High-safety flame-retardant electrolyte, preparation method thereof and application thereof in fluorinated iron-based lithium metal battery

Abstract

The application discloses a high-safety flame-retardant electrolyte, a preparation method thereof and application of the electrolyte in a fluorinated iron-based lithium metal battery. The electrolyte comprises a lithium salt, an organic solvent and a sulfonyl additive. By regulating the solvation structure of lithium ions in the electrolyte, the compatibility of the electrolyte and the electrode interface is improved, the occurrence of the interface side reaction is reduced, and the cycle stability of the lithium metal battery is effectively improved. Meanwhile, under the premise of ensuring the electrochemical performance, the electrolyte has good flame-retardant characteristics and safety performance, and the application range of the electrolyte in a high-energy-density and high-safety lithium metal battery system is widened.

Description

Technical Field

[0001] This invention belongs to the field of lithium metal battery technology, specifically relating to a high-safety flame-retardant electrolyte, its preparation method, and its application in iron fluoride-based lithium metal batteries. Background Technology

[0002] Since the commercialization of the first lithium-ion battery in 1991, lithium batteries have become the most mature and widely used rechargeable battery system due to their high energy density, long cycle life, and excellent performance. They serve as a crucial technological support for the Fourth Industrial Revolution, continuously driving the energy structure towards a low-carbon and cleaner direction. However, limited by the intercalation reaction mechanism, the energy density of existing lithium-ion batteries is gradually approaching its theoretical upper limit, making it difficult to meet the future demands for high-energy-density energy storage and power applications.

[0003] Lithium-iron fluoride-based batteries, based on the conversion reaction mechanism, are advantageous due to their abundant raw material sources, high theoretical specific capacity, and high energy density (approximately 1950 Wh / kg). -1 With its advantages such as high energy density, iron fluoride cathode material is considered a promising next-generation high-energy-density lithium battery system. However, iron fluoride cathode materials still face many challenges in practical applications: their intrinsic electronic conductivity is low, leading to slow conversion reaction kinetics and poor electrochemical reversibility; the large volume changes during charge and discharge easily cause electrode structure damage, active material deactivation and dissolution, thus seriously affecting the cycle stability and energy efficiency of the battery. In addition, existing commercial lithium battery electrolytes are mainly designed for intercalated cathode materials, and their compatibility with conversion-type iron fluoride cathodes and highly active lithium metal anodes is poor in terms of interfacial chemistry and electrochemical stability, easily causing serious interfacial side reactions, leading to continuous electrolyte consumption, increased electrode polarization and reduced cycle life. At the same time, traditional organic electrolytes generally have disadvantages such as flammability and poor thermal stability, posing significant safety hazards in high-energy-density lithium metal batteries. On the negative electrode side, lithium metal negative electrodes are prone to forming lithium dendrites during charging and discharging. Their growth may pierce the separator and cause internal short circuits. At the same time, the surface of lithium metal is highly reactive and easily reacts with the electrolyte, further aggravating safety risks and deteriorating cycle performance.

[0004] Therefore, developing an electrolyte system that combines excellent flame retardant safety performance, good electrochemical stability, and compatibility with both iron fluoride cathodes and lithium metal anodes is of significant research importance and engineering value for promoting the practical application of iron fluoride-based lithium metal batteries. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to solve the safety problems of poor compatibility between existing electrolytes and novel conversion-type positive electrode iron fluoride-based materials, and the tendency for side reactions to occur in lithium metal batteries, leading to combustion and explosion. This invention overcomes the shortcomings of the prior art and provides a highly safe flame-retardant electrolyte.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including, (i) Contains lithium salt, organic solvent and sulfonyl additive; (ii) The organic solvent consists of an organic ether-based main solvent and a fluorinated diluent; (iii) The sulfonyl additives account for 3wt% to 5wt% of the electrolyte.

[0009] As a preferred embodiment of the high-safety flame-retardant electrolyte of the present invention, the lithium salt is selected from at least two of lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluorosulfonyl)imide (LiTFSI), lithium difluorooxalate borate (LiDFOB), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium hexafluorophosphate (LiPF6), lithium perchlorate (LiClO4), and lithium nitrate (LiNO3), and the total molar concentration of the lithium salt in the electrolyte is 1.2~3.0 mol / L.

[0010] As a preferred embodiment of the high-safety flame-retardant electrolyte of the present invention, the organic ether main solvent is selected from at least one of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (G2), triethylene glycol dimethyl ether (G3), ethylene glycol diethyl ether (DEE), 1,3-dioxolane (DOL), and tetrahydrofuran (THF).

[0011] As a preferred embodiment of the high-safety flame-retardant electrolyte of the present invention, the fluorinated diluent is selected from at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE), 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether (TTE), fluorobenzene (FB), and bis(2,2,2-trifluoroethyl) carbonate (BTFEC).

[0012] As a preferred embodiment of the high-safety flame-retardant electrolyte of the present invention, the volume ratio of the organic ether main solvent to the fluorinated diluent is 1:0.5~2.

[0013] As a preferred embodiment of the high-safety flame-retardant electrolyte of the present invention, the sulfonyl additive is at least one of N,N-dimethylaminosulfonyl fluoride (DSF), 1-butanesulfonyl fluoride, and pyrrolidinylsulfonyl fluoride.

[0014] Another object of the present invention is to provide a method for preparing a highly safe flame-retardant electrolyte.

[0015] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including, Under the protection of high-purity argon, organic ether-based main solvent is added dropwise to lithium salt, shaken thoroughly, and magnetically stirred at room temperature until the lithium salt is completely dissolved. Then, additives are added, and finally, a fluorine-containing diluent is added to obtain a high-safety flame-retardant electrolyte.

[0016] Another object of the present invention is to provide an application of a high-safety flame-retardant electrolyte in a lithium iron fluoride-based lithium metal battery, wherein the lithium iron fluoride-based lithium metal battery comprises the high-safety flame-retardant electrolyte, and further comprises, Ferric fluoride-based cathode materials, lithium anode materials, and polypropylene separators.

[0017] The active material of the iron fluoride-based cathode material is selected from at least one of the conversion-type iron fluoride-based cathode materials FeF3 and FeF2.

[0018] Beneficial effects of this invention: (1) The present invention provides a high safety flame retardant electrolyte suitable for iron fluoride-based lithium metal batteries. The electrolyte is composed of lithium salt, organic solvent and additives, wherein the organic solvent includes ether-based main solvent and fluorine-containing diluent, thereby achieving synergistic adaptation of conversion iron fluoride positive electrode and lithium metal negative electrode.

[0019] (2) By using ether solvents as the main solvent, this invention significantly improves the interfacial compatibility with the lithium metal anode, effectively reduces the degree of side reactions of the electrolyte on the lithium metal surface, and inhibits the growth of lithium dendrites, thereby improving the cycle stability and coulombic efficiency of the lithium metal anode. This invention also introduces fluorine-containing diluents, which, while ensuring the ion transport performance of the electrolyte, significantly improve the thermal stability and flame retardant properties of the electrolyte, effectively reducing the safety risks of the battery under high energy density operating conditions and meeting the application requirements of high-safety lithium metal batteries.

[0020] (3) By adding a small amount of sulfonyl additive to the electrolyte, the present invention achieves effective control of the electrolyte solvation structure and electrode / electrolyte interface chemistry, so that a stable interface protective layer rich in inorganic components is formed on the surface of the converted iron fluoride cathode, which significantly inhibits interface side reactions and active material deactivation.

[0021] (4) Based on the above synergistic effect, the electrolyte of the present invention can achieve excellent cycle stability and long life performance of lithium metal batteries while taking into account high safety, and provides an effective electrolyte solution for the practical application of iron fluoride-based lithium metal batteries. Attached Figure Description

[0022] Figure 1 The charge / discharge capacity curves of the iron fluoride-based lithium metal battery assembled using the electrolyte prepared in Example 1 of this invention are shown.

[0023] Figure 2 The charge-discharge capacity curves of the iron fluoride-based lithium metal battery assembled using the electrolyte prepared in Comparative Example 1 of this invention are shown.

[0024] Figure 3 The results show the rate performance comparison of the iron fluoride-based lithium metal batteries assembled using the electrolytes prepared in Example 1 and Comparative Example 1 of this invention.

[0025] Figure 4 The flame retardant performance test results of the electrolyte prepared in Example 1 of this invention are presented. Detailed Implementation

[0026] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0027] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0028] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0029] Unless otherwise specified, all raw materials used in this invention are commercially available in the field.

[0030] The performance of the product of this application was tested according to the following method: Charge-discharge cycle test: At a constant temperature of 25℃, the battery was charged and discharged once each at a constant current of 0.1 C (1C = 571 mAh / g) and 0.5 C within a voltage range of 1.0 V to 4.0 V. Subsequent long cycles were performed with constant current charging at 1.0 C and constant current discharging at 1.0 C. The capacity retention rate of the battery after 100 cycles was calculated, where the capacity retention rate (%) of the Nth cycle was calculated as (Nth discharge capacity / 3rd discharge capacity) × 100%.

[0031] Rate performance test: At a constant temperature of 25℃, with a voltage range of 1.0 V to 4.0 V, the system was charged and discharged 5 times at a constant current of 0.2 C (1 C = 571 mAh / g), and then charged and discharged 6 times each at constant currents of 0.5 C, 1.0 C, 2.0 C, 3.0 C, 4.0 C, and 5.0 C, before returning to 1.0 C for constant current charge and discharge cycle.

[0032] Ignition test: 1g of the prepared electrolyte was added to the positive electrode shell of the button battery using a dropper. The electrolyte was then ignited using a high-temperature flame gun (mainly butane, flame temperature 1300~1500℃). After ignition, the continued combustion was observed and recorded on video.

[0033] Example 1 This embodiment provides a method for preparing a high-safety flame-retardant electrolyte, specifically: 1) Weigh the raw materials according to the following formula: Lithium salts: lithium bis(fluorosulfonyl)imide (LiFSI) and lithium difluorooxalate borate (LiDFOB), with a molar ratio of 1.8:0.2; The total molar concentration of lithium salt in the electrolyte is 2.0 mol / L; Organic ether primary solvent: Dimethyl ethylene glycol ether (DME); Fluorinated diluent: 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE); The volume ratio of DME to HFE is 1:1; Sulfonyl additive: N,N-dimethylaminosulfonyl fluoride (DSF); The sulfonyl additive accounts for 5 wt% of the mass of the electrolyte; 2) Prepare a high-safety flame-retardant electrolyte using the following method: Under a high-purity argon atmosphere, an organic ether-based main solvent is added dropwise to the lithium salt, shaken thoroughly, and magnetically stirred at room temperature until the lithium salt is completely dissolved. Then, additives are added, followed by a fluorine-containing diluent. After mixing, the mixture is stirred thoroughly for 20 minutes to obtain the electrolyte, which is the high-safety flame-retardant electrolyte LLDHD suitable for iron fluoride-based lithium metal batteries in this embodiment.

[0034] Comparative Example 1 The difference between this comparative example and Example 1 is that the additive DSF is omitted, while the remaining steps and processes are the same as in Example 1, resulting in the electrolyte LLDH of this comparative example.

[0035] The electrolytes obtained in Example 1 and Comparative Example 1 were used to prepare lithium metal batteries according to the following method: A positive electrode sheet was prepared by using ferrous fluoride (FeF2) as the active material, combined with conductive carbon and binder (in a mass ratio of active material: conductive carbon: binder of 7:2:1). A lithium sheet was used as the negative electrode, and 50 μL of the electrolyte from each embodiment was added. Polypropylene (PP) was used as the separator to assemble a Li|FeF2 coin cell.

[0036] The lithium metal batteries prepared in Application Example 1 and Comparative Example 1 were subjected to charge-discharge cycle tests, rate performance tests, and ignition tests. The results are shown in Table 1. Figures 1-4 As shown.

[0037] Table 1. Long-cycle performance test results The discharge capacity curve of Example 1 is as follows: Figure 1 As shown, the discharge capacity curve of Comparative Example 1 is as follows: Figure 2 As shown in Table 1, the results of the long-cycle performance test are as follows. It can be seen that the overall performance of the electrolyte regulated by the additive in the example is significantly better than that of the comparative example, indicating that the electrolyte of the present invention has better long-cycle stability than the unmodified electrolyte by introducing the sulfonyl acyl additive DSF.

[0038] Figure 3 The results of the rate performance test of the lithium batteries prepared with the electrolytes of Example 1 and Comparative Example 1 show that the overall performance of the electrolyte regulated by the additives in the examples is significantly better than that of the comparative example. This indicates that the present invention, by introducing the strongly dipolar additive DSF, has superior rate performance compared to the unmodified electrolyte.

[0039] An ignition experiment was conducted using the LLDHD electrolyte obtained in Example 1. The results are as follows: Figure 4 As shown, the ether-based electrolyte of this application does not burn after being burned under a high-temperature flame gun, thus greatly improving the safety of the battery.

[0040] Example 2 The difference between this embodiment and Example 1 is that the molar ratio of lithium bis(fluorosulfonyl)imide (LiFSI) to lithium difluorooxalate borate (LiDFOB) in step 1) is adjusted to 1.3:0.2, and the total molar concentration of lithium salt is 1.5 mol / L; the remaining steps are the same as in Example 1, and the high-safety flame-retardant electrolyte LLDHD-2 of this embodiment is obtained.

[0041] Example 3 The difference between this embodiment and Example 1 is that the volume ratio of the solvent dimethyl glycol ether (DME) and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (HFE) in step 1) is adjusted to 1:2; the remaining steps are the same as in Example 1, resulting in the high-safety flame-retardant electrolyte LLDHD-3 of this embodiment.

[0042] Example 4 The difference between this embodiment and Embodiment 1 is that, in step 1), lithium bis(fluorosulfonyl)imide (LiFSI) in the lithium salt is changed to lithium bis(trifluorosulfonyl)imide (LiTFSI); the remaining steps are the same as in Embodiment 1, resulting in the high-safety flame-retardant electrolyte LTDHD of this embodiment.

[0043] Example 5 The difference between this embodiment and Embodiment 1 is that, in step 1), lithium bis(fluorosulfonyl)imide (LiFSI) in the lithium salt is changed to lithium tetrafluoroborate (LiBF4); the remaining steps are the same as in Embodiment 1, resulting in the high-safety flame-retardant electrolyte LBDHD of this embodiment.

[0044] Example 6 The difference between this embodiment and Embodiment 1 is that, in step 1), lithium difluorosulfonyl imide (LiFSI) in the lithium salt is changed to lithium difluorophosphate (LiPO2F2); the remaining steps are the same as in Embodiment 1, resulting in the high-safety flame-retardant electrolyte LP2DHD of this embodiment.

[0045] The electrolytes prepared in Examples 2 to 6 all exhibited good overall performance.

[0046] Comparative Example 2 The difference between this comparative example and Example 1 is that the main solvent, ethylene glycol dimethyl ether (DME), is replaced with diethylene glycol dimethyl ether (G2). The remaining steps and processes are the same as in Example 1, resulting in the electrolyte LLG2HD of this comparative example.

[0047] Comparative Example 3 The difference between this comparative example and Example 1 is that the main solvent, ethylene glycol dimethyl ether (DME), is replaced with triethylene glycol dimethyl ether (G3). The remaining steps and processes are the same as in Example 1, resulting in the electrolyte LLG3HD of this comparative example.

[0048] Comparative Example 4 The difference between this comparative example and Example 1 is that the main solvent, ethylene glycol dimethyl ether (DME), is replaced with tetrahydrofuran (THF). The remaining steps and processes are the same as in Example 1, resulting in the electrolyte LLTHD of this comparative example.

[0049] Lithium metal batteries were prepared using the electrolytes obtained in Comparative Examples 2 to 4 according to the aforementioned method. The relevant electrochemical performance was measured and compared with that of Example 1. The results are shown in Table 2.

[0050] Table 2 Electrochemical performance of different ether-based main solvents As shown in Table 2, for the selection of ether-based main solvents, ethylene glycol dimethyl ether exhibits more stable long-cycle performance compared to diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether, which have longer chain lengths. However, the formulation and electrode corresponding to Comparative Example 4 are incompatible, resulting in an intermediate capacity drop to 0, therefore capacity retention cannot be calculated.

[0051] Comparative Example 5 The difference between this comparative example and Example 1 is that the additive N,N-dimethylaminosulfonyl fluoride (DSF) is replaced with 3-cyanoethylmethyldiethoxysilane (CPMDES). The remaining steps and processes are the same as in Example 1, and the electrolyte LLDHC of this comparative example is obtained.

[0052] Comparative Example 6 The difference between this comparative example and Example 1 is that the additive N,N-dimethylaminosulfonyl fluoride (DSF) is replaced with fluoroethylene carbonate (FEC). The remaining steps and processes are the same as in Example 1, and the electrolyte LLDHF of this comparative example is obtained.

[0053] Comparative Example 7 The difference between this comparative example and Example 1 is that the additive N,N-dimethylaminosulfonyl fluoride (DSF) is replaced with tris(pentafluorophenyl)borane (FBB). The remaining steps and processes are the same as in Example 1, and the electrolyte LLDHFB of this comparative example is obtained.

[0054] Comparative Example 8 The difference between this comparative example and Example 1 is that the additive N,N-dimethylaminosulfonyl fluoride (DSF) is replaced with tetramethyldivinyldisiloxane (TMDVS), while the remaining steps and processes are the same as in Example 1, to obtain the electrolyte LLDHT of this comparative example.

[0055] Comparative Example 9 The difference between this comparative example and Example 1 is that the additive N,N-dimethylaminosulfonyl fluoride (DSF) is replaced with hexaphenoxycyclotriphosphazene (HPCTP). The remaining steps and processes are the same as in Example 1, and the electrolyte LLDPH of this comparative example is obtained.

[0056] Lithium metal batteries were prepared using the electrolytes obtained in Comparative Examples 5 to 9 according to the aforementioned method. The relevant electrochemical performance was measured and compared with that of Example 1. The results are shown in Table 3.

[0057] Table 3 Electrochemical properties of different types of additives As can be seen from Table 3, compared with other additives containing nitrile, silane, and olefin, sulfonyl solvents are better at modifying electrolytes, further indicating that the additive improves the compatibility between the electrolyte and the positive and negative electrodes. Among them, the formulations and electrodes corresponding to Comparative Examples 7 and 8 are incompatible, and the intermediate capacity drops to 0, so the capacity retention rate cannot be calculated.

[0058] Example 7 The difference between this comparative example and Example 1 is that the mass ratio of the additive N,N-dimethylaminosulfonyl fluoride (DSF) in the electrolyte is adjusted to 3wt%, while the remaining steps and processes are the same as in Example 1, resulting in the electrolyte LLDHD-3wt of this example.

[0059] Comparative Example 10 The difference between this comparative example and Example 1 is that the mass ratio of the additive N,N-dimethylaminosulfonyl fluoride (DSF) in the electrolyte is adjusted to 1 wt%, while the remaining steps and processes are the same as in Example 1, resulting in the electrolyte LLDHD-1wt of this comparative example.

[0060] Comparative Example 11 The difference between this comparative example and Example 1 is that the mass ratio of the additive N,N-dimethylaminosulfonyl fluoride (DSF) in the electrolyte is adjusted to 10wt%, while the remaining steps and processes are the same as in Example 1, resulting in the electrolyte LLDHD-10wt of this comparative example.

[0061] The electrolytes obtained in Examples 7, 10 and 11 were used to prepare lithium metal batteries according to the aforementioned method. The relevant electrochemical performance was measured and compared with that of 5 wt% in Example 1. The results are shown in Table 4.

[0062] Table 4 Electrochemical performance of additives (DSF) with different contents As can be seen from Table 4, adjusting the amount of additive DSF has a significant impact on long-cycle performance. Too little DSF cannot guarantee the stability of the electrolyte; too much DSF may lead to excessive harmful side reactions and reduce compatibility with the electrode.

[0063] It can be seen that the electrolyte prepared in the embodiments of the present invention has significantly better overall performance than the comparative example in the voltage range of 1.0 V to 4.0 V, indicating that the electrolyte of the present invention can maintain good compatibility with both the conversion-type iron fluoride-based positive electrode material and the lithium metal negative electrode.

[0064] In summary, this invention provides a highly safe, flame-retardant functionalized electrolyte that exhibits superior cycle stability and interfacial compatibility in iron fluoride-based lithium metal batteries. It is particularly suitable for conversion-type cathode systems, better meeting the application requirements of high-energy-density and high-safety batteries. The electrolyte system described in this invention requires no complex preparation process, is easily compatible with existing battery manufacturing processes, and has promising engineering application prospects.

[0065] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A high-safety flame-retardant electrolyte, characterized in that: include, (i) Contains lithium salt, organic solvent and sulfonyl additive; (ii) The organic solvent consists of an organic ether-based main solvent and a fluorinated diluent; (iii) The sulfonyl additives account for 3wt% to 5wt% of the electrolyte.

2. The high-safety flame-retardant electrolyte as described in claim 1, characterized in that: The lithium salt is selected from at least two of lithium bis(fluorosulfonyl)imide, lithium bis(trifluorosulfonyl)imide, lithium difluorooxalateborate, lithium tetrafluoroborate, lithium difluorophosphate, lithium hexafluorophosphate, lithium perchlorate, and lithium nitrate, and the total molar concentration of the lithium salt in the electrolyte is 1.2~3.0 mol / L.

3. The high-safety flame-retardant electrolyte as described in claim 1, characterized in that: The organic ether main solvent is selected from at least one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, ethylene glycol diethyl ether, 1,3-dioxolane, and tetrahydrofuran; the fluorinated diluent is selected from at least one of 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, 1,1,2,2-tetrafluoroethyl-2,2,2-trifluoroethyl ether, fluorobenzene, and di(2,2,2-trifluoroethyl) carbonate.

4. The high-safety flame-retardant electrolyte as described in claim 1, characterized in that: The volume ratio of the organic ether main solvent to the fluorinated diluent is 1:0.5~2.

5. The high-safety flame-retardant electrolyte as described in claim 1, characterized in that: The sulfonyl additive is at least one of N,N-dimethylaminosulfonyl fluoride, 1-butanesulfonyl fluoride, and pyrrolidinylsulfonyl fluoride.

6. The method for preparing the high-safety flame-retardant electrolyte as described in any one of claims 1 to 5, characterized in that: include, Under the protection of high-purity argon, organic ether-based main solvent is added dropwise to lithium salt, shaken thoroughly, and magnetically stirred at room temperature until the lithium salt is completely dissolved. Then, additives are added, and finally, a fluorine-containing diluent is added to obtain a high-safety flame-retardant electrolyte.

7. The application of the high-safety flame-retardant electrolyte as described in any one of claims 1 to 5 in iron fluoride-based lithium metal batteries.

8. A lithium metal battery based on iron fluoride, characterized in that: The electrolyte comprises the high-safety flame-retardant electrolyte according to any one of claims 1 to 5, and further comprises, Ferric fluoride-based cathode materials, lithium anode materials, and polypropylene separators.

9. The fluoride-based lithium metal battery as described in claim 8, characterized in that: The active material of the iron fluoride-based cathode material is selected from at least one of the conversion-type iron fluoride-based cathode materials FeF3 and FeF2.

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