A halogen-free electrolyte for magnesium metal batteries and a preparation method thereof

Abstract

The present invention relates to the field of battery materials, and specifically to a halogen-free electrolyte for magnesium metal batteries and a preparation method thereof. The electrolyte comprises a magnesium salt, an additive, and an organic solvent; the magnesium salt comprises at least one of magnesium bis(trifluoromethanesulfonyl)imide and magnesium trifluoromethanesulfonate; the additive comprises at least one of indole, 3-azaindole, 4-azaindole, 5-azaindole, 6-azaindole, 4-aminoindole, 5-aminoindole, 6-aminoindole, or 7-aminoindole; and the organic solvent comprises ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, or 1,3-dioxane. The preparation method comprises: sequentially adding the magnesium salt and the additive to the organic solvent, stirring the reaction at room temperature for 1 minute to 24 hours, to obtain the halogen-free electrolyte for magnesium metal batteries. The resulting electrolyte exhibits excellent properties, including low overpotential, long life, and a wide electrochemical window, and has promising commercial application prospects.

Description

Technical Field

[0001] The present invention relates to the field of battery materials, and in particular to a halogen-free electrolyte for a magnesium metal battery and a preparation method thereof. Background Art

[0002] Interest in magnesium metal batteries has been growing recently. Compared to lithium, magnesium is more abundant and significantly less expensive. Unlike lithium metal anodes, which are prone to dendrite formation, magnesium anodes are less susceptible to dendrite formation and offer greater air stability and safety. Based on these advantages, magnesium metal batteries are considered a promising energy storage and conversion solution.

[0003] As an important component of the battery, the electrolyte has a significant impact on the battery's performance. However, due to the easy passivation of the magnesium negative electrode and the high Coulomb force of magnesium ions, magnesium metal batteries can easily lead to high overpotentials when using commercial simple salts without adding corrosive halogen additives. This electrolyte cannot be adapted to the positive electrode or may cause solvent decomposition. To solve this problem, some amine or phosphate additives have been developed to reduce the overpotential through chelation, but these additives also face problems such as large addition amounts, high costs, poor lifespan, and incompatibility with some positive electrode materials. Therefore, continuing to develop more low-corrosive additives that can be directly used in commercial salts can broaden the selection of magnesium battery electrolytes, adapt to more positive electrode materials, and thus promote the development of magnesium metal batteries. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the object of the present invention is to provide a halogen-free magnesium metal battery electrolyte that can use commercial simple magnesium salts and has excellent electrochemical properties.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] In a first aspect, the present invention provides a halogen-free electrolyte for a magnesium metal battery, comprising a magnesium salt, an additive, and an organic solvent; the magnesium salt comprises at least one of magnesium bis(trifluoromethanesulfonyl)imide and magnesium trifluoromethanesulfonate; the additive comprises at least one of indole, 3-azaindole, 4-azaindole, 5-azaindole, 6-azaindole, 4-aminoindole, 5-aminoindole, 6-aminoindole, and 7-aminoindole; and the organic solvent comprises ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, or 1,3-dioxane.

[0007] Furthermore, the molar ratio of the magnesium salt, the additive and the organic solvent is 1:0.5~10:10~100.

[0008] Furthermore, the concentration of the magnesium salt in the halogen-free electrolyte is 0.1 mol / L to 0.5 mol / L.

[0009] Furthermore, the mass ratio of the additive to the magnesium salt is 0.1~10:1.

[0010] Furthermore, the additive further includes a dehydrating agent, and the dehydrating agent includes at least one of magnesium powder and dibutyl magnesium.

[0011] Furthermore, the mass ratio of the dehydrating agent to the magnesium salt is 0.1~40:1.

[0012] In a second aspect, the present invention provides a method for preparing a halogen-free electrolyte for a magnesium metal battery, comprising: sequentially adding a magnesium salt and an additive to an organic solvent, stirring the reaction at room temperature for 1 minute to 24 hours, and the resulting solution is the above-mentioned halogen-free electrolyte for a magnesium metal battery.

[0013] Furthermore, the preparation method further comprises: after the stirring reaction is completed, filtering the mixture, and the obtained filtrate is the above-mentioned halogen-free electrolyte for magnesium metal batteries.

[0014] Furthermore, the reaction was stirred under an inert atmosphere, and the water and oxygen contents were both lower than 0.01 ppm.

[0015] The present invention has the following unexpected beneficial effects:

[0016] 1. The halogen-free electrolyte for magnesium metal batteries of the present invention uses commercial magnesium salt, additives and organic solvents as raw materials and has the characteristics of being non-corrosive. 2+ The additive includes at least one of indole, 3-azaindole, 4-azaindole, 5-azaindole, 6-azaindole, 4-aminoindole, 5-aminoindole, 6-aminoindole, and 7-aminoindole, which can reduce the Mg content by optimizing the solvation shell. 2+ The desolvation energy is reduced, thereby lowering the deposition-dissolution overpotential of magnesium metal, inhibiting electrolyte decomposition and enabling the adaptation of cathode materials. The synergistic interaction between the various components gives the electrolyte excellent properties of low overpotential, long life, and a wide electrochemical window, promising promising commercial applications.

[0017] 2. The additives of the present invention also include a dehydrating agent. The use of the dehydrating agent can further reduce the trace water contained in the organic solvent and assist in optimizing the solvation shell.

[0018] 3. The present invention's method for preparing a halogen-free electrolyte for magnesium metal batteries utilizes a one-step in-situ synthesis method. Raw materials are readily available and inexpensive, and the preparation process is simple and easily controllable, making it amenable to large-scale industrial production. The resulting electrolyte exhibits minimal corrosiveness to battery components, enabling magnesium metal batteries to exhibit a low overpotential and a relatively long lifespan without the presence of corrosive substances such as halogens. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 Schematic diagram of the constant current test results of the Mg / Mg symmetrical battery assembled with the electrolyte prepared in Example 1 of the present invention.

[0020] Figure 2 Schematic diagram of the rate test results of the Mg / Mg symmetrical battery assembled with the electrolyte prepared in Example 1 of the present invention.

[0021] Figure 3 Schematic diagram of the electrochemical impedance spectroscopy test results of a Mg / Mg symmetrical battery assembled with the electrolyte prepared in Example 1 of the present invention.

[0022] Figure 4 This is a schematic diagram of the cyclic voltammetry test results of the electrolyte prepared in Example 1 of the present invention using copper foil as the working electrode.

[0023] Figure 5 This is a linear scanning test curve diagram of the electrolyte prepared in Example 2 of the present invention using copper foil, aluminum foil and stainless steel foil as working electrodes.

[0024] Figure 6 This is a discharge curve diagram of the 150th cycle of a full battery assembled with the electrolyte prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0025] The following describes the embodiments of the present invention with reference to the accompanying drawings and preferred embodiments. Those skilled in the art will readily appreciate the other advantages and benefits of the present invention from the disclosure herein. The present invention may also be implemented or applied through various other specific embodiments, and the various details in this specification may be modified or altered based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are intended only to illustrate the present invention and are not intended to limit the scope of protection of the present invention.

[0026] In one embodiment, the present invention provides a halogen-free electrolyte for a magnesium metal battery, comprising a magnesium salt, an additive, and an organic solvent; the magnesium salt comprises at least one of magnesium bis(trifluoromethanesulfonyl)imide and magnesium trifluoromethanesulfonate; the additive comprises at least one of indole, 3-azaindole, 4-azaindole, 5-azaindole, 6-azaindole, 4-aminoindole, 5-aminoindole, 6-aminoindole, and 7-aminoindole; and the organic solvent comprises ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, or 1,3-dioxane.

[0027] First, as one of the main components of the electrolyte, the selection of magnesium salt is crucial to the performance of the battery. In this embodiment, the magnesium salt is at least one of magnesium bis(trifluoromethanesulfonyl)imide and magnesium trifluoromethanesulfonate. These two magnesium salts can well dissociate Mg in a suitable organic solvent. 2+ , thus providing an excellent ion channel for charge transfer within the battery, helping to improve the battery's charge-discharge efficiency and rate performance. Furthermore, its anionic structure is relatively stable, maintaining stability over a wide voltage range and being less susceptible to oxidative decomposition reactions. Therefore, it is compatible with a variety of high-voltage cathode materials, broadening the application range of magnesium batteries and helping to increase their energy density. Furthermore, compared to some other magnesium salts with complex structures, the synthesis routes of magnesium bis(trifluoromethanesulfonyl)imide and magnesium trifluoromethanesulfonate are relatively simple. The synthesis process does not require numerous complex reaction steps or harsh reaction conditions, making them amenable to large-scale industrial production and effectively reducing production costs. The raw materials used to produce these two magnesium salts are relatively common and inexpensive, enabling better cost control during large-scale production, thereby enhancing the competitiveness of magnesium batteries in the market.

[0028] Magnesium bis(trifluoromethanesulfonyl)imide and magnesium trifluoromethanesulfonate do not contain halogen elements, which avoids the current collector corrosion problem caused by the presence of halogens, improves the safety and stability of the battery, and also reduces potential harm to the environment, meeting the development requirements of green chemistry.

[0029] Magnesium bis(trifluoromethanesulfonyl)imide and magnesium trifluoromethanesulfonate are well miscible with common organic solvents such as ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, and triethylene glycol dimethyl ether to form a stable electrolyte system, ensuring the uniformity and stability of the electrolyte and facilitating the normal operation of the battery.

[0030] Secondly, the addition of additives can further improve the performance of the electrolyte. In this embodiment, the additive includes at least one of indole and its derivatives (such as 3-azaindole, 4-azaindole, 5-azaindole, and 6-azaindole) and aminoindole (such as 4-aminoindole, 5-aminoindole, 6-aminoindole, and 7-aminoindole). These additives can optimize the chemical properties of the electrolyte and improve the battery's cycling stability and capacity retention.

[0031] Indole additives can coordinate with magnesium ions to a certain extent, changing the Mg 2+ Solvation state in the electrolyte. For example, they can replace some of the 2+ The coordinated solvent molecules form a more stable and favorable 2 + The solvated structure of the transported 2+ The desolvation barrier promotes Mg 2+ Reversible deposition and dissolution on the electrode surface improve the reversibility of the electrode reaction. By interacting with the active components in the electrolyte, indoles can reduce the activity of the electrolyte, inhibit its oxidative decomposition reaction during the battery charge and discharge process, extend the service life of the electrolyte, and improve the cycle stability of the battery.

[0032] Finally, the choice of organic solvent as a carrier for the electrolyte is also very important. In this embodiment, the organic solvent can be any one of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane, or 1,3-dioxane. These solvents have good solubility and electrochemical stability, and can effectively dissolve magnesium salts and additives to form a uniform electrolyte.

[0033] Organic solvents are excellent solvents for magnesium salts and additives. For example, ether solvents such as ethylene glycol dimethyl ether and diethylene glycol dimethyl ether fully dissolve magnesium salts such as magnesium bis(trifluoromethanesulfonyl)imide and magnesium trifluoromethanesulfonate. This, like salt dissolving in water, creates a uniform electrolyte system, ensuring that magnesium ions are evenly dispersed throughout the electrolyte. Only when magnesium salts are fully dissolved can sufficient, mobile magnesium ions be provided for the battery's charge and discharge processes, ensuring the proper functioning of the battery reaction.

[0034] Organic solvents, as a medium for ion conduction, provide a channel for the migration of magnesium ions. Magnesium ions migrate within the environment formed by organic solvent molecules, moving from the negative electrode to the positive electrode (during the discharge process) or from the positive electrode to the negative electrode (during the charge process). Taking tetraethylene glycol dimethyl ether as an example, its molecular structure can affect the solvation structure of magnesium ions to a certain extent, thereby affecting the migration rate of magnesium ions. Suitable organic solvents can reduce the activation energy of magnesium ion migration, allowing magnesium ions to shuttle through the electrolyte at relatively low energy, helping to improve the battery's charge and discharge efficiency and rate performance.

[0035] These organic solvents can prevent precipitation or stratification of components in the electrolyte. Because magnesium salts and additives have a certain solubility in organic solvents, and the organic solvents themselves have a certain degree of stability, the electrolyte can maintain a stable liquid state over a wide temperature and voltage range. For example, cyclic ether solvents such as 1,3-dioxolane and 1,3-dioxane have relatively stable chemical structures. Under the battery's operating environment, they can maintain the uniformity of the electrolyte system and avoid battery performance degradation caused by local concentration changes.

[0036] Organic solvents can participate in the reaction process on the electrode surface and regulate the interfacial properties between the electrode and the electrolyte. During battery operation, organic solvent molecules may adsorb on the electrode surface, forming an interfacial film. This film protects the electrode, preventing adverse reactions with certain components in the electrolyte, such as corrosion or passivation. For example, ethylene glycol dimethyl ether may interact with magnesium ions on the negative electrode surface of a magnesium metal battery, forming a protective film with excellent ionic conductivity. This facilitates the deposition and dissolution of magnesium ions on the electrode surface and improves the reversibility of the electrode reaction.

[0037] The choice of organic solvent has a significant impact on battery safety. These organic solvents, such as diethylene glycol dimethyl ether, generally have a high flash point and low volatility, which can reduce safety hazards associated with organic solvent volatilization or combustion during battery use. Furthermore, suitable organic solvents can inhibit electrolyte decomposition and side reactions to a certain extent, reducing gassing within the battery, thereby improving battery safety and stability.

[0038] In summary, the halogen-free electrolyte in this embodiment has the characteristics of being non-corrosive by carefully selecting magnesium salts, additives and organic solvents, and has achieved a significant improvement in the performance of magnesium metal batteries. 2+The additive includes at least one of indole, 3-azaindole, 4-azaindole, 5-azaindole, 6-azaindole, 4-aminoindole, 5-aminoindole, 6-aminoindole, and 7-aminoindole, which can reduce the Mg content by optimizing the solvation shell. 2+ The desolvation energy is reduced, thereby lowering the deposition-dissolution overpotential of magnesium metal, inhibiting electrolyte decomposition and enabling the adaptation of cathode materials. The synergistic interaction between the various components gives the electrolyte excellent properties of low overpotential, long life, and a wide electrochemical window, promising promising commercial applications.

[0039] In a preferred embodiment, the molar ratio of the magnesium salt, the additive and the organic solvent is 1:0.5~10:10~100.

[0040] The ratio of magnesium salt is set to ensure that there are enough magnesium ions in the electrolyte to support the charge and discharge process of the battery. If the ratio of magnesium salt is too low, the magnesium ions Mg 2+ Insufficient quantities can limit the battery's capacity because, during discharge, the number of magnesium ions migrating from the negative electrode to the positive electrode decreases, leaving insufficient ions available for reaction. For example, in a magnesium-sulfur battery, if the magnesium ion concentration is too low, the reaction between the positive electrode sulfur and the magnesium ions cannot proceed fully, and the actual battery capacity will be far lower than the theoretical capacity. On the other hand, an excessively high magnesium salt ratio may prevent the magnesium salt from being completely dissolved in the organic solvent, resulting in precipitation and affecting the uniformity and stability of the electrolyte. Furthermore, an excessively high magnesium salt concentration may alter the electrolyte's ionic environment, increasing interactions between ions and hindering the migration of magnesium ions, leading to increased internal resistance of the battery and reduced charge and discharge efficiency.

[0041] The molar ratio of biomass additives to magnesium salts is between 0.5 and 10, and this range is of great significance. An appropriate amount of additives can effectively improve battery performance. When the amount of additives is small, it may not be able to fully play its role in improving the electrode / electrolyte interface and optimizing the solvation structure of magnesium ions. For example, when forming a protective film on the electrode surface, if the amount of additives is insufficient, the protective film may be incomplete and cannot effectively block harmful components in the electrolyte from contacting the electrode, resulting in electrode passivation and corrosion. When the amount of additives is too much, it may interfere with the normal function of the main components of the electrolyte, magnesium salts and organic solvents. For example, too many additives may change the physical properties of the electrolyte, such as viscosity, increase the resistance to magnesium ion migration, or compete with magnesium salts for solvation, making the solvation structure of magnesium ions unfavorable for their deposition and dissolution on the electrode surface, thereby affecting battery performance.

[0042] The molar ratio of organic solvent to magnesium salt is between 10 and 100. A sufficient amount of organic solvent is key to ensuring the full dissolution of the magnesium salt. As a solvent for the magnesium salt and additives, the presence of a large amount of organic solvent can make the electrolyte system more stable. Just as adding more water to a glass of concentrated brine prevents salt crystallization, a large amount of organic solvent can prevent magnesium salt crystallization. Furthermore, a larger amount of organic solvent provides a wider channel and a suitable environment for the migration of magnesium ions. It can adjust the ionic strength and viscosity of the electrolyte, facilitating the diffusion and conduction of magnesium ions. If the amount of organic solvent is too small, the viscosity of the electrolyte may be too high, significantly hindering the migration of magnesium ions, significantly increasing the internal resistance of the battery and deteriorating the charge and discharge performance.

[0043] In a preferred embodiment, the concentration of the magnesium salt in the halogen-free electrolyte is 0.1 mol / L to 0.5 mol / L.

[0044] The lower limit concentration of magnesium salt is set at 0.1 mol / L, which can provide sufficient magnesium ions for magnesium metal batteries to maintain the basic charge and discharge process. During the battery discharge process, magnesium ions migrate from the negative electrode to the positive electrode and participate in the electrochemical reaction of the positive electrode. This concentration can ensure that there is a certain number of magnesium ions to support the battery reaction, so that the battery can produce a stable current output. For example, in a magnesium battery with manganese dioxide as the positive electrode material, magnesium ions need to diffuse into the manganese dioxide lattice for intercalation reaction. A magnesium salt concentration of 0.1 mol / L can ensure the supply of magnesium ions, so that the battery can work normally and produce a certain capacity.

[0045] Furthermore, a lower magnesium salt concentration can reduce the cost of the electrolyte to a certain extent. Because magnesium salt accounts for a relatively small proportion of the electrolyte, the use of expensive magnesium salt materials is reduced. At the same time, a lower concentration helps control the viscosity of the electrolyte. If the magnesium salt concentration is too high, the viscosity of the electrolyte will increase, which will hinder the migration of magnesium ions in the electrolyte and increase the internal resistance of the battery. A concentration of 0.1 mol / L gives the electrolyte a relatively low viscosity, which is conducive to the diffusion of magnesium ions and the rapid charging and discharging of the battery.

[0046] The upper limit of magnesium salt concentration is set at 0.5 mol / L, which can increase the amount of magnesium ions available in the electrolyte. In battery reactions, more magnesium ions means more charge can participate in the reaction under the same electrode materials and reaction conditions, thereby increasing the battery's capacity. For example, in a magnesium-sulfur battery system, a high concentration of magnesium ions can react with more sulfur, bringing the battery's theoretical capacity closer to its actual output capacity and improving the battery's energy density.

[0047] The key to avoiding excessive magnesium salt concentrations is to prevent negative consequences. Excessive magnesium salt concentrations can lead to incomplete dissolution of the magnesium salt in the organic solvent, resulting in precipitation, which can disrupt the uniformity of the electrolyte and affect battery stability and performance. Furthermore, excessive magnesium salt concentrations can enhance interactions between magnesium ions, altering their solvation environment and increasing the difficulty of desolvation. This can hinder their deposition and dissolution on the electrode surface, ultimately reducing the battery's charge and discharge efficiency.

[0048] In a preferred embodiment, the mass ratio of the additive to the magnesium salt is 0.1-10:1.

[0049] The lower limit of the mass ratio of additives to magnesium salts is set at 0.1:1. Although the amount of additives is relatively small, it can still have a certain positive impact on the electrolyte and battery performance. At this relatively low ratio, the battery performance can be initially optimized without increasing the cost of additives too much. Because the amount of additives used is relatively small, costs can be effectively controlled during the large-scale production of battery electrolytes. At the same time, excessive additives will not significantly interfere with the normal function of the magnesium salt, the main component of the electrolyte. For example, the solvation structure of the magnesium ions will not be excessively changed, ensuring the normal migration and reaction of the magnesium ions in the electrolyte.

[0050] The upper limit of the mass ratio of additives to magnesium salts is set at 10:1. The content of additives in the electrolyte is relatively high, which can deeply optimize the battery performance. A high proportion of additives can also give full play to their role in optimizing the solvation structure of magnesium ions and promoting the diffusion of magnesium ions. Additives can fully coordinate with magnesium ions, change the solvation environment of magnesium ions, reduce the desolvation energy barrier of magnesium ions, and make the diffusion of magnesium ions in the electrolyte smoother. At the same time, additives can also adjust the physicochemical properties of the electrolyte, such as lowering the freezing point of the electrolyte, broadening the operating temperature range of the battery, and improving the stability and adaptability of the battery. However, this high ratio also requires attention to the possible negative effects of additives, such as increasing the viscosity of the electrolyte, which may hinder the migration of magnesium ions to a certain extent, and its impact on battery performance needs to be comprehensively considered.

[0051] In a preferred embodiment, the additive further includes a dehydrating agent, and the dehydrating agent includes at least one of magnesium powder and dibutyl magnesium.

[0052] Magnesium powder (Mg) is an effective dehydration agent. In the electrolyte, magnesium powder reacts chemically with water, converting it into magnesium hydroxide precipitate and hydrogen gas. Water in the electrolyte can cause numerous problems, such as reacting with magnesium salts to form insoluble substances or reacting with magnesium metal electrodes, leading to corrosion and passivation. Removing water with magnesium powder effectively reduces these detrimental effects. Removing water improves electrolyte stability. A stable electrolyte environment is crucial for magnesium metal batteries. For example, in an electrolyte containing magnesium bis(trifluoromethanesulfonyl)imide, the presence of water can cause hydrolysis, destroying the structure of the magnesium salt. The presence of magnesium powder prevents this, ensuring a stable magnesium salt composition in the electrolyte and ensuring proper battery operation and stable performance.

[0053] Furthermore, removing water from magnesium powder can indirectly improve battery charge and discharge performance by reducing water interference. Water can increase the battery's internal resistance, reducing its rate capability and cycle life. When magnesium powder is dehydrated, the electrolyte's conductivity is optimized, allowing magnesium ions to migrate more smoothly within the electrolyte and improving battery charge and discharge efficiency.

[0054] Dibutylmagnesium (Mg(C4H9)2) is also an excellent dehydrating agent. It is highly hydrophilic and reacts with water. The magnesium-carbon bond in dibutylmagnesium breaks when it encounters water, combining with hydroxide ions in the water to remove the water. This reaction may be milder than that of magnesium powder and more thoroughly removes trace moisture from the electrolyte. Like magnesium powder, dibutylmagnesium can protect other electrolyte components by removing water. In addition to magnesium salts, additives and organic solvents in the electrolyte may also be affected by water. For example, some organic solvents may miscible or react with water, causing changes in the electrolyte's composition. Dibutylmagnesium prevents this, preserving the electrolyte's original composition and properties.

[0055] Dehydrating dibutylmagnesium helps improve the reaction environment on the electrode surface. Without water interference, the interfacial reaction between the electrode and the electrolyte is more stable and reversible. For example, on the surface of a magnesium metal anode, removing water can reduce the formation of byproducts such as magnesium hydroxide, making the deposition and dissolution of magnesium ions smoother, thereby improving the battery's cycle life and energy efficiency.

[0056] In a preferred embodiment, the mass ratio of the dehydrating agent to the magnesium salt is 0.1-40:1.

[0057] The lower limit of the dehydrator-to-magnesium salt mass ratio is set at 0.1:1. Although the amount of dehydrator is relatively small, it still provides a certain degree of dehydration. Even a small amount of water in the electrolyte can adversely affect battery performance. For example, trace amounts of water may hydrolyze the magnesium salt or trigger side reactions on the electrode surface. This dehydrator ratio can remove some of the water in the electrolyte, ensuring basic electrochemical performance and preventing initial problems such as electrolyte decomposition and electrode corrosion caused by the presence of water.

[0058] A lower desiccant ratio helps control costs. In industrial production, excessive desiccant use can increase production costs. A mass ratio of 0.1:1 achieves a moderate desiccant effect while striking a good balance between cost and performance, avoiding unnecessary cost increases caused by excessive desiccant use.

[0059] The upper limit of the dehydrator-to-magnesium salt mass ratio is set at 40:1, enabling deep dehydration of the electrolyte. For some magnesium metal battery systems that are extremely sensitive to moisture, this high dehydrator ratio ensures that the electrolyte is dehydrated as much as possible. For example, in high-precision experimental cells or battery applications with extremely high performance requirements, even extremely low concentrations of moisture can cause a significant decline in battery performance. In these cases, a high dehydrator ratio can reduce the moisture content in the electrolyte to extremely low levels, ensuring high purity and stability. In some special operating environments or battery material systems, increased moisture may enter the electrolyte or the electrolyte itself may have extremely low tolerance to moisture. For example, in magnesium metal batteries operating in high humidity environments or electrolytes using novel, water-sensitive additives, a high dehydrator ratio can effectively address these situations, preventing moisture from damaging battery performance and ensuring reliable operation and long battery life in complex environments. However, it should be noted that too high a proportion of dehydrating agent may also bring some potential problems. For example, the dehydrating agent itself may affect other properties of the electrolyte, which requires comprehensive consideration and balance.

[0060] In another embodiment, the present invention provides a method for preparing a halogen-free electrolyte for a magnesium metal battery, comprising: sequentially adding a magnesium salt and an additive to an organic solvent, stirring the reaction at room temperature for 1 minute to 24 hours, and obtaining the resulting solution as the halogen-free electrolyte for a magnesium metal battery.

[0061] The preparation method of the present invention selects to add the organic solvent to the reaction system first because the organic solvent plays a key role as a solvent here, which can provide a uniformly dispersed medium environment for the magnesium salt and additives added subsequently. Organic solvents such as ethylene glycol dimethyl ether and diethylene glycol dimethyl ether have good solubility and can fully dissolve the magnesium salt and additives therein, facilitating subsequent reactions and interactions.

[0062] The sequential addition of magnesium salts and additives is based on the consideration that magnesium salts, as a key component for providing magnesium ions, should be dissolved and evenly dispersed in the organic solvent first to better establish a suitable ionic environment in the electrolyte. Additives are then added, allowing them to play a role in the already formed organic solvent system containing magnesium salts, such as optimizing the solvation structure of magnesium ions. For example, the addition of indole additives can interact with the magnesium ions in the dissolved magnesium salts, thereby optimizing the performance of the entire electrolyte.

[0063] Choosing room temperature (typically around 25°C) as the reaction temperature offers several advantages. Firstly, it eliminates the need for additional heating or cooling equipment, making it easy to operate and effectively reducing energy costs, meeting the cost-control requirements of large-scale industrial production. Secondly, at this temperature, most magnesium salts dissolve smoothly in organic solvents and interact with additives, avoiding undesirable issues such as solvent volatilization and magnesium salt decomposition caused by excessively high temperatures, or slow dissolution and reaction difficulties caused by excessively low temperatures. For example, magnesium bis(trifluoromethanesulfonyl)imide dissolves smoothly in ethylene glycol dimethyl ether at room temperature and interacts with subsequent additives, including coordination.

[0064] The lower limit of the stirring reaction time is set at 1 minute: A short stirring reaction time (1 minute) indicates good compatibility and reactivity among the components of the electrolyte system. In such a short time, simple stirring can initially dissolve the magnesium salt in the organic solvent, allowing the additive to interact with the magnesium salt and other components to form an electrolyte with certain performance. This is advantageous for quickly preparing small batches of electrolyte for preliminary performance testing.

[0065] The upper limit of the stirring reaction time is set at 24 hours: The longer stirring reaction time (24 hours) is taken into consideration to ensure that all components are fully and evenly mixed and completely reacted. For some magnesium salts that dissolve relatively slowly or additives that require time to fully exert their effect, a longer stirring reaction time can allow the magnesium salt to completely dissolve, allowing the additive to better integrate into the system and achieve optimal interaction with the magnesium salt, organic solvent, etc., thereby maximizing the performance of the electrolyte. For example, some aminoindole additives may require a longer time to form a stable coordination structure with the magnesium ions in the magnesium salt. A 24-hour stirring reaction can ensure the full formation of this structure, improving the overall quality and performance of the electrolyte.

[0066] Through this preparation method, a halogen-free electrolyte for magnesium metal batteries that meets the requirements can be prepared relatively simply and efficiently, laying a good foundation for the performance of magnesium metal batteries.

[0067] In a preferred embodiment, the preparation method further comprises: after the stirring reaction is completed, filtering the mixture, and the obtained filtrate is the above-mentioned halogen-free electrolyte for magnesium metal batteries.

[0068] While most components dissolve and interact with each other during the sequential addition of magnesium salt and additives to an organic solvent and the subsequent stirring, some insoluble impurities may still form. These include small amounts of unreacted raw material impurities in the magnesium salt raw material, fine particles introduced during storage or transportation, and very small amounts of precipitated matter generated during the reaction due to local variations in reaction conditions. Filtration effectively removes these insoluble impurities, ensuring the purity of the electrolyte and preventing them from adversely affecting the performance of magnesium metal batteries.

[0069] A pure electrolyte helps maintain better stability. If insoluble impurities remain in the electrolyte, they may become "active sites" that trigger side reactions. For example, during the battery's charge and discharge process, impurity particles may adsorb components in the electrolyte, changing the local ion concentration or reaction environment, thereby affecting the migration of magnesium ions and the reaction on the electrode surface, thereby reducing the battery's charge and discharge efficiency and cycle life. The pure filtrate obtained after filtration serves as the electrolyte, ensuring the normal operation of the battery in a more stable state.

[0070] Filtration is a relatively simple and common chemical laboratory operation, easily implemented in both small-scale laboratory preparation of electrolytes and large-scale industrial production. By selecting appropriate filter media, such as filter paper or membranes, targeted filtration can be performed based on the size of impurity particles. For example, for relatively large impurity particles, ordinary filter paper can effectively filter them; for finer impurities, microporous membranes can achieve even better filtration results.

[0071] After filtration, the resulting filtrate, the final halogen-free electrolyte for magnesium metal batteries, exhibits significantly improved quality. The electrolyte exhibits improved transparency and uniformity, allowing magnesium ions to migrate more smoothly within a pure organic solvent environment. The additives can also better optimize the solvation structure of magnesium ions without interference from impurities. This improves the overall performance of magnesium metal batteries, such as reducing internal resistance, increasing charge and discharge efficiency, and extending cycle life, making the prepared electrolyte more compatible with the high-performance operation requirements of magnesium metal batteries.

[0072] In summary, adding the filtration treatment step after the stirring reaction is completed is of great significance for optimizing the quality of the electrolyte and ensuring the good performance of the magnesium metal battery.

[0073] In a preferred embodiment, the stirring reaction is carried out under an inert atmosphere, and the water and oxygen contents are both lower than 0.01 ppm.

[0074] An inert atmosphere can prevent oxidation reactions. During the preparation of magnesium metal battery electrolytes, magnesium salts and additives may undergo oxidation reactions with oxygen. For example, the magnesium ions in magnesium salts have a certain reducing property and may be oxidized in the presence of oxygen, altering the chemical properties of the magnesium salt. Furthermore, some additives, such as indole compounds, may also be oxidized, losing their ability to optimize the solvation structure of magnesium ions. An inert atmosphere, such as argon (Ar) or nitrogen (N2), can effectively prevent these oxidation reactions and ensure the stability of the electrolyte components. Furthermore, an inert atmosphere can inhibit hydrolysis reactions, as water can have a number of adverse effects on electrolyte preparation. Magnesium salts may undergo hydrolysis, especially those containing certain reactive groups. For example, magnesium bis(trifluoromethanesulfonyl)imide can undergo hydrolysis in the presence of water, producing byproducts that affect the quality of the electrolyte. Strictly controlling the water content to below 0.01 ppm in an inert atmosphere can significantly reduce this hydrolysis reaction and ensure the purity and performance of the electrolyte.

[0075] Extremely low water and oxygen content (less than 0.01 ppm) ensures high performance and long life of the electrolyte. Such low water and oxygen content ensures high stability during the preparation process. For magnesium metal batteries, electrolyte stability is directly related to battery performance and life. The electrolyte prepared in this nearly water-free and oxygen-free environment maintains its components in excellent condition. When used in magnesium metal batteries, it can reduce electrode corrosion and passivation, improve the transport efficiency of magnesium ions in the electrolyte, and thus enhance the battery's charge and discharge performance and cycle life.

[0076] Applications requiring extremely high battery performance, such as magnesium metal batteries used in high-performance electronics and electric vehicles, require electrolytes with exceptional purity and stability. This low water and oxygen content preparation method meets these high-precision requirements, making the prepared electrolyte better suited for these high-end applications and providing a more stable and efficient ion transport environment for the battery, thereby improving its overall quality and reliability.

[0077] The following analysis and explanation are combined with specific examples.

[0078] Example 1: A method for preparing a halogen-free electrolyte for magnesium metal batteries, comprising: conducting all reactions under an inert atmosphere, with water and oxygen contents below 0.01 ppm. 29.38 g of magnesium bis(trifluoromethanesulfonyl)imide was dissolved in 100 mL of diethylene glycol dimethyl ether. 13.8 g of 7-aminoindole was then added and allowed to dissolve under magnetic stirring at room temperature for 12 hours. 1 g of magnesium powder was then added, and the mixture was stirred at room temperature for 24 hours. The mixture was filtered, and the resulting filtrate was the halogen-free electrolyte for magnesium metal batteries according to the present invention.

[0079] The conventional electrolyte used as the control group was a solution without 7-aminoindole. This solution consisted of 29.38 g of magnesium bis(trifluoromethanesulfonyl)imide dissolved in 100 mL of diethylene glycol dimethyl ether and allowed to dissolve under magnetic stirring at room temperature for 12 hours. One g of magnesium powder was then added, and the mixture was stirred at room temperature for 24 hours. The resulting filtrate was filtered, and this served as the control electrolyte.

[0080] The following electrochemical performance tests were performed on this embodiment.

[0081] a. Polarization performance test: The polarization performance of the electrolyte is obtained through constant current testing. Constant current testing is completed using the Xinwei battery testing system.

[0082] A two-electrode system was used, with clean magnesium sheets (14 mm in diameter) as the working electrode and counter electrode. -2 The current is tested.

[0083] b. Rate performance test: The rate performance of the electrolyte is obtained through rate testing, which is completed using the Xinwei battery testing system.

[0084] A two-electrode system was used, with clean magnesium sheets (14 mm thick) as the working electrode and counter electrode. For rate testing, 0.05~0.5 mA·cm -2 Conduct a test.

[0085] c. Electrochemical Activity Test: The electrochemical activity of the electrolyte was measured by electrochemical impedance spectroscopy and cyclic voltammetry, both performed using a Princeton electrochemical workstation. EIS employed a two-electrode system, with clean magnesium sheets (14 mm thick) serving as the working and counter electrodes. The applied excitation signal was 5 mV, the test frequency ranged from 105 to 0.01 Hz, and the test temperature was 25°C.

[0086] Cyclic voltammetry was performed using a Princeton electrochemical workstation. A two-electrode system was employed, with a clean magnesium foil (14 mm diameter) as the counter electrode and a clean stainless steel foil (12 mm diameter) as the working electrode. The test voltage range was -1 V to 2 V, and the scan rate was 0.5 mV / s.

[0087] The specific test results are as follows: Figure 1 In the constant current test, the overpotential of the electrolyte was 0.25V after 100 cycles, and it cycled stably for more than 300 hours. Compared with traditional electrolytes, its overpotential decreased by 87.5%.

[0088] See also Figure 2 In the rate test, when the current returns to the initial value, the voltage can also return to the initial size. Compared with traditional electrolytes, the stability is greatly improved.

[0089] See also Figure 3 In the electrochemical impedance spectroscopy, the electrochemical transfer resistance of the present invention is 30.17 kΩ, which is much lower than the 221.97 kΩ of the traditional electrolyte.

[0090] See also Figure 4 In the cyclic voltammetry curve, the reaction current of the traditional electrolyte is very weak and the deposition potential is large. The deposition potential of the present invention is significantly shifted to the right, and the oxidation peak becomes stronger and shifts to the left. The reaction starts at around 0.2V, indicating that the electrochemical activity of the present electrolyte is better. The above performance test results show that compared with traditional electrolytes, the present electrolyte has the characteristics of small overpotential, good stability and high electrochemical activity.

[0091] Example 2: A method for preparing a halogen-free electrolyte for magnesium metal batteries, comprising: conducting all reactions under an inert atmosphere, with water and oxygen contents below 0.01 ppm. 29.38 g of magnesium bis(trifluoromethanesulfonyl)imide was dissolved in 100 mL of ethylene glycol dimethyl ether. 13.8 g of 7-aminoindole was then added and allowed to dissolve under magnetic stirring at room temperature for 12 hours. 1 g of magnesium powder was then added, and the mixture was stirred at room temperature for 48 hours. The filtrate was filtered, and the resulting filtrate was the halogen-free electrolyte for magnesium metal batteries according to the present invention.

[0092] The conventional electrolyte used as a control group consisted of the aforementioned electrolyte without 7-aminoindole. Specifically, 29.38 g of magnesium bis(trifluoromethanesulfonyl)imide was dissolved in 100 mL of ethylene glycol dimethyl ether and allowed to dissolve under magnetic stirring at room temperature for 12 hours. 5 g of magnesium powder was then added and stirred at room temperature for 48 hours. The resulting filtrate was filtered and used as the control electrolyte.

[0093] The following electrochemical performance tests were performed on this embodiment.

[0094] a. Electrochemical stability test: The electrochemical stability of the electrolyte was determined by linear sweep voltammetry. The linear sweep voltammetry test was performed using a Princeton electrochemical workstation.

[0095] A two-electrode system was used, with a magnesium sheet (14 mm in diameter) as the counter electrode and a copper sheet, nickel sheet, etc. (10 mm in diameter) as the working electrode. The potential range was from open circuit voltage to 5 V, and the scan rate was 0.5 mV / s.

[0096] b. Full-cell performance testing: The full-cell performance of the electrolyte was tested using a Xinwei battery testing system. 2032-type batteries were used, with a V2O5-based positive electrode and a magnesium sheet (14mm diameter) negative electrode. The test current was 0.2A / g, and the test voltage range was 0.01-2V.

[0097] The specific test results are as follows: Figure 5 The electrolyte's oxidation stability potential (vs. Mg / Mg2+) on stainless steel, copper, and aluminum electrodes was tested using linear sweep voltammetry. Aluminum foil exhibited the highest electrochemical stability, generally exceeding 3 V. This suggests that the electrolyte can accommodate a wide range of positive electrodes.

[0098] See also Figure 6 In the full-cell performance test graph, the electrolyte's discharge capacity at cycle 150 was approximately 167.8 mAh / g. Conventional electrolytes, due to their high overpotential with the magnesium anode, are unable to release the positive electrode's capacity. Compared to conventional electrolytes, this electrolyte can be used with magnesium metal anodes, demonstrating practical application value.

[0099] Example 3: A method for preparing a halogen-free electrolyte for a magnesium metal battery, comprising: all reactions are carried out under an inert atmosphere, and the water and oxygen contents are both less than 0.01 ppm. 8.82 g of magnesium trifluoromethanesulfonate is dissolved in 100 mL of diethylene glycol dimethyl ether solvent, followed by the addition of 13.8 g of 7-aminoindole, which is magnetically stirred at room temperature for 12 hours. 5 g of magnesium powder is then added, and the mixture is stirred at room temperature for 24 hours. The mixture is filtered, and the resulting filtrate is the halogen-free electrolyte for a magnesium metal battery according to the present invention.

[0100] Example 4: A method for preparing a halogen-free electrolyte for magnesium metal batteries, comprising: conducting all reactions under an inert atmosphere, with water and oxygen contents below 0.01 ppm. 29.38 g of magnesium bis(trifluoromethanesulfonyl)imide was dissolved in 100 mL of ethylene glycol dimethyl ether. 13.8 g of 6-aminoindole was then added and allowed to dissolve under magnetic stirring at room temperature for 12 hours. 5 g of magnesium powder was then added, and the mixture was stirred at room temperature for 48 hours. The filtrate was filtered, and the resulting filtrate was the halogen-free electrolyte for magnesium metal batteries according to the present invention.

[0101] Example 5: A method for preparing a halogen-free electrolyte for magnesium metal batteries, comprising: conducting all reactions under an inert atmosphere, with water and oxygen contents below 0.01 ppm. 29.38 g of magnesium bis(trifluoromethanesulfonyl)imide was dissolved in 100 mL of ethylene glycol dimethyl ether. 13.8 g of 6-aminoindole was then added and allowed to dissolve under magnetic stirring at room temperature for 12 hours. 5 g of magnesium powder was then added, and the mixture was stirred at room temperature for 48 hours. The filtrate was filtered, and the resulting filtrate was the halogen-free electrolyte for magnesium metal batteries according to the present invention.

[0102] Example 6: A method for preparing a halogen-free electrolyte for magnesium metal batteries, comprising: conducting all reactions under an inert atmosphere, with water and oxygen contents below 0.01 ppm. 29.38 g of magnesium bis(trifluoromethanesulfonyl)imide was dissolved in 100 mL of ethylene glycol dimethyl ether. 12.06 g of 5-nitroindole was then added and allowed to dissolve under magnetic stirring at room temperature for 12 hours. 5 g of magnesium powder was then added, and the mixture was stirred at room temperature for 48 hours. The filtrate was filtered, and the resulting filtrate was the halogen-free electrolyte for magnesium metal batteries according to the present invention.

[0103] The above performance test results show that the halogen-free electrolyte for magnesium metal batteries described in the present invention has the characteristics of small overpotential, good stability and high electrochemical activity compared with traditional electrolytes. It also has good electrochemical stability and can be used in magnesium metal batteries, with good practical prospects.

[0104] In summary, the present invention utilizes a one-step, in-situ, halogen-free magnesium metal battery electrolyte. Raw materials are readily available and inexpensive. The synergistic interaction between the various components imparts the electrolyte with excellent performance, including low overpotential, a wide electrochemical window, and a long lifespan. Furthermore, the electrolyte can be used in full batteries using magnesium metal as the negative electrode, demonstrating promising commercial application prospects. Furthermore, the present invention features a simple preparation process and is amenable to large-scale industrial production.

[0105] The above embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Any equivalent substitution or modification made by those skilled in the art based on the present invention is within the protection scope of the present invention.

Claims

1. A halogen-free electrolyte for magnesium metal batteries, characterized in that: including magnesium salts, additives and organic solvents; The magnesium salt includes at least one of magnesium bis(trifluoromethanesulfonyl)imide and magnesium trifluoromethanesulfonate; The additive includes at least one of indole, 3-azaindole, 4-azaindole, 5-azaindole, 6-azaindole, 4-aminoindole, 5-aminoindole, 6-aminoindole, and 7-aminoindole; The organic solvent includes ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,3-dioxolane or 1,3-dioxane.

2. The halogen-free electrolyte for magnesium metal batteries according to claim 1, characterized in that: The molar ratio of the magnesium salt, the additive and the organic solvent is 1:0.5~10:10~100.

3. The halogen-free electrolyte for magnesium metal batteries according to claim 1, wherein: The concentration of the magnesium salt in the halogen-free electrolyte is 0.1 mol / L to 0.5 mol / L.

4. The halogen-free electrolyte for magnesium metal batteries according to claim 1, wherein: The mass ratio of the additive to the magnesium salt is 0.1-10:

1.

5. The halogen-free electrolyte for magnesium metal batteries according to claim 1, wherein: The additive further includes a dehydrating agent, and the dehydrating agent includes at least one of magnesium powder and dibutyl magnesium.

6. The halogen-free electrolyte for magnesium metal batteries according to claim 5, characterized in that: The mass ratio of the dehydrating agent to the magnesium salt is 0.1-40:

1.

7. A method for preparing a halogen-free electrolyte for a magnesium metal battery, characterized in that: include: A magnesium salt and an additive are sequentially added to an organic solvent, and the mixture is stirred and reacted at room temperature for 1 minute to 24 hours. The resulting solution is the halogen-free electrolyte for a magnesium metal battery according to any one of claims 1 to 6.

8. The method for preparing a halogen-free electrolyte for a magnesium metal battery according to claim 7, wherein: Also includes: After the stirring reaction is completed, filtration is performed, and the obtained filtrate is the halogen-free electrolyte for magnesium metal batteries according to any one of claims 1 to 6.

9. The method for preparing a halogen-free electrolyte for a magnesium metal battery according to claim 7, wherein: The reaction was stirred under an inert atmosphere, and the water and oxygen contents were both lower than 0.01 ppm.

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