A lithium metal battery fluorine-free electrolyte additive, electrolyte and lithium metal battery

Abstract

This invention provides a fluorine-free electrolyte additive for lithium metal batteries, an electrolyte, and a lithium metal battery, belonging to the field of battery technology. The fluorine-free electrolyte additive for lithium metal batteries includes 1-methanesulfonyl-2-imidazolium ketone, which can enter the lithium metal electrolyte... + The inner solvation structure promotes the migration of lithium salt anions to the inner solvated sheath layer and their enrichment in the inner Helmholtz layer at the electrode interface, allowing the anions to be preferentially reduced at the electrode interface to form a solid electrolyte interface film. Furthermore, this invention provides a fluorine-free electrolyte for lithium metal batteries containing the aforementioned fluorine-free electrolyte additive, and a lithium metal battery containing this electrolyte. This invention regulates the Li... + The solvation structure improves the interfacial stability of the lithium metal anode without relying on fluorinated solvents, thereby enhancing the cycle life and safety of lithium metal batteries.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a fluorine-free electrolyte additive for lithium metal batteries, an electrolyte, and a lithium metal battery. Background Technology

[0002] The lithium metal anode has a theoretical specific capacity of 3860 mAh / g, a low reduction potential of -3.04 V (relative to the standard hydrogen electrode), and a low density. When used in conjunction with high-voltage nickel-rich ternary cathode materials, the constructed lithium metal battery has a high energy density advantage.

[0003] Currently, the commercialization of lithium metal batteries is constrained by interfacial instability. Due to the high chemical reactivity of lithium metal, severe reduction side reactions occur when it comes into contact with traditional carbonate electrolytes. During charge and discharge, it is difficult to form a stable solid-state electrolyte interface (SEI) on the lithium metal surface. Repeated rupture of the SEI layer leads to continuous reaction between the electrolyte and active lithium, producing electrochemically inactive dead lithium. At the same time, the uneven ionic conductivity caused by local SEI rupture can induce the growth of lithium dendrites. These dendrites may penetrate the separator, causing a short circuit in the battery and thus affecting the battery's cycle life.

[0004] Electrolyte regulation is an important approach to improving the interfacial performance of lithium anodes. In related technologies, high-concentration electrolytes and locally high-concentration electrolytes, by increasing the lithium salt concentration or introducing an inert diluent, allow lithium salt anions to enter the Li-ion interface. + The first solvation shell forms a solvation structure enriched with contact ion pairs and aggregates. Since the lowest unoccupied molecular orbital energy level of lithium salt anions is typically lower than that of solvent molecules, the anions are preferentially reduced at the negative electrode, generating an SEI layer rich in inorganic substances such as LiF in situ. This improves the stability of the electrode / electrolyte interface and inhibits the growth of lithium dendrites. However, high-concentration electrolytes have drawbacks such as high viscosity, poor low-temperature performance, and high cost; while locally high-concentration electrolytes reduce macroscopic viscosity, the diluent reduces the lithium-ion transport number, and fluorinated diluents are expensive and have poor environmental compatibility. Furthermore, under conventional low-concentration electrolyte conditions, lithium salt anions have difficulty entering the LiF layer. + The inner solvation structure of the SEI layer results in insufficient ability to participate in interfacial film-forming reactions, making it difficult to form a stable SEI layer.

[0005] Therefore, how to promote the participation of lithium salt anions in interfacial film formation in conventional low-concentration electrolytes, reduce dependence on fluorinated components, and improve the cycle performance of lithium metal batteries is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, the present invention aims to provide a fluorine-free electrolyte additive for lithium metal batteries, an electrolyte, and a lithium metal battery. This additive can regulate the electrolyte concentration of Li without relying on fluorine-containing solvents. + The solvation structure promotes the migration of lithium salt anions to the inner solvation sheath and their enrichment in the inner Helmholtz layer at the electrode interface. This allows the anions to be preferentially reduced at the electrode interface to form a stable solid electrolyte interface film rich in inorganic matter, thereby significantly improving the interface stability of the lithium metal anode and the reversibility of lithium deposition / stripping, inhibiting lithium dendrite growth, and improving the cycle life and safety of lithium metal batteries.

[0007] To achieve the above objectives, the present invention provides the following solution: In a first aspect, the present invention provides a fluorine-free electrolyte additive for lithium metal batteries, comprising 1-methanesulfonyl-2-imidazolium ketone.

[0008] Preferably, the 1-methanesulfonyl-2-imidazolidineone is capable of entering Li + The inner solvation structure promotes the migration of lithium salt anions to the inner solvation sheath.

[0009] Preferably, the 1-methanesulfonyl-2-imidazolium ketone can promote the enrichment of lithium salt anions in the inner Helmholtz layer at the electrode interface.

[0010] Secondly, the present invention provides a fluorine-free electrolyte for lithium metal batteries, comprising a lithium salt, a non-aqueous organic solvent, and the fluorine-free electrolyte additives for lithium metal batteries as described above.

[0011] Preferably, the amount of 1-methanesulfonyl-2-imidazolidine ketone added to the electrolyte is 0.5 wt% to 5 wt%.

[0012] Preferably, the lithium salt is LiPF6, and the concentration of the lithium salt in the electrolyte is 1 mol·L⁻¹. -1 ~2mol·L -1 .

[0013] Preferably, the non-aqueous organic solvent is selected from at least one of ethylene carbonate, diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate.

[0014] Thirdly, the present invention provides a lithium metal battery, comprising a positive electrode, a negative electrode, a separator, and a fluorine-free electrolyte for lithium metal batteries as described above.

[0015] Preferably, the lithium metal battery is a high-voltage lithium metal battery, the positive electrode includes a nickel-rich ternary positive electrode material, and the negative electrode is a lithium metal negative electrode.

[0016] Fourthly, this invention provides a 1-methanesulfonyl-2-imidazolium ketone as an additive for fluorine-free electrolytes in lithium metal batteries to regulate the performance of Li... + Application in solvation structures, the 1-methanesulfonyl-2-imidazolidine ketone enters Li + The inner solvation structure enhances the proportion of lithium salt anions in the inner solvation sheath, enabling the anions to be preferentially reduced at the electrode interface to form a solid electrolyte interface film.

[0017] Compared with the prior art, the present invention discloses at least the following technical effects: (1) This invention introduces 1-methanesulfonyl-2-imidazolium ketone into a conventional low-concentration carbonate electrolyte, allowing the additive to enter the Li + The inner solvation structure promotes the migration of lithium salt anions to the inner solvation sheath and their enrichment in the inner Helmholtz layer at the electrode interface. This preferentially reduces and forms a solid electrolyte interfacial film at the electrode interface. Thus, this invention can construct a stable and dense SEI layer in situ on the lithium metal surface without relying on fluorinated solvents or fluorinated additives. This solves the problem of insufficient ability of lithium salt anions to participate in interfacial film formation in conventional low-concentration electrolytes and avoids the defects of high cost and easy initiation of interfacial side reactions by fluorinated components.

[0018] (2) The average coulombic efficiency of the Li||Cu half-cell using the electrolyte of this invention increased from 86.5% to 97.8%, and the reversibility of lithium deposition / stripping was significantly improved; the Li||NCM811 full cell exhibited better cycle performance and capacity retention in the voltage range of 2.7~4.5V; and the Li||Li symmetric cell also showed more stable cycle performance. Based on the above results, it can be concluded that this invention can effectively suppress lithium dendrite growth and improve the cycle life of lithium metal batteries.

[0019] (3) The present invention only requires the addition of a small amount of 1-methanesulfonyl-2-imidazolidine ketone additive to commercial carbonate electrolyte, without the need to modify the existing battery production line. The preparation process is simple and easy to achieve large-scale application. At the same time, the additive still shows good cycle stability in soft-pack batteries under practical conditions of less lithium source and less electrolyte, further proving its feasibility in the practical application of high voltage lithium metal batteries and has good industrialization prospects. Attached Figure Description

[0020] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0021] Figure 1A comparison chart of the average coulombic efficiency of Example 1 and Comparative Example 1 in Li||Cu half-cells provided by the present invention.

[0022] Figure 2 Cyclic performance graphs of Example 1 and Comparative Example 1 provided by the present invention in Li||NCM811 button cells.

[0023] Figure 3 The figures show the electrochemical response curves of Example 1 and Comparative Example 1 of the present invention.

[0024] Figure 4 A comparison chart of the average coulombic efficiency of Example 2 and Comparative Example 1 in Li / Cu half-cells provided by the present invention.

[0025] Figure 5 A comparison of the cycle stability of Example 3 and Comparative Example 1 in a Li||Li symmetric battery provided by the present invention.

[0026] Figure 6 The images show the XPS high-resolution spectra of the baseline sample and the MSMI-treated electrode provided by this invention, where a is the untreated baseline sample and b is the MSMI-modified electrode. Detailed Implementation

[0027] 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.

[0028] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] Comparative Example 1 A commercial carbonate electrolyte was prepared as a comparative electrolyte by dissolving LiPF6 in a mixed solvent of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) at a volume ratio of 3:7 and a LiPF6 concentration of 1 mol·L⁻¹. -1 All electrolyte preparations and battery assembly were performed in an argon-filled glove box with a water content below 0.1 ppm and an oxygen content below 0.1 ppm. Based on the obtained comparative electrolyte, the following battery assembly tests were conducted, including: First, the Li||Li symmetric cells were assembled and tested. Two identical lithium foils (approximately 100 μm thick) were coupled together in an argon-filled glove box. A Celgard 2400 polypropylene porous membrane was used as a separator to separate the two lithium electrodes. 40 μL of comparative electrolyte was injected into each symmetric cell to assemble the Li||Li symmetric cells. The assembled Li||Li symmetric cells were then subjected to constant current charge-discharge cycle tests under different current densities and capacity conditions.

[0030] Next, the Li / Cu half-cells were assembled and tested, specifically the CR2025 coin cells assembled in an argon-filled glove box. A 500μm thick lithium foil was used as the counter electrode, Celgard 2400 as the separator, and copper foil as the working electrode to form the Li / Cu half-cells. Each cell was injected with 40μL of comparative electrolyte. Constant current testing was performed using a Neware multichannel battery tester.

[0031] The test procedure includes: first, at 0.05 mA·cm -2 The current density was used to activate it for 5 cycles within a voltage range of 0.01~1V; then it was activated at 1mA·cm⁻¹. -2 Lithium deposition was performed at a current density of 1 hour, followed by delithiation at a voltage of 1V. This process was repeated as one cycle for cyclic testing.

[0032] Finally, the button cell was assembled and tested, specifically the NCM811 (LiNi) battery. 0.8 Co 0.1 Mn 0.1 The O2 cathode is paired with a 50 μm thick coin cell to form a full cell with a lithium foil having an areal capacity of approximately 10 mAh·cm³. -2 The separator used was Celgard 2400, and each cell was injected with 40 μL of comparative electrolyte. The NCM811-based full cell operated in the voltage range of 2.7–4.5 V (vs. Li / Li). + The circuit undergoes constant current charge-discharge cycling with a cycle current density of 1C, where 1C = 200 mAh·g. -1 Each button cell was activated for 5 cycles at a current density of 0.1C before the formal cycle test.

[0033] Record the above test results as comparative data.

[0034] Example 1 1-Methanesulfonyl-2-imidazolium ketone (MSMI) was added as an additive to a commercial carbonate electrolyte that was exactly the same as the comparative example, with the amount of MSMI added to the electrolyte being 2 wt%. The mixture was stirred at room temperature until completely dissolved to obtain the fluorine-free electrolyte for lithium metal batteries of Example 1 of the present invention.

[0035] Following the exact same battery assembly method and testing conditions as the comparative example, the electrolyte from Example 1 was used for the assembly and testing of Li||Li symmetric cells, Li / Cu half-cells, and button cells, respectively. The results obtained include: First, the Li / Cu half-cell test results of this embodiment (Baseline+MSMI) and Comparative Example 1 (Baseline) are as follows: Figure 1 As shown. A Li / Cu half-cell using a comparative electrolyte at 0.5 mAh / cm² is shown. 2 -2mAh / cm 2 Lithium deposition / stripping cycle tests were conducted at the specified current and capacity density, and the average coulombic efficiency was 86.5%. Under the same test conditions, the Li / Cu half-cell using the electrolyte from Example 1 achieved an average coulombic efficiency of 97.8%. The increase in coulombic efficiency from 86.5% to 97.8% indicates that the addition of MSMI significantly improved the reversibility of the lithium deposition / stripping process.

[0036] Then, the test results of the button cell full battery in this embodiment and Comparative Example 1 are as follows: Figure 2 As shown. The battery using a comparative commercial ester electrolyte (Baseline) has an initial discharge specific capacity of approximately 176.3 mAh·g. -1 The capacity decays rapidly during cycling, with capacity retention falling below 80% after 100-120 cycles; and the discharge specific capacity drops to 103.5 mAh·g after approximately 170 cycles. -1 The corresponding capacity retention rate is approximately 58.7%. The coulombic efficiency fluctuates significantly during the cycling process, and remains in the range of 99.2% to 99.5% during the stable cycling phase.

[0037] The battery using the example electrolyte with added MSMI additive (Baseline+MSMI) exhibits an initial discharge specific capacity of approximately 173.5 mAh·g under the same test conditions. -1 Capacity decay was significantly suppressed during cycling, with capacity retention still above 80% after 210 cycles, and a discharge specific capacity of 146.9 mAh·g. -1 The corresponding capacity retention rate is approximately 84.7%. The coulombic efficiency remains stable during the cycle, and the coulombic efficiency in the steady-state cycle phase is maintained above 99.8%.

[0038] The above results indicate that the introduction of MSMI additives can effectively delay the capacity decay of lithium metal full batteries during long-term cycling, while improving the reversibility of the charge-discharge process and significantly optimizing the long-term cycling stability of the battery.

[0039] Furthermore, the test results of this embodiment and Comparative Example 1 for the Li||Li symmetric cell are as follows: Figure 3As can be seen, compared with the untreated Comparative Example 1 (Baseline) sample, the charge-discharge curve of the electrode of Example 1 treated with MSMI (Baseline+MSMI) shifts in a favorable direction overall, exhibiting a higher operating voltage at the same capacitance areal density, indicating that its electrode polarization is effectively alleviated. Specifically, the polarization overpotential corresponding to the Comparative Example 1 sample is 190.6 mV, while the polarization overpotential of the Example 1 sample is only 90.8 mV. This result demonstrates that MSMI treatment can significantly reduce the electrochemical polarization resistance inside the electrode and at the interface, improve the electron / ion transport process, and thus enhance the electrochemical performance of the electrode material.

[0040] Example 2 MSMI was added as an additive to a commercial carbonate electrolyte that was exactly the same as the comparative example, with an addition amount of 0.5 wt%. The mixture was stirred at room temperature until completely dissolved to obtain the fluorine-free electrolyte for lithium metal batteries of Example 2 of the present invention.

[0041] Following the exact same battery assembly method and testing conditions as in Example 1, the electrolyte from Example 2 was used for the assembly and testing of Li||Li symmetric cells, Li / Cu half-cells, and coin cells, respectively. Test results showed that, as Figure 4 As shown, at 0.5 mAh / cm 2 -1mAh / cm 2 At the specified current and capacity density, the electrolyte of Example 2 (Baseline + MSMI) exhibited an average coulombic efficiency of 97.2% in Li / Cu half-cells, significantly higher than the 87.3% of Comparative Example 1 (Baseline). Furthermore, Example 2 maintained a capacity retention of over 80% in Li||NCM811 button cells after 200 cycles, outperforming Comparative Example 1. Example 2 achieved cycle stability exceeding 600 hours in Li||Li symmetric cells, while Comparative Example 1 achieved approximately 250 hours, thus demonstrating that Example 2 outperformed Comparative Example 1. In summary, while the performance improvement of the electrolyte in Example 2 was slightly less than that in Example 1, it was still significantly superior to the Comparative Example.

[0042] Example 3 MSMI was added as an additive to a commercial carbonate electrolyte that was exactly the same as the comparative example, with an addition amount of 5 wt%. The mixture was stirred at room temperature until completely dissolved to obtain the fluorine-free electrolyte for lithium metal batteries of Example 3 of the present invention.

[0043] Following the exact same battery assembly method and testing conditions as Example 1, the electrolyte of Example 3 was used for the assembly and testing of Li||Li symmetric cells, Li / Cu half-cells, and coin cells. Test results showed that the average coulombic efficiency of the electrolyte of Example 3 in Li / Cu half-cells was 89.2%, higher than that of Comparative Example 1. In Li||NCM811 coin cells, the capacity retention rate was 65.4% after 200 cycles, while that of Comparative Example 1 was 58.7% after 170 cycles. Figure 5 As shown, the cycle stability of Example 3 in a Li||Li symmetric battery is greater than 800 h, while the cycle stability of Comparative Example 1 is approximately 250 h. Considering the results of the three tests, the performance improvement of the electrolyte in Example 3 is essentially equivalent to that in Example 1.

[0044] Example 4 Using the exact same electrolyte formulation as in Example 1, i.e., with an MSMI addition of 2 wt%, pouch cells were assembled. All pouch cells were assembled on a semi-automated battery production line. Assembly was carried out in a dry room with a relative humidity of 0.1%, a dew point controlled below -50°C, and a constant temperature of 25°C.

[0045] The assembly process includes: preparing electrode slurry using a slurry mixer; coating the electrodes using a coating machine; calendering the electrodes using a calender; stacking the cathode, anode, and separator using a Z-type stacker; ultrasonically welding the aluminum tabs (cathode) and nickel tabs (anode); packaging and sealing the top and sides; injecting the electrolyte from Example 1 and vacuum sealing. To ensure energy density, all pouch cells operate with relatively low lithium source and low electrolyte conditions.

[0046] Based on the above, the testing process for the pouch cell included: testing the pouch cell on a battery cycler at a temperature of 25°C and a test voltage range of 2.7~4.5V. Cycling tests were conducted under 0.1C charging and 0.3C discharging conditions; before long-cycle testing, it was first cycled 3 times at 0.05C / 0.05C to form a stable SEI layer. Test results showed that the Li||NCM811 pouch cell using the electrolyte from Example 1 exhibited good cycle stability under practical conditions with less lithium source and less electrolyte. Specifically, it achieved stable cycling for over 90 cycles in high-energy-density pouch cells with a capacity retention rate exceeding 80% at concentrations above 500Wh / kg.

[0047] Based on the above test results, the sulfonyl and carbonyl groups in the MSMI molecular structure have strong coordination ability, enabling them to enter Li + The inner solvation structure of Li changes + The original solvation environment. MSMI enters Li +After the first solvation sheath layer, it partially replaces the original carbonate solvent molecules, breaking the solvent molecules surrounding Li. + The tight coordination structure provides a suitable environment for lithium salt anions (PF6). - This creates favorable spatial and energy conditions for the entry into the inner solvation sheath. With PF6... - As PF6 migrates into the inner solvated sheath, its concentration in the inner Helmholtz layer at the electrode interface gradually increases. - The lowest unoccupied molecular orbital energy level is lower than that of carbonate solvent molecules, and PF6 at the negative electrode interface - Lithium preferentially gains electrons and is reduced, with its decomposition products mainly being LiF and sulfur-containing compounds, which are deposited in situ on the lithium metal surface to form an inorganic-rich SEI layer. This SEI layer possesses high mechanical strength to resist the volume expansion stress during lithium deposition, while also having uniform ion channels to ensure the Li... + The rapid conduction effectively inhibits the nucleation and growth of lithium dendrites, reduces the direct contact and side reactions between the electrolyte and lithium metal, and ultimately achieves a significant improvement in the stability and cycle life of the lithium metal anode interface.

[0048] like Figure 6 As shown in a and b, after MSMI treatment, the XPS peak positions and peak area ratios of the corresponding elements on the electrode surface changed significantly, indicating that MSMI interacted with the electrode interface and modulated the electronic structure and chemical valence distribution of the surface elements. This interface regulation helps to reduce the charge transport impedance during the electrode reaction process, which corroborates the aforementioned result of reduced polarization overpotential, demonstrating that MSMI can effectively improve the reaction kinetics of the electrode interface.

[0049] Compared with related technologies that rely on high-concentration lithium salts or large amounts of fluorinated diluents, the present invention can achieve the above effects in conventional concentrations of fluorinated carbonate electrolytes, with lower raw material costs, greater environmental friendliness, and no need to modify existing battery production lines.

[0050] It should be noted that in Examples 1-3 above, the MSMI addition amounts were 2wt%, 0.5wt%, and 5wt%, respectively, all of which achieved the technical effects of the present invention. The test results of Examples 1-3 show that, within the range of 0.5wt% to 5wt%, as the MSMI addition amount increases, the battery performance exhibits a trend of first improving and then stabilizing. When the addition amount is 0.5wt%, MSMI has a significant effect on Li... + The modulating effect of solvation structure can significantly improve battery performance; when the addition amount is increased to 2 wt%, the performance improvement reaches a relatively good level; further increasing to 5 wt%, the performance remains at a similar level. When the addition amount is below 0.5 wt%, the absolute amount of MSMI is insufficient to affect Li. +The solvation environment provides sufficient regulation, but the enrichment effect of anions at the electrode interface is not significant; when the addition amount is higher than 5 wt%, excessive MSMI may increase the viscosity of the electrolyte and affect Li. + The migration rate of MSMI is affected, and excessive additives participating in interfacial reactions may alter the composition and thickness of the SEI layer, thus adversely affecting battery performance. Therefore, the preferred addition amount of MSMI in the electrolyte is 0.5wt%~5wt%.

[0051] In addition, the lithium salt concentration is 1 mol·L -1 ~2mol·L -1 The technical effects of this invention can be achieved within the specified range. When the lithium salt concentration is below 1 mol·L⁻¹ -1 At this point, the absolute number of lithium salt anions in the electrolyte is insufficient. Even if MSMI promotes the entry of anions into the inner solvated sheath layer, the total amount of anions available for interfacial film formation remains limited. When the lithium salt concentration is higher than 2 mol·L⁻¹, the concentration of lithium salt anions is still insufficient. -1 At this rate, the electrolyte viscosity increases, the ionic conductivity decreases, and the cost increases. Therefore, the preferred lithium salt concentration is 1 mol·L⁻¹. -1 ~2mol·L -1 .

[0052] The solvent can be one or more of ethylene carbonate (EC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). These solvents are all conventional non-aqueous organic solvents used in the lithium-ion and lithium metal battery fields. Those skilled in the art can select and proportion them according to actual requirements such as electrolyte viscosity, dielectric constant, and film-forming properties.

[0053] Therefore, by employing the aforementioned fluorine-free electrolyte additive, electrolyte, and lithium metal battery for lithium metal batteries, this additive can regulate the lithium content without relying on fluorine-containing solvents. + The solvation structure promotes the migration of lithium salt anions to the inner solvation sheath and their enrichment in the inner Helmholtz layer at the electrode interface. This allows the anions to be preferentially reduced at the electrode interface to form a stable solid electrolyte interface film rich in inorganic matter, thereby significantly improving the interface stability of the lithium metal anode and the reversibility of lithium deposition / stripping, inhibiting lithium dendrite growth, and improving the cycle life and safety of lithium metal batteries.

[0054] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0055] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A fluorine-free electrolyte additive for lithium metal batteries, characterized in that, The additive includes 1-methanesulfonyl-2-imidazolidineone.

2. The fluorine-free electrolyte additive for lithium metal batteries according to claim 1, characterized in that, The 1-methanesulfonyl-2-imidazolidine ketone can enter Li + The inner solvation structure promotes the migration of lithium salt anions to the inner solvation sheath.

3. The fluorine-free electrolyte additive for lithium metal batteries according to claim 1, characterized in that, The 1-methanesulfonyl-2-imidazolium ketone can promote the enrichment of lithium salt anions in the inner Helmholtz layer at the electrode interface.

4. A fluorine-free electrolyte for lithium metal batteries, characterized in that, It includes lithium salts, non-aqueous organic solvents, and the fluorine-free electrolyte additives for lithium metal batteries as described in any one of claims 1 to 3.

5. The fluorine-free electrolyte for lithium metal batteries according to claim 4, characterized in that, The amount of 1-methanesulfonyl-2-imidazolium ketone added to the electrolyte is 0.5 wt% to 5 wt%.

6. The fluorine-free electrolyte for lithium metal batteries according to claim 4, characterized in that, The lithium salt is LiPF6, and the concentration of the lithium salt in the electrolyte is 1 mol·L⁻¹. -1 ~2mol·L -1 .

7. The fluorine-free electrolyte for lithium metal batteries according to claim 4, characterized in that, The non-aqueous organic solvent is selected from at least one of ethylene carbonate, diethyl carbonate, methyl ethyl carbonate, and dimethyl carbonate.

8. A lithium metal battery, characterized in that, It includes a positive electrode, a negative electrode, a separator, and a fluorine-free electrolyte for lithium metal batteries as described in claim 4.

9. A lithium metal battery according to claim 8, characterized in that, The lithium metal battery is a high-voltage lithium metal battery, the positive electrode includes a nickel-rich ternary positive electrode material, and the negative electrode is a lithium metal negative electrode.

10. A 1-methanesulfonyl-2-imidazolium ketone as an additive in the fluorine-free electrolyte of lithium metal batteries for regulating Li + Applications in solvation structures, characterized by: The 1-methanesulfonyl-2-imidazolidine ketone enters Li + The inner solvation structure enhances the proportion of lithium salt anions in the inner solvation sheath, enabling the anions to be preferentially reduced at the electrode interface to form a solid electrolyte interface film.

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