A low-temperature, high-entropy rechargeable magnesium battery electrolyte, its preparation method, and its application.

Abstract

This invention belongs to the field of electrochemical technology, specifically relating to a method for preparing and applying a low-temperature, high-entropy rechargeable magnesium battery electrolyte. The electrolyte comprises a magnesium salt, a low-melting-point solvent, and a strongly coordinating solvent, wherein the quantities of the magnesium salt, the low-melting-point solvent, and the strongly coordinating solvent are X, Y, and Z, respectively, where X+Y+Z≥5, X≥1, Y≥0, and Z≥1; and the mole fractions of the magnesium salt, the low-melting-point solvent, and the strongly coordinating solvent are Xi, Yi, and Zi, respectively, where Xi≥5%, and must satisfy the quantitative description formula for configuration entropy: S config Let S be the configuration entropy, R be the universal gas constant, and S be the configuration entropy. config With an entropy ≥1.5R, this electrolyte exhibits high entropy. The electrolyte provided by this invention demonstrates good electrochemical performance and stability at low temperatures, and its preparation process is simple.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical technology, specifically relating to a method for preparing and applying a low-temperature, high-entropy rechargeable magnesium battery electrolyte. Background Technology

[0002] The development of electrochemical energy storage (EES) technology has driven the widespread adoption of battery-powered electronic devices, enabling a more sustainable and cleaner society. Beyond portable electronic devices, batteries are attracting increasing attention in many emerging fields, such as electric vehicles, grid storage, space exploration, defense applications, and underwater operations. These applications typically operate in harsh environments, demanding higher battery performance, particularly in low-temperature operating ranges; for example, high-altitude or low-latitude environments require operating temperatures of -60°C, while space exploration may require temperatures as low as -100°C.

[0003] Rechargeable magnesium batteries, as an emerging industry in energy storage, have attracted widespread attention from researchers due to their advantages such as low cost, low dendrite formation, and high safety performance. However, due to the effects of extreme low temperatures, batteries are prone to capacity loss, shortened cycle life, and reduced solubility and ionic conductivity. Summary of the Invention

[0004] To address the above problems, this invention increases the diversity of components in the electrolyte to obtain a larger configurational entropy, enabling the electrolyte to form a small-sized, high-diffusivity ion cluster solvation structure. This improves the ionic conductivity of the electrolyte at low temperatures, achieving high deposition and dissolution efficiency. Furthermore, the preparation method is simple and the preparation conditions are mild, which is conducive to large-scale production.

[0005] To achieve the above objectives, the present invention can adopt the following technical solutions:

[0006] This invention provides a low-temperature, high-entropy rechargeable magnesium battery electrolyte, comprising a magnesium salt, a low-melting-point solvent, and a strong coordination solvent. The quantities of the magnesium salt, the low-melting-point solvent, and the strong coordination solvent are X, Y, and Z, respectively, where X+Y+Z≥5, X≥1, Y≥0, and Z≥1. Furthermore, the molar fractions of the magnesium salt, the low-melting-point solvent, and the strong coordination solvent are Xi, Yi, and Zi, respectively, where Xi≥5%. S config S is the configuration entropy. config ≥1.5R, where R is the universal gas constant.

[0007] It should be noted that the electrolyte of this invention mainly contains solvated magnesium ions (SSIP), solvated contact ion pairs (CIP), and anion-solvent-magnesium ion clusters (AGG). The presence of multiple components helps to reduce the order and size of local magnesium ion clusters, lower the freezing point of the electrolyte, and improve the ionic conductivity. At the same time, the diverse solvation structure of the high-entropy electrolyte induces the formation of a uniform, dense, and dispersed organic-inorganic composite SEI film, improving the ion transport kinetics and stability at the magnesium-electrolyte interface. In addition, the introduction of a weakly coordinated low-melting-point solvent can also reduce the desolvation energy barrier of magnesium ion clusters and lower the interfacial ion transport energy barrier.

[0008] It should also be noted that the term "number of components" in this invention refers to the number of different types of the same substance. For example, "X" for magnesium salt means that there are X types of magnesium salts, "Y" for low-melting-point solvents means that there are Y types of low-melting-point solvents, and "Z" for strong-coordination solvents means that there are Y types of strong-coordination solvents. Furthermore, the general gas constant (R) mentioned above is well known in the art, and R = 8.314 JK. -1 ·mol -1 .

[0009] It should also be noted that in this invention, "mole fraction" refers to the percentage of the total molar amount of a certain substance relative to the total molar amount of all components. For example, if the mole fraction of a magnesium salt is Xi and Xi is 30%, it means that the molar amount of the magnesium salt accounts for 30% of the total molar amount of the magnesium salt, the low-melting-point solvent, and the strong-coordination solvent. Similarly, if the mole fraction of a low-melting-point solvent is Yi and Yi is 35%, it means that the molar amount of the low-melting-point solvent accounts for 35% of the total molar amount of the magnesium salt, the low-melting-point solvent, and the strong-coordination solvent. Furthermore, if the mole fraction of a strong-coordination solvent is Zi and Zi is 35%, it means that the molar amount of the strong-coordination solvent accounts for 35% of the total molar amount of the magnesium salt, the low-melting-point solvent, and the strong-coordination solvent.

[0010] It should also be noted that the purpose of using a "low-melting-point solvent" in this invention is to ensure that the magnesium salt is well dispersed in the solvent at low temperatures while preventing the electrolyte from solidifying. Therefore, the "low-melting-point solvent" can be selected according to the required operating temperature, preferably a solvent with a melting point below -40°C or below -60°C. Of course, if the operating temperature is around -20°C, the "low-melting-point solvent" also includes solvents with a melting point below -20°C. In addition, the role of a strong coordination solvent is to improve the solubility of the electrolyte and achieve reversible deposition and dissolution at low temperatures.

[0011] It should also be noted that, regarding the molar fractions of magnesium salt, low-melting-point solvent, and strong coordinating solvent, if two or more of these solvents are selected, the calculation should be based on the sum of the two. Furthermore, when two or more of these solvents are selected, their proportions can be adjusted arbitrarily, but it is necessary to ensure that the sulfur content in the electrolyte is maintained at a certain level. config ≥1.5R; For example, there are two or more magnesium salts, and the molar ratio between the two or more magnesium salts can be the same or different. If there are two or more low-melting-point solvents, the volumes of the two or more low-melting-point solvents can also be the same or different. If there are two or more strong coordination solvents, the volumes of the two or more low-melting-point solvents can also be the same or different.

[0012] It should also be noted that, as mentioned above, the low-temperature high-entropy rechargeable magnesium battery electrolyte of the present invention may or may not include low-melting-point solvents. Furthermore, it is worth noting that since some strong coordination solvents in the present invention may also possess low-melting-point properties and thus belong to the category of low-melting-point solvents, the technical solution of the present invention that does not include low-melting-point solvents does not mean that it does not include strong coordination solvents with low-melting-point properties, but merely that it does not include other low-melting-point solvents that do not possess strong coordination ability. That is, when the strong coordination solvent in the present invention is also a low-melting-point solvent, the technical solution that does not include low-melting-point solvents may still include that strong coordination solvent that is a low-melting-point solvent.

[0013] Specifically, examples are given below: In some specific embodiments, the low-temperature high-entropy rechargeable magnesium battery electrolyte of the present invention may be as follows: it includes a magnesium salt and a strong coordination solvent, wherein the strong coordination solvent also has a low melting point property and belongs to the category of low-melting-point solvents; In some specific embodiments, the low-temperature high-entropy rechargeable magnesium battery electrolyte of the present invention may also be as follows: it includes a magnesium salt and a strong coordination solvent, wherein the strong coordination solvent does not have a low melting point property; In some specific embodiments, the low-temperature high-entropy rechargeable magnesium battery electrolyte of the present invention may also be as follows: it includes a magnesium salt, a low-melting-point solvent, and a strong coordination solvent, wherein the strong coordination solvent may have a low melting point property or may not have a low melting point property, and the low-melting-point solvent is another solvent with a low melting point property that does not have strong coordination ability.

[0014] It should also be noted that, based on the above, when the low-temperature high-entropy rechargeable magnesium battery electrolyte in this invention contains only magnesium salt and a strong coordination solvent, the strong coordination solvent can preferably be a solvent with low melting point properties.

[0015] Preferably, the magnesium salt can be selected from at least one of magnesium hexafluoroisopropylborate, magnesium trifluoroethylborate, magnesium methylborate, magnesium hexafluoroisopropyl, magnesium trifluoroethyl, magnesium perfluorotert-butyl, magnesium bis(hexamethyldisilazon), magnesium bis(trifluoromethanesulfonyl)imide, magnesium trifluoromethanesulfonate, magnesium tri(2,2,2-trifluoroethyl)borate, and magnesium monocarbonodeborane.

[0016] It should be noted that, as described above, the number of components in this invention—magnesium salt, low-melting-point solvent, and strong coordination solvent—must be ≥5, and the number of magnesium salt components, X, must be ≥1. When X is 1, any one of the magnesium salts mentioned above is preferred; when X is 2, any two of the magnesium salts mentioned above are preferred, and so on. Furthermore, when the aforementioned magnesium salts are used in the electrolyte of this invention, the performance of the prepared electrolyte is superior to that of other magnesium salts.

[0017] Preferably, the low-melting-point solvent can be selected from ether solvents. It should be noted that ether solvents have superior chemical stability, low melting point, and high dielectric constant, which can provide a better low-temperature working environment for the electrolyte. Therefore, ether solvents are preferred as the low-melting-point solvent in this invention.

[0018] Preferably, the ether solvent is selected from at least one of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, 4-methyl-1,3-dioxane, tetrahydropyran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0019] It should be noted that, as mentioned above, the number of components of magnesium salt, low-melting-point solvent, and strong coordination solvent needs to be ≥5, and the number of components of low-melting-point solvent Y can be ≥0. In some specific embodiments, when Y is 1, any one of the above-mentioned ether solvents can be preferred as the low-melting-point solvent; in some specific embodiments, when Y is 2, any two of the above-mentioned ether solvents can be preferred as the low-melting-point solvent, and so on. In addition, when the above-mentioned ether solvents are used as low-melting-point solvents in the electrolyte of the present invention, the performance of the prepared electrolyte is superior to that of other low-melting-point solvents.

[0020] Preferably, the strong coordination solvent can be selected from amine solvents. It should be noted that amine solvents have higher coordination ability than other strong coordination solvents and have better compatibility with magnesium salt electrolytes, especially sulfonic acid magnesium salts.

[0021] Preferably, the amine solvent is selected from at least one of 2-methoxyethylamine, 3-methoxypropylamine, 1-methoxy-2-propylamine and 2-ethoxyethylamine, diaminomethoxymethane, 4-methoxybutylamine, 3-ethoxypropylamine, 3-isopropylpropylamine, 3-butylpropylamine and 2-propoxyethylamine.

[0022] It should be noted that, as described above, the number of components of magnesium salt, low-melting-point solvent, and strong coordination solvent needs to be ≥5, and the number of components of strong coordination solvent Z needs to be ≥1. When Z is 1, any one of the above-mentioned ether solvents can be preferred as the strong coordination solvent; when Z is 2, any two of the above-mentioned amine solvents can be preferred as the strong coordination solvent, and so on. Furthermore, when the above-mentioned amine solvents are used as strong coordination solvents in the electrolyte of this invention, the performance of the prepared electrolyte is superior to that of other strong coordination solvents.

[0023] Another aspect of the present invention provides a method for preparing the low-temperature high-entropy rechargeable magnesium battery electrolyte of the present invention, which includes mixing magnesium salt, low-melting-point solvent and strong coordination solvent, stirring, and obtaining the low-temperature high-entropy rechargeable magnesium battery electrolyte.

[0024] It should be understood that the mixing and stirring in the above preparation method are conventional operations in the art. Furthermore, it should be noted that in this invention, the magnesium salt, low-melting-point solvent, and strong coordination solvent can be mixed at room temperature, without requiring stringent mixing conditions, which is beneficial for the large-scale production of the low-temperature, high-entropy rechargeable magnesium battery electrolyte of this invention.

[0025] Preferably, the entire preparation process is carried out under an inert atmosphere, where the water and oxygen content is below 0.01 ppm. Specifically, to prevent the raw materials from reacting with oxygen and water during the reaction, the raw materials can be placed in an inert atmosphere with a water and oxygen content below 0.01 ppm for the reaction.

[0026] Preferably, the stirring described above may include magnetic stirring for 12-24 hours. It should be noted that the purpose of stirring in this invention is to ensure more thorough mixing. The stirring method can be any method known in the art, such as using a mixer or magnetic stirring. In this invention, magnetic stirring for 12-24 hours is preferred, for example, 15 hours, 17 hours, 19 hours, 21 hours, or 23 hours. A stirring time of less than 12 hours results in an insufficient reaction, while a stirring time of more than 24 hours leads to unnecessary energy loss when the reaction is already sufficiently complete.

[0027] Preferably, the above preparation method further includes pretreating the low-melting-point solvent and the strong coordination solvent respectively. The pretreatment method includes: mixing the low-melting-point solvent or the strong coordination solvent with sodium, redistilling under an inert atmosphere, adding 4A molecular sieve activated at a high temperature of 300℃-400℃ to the distilled solvent, sealing and storing under an inert atmosphere.

[0028] Another aspect of the present invention provides a low-temperature rechargeable magnesium battery, which includes the low-temperature high-entropy rechargeable magnesium battery electrolyte of the present invention.

[0029] Specifically, the low-temperature, high-entropy rechargeable magnesium battery electrolyte of this invention, combined with magnesium battery positive and negative electrode materials, can be assembled into a battery with excellent electrical performance. It should be noted that the magnesium battery positive electrode material is a material known in the art, and the negative electrode material is a material known in the art, such as magnesium foil or magnesium alloy.

[0030] The beneficial effects of this invention include at least the following:

[0031] (1) The low-temperature high-entropy rechargeable magnesium battery electrolyte provided by the present invention has the unique property of high entropy, which allows the electrolyte to remain liquid at extremely low temperatures, providing a good environment for the electrolyte to work at low temperatures;

[0032] (2) The low-temperature high-entropy rechargeable magnesium battery electrolyte provided by the present invention has an oxidation stability potential of up to 4.82V on SS at temperatures of -20℃ and -40℃, indicating that its oxidation stability at low temperatures is still very high.

[0033] (3) The low-temperature high-entropy rechargeable magnesium battery electrolyte provided by the present invention still maintains an ionic conductivity of more than 1 mS / cm at -60℃, and the ionic conductivity at -40℃ can still reach more than 2.27 mS / cm, indicating that it can still provide sufficient transport dynamics at low temperature and meet the requirements for use of low-temperature rechargeable magnesium battery electrolyte.

[0034] (4) The low-temperature high-entropy rechargeable magnesium battery electrolyte provided by the present invention can still reversibly deposit and dissolve magnesium at -40°C using stainless steel SS as the working electrode;

[0035] (5) The low-temperature high-entropy rechargeable magnesium battery electrolyte provided by the present invention gradually increases the coulombic efficiency of magnesium reversible deposition and dissolution on a stainless steel SS substrate at -40℃. The coulombic efficiency of the first cycle reaches 89.19%, and the average coulombic efficiency after 1600 stable cycles is 99.80%.

[0036] (6) The polarization performance test of Mg / Mg assembled based on the low-temperature high-entropy rechargeable magnesium battery electrolyte provided by the present invention at -40℃ shows that at a current density of 1.0 mA·cm -2 1.0mAh·cm -2 When the battery is stably cycled for 2000 hours, the polarization potential does not increase significantly, and the overpotential is 603mV; this indicates that the electrolyte in this invention still has excellent stability for magnesium under low temperature and high current.

[0037] (7) The coulombic efficiency test results of the low temperature high entropy rechargeable magnesium battery electrolyte provided by the present invention on a stainless steel working electrode at -60℃ showed that the coulombic efficiency of magnesium reversible deposition and dissolution gradually increased. The coulombic efficiency of the first cycle reached 87.72%, and increased to 97.17% after 10 cycles. The average coulombic efficiency after 400 cycles was 98.38%.

[0038] (8) The low-temperature high-entropy rechargeable magnesium battery electrolyte provided by the present invention can be prepared by simply mixing and dissolving magnesium salt, low-melting-point solvent and strong coordination solvent. The preparation method is simple and the preparation conditions are mild, which is conducive to large-scale production. Attached Figure Description

[0039] Figure 1 Differential scanning calorimetry curves of the electrolytes prepared in Examples 1 and 2 of this invention;

[0040] Figure 2 The linear sweep voltammetry curves of the electrolyte prepared in Example 1 of this invention at -20°C and -40°C, with stainless steel foil as the working electrode;

[0041] Figure 3 The ionic conductivity of the electrolyte prepared in Example 1 of this invention was tested at different temperatures.

[0042] Figure 4 The cyclic voltammetry curve of the electrolyte prepared in Example 1 of this invention at -40°C with stainless steel foil as the working electrode;

[0043] Figure 5 The electrolyte prepared in Example 1 of this invention uses stainless steel foil as the working electrode at 0.5 mA·cm. -2 Coulombic efficiency of reversible magnesium deposition / dissolution at -40°C under current density;

[0044] Figure 6 The Mg / Mg symmetric battery assembled with the electrolyte prepared in Example 1 of this invention operates at 1.0 mA·cm⁻¹. -2 Polarization performance curves at -40℃ under current density;

[0045] Figure 7 The electrolyte prepared in Example 1 of this invention uses stainless steel foil as the working electrode at 0.5 mA·cm. -2 Coulombic efficiency of reversible magnesium deposition / dissolution at -60°C under current density;

[0046] Figure 8 The electrolyte prepared in Example 2 of this invention uses stainless steel foil as the working electrode at 0.5 mA·cm. -2 Coulombic efficiency of reversible magnesium deposition / dissolution at -60°C under current density;

[0047] Figure 9 The electrolyte prepared in Example 3 of this invention uses stainless steel foil as the working electrode at 0.5 mA·cm. -2 Coulombic efficiency of reversible magnesium deposition / dissolution at -60°C under current density;

[0048] Figure 10 The electrolyte prepared in Example 4 of this invention uses stainless steel foil as the working electrode at 0.5 mA·cm. -2 Coulombic efficiency of reversible magnesium deposition / dissolution at -60°C under current density;

[0049] Figure 11 The electrolyte prepared in Example 5 of this invention uses stainless steel foil as the working electrode at 0.5 mA·cm. -2 Coulombic efficiency of reversible magnesium deposition / dissolution at -60°C under current density;

[0050] Figure 12 The electrolyte prepared in Example 6 of this invention uses stainless steel foil as the working electrode at 0.5 mA·cm. -2 Coulombic efficiency of reversible magnesium deposition / dissolution at -60°C under current density. Detailed Implementation

[0051] The examples are provided to better illustrate the present invention, but are not intended to limit the present invention to the examples. Therefore, non-essential improvements and adjustments to the embodiments made by those skilled in the art based on the above-mentioned invention still fall within the scope of protection of the present invention.

[0052] 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 a feature, number, operation, material, or combination 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, materials, or combinations thereof may be present or added. As used herein, “ / ” may be interpreted as “and” or “or,” depending on the context.

[0053] 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.

[0054] I. Electrolyte Preparation

[0055] Example 1

[0056] 0.8706 g of Mg(CF3SO3)2 was dissolved in a reagent bottle containing 1.5 mL of dried ethylene glycol dimethyl ether, 1.5 mL of 1,3-dioxolane, and 1.5 mL of tetrahydrofuran. Then, 0.45 mL of 2-methoxyethylamine and 0.45 mL of 2-ethoxyethylamine were slowly added to the above solution. The mixture was then stirred at 400 r / min at 25 °C for 12 h to obtain the electrolyte.

[0057] In addition, the above solvents are pretreated before use, specifically including: adding 50 mL of the above solvent (single solvent) to a container, adding 1.5 g of metallic sodium, redistilling under an inert atmosphere, and adding sodium that has been activated at 350°C for 15 hours to the distilled solvent. Type of molecular sieve, sealed and stored under an inert atmosphere.

[0058] In addition, all operations were carried out in an argon-filled glove box, with water and oxygen concentrations below 0.01 ppm at room temperature.

[0059] Examples 2 to 6

[0060] The electrolyte was prepared according to the magnesium salt, low-melting-point solvent and strong coordination solvent shown in Table 1 below, and the other steps were the same as in Example 1.

[0061] Table 1. Raw materials used in the preparation of electrolytes in Examples 1 to 6.

[0062]

[0063] II. Electrolyte Performance Testing

[0064] In this embodiment of the invention, the reversible magnesium deposition dissolution performance and oxidative stability of the electrolyte were obtained by cyclic voltammetry and linear sweep voltammetry, respectively. Specifically, a two-electrode system was used, with a 12mm magnesium sheet electrode as the reference electrode and counter electrode, and a 16mm stainless steel foil (SS) current collector electrode as the working electrode. For cyclic voltammetry, the potential range during testing was -1V to 2V, the scan rate was 25mV / s, and the scan was performed from the negative direction of the open-circuit voltage. For linear sweep voltammetry, the potential range during testing was approximately 5.5V open-circuit voltage, the scan rate was 1mV / s, and the test temperatures were -20℃, -40℃, and -60℃. Furthermore, all electrodes were sequentially cleaned three times with alternating ethanol and deionized water to thoroughly remove impurities from the entire electrode surface. After vacuum drying for 12 hours, the cleaned electrodes were placed in a glove box for later use.

[0065] In this embodiment of the invention, the deposition-dissolution cycle efficiency and charge-discharge characteristics of magnesium in the electrolyte were tested by assembling a CR2032 coin cell. Specifically, the assembly was carried out in an inert atmosphere glove box with water and oxygen content both less than 0.01 ppm; the working electrode was polished stainless steel foil (SS), and the counter and reference electrodes were made of polished magnesium sheets; the separator was a GF / A membrane; the CR2032 coin cell was assembled together with the electrolyte of this invention; after assembly, the cell was allowed to stand at room temperature for 12 hours before measurement; the entire test was conducted on a Newway charge-discharge testing system; during discharge, an electrochemical deposition reaction of magnesium occurred on the working electrode, with a current density of 0.1 mA·cm⁻¹. -2 -1.0mA·cm -2 The discharge process is time-controlled (1 hour); the charging process corresponds to the dissolution reaction of magnesium deposited on the working electrode, with a current density of 0.1 mA·cm⁻¹. -2 -1.0mA·cm -2 Voltage control is employed (charging to 1.2V vs. Mg RE).

[0066] In this embodiment of the invention, the cycling and rate polarization performance of magnesium in the electrolyte were tested by assembling CR2032 coin cells. Specifically, the assembly was carried out in an inert atmosphere glove box with water and oxygen content both less than 0.01 ppm; polished magnesium sheets (12 mm) were used for the counter and reference electrodes, and a GF / A membrane was used for the separator, all assembled with a self-made electrolyte to form a CR2032 coin cell; after assembly, the cell was allowed to stand at room temperature for 12 hours before measurement; the entire testing process was conducted on a Newway charge-discharge testing system; during discharge, an electrochemical deposition reaction of magnesium occurred on the working electrode, with a current density of 0.1 mA·cm⁻¹. -2 -3.0mA·cm -2 The discharge process is time-controlled (30 min discharge); the charging process corresponds to the dissolution reaction of magnesium deposited on the working electrode, with a current density of 0.1 mA·cm⁻¹. -2 -3.0mA·cm -2 It uses time control (charging for 30 minutes).

[0067] (1) Differential Scanning Calorimetry (DSC)

[0068] Differential scanning calorimetry (DSC) was performed on the electrolytes prepared in Examples 1 and 2 above. The test conditions were as follows: ① Cooling from 25℃ to -100℃ at a cooling rate of 1℃ / min; ② Holding at -100℃ for 5 minutes; ③ Heating from -100℃ to 60℃ at a heating rate of 5℃ / min. The results are as follows: Figure 1As shown, the results indicate that the unique property of high entropy allows the electrolyte to remain liquid at extremely low temperatures, providing a favorable environment for the electrolyte to operate at low temperatures.

[0069] (2) Oxidation stability potential (vs. Mg / Mg) 2+ )

[0070] The oxidation stability potential (vs. Mg / Mg) of the electrolyte prepared in Example 1 was tested at -20°C and -40°C on a stainless steel working electrode using the above test method. 2+ The test results are as follows: Figure 2 As shown in the figure, the results show that the electrolyte prepared in Example 1 has an oxidation stability potential of up to 4.82V on SS, indicating that the electrolyte has high oxidation stability and can meet the requirements for use.

[0071] (3) Ionic conductivity test (mS / cm)

[0072] The ionic conductivity (mS / cm) of the electrolyte prepared in Example 1 was tested on a stainless steel working electrode at temperatures of 25°C, 0°C, -20°C, -40°C, and -60°C using the above testing method. The test results are as follows: Figure 3 As shown, the results indicate that the electrolyte prepared in Example 1 still maintains an ionic conductivity of 1.24 mS / cm at -60°C, indicating that the electrolyte can provide sufficient transport kinetics to meet the requirements for use as an electrolyte in low-temperature rechargeable magnesium batteries.

[0073] (4) Reversible magnesium deposition and dissolution properties

[0074] The reversible magnesium deposition and dissolution performance of the electrolyte prepared in Example 1 was tested at -40°C on a stainless steel working electrode using the above test method. The test results are as follows: Figure 4 As shown, the results indicate that, using stainless steel SS as the working electrode, the electrolyte prepared in this invention can reversibly deposit and dissolve magnesium at -40°C.

[0075] (5) Coulomb efficiency test at -40℃

[0076] The coulombic efficiency of the electrolyte prepared in Example 1 was tested at -40°C on a stainless steel working electrode using the above test method. The test results are as follows: Figure 5 As shown, the results indicate that the coulombic efficiency of magnesium reversible deposition and dissolution in the electrolyte (on a stainless steel SS substrate) prepared in Example 1 gradually increases, reaching 89.19% in the first cycle and 99.80% after 1600 stable cycles.

[0077] (6) Polarization performance test

[0078] The polarization performance of the Mg / Mg electrolyte assembly prepared in Example 1 was tested at -40℃ using the above testing method. The test results are as follows: Figure 6 As shown, the results indicate that at a current density of 1.0 mA·cm⁻¹, -2 The battery cycled stably for 2000 hours without a significant increase in polarization potential, and the overpotential was 603 mV. The results indicate that the electrolyte still exhibits excellent stability for magnesium under low temperature and high current conditions.

[0079] (7) Coulomb efficiency test at -60℃

[0080] The coulombic efficiency of the electrolytes prepared in Examples 1 to 6 was tested at -60°C on a stainless steel working electrode using the above testing method; the test results of the electrolyte prepared in Example 1 are as follows. Figure 7 As shown, the results indicate that the coulombic efficiency of magnesium reversible deposition dissolution in the electrolyte (on a stainless steel SS substrate) prepared in Example 1 gradually increases, reaching 87.72% in the first cycle, increasing to 97.17% after 10 cycles, and the average coulombic efficiency after 400 cycles is 98.38%.

[0081] In addition, the test results of the electrolytes prepared in Examples 2 to 6 are as follows: Figure 8 , Figure 9 , Figure 10 , Figure 11 and Figure 12 As shown, the results indicate that the electrolytes prepared in Examples 2 to 6 can operate stably for 200 cycles at -60°C, maintaining a coulombic efficiency of 98.1%-98.5% and exhibiting a long lifespan.

[0082] (8) Oxidation stability potential, ionic conductivity and long-cycle performance testing

[0083] The electrolytes prepared in Examples 1 to 6 were tested for oxidation stability potential, ionic conductivity and long-cycle performance at low temperature using the above test methods. The test results are shown in Table 2 below.

[0084] Table 2 Electrochemical performance of the electrolytes prepared in Examples 1 to 6 at low temperatures

[0085]

[0086]

[0087] As can be seen from Table 2 above, the electrolytes prepared in Examples 1 to 6 have high oxidation stability potential, strong ionic conductivity, and good cycle performance at low temperatures, meaning they all have good electrochemical performance at low temperatures.

[0088] 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 low-temperature, high-entropy rechargeable magnesium battery electrolyte, characterized in that, It includes a magnesium salt, a low-melting-point solvent, and a strong coordination solvent, wherein the quantities of the magnesium salt, the low-melting-point solvent, and the strong coordination solvent are X, Y, and Z, respectively, X+Y+Z≥5, X≥1, Y≥0, and Z≥1; and the mole fractions of the magnesium salt, the low-melting-point solvent, and the strong coordination solvent are Xi, Yi, and Zi, respectively, Xi≥5%, and S config S is the configuration entropy. config ≥1.5R, where R is a universal gas constant; the operating temperature of the low-temperature, high-entropy rechargeable magnesium battery electrolyte is as low as -60℃; the low-melting-point solvent is selected from at least one of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, 4-methyl-1,3-dioxane, tetrahydropyran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; the strong coordination solvent is selected from at least one of 2-methoxyethylamine, 3-methoxypropylamine, 1-methoxy-2-propylamine and 2-ethoxyethylamine, diaminomethoxymethane, 4-methoxybutylamine, 3-ethoxypropylamine, 3-isopropylpropylamine, 3-butylpropylamine, and 2-propoxyethylamine.

2. The low-temperature, high-entropy rechargeable magnesium battery electrolyte according to claim 1, characterized in that, The magnesium salt is selected from at least one of magnesium hexafluoroisopropylborate, magnesium tris(2,2,2-trifluoroethyl)borate, magnesium trifluoroethylborate, magnesium methylborate, magnesium hexafluoroisopropyl, magnesium perfluorotert-butyl, magnesium trifluoroethyl, magnesium bis(hexamethyldisilazon), magnesium bis(trifluoromethanesulfonyl)imide, magnesium trifluoromethanesulfonate, and magnesium monocarbonylborane.

3. The method for preparing the low-temperature, high-entropy rechargeable magnesium battery electrolyte according to claim 1 or 2, characterized in that, This involves mixing and stirring magnesium salts, low-melting-point solvents, and strong coordination solvents to prepare a low-temperature, high-entropy rechargeable magnesium battery electrolyte.

4. The method for preparing the low-temperature, high-entropy rechargeable magnesium battery electrolyte according to claim 3, characterized in that, The stirring includes magnetic stirring for 12-24 hours and / or the entire preparation process is carried out under an inert atmosphere, with water and oxygen content below 0.01 ppm.

5. The method for preparing the low-temperature high-entropy rechargeable magnesium battery electrolyte according to claim 3 or 4, characterized in that, The preparation method also includes pretreatment of the low-melting-point solvent and the strong coordination solvent respectively. The pretreatment method includes: mixing the low-melting-point solvent or the strong coordination solvent with sodium, redistilling under an inert atmosphere, adding 4A molecular sieve activated at a high temperature of 300℃-400℃ to the distilled solvent, sealing and storing under an inert atmosphere.

6. A low-temperature rechargeable magnesium battery, characterized in that, Includes the low-temperature, high-entropy rechargeable magnesium battery electrolyte as described in claim 1 or 2.

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