] The button battery is assembled in order from the negative electrode to the positive electrode: a funnel-shaped spring piece, a gasket, a lithium sheet and a separator are placed on the negative electrode shell in sequence, an electrolyte is dripped on the separator from the middle to the surrounding area, and the positive electrode active material surface is quickly placed facing the separator. After the positive electrode shell is buckled, it is packaged using a packaging machine.

[0052] In some specific embodiments, a pouch-type soft-pack battery includes a negative electrode, a positive electrode, an electrolyte, an aluminum plastic seal, and a separator;

[0053] The assembly of the soft-pack battery is as follows: the aluminum-plastic seal, the negative electrode, the separator, and the positive electrode are stacked in sequence, three sides are heat-sealed, and then the electrolyte is dripped from the fourth side, and finally vacuum heat-sealed using a heat sealer.

[0054] Among them, the negative electrode of the button battery or pouch-type soft-pack battery is metallic lithium; the positive electrode is a positive electrode membrane including a positive electrode current collector, a positive electrode active material, a conductive agent and a binder, and the positive electrode active material is high-voltage lithium cobalt oxide, lithium manganese oxide or ternary nickel cobalt manganese; the diaphragm is a glass fiber membrane, a polyethylene microporous membrane or a polypropylene microporous membrane.

[0055] The raw materials and reagents involved in the specific embodiments of the present invention are all commercially available products.

[0056] It should be pointed out that the matters not described in detail in the embodiments and comparative examples are conventional operating means in the art and are not the focus of the present invention.

[0057] Unless otherwise specified, the normal temperature and room temperature involved in the specific embodiments of the present invention refer to 20-30°C.

[0058] Comparative Example 1

[0059] Electrolyte: lithium salt is lithium hexafluorophosphate with a concentration of 1.0 mol / L, and the solvent is ethylene carbonate and diethyl carbonate with a volume ratio of 3:7;

[0060] The above electrolyte is combined with lithium metal, stainless steel gasket (SS), and glass fiber separator to form a Li||SS battery;

[0061] The above electrolyte is combined with lithium metal, copper foil and glass fiber separator to form a Li||Cu battery;

[0062] The above electrolyte is combined with lithium metal, high-voltage lithium cobalt oxide, and glass fiber separator to form a Li||LiCoO2 battery;

[0063] The above electrolyte, lithium metal and glass fiber separator are assembled into a Li||Li battery.

[0064] Comparative Example 2

[0065] Electrolyte: lithium hexafluorophosphate (1.0 mol / L) as lithium salt, and fluoroethylene carbonate and fluorobenzene (8:2 by volume) as solvent.

[0066] The above electrolyte is combined with lithium metal, copper foil and glass fiber separator to form a Li||Cu battery;

[0067] The above electrolyte is assembled with lithium metal, high-voltage lithium cobalt oxide, and glass fiber separator to form a Li||LiCoO2 battery.

[0068] Example 1

[0069] Perfluoroester-based electrolyte: lithium hexafluorophosphate (1.0 mol / L) as the lithium salt, and bis(2-fluoroethyl) carbonate, fluoroethylene carbonate, and fluorobenzene in a volume ratio of 6:2:2 as the solvent.

[0070] The perfluoroester-based electrolyte is assembled with lithium metal, stainless steel gasket, and glass fiber separator to form a Li||SS battery;

[0071] The perfluoroester-based electrolyte is assembled with lithium metal, copper foil, and glass fiber separator to form a Li||Cu battery;

[0072] The perfluoroester-based electrolyte is assembled with lithium metal, high-voltage lithium cobalt oxide, and a glass fiber separator to form a Li||LiCoO2 battery;

[0073] The above-mentioned perfluoroester-based electrolyte, lithium metal, and glass fiber separator are assembled into a Li||Li battery.

[0074] Example 2

[0075] Perfluoroester-based electrolyte: The lithium salt is lithium hexafluorophosphate with a concentration of 0.6 mol / L and lithium bis(trifluoromethanesulfonyl)imide with a concentration of 0.4 mol / L, and the solvent is bis(2-fluoroethyl) carbonate, fluoroethylene carbonate, and fluorobenzene with a volume ratio of 6:2:2;

[0076] The perfluoroester-based electrolyte is assembled with lithium metal, stainless steel gasket, and glass fiber separator to form a Li||SS battery;

[0077] The perfluoroester-based electrolyte is assembled with lithium metal, copper foil, and glass fiber separator to form a Li||Cu battery;

[0078] The perfluoroester-based electrolyte is assembled with lithium metal, high-voltage lithium cobalt oxide, and a glass fiber separator to form a Li||LiCoO2 battery;

[0079] The above perfluoroester-based electrolyte is combined with lithium metal, layered lithium nickel cobalt manganese oxide, and glass fiber separator to form Li||LiNi 0.8 Co 0.1 Mn 0.1 O2 battery.

[0080] Test example

[0081] The Li||SS batteries prepared in Examples 1-2 and Comparative Example 1 were subjected to linear sweep voltammetry tests. The results are shown in Figure 2. Figure 1 As shown, specifically:

[0082] The electrolyte was used to assemble a Li||SS battery, and a linear sweep voltammetry test was performed at a sweep voltage of 3.0-5.5 V and a sweep rate of 1 mV / s.

[0083] Figure 1 Linear sweep voltammetry results for the Li||SS batteries prepared in Examples 1-2 and Comparative Example 1. The figure shows that the oxidation potential of the electrolyte in Comparative Example 1 is 4.3V. The electrolytes in Examples 1 and 2 show no significant current response in the voltage range of 4V-4.7V, indicating good antioxidant properties.

[0084] The coulombic efficiency of the Li||Cu batteries prepared in Example 1 and Comparative Example 1 was tested. Figure 2 As shown, specifically:

[0085] At a current density of 0.7 mA cm -2 and a capacity of 1.4 mAh cm -2 Next proceed.

[0086] Figure 2 The figure shows a comparison of the coulombic efficiency of the Li||Cu batteries prepared in Example 1 and Comparative Examples 1-2. The figure shows that the coulombic efficiency of the Li||Cu batteries prepared in Comparative Examples 1-2 is extremely unstable; the coulombic efficiency of the Li||Cu battery prepared in Example 1 is as high as 97.7%.

[0087] The long cycle performance of the Li||LiCoO2 batteries prepared in Example 1-2 and Comparative Example 1-2 was tested, and the results were as follows: Figure 3 As shown, specifically:

[0088] The electrolyte is used to assemble Li||LiCoO2 batteries with glass fiber as the separator, lithium metal as the negative electrode, and high-voltage lithium cobalt oxide as the positive electrode. It can be normally cycled under the conditions of 1C discharge rate after 0.5C charge in the voltage range of 3V-4.6V.

[0089] Figure 3 The long-cycle performance graphs of the Li||LiCoO2 batteries prepared in Examples 1-2 and Comparative Examples 1-2 show that the discharge capacity of the Li||LiCoO2 batteries prepared in Comparative Examples 1-2 is low and the coulombic efficiency is extremely unstable. The capacity retention rate of the Li||LiCoO2 battery prepared in Example 1 after 1000 cycles is 92% of the initial discharge specific capacity. The capacity retention rate of the Li||LiCoO2 battery prepared in Example 2 after 1000 cycles is 94% of the initial discharge specific capacity.

[0090] The polarization performance of the Li||Li battery prepared in Example 1 and Comparative Example 1 was compared. Figure 4 As shown, specifically:

[0091] At a current density of 0.7 mA cm -2 and a capacity of 0.7 mAh cm -2 Test it below.

[0092] Figure 4 The voltage curves of the Li||Li batteries prepared in Example 1 and Comparative Example 1 are shown. The figure shows that the electrolyte system of the Li||Li battery of Example 1 exhibits smaller polarization, while the electrolyte system of the Li||Li battery of Comparative Example 1 exhibits larger polarization.

[0093] The charge and discharge performance of the Li||LiCoO2 battery prepared in Example 1 and Comparative Example 1 was tested, and the results are as follows: Figure 5 As shown, specifically:

[0094] The test was conducted in the voltage range of 3V-4.6V, with a charge rate of 0.5C and a discharge rate of 1C.

[0095] Figure 5 Figure 1 shows the charge and discharge performance of the Li||LiCoO2 batteries prepared in Example 1 and Comparative Example 1, where a is Comparative Example 1 and b is Example 1. The figure shows that the Li||LiCoO2 battery prepared in Example 1 can cycle normally under the voltage range of 3V-4.6V, 0.5C charge and 1C discharge rates; the Li||LiCoO2 battery prepared in Comparative Example 1 experiences rapid capacity decay under the voltage range of 3V-4.6V, 0.5C charge and 1C discharge rates.

[0096] The Li||LiNi prepared in Example 2 0.8 Co 0.1 Mn 0.1 The stable cycle of O2 battery was tested, and the results were as follows Figure 6 As shown, specifically:

[0097] The test was carried out in the voltage range of 3V-4.5V and the charge / discharge rate of 0.5C / 1C.

[0098] Figure 6 Li||LiNi prepared in Example 2 0.8 Co 0.1 Mn 0.1 The stable cycle test results of O2 battery. The figure shows that the Li||LiNi prepared in Example 2 0.8 Co 0.1 Mn 0.1 The O2 battery can be stably cycled in the voltage range of 3V-4.5V and the charge / discharge rate of 0.1C / 0.1C.

[0099] The flame retardant properties of Example 1 and Comparative Example 1 were tested, and the results were as follows: Figure 7 As shown, specifically:

[0100] Use a pipette to draw 0.2 mL of electrolyte and drop it on the glass fiber separator, pick it up with clean tweezers, and ignite it with a lighter. The glass fiber separator of comparative example 1 burns quickly, while the glass fiber separator of experimental example 1 cannot be ignited.

[0101] Figure 7 The flame retardant performance comparison between Example 1 and Comparative Example 1 is shown in FIG. 1 , wherein a is Comparative Example 1 and b is Example 1.

[0102] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0103] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present invention. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention is not limited to the embodiments shown herein but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A perfluoroester-based electrolyte, characterized in that The components include a perfluorinated organic solvent and a lithium salt; The perfluorinated organic solvent includes a fluorinated chain ester, a fluorinated cyclic film-forming agent and a fluorinated diluent.

2. The perfluoroester-based electrolyte according to claim 1, wherein The lithium salt includes at least one of lithium hexafluorophosphate, lithium bis(fluorosulfonyl)imide and lithium bis(trifluoromethanesulfonyl)imide.

3. The perfluoroester-based electrolyte according to claim 1, wherein The fluorinated chain ester includes at least one of bis(2-fluoroethyl) carbonate, bis(2,2,2-trifluoroethyl) carbonate, methyl trifluoroethyl carbonate and ethyl trifluoroethyl carbonate.

4. The perfluoroester-based electrolyte according to claim 1, wherein The fluorinated cyclic film-forming agent includes at least one of fluoroethylene carbonate, difluoroethylene carbonate and 3,3,3-trifluoropropylene carbonate.

5. The perfluoroester-based electrolyte according to claim 1, wherein The fluorinated diluent includes at least one of fluorobenzene, 1,2-difluorobenzene and 1,3,5-trifluorobenzene.

6. The perfluoroester-based electrolyte according to claim 1, wherein The volume ratio of the fluorinated chain ester, the fluorinated cyclic film-forming agent and the fluorinated diluent in the perfluorinated organic solvent is 6-8:1-2:1-2.

7. The perfluoroester-based electrolyte according to claim 1, wherein The concentration of the lithium salt in the perfluoroester-based electrolyte is 0.5-1 mol / L.

8. Use of the perfluoroester-based electrolyte according to any one of claims 1 to 7 in a lithium metal battery.

9. A lithium metal battery, characterized in that: The electrolyte of the lithium metal battery is the perfluoroester-based electrolyte according to any one of claims 1 to 7.

10. A method for improving the flame retardancy of lithium metal batteries, characterized in that: The electrolyte of the lithium metal battery uses the perfluoroester-based electrolyte according to any one of claims 1 to 7.

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