Long-circulation, low-overpotential and high-current-density electrolyte

Abstract

The invention discloses an electrolyte with long circulation, low overpotential and high current density. The electrolyte comprises an organic solvent, magnesium salt and a trifluoromethanesulfonate additive, the organic solvent is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and tetrahydrofuran; the magnesium salt is magnesium chloride; in the organic solvent, the concentration of the magnesium chloride is 0.1 mol / L to 0.4 mol / L, and the concentration of the trifluoromethanesulfonate additive is 0.1 mol / L to 1.0 mol / L. According to the rechargeable magnesium battery electrolyte, dissolution of magnesium salt is promoted, interface regulation and control can be carried out on a magnesium negative electrode interface, a double-electrode-layer structure beneficial to Mg < 2 + > migration and a stable SEI film are constructed, and therefore the battery has low overpotential, high ionic conductivity and excellent cycling stability under large current. The electrolyte is simple in preparation process and convenient for industrial popularization.

Description

Technical Field

[0001] This invention relates to the field of magnesium-ion battery technology, specifically to an electrolyte with long cycle life, low overpotential and high current density, its preparation method and application. Background Technology

[0002] Rechargeable magnesium metal batteries possess advantages such as high volumetric energy density, high safety, and abundant resource reserves. The theoretical volumetric capacity of the magnesium metal anode is 3833 mAh cm⁻¹. -3 Meanwhile, the reduction potential is low (-2.37V vs. standard hydrogen electrode, SHE). As the core of ion transport and interface regulation, the performance of the electrolyte directly determines the battery's cycle life and safety stability, making it crucial for industrial breakthroughs. Magnesium electrolytes currently suffer from problems such as low magnesium salt solubility, high desolvation energy, easy passivation of the negative electrode, and slow ion migration kinetics. Liquid electrolytes are currently the main research focus, encompassing two main branches: nucleophilic and non-nucleophilic. While nucleophilic electrolytes (such as Grignard reagent all-phenyl complexes [PhMgCl-AlCl3]) can break down the passivation layer on the magnesium surface through active components such as chloride ions, achieving efficient and reversible deposition, their electrochemical stability window is narrow (typically below 2.5 V vs. Mg / Mg). 2+ Furthermore, the interfacial reaction control steps during deposition / dissolution are slow, resulting in a significant increase in polarization voltage, especially a sharp rise in overpotential at high current densities. Its active components are continuously consumed during long-term cycling, accompanied by severe interfacial side reactions, leading to changes in the magnesium anode surface structure and extremely rapid capacity decay. Non-nucleophilic electrolytes are mainly based on weakly coordinated magnesium salt anions, such as magnesium aluminum chloride complex (MACC), hexamethyldisilazine magnesium (HMDS)-based electrolytes, boron-based magnesium electrolytes, and Mg(TFSI)2-based electrolytes dissolved in ethers and other solvents. Although they have a wide electrochemical window (up to 3.0 V or higher), they cannot effectively control the magnesium deposition interface, resulting in extremely high initial nucleation overpotentials and a large desolvation barrier for magnesium ions during deposition / dissolution, leading to significantly sluggish kinetics. More importantly, Mg... 2+ The high charge density and poor compatibility with many common solvents result in generally low solubility of magnesium salts, which in turn reduces ionic conductivity. Furthermore, the continuous growth and uneven deposition of the passivation layer during cycling accelerates interfacial failure, leading to a sharp decline in cycling performance. Summary of the Invention

[0003] To address the aforementioned shortcomings of existing technologies, the present invention aims to overcome the problems of low magnesium salt solubility, high polarization overpotential, and poor cycle performance in magnesium-ion batteries. It provides an electrolyte containing trifluoromethanesulfonate as a functional additive. This electrolyte promotes the dissolution of magnesium salts, enables interface regulation of the magnesium anode interface, and constructs a structure favorable for magnesium... 2+The migrating double-layer structure and stable SEI film reduce electrolyte decomposition, improve electronic conductivity, and reduce electrolyte side reactions, enabling magnesium-ion batteries to have low overpotential and ultra-long cycle stability. This solves the problems of large deposition / dissolution overpotential, magnesium anode passivation, low magnesium salt solubility, and cycle performance defects in existing technologies.

[0004] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0005] In a first aspect, the present invention provides an electrolyte with long-cycle, low overpotential, and high current density, the electrolyte comprising an additive, a magnesium salt, and an organic solvent; wherein the additive is a trifluoromethanesulfonate compound with the following general structural formula:

[0006] ;

[0007] In the formula, R is selected from one of straight-chain or branched alkyl or silane groups with 1-5 carbon atoms;

[0008] The magnesium salt is magnesium chloride; the organic solvent is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or tetrahydrofuran;

[0009] In the electrolyte, the concentration of magnesium chloride is 0.1 mol / L to 0.4 mol / L, and the concentration of the additive is 0.1 mol / L to 1.0 mol / L.

[0010] Preferably, the additive is one of (trimethylsilylmethyl)trifluoromethanesulfonate, trimethylsilyltrifluoromethanesulfonate, or ethyl trifluoromethanesulfonate.

[0011] Secondly, the present invention provides a method for preparing the above-mentioned electrolyte, the specific steps of which are as follows:

[0012] Step 1: Prepare the electrolyte according to claim 1 by mixing the magnesium salt and organic solvent evenly;

[0013] Step 2: Add additives to the mixture prepared in Step 1 and continue stirring until homogeneous to obtain the electrolyte.

[0014] Preferably, the method is carried out in an inert gas atmosphere.

[0015] Preferably, in the mixing system of the method, the water content and oxygen content are both less than 0.01 ppm.

[0016] Preferably, the magnesium salt undergoes the following pretreatment before step 1:

[0017] The magnesium salt is vacuum dried at 60℃~200℃ for at least 24 hours and then sealed for later use.

[0018] Preferably, the organic solvent undergoes the following pretreatment before step 1:

[0019] The 3 Å molecular sieve was heated to 300 °C and activated for 5 h before being added to an organic solvent and then sealed for storage. The activation process involved heating the 3 Å molecular sieve to 300 °C and holding it there for 5 h, then adding it to the organic solvent while still hot.

[0020] Thirdly, the present invention provides an application of an electrolyte, wherein the electrolyte described above or the electrolyte prepared by the above method is used to prepare a magnesium-ion battery.

[0021] Fourthly, the present invention also provides a magnesium-ion battery, wherein the magnesium-ion battery contains the above-described electrolyte or an electrolyte prepared by the above-described method.

[0022] Preferably, the magnesium-ion battery is a rechargeable magnesium-ion battery.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] 1. During the research on existing magnesium battery electrolytes, this invention unexpectedly discovered that by introducing trifluoromethanesulfonate molecules with a specific structure into the traditional magnesium chloride / ether solvent system, the solubility of magnesium salts in organic solvents can be effectively improved, and a stable solid electrolyte interface (SEI) film rich in inorganic components and with excellent ion conductivity can be constructed in situ on the magnesium anode surface. The trifluoromethanesulfonyl group in this additive molecule has strong electron-withdrawing and weak coordination capabilities, which can, on the one hand, react with Mg... 2+ It forms a dynamic weak coordination structure, lowers its desolvation energy barrier, and preferentially reduces and decomposes under electrochemical polarization to participate in the formation of SEI film. At the same time, it regulates the double layer structure of the electrode interface, thereby suppressing the problems of ion transport obstruction and side reaction aggravation caused by strong coordination of solvent molecules or the formation of interface passivation layer in traditional systems, fundamentally improving the interfacial compatibility and chemical stability of electrolyte.

[0025] 2. Regarding electrochemical performance, the electrolyte of this invention significantly reduces the overpotential during magnesium deposition / dissolution and substantially extends cycle life. This is attributed to the high ionic conductivity and uniformity of the interfacial SEI film, which reduces Mg... 2+ Uniform deposition with low nucleation barriers can be achieved on the negative electrode surface, effectively avoiding dendrite growth and local passivation; measured data show that at 1.0 mA / cm 2 The overpotential of the symmetrical cell stabilizes at around 88 mV at current density and can cycle stably for over 1600 hours, even at current densities as high as 8 mA / cm².2 It maintains good stability even under high current density. Furthermore, in Mg||Mo half-cell and Mg||Mo6S8 full-cell systems, this electrolyte also exhibits high initial coulombic efficiency (99.13%), high average coulombic efficiency (99.7%), and excellent rate capability and long cycling performance (capacity retention of 102 mAh / g after 600 cycles in the full cell). This fully verifies the high reversibility and durability of the electrolyte described in this invention in practical battery applications.

[0026] 3. The synthesis route of the electrolyte in this invention is extremely simple and efficient. A high-performance electrolyte can be obtained simply by stirring pretreated magnesium chloride, ether solvents, and trifluoromethanesulfonate additives under an inert atmosphere, without the need for high temperature, high pressure, or complex reaction steps. Key raw materials such as magnesium chloride and organic solvents can meet the requirements for ultra-low water and oxygen content (<0.01 ppm) through conventional vacuum drying and molecular sieve dehydration pretreatment. The additives themselves have well-defined structures, mature synthesis methods, and controllable costs, avoiding the high viscosity, high cost, and process complexity problems associated with using expensive ionic liquids or multi-component complex systems. The entire preparation process is mild, generates no toxic byproducts, conforms to green chemistry principles, and possesses good scalability and industrial application prospects. Attached Figure Description

[0027] Figure 1 The following are the (a) first-cycle charge-discharge curves and (b) nucleation overpotentials of the electrolytes prepared in Example 1 and the comparative example of this invention in a Mg||Mo half-cell.

[0028] Figure 2 Linear scanning voltammetry diagrams of the electrolyte prepared in Example 1 of this invention on different working electrodes.

[0029] Figure 3 The electrolyte prepared in Example 1 of this invention, with molybdenum (Mo) as the working electrode, at 1 mA / cm 2 Long-cycle performance of half-cell at current density.

[0030] Figure 4 The Mg||Mg symmetric cell with electrolyte prepared in Example 1 of this invention operates at 1 mA / cm². 2 Long-cycle performance at current density.

[0031] Figure 5 for Figure 4 The Mg||Mg symmetric cell with the electrolyte prepared in Example 1 operates at 1 mA / cm². 2 Enlarged view of local cycling performance under current density; where a represents the cycling performance during the period of 308h to 328h, and b represents the cycling performance during the period of 1270h to 1290h.

[0032] Figure 6 The Mg||Mg symmetric cell with the electrolyte prepared in Example 1 of this invention operates at 8 mA / cm. 2 Long-cycle performance at current density.

[0033] Figure 7 for Figure 6 The Mg||Mg symmetric cell with the electrolyte prepared in Example 1 operates at 8 mA / cm². 2 Enlarged view of local cycling performance under current density; where a represents the cycling performance during the period of 200h to 220h, and b represents the cycling performance during the period of 40h to 60h.

[0034] Figure 8 The diagram shows the long-cycle performance of the full cell prepared in Example 1 of this invention with molybdenum octasulfide (Mo6S8) as the positive electrode at a 1C rate. Detailed Implementation

[0035] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments described herein are only for the purpose of helping to understand the present invention and are not intended to limit the present invention. Based on the content disclosed in this invention, all other technical solutions that can be obtained by those skilled in the art without creative effort should fall within the scope of protection of the claims of this invention.

[0036] The definitions of all numerical ranges in this invention are intended as an independent disclosure of each individual value within that range. Any value falling between the lower and upper limits of the range, even if not specifically listed in the embodiments, is also considered to be included in this invention.

[0037] I. An electrolyte with long-cycle operation, low overpotential, and high current density

[0038] In the existing research field of magnesium-ion battery electrolytes, this invention, after in-depth analysis, reveals that current technologies face core challenges such as low magnesium salt solubility, high desolvation energy, severe interfacial passivation, and slow ion migration kinetics. While nucleophilic electrolytes can break down the passivation layer on the magnesium surface through active components such as chloride ions, their electrochemical stability window is narrow (typically below 2.5V vs. Mg). 2+ The slow rate of interfacial reaction control during deposition / dissolution leads to a sharp increase in overpotential at high current densities, resulting in continuous consumption of active components and severe interfacial side reactions. While non-nucleophilic electrolytes possess a wider electrochemical window (above 3.0V), they suffer from extremely high initial nucleation overpotentials due to their inability to effectively control the magnesium deposition interface. Simultaneously, Mg... 2+High charge density and poor compatibility with conventional solvents result in generally low solubility and insufficient ionic conductivity of magnesium salts. Furthermore, the continuous growth and uneven deposition of the passivation layer during cycling accelerates interfacial failure. This technical problem makes it difficult for existing magnesium electrolytes to simultaneously achieve high ionic conductivity, low interfacial impedance, and long-term cycling stability, especially with performance degradation under high current density conditions. During the conceptualization of this invention, it was discovered that precise control of the electrolyte interfacial microenvironment and synergistic optimization of magnesium salt dissolution behavior are key to solving this technical problem. Therefore, this invention designs a dual-effect synergistic mechanism by adding functional additives such as organic trifluoromethanesulfonates: on the one hand, the oxygen atoms in trifluoromethanesulfonate molecules have a relatively negative electrostatic potential, easily adsorbing onto the surface of metallic magnesium, effectively controlling the interfacial microenvironment and regulating the double-layer structure of the electrode interface; on the other hand, its unique electronic structure (high HOMO and low LUMO energy levels) allows it to preferentially decompose during the first cycle to form a stable SEI film rich in inorganic components, blocking the formation of the magnesium passivation film. More importantly, this invention breaks through the limitations of traditional complex synthetic routes, innovatively employing a simple stirring process. It only requires stirring pretreated magnesium chloride, organic solvents, and trifluoromethanesulfonate additives under an inert atmosphere for a period of time to construct a high-performance electrolyte system, avoiding the high viscosity, high cost, and process complexity problems associated with high-cost ionic liquids or multi-component complexes. Based on the above concepts, this invention forms a complete technical solution from molecular design and interface control to process simplification, achieving a high viscosity of 1.0 mA / cm². 2 The breakthrough performance of a symmetrical cell with an overpotential as low as 88 mV at current density and a cycle life exceeding 1600 hours further demonstrates excellent high current density tolerance (8 mA / cm²). 2 The high performance and scalability of magnesium-ion battery electrolytes provide a technological path for their practical application. This invention proposes a magnesium battery electrolyte system containing trifluoromethanesulfonate additives through precise molecular structure design and deep synergy of interface regulation mechanisms. The aim is to achieve a triple objective of improved magnesium salt solubility, stabilized SEI film, and optimized ion migration kinetics through a simple process, fundamentally solving the core technical problems of high overpotential, interface passivation, and short cycle life in existing magnesium electrolytes. The electrolyte of this invention comprises additives, magnesium salts, and an organic solvent; wherein the additives are trifluoromethanesulfonate compounds with the following general structural formula:

[0039] ;

[0040] In the formula, R is selected from one of straight-chain or branched alkyl or silane groups with 1-5 carbon atoms; the magnesium salt is magnesium chloride; the organic solvent is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or tetrahydrofuran; in the electrolyte, the concentration of magnesium chloride is 0.1 mol / L to 0.4 mol / L, and the concentration of the additive is 0.1 mol / L to 1.0 mol / L.

[0041] In some embodiments of this invention, magnesium chloride, as a simple inorganic magnesium salt, is often used as a magnesium electrolyte due to its simple structure and high magnesium deposition / dissolution reversibility, offering advantages such as low cost, abundant resources, and easy availability. The strong Lewis basicity of chloride ions helps weaken the strong binding interaction between the solvent and magnesium ions, thereby alleviating the solvation effect; simultaneously, the chloride-containing coordination structure can selectively adsorb onto the magnesium anode surface, inhibiting the formation of the passivation layer. This invention has found that excessively high magnesium chloride concentrations (>0.4 mol / L) lead to enhanced interionic interactions in the solution, reducing ion transport number, increasing ion transport resistance, and simultaneously increasing electrolyte viscosity, hindering the formation of magnesium chloride. 2+ Rapid migration of magnesium chloride is observed; however, if the magnesium chloride concentration is too low (<0.1 mol / L), it cannot provide sufficient carrier concentration, leading to a significant decrease in the ionic conductivity of the system. A stable SEI film cannot form on the magnesium anode surface, resulting in a sharp increase in battery internal resistance and affecting rate performance. This concentration range precisely maintains the effective protective effect of chloride ions on the magnesium anode surface while avoiding the corrosive problems caused by high chloride concentrations, achieving the optimal balance between solubility and electrochemical performance. Therefore, the concentration of magnesium chloride in the electrolyte can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, etc., as well as all ranges and sub-ranges between these values. It should be understood that, in the embodiments, any of the above ranges can be combined with any other range.

[0042] In some embodiments of the present invention, it has been found that magnesium chloride has limited solubility in ether solvents, and the corrosiveness of chloride ions limits its compatibility with high-voltage positive electrodes. Furthermore, the present invention has also found that the molecular design of trifluoromethanesulfonate additives (especially (trimethylsilylmethyl)trifluoromethanesulfonate, trimethylsilyltrifluoromethanesulfonate, or ethyl trifluoromethanesulfonate) has precise controllability; their oxygen atoms carry a relatively negative electrostatic potential, making them easily adsorbed onto the magnesium surface to construct structures favorable for Mg… 2+The migrating double-layer structure, along with its unique electronic structure (high HOMO, low LUMO energy levels), ensures preferential reduction and decomposition to form a stable SEI film during the first cycle. The electronic effects and steric hindrance of the R groups (alkyl or silane groups with 1-5 carbon atoms) in these specific trifluoromethanesulfonate molecules have been carefully optimized to ensure both molecular stability and precise interface control, thereby synergistically solving the core technical problems of low solubility, interface passivation, and sluggish kinetics in magnesium electrolytes. Therefore, in this invention, the additive is one of (trimethylsilylmethyl)trifluoromethanesulfonate, trimethylsilyltrifluoromethanesulfonate, or ethyl trifluoromethanesulfonate.

[0043] In some embodiments of the present invention, it has been found that the concentration of the additive also affects the performance of the electrolyte: when the additive concentration is below 0.1 mol / L, the additive molecules cannot form a complete and effective adsorption layer on the magnesium anode surface, leading to easy decomposition of the electrolyte and triggering side reactions. Simultaneously, the additive does not react sufficiently with the magnesium salt, resulting in some magnesium salts being difficult to dissolve and a stable SEI film failing to form. Conversely, when the additive concentration exceeds 1.0 mol / L, excessive additive molecules increase the electrolyte viscosity, reduce ionic conductivity, and may form an excessively thick interfacial layer, hindering the formation of Mg. 2+ Transport. By controlling the concentration of the additive within the specified range, the additive can both sufficiently promote the dissolution of magnesium chloride and preferentially decompose in the first cycle to form a thin and dense SEI film rich in inorganic components, achieving a balance between minimizing interfacial impedance and maximizing ion transport. Therefore, the concentration of the additive in the electrolyte can be 0.1 mol / L, 0.2 mol / L, 0.3 mol / L, 0.4 mol / L, 0.5 mol / L, 0.6 mol / L, 0.7 mol / L, 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, etc., as well as all ranges and sub-ranges between the above values. It should be understood that, in the embodiments, any of the above ranges can be combined with any other range.

[0044] II. A method for preparing the above-mentioned electrolyte

[0045] Step 1: Prepare the electrolyte according to claim 1 by mixing and stirring the magnesium salt and organic solvent evenly;

[0046] Step 2: Under stirring conditions, add the additive to the mixture prepared in Step 1, and continue stirring for 10-15 minutes to obtain the electrolyte. The additive is a trifluoromethanesulfonate compound with the following general structural formula:

[0047] ;

[0048] In the formula, R is selected from one of straight-chain or branched alkyl or silane groups with 1-5 carbon atoms; the magnesium salt is magnesium chloride; the organic solvent is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or tetrahydrofuran; in the electrolyte, the concentration of magnesium chloride is 0.1 mol / L to 0.4 mol / L, and the concentration of the additive is 0.1 mol / L to 1.0 mol / L.

[0049] In some embodiments of the present invention, the method is carried out under an inert gas atmosphere. The inert atmosphere effectively isolates oxygen, preventing it from dissolving into the electrolyte system, thereby avoiding oxidation of the magnesium anode surface and maintaining the chemical stability of the electrolyte composition.

[0050] In some embodiments of the present invention, the water content and oxygen content in the mixing system of the method are both less than 0.01 ppm, thereby eliminating the side reactions of water and oxygen in the entire system.

[0051] In some embodiments of the present invention, the magnesium salt undergoes the following pretreatment prior to step 1:

[0052] The magnesium salt is vacuum dried at 60℃~200℃ for at least 24 hours and then sealed for later use to remove water and oxygen from the magnesium salt.

[0053] In some embodiments of the present invention, the organic solvent undergoes the following pretreatment prior to step 1:

[0054] The 3 Å molecular sieve was heated to 300 °C and activated for 5 h before being added to an organic solvent and then sealed for storage. The activation process involved heating the 3 Å molecular sieve to 300 °C and holding it there for 5 h, then adding it to the organic solvent while still hot.

[0055] III. Application of an Electrolyte

[0056] The electrolyte described in this invention, or the electrolyte prepared by the method described in this invention, is used to prepare a magnesium-ion battery. The magnesium-ion battery is a rechargeable magnesium-ion battery.

[0057] IV. A magnesium-ion battery

[0058] The magnesium-ion battery of the present invention contains the electrolyte described above or the electrolyte prepared by the above method. The magnesium-ion battery is a rechargeable magnesium-ion battery.

[0059] V. Examples and Comparative Examples

[0060] Example 1:

[0061] Step 1 Solvent pretreatment: After heating the organic solvent ethylene glycol dimethyl ether, add 3 Å molecular sieve that has been activated at 300 °C for 5 h, and transfer to a glove box for sealed storage.

[0062] Step 2: Magnesium salt pretreatment: Magnesium chloride is vacuum dried at 70 °C for 24 hours and then transferred to a glove box for sealed storage.

[0063] Step 3: Preparation of the electrolyte: All reactions were carried out under an anhydrous and oxygen-free inert atmosphere. 0.0286 g of magnesium chloride (0.2 M concentration) was slowly added to 1.5 mL of ethylene glycol dimethyl ether while stirring; then, 0.0015 mol of (trimethylsilylmethyl) trifluoromethanesulfonate (denoted as S1) was added while stirring, and the mixture was stirred for 10 min to obtain the target electrolyte.

[0064] Example 2:

[0065] The method is based on Example 1, but with the following adjustment: the additive is replaced with trimethylsilyl trifluoromethanesulfonate (denoted as S2). The other steps are exactly the same as in Example 1.

[0066] Example 3

[0067] The method is based on Example 1, but with the following adjustment: the additive is replaced with ethyl trifluoromethanesulfonate (denoted as C1). The other steps are exactly the same as in Example 1.

[0068] Comparative Example 1

[0069] This example is an adjustment based on Example 1, except that the electrolyte does not contain any additives. All other steps are exactly the same as in Example 1.

[0070] VI. Performance Comparison

[0071] The performance testing method for the electrolyte in Example 1 is as follows; the testing methods for other examples are the same.

[0072] (1) Coulombic efficiency test of reversible deposition / dissolution of magnesium

[0073] The reversible deposition / dissolution coulombic efficiency of the electrolytes prepared in Examples 1-3 and the comparative examples was tested using a constant current charge-discharge (GCD) tester. Testing was conducted by assembling CR2032 coin cells, with molybdenum foil (Mo) as the positive electrode current collector, polished magnesium sheet as the negative electrode, and glass fiber membrane (GF / A) as the separator. The assembled cells were allowed to stand at room temperature for at least 4 hours before testing. The charging cutoff voltage was 2V, and the current density and areal capacity were 1.0 mA / cm². 2 0.5 mA / cm 2 .

[0074] The results obtained by testing the electrolytes prepared in Examples 1-3 and the comparative examples using the above-mentioned methods are as follows: The electrolyte prepared in Example 1 has a coulombic efficiency of over 99% after 100 cycles of a Mg||Mo half-cell, and the deposition / dissolution overpotential is 250 mV.

[0075] The relevant electrochemical performance of other examples and comparative examples is shown in Table 1 below. The electrolyte prepared in Example 2 achieved a deposition / dissolution coulombic efficiency of over 99% after 100 cycles, with a deposition / dissolution overpotential of 330 mV; the electrolyte prepared in Example 3 achieved a deposition / dissolution coulombic efficiency of over 99% after 100 cycles, with a deposition / dissolution overpotential of 200 mV; while the electrolyte prepared in the comparative example could not undergo a reversible deposition / dissolution process, had a high overpotential during charging (approximately 1 V), and a coulombic efficiency of less than 50%. Figure 1 As shown in (a).

[0076] Table 1

[0077] The electrolyte prepared in Example 1 exhibited a first-cycle deposition overpotential of 0.21 V and a nucleation overpotential of 0.09 V in a Mg||Mo half-cell; the electrolyte prepared in the comparative example exhibited a first-cycle deposition overpotential of 1.27 V and a nucleation overpotential of 0.31 V in a Mg||Mo half-cell. Figure 1 As shown in (b).

[0078] Figure 1 The electrochemical performance of electrolytes containing trifluoromethanesulfonate additives and electrolytes without additives in Mg||Mo half-cells is compared. Figure 1 (a) Comparative Example 1 (without additives) exhibits an overpotential as high as 1V and a coulombic efficiency of less than 50% during the first charge, indicating that magnesium ions are difficult to effectively deposit on the negative electrode surface; while Figure 1 (b) Compared to the initial deposition behavior, Example 1 exhibited a deposition overpotential of only 0.21V and a nucleation overpotential of 0.09V, significantly lower than the comparative examples' 1.27V and 0.31V. This substantial difference stems from the trifluoromethanesulfonate additive constructing a favorable environment for Mg deposition on the magnesium surface. 2+ The migrating electric double layer structure preferentially decomposes during the first cycle to form a stable SEI film rich in inorganic components, effectively reducing interfacial impedance and nucleation energy barrier. This demonstrates the significant effectiveness of this invention in addressing the high overpotential and interfacial passivation issues in magnesium batteries, verifying the additive's ability to precisely regulate the interfacial microenvironment.

[0079] (2) Stability test of magnesium deposition / dissolution oxidation

[0080] The electrolyte prepared in Example 1 was tested for magnesium reversible deposition / dissolution coulombic efficiency and oxidative stability using cyclic voltammetry (CV) and linear voltammetry (LSV), respectively. The tests were conducted using assembled CR2032 coin cells, with a stainless steel (Mo) positive electrode current collector, a magnesium sheet negative electrode, and a glass fiber membrane (GF / A) separator. The LSV voltage range was from open-circuit voltage to 5.0 V, and the scan rate was 5 mV / s.

[0081] Figure 2 The electrochemical stability windows of the electrolyte in Example 1 on different current collectors (stainless steel SS, molybdenum foil Mo, aluminum foil C / Al, and copper foil Cu) are shown to be 3.26 V, 2.89 V, 3.05 V, and 2.86 V vs. Mg. 2+ / Mg. This excellent electrochemical stability stems from the stable SEI film formed by the trifluoromethanesulfonate additive, which effectively blocks continuous side reactions between the electrolyte and the electrode, while simultaneously suppressing the oxidative decomposition of the electrolyte under high voltage. This indicates that the present invention significantly improves the electrochemical stability of the electrolyte, making it possible to match high-voltage cathode materials and solving the technical problem of narrow electrochemical window in existing magnesium electrolytes.

[0082] (3) Magnesium reversible deposition / dissolution performance test

[0083] The reversible deposition / dissolution performance and coulombic efficiency of the electrolyte prepared in Example 1 were tested using a galvanostatic charge-discharge (GCD) test. The test was conducted using an assembled CR2032 coin cell, with a stainless steel (Mo) positive electrode current collector, a magnesium sheet negative electrode, and a glass fiber membrane (GF / A) separator. The GCD charge-discharge test was performed at a current density of 0.1 mA / cm². 2 ~1mA / cm 2 .

[0084] The electrolyte prepared in Example 1, when used in practical applications at a current density of 1 mA / cm², 2 Under certain conditions, the cycle life of Mg||Mo cells can reach over 2600 hours, while the overpotential remains stable at around 250 mV, and the coulombic efficiency remains stable at over 99.7%. Figure 3 As shown. This superior long-cycle performance stems from the self-healing properties of the SEI film formed at the interface by the trifluoromethanesulfonate additive, which maintains structural integrity during long-term cycling and effectively prevents continuous electrolyte decomposition and interfacial side reactions. Simultaneously, the optimized double-layer structure of the additive ensures the protection of Mg... 2+Uniform deposition / dissolution throughout the cycle process avoids localized passivation and dendrite growth. This strongly demonstrates the breakthrough progress of this invention in solving the core problem of short cycle life in magnesium batteries, and in particular, verifies the long-term stability of the electrolyte prepared by the "simple stirring method" in practical applications.

[0085] (4) Magnesium reversible deposition / dissolution performance test

[0086] The reversible deposition / dissolution performance and coulombic efficiency of the electrolyte prepared in Example 1 were tested using a galvanostatic charge-discharge (GCD) test. The test was conducted using a CR2032 coin cell symmetric battery, with magnesium sheets as the positive and negative electrodes and a glass fiber membrane (GF / A) as the separator. The GCD charge-discharge test was performed at a current density of 0.5 mA / cm². 2 ~8 mA / cm 2 .

[0087] The electrolyte prepared in Example 1, when used in practical applications at a current density of 1 mA / cm², performs well. 2 Under these conditions, the Mg||Mg battery can cycle stably for over 1600 hours, with the overpotential remaining stable at around 88mV and at 8mA / cm². 2 It can maintain stable cycling even at high current densities, such as Figures 4-7 As shown, where Figure 5 for Figure 4 The small image in the middle, Figure 7 for Figure 6 The small image in the image shows the excellent high-current performance. This superior high-current performance stems from the fact that the double-layer structure optimized by the trifluoromethanesulfonate additive can suppress the risk of dendrite growth caused by the enhancement of the local electric field. Simultaneously, the addition of the trifluoromethanesulfonate additive promotes the solubility of magnesium chloride in ether solvents, which helps to improve the interfacial ion transport efficiency and comprehensively enhances the interfacial charge transfer kinetics. The low overpotential indicates extremely low interfacial impedance and unobstructed ion transport pathways, suggesting that the additive used in this invention constructs an inorganic-rich SEI film on the magnesium surface with high Mg content. 2+ Electrical conductivity. This also demonstrates the significant effectiveness of the present invention in solving the performance degradation problem under high current density, and verifies the feasibility of the electrolyte in practical high-power applications.

[0088] (5) Full battery charge and discharge performance test

[0089] The electrolyte prepared in Example 1 was used for full-cell constant current charge-discharge testing. The test was conducted by assembling a CR2032 coin cell, with Mo6S8 as the positive electrode, carbon paper (CF) as the substrate, a magnesium sheet as the negative electrode, and a glass fiber membrane (GF / A) as the separator. The current was 1C.

[0090] The Mg||Mo6S8 full cell assembled with the electrolyte prepared in Example 1 cycled stably for over 600 cycles at a high current density of 1C, maintaining a capacity of 102 mAh / g, reaching 80% of its theoretical capacity (128 mAh / g). Figure 8 As shown, this superior full-cell performance stems from the overall synergistic effect of the electrolyte system: the trifluoromethanesulfonate additive not only optimizes the negative electrode interface but also achieves good interfacial compatibility with the positive electrode material Mo6S8, reducing interfacial side reactions and active material loss. More importantly, the high ionic conductivity and low interfacial impedance of this electrolyte ensure rapid ion transport kinetics throughout the charge-discharge process, allowing for full utilization of the active material. This demonstrates the practical value of the invention at the full-cell level, verifying that the electrolyte system not only performs excellently in half-cells but also exhibits outstanding performance in practical energy storage applications, providing reliable technical support for the industrial application of magnesium-ion batteries.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. An electrolyte with long-cycle operation, low overpotential, and high current density, characterized in that, The electrolyte comprises additives, magnesium salts, and organic solvents; wherein the additives are trifluoromethanesulfonate compounds with the following general structural formula: ； In the formula, R is selected from one of straight-chain or branched alkyl or silane groups with 1-5 carbon atoms; The magnesium salt is magnesium chloride; the organic solvent is selected from one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether or tetrahydrofuran; In the electrolyte, the concentration of magnesium chloride is 0.1 mol / L to 0.4 mol / L, and the concentration of the additive is 0.1 mol / L to 1.0 mol / L.

2. The electrolyte according to claim 1, characterized in that, The additive is one of (trimethylsilylmethyl)trifluoromethanesulfonate, trimethylsilyltrifluoromethanesulfonate, or ethyl trifluoromethanesulfonate.

3. A method for preparing the electrolyte according to claim 1 or 2, characterized in that, The specific steps are as follows: Step 1: Prepare the electrolyte according to claim 1 by mixing the magnesium salt and organic solvent evenly; Step 2: Add additives to the mixture prepared in Step 1 and continue stirring until homogeneous to obtain the electrolyte.

4. The method according to claim 3, characterized in that, The method is carried out in an inert gas atmosphere.

5. The method according to claim 3, characterized in that, In the mixing system of the method, the water content and oxygen content are both less than 0.01 ppm.

6. The method according to claim 3, characterized in that, The magnesium salt undergoes the following pretreatment before step 1: The magnesium salt is vacuum dried at 60℃~200℃ for at least 24 hours and then sealed for later use.

7. The method according to claim 3, characterized in that, The organic solvent undergoes the following pretreatment prior to step 1: The 3 Å molecular sieve was heated to 300 °C and activated for 5 h before being added to an organic solvent and then sealed for storage.

8. An application of an electrolyte, characterized in that, The electrolyte according to any one of claims 1 to 2 or the electrolyte prepared by any one of claims 3 to 7 is used to prepare a magnesium-ion battery.

9. A magnesium-ion battery, characterized in that, The magnesium-ion battery contains the electrolyte according to any one of claims 1 to 2 or the electrolyte prepared by any one of claims 3 to 7.

10. The magnesium-ion battery according to claim 9, characterized in that, The magnesium-ion battery is a rechargeable magnesium-ion battery.

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