Chlorine-free simple magnesium salt electrolyte for magnesium-sulfur battery as well as preparation method and application of chlorine-free simple magnesium salt electrolyte

Abstract

The invention belongs to the technical field of electrochemical energy storage batteries, and particularly relates to a chlorine-free simple magnesium salt electrolyte for a magnesium-sulfur battery as well as a preparation method and application of the chlorine-free simple magnesium salt electrolyte. The electrolyte comprises magnesium salt, ionic liquid, an organic ether solvent, an amine solvent and an organic phosphide additive. The solvation structure is regulated and controlled through the synergistic effect of multiple components, the compatibility of the electrolyte with the sulfur positive electrode and the magnesium negative electrode is improved, and the electrochemical performance of the magnesium-sulfur battery is improved. Specifically, the amine solvent is used as a strong polar solvent to improve the solubility of the magnesium polysulfide, so that the diffusion and redox conversion kinetics of the magnesium polysulfide are promoted, and the organic phosphide is used as an additive to effectively improve the specific discharge capacity and voltage platform of the magnesium-sulfur battery. Meanwhile, due to the addition of the ionic liquid, the stability of a magnesium negative electrode / electrolyte interface is improved, the transmission capacity of Mg < 2 + > is enhanced, and the overpotential of magnesium deposition / dissolution is reduced. In addition, the electrolyte does not contain chloride ions, so that the corrosion problem caused by the chloride ions is avoided.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical energy storage battery technology, specifically relating to a chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries, its preparation method, and its application. Background Technology

[0002] With the continuous upgrading of global energy demand and the increasing prominence of environmental problems, the development of efficient, low-cost, and environmentally friendly new battery energy storage systems has become a research hotspot in the energy field. Magnesium-sulfur (Mg-S) batteries, due to their extremely high theoretical energy density (3221 Wh·L), are particularly promising. -1 and 1684Wh·kg -1 With its significant advantages such as low raw material cost and high safety of magnesium metal anode, it is considered one of the most promising next-generation electrochemical energy storage technologies and has received widespread attention from academia and industry in recent years.

[0003] However, the practical application of magnesium-sulfur batteries still faces many key technological bottlenecks. Early-developed Grignard reagent-based electrolytes have strong nucleophilicity, reacting chemically with the sulfur cathode, leading to rapid capacity decay and self-discharge. Simultaneously, the polysulfides formed during magnesium-sulfur battery discharge have limited solubility in traditional ether-based electrolytes, primarily undergoing solid-phase transformation reactions, resulting in slow reduction kinetics and low battery specific capacity. Furthermore, soluble polysulfide intermediates migrate to the magnesium anode during discharge (i.e., the "shuttle effect"), exacerbating anode corrosion and passivation.

[0004] To address the aforementioned challenges, existing technologies primarily employ two types of electrolyte systems: one is a chloride-containing non-nucleophilic electrolyte (such as Mg(HMDS)2 / MgCl2 / AlCl3, MACC, etc.), which, while achieving good reversibility of magnesium deposition / dissolution, suffers from the presence of chloride ions that easily corrode current collectors (such as aluminum foil), and exhibits low specific capacity at the sulfur cathode discharge; the other is boron-based magnesium salt ether electrolytes, which, although non-corrosive, struggle to improve the reduction and conversion kinetics of magnesium polysulfides and are extremely expensive. In contrast, simple magnesium salt electrolytes (such as non-nucleophilic Mg(TFSI)2 / ether solvent systems) are inexpensive, but typically passivate the metallic magnesium foil without introducing chloride ions, hindering the deposition of magnesium. 2+ The uniform deposition and dissolution of MgO prevents magnesium-sulfur batteries from functioning properly. Therefore, it is necessary to develop a method that combines chlorine-free operation, high sulfur compatibility, and high MgO content. 2+ A novel electrolyte system with good transport dynamics and anode interface stability is of great significance for promoting the practical application of magnesium-sulfur batteries. Summary of the Invention

[0005] Based on this, the purpose of this invention is to provide a chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention can adopt the following technical solutions: One aspect of this invention provides a chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries, which includes magnesium salt, ionic liquid, organic ether solvent, amine solvent, and organophosphorus compound.

[0007] Preferably, in the above-mentioned chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries, the magnesium salt is selected from magnesium bis(trifluoromethanesulfonyl)imide and / or magnesium trifluoromethanesulfonate; and / or the ionic liquid is selected from one or more combinations of pyrrolidine ionic liquids, piperidine ionic liquids, or quaternary ammonium salt ionic liquids; and / or the organic ether solvent is selected from one or more combinations of ethylene glycol dimethyl ether, tetrahydrofuran, ethylene glycol formaldehyde, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or 1,3-dioxolane; and / or the amine solvent is selected from one or more combinations of 2-ethoxyethylamine, 2-methoxyethylamine, 2,2-dimethoxyethylamine, or 2,2-diethoxyethylamine; and the organophosphonate is selected from one or more combinations of triphenylphosphine oxide, triphenyl phosphate, or (aminoethyl)diphenylphosphine oxide.

[0008] More preferably, in the above-mentioned chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries, the ionic liquid is selected from one or more combinations of 1-ethyl-1-methylpyrrolidine trifluoromethanesulfonate, 1-butyl-1-methylpyrrolidine trifluoromethanesulfonate, 1-ethyl-1-methylpyrrolidine bis(trifluoromethanesulfonyl)imide, 1-ethyl-1-methylpiperidine trifluoromethanesulfonate, or N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide.

[0009] More preferably, in the above-mentioned chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries, the organic ether solvent is ethylene glycol dimethyl ether, the amine solvent is 2-ethoxyethylamine, the organophosphonate is triphenylphosphine oxide, and the ionic liquid is 1-butyl-1-methylpyrrole trifluoromethanesulfonate.

[0010] Preferably, in the above-mentioned chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries, the molar concentration of magnesium salt is 0.1 mol / L to 1 mol / L; and / or the concentration of ionic liquid is 0.1 mol / L to 1 mol / L; and / or the volume of organic ether solvent is 0 < v(%) ≤ 90% of the total volume of organic ether solvent and amine solvent; and / or the molar concentration of organophosphine compound is 0.01 mol / L to 0.2 mol / L.

[0011] More preferably, in the above-mentioned chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries, the concentration of the ionic liquid is 0.5 mol / L; and / or the volume of the organic ether solvent is 71% of the total volume of the organic ether solvent and the amine solvent; and / or the molar concentration of the organophosphine compound is 0.05 mol / L.

[0012] Another aspect of the present invention provides a method for preparing the above-mentioned chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries. The preparation method includes: mixing magnesium salt, ionic liquid, organic ether solvent, amine solvent and organophosphonate to obtain the chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries.

[0013] Preferably, the above preparation method includes (1) dissolving magnesium salt in an organic ether solvent to obtain a magnesium salt solution; and (2) adding an amine solvent, an organophosphorus compound, and an ionic liquid to the magnesium salt solution to obtain a chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries.

[0014] Another aspect of the present invention provides a magnesium-sulfur battery comprising the above-described chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries.

[0015] Preferably, the magnesium-sulfur battery further includes: a positive electrode, a negative electrode, and a battery separator; wherein the material for preparing the positive electrode is selected from one or more combinations of sulfur-carbon composite materials, sulfur metal compound composite materials, or sulfur polymer composite materials; and / or the material for preparing the negative electrode is selected from one or more of metallic magnesium, magnesium alloy, or magnesium-based composite materials; and / or the battery separator is selected from glass fiber membrane separators.

[0016] The beneficial effects of this invention include at least the following: The chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries provided by this invention effectively improves its compatibility with sulfur cathodes and magnesium anodes through the synergistic effect of multiple components regulating the solvation structure. Specifically, the solubility of magnesium polysulfides is increased by introducing amine solvents, thereby promoting the diffusion and redox conversion kinetics of magnesium polysulfides; the introduction of organophosphorus compounds as additives effectively improves the reversibility, discharge specific capacity, and voltage plateau of magnesium-sulfur batteries; and the addition of ionic liquids improves the stability of the magnesium anode / electrolyte interface, enhancing the Mg... 2+ The high transport capacity reduces the overpotential for magnesium deposition / dissolution; furthermore, the electrolyte is chloride-free, avoiding corrosion problems caused by chloride ions. Attached Figure Description

[0017] Figure 1 The cyclic voltammetry curve of the electrolyte prepared in Example 1 of this invention, with molybdenum foil as the working electrode; Figure 2 Linear scan voltammetric curves of the electrolyte prepared in Example 1 of this invention on different working electrodes; Figure 3 The ionic conductivity of the electrolyte prepared in Example 1 of this invention; Figure 4 The Mg / Mg symmetric battery assembled with the electrolyte prepared in Example 1 of this invention operates at 0.1 mA·cm⁻¹. -2 Long-term polarization performance curves at current density; Figure 5These are scanning electron microscope (SEM) images of the electrolytes prepared in Example 1 and Comparative Examples 3 to 5 of this invention after electrochemical testing of magnesium metal deposition. Figure 6 This is a second charge-discharge curve of the magnesium-sulfur battery assembled in Example 1 and Comparative Examples 1 to 2 of the present invention; Figure 7 The graphs show the second charge-discharge curves of the magnesium-sulfur batteries assembled in Example 1 and Comparative Examples 3 to 5 of this invention. Figure 8 This is the 10th cycle voltammogram of the magnesium polysulfide symmetric battery assembled in Example 1 and Comparative Examples 3 to 5 of the present invention. Detailed Implementation

[0018] The illustrated embodiments are provided to better illustrate the present invention, but are not intended to limit the scope of the invention to the illustrated embodiments. Therefore, non-essential improvements and adjustments made to the embodiments by those skilled in the art based on the above description of the invention still fall within the protection scope of the present invention.

[0019] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit this disclosure. Singular expressions include plural expressions unless they have a distinct meaning in the context. As used herein, it should be understood that terms such as “comprising,” “having,” “including,” are intended to indicate the presence of features, numbers, operations, components, parts, elements, materials, or combinations thereof. The terminology of the invention is disclosed in the specification and is not intended to exclude the possibility that one or more other features, numbers, operations, components, parts, elements, materials, or combinations thereof may be present or added. As used herein, “ / ” may be interpreted as “and” or “or,” depending on the context.

[0020] In a first aspect, embodiments of the present invention provide a chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries, the chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries comprising magnesium salts, ionic liquids, organic ether solvents, amine solvents, and organophosphides.

[0021] It should be noted that this invention improves the electrode / electrolyte interface by regulating the solvation structure of the electrolyte through the synergistic effect of multiple components. This improves the compatibility of the sulfur cathode, effectively immobilizes and restricts polysulfides, thereby enhancing the reversibility, discharge specific capacity, and voltage plateau of the magnesium-sulfur battery. Simultaneously, it activates the surface of the magnesium anode, improving its compatibility with the magnesium anode and enhancing the performance of the magnesium anode. 2+ This enhances the transport capacity, reduces the overpotential for magnesium anode dissolution / deposition, and improves Mg... 2+Kinetic performance and reversibility are as follows: Ionic liquids help regulate the solvation structure of magnesium ions and reduce electrolyte and impurity decomposition on the magnesium surface, thus improving interfacial stability; organic ether solvents ensure the dissolution of simple magnesium salts and the basic ionic conductivity of the electrolyte; amine solvents, as strongly polar solvents, allow the amine groups to interact with polysulfides, accelerating the conversion kinetics of MgS and S, while catalyzing the redox reactions of polysulfides, helping to inhibit their free migration in the electrolyte and reduce the shuttle effect; organophosphine compounds are mainly used to improve the deposition morphology and interfacial stability of the magnesium anode surface. Furthermore, this electrolyte system is chloride-free, which can inhibit corrosion of the magnesium anode and deterioration of the passivation film, prevent corrosion of the cathode and current collector, reduce side reactions in the electrolyte, improve stability, and enhance battery safety.

[0022] In some specific examples, in the above-mentioned magnesium-sulfur battery using a chlorine-free simple magnesium salt electrolyte, the magnesium salt is selected from bis(trifluoromethanesulfonyl)imide magnesium and / or trifluoromethanesulfonate magnesium.

[0023] It should be noted that the magnesium salts used in this invention are well known in the art. The preferred magnesium salts used in this invention are bis(trifluoromethanesulfonyl)imide magnesium, and the electrolyte prepared by bis(trifluoromethanesulfonyl)imide has better electrochemical performance than electrolytes prepared by other magnesium salts under the same test conditions.

[0024] In some specific examples, the molar concentration of magnesium salt in the chlorine-free simple magnesium salt electrolyte for the above-mentioned magnesium-sulfur batteries is 0.1 mol / L to 1 mol / L.

[0025] It should be noted that the molar concentration of the electrolyte in this invention has a certain impact on the electrolyte. When the molar concentration of magnesium salt is below 0.1 mol / L, the magnesium salt content is low, and the ionic conductivity is low; when the molar concentration of magnesium salt is greater than 1 mol / L, the electrolyte viscosity increases and the reaction rate decreases. Therefore, the molar concentration of magnesium salt in this invention can be 0.1 mol / L to 1 mol / L (this concentration calculation does not include the volume of ionic liquid), such as 0.3 mol / L, 0.5 mol / L, or 0.7 mol / L. Electrolytes prepared at these concentrations exhibit superior electrochemical performance, especially at a concentration of 0.5 mol / L, where the performance is better than other concentrations.

[0026] In some specific examples, in the above-mentioned chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries, the ionic liquid is selected from one or more combinations of 1-ethyl-1-methylpyrrolidine trifluoromethanesulfonate, 1-butyl-1-methylpyrrolidine trifluoromethanesulfonate, 1-ethyl-1-methylpyrrolidine bis(trifluoromethanesulfonyl)imide, 1-ethyl-1-methylpiperidine trifluoromethanesulfonate, or N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide.

[0027] It should be noted that the ionic liquid in this invention can be further preferably the ionic liquid listed above, which, when used in combination with other components of the electrolyte in this invention, exhibits better electrochemical performance than other ionic liquids under the same test conditions.

[0028] In some specific examples, the concentration of the ionic liquid in the chlorine-free simple magnesium salt electrolyte used in the above-mentioned magnesium-sulfur batteries is 0.1 mol / L to 1 mol / L.

[0029] It should be noted that the concentration of the ionic liquid in this invention can be further preferably 0.1 mol / L to 1 mol / L (this concentration calculation does not include the volume of the ionic liquid), such as 0.3 mol / L, 0.5 mol / L, 0.7 mol / L, or 0.9 mol / L. Electrolytes prepared at these concentrations exhibit superior electrochemical performance, especially at a concentration of 0.5 mol / L, where the performance is better than at other concentrations.

[0030] In some specific examples, the organic ether solvent in the above-mentioned chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries is selected from one or more combinations of ethylene glycol dimethyl ether, tetrahydrofuran, ethylene glycol formaldehyde, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or 1,3-dioxolane.

[0031] It should be noted that the organic ether solvents used in this invention are known in the art, including but not limited to the organic ether solvents listed above.

[0032] In some specific examples, in the chlorine-free simple magnesium salt electrolyte for the magnesium-sulfur battery described above, the amine solvent is selected from one or more combinations of 2-ethoxyethylamine, 2-methoxyethylamine, 2,2-dimethoxyethylamine, and 2,2-diethoxyethylamine.

[0033] It should be noted that the amine solvents used in this invention are known in the art, including but not limited to the amine solvents listed above.

[0034] In some specific examples, in the above-mentioned chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries, the volume of organic ether solvent is 0 < v(%) ≤ 90% of the total volume of organic ether solvent and amine solvent.

[0035] It should be noted that the volume of the organic ether solvent in this invention is preferably 0 < v(%) ≤ 90% of the total volume of the organic ether solvent and amine solvent, such as 5%, 10%, 15%, 20%, 25%, 50%, 60%, 70%, or 80%. Particularly preferred is that the volume of the organic ether solvent is 71% of the total volume of the organic ether solvent and amine solvent, that is, the organic ether solvent accounts for 71% of the volume and the amine solvent accounts for 29%. The electrolyte prepared under this ratio exhibits better electrochemical performance than electrolytes prepared under the same test conditions than those prepared under other ratios.

[0036] In some specific examples, in the chlorine-free simple magnesium salt electrolyte for the magnesium-sulfur battery described above, the organophosphorus compound is selected from one or more combinations of triphenylphosphine oxide, triphenyl phosphate, and (aminoethyl)diphenylphosphine oxide.

[0037] It should be noted that the organophosphorus compounds in this invention are known in the art, including but not limited to the organophosphorus compounds listed above.

[0038] In some specific examples, the molar concentration of organophosphorus compounds in the chlorine-free simple magnesium salt electrolyte for the above-mentioned magnesium-sulfur batteries is 0.01 mol / L to 0.2 mol / L.

[0039] It should be noted that the molar concentration of the organophosphorus compound in this invention can preferably be 0.05 mol / L, 0.07 mol / L, 0.1 mol / L, 0.13 mol / L, 0.15 mol / L, 0.17 mol / L, or 0.19 mol / L, etc. Electrolytes prepared at these molar concentrations have better performance, especially the electrolyte prepared at a molar concentration of 0.05 mol / L has better electrochemical performance than other molar concentrations.

[0040] In some specific examples, in the above-mentioned chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries, the ionic liquid is 1-butyl-1-methylpyrrole trifluoromethanesulfonate, the organic ether solvent is ethylene glycol dimethyl ether, the amine solvent is 2-ethoxyethylamine, and the organophosphonate is triphenylphosphine oxide.

[0041] It should be noted that the electrolyte used in this invention is preferably the electrolyte described above, namely, 1-butyl-1-methylpyrrole trifluoromethanesulfonate as the ionic liquid, ethylene glycol dimethyl ether as the organic ether solvent, 2-ethoxyethylamine as the amine solvent, and triphenylphosphine oxide as the organophosphine compound. The electrochemical performance of the electrolyte prepared by this combination is superior to other combinations.

[0042] In some specific examples, in the above-mentioned simple magnesium salt electrolyte for magnesium-sulfur batteries without chloride, the ionic liquid is 1-butyl-1-methylpyrrole trifluoromethanesulfonate, the organic ether solvent is ethylene glycol dimethyl ether, the amine solvent is 2-ethoxyethylamine, and the organophosphine compound is triphenylphosphine oxide; and the concentration of the ionic liquid is 0.5 mol / L, the volume of the organic ether solvent is 71% of the total volume of the organic ether solvent and the amine solvent, and the molar concentration of the organophosphine compound is 0.05 mol / L.

[0043] It should be noted that the electrolytes prepared with the components and concentrations listed above have superior electrochemical performance.

[0044] Secondly, embodiments of the present invention provide a method for preparing the above-mentioned chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries. The preparation method includes: mixing magnesium salt, ionic liquid, organic ether solvent, amine solvent and organophosphorus compound to obtain the chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries.

[0045] It should be noted that the preparation method in this invention is simple, the conditions are mild, and it is easy to implement industrially.

[0046] In some specific examples, the above preparation method includes (1) dissolving the magnesium salt in an organic ether solvent to obtain a magnesium salt solution; (2) Add amine solvent, organophosphorus compound and ionic liquid to magnesium salt solution to obtain chlorine-free simple magnesium salt electrolyte for magnesium-sulfur battery.

[0047] It should be noted that, in the preparation of the electrolyte in this invention, the magnesium salt can be dissolved in an organic ether solvent before being mixed with other components, which can improve the reaction rate. Furthermore, the preparation process of this invention is carried out in an environment where both oxygen and moisture content are below 0.01 ppm.

[0048] Thirdly, embodiments of the present invention provide a magnesium-sulfur battery, which includes the above-mentioned chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries.

[0049] It should be noted that, based on the excellent electrochemical performance of the electrolyte in this invention, it can be used to prepare magnesium-sulfur batteries, which also have excellent electrochemical performance.

[0050] In some specific examples, the above-mentioned magnesium-sulfur battery further includes: a positive electrode, a negative electrode, and a battery separator; wherein the material for preparing the positive electrode is selected from one or more combinations of sulfur-carbon composite materials, sulfur metal compound composite materials, or sulfur polymer composite materials; and / or the material for preparing the negative electrode is selected from one or more of metallic magnesium, magnesium alloy, or magnesium-based composite materials; and / or the battery separator is selected from glass fiber membrane separators.

[0051] To better understand the present invention, specific examples are provided below to further illustrate the content of the present invention, but the content of the present invention is not limited to the examples below.

[0052] Preparation Examples and Comparative Examples In the following examples and comparative examples, all operating steps were carried out in a glove box filled with argon (with water and oxygen content both below 0.01 ppm).

[0053] Example 1 Weigh 0.4292 g of magnesium (II) bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2) and add it to a dried 5 mL reagent bottle. Then, slowly add 1 mL of ethylene glycol dimethyl ether and 0.4 mL of 2-ethoxyethylamine in sequence. Next, add 0.0194 g of triphenylphosphine oxide and 0.2039 g of 1-butyl-1-methylpyrrole trifluoromethanesulfonate. Stir the mixture at 400 r / min at 25 °C for 12 h to obtain the electrolyte.

[0054] Examples 2 to 5 Examples 2 to 5 are largely the same as Example 1, except that the raw materials or amounts added are different. Otherwise, they are the same as Example 1, and different electrolytes are prepared. The raw materials and amounts used in Examples 2 to 5 are shown in Table 1 below and are compared with those in Example 1.

[0055] Table 1. Raw materials and dosages used in the preparation of Examples 1 to 5

[0056] Comparative Example 1 Weigh 0.2923 g of magnesium bis(trifluoromethanesulfonyl)imide(II) (Mg(TFSI)2) and add it to 1 mL of dimethyl ethylene glycol (DME). Stir thoroughly to dissolve and obtain an electrolyte. The concentration of Mg(TFSI)2 in the electrolyte is 0.5 M.

[0057] Comparative Example 2 Weigh 0.2923 g of magnesium bis(trifluoromethanesulfonyl)imide(II) (Mg(TFSI)2) and 0.09521 g of anhydrous magnesium chloride (MgCl2) and add them to 1 mL of dimethyl ethylene glycol (DME). Stir at 60°C overnight until completely dissolved to obtain an electrolyte. The concentration of Mg(TFSI)2 in the electrolyte is 0.5 M and the concentration of MgCl2 is 1 M.

[0058] Comparative Example 3 Weigh 0.4092 g of magnesium bis(trifluoromethanesulfonyl)imide(II) (Mg(TFSI)2) and add it to 1 mL of ethylene glycol dimethyl ether (DME) and 0.4 mL of 2-ethoxyethylamine. Stir thoroughly to dissolve and obtain an electrolyte. The concentration of Mg(TFSI)2 in the electrolyte is 0.5 M.

[0059] Comparative Example 4 Weigh 0.4092 g of magnesium bis(trifluoromethanesulfonyl)imide(II) (Mg(TFSI)2) and add it to a dried 5 mL reagent bottle. Then, slowly add 1 mL of ethylene glycol dimethyl ether and 0.4 mL of 2-ethoxyethylamine in sequence, followed by 0.0194 g of triphenylphosphine oxide. Stir the mixture at 400 r / min at 25 °C for 12 h to obtain an electrolyte. The concentration of magnesium bis(trifluoromethanesulfonyl)imide(II) in the electrolyte is 0.5 M.

[0060] Comparative Example 5 Weigh 0.4092 g of magnesium bis(trifluoromethanesulfonyl)imide(II) (Mg(TFSI)2) and add it to a dried 5 mL reagent bottle. Then, slowly add 1 mL of ethylene glycol dimethyl ether and 0.4 mL of 2-ethoxyethylamine in sequence, followed by 0.2039 g of 1-butyl-1-methylpyrrole trifluoromethanesulfonate. Stir the mixture at 400 r / min at 25 °C for 12 h to obtain an electrolyte. The concentration of magnesium bis(trifluoromethanesulfonyl)imide(II) in the electrolyte is 0.5 M.

[0061] Performance testing (a) Testing of reversible magnesium deposition dissolution performance and oxidative stability of electrolyte The reversible magnesium deposition dissolution performance and oxidation stability of the electrolyte prepared in Example 1 were tested by cyclic voltammetry and linear sweep voltammetry, respectively. Specifically, a two-electrode system was used, with a magnesium sheet (12mm) electrode as the reference electrode and counter electrode, and electrodes with different current collectors (SS (stainless steel), C-Al (carbon-coated aluminum), Ni (nickel), Mo (molybdenum), GP (graphene-based), and CF (carbon fiber)) as working electrodes. All electrodes were cleaned three times with deionized water and ethanol to thoroughly remove impurities from the entire electrode surface. After vacuum drying for 6 hours, the cleaned electrodes were placed in a glove box for later use. For cyclic voltammetry, the test potential range is -1V to 2.0V, the scan rate is 25mV / s, the scan is performed from the negative direction of the open-circuit voltage, and the test temperature is 25°C. The cyclic voltammetry curve using molybdenum (Mo) foil as the working electrode is shown below. Figure 1 As shown, the results indicate that the electrolyte prepared in Example 1 can undergo reversible deposition and dissolution.

[0062] For linear sweep voltammetry, the potential range during testing is open-circuit voltage - 3V, the sweep rate is 1mV / s, and the testing temperature is 25°C. The linear voltammetric curves of the electrolyte prepared in Example 1 for different current collector electrodes are shown below. Figure 2 As shown, the results indicate that the electrolyte prepared in Example 1 has an oxidation stability potential greater than 2.5V on stainless steel and molybdenum foil at room temperature. This result indicates that the electrolyte has good oxidation stability and can be matched with sulfur cathode.

[0063] (ii) Electrolyte conductivity test The conductivity of the electrolyte prepared in Example 1 was tested using electrochemical impedance spectroscopy (CHI660E electrochemical workstation); specifically as follows: a stainless steel foil (12mm) electrode was used as the reference electrode, working electrode, and counter electrode; the voltage amplitude during the test was 5mV, and the frequency range was set to 0.01Hz~10 Hz. 5 Hz, test temperature 25°C. Test results are as follows. Figure 3 As shown, the results indicate that the conductivity of Example 1 is 7.96 mS·cm. -1 .

[0064] (III) Electrolyte polarization performance test The polarization performance of the electrolyte prepared in Example 1 was tested according to the following method: assembly was carried out in an inert atmosphere glove box, with water and oxygen content both less than 0.01 ppm; a bright magnesium sheet (12 mm) after acid washing was used as the counter electrode and reference electrode, and assembled with a Whatman GF / F glass fiber separator and electrolyte to form a CR2032 coin cell; after the battery was assembled, it was left to stand at room temperature for 12 hours before testing; the entire testing process was carried out on the Wuhan Neware charge and discharge testing system.

[0065] Test results are as follows Figure 4 As shown, the results indicate that the electrolyte prepared in Example 1 performs well at 0.1 mA·cm⁻¹. -2 At a low polarization voltage of 87mV, it exhibits stable cycling for approximately 340 hours.

[0066] (iv) Scanning test of magnesium deposition in electrolyte The electrolytes prepared in Example 1 and Comparative Examples 3 to 5 were subjected to magnesium deposition scanning tests according to the following method: assembly was carried out in an inert atmosphere glove box, with water and oxygen content less than 0.01 ppm; a bright magnesium sheet (12 mm) after acid washing was used as the counter electrode, and molybdenum foil was used as the working electrode. These were assembled with a battery separator (a combination of Whatman GF / F glass fiber separator and polyethylene separator) and electrolyte to form a CR2032 coin cell; after assembly, the battery was allowed to stand at room temperature for 12 hours before testing; the entire testing process was conducted on a Wuhan Neware charge-discharge testing system; the discharge current density was 0.05 mA·cm⁻¹. -2 ~1mA·cm -2 The discharge was controlled by time (2h to 10h). After the test was completed, the coin cell was removed and the molybdenum foil with deposited magnesium was obtained and characterized by scanning electron microscopy.

[0067] Scanning electron microscope (SEM) images of magnesium metal deposited in different electrolytes after electrochemical testing are shown below. Figure 5As shown, the results indicate that the surface morphology of magnesium metal changed in the electrolytes prepared in Example 1 and Comparative Examples 3 to 5. The magnesium metal surface deposit in the electrolyte of Example 1 was smoother and denser, and was evenly distributed on the surface.

[0068] (v) Electrolyte-based magnesium-sulfur full cell testing The electrolytes prepared in Example 1 and Comparative Examples 1 to 5 were assembled into magnesium-sulfur full cells, and their electrochemical performance was tested, as follows: (1) The sulfur-carbon composite cathode material (75wt% S content, purchased from KELOD), conductive carbon black and polyvinylidene fluoride were mixed in a mass ratio of 7:2:1 and ground for 30 min. Then, the mixture was magnetically stirred for 12 h to obtain a conductive paste. The conductive paste was coated on graphite foil, dried and cut into sheets to obtain a sulfur-carbon composite electrode sheet. (2) Different CR2032 coin cells (magnesium-sulfur full cells) were assembled by combining the negative electrode (bright magnesium sheet after acid washing), the positive electrode (sulfur-carbon composite electrode sheet in (1) above), the Whatman GF / F glass fiber separator, and the electrolyte. Constant current charge-discharge tests were conducted at a rate of 0.1C within a voltage window of 0.2V to 2.5V (1C = 1675mAh·g). -1 ( ), scanning from open circuit voltage to negative direction at a scan rate of 1mV / s within a voltage window of 0.2V to 2.5V.

[0069] The second charge-discharge curves of the CR2032 coin cells assembled based on the electrolytes prepared in Example 1 and Comparative Examples 1 to 5 are shown below. Figure 6 and Figure 7 As shown, the results indicate that, compared to Comparative Examples 1 to 5, the CR2032 coin cell assembled based on the electrolyte prepared in Example 1 has a maximum discharge specific capacity of 835 mAh·g. -1 Discharge platform (1.6V / 1.3V vs. Mg / Mg) 2+ It exhibits relatively optimal discharge specific capacity and discharge plateau.

[0070] (vi) Performance testing of magnesium polysulfide symmetric cells based on electrolyte Magnesium polysulfide (MgS) xThe preparation method of the electrode (the preparation process is carried out in an inert atmosphere glove box) is as follows: 0.02368g of magnesium sulfide and 0.0672g of sulfur powder are dissolved in a mixed solvent of 1.5mL of ethylene glycol dimethyl ether and 0.6mL of 2-ethoxyethylamine at a molar ratio of 1:5. The mixture is stirred at 60°C for 24h. The incompletely reacted sulfur powder is filtered through a needle filter to obtain a brownish-red solution, namely magnesium polysulfide solution. 0.4092g of Mg(TFSI)2 is dissolved in 1.4mL of magnesium polysulfide solution. 0.0194g of triphenylphosphine oxide and 0.2039g of 1-butyl-1-methylpyrrole trifluoromethanesulfonate are added sequentially and stirred for 12h to obtain the electrolyte. 10μL of the obtained electrolyte is loaded onto a porous carbon cloth current collector (14mm in diameter) to allow for full adsorption, and then used as the electrode.

[0071] The electrolytes prepared in Example 1 and Comparative Examples 3 to 5 were assembled into magnesium polysulfide symmetric cells, and their electrochemical performance was tested as follows: Magnesium polysulfide electrodes (the magnesium polysulfide electrodes mentioned in (VI) above) were used as the counter electrode and working electrode, respectively, and were assembled into CR2032 coin cells together with the electrolyte and Whatman GF / F glass fiber separator. After assembly, the cells were allowed to stand at room temperature for 12 hours before cyclic voltammetry testing (CHI660E electrochemical workstation) was performed. The potential range was -1V to 1V, the scan rate was 1mV / s, the scan was performed from the negative direction of the open-circuit voltage, and the test temperature was 25°C. The cyclic voltammetry curves of the CR2032 coin cells assembled based on the electrolyte prepared in Example 1 after 10 cycles are shown below. Figure 8 As shown, the results indicate that the CR2032 coin cell assembled using the electrolyte prepared in Example 1 exhibits a more pronounced peak current in the cyclic voltammetry test. Compared to Comparative Examples 3 to 5, the CR2032 coin cell based on Example 1 shows a more distinct peak shape and better symmetry, indicating that the electrochemical conversion reaction of polysulfides in the electrolyte prepared in Example 1 is more reversible and the reaction kinetics are accelerated. Furthermore, the peak current decreases after cycling, and the peak position shifts, suggesting a reduction in the concentration of active polysulfides participating in the rapid redox reaction on the electrode surface. This is due to the coordination or reaction between magnesium polysulfide and electrolyte components.

[0072] In addition, for ease of comparison, the electrochemical performance of the electrolytes prepared in Examples 2 to 5 and Comparative Examples 1 to 5 was tested according to the above method, and summarized together with Example 1, as shown in Table 2 below; wherein, the ionic conductivity was tested according to the method in (II) above, the symmetric cell deposition overpotential was tested according to the method in (III) above, and the maximum discharge specific capacity and discharge plateau were tested according to the method in (V) above.

[0073] Table 2 shows the electrochemical performance of the electrolytes prepared in Examples 1 to 5 and Comparative Examples 1 to 5.

[0074] 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 it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries, characterized in that, The chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries includes magnesium salts, ionic liquids, organic ether solvents, amine solvents, and organophosphides.

2. The chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries according to claim 1, characterized in that, The magnesium salt is selected from magnesium bis(trifluoromethanesulfonyl)imide and / or magnesium trifluoromethanesulfonate; and / or The ionic liquid is selected from one or more combinations of pyrrolidine ionic liquids, piperidine ionic liquids, or quaternary ammonium salt ionic liquids; and / or Organic ether solvents are selected from one or more combinations of ethylene glycol dimethyl ether, tetrahydrofuran, ethylene glycol formaldehyde, diethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, or 1,3-dioxolane; and / or The amine solvent is selected from one or more combinations of 2-ethoxyethylamine, 2-methoxyethylamine, 2,2-dimethoxyethylamine or 2,2-diethoxyethylamine; The organophosphorus compound is selected from one or more combinations of triphenylphosphine oxide, triphenyl phosphate, or (aminoethyl) diphenylphosphine oxide.

3. The chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries according to claim 2, characterized in that, The ionic liquid is selected from one or more combinations of 1-ethyl-1-methylpyrrolidine trifluoromethanesulfonate, 1-butyl-1-methylpyrrolidine trifluoromethanesulfonate, 1-ethyl-1-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt, 1-butyl-1-methylpyrrolidine bis(trifluoromethanesulfonyl)imide salt, 1-ethyl-1-methylpiperidine trifluoromethanesulfonate, or N,N-diethyl-N-methyl-N-(2-methoxyethyl)ammonium bis(trifluoromethanesulfonyl)imide salt.

4. The chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries according to claim 2, characterized in that, The ionic liquid is 1-butyl-1-methylpyrrole trifluoromethanesulfonate. The organic ether solvent is ethylene glycol dimethyl ether. The amine solvent is 2-ethoxyethylamine. The organophosphorus compound is triphenylphosphine oxide.

5. The chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries according to any one of claims 1 to 4, characterized in that, The molar concentration of the magnesium salt is 0.1 mol / L to 1 mol / L; and / or The concentration of the ionic liquid is 0.1 mol / L to 1 mol / L; and / or The volume of organic ether solvents is 0 < v(%) ≤ 90% of the total volume of organic ether solvents and amine solvents; and / or The molar concentration of organophosphorus compounds is 0.01 mol / L to 0.2 mol / L.

6. The chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries according to claim 5, characterized in that, The concentration of the ionic liquid is 0.5 mol / L; and / or The volume of organic ether solvents is 71% of the total volume of organic ether solvents and amine solvents; and / or The molar concentration of the organophosphorus compound is 0.05 mol / L.

7. The method for preparing the chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries according to any one of claims 1 to 6, characterized in that, The preparation method includes mixing magnesium salt, ionic liquid, organic ether solvent, amine solvent and organophosphonate to obtain a chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries.

8. The preparation method according to claim 7, characterized in that, Preparation methods include: (1) Dissolve the magnesium salt in an organic ether solvent to obtain a magnesium salt solution; (2) Add amine solvent, organophosphorus compound and ionic liquid to magnesium salt solution to obtain chlorine-free simple magnesium salt electrolyte for magnesium-sulfur battery.

9. A magnesium-sulfur battery, characterized in that, Includes the chlorine-free simple magnesium salt electrolyte for magnesium-sulfur batteries as described in any one of claims 1 to 6.

10. The magnesium-sulfur battery according to claim 9, characterized in that, Magnesium-sulfur batteries also include: a positive electrode, a negative electrode, and a battery separator; among which, The cathode material is selected from one or more combinations of sulfur-carbon composite materials, sulfur metal compound composite materials, or sulfur polymer composite materials; and / or The negative electrode material is selected from one or more of metallic magnesium, magnesium alloys, or magnesium-based composite materials; and / or The battery separator is selected from glass fiber membrane separators.

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