Organic deep eutectic high-temperature magnesium electrolyte with ultra-low overpotential, preparation method and application thereof

Abstract

The application discloses an organic deep eutectic high-temperature magnesium electrolyte with an ultra-low overpotential, a preparation method and application, and the electrolyte is composed of a magnesium salt, an imidazole and an amine additive; the molar ratio of the magnesium salt and the imidazole is 1: (4-30), and the molar ratio of the magnesium salt and the amine additive is (1:8) to (3:1) ; wherein the magnesium salt is magnesium bistrifluoromethylsulfonylimide, the imidazole is 1,2-dimethylimidazole, and the amine is selected from one of 2-(methylthio) ethylamine, 3-methoxypropylamine, 1-methoxypropan-2-amine, 3-isopropoxypropylamine and 2-methoxyethylamine. The raw material of the electrolyte is easy to obtain and low in price, the preparation process is simple, the electrolyte has an ultra-long cycle performance and good high-temperature stability, and has the value of large-scale commercial application.

Description

Technical Field

[0001] This invention relates to the field of rechargeable magnesium battery technology, specifically to an ultra-low overpotential organic deep eutectic high-temperature magnesium electrolyte, its preparation method, and its application. Background Technology

[0002] Magnesium metal is valued for its low price, high safety, abundant reserves in the Earth's crust, and high volumetric capacity (3833 mAh cm⁻¹). -3 Magnesium chloride (MCC) is considered an ideal alternative to lithium-ion batteries due to its characteristics such as low cost and abundant resources, and its low reduction potential (-2.37V vs. standard hydrogen electrode, SHE). As a potential electrolyte material for magnesium-ion batteries, MCC has attracted widespread attention due to its low cost and abundant resources. Since most conventional electrolyte solvents and magnesium salts readily form a robust passivation layer on the Mg anode, current mainstream RMB research uses ethers as solvents for electrolyte preparation. Although ethers avoid the high reactivity with magnesium, their naturally low boiling and flash point characteristics make ether solvents volatile, flammable, and extremely unstable in high-temperature environments.

[0003] Therefore, magnesium-ion batteries using ether solvents often have a very narrow operating temperature range, typically only usable near room temperature. Furthermore, a passivation layer easily forms on the Mg anode surface, increasing the Mg content. 2+ Transmission resistance. At high temperatures, ether electrolytes suffer from severe performance degradation and safety hazards, which seriously limits the application and development of RMBs. Summary of the Invention

[0004] To address the aforementioned shortcomings of existing technologies, the present invention aims to provide an ultra-low overpotential organic deep eutectic high-temperature magnesium electrolyte, its preparation method, and its applications. This invention discovers that a novel magnesium-based electrolyte can be synthesized from solid magnesium salts, specific solid imidazole compounds, and amine additives. This electrolyte possesses advantages such as simple preparation process, low cost, wide operating temperature range, good high-temperature stability and flame retardancy, ultra-low overpotential, long cycle life, and high coulombic efficiency, thereby solving the problems of narrow operating temperature range, flammability and explosiveness, large overpotential, low deposition and dissolution efficiency, and short cycle life in existing electrolytes.

[0005] To address the aforementioned technical problems, in a first aspect, the present invention provides an ultra-low overpotential organic deep eutectic high-temperature magnesium electrolyte, wherein the electrolyte is composed of a magnesium salt, an imidazole, and an amine additive; the molar ratio of the magnesium salt to the imidazole is 1:(4-30), and the molar ratio of the magnesium salt to the amine additive is (1:8) to (3:1); wherein the magnesium salt is bis(trifluoromethanesulfonyl)imide magnesium, the imidazole is 1,2-dimethylimidazole; and the amine is selected from one of 2-(methylthio)ethylamine, 3-methoxypropylamine, 1-methoxypropyl-2-amine, 3-isopropoxypropylamine, and 2-methoxyethylamine.

[0006] Secondly, the present invention provides a method for preparing an organic deep eutectic high-temperature magnesium electrolyte with ultra-low overpotential, wherein the electrolyte is prepared by the following specific steps: Step 1: Mix solid magnesium salt and solid imidazole at 80°C to obtain a clear solution; Step 2: Add an amine reagent to the clear solution obtained in Step 1, and stir to obtain the organic deep eutectic high-temperature magnesium electrolyte.

[0007] Preferably, the molar ratio of magnesium salt to imidazole is 1:(4-30), and the molar ratio of magnesium salt to amine additive is (1:8)~(3:1).

[0008] Preferably, the magnesium salt is magnesium bis(trifluoromethanesulfonyl)imide, the imidazole is 1,2-dimethylimidazole, and the amine is selected from one of 2-(methylthio)ethylamine, 3-methoxypropylamine, 1-methoxypropyl-2-amine, 3-isopropoxypropylamine, and 2-methoxyethylamine.

[0009] Preferably, steps 1 and 2 are carried out under an inert gas atmosphere.

[0010] Preferably, the water content and oxygen content in the clarified solution system are both less than 0.01 ppm.

[0011] Preferably, the magnesium salt is pretreated as follows: The magnesium salt is vacuum dried at 40℃~200℃ for at least 24 hours and then sealed and stored.

[0012] Thirdly, the present invention provides an application of an organic deep eutectic high-temperature magnesium electrolyte with ultra-low overpotential, wherein the electrolyte or the electrolyte obtained by the above preparation method is used to prepare a rechargeable magnesium-ion battery.

[0013] Fourthly, the present invention provides a magnesium-ion battery containing an organic deep eutectic high-temperature magnesium electrolyte with ultra-low overpotential, wherein the magnesium-ion battery contains the above-mentioned electrolyte.

[0014] Compared with the prior art, the present invention has the following beneficial effects: 1. In researching existing electrolyte technologies to address issues such as narrow operating temperature range, flammability, explosiveness, and high overpotential, this invention discovers that combining a specific magnesium salt, solid bis(trifluoromethanesulfonyl)imide magnesium, solid 1,2-dimethylimidazolium compounds, and amine additives such as 2-methoxyethylamine can form an organic deep eutectic high-temperature magnesium electrolyte with performance far exceeding expectations. This discovered combination of electrolytes not only operates stably at 80°C but also possesses excellent flame retardancy, fundamentally solving the safety hazards of traditional electrolytes. Even more surprisingly, it exhibits ultra-low overpotential characteristics at both room and high temperatures, with an overpotential below 35mV at room temperature and even below 25mV at 80°C, while also possessing a good ionic conductivity of 4.103 mS·cm. -1 With a low diffusion activation energy of 0.192 eV, the ion diffusion efficiency is significantly improved. The electrolyte also exhibits unexpected performance in cycle stability and coulombic efficiency, such as 0.1 mA / cm². 2 At the specified current density, the Mg||Mg battery can achieve an ultra-long cycle life of 1200 hours at room temperature and 400 hours at 80°C. The Mg||Mo battery has a coulombic efficiency of over 93.2%, and the Mg|DMSA|Mo6S8 battery can stably cycle 1000 times at a high current density of 5C with a capacity retention of 65.05%. These excellent performances all stem from the initial discovery of the effects of this combination, which also reflects that the electrolyte described in this invention can bring excellent results in different magnesium-ion battery systems.

[0015] 2. The preparation method of the electrolyte in this invention is greatly simplified. It only requires mixing magnesium salt pretreated by vacuum drying at 40℃~200℃ for at least 24 hours with 1,2-dimethylimidazole at 80℃, followed by the addition of an amine reagent and further mixing to obtain the target electrolyte. This preparation method, which eliminates the need for complex auxiliary materials, not only avoids the problems of high viscosity and high cost in traditional processes, but also significantly improves production efficiency due to its simple steps and short synthesis time. Furthermore, the preparation conditions, where the water and oxygen content of the system are controlled to be less than 0.01 ppm under an inert gas atmosphere, ensure the stability of the electrolyte performance. Moreover, the entire process does not generate any toxic gases, meeting green environmental protection requirements and providing convenience for large-scale industrial production. 3. The electrolyte constructed in this invention exhibits extremely high practical value and broad application prospects. The electrolyte, with its high-temperature stability, flame retardancy, ultra-low overpotential, and long cycle life, perfectly meets the stringent requirements of rechargeable magnesium-ion batteries for electrolytes. Furthermore, its simple, environmentally friendly, low-cost, and easily industrialized preparation process makes it suitable for large-scale applications. Simultaneously, magnesium-ion batteries constructed based on this electrolyte maintain stable electrochemical performance under different temperatures and current densities, further enhancing its significant application value in fields such as new energy storage. Attached Figure Description

[0016] Figure 1 This is a graph showing the long-cycle performance of a symmetrical battery at 80°C for the electrolyte prepared in Example 1 of this invention.

[0017] Figure 2 Linear scanning voltammetry diagrams of the electrolyte prepared in Example 1 of this invention on different working electrodes.

[0018] Figure 3 The diagram shows the long-cycle performance of the Mg||Mg symmetric battery at room temperature using the electrolyte prepared in Example 1 of this invention.

[0019] Figure 4 This is a diagram showing the ionic conductivity and activation energy of the electrolyte prepared in Example 1 of the present invention.

[0020] Figure 5 The graph shows the long-cycle performance of the Mg||Mo6S8 full cell with electrolyte prepared in Example 1 of this invention under a high current of 5C. Detailed Implementation

[0021] The technical solutions of the present invention will be clearly and completely described in conjunction with the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the present invention are within the scope of protection of the present invention.

[0022] Unless otherwise specified in the specific circumstances, the numerical ranges listed herein include upper and lower limits, as well as all integers and fractions within that range, but are not limited to the specific values ​​listed when the range is defined.

[0023] I. An organic deep eutectic high-temperature magnesium electrolyte with ultra-low overpotential The magnesium electrolyte (DMSA) of this invention is composed of magnesium salt, imidazole, and amine additives; the molar ratio of magnesium salt to imidazole is 1:(4-30), and the molar ratio of magnesium salt to amine additives is (1:8)~(3:1); wherein, the magnesium salt is magnesium bis(TFSI)2, the imidazole is 1,2-dimethylimidazolium (DMMIm); and the amine is selected from one of 2-(methylthio)ethylamine, 3-methoxypropylamine, 1-methoxypropyl-2-amine, 3-isopropoxypropylamine, and 2-methoxyethylamine.

[0024] After conducting a systematic and in-depth study on the technical problems of existing rechargeable magnesium-ion battery electrolytes, this invention found that the current mainstream ether-based electrolytes and organic eutectic electrolytes generally have performance limitations that are difficult to overcome. Among them, ether-based electrolytes suffer from inherently insufficient thermal stability due to the ether solvent, making them prone to bond breaking and decomposition at high temperatures. This not only limits their operating temperature range to the medium and low temperature range but also poses a significant risk of combustion or even explosion during battery charging and discharging due to the flammability of the ether solvent itself and the potential for localized overheating. While organic eutectic electrolytes improve the flammability of ethers to some extent, they are limited by the thermodynamic stability of the eutectic system, making them prone to phase separation at high temperatures. This results in a sharp drop in ionic conductivity, and their passivation problem on magnesium metal anodes is particularly prominent. These electrolytes cannot form a stable, highly ionicly conductive interface layer on the magnesium anode surface. Instead, they generate non-conductive oxide or carbonate deposits during cycling. These deposits continuously hinder the insertion, extraction, and transport of magnesium ions, directly causing a significant increase in electrolyte overpotential (usually exceeding 1V). Furthermore, as the number of cycles increases, the passivation layer thickens, ultimately leading to a significant reduction in battery cycle life. To address the technical problems of the prior art, this invention proposes an improved concept to achieve performance breakthroughs by optimizing electrolyte components. Starting from three dimensions—magnesium ion source, solvent ligand, and interface modifier—it considers that magnesium salts, as the core magnesium ion supplier in the electrolyte, directly affect ionic conductivity due to their type and dissociation ability. Imidazole compounds, due to their conjugated cyclic structure, possess excellent thermal stability and solvation ability, serving as a stable solvent framework at high temperatures. Amine compounds, due to their amino groups, can form strong coordination with magnesium ions, exhibiting strong adsorption and regulating the interfacial tension between the electrolyte and the magnesium anode, potentially alleviating anode passivation. Therefore, this invention, by screening specific magnesium salts, imidazoles, and amine components, utilizes an in-situ one-pot reaction to allow the three to form a synergistic effect during preparation. This avoids the limitations of single-component performance and optimizes the electrolyte's thermal stability, ion transport efficiency, and interfacial compatibility through component interactions, ultimately achieving the goals of widening the electrolyte's application temperature range, improving thermal stability, and enhancing cycle stability. In subsequent component screening and experimental verification, this invention further discovered that when using magnesium salts with high dissociation degrees, such as magnesium bis(trifluoromethanesulfonyl)imide, imidazole compounds with stable spatial structures, such as 1,2-dimethylimidazolium, and amine additives containing functional groups, such as 2-methoxyethylamine, the three can form a homogeneous and stable organic deep eutectic system through in-situ one-pot reaction. The resulting new electrolyte exhibits performance far exceeding expectations: its thermal stability is not only reflected in its ability to achieve stable cycling at a high temperature of 80℃, but also in its ability to maintain stable viscosity and ionic conductivity over a wide temperature range, without exhibiting the low-temperature solidification or high-temperature decomposition phenomena of traditional electrolytes; simultaneously, the electrolyte also has ultra-low circulation... The overpotential (below 35mV at room temperature and below 25mV at 80℃) effectively reduces energy loss during battery charging and discharging, avoids local overheating caused by excessive overpotential, and thus ensures that the rechargeable magnesium-ion battery maintains a stable output voltage and capacity during hundreds of hours of continuous operation. More surprisingly, when this electrolyte is used to assemble Mg|DMSA|Mo6S8 full cells, it not only achieves more than 1,000 stable cycles under 5C high-rate charge and discharge conditions, but also exhibits a slow capacity decay rate during the cycle and ultimately maintains a high proportion of the initial capacity, fully verifying the application potential of this electrolyte in high-rate, long-life magnesium-ion batteries.

[0025] In some embodiments of the present invention, the magnesium salt is magnesium bis(TFSI)2 trifluoromethanesulfonylimide (Mg(TFSI)2); the imidazole is 1,2-dimethylimidazole (DMIm); and the amine is one of 2-(methylthio)ethylamine, 3-methoxypropylamine, 1-methoxypropyl-2-amine, 3-isopropoxypropylamine, and 2-methoxyethylamine. The present invention has found that by selecting these types of magnesium salts, imidazoles, and amines, magnesium bis(TFSI)2 trifluoromethanesulfonylimide (Mg(TFSI)2) and 1,2-dimethylimidazole can form a deep eutectic solution; simultaneously, the amine and imidazole engage in a strong bis(strong) coordination competition for Mg. 2+ Reduced Mg 2+ The desolvation process significantly reduces the overpotential and improves ionic conductivity. Furthermore, imidazoles and amines can form a robust organic-inorganic composite SEI layer on the magnesium anode surface, promoting the cycle stability of the battery.

[0026] In some embodiments of the present invention, the molar ratio of magnesium bis(trifluoromethanesulfonylimide) (Mg(TFSI)2) to the organic imidazole 1,2-dimethylimidazole (DMIm) is 1:(4-30). Imidazole, as a solvent ligand in the magnesium electrolyte, plays a crucial role in providing a thermally stable environment through its conjugated cyclic structure and promoting the dissociation of magnesium salts through solvation. If the proportion of magnesium salt is too low, it will lead to... 2+Insufficient ion concentration leads to a significant decrease in ion conductivity, an increase in battery internal resistance, and exacerbated energy loss during charging and discharging, potentially failing to meet the basic conductivity requirements of rechargeable magnesium-ion batteries. On the other hand, a relative excess of imidazole increases the system viscosity, as the enhanced intermolecular forces of excess imidazole hinder the absorption of magnesium... 2+ The high migration rate of magnesium salts not only increases the overpotential during cycling but also hinders ion migration, leading to accelerated capacity decay at high-rate cycles and making stable cycling difficult. However, if the magnesium salt content is too high, it will exceed the solubility and coordination capacity of imidazole. Undissociated magnesium salts will precipitate as solid particles, resulting in an inhomogeneous electrolyte system, preventing the formation of a uniform deep eutectic structure, and potentially clogging electrode pores, interrupting ion transport pathways and significantly shortening cycle life. Simultaneously, excessive magnesium salts will disrupt the charge balance of the system, making the magnesium anode surface susceptible to localized Mg deposition. 2+ Excessive concentration can lead to irregular deposits, exacerbating anodic passivation, causing a sharp increase in overpotential, and even making it impossible to achieve stable cycling over extended periods. Simultaneously, undissolved magnesium salts at high temperatures may accelerate electrolyte decomposition, undermining the electrolyte's thermal stability advantage in high-temperature environments. Therefore, in this electrolyte, the molar ratio of magnesium bis(TFSI)2-trifluoromethanesulfonylimide (Mg(TFSI)2) to 1,2-dimethylimidazole (DMIm) can be 1:4, 1:8, 1:12, 1:16, 1:20, 1:24, 1:28, 1:30, etc., as well as all ranges and sub-ranges between these values. It should be understood that, in the implementation scheme, any of the above ranges can be combined with any other range.

[0027] In some embodiments of the present invention, the molar ratio of magnesium bis(TFSI)2 bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2) to the amine is (1:8) to (3:1). A molar ratio below this range leads to passivation of the magnesium anode surface and difficulty in desolvating magnesium ions, resulting in decreased stability of the magnesium-ion battery. Conversely, a molar ratio above this range decreases electrolyte stability, making it prone to decomposition and reducing the voltage window. Therefore, the molar ratio of magnesium bis(TFSI)2 bis(trifluoromethanesulfonyl)imide (Mg(TFSI)2) to the amine is 3:1, 3:2, 1:1, 1:2, 1:4, 1:6, 1:8, etc., as well as all ranges and sub-ranges between these values. It should be understood that, in embodiments, any of the above ranges can be combined with any other range.

[0028] II. A method for preparing an organic deep eutectic high-temperature magnesium electrolyte with ultra-low overpotential Step 1: Mix solid magnesium salt and solid imidazole at 80°C to obtain a clear solution; Step 2: Add an amine reagent to the mixed solution obtained in Step 1, mix and stir to obtain the electrolyte.

[0029] In some embodiments of the present invention, the molar ratio of magnesium salt to imidazole is 1:(4-30), and the molar ratio of magnesium salt to amine additive is (1:8) to (3:1).

[0030] In some embodiments of the present invention, the magnesium salt is magnesium bis(trifluoromethanesulfonyl)imide, the imidazole is 1,2-dimethylimidazole, and the amine is selected from one of 2-(methylthio)ethylamine, 3-methoxypropylamine, 1-methoxypropyl-2-amine, 3-isopropoxypropylamine, and 2-methoxyethylamine.

[0031] In some embodiments of the present invention, steps 1 and 2 are performed under an inert gas atmosphere. The protection of the inert gas atmosphere prevents oxygen from entering the electrolyte, thereby protecting the magnesium anode from oxidation and also maintaining the stability of the electrolyte.

[0032] In some embodiments of the present invention, the water content and oxygen content in the mixed solution system are both less than 0.01 ppm, thereby eliminating side reactions of water and oxygen in the system and reducing the generation of by-products.

[0033] In some embodiments of the present invention, the magnesium salt is pretreated as follows: The magnesium salt is vacuum dried at 40℃~200℃ for at least 24 hours and then sealed for storage to remove water and oxygen from the magnesium salt.

[0034] III. Application of an ultra-low overpotential organic deep eutectic high-temperature magnesium electrolyte The electrolyte described in this invention or the electrolyte obtained by the preparation method described herein is used to prepare rechargeable magnesium-ion batteries.

[0035] IV. A magnesium-ion battery containing an organic deep eutectic high-temperature magnesium electrolyte with ultra-low overpotential The magnesium-ion battery of the present invention contains the above-mentioned electrolyte.

[0036] V. Examples and Comparative Examples Example 1 Step 1: Pretreatment of magnesium salt electrolyte: After being vacuum dried at 80°C for 24 hours, magnesium bis(trifluoromethanesulfonyl)imide is placed in a glove box and sealed for storage.

[0037] Step 2: Preparation of the electrolyte: All reactions were carried out under an anhydrous and oxygen-free inert atmosphere. Take 0.650 g of 1,2-2-methylimidazole and 0.175 g of magnesium bis(trifluoromethanesulfonyl)imide, and stir at 80°C for 30 min. Then, after stirring, add 165 μl of 2-methoxyethylamine at room temperature and stir for 24 hours to obtain the electrolyte.

[0038] Example 2 This is an improvement on Example 1, except that the amine used is 3-methoxypropylamine. All other steps are exactly the same as in Example 1.

[0039] Example 3 This is an improvement on Example 1, except that the amine used is 1-methoxypropyl-2-amine. All other steps are exactly the same as in Example 1.

[0040] Example 4 The improvement on Example 1 is as follows: 0.650 g of 1,2-2-methylimidazole and 0.125 g of magnesium bis(trifluoromethanesulfonyl)imide are used. All other steps are exactly the same as in Example 1.

[0041] Example 5 This is an improvement on Example 1, except that 120 μl of 2-methoxyethylamine is added. All other steps are exactly the same as in Example 1.

[0042] Comparative Example 1 This is an improvement on Example 1, except that the magnesium salt used is 0.175g of magnesium chloride. All other steps are exactly the same as in Example 1.

[0043] Comparative Example 2 This is an improvement on Example 1, except that 0.650g imidazole is replaced with 0.75ml DME. All other steps are exactly the same as in Example 1.

[0044] Comparative Example 3 This is an improvement on Example 1, except that the magnesium salt used is 0.175 g magnesium ethoxide. All other steps are exactly the same as in Example 1.

[0045] Comparative Example 4 This is an improvement on Example 1, except that the amine is replaced with 165 μl of tetrahydrofuran. All other steps are exactly the same as in Example 1.

[0046] V. Performance Description (1) Overpotential test and performance comparison of magnesium symmetric cells at 80℃ during long-cycle operation: Long-cycle testing of the magnesium symmetric battery with electrolyte was conducted using constant current charge-discharge. The test was performed using assembled CR2032 coin cells, with both the positive and negative electrodes being magnesium sheets and the separator being a glass fiber membrane (GF / A). The charge-discharge test duration was 30 min, and the current density was 0.1 mA / cm². 2 .

[0047] Taking Example 1 as an example, the results obtained by comparing it with the comparative example through the above test method are as follows: Example 1: Electrolyte at 80°C, 0.1 mA / cm 2 The average overpotential after 400 cycles at a current density is 25mV. Figure 1 As shown.

[0048] from Figure 1 It can be seen that: First, overpotential is the difference between the actual charge / discharge potential and the battery equilibrium potential, reflecting the degree of polarization of the electrode reaction. Figure 1 For most of the time, the potential was close to 0V, with an average overpotential of 25mV. This indicates that the deposition / dissolution reaction polarization of the magnesium electrode under this electrolyte is minimal, resulting in excellent electrochemical kinetic performance. Secondly, the horizontal axis spans 400 hours (corresponding to 400 charge-discharge cycles). The potential showed almost no fluctuation in the early stages, indicating long-term stability of the battery interface and the absence of potential abrupt changes caused by magnesium dendrite growth, battery short circuits, or accumulation of interfacial side reactions. While the potential changed in the later stages, it exhibited a gradual trend without sudden failure, demonstrating that the compatibility between the electrolyte and the magnesium electrode remains intact under 80℃ high temperature and long-term cycling, demonstrating outstanding cycle stability. Thirdly, at 80℃ high temperature and 0.1 mA / cm², the potential remained stable. 2 Under current density conditions, the battery still exhibits low overpotential and long cycle stability, indicating that the electrolyte described in this invention has good ionic conductivity and interfacial stability at higher temperatures, effectively supporting the reversible reaction of the magnesium electrode and providing performance assurance for the application of magnesium batteries under harsh conditions. Therefore, the electrolyte of Example 1 demonstrates advantages such as low polarization, long cycle life, and strong high-temperature adaptability in magnesium symmetrical batteries, making it a high-performance magnesium battery electrolyte.

[0049] The relevant electrochemical performance of the comparative examples and Example 1 is shown in the table below. The electrolytes of Comparative Examples 1-4 at 80°C showed a performance of 0.1 mA / cm². 2 The average overpotential after 400 cycles at a current density exceeding 25 mV or a short circuit indicates that the electrolytes in Comparative Examples 1-4 may suffer from severe passivation or decomposition. In contrast, the electrolyte in Example 1, at 80°C and 0.1 mA / cm², showed a similar overpotential. 2 The average overpotential after 300 cycles at the current density is 25mV. For example... Figure 1 As shown.

[0050] Table 1 Performance items overpotential Example 1 25 mV Comparative Example 1 499 mV Comparative Example 2 Short circuit Comparative Example 3 891 mV Comparative Example 4 393 mV It is evident that Example 1 outperforms the comparative example in all aspects.

[0051] (2) Stability test of magnesium deposition / dissolution oxidation The electrolyte prepared in Example 1 was tested for magnesium reversible deposition / dissolution coulombic efficiency and oxidative stability using linear voltammetry (LSV). The tests were conducted using assembled CR2032 coin cells, with a stainless steel (SS) positive electrode current collector, a magnesium sheet negative electrode, and a glass fiber membrane separator. The LSV voltage range was from open-circuit voltage to 4.6 V, and the scan rate was 25 mV / s.

[0052] The electrochemically stable potentials of the electrolyte prepared in Example 1 on stainless steel (SS), molybdenum foil (Mo), aluminum foil (Al), carbon paper (C), and copper foil (Cu) were 3.13 V, 3.56 V, 3.53 V, 3.22 V, and 1.73 V, respectively. (The results are as follows...) Figure 2 As shown. From Figure 2 As can be seen from the LSV curve, the potential point where the current rises sharply corresponds to the oxidation decomposition initiation potential (i.e., electrochemical stability potential) of the electrolyte. A higher potential indicates stronger oxidation stability of the electrolyte on the current collector, which is beneficial for enabling the full cell to operate at higher voltages. Different current collectors exhibit different oxidation stabilities in the electrolyte of this invention. Copper foil (Cu) shows a sharp current rise at 1.73V, the lowest oxidation stability potential among all materials, indicating that the electrolyte readily undergoes oxidation decomposition on Cu and is unsuitable as the positive electrode current collector for this electrolyte system. Stainless steel (SS) has an oxidation stability potential of 3.13V, after which the current rises rapidly, indicating moderate oxidation stability. Carbon paper (C) has an oxidation stability potential of 3.22V, slightly higher than stainless steel, indicating moderate oxidation stability. Aluminum foil (Al) has an oxidation stability potential of 3.53V, with a significantly delayed current abrupt change, indicating good oxidation stability. Molybdenum foil (Mo) has an oxidation stability potential of 3.56V, the highest among all tested materials, indicating that the electrolyte exhibits optimal oxidation stability on Mo and can withstand higher positive electrode potentials. In existing magnesium-ion batteries, mainstream current collectors include aluminum foil (Al), stainless steel (SS), carbon materials (such as carbon paper and graphite), and molybdenum foil (Mo); while copper foil (Cu) is not a mainstream choice in magnesium-ion batteries due to the deposition behavior of magnesium on copper and its oxidation stability issues, resulting in limited application. The LSV test results of Example 1 show that aluminum foil (3.53V), molybdenum foil (3.56V), stainless steel (3.13V), and carbon paper (3.22V) all exhibit high oxidation stability potentials. The electrolyte described herein is compatible with the application scenarios of these current collectors in magnesium-ion batteries, therefore, the electrolyte is suitable for most magnesium-ion batteries.

[0053] (3) Long-cycle performance of Mg||Mg symmetric cells at room temperature The reversible deposition / dissolution performance and coulombic efficiency of the electrolyte prepared in Example 1 were tested using a constant current charge-discharge method. 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 charge-discharge test lasted 30 min at a current density of 0.1 mA / cm². 2 .

[0054] The electrolyte prepared in Example 1, when used in practical applications at 25°C and a current density of 0.1 mA / cm², performs well. 2 Under certain conditions, Mg||Mg can be stably cycled for 1200 hours with an overpotential of less than 35mV, such as Figure 3 As shown.

[0055] Figure 3 The electrolyte of Example 1 was demonstrated at 25°C and 0.1 mA / cm². 2 The constant current charge-discharge cycle performance of the Mg||Mg symmetric battery at the specified current density is shown in the graph. The horizontal axis represents a time period of up to 1200 hours, corresponding to a large number of charge-discharge cycles. Throughout this process, the curve exhibits continuous and stable periodic potential fluctuations without significant potential abrupt changes or decay. This indicates that the deposition / dissolution reaction of the magnesium electrode in the electrolyte possesses ultra-long cycle stability and can maintain reversible electrochemical behavior over a long period. The overpotential (the difference between the actual charge / discharge potential and the equilibrium potential) reflects the degree of polarization of the electrode reaction. Figure 3 The minimal fluctuations in the mid-potential and the overpotential of less than 35mV indicate extremely low polarization of magnesium during deposition / dissolution, resulting in excellent electrochemical kinetics performance. Three magnified images further clearly show the charge-discharge curves at different time points, all exhibiting regular, symmetrical, periodic waveforms. This demonstrates the strong reversibility of magnesium deposition / dissolution, with no significant side reactions or potential distortion caused by dendrite growth. The interface between the electrolyte and the magnesium electrode remains stable over a long period, maintaining consistent electrochemical performance even after thousands of cycles. At room temperature (25°C), the electrolyte still supports the magnesium electrode for stable cycling with ultra-long durations and low overpotentials, indicating excellent ionic conductivity and interfacial compatibility at room temperature, making it suitable for practical room-temperature applications. In summary, the electrolyte in Example 1 exhibits advantages such as ultra-long cycle stability, ultra-low overpotential, and excellent abnormal temperature adaptability in magnesium symmetric batteries, making it a high-performance electrolyte capable of supporting reversible deposition / dissolution of magnesium electrodes at room temperature.

[0056] (4) Ionic conductivity and activation energy of the electrolyte In practical applications, the electrolyte prepared in Example 1 was tested for its ionic conductivity at different temperatures, resulting in an activation energy of 0.192 eV. Figure 4 As shown. Figure 4The Arrhenius curve for ionic conductivity (plotted against 1000 / T) is used to analyze the activation energy of ion migration in the electrolyte. The activation energy reflects the energy barrier that ions must overcome to migrate in the electrolyte. The smaller the Ea, the lower the kinetic resistance to ion migration, and the better the ion conduction performance of the electrolyte over a wide temperature range. The activation energy Ea of the electrolyte in Example 1 (DMSA) is 0.192 eV; the activation energy Ea of the comparative electrolyte (DMSI) is 0.271 eV. It can be seen that the activation energy of the electrolyte in Example 1 is significantly lower than that of DMSI, indicating that its energy barrier for ion migration is lower, and ions migrate more smoothly in DMSA. At the same time, a low activation energy means wide temperature adaptability; even at low temperatures, ions can still migrate at a lower energy cost, ensuring the ionic conductivity of the battery under low-temperature conditions and avoiding performance degradation due to a sudden drop in conductivity. The electrolyte in Example 1 also exhibits stable kinetic properties and low ion migration resistance, providing sufficient ion transport dynamics for the reversible deposition / dissolution of the magnesium electrode and the charge / discharge reaction of the battery. This is one of the core foundations for the stable operation of magnesium-ion batteries at different temperatures. In summary, the electrolyte in Example 1 has a lower ion migration activation energy and superior ion conduction kinetics over a wide temperature range, providing crucial support for the adaptability and stable operation of magnesium-ion batteries.

[0057] (5) Full battery charge and discharge test The electrolyte prepared in Example 1 was subjected to a full-cell charge-discharge test using constant current charge-discharge (CP). The test was conducted using a CR2032 coin cell symmetric battery, 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 5C.

[0058] The Mg|DMSA|Mo6S8 full cell stably cycled 1000 times at a high current density of 5C with a capacity retention of up to 65.05%. Figure 5 As shown. Figure 5The cycling performance of the Mg|DMSA|Mo6S8 full cell under 5C high current density and 25℃ conditions was demonstrated. The blue curve shows that the cell maintains approximately 100% capacity almost throughout the cycle, indicating extremely high energy reversibility efficiency during charge and discharge. The charged charge is almost completely discharged, demonstrating excellent reversibility of electrode reactions (magnesium deposition / dissolution and Mo6S8 magnesium intercalation / deintercalation), with virtually no capacity loss due to side reactions. The red curve represents the change in specific capacity during charge and discharge. The initial specific capacity is approximately 60 mAh / g, and it maintains a high capacity retention of 65.05% after 1000 cycles. Even at a high current density of 5C (rapid charge and discharge rates, requiring high battery kinetics and interface stability), the cell still achieves 1000 long cycles with gradual capacity decay, indicating extremely strong cycle stability. The interface between the electrode materials (Mo6S8, magnesium anode) and the electrolyte of Example 1 remains stable under high current and long cycling conditions, without significant dendrite growth, active material shedding, or electrolyte decomposition. In summary, Figure 5 This demonstrates that the Mg|DMSA|Mo6S8 full cell exhibits extremely high charge-discharge reversibility (coulombic efficiency close to 100%) and excellent long-cycle stability (capacity retention rate exceeding 65% after 1000 cycles) under a high current of 5C, fully showcasing the superior performance of the electrolyte in Example 1 in supporting high current and long-cycle high-efficiency operation in the full cell system.

[0059] Examples 2-5, after undergoing the above electrochemical performance tests, showed little difference in performance compared to Example 1. In summary, the electrolyte of this invention exhibits wide temperature range, high high-temperature stability, ultra-low overpotential, long cycle stability, and high ionic conductivity (Mg). 2+ It has the characteristics of low solvation energy.

[0060] 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 organic deep eutectic high-temperature magnesium electrolyte with ultra-low overpotential, characterized in that, The electrolyte is composed of magnesium salt, imidazole and amine additives; the molar ratio of magnesium salt to imidazole is 1:(4-30), and the molar ratio of magnesium salt to amine additives is (1:8)~(3:1). Wherein, the magnesium salt is magnesium bis(trifluoromethanesulfonyl)imide, the imidazole is 1,2-dimethylimidazole, and the amine is selected from one of 2-(methylthio)ethylamine, 3-methoxypropylamine, 1-methoxypropyl-2-amine, 3-isopropoxypropylamine, and 2-methoxyethylamine.

2. A method for preparing an ultra-low overpotential organic deep eutectic high-temperature magnesium electrolyte, characterized in that, The electrolyte of claim 1 is prepared by the following steps: Step 1: Mix magnesium salt and imidazole at 80°C to obtain a mixed solution; Step 2: Add amine additives to the mixed solution obtained in Step 1, and mix and stir to obtain the electrolyte.

3. The preparation method according to claim 2, characterized in that, The molar ratio of magnesium salt to imidazole is 1:(4-30), and the molar ratio of magnesium salt to amine additives is (1:8)~(3:1).

4. The preparation method according to claim 3, characterized in that, The magnesium salt is magnesium bis(trifluoromethanesulfonyl)imide, the imidazole is 1,2-dimethylimidazole, and the amine is selected from one of 2-(methylthio)ethylamine, 3-methoxypropylamine, 1-methoxypropyl-2-amine, 3-isopropoxypropylamine, and 2-methoxyethylamine.

5. The preparation method according to claim 2, characterized in that, Steps 1 and 2 are carried out under an inert gas atmosphere.

6. The preparation method according to claim 5, characterized in that, In the mixed solution system, the water content and oxygen content are both less than 0.01 ppm.

7. The preparation method according to claim 2, characterized in that, The magnesium salt was pretreated as follows: The magnesium salt is vacuum dried at 40℃~200℃ for at least 24 hours and then sealed and stored.

8. An application of an ultra-low overpotential organic deep eutectic high-temperature magnesium electrolyte, characterized in that, The electrolyte of claim 1 or the electrolyte obtained by the preparation method of any one of claims 2-7 is used to prepare a rechargeable magnesium-ion battery.

9. A magnesium-ion battery containing an organic deep eutectic high-temperature magnesium electrolyte with ultra-low overpotential, characterized in that, The magnesium-ion battery contains the electrolyte as described in any one of claims 1 to 7.

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