Electrolyte stabilizing high-voltage cathode interface and preparation method thereof

Abstract

This invention discloses an electrolyte for stabilizing the high-voltage cathode interface and its preparation method, relating to the field of battery electrolyte materials technology. The electrolyte is a carbonate electrolyte containing 1-3 wt% 4-trifluoromethoxybenzenesulfonamide. By adding 4-trifluoromethoxybenzenesulfonamide, a component with a unique molecular structure, to the carbonate electrolyte, this invention promotes a multi-level synergistic effect between the electrolyte bulk and the electrode interface, achieving a multi-functional integration of "solventization structure regulation - reactive oxygen species capture - in-situ interface construction." This significantly improves the interfacial compatibility between the high-voltage LCO cathode and the lithium metal anode, as well as the long-cycle stability of the battery. It is particularly suitable for high-energy-density, high-voltage, and fast-charging lithium metal battery systems, and is suitable for large-scale application in lithium metal batteries.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, mainly to the field of lithium metal battery electrolyte technology, and specifically to an electrolyte that stabilizes the high-voltage cathode interface and its preparation method. Background Technology

[0002] With the ever-increasing demand for battery energy density from new energy vehicles, high-end consumer electronics, and large-scale energy storage systems, developing next-generation electrochemical energy storage technologies with higher energy density has become an inevitable direction for industrial development. Lithium metal batteries, due to their negative electrode, possess a theoretically extremely high specific capacity (3860 mAh g⁻¹). -1 Lithium metal, also known as lithium cobalt oxide, is widely recognized as one of the ultimate solutions to overcome the current energy density bottleneck of lithium-ion batteries. To fully realize the potential of this system, it is usually necessary to match it with a cathode material that has both high operating voltage and high specific capacity, such as increasing the operating voltage of lithium cobalt oxide (LiCoO2) to 4.4V (vs. Li...). + / Li) or even higher.

[0003] However, the severe interface failure problem of cathode materials under high voltage has become the primary technical obstacle restricting the achievement of long cycle life and high safety of high-energy-density lithium metal batteries. The failure mechanism and core challenge of high-voltage cathode interfaces are as follows: When layered oxide cathodes (such as LCO) operate under high voltage, the thermodynamic instability between them and conventional organic electrolytes (mainly carbonates) is amplified sharply, triggering a series of interconnected malignant side reactions. These mainly include: (i) continuous oxidative decomposition of electrolyte: Carbonate solvents and lithium salts undergo irreversible electrochemical oxidation at high potentials, forming a thick and unstable cathode electrolyte interface (CEI) film on the cathode surface. This film has high impedance and poor mechanical properties, which not only leads to a significant increase in polarization voltage, but also consumes active lithium sources. Its repeated rupture and regeneration process further consumes electrolyte, accelerating capacity decay. (ii) Lattice oxygen loss and structural phase transition: Under high voltage, the oxygen element in the surface lattice of the cathode material becomes more active, easily forming reactive oxygen free radicals (such as O2). - O2 2- Irreversible precipitation in the form of transition metal ions. This process directly destroys the crystal structure of the material, initiating an irreversible phase transition from an ordered layered structure to a disordered spinel phase and even an insulating rock salt phase, resulting in the permanent loss of the host material's lithium storage capacity. At the same time, the released highly reactive oxygen species will further oxidize and decompose the electrolyte, generating gas and exacerbating interface failure. (iii) Dissolution and cross-migration of transition metal ions: The unstable interface accelerates the dissolution and cross-migration of transition metal ions (such as Co). 3+ / Co 4+The dissolved ions migrate through the electrolyte and are reduced on the surface of the lithium metal anode, poisoning the solid electrolyte interface (SEI) and disrupting its uniformity and stability, thus creating a vicious cycle in which the performance of the positive and negative electrodes mutually deteriorates.

[0004] Currently, to address these challenges, existing research mainly focuses on local optimization of a single interface, or faces significant performance trade-offs. For example, while high-concentration electrolytes can construct a stable SEI layer at the negative electrode through anion-dominated solvation structures, their high cost, high viscosity, and insufficient protection of the high-voltage positive electrode limit their application. Furthermore, many additive strategies (such as CN118572193A, CN116435594A, CN114142088A, etc.) often only target positive electrode protection or negative electrode SEI optimization, making it difficult to simultaneously address both sides at the molecular level. Among them, Chinese Patent Publication No. CN114142088A discloses a high-voltage electrolyte for lithium batteries. This electrolyte uses fluorosulfonamide compounds as additives. Although this electrolyte can form a stable interfacial protective layer at the positive electrode and has excellent compatibility with both the positive and negative electrodes, reducing side reactions of the electrolyte and achieving relatively good cycle performance and high coulombic efficiency, it only forms a stable interfacial protective layer at the positive electrode and does not take into account the needs of both the positive and negative electrodes. Moreover, the total amount of fluorine source that fluorosulfonamides can provide is low, resulting in low LiF content in the formed positive electrode interfacial protective layer and poor protective layer quality. Therefore, its effect on improving battery cycle performance is limited.

[0005] It is evident that most existing strategies fail to systematically address the root cause of electrolyte solvation structure, which directly determines the thermodynamics and kinetics of interfacial reactions. An ideal solution should simultaneously satisfy the following: in the bulk phase, it should guide the formation of anion-rich solvation structures; at the positive electrode interface, it should actively passivate the surface, capture reactive oxygen species, and form a dense and stable CEI; and at the negative electrode interface, it should induce the formation of a uniform and robust SEI. However, in current technology, strategies that can achieve these multiple synergistic functions through a single molecule additive remain lacking. Therefore, developing an electrolyte system capable of integrated design from solvation structure regulation to in-situ construction of both interfaces is crucial for achieving long-cycle stability in high-voltage lithium metal batteries. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of unstable positive and negative electrode / electrolyte interfaces, release of reactive oxygen species, and poor compatibility of lithium metal anodes under high-voltage conditions in existing lithium metal batteries. This invention proposes an electrolyte for stabilizing the high-voltage positive electrode interface and its preparation method. By introducing additives with specific functions, this electrolyte can capture reactive oxygen species on the surfaces of the high-voltage positive and negative electrodes and construct a stable interface layer in situ. It also effectively regulates the lithium-ion solvation structure, synergistically improving the compatibility and long-cycle stability of the interface between the high-voltage lithium cobalt oxide (LiCoO2, LCO) positive electrode and the lithium metal anode, making it suitable for large-scale application.

[0007] To achieve the above-mentioned objective, this invention proposes an electrolyte for stabilizing the high-voltage positive electrode interface, wherein the electrolyte is a carbonate electrolyte containing 1-3 wt% 4-trifluoromethoxybenzenesulfonamide.

[0008] This invention provides an electrolyte for stabilizing a high-voltage positive electrode interface. By adding 4-trifluoromethoxybenzenesulfonamide, a component with a unique molecular structure, to a carbonate electrolyte, a multi-level synergistic effect is achieved between the electrolyte bulk and the electrode interface. This effect not only occurs within the electrolyte bulk, but also utilizes the sulfonyl oxygen site of the 4-trifluoromethoxybenzenesulfonamide molecule as a Lewis base to react with Li. + The principle of weak coordination involves actively participating in and reconstructing Li. + The primary solvation sheath structure significantly reduces the coordination ratio of polar solvents such as ethylene carbonate (EC) and enhances the coordination ratio of anions (such as PF6). - The coordination probability of 4-trifluoromethoxybenzenesulfonamide induces the formation of anion-rich solvation structures, which helps to guide the formation of a uniform and stable SEI layer on the lithium metal anode surface, significantly improving the uniformity of lithium deposition. Furthermore, at the cathode interface, utilizing the principle that the sulfonamide bond (-SO2NH-) of 4-trifluoromethoxybenzenesulfonamide is susceptible to nucleophilic attack due to the electron-withdrawing group (-CF3), the electron cloud density of the sulfonamide bond is significantly reduced, making it susceptible to nucleophilic attack by highly reactive oxygen species on the cathode surface. This allows it to preferentially bind to reactive oxygen species on the LCO surface, capturing and stabilizing reactive oxygen species, thus helping to stabilize the oxygen structure and significantly reducing irreversible oxygen release, thereby improving the structural stability of the cathode from the source. Simultaneously, 4-trifluoromethoxybenzenesulfonamide can also preferentially oxidize on the cathode surface and construct an in-situ layer rich in LiF, Li3N, and Li. -The thin and dense CEI film composed of inorganic components such as sulfur effectively blocks the continuous oxidation of the electrolyte (effectively isolating the electrolyte from direct contact with the highly active cathode material and inhibiting continuous interfacial side reactions). Furthermore, this film possesses high ionic conductivity and mechanical strength, without significantly affecting ion conduction or reducing battery performance. This invention, through the addition of 4-trifluoromethoxybenzenesulfonamide, achieves multifunctional integration of "solventization structure regulation - reactive oxygen capture - in-situ interface construction," significantly improving the interfacial compatibility between the high-voltage LCO cathode and the lithium metal anode, as well as the long-cycle stability of the battery. It is particularly suitable for high-energy-density, high-voltage, and fast-charging lithium metal battery systems, making it suitable for large-scale application in lithium metal batteries.

[0009] Preferably, the carbonate electrolyte further includes ethylene carbonate, ethyl methyl carbonate, and lithium salt.

[0010] Preferably, the concentration of lithium salt in the carbonate electrolyte is 1-1.2 mol / L.

[0011] Preferably, the lithium salt is lithium hexafluorophosphate.

[0012] Preferably, in the carbonate electrolyte, the volume ratio of ethylene carbonate to methyl ethyl carbonate is 6-7:13-14.

[0013] Preferably, the electrolyte contains 1.8-2.2 wt% 4-trifluoromethoxybenzenesulfonamide. More preferably, the content is 2 wt%.

[0014] To achieve the above-mentioned objective, the present invention further proposes a method for preparing an electrolyte with a stable high-voltage positive electrode interface, comprising the steps of: dissolving 4-trifluoromethoxybenzenesulfonamide in a carbonate electrolyte and allowing it to stand for at least 2 hours to reach equilibrium.

[0015] Among these methods, static balancing allows for more uniform mixing of the electrolyte components, resulting in more stable physicochemical properties and facilitating safe use and accurate testing of electrical performance.

[0016] Preferably, 4-trifluoromethoxybenzenesulfonamide is dissolved in carbonate electrolyte under stirring at 25-30°C.

[0017] Preferably, during the stirring and dissolving process, the stirring speed is 50-100 r / min and the time is 0.5-1 h; this can better dissolve 4-trifluoromethoxybenzenesulfonamide.

[0018] To achieve the above-mentioned objectives, the present invention further proposes a lithium metal battery (with lithium metal as the negative electrode), wherein the lithium metal battery contains the above-mentioned electrolyte; the lithium metal battery containing the electrolyte of the present invention has significantly improved cycle performance.

[0019] Preferably, the positive electrode material of the lithium metal battery is LCO.

[0020] The beneficial effects of the technical solution of this invention are as follows: 1. The electrolyte of this invention can utilize the sulfonyl oxygen site of the 4-trifluoromethoxybenzenesulfonamide molecule as a Lewis base to react with Li in the electrolyte bulk. + The principle of weak coordination participates in and reconstructs Li + The primary solvation sheath structure induces the formation of anion-rich solvation structure, which helps to guide the formation of a uniform and stable SEI layer on the lithium metal anode surface and significantly improves the uniformity of lithium deposition.

[0021] 2. The electrolyte of this invention can bind to reactive oxygen species on the LCO surface at the positive electrode interface by utilizing the principle that the sulfonamide bond (–SO2NH–) of 4-trifluoromethoxybenzenesulfonamide is easily attacked by nucleophilic groups (-CF3) due to the electron-attracting group. This helps to stabilize the oxygen structure and significantly reduces the release of irreversible oxygen.

[0022] 3. The 4-trifluoromethoxybenzenesulfonamide contained in the electrolyte of this invention can preferentially oxidize on the surface of the positive electrode and form a thin and dense CEI film rich in inorganic components such as LiF, Li3N, and Li-S in situ, which effectively blocks the continuous oxidation of the electrolyte. Moreover, the film has high ionic conductivity and mechanical strength and will not significantly affect ion conduction or reduce battery performance.

[0023] 4. The electrolyte of this invention achieves multifunctional integration of "solventization structure regulation - reactive oxygen capture - in-situ interface construction" through the addition of 4-trifluoromethoxybenzenesulfonamide, which significantly improves the interfacial compatibility between the high-voltage LCO cathode and the lithium metal anode and the long-term cycle stability of the battery (the LCO / / Li battery assembled with this electrolyte retains more than 80% of its capacity after 600 cycles at a voltage range of 3.0-4.5V and a 1C rate). It is especially suitable for high-energy-density, high-voltage and fast-charging lithium metal battery systems and is suitable for large-scale application in lithium metal batteries. Attached Figure Description

[0024] Figure 1 The electrolyte used in Example 3 of this invention to stabilize the high-voltage positive electrode interface and the reference electrolyte used in the blank example. 7 LiNMR spectrum; Figure 2 Linear sweep voltammetric curves of the electrolyte with a stable high-voltage positive electrode interface and the reference electrolyte in the blank example of Example 3 of the present invention; Figure 3 The lithium-ion diffusion coefficient (logD) of the battery using the electrolyte with a stable high-voltage positive electrode interface and the reference electrolyte in the blank example is shown in Example 3 of this invention. Li+ ); Figure 4 The LCO / / Li battery, composed of the electrolyte with a stable high-voltage positive electrode interface in Example 3 of the present invention and the reference electrolyte in the blank example, is shown in the CEI scanning electron microscope image of the LCO surface after 100 cycles under specified conditions. Figure 5 The SEI scanning electron microscope image of the lithium metal surface after 50 cycles under specified conditions for an LCO / / Li battery composed of an electrolyte with a stable high-voltage positive electrode interface in Example 3 of the present invention and a reference electrolyte in a blank example. Figure 6 The graph shows a comparison of the cycle performance of an LCO / / Li battery composed of the electrolyte with a stable high-voltage positive electrode interface in Example 3 of this invention and the reference electrolyte in the blank example, under the conditions of 3.0-4.5V, 25℃, and 1C. Figure 7 The graph shows a comparison of the cycle performance of an LCO / / Li battery composed of the electrolyte with a stable high-voltage positive electrode interface in Example 3 of this invention and the reference electrolyte in the blank example, under the conditions of 3.0-4.5V, 25℃, and 4C. Figure 8 The graph shows a comparison of the cycle performance of an LCO / / Li battery composed of the electrolyte used in Example 3 (which stabilizes the high-voltage positive electrode interface) and the electrolyte used in Comparative Example 5, under conditions of 3.0-4.5V, 25℃, and 1C. Detailed Implementation

[0025] The specific embodiments of the present invention will be further described below with reference to examples, but the present invention is not limited to the scope of the embodiments described herein.

[0026] Examples 1-5

[0027] An electrolyte that stabilizes the high-voltage positive electrode interface is a carbonate electrolyte containing 4-trifluoromethoxybenzenesulfonamide (specific contents are shown in Table 1) (ethylene carbonate and ethyl methyl carbonate in a volume ratio of 3:7; 1 mol / L LiPF6). The specific preparation method is as follows: 4-trifluoromethoxybenzenesulfonamide is stirred and dissolved in carbonate electrolyte at 25℃ (100r / min, 30min), and then allowed to stand for equilibration for 2.5 hours.

[0028] Table 1. Amount of 4-trifluoromethoxybenzenesulfonamide added in Examples 1-5

[0029] Example 6

[0030] An electrolyte for stabilizing the high-voltage cathode interface is a carbonate electrolyte containing 2 wt% 4-trifluoromethoxybenzenesulfonamide (ethylene carbonate and ethyl methyl carbonate in a volume ratio of 6:14; 1.2 mol / L LiPF6). The specific preparation method is as follows: 4-trifluoromethoxybenzenesulfonamide is stirred and dissolved in carbonate electrolyte at 30℃ (50r / min, 60min), and then allowed to stand for equilibration for 2.0 hours.

[0031] Example 7

[0032] An electrolyte for stabilizing the high-voltage cathode interface is a carbonate electrolyte containing 2 wt% 4-trifluoromethoxybenzenesulfonamide (ethylene carbonate and ethyl methyl carbonate in a volume ratio of 7:13; 1.0 mol / L LiPF6). The specific preparation method is as follows: 4-trifluoromethoxybenzenesulfonamide is stirred and dissolved in carbonate electrolyte at 25℃ (80r / min, 45min), and then allowed to stand for equilibration for 3.0 hours.

[0033] Comparative Example 1

[0034] The electrolyte was prepared according to the formulation and steps of Example 3, except that the amount of 4-trifluoromethoxybenzenesulfonamide added was changed to 0.5 wt%.

[0035] Comparative Example 2

[0036] The electrolyte was prepared according to the formulation and steps of Example 3, except that the amount of 4-trifluoromethoxybenzenesulfonamide added was changed to 3.5 wt%.

[0037] Comparative Example 3

[0038] The electrolyte was prepared according to the formula and steps of Example 3, with the only difference being that the settling time was only 1.5 hours.

[0039] Comparative Example 4

[0040] The electrolyte was prepared according to the formulation and steps of Example 3, except that LiPF6 in the carbonate electrolyte was replaced with LiFSI.

[0041] Comparative Example 5

[0042] The electrolyte was prepared according to the formulation and steps of Example 3, with the only difference being that 4-trifluoromethoxybenzenesulfonamide was replaced with N-fluorobisbenzenesulfonamide.

[0043] Blank example: A carbonate electrolyte (standard electrolyte) is composed of 1 mol / L LiPF6 and ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7.

[0044] Experimental example: 1. Nuclear Magnetic Resonance Spectroscopy (NMR) Testing The stable high-voltage positive electrode interface electrolyte from Example 3 and the reference electrolyte from the blank example were subjected to nuclear magnetic resonance spectroscopy tests, and the results were obtained. 7 LiNMR spectrum as shown Figure 1 As shown.

[0045] Depend on Figure 1 As can be seen, compared with the reference electrolyte, the stable high-voltage positive electrode interface electrolyte in Example 3... 7 The LiNMR signal clearly shifts towards the lower field, indicating that 4-trifluoromethoxybenzenesulfonamide reacts with Li + Weak coordination occurs, altering Li + The coordination environment.

[0046] 2. Linear sweep voltammetry curve test

[0047] The stable high-voltage positive electrode interface electrolyte from Example 3 and the reference electrolyte from the blank example were subjected to linear sweep voltammetry curve determination. The results of the linear sweep voltammetry curve determination are as follows: Figure 2 As shown.

[0048] Depend on Figure 2 As shown in the cyclic voltammetry curves, a distinct oxidation peak appeared at approximately 4.2 V after the addition of 4-trifluoromethoxybenzenesulfonamide to the reference electrolyte. This oxidation peak can be attributed to the preferential oxidative decomposition of 4-trifluoromethoxybenzenesulfonamide molecules under high voltage, indicating that during electrochemical cycling, the additive can undergo an electrochemical reaction on the cathode surface, participating in situ and promoting the formation of the cathode-electrolyte interface (CEI). This phenomenon directly confirms from an electrochemical perspective that the introduction of 4-trifluoromethoxybenzenesulfonamide can effectively regulate and stabilize the high-voltage cathode interface through an active oxidative decomposition mechanism.

[0049] 3. Ion transport number test

[0050] LCO / / Li symmetric cells were prepared using the stable high-voltage positive electrode interface electrolyte from Example 3 and the reference electrolyte from the blank example, respectively. The relaxation voltage curves of the cells were tested at 25°C and a voltage range of 3.0-4.5V. The results are as follows: Figure 3 As shown; Depend on Figure 3 The relaxation voltage curve analysis results show that, based on the stable high-voltage cathode interface electrolyte system in Example 3 of this invention, the calculated diffusion coefficient (D) of lithium ions in the lithium cobalt oxide (LCO) cathode material is... Li +The efficiency was significantly higher than that of the system using the reference electrolyte. This result indicates that the introduction of the additive 4-trifluoromethoxybenzenesulfonamide not only forms a stable positive electrode electrolyte interface (CEI), but also that this interface has superior ion conduction characteristics. Specifically, the CEI layer constructed with the participation of 4-trifluoromethoxybenzenesulfonamide may be thinner, more uniform, and rich in fast ion conductor components (such as LiF, Li3N, etc.), thereby effectively reducing the lithium-ion transport barrier at the interface and optimizing the ion transport kinetics at the positive electrode interface. This improvement plays a crucial role in enhancing the rate performance of the battery, reducing polarization, and achieving long-term cycle stability.

[0051] 4. CEI morphology on LCO cathode surface

[0052] LCO / / Li batteries were prepared using the stable high-voltage cathode interface electrolyte from Example 3 and the reference electrolyte from the blank example, respectively. After 100 cycles at 4.5V (3.0-4.5V), 1C, and 25℃, the CEI scanning electron microscope image of the LCO cathode surface is shown below. Figure 5 As shown; Depend on Figure 5 As can be seen, LCO particles using the stable high-voltage cathode interface electrolyte of the present invention remain intact without cracks, while LCO particles using the reference electrolyte are severely broken; this indicates that the addition of 4-trifluoromethoxybenzenesulfonamide forms a stable CEI, protecting the structural integrity of the LCO cathode particles.

[0053] 5. SEI morphology of lithium metal surface

[0054] Li / / Li symmetric cells were prepared using the stable high-voltage positive electrode interface electrolyte from Example 3 and the reference electrolyte from the blank example as electrolytes, respectively. The cells were then tested at 25°C and 1 mA / cm². -2 After 50 cycles, the scanning electron microscope image of the lithium metal surface is as follows: Figure 4 As shown; Depend on Figure 4 As shown in the comparison of the surface morphology of the lithium metal anode, after using the stable high-voltage cathode interface electrolyte in Example 3 of this invention, the lithium metal deposition layer exhibits a dense, flat, and regular blocky morphology, with significantly improved interface uniformity. In contrast, the lithium metal surface deposition layer using the reference electrolyte exhibits uneven thickness, loose structure, and porous characteristics. These morphological differences indicate that the introduction of 4-trifluoromethoxybenzenesulfonamide effectively regulates the deposition behavior of lithium ions, inhibits the formation and irregular growth of lithium dendrites, and significantly reduces side reactions between lithium metal and the electrolyte. This is mainly due to the anion-rich solvation structure induced by 4-trifluoromethoxybenzenesulfonamide and its participation in the construction of a stable SEI film at the anode interface, which jointly promotes uniform nucleation and dense deposition of lithium, thereby improving the cycle reversibility and interface stability of the lithium metal anode.

[0055] 6. Atmospheric pressure and room temperature cycling performance test

[0056] LCO / / Li batteries were prepared using the stable high-voltage cathode interface electrolyte from Example 3 and the reference electrolyte from the blank example as electrolytes, respectively. Cyclic performance tests were conducted under the conditions of a cutoff voltage of 4.5V (3.0-4.5V), 1C, and 25℃. The resulting cycle performance comparison graph is shown below. Figure 6 As shown.

[0057] Depend on Figure 6 The long-cycle performance test results show that the LCO / / Li battery assembled using the stable high-voltage cathode interface electrolyte of Example 3 of this invention can stably cycle for more than 600 times in the voltage range of 3.0-4.5V and at a 1C rate, and the capacity retention rate is still as high as 80.1% after the 600th cycle, demonstrating excellent long-cycle stability and capacity retention capability. In contrast, the control battery using the reference electrolyte has a faster capacity decay, and the capacity retention rate has dropped to 79.1% after only 250 cycles. This significant comparison proves that the introduction of 4-trifluoromethoxybenzenesulfonamide, through its dual function of synergistically stabilizing the cathode interface and regulating the deposition of the anode, effectively suppresses the loss of active materials and the aggravation of interfacial side reactions during cycling, thereby significantly improving the cycle life and electrochemical reversibility of high-voltage lithium metal batteries.

[0058] 7. Room temperature fast charging cycle performance test

[0059] LCO / / Li batteries were prepared using the stable high-voltage cathode interface electrolyte from Examples 1-7, the electrolyte samples from Comparative Examples 1-5, and the blank example as electrolytes. Cyclic performance tests were conducted under the following conditions: cutoff voltage 4.5V (3.0-4.5V), 25℃, and 1C (4C) rate (the cycle was stopped when the capacity retention rate was below 80%). The results are shown in Table 2. The performance of the battery systems composed of Example 3 and the blank example under 4C conditions was plotted (e.g., ...). Figure 7 (As shown); The performance of the battery system composed of Example 3 and Comparative Example 5 under 1C is plotted as a graph (e.g. Figure 8 (As shown).

[0060] Table 2. Experimental results of Examples 1-7, Comparative Examples 1-5, and Blank Examples.

[0061] Depend on Figure 7A comparison of long-cycle performance shows that the LCO / / Li battery using the stable high-voltage cathode interface electrolyte of Example 3 of this invention retains a capacity retention rate of 86.1% after 330 cycles under specific test conditions, demonstrating excellent capacity retention and cycle stability. In stark contrast, the battery using the reference electrolyte exhibits rapid capacity decay during cycling, with the capacity retention rate dropping significantly to 43.4% after 460 cycles. Notably, the electrolyte system of this invention demonstrates a much higher capacity retention rate than the comparative system within a shorter cycle period. This further confirms that 4-trifluoromethoxybenzenesulfonamide can significantly delay battery capacity decay during long-cycle processes through multiple mechanisms, including simultaneously stabilizing the positive and negative electrode interfaces, suppressing side reactions, and maintaining structural integrity, thereby effectively improving the cycle life and overall electrochemical performance of high-voltage lithium metal batteries.

[0062] Depend on Figure 8 The comparison of long-cycle performance shows that, although Comparative Example 5, which uses N-fluorobisbenzenesulfonamide as an additive, can also significantly improve the cycle performance of the reference electrolyte, it still has a significant difference compared with Example 3 of the present invention. The reasons are: (1) "N-fluorobisbenzenesulfonamide" only forms a stable interface protective layer at the positive electrode; (2) The number of fluorine atoms is limited, and the distribution of fluorine functional groups in the molecule is relatively simple, which leads to a limited total amount of fluorine source that it can provide at the interface, making it difficult to form a high-quality interface layer with high LiF content. The reason why Example 3 of the present invention has significantly improved performance is: (1) "4-trifluoromethoxybenzenesulfonamide" uses an "anion-dominant" regulation strategy, and actively intervenes in the first solvation sheath of lithium ions through "4-trifluoromethoxybenzenesulfonamide", guiding anions to enter the solvation structure on a large scale and forming an anion-rich solvation sheath layer; (2) "4-trifluoromethoxybenzenesulfonamide" works synergistically with the solvation structure, on the one hand promoting more anions (such as PF6) - ) preferentially migrate to the electrode interface to decompose and generate an interface layer rich in LiF. On the other hand, “4-trifluoromethoxybenzenesulfonamide” itself achieves targeted adsorption and conversion through F-containing functional groups, thereby actively and synergistically constructing a dense and stable SEI / CEI on both sides of the positive and negative electrodes; (3) In the structural design of the “4-trifluoromethoxybenzenesulfonamide” of the present invention, more fluorine atoms are introduced (and the number of fluorine atoms is significantly more than that of Comparative Example 5). This structural feature enables “4-trifluoromethoxybenzenesulfonamide” to release sufficient fluorine ions when decomposed on the electrode surface, thereby constructing a thin and dense SEI and CEI layer rich in LiF in situ at the positive and negative electrode interface; the high content of LiF interface layer can not only significantly enhance the mechanical strength and electrochemical stability of the interface film, but also effectively inhibit the continuous decomposition of the electrolyte on the electrode surface, thereby enabling the interface performance and cycle life of Example 3 of the present invention to be significantly improved under high voltage and high pressure stress conditions.

[0063] The above description is merely a specific embodiment of the present invention and the technical principles used, 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. An electrolyte for stabilizing a high-voltage positive electrode interface, characterized in that, The electrolyte is a carbonate electrolyte containing 1-3 wt% 4-trifluoromethoxybenzenesulfonamide.

2. The electrolyte according to claim 1, characterized in that, The carbonate electrolyte also includes ethylene carbonate, ethyl methyl carbonate, and lithium salt.

3. The electrolyte according to claim 2, characterized in that, The concentration of lithium salt in the carbonate electrolyte is 1-1.2 mol / L.

4. The electrolyte according to claim 2, characterized in that, The lithium salt is lithium hexafluorophosphate.

5. The electrolyte according to claim 2, characterized in that, In the carbonate electrolyte, the volume ratio of ethylene carbonate to methyl ethyl carbonate is 6-7:13-14.

6. The electrolyte according to claim 1, characterized in that, The electrolyte contains 1.8-2.2 wt% 4-trifluoromethoxybenzenesulfonamide.

7. A method for preparing an electrolyte with a stable high-voltage positive electrode interface as described in any one of claims 1-6, characterized in that, The steps include: dissolving 4-trifluoromethoxybenzenesulfonamide in carbonate electrolyte and allowing it to stand for at least 2 hours to equilibrate.

8. The method for preparing the electrolyte according to claim 7, characterized in that, 4-Trifluoromethoxybenzenesulfonamide was dissolved in carbonate electrolyte under stirring at 25-30°C.

9. A lithium metal battery, characterized in that, The lithium metal battery contains the electrolyte according to any one of claims 1-8.

10. The lithium metal battery according to claim 9, characterized in that, The positive electrode material of the lithium battery is LCO.

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