Non-combustible deep eutectic electrolyte based on LiTFSI-NMF-FEC and preparation method of lithium metal battery

Abstract

The invention provides a preparation method of a non-combustible deep eutectic electrolyte based on LiTFSI-NMF-FEC and a lithium metal battery, and the preparation method comprises the following steps: S1, taking lithium bis (trifluoromethanesulfonimide) (LiTFSI) as a lithium salt and N-methylformamide (NMF) as a hydrogen bond donor, accurately weighing LiTFSI and NMF according to a molar ratio of 1: 4, placing the LiTFSI and NMF in a polytetrafluoroethylene sealed container which is subjected to vacuum drying at 120 DEG C for 8 hours, and in a constant-temperature water bath at 80 + / -2 DEG C, carrying out vacuum drying at 120 DEG C for 8 hours; stirring for 12 + / -1h at 400 + / -50rpm, sampling and observing every 2h during the period to ensure that the system is clear, transparent and free of precipitates, and naturally cooling to 25 + / -2 DEG C to obtain a deep eutectic substrate solution; s2, using fluoroethylene carbonate (FEC) as an SEI regulation and control additive, slowly adding the SEI regulation and control additive into the deep eutectic substrate liquid according to the proportion of 5wt% of the total mass of the electrolyte, stirring at 250 + / -30rpm for 3 + / -0.5 h to ensure that the FEC is uniformly dispersed, and standing for 1.5 + / -0.5 h to remove tiny bubbles, so as to obtain uniform deep eutectic electrolyte slurry; and S3, the deep eutectic electrolyte slurry is subjected to battery assembly in an argon glove box, and the lithium metal battery carrying the target electrolyte is obtained through assembly.

Description

Technical Field

[0001] This invention relates to the field of lithium metal battery electrolyte technology, and more specifically, to a method for preparing a non-flammable deep eutectic electrolyte based on LiTFSI-NMF-FEC and a lithium metal battery, which is suitable for scenarios with high requirements for energy density and safety, such as portable electronic devices, electric vehicles and large-scale energy storage systems. Background Technology

[0002] With the rapid development of the global new energy industry, energy storage technology has become the core support for grid connection of renewable energy, the popularization of electric vehicles, and the upgrading of portable electronic devices. Currently, lithium-ion batteries (LIBs) have become the mainstream energy storage technology, but are limited by the low theoretical specific capacity of graphite anodes (372 mAh g / g). -1 Its energy density is approaching the theoretical limit, making it difficult to meet the needs of the next generation of energy storage.

[0003] Lithium metal batteries (LMBs) possess advantages such as extremely high theoretical specific capacity, ultra-low reduction potential, and low energy density due to the lithium metal anode, achieving an energy density exceeding 500 Wh / kg. -1 It is widely recognized as the core candidate for the next generation of high energy density energy storage technology. However, the commercialization of LMBs has long been limited by four key technical bottlenecks and has not yet achieved large-scale application: (1) Lithium dendrite growth and safety risks: The surface of lithium metal is highly chemically active. During charging and discharging, lithium ions are easily deposited unevenly on the electrode surface to form dendritic lithium dendrites. The lithium dendrites will continue to grow and pierce the separator, causing short circuits inside the battery, thermal runaway, and inducing safety accidents such as combustion and explosion, which seriously restricts its application in the fields of power batteries and large-scale energy storage; (2) Unstable SEI layer and low cycle efficiency: After the electrolyte comes into contact with the lithium metal anode, a spontaneous interface reaction will occur to form a solid electrolyte interface (SEI) layer. The SEI layer formed by traditional electrolytes (such as carbonate systems) is mainly composed of components such as LiOH, Li2O, and Li2CO3. The structure is loose, the mechanical strength is low, and the ionic conductivity is poor (usually ≤1×10). -6 Scm -1(3) Flammability and thermal runaway hazards of electrolytes: Carbonate electrolytes (such as EC / DMC / EMC system) widely used in commercial lithium batteries have high volatility and flammability. Their flash point is usually below 25°C. Under abnormal conditions such as battery overheating (≥120°C), short circuit or puncture, they are very easy to burn, and may even trigger a chain reaction, leading to battery fire and explosion, with prominent safety risks; (4) Performance defects of existing deep eutectic electrolytes: Deep eutectic electrolytes (DEEs) are an important development direction of the next generation of electrolytes. They have advantages such as low toxicity, environmental protection and good thermal stability, and are considered ideal candidates to replace traditional carbonate electrolytes. In existing studies, although the deep eutectic system formed by LiNO3 and N-methylacetamide (MAc) has certain non-flammable properties and a wide electrochemical stability window, the viscosity at room temperature is as high as ~107 mPa·s and the ionic conductivity is only ~0.76 mScm. -1 This severely limits lithium-ion transport efficiency, requiring high temperatures of 60-80℃ to achieve good electrochemical performance, which cannot meet the requirements of room temperature applications. In addition, when this binary system is used alone, the SEI layer is mainly composed of LiOH and Li2O, which has poor stability and is difficult to effectively suppress lithium dendrite growth, resulting in limited cycle life.

[0004] To address these issues, researchers have conducted extensive studies. For example, using high-concentration electrolytes to improve ionic conductivity leads to further increases in viscosity, hindering ion transport; developing polymer electrolytes or solid-state electrolytes to suppress lithium dendrites results in ionic conductivity that is insufficient for high-rate performance requirements; and using ionic liquids as solvents to improve safety is costly and results in poor low-temperature performance.

[0005] Therefore, developing a deep eutectic electrolyte system that combines low viscosity, high ionic conductivity, stable SEI formation capability, and inherent non-flammability, clarifying the synergistic mechanism between additives and deep eutectic substrates, and breaking through the practical application bottleneck of LMBs have become key research directions in the current lithium metal battery field, and are of great significance to promoting the development of new energy storage technology. Summary of the Invention

[0006] The present invention aims to address the defects of lithium metal battery electrolytes in the prior art mentioned above, such as lithium dendrite growth, SEI layer instability, low coulombic efficiency, and flammability. It provides a non-flammable deep eutectic electrolyte based on LiTFSI-NMF-FEC and a method for preparing a lithium metal battery. Specifically, it relates to a non-flammable deep eutectic electrolyte using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the lithium salt, N-methylformamide (NMF) as the hydrogen bond donor, and fluoroethylene carbonate (FEC) as the SEI regulating additive, and a lithium metal battery containing the electrolyte.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing a non-flammable deep eutectic electrolyte and lithium metal battery based on LiTFSI-NMF-FEC, comprising the following steps: S1: Using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the lithium salt and N-methylformamide (NMF) as the hydrogen bond donor, accurately weigh LiTFSI and NMF in a molar ratio of 1:4, place them in a polytetrafluoroethylene sealed container that has been vacuum dried at 120℃ for 8h, stir at 400±50rpm for 12±1h in a constant temperature water bath at 80±2℃, and take samples every 2h to ensure that the system is clear, transparent and free of precipitation, and cool naturally to 25±2℃ to obtain a deep eutectic base liquid; S2: Fluoroethylene carbonate (FEC) is used as an SEI regulating additive and is slowly added to the deep eutectic base liquid at a ratio of 5wt% of the total electrolyte mass. The mixture is stirred at 250±30rpm for 3±0.5h to ensure uniform dispersion of FEC. After standing for 1.5±0.5h, micro bubbles are removed to obtain a uniform deep eutectic electrolyte slurry. S3: The deep eutectic electrolyte slurry is used to complete the battery assembly in an argon glove box to obtain a lithium metal battery carrying the target electrolyte.

[0008] Furthermore, the specific process of battery assembly in step S3 is as follows: S31: Positive electrode preparation: A positive electrode slurry was prepared using LiFePO4 active material, SuperP conductive agent, and PVDF binder in a weight ratio of 80:10:10. The slurry was coated onto a 12μm aluminum foil and vacuum dried at 100±5℃ for 8 hours. The slurry was then rolled to a compaction density of 2.1~2.2g / cm⁻³ and cut into 12mm diameter electrode sheets with a loading of 2.0±0.2mg / cm². S32: Negative electrode preparation: 100±10μm lithium metal foil is selected, the lithium metal purity of the lithium metal foil is ≥99.9%, it is cut to a diameter of 16mm and the oxide layer is removed by wiping with anhydrous ethanol; S33: Battery assembly: Assemble CR2032 coin cells in the order of positive electrode, 30μm glass fiber separator, and negative electrode, inject 170±10μL of the deep eutectic electrolyte slurry, seal at 0.8±0.1MPa, and activate at room temperature for 12±2h to obtain lithium metal batteries.

[0009] Furthermore, the moisture and oxygen content of the argon glove box is ≤0.1ppm.

[0010] A non-flammable deep eutectic electrolyte based on LiTFSI-NMF-FEC is prepared by the preparation method described above. The electrolyte is based on a deep eutectic system formed by LiTFSI and NMF in a molar ratio of 1:4, and contains 5 wt% FEC as an SEI regulating additive.

[0011] A lithium metal battery, comprising a LiFePO4 positive electrode, a lithium metal negative electrode, a glass fiber separator, and an electrolyte, wherein the electrolyte is the non-flammable deep eutectic electrolyte based on LiTFSI-NMF-FEC as described in claim 4.

[0012] The beneficial effects of this invention are as follows: The method for preparing a non-flammable deep eutectic electrolyte and lithium metal battery based on LiTFSI-NMF-FEC of this invention produces a deep eutectic electrolyte that combines low viscosity, high ionic conductivity, and inherent non-flammability. Under optimal process conditions (FEC addition of 5 wt%), the electrolyte achieves an ionic conductivity of 1.65 mS / cm at 25°C. -1 The electrolyte exhibits a viscosity as low as 60.2 cp at 30°C, remains liquid and stable within a temperature range of -40 to 60°C, and does not burn under open flame, effectively solving the problems of flammability in traditional carbonate electrolytes and high viscosity in existing deep eutectic systems. By adding FEC, this invention optimizes the composition and structure of the SEI layer. Spectroscopic analysis confirms that FEC promotes the formation of highly ionicly conductive LiF, Li2CO3, and Li3N phases in the SEI layer, inhibits the formation of low-conductivity phases (LiNO2, LiOH, Li2O), constructs a dense and stable SEI layer, effectively suppresses lithium dendrite growth, and improves the cycle stability and coulombic efficiency of the battery. Lithium metal batteries using this electrolyte exhibit excellent performance; the Li / / LiFePO4 battery achieves a performance of 100 mAg. ⁻¹ At current density, the initial discharge capacity reaches 156 mAh g. ⁻¹ After 800 cycles, the capacity retention rate is 83%, and the average coulombic efficiency is 99.8%, which is significantly better than the deep eutectic system without FEC and the traditional carbonate electrolyte. The preparation process of this invention is simple, cost-controllable, environmentally friendly, and the raw materials are readily available. The preparation process does not require complex equipment and has good compatibility with existing lithium battery production equipment, making it suitable for industrial application. It provides key technical support for the industrialization of high energy density and high safety LMBs. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are only drawings of some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings. In addition, the drawings in the following description can be regarded as schematic diagrams and are not intended to limit the actual size of the product, the actual flow of the method, the actual timing of the signals, etc. involved in the embodiments of the present invention.

[0014] Figure 1 This is a schematic diagram of the preparation method steps of the present invention. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example

[0016] like Figure 1 As shown in the figure, the present invention provides a method for preparing a non-flammable deep eutectic electrolyte and lithium metal battery based on LiTFSI-NMF-FEC, comprising the following steps: S1: Preparation of deep eutectic base liquid: Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was used as lithium salt and N-methylformamide (NMF) was used as hydrogen bond donor. LiTFSI and NMF were accurately weighed in a molar ratio of 1:4 and placed in a polytetrafluoroethylene sealed container that had been vacuum dried at 120℃ for 8h. The mixture was stirred at 400±50rpm for 12±1h in a constant temperature water bath at 80±2℃. During the process, samples were taken every 2h to ensure that the system was clear, transparent and free of precipitation. The mixture was then naturally cooled to 25±2℃ to obtain the deep eutectic base liquid. S2: Preparation of deep eutectic electrolyte slurry: Fluoroethylene carbonate (FEC) was used as an SEI regulating additive and slowly added to the deep eutectic base liquid at a ratio of 5wt% of the total electrolyte mass. The mixture was stirred at 250±30rpm for 3±0.5h to ensure uniform dispersion of FEC. After standing for 1.5±0.5h, micro bubbles were removed to obtain a uniform deep eutectic electrolyte slurry. S3: Battery assembly: The deep eutectic electrolyte slurry is assembled in an argon glove box to obtain a lithium metal battery carrying the target electrolyte.

[0017] In one embodiment, the specific process of battery assembly in step S3 is as follows: S31: Positive electrode preparation: A positive electrode slurry was prepared using LiFePO4 active material, SuperP conductive agent, and PVDF binder in a weight ratio of 80:10:10. The slurry was coated onto a 12μm aluminum foil and vacuum dried at 100±5℃ for 8 hours. The slurry was then rolled to a compaction density of 2.1~2.2g / cm⁻³ and cut into 12mm diameter electrode sheets with an electrode loading of 2.0±0.2mg / cm². S32: Negative electrode preparation: 100±10μm lithium metal foil with lithium metal purity ≥99.9% is selected, cut to a diameter of 16mm and wiped with anhydrous ethanol to remove the oxide layer; S33: Battery assembly: Assemble CR2032 coin cells in the order of positive electrode, 30μm glass fiber separator, and negative electrode, inject 170±10μL of deep eutectic electrolyte slurry, seal at 0.8±0.1MPa, and activate at room temperature for 12±2h to obtain lithium metal batteries.

[0018] In one embodiment, the moisture and oxygen content of the argon glove box is ≤0.1ppm to avoid adverse effects of moisture and oxygen on electrolyte performance and battery assembly process.

[0019] A non-flammable deep eutectic electrolyte based on LiTFSI-NMF-FEC is prepared by the above preparation method. The electrolyte is based on a deep eutectic system formed by LiTFSI and NMF in a molar ratio of 1:4, and contains 5 wt% FEC as an SEI regulating additive.

[0020] A lithium metal battery includes a LiFePO4 positive electrode, a lithium metal negative electrode, a glass fiber separator, and an electrolyte, wherein the electrolyte is the aforementioned non-flammable deep eutectic electrolyte based on LiTFSI-NMF-FEC.

[0021] The experimental materials used in this embodiment and their purchase sources are as follows: Lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) was purchased from Ambeed China Ltd. N-methylformamide (NMF) was purchased from Hefei TNJ Chemical Industry Co., Ltd. Fluoroethylene carbonate (FEC) was purchased from Arkema China Ltd. The conductive agent (Super P) was purchased from Timcal Switzerland GmbH; The adhesive (PVDF) was purchased from Arkema China Ltd.; The lithium iron phosphate (LiFePO4) was purchased from Hunan Yuneng New Energy Battery Materials Co., Ltd. N-methylpyrrolidone (NMP) was purchased from Tianjin Concord Technology Co., Ltd. Anhydrous ethanol was purchased from Aladdin Reagent (Shanghai) Co., Ltd. The fiberglass diaphragm was purchased from Whatman Ltd., UK.

[0022] Comparative Example Comparative Example 1: The electrolyte composition was LiTFSI to NMF in a molar ratio of 1:4 (without FEC addition), and the rest of the preparation process was the same as in Example 1, denoted as LiTFSI-NMF.

[0023] Comparative Example 2: A commercially available carbonate electrolyte (1.0MLiPF6 in EC:DMC=50:50, vol%) was used directly for subsequent battery testing.

[0024] Test case Test Example 1: Electrolyte Physicochemical Properties Test The electrolyte samples from Example 1 and Comparative Examples 1 and 2 were subjected to the following analyses and tests: 1. Ionic conductivity test: The purpose is to characterize the lithium ion migration efficiency in the electrolyte. A Mettler Toledo FiveEasy F30 conductivity meter was used. The test conditions were 25°C room temperature environment, the electrode spacing was fixed at 1 cm, and each test was repeated 3 times and the average value was taken to ensure the accuracy of the data. Finally, the ionic conductivity value of the electrolyte was obtained. 2. Viscosity test: used to evaluate the flow characteristics of the electrolyte and the resistance to lithium-ion migration. An AntonPaar Instrument ViscoQC rotational viscometer was used. The test temperature was controlled at 30℃, the rotor speed was set to 100 rpm, and the data was recorded after equilibration for 5 minutes to determine the electrolyte viscosity level. 3. Flammability test: The prepared electrolyte sample is directly burned with an open flame, and the sample is observed to see if it ignites.

[0025] The test results are shown in Table (I) below: Table (I) Physicochemical Properties of Electrolytes system <![CDATA[Ionic conductivity (mScm -1 )]]> Viscosity (cp) Flammability Example 1 1.65 60.2 non-flammable 1 / 1 1.40 75.2 non-flammable Ratio 2 8.50 9.2 Flammable As can be seen from Table (I), the LiTFSI-NMF-FEC electrolyte of Example 1 of the present invention has a 20.0% lower viscosity and a 17.9% higher ionic conductivity compared to Comparative Example 1 (without FEC). Compared with traditional electrolytes, it is superior in all aspects. Compared with the traditional carbonate electrolyte of Comparative Example 2, although the ionic conductivity is slightly lower, it has inherent non-flammable properties, significantly improves safety, and the viscosity can meet the requirements for room temperature applications.

[0026] Test Example 2: Battery Electrochemical Performance Test 1. Battery fabrication: A LiFePO4 cathode with a diameter of 12 nm (active material loading 2.0 mg / cm³) of the same specifications as in Example 1 was selected. -2 A coin cell was assembled by injecting 170 μL of the electrolytes from Example 1, Comparative Example 1, and Comparative Example 2 into a lithium metal anode (16 nm in diameter and 100 μm in thickness) and a glass fiber separator. 2. Test steps: (1) Cyclic performance test: BTS4000 battery tester was used, with a charge / discharge voltage range of 2.0~3.75V and a current density of 100mAg.-1 The system was cycled 800 times at room temperature (25°C), and the discharge capacity and coulombic efficiency were recorded for each cycle. (2) Observation of lithium dendrites: After 800 cycles, the battery was disassembled, the lithium metal anode was removed, and the surface lithium deposition morphology was observed by SEM. (3) Battery impedance test after cycling: The ohmic impedance of the battery is tested after 800 cycles.

[0027] The results of the cyclic performance test are shown in Table (II) below: Table (II) Battery Electrochemical Performance system <![CDATA[Initial discharge capacity (mAhg -1 )]]> Capacity retention rate after cycling (%) Example 1 156 83.0 Comparative Example 1 142 62.5 Comparative Example 2 148 67.8 As can be seen from Table (II), the battery using the electrolyte of Example 1 of the present invention has a higher initial discharge capacity and higher capacity retention after cycling compared with Comparative Example 1 and Comparative Example 2. SEM observation results show that the lithium metal anode surface of Example 1 has uniform lithium deposition and no obvious lithium dendrite growth, while the anode surfaces of Comparative Example 1 and Comparative Example 2 have a large number of lithium dendrites. The impedance test results after cycling show that the ohmic impedance of the battery of Example 1 is significantly lower than that of Comparative Example 1 and Comparative Example 2, indicating that the electrolyte of the present invention can construct a stable SEI layer, effectively reduce the interface impedance, and improve the cycle stability of the battery.

[0028] The above data demonstrates that this invention achieves a synergistic breakthrough in electrolyte physicochemical properties, battery cycle stability, and safety through the synergistic design of the LiTFSI-NMF deep eutectic substrate and FEC additives. The preparation process is simple and repeatable, with good raw material compatibility, making it suitable for industrial applications and providing a key technical solution for the practical application of high-energy-density lithium metal batteries.

[0029] According to the present invention, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) possesses high ionic dissociation and low lattice energy, and the TFSI⁻ anion has large steric hindrance, which can effectively promote Li⁺ migration; N-methylformamide (NMF) has a short molecular chain and low steric hindrance, which can more strongly coordinate with Li⁺ and significantly reduce the viscosity of the system. The deep eutectic substrate formed by the two has both good liquid stability and ion transport potential, but the pure substrate SEI layer is mainly composed of LiOH and Li₂O, with a loose structure, making it difficult to suppress lithium dendrites. SEI-regulating additives need to be introduced to optimize the interface structure.

[0030] Furthermore, the inventors of this invention discovered that FEC can optimize the SEI layer through a "preferential reduction-synergistic regulation" mechanism: the LiF generated by FEC reduction possesses extremely high mechanical strength and chemical stability, and can physically block lithium dendrite penetration; simultaneously, the generated Li2CO3 can modulate the interfacial electron flux, guide the uniform deposition of Li⁺, and promote the reduction reaction of TFSI⁻ in LiTFSI, generating highly conductive Li3N, synergistically constructing a "LiF-Li2CO3-Li3N" composite SEI layer, and suppressing the formation of low-conductivity intermediates. The results show that the LiTFSI-NMF-FEC deep eutectic electrolyte prepared in this way achieves an ionic conductivity of 1.65 mS / cm at 25℃. -1 With a viscosity as low as 60.2 cp at 30℃, it is stable in liquid state at -40~60℃ and is inherently non-flammable. When paired with a LiFePO4 / LiMn2O4 cathode, the battery cycle life is increased by 5~12 times compared to the additive-free system. Its resistance to lithium dendrite formation and safety performance are significantly better than traditional carbonate electrolytes. Moreover, the preparation process is simple, the raw materials are readily available, and the cost is controllable, making it suitable for industrial applications.

[0031] The electrolyte of this invention uses a deep eutectic substrate formed by LiTFSI and NMF in a molar ratio of 1:4, and adds 3-6 wt% FEC as a functional additive. The composition and structure of the SEI layer are optimized through the synergistic effect of FEC and the substrate. Under optimal process conditions (5 wt% FEC), the electrolyte achieves an ionic conductivity of 1.65 mS / cm at 25°C. -1 The viscosity is as low as 60.2 cp at 30℃, and it remains stable in a liquid state within the temperature range of -40 to 60℃, exhibiting inherent non-flammability. Spectroscopic analysis confirms that FEC can promote the formation of highly ionicly conductive LiF, Li2CO3, and Li3N in the SEI layer, while inhibiting the formation of low-conductivity phases (LiNO2, LiOH, Li2O), thus constructing a dense and stable SEI layer. When applied to LMBs and paired with a LiFePO4 cathode, this electrolyte exhibits excellent performance: the Li / / LiFePO4 battery achieves a performance of 100 mAg... ⁻¹ At current density, the initial discharge capacity reaches 156 mAh g. ⁻¹ After 800 cycles, the capacity retention rate was 83%, and the average coulombic efficiency was 99.8%, significantly better than the deep eutectic system without FEC and traditional carbonate electrolytes. The electrolyte preparation process of this invention is simple, cost-controllable, and environmentally friendly, and it has good compatibility with existing lithium battery production equipment. It provides key technical support for the industrialization of high-energy-density, high-safety lithium-ion batteries (LMBs), and has significant practical value and broad application prospects.

[0032] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a non-flammable deep eutectic electrolyte and lithium metal battery based on LiTFSI-NMF-FEC, characterized in that, Includes the following steps: S1: Using lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) as the lithium salt and N-methylformamide (NMF) as the hydrogen bond donor, accurately weigh LiTFSI and NMF in a molar ratio of 1:4, place them in a polytetrafluoroethylene sealed container that has been vacuum dried at 120℃ for 8h, stir at 400±50rpm for 12±1h in a constant temperature water bath at 80±2℃, and take samples every 2h to ensure that the system is clear, transparent and free of precipitation, and cool naturally to 25±2℃ to obtain a deep eutectic base liquid; S2: Fluoroethylene carbonate (FEC) is used as an SEI regulating additive and is slowly added to the deep eutectic base liquid at a ratio of 5wt% of the total electrolyte mass. The mixture is stirred at 250±30rpm for 3±0.5h to ensure uniform dispersion of FEC. After standing for 1.5±0.5h, micro bubbles are removed to obtain a uniform deep eutectic electrolyte slurry. S3: The deep eutectic electrolyte slurry is used to complete the battery assembly in an argon glove box to obtain a lithium metal battery carrying the target electrolyte.

2. The method for preparing a non-flammable deep eutectic electrolyte and lithium metal battery based on LiTFSI-NMF-FEC according to claim 1, characterized in that, The specific process of battery assembly in step S3 is as follows: S31: Positive electrode preparation: A positive electrode slurry was prepared using LiFePO4 active material, SuperP conductive agent, and PVDF binder in a weight ratio of 80:10:

10. The slurry was coated onto a 12μm aluminum foil and vacuum dried at 100±5℃ for 8 hours. The slurry was then rolled to a compaction density of 2.1~2.2g / cm⁻³ and cut into 12mm diameter electrode sheets with a loading of 2.0±0.2mg / cm². S32: Negative electrode preparation: 100±10μm lithium metal foil is selected, the lithium metal purity of the lithium metal foil is ≥99.9%, it is cut to a diameter of 16mm and the oxide layer is removed by wiping with anhydrous ethanol; S33: Battery assembly: Assemble CR2032 coin cells in the order of positive electrode, 30μm glass fiber separator, and negative electrode, inject 170±10μL of the deep eutectic electrolyte slurry, seal at 0.8±0.1MPa, and activate at room temperature for 12±2h to obtain lithium metal batteries.

3. The method for preparing a non-flammable deep eutectic electrolyte and lithium metal battery based on LiTFSI-NMF-FEC according to claim 1, characterized in that, The moisture and oxygen content of the argon glove box is ≤0.1ppm.

4. A non-flammable deep eutectic electrolyte based on LiTFSI-NMF-FEC, characterized in that, The electrolyte is prepared by any one of claims 1 to 3, wherein the electrolyte is based on a deep eutectic system formed by LiTFSI and NMF in a molar ratio of 1:4, and contains 5 wt% FEC as an SEI regulating additive.

5. A lithium metal battery, characterized in that, The lithium metal battery includes a LiFePO4 positive electrode, a lithium metal negative electrode, a glass fiber separator, and an electrolyte, wherein the electrolyte is the non-flammable deep eutectic electrolyte based on LiTFSI-NMF-FEC as described in claim 4.

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