Imidazolium ionic liquid modified magnesium ion battery electrolyte as well as preparation method and application thereof

Abstract

The invention discloses an imidazolium ionic liquid modified magnesium ion battery electrolyte and a preparation method and application thereof. The imidazolium ionic liquid modified magnesium ion battery electrolyte is obtained by fully dissolving [EOE-A-Im] [TFSI] ionic liquid in an APC electrolyte. Wherein [EOE-A-Im] [TFSI] is a 1-allyl-3-(2-ethoxyethyl)-1H-imidazole-3-onium bis (trifluoromethylsulfonyl) imine salt, and APC is a total phenyl complex. The imidazolium ionic liquid modified magnesium ion battery electrolyte disclosed by the invention is relatively wide in electrochemical window, excellent in compatibility with electrodes, high in magnesium deposition-dissolution efficiency, low in overpotential and good in cycling stability; and the preparation method of the imidazolium ionic liquid modified magnesium ion battery electrolyte is simple and environment-friendly, and accords with green industrial production.

Description

Technical Field

[0001] The present invention relates to the field of magnesium ion battery electrolytes, and in particular to an imidazole ionic liquid-modified magnesium ion battery electrolyte, a preparation method thereof, and applications thereof. Background Art

[0002] With the global energy transition and the deepening of national sustainable development strategies, the development of efficient, safe, and low-cost new energy storage technologies has become a hot topic in current scientific research. The currently dominant lithium-ion battery technology is limited by its limited resources, high costs, and significant safety risks, prompting researchers to turn their attention to other novel secondary battery systems. Magnesium is abundant in the Earth's crust, and magnesium-ion batteries, with their high volumetric energy density, high safety, environmental friendliness, and low cost, have shown great potential for development and are a strong contender for next-generation energy storage devices.

[0003] As a core component of magnesium-ion batteries, the electrolyte plays a key role in ion transport kinetics and interfacial electrochemical behavior, directly affecting their electrochemical performance. However, current magnesium-ion battery electrolytes face problems such as a narrow electrochemical window, low magnesium ion transport efficiency, and poor stability.

[0004] Ionic liquids have a broad electrochemical window, excellent ionic conductivity, and outstanding thermal stability. Developing new ionic liquids and using them to modify existing magnesium-ion battery electrolytes can improve the electrochemical performance of electrolytes and provide new insights into the development of magnesium-ion battery electrolyte technology.

[0005] Compared to ionic liquids such as pyrrolidine and quaternary ammonium salts, imidazolium ionic liquids exhibit multiple advantages in magnesium-ion battery systems: the strong coordination of the nitrogen atom in the imidazole ring forms a stable solvation structure, increasing the solubility of magnesium salts and ensuring high ion concentration; their conjugated structure provides high oxidative stability and a wide electrochemical window, and is compatible with high-voltage cathode materials; their unique solvation sheath reduces the desolvation energy barrier of magnesium ions, achieving a magnesium deposition / dissolution Coulombic efficiency of >98% and forming a stable SEI film; and their non-flammability and high thermal stability fundamentally address the safety risks of traditional ether electrolytes. These properties make imidazolium ionic liquids ideal electrolyte candidates for high-energy-density, high-safety magnesium-ion batteries.

[0006] Therefore, it is necessary to develop a high-performance magnesium ion battery electrolyte modified by a new imidazolium ionic liquid. Summary of the Invention

[0007] In view of this, in order to solve the above technical problems, the purpose of the present invention is to provide an imidazole ionic liquid modified magnesium ion battery electrolyte and its preparation method and application. The imidazole ionic liquid modified magnesium ion battery electrolyte has a wide electrochemical window, excellent compatibility with electrodes, high magnesium deposition-dissolution efficiency, low overpotential and good cycle stability; and the preparation method of the imidazole ionic liquid modified magnesium ion battery electrolyte is simple, environmentally friendly, and conforms to green industrial production.

[0008] The technical solutions adopted are:

[0009] The present invention discloses an imidazole ionic liquid-modified magnesium ion battery electrolyte, which is obtained by fully dissolving the [EOE-A-Im][TFSI] ionic liquid in an APC electrolyte; wherein [EOE-A-Im][TFSI] is 1-allyl-3-(2-ethoxyethyl)-1H-imidazol-3-ium bis(trifluoromethylsulfonyl)imide, and its chemical structure is shown in Formula I; APC is an all-phenyl complex;

[0010]

[0011] Furthermore, the mass concentration of the [EOE-A-Im][TFSI] ionic liquid is 1-15 mg / mL, further preferably 5-15 mg / mL, and more preferably 5 mg / mL.

[0012] The present invention provides a method for preparing an imidazole ionic liquid-modified magnesium ion battery electrolyte, comprising the following steps: adding [EOE-A-Im][TFSI] ionic liquid to an APC electrolyte, stirring to fully dissolve the ionic liquid, and obtaining the electrolyte.

[0013] Furthermore, [EOE-A-Im][TFSI] ionic liquid is added to the APC electrolyte, and stirred at 500-800 rpm for 24-48 hours at 20-30° C. under an inert atmosphere and a water oxygen content of less than 0.01 ppm to fully dissolve it.

[0014] Furthermore, the [EOE-A-Im][TFSI] ionic liquid is prepared by the following preparation method, which adopts a two-step synthesis method:

[0015] S1. 1-allylimidazole and 2-bromoethyl ethyl ether were refluxed in THF under nitrogen protection, and 1-allyl-3-(2-ethoxyethyl)imidazolium bromide intermediate was obtained by vacuum distillation and recrystallization;

[0016] S2. The 1-allyl-3-(2-ethoxyethyl)imidazolium bromide intermediate is stirred with Mg(TFSI)2 in THF, purified with activated carbon, and dried under reduced pressure to obtain the product; wherein THF is tetrahydrofuran; Mg(TFSI)2 is magnesium bis(trifluoromethylsulfonyl)imide.

[0017] Furthermore, in step S1, 1-allylimidazole and 2-bromoethyl ethyl ether are mixed in THF at a molar ratio of 1:1; in step S2, the 1-allyl-3-(2-ethoxyethyl)imidazolium bromide intermediate and Mg(TFSI)2 are mixed in THF at a molar ratio of 1:1.

[0018] Furthermore, in step S1, 1-allylimidazole and 2-bromoethyl ethyl ether were refluxed in THF at 80° C. under nitrogen protection for 2 hours.

[0019] Furthermore, in step S1, the reaction of 1-allylimidazole and 2-bromoethyl ethyl ether is carried out in THF solvent, and the amount of THF used is 12 parts by volume of THF for every 2 parts by weight of 1-allylimidazole, wherein parts by weight:parts by volume=g:mL.

[0020] The magnesium ion battery of the present invention adopts the magnesium ion battery electrolyte modified by the imidazole ionic liquid and is provided with a working electrode, a counter electrode and a reference electrode.

[0021] Application of the imidazole ionic liquid modified magnesium ion battery electrolyte in magnesium ion batteries.

[0022] In the above technical solution, on the one hand, 1-allylimidazole, 2-bromoethyl ethyl ether, Mg(TFSI)2 and THF are used as raw materials for the preparation of ionic liquids. The allyl side chain of 1-allylimidazole gives it high chemical reactivity, which improves the reaction efficiency of the synthetic ionic liquid; the introduction of ether bond (-O-) through 2-bromoethyl ethyl ether increases the flexibility of the chain, reduces the interaction between chains, and reduces the effective steric hindrance. The ether oxygen atom and the cationic center produce a certain repulsive effect, preventing the side chain from folding back to the vicinity of the cationic head, thereby optimizing the cationic side chain structure. In addition, the introduction of a larger anion ([TFSI] - ), better "filling" the space around the long cationic side chains, reducing the ineffective gaps, and reducing the friction and steric hindrance caused by close packing. Ether bonds and bulky anions ([TFSI] -) work together to reduce the viscosity of the ionic liquid, improve ion mobility, and enhance the conductivity of the ionic liquid electrolyte. Furthermore, the addition of THF increases the contact opportunities between the reactant molecules, significantly improving the reaction rate and efficiency. It also provides mild reaction conditions, stabilizes the reaction intermediate 1-allyl-3-(2-ethoxyethyl)imidazolium bromide, prevents the decomposition of the imidazole ring and other side reactions, and increases the yield of the ionic liquid.

[0023] On the other hand, the synthesized [EOE-A-Im][TFSI] ionic liquid has a broad electrochemical window, excellent ionic conductivity, and outstanding thermal stability. Its addition to the APC electrolyte is the key to the excellent electrochemical performance of the ionic liquid-modified APC electrolyte.

[0024] In summary, the beneficial effects of the present invention are:

[0025] (1) The present invention provides a method for preparing imidazole ionic liquids, which is a two-step synthesis method with the advantages of good universality and high yield (>80%).

[0026] (2) The magnesium ion battery electrolyte modified by imidazole ionic liquid provided by the present invention improves the electrochemical performance of traditional APC electrolyte. It has good compatibility with electrodes, a wide electrochemical window, high magnesium deposition-dissolution efficiency, low overpotential and good cycle stability.

[0027] (3) The magnesium ion battery electrolyte modified by imidazole ionic liquid provided by the present invention is simple to prepare. It only needs to add [EOE-A-Im][TFSI] ionic liquid to APC electrolyte at room temperature and stir the reaction for more than 24 hours to obtain it. The reaction conditions are mild, the preparation is simple, it is beneficial to industrialization, and it is environmentally friendly and conforms to green industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Schematic diagram of the reaction process for preparing [EOE-A-Im][TFSI] ionic liquid using the two-step synthesis method of the present invention;

[0029] Figure 2 The cyclic voltammetry curve of the electrolyte prepared by the present invention using copper foil as the working electrode in Example 1;

[0030] Figure 3 Comparison of linear sweep voltammetry curves of the electrolyte prepared by the present invention using stainless steel foil as the working electrode in Examples 1, 2, 3 and Comparative Example 1;

[0031] Figure 4 Comparison of linear sweep voltammetry curves of stainless steel foil and copper foil as working electrodes using the electrolyte prepared by the present invention in Example 1;

[0032] Figure 5 The electrochemical impedance spectroscopy diagram of the SS / SS symmetrical battery assembled using the electrolyte prepared by the present invention in Comparative Example 1 (the embedded diagram is the equivalent circuit model);

[0033] Figure 6 The electrochemical impedance spectroscopy diagram of the SS / SS symmetrical battery assembled using the electrolyte prepared by the present invention in Example 1 (the embedded figure is the equivalent circuit model);

[0034] Figure 7 The Mg / Cu asymmetric battery assembled with the electrolyte prepared by the present invention in Example 1 was tested at 0.5 mA·cm -2 Reversible magnesium deposition / dissolution cycle curves and Coulombic efficiency under different current densities;

[0035] Figure 8 The Mg / Mg symmetrical battery assembled with the electrolyte prepared by the present invention in Example 1 was subjected to different current densities (0.1 mA·cm -2 , 0.3mA·cm -2 , 0.5mA·cm -2 , 1mA·cm -2 , 1.5mA·cm -2 , 2mA·cm -2 , 2.5mA·cm -2 、3mA·cm -2 , 4mA·cm -2 , 5mA·cm -2 ) under the polarization performance curve;

[0036] Figure 9 The Mg / Mg symmetrical battery assembled with the electrolyte prepared by the present invention in Comparative Example 1 was -2 Polarization performance curve under

[0037] Figure 10 The Mg / Mg symmetrical battery assembled with the electrolyte prepared by the present invention in Example 1 was -2 Polarization performance curve below. DETAILED DESCRIPTION

[0038] The embodiments in the specification are intended to better illustrate the present invention, but are not intended to limit the present invention to the embodiments. 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.

[0039] An embodiment of the present invention provides a magnesium ion battery electrolyte modified by an imidazole ionic liquid, wherein the raw materials for preparing the electrolyte include: [EOE-A-Im][TFSI] ionic liquid and APC electrolyte.

[0040] It should be noted that, in the ionic liquid electrolyte of the embodiment of the present invention, the viscosity of the ionic liquid is a key parameter for regulating the conductivity of the electrolyte, which directly affects the migration ability of magnesium ions in the electrolyte and the stability during long-term cyclic use. In imidazole ionic liquids, the imidazole cation usually has a long side chain. The growth of the side chain will produce greater steric hindrance at the molecular level, thereby increasing the viscosity of the ionic liquid, resulting in a weakening of the ion migration ability and a decrease in the conductivity of the electrolyte. In the present invention, on the one hand, a larger volume of anion ([TFSI] - ) replaces small anions (such as [BF4] - ), better "filling" the space around the long cationic side chains, reducing ineffective gaps and lowering the friction and steric hindrance caused by close packing. Furthermore, 2-bromoethyl ethyl ether, a raw material for preparing the ionic liquid, introduces an ether bond (-O-) that increases chain flexibility, reduces interchain interactions, and minimizes effective steric hindrance. The ether oxygen atom repel the cationic center, preventing the side chains from folding back near the cationic head, thus optimizing the cationic side chain structure. These two aspects, combined, can reduce the viscosity of the ionic liquid, improve ion mobility, and enhance the conductivity of the electrolyte.

[0041] It should also be noted that in the ionic liquid electrolyte in the embodiment of the present invention, the reason why the matrix solvent is APC electrolyte is: APC electrolyte is generated by the reaction of Grignard reagent benzene magnesium chloride (PhMgCl) and aluminum chloride (AlCl3) in tetrahydrofuran (THF). The preparation process of [EOE-A-Im][TFSI] ionic liquid is also carried out in THF. [EOE-A-Im][TFSI] ionic liquid has high compatibility with APC electrolyte. Using APC electrolyte as a modified matrix solvent can avoid the occurrence of side reactions and shorten the modification time. In the ionic liquid electrolyte in the embodiment of the present invention, PhMgCl in the solvent APC electrolyte and Mg(TFSI)2 added during the preparation of the ionic liquid are magnesium ions (Mg 2+ ), which is the key component of the electrolyte to achieve reversible deposition and dissolution of magnesium.

[0042] In the present invention, unless otherwise specified or specified in the preparation process, all other raw materials are commercially available products well known to those skilled in the art.

[0043] In the present invention, THF is added during the preparation of the [EOE-A-Im][TFSI] ionic liquid. This increases the contact opportunities between the reactant molecules, significantly improving the reaction rate and efficiency. It also creates mild reaction conditions, stabilizes the reaction intermediate, 1-allyl-3-(2-ethoxyethyl)imidazolium bromide, and prevents decomposition of the imidazole ring and other side reactions. Furthermore, THF has a low boiling point and is easily removed from the ionic liquid by subsequent evaporation under reduced pressure, simplifying the product isolation and purification steps.

[0044] In the present invention, when the [EOE-A-Im][TFSI] ionic liquid is prepared by a two-step synthesis method, the molar ratio of the reactants in the two-step reaction is 1:1, that is, the molar ratio of 1-allylimidazole to 2-bromoethyl ethyl ether is 1:1; and the molar ratio of 1-allyl-3-(2-ethoxyethyl)imidazolium bromide to Mg(TFSI)2 is 1:1. The molar ratio is also called the molar ratio.

[0045] In the present invention, when preparing the magnesium ion battery electrolyte modified with the imidazole ionic liquid, the weighed ionic liquid is added to the APC electrolyte. This addition order can avoid the agglomeration of the ionic liquid, improve the dissolution efficiency, and prevent the occurrence of side reactions caused by the ultra-high concentration of surface powder when the two are first contacted.

[0046] An embodiment of the present invention provides a method for preparing the above-mentioned magnesium ion battery electrolyte modified by imidazole ionic liquid. The preparation method has mild conditions and is simple to prepare.

[0047] In some embodiments, the above-mentioned magnesium ion battery electrolyte modified by imidazole ionic liquid is prepared by a method comprising: adding [EOE-A-Im][TFSI] ionic liquid to APC electrolyte, stirring at room temperature for 24 hours to fully dissolve it, and obtaining an imidazole ionic liquid-modified magnesium ion battery electrolyte.

[0048] In some embodiments, the mass concentration of the [EOE-A-Im][TFSI] ionic liquid in the magnesium ion battery electrolyte modified with the imidazole ionic liquid is 5 mg / mL, 10 mg / mL, and 15 mg / mL. It should be noted that the addition of the [EOE-A-Im][TFSI] ionic liquid is key to the excellent electrochemical performance of the ionic liquid electrolyte. Only when the [EOE-A-Im][TFSI] ionic liquid reaches a certain concentration in the APC electrolyte and is completely mixed and modified, does the resulting ionic liquid electrolyte exhibit good electrochemical performance. Furthermore, regarding the concentration of the [EOE-A-Im][TFSI] ionic liquid, if the [EOE-A-Im][TFSI] ionic liquid concentration is too low, the electrochemical performance of the electrolyte will not be significantly improved. If the concentration is too high, the viscosity of the electrolyte will increase, the electrolyte will become turbid, and the diffusion of magnesium ions therein will be slow, reducing the conductivity of the electrolyte.

[0049] In some specific embodiments, the temperature referred to by normal temperature is preferably 20-30° C., the speed of the magnetic stirrer is preferably 500 rpm, and the stirring time is preferably 24 hours.

[0050] In some specific embodiments, when preparing an imidazole-based ionic liquid-modified magnesium ion battery electrolyte, the reaction is carried out under an inert atmosphere, and the water and oxygen content is less than 0.01 ppm. Specifically, to prevent the raw materials for preparing the ionic liquid electrolyte from reacting with water and oxygen during the reaction and causing deterioration, all raw materials are reacted under an inert atmosphere and the water and oxygen content is less than 0.01 ppm.

[0051] 1. Synthesis and preparation of [EOE-A-Im][TFSI] ionic liquid

[0052] The [EOE-A-Im][TFSI] ionic liquid was synthesized by a two-step method. The first step was to prepare the intermediate 1-allyl-3-(2-ethoxyethyl)imidazolium bromide; the second step was to prepare the [EOE-A-Im][TFSI] ionic liquid powder.

[0053] The specific steps may include:

[0054] (1) 1-Allyl imidazole (2 g, 18.6 mmol) and THF (12 mL) were weighed using an electronic balance and a graduated cylinder, respectively, and added to a 50 mL two-necked flask.

[0055] (2) 2-Bromoethyl ethyl ether (2.83 g, 18.6 mmol) was added with heating and stirring at 80°C, and the resulting mixture was refluxed at 80°C under N2 protection for 2 hours.

[0056] (3) After the reaction is completed, the product is placed in a vacuum drying oven and dried under vacuum for 24 h. The excess solvent and 2-bromoethyl ethyl ether are removed under reduced pressure to obtain a light yellow solid.

[0057] (4) The obtained light yellow solid is recrystallized from ethyl acetate, and the obtained solid product is further dried at 80° C. (or evaporated to dryness under reduced pressure) to obtain the intermediate product 1-allyl-3-(2-ethoxyethyl)imidazolium bromide.

[0058] (5) The above intermediate product (2 g, 7.66 mmol), Mg(TFSI)2 (4.48 g, 7.66 mmol) and THF (50 mL) were respectively transferred into a 100 mL two-necked flask and stirred at room temperature for 48 h.

[0059] (6) The suspension was filtered to remove the precipitated bromide salt, and the organic phase was repeatedly washed with small volumes of water (about 10 mL) to obtain a mixture of ionic liquid and tetrahydrofuran.

[0060] (7) The resulting organic phase was stirred with activated carbon for 12 h, and then the suspension was filtered to remove the activated carbon. The solvent was removed in vacuo at 80 °C to obtain a colorless ionic liquid. Ethyl acetate was added for filtration, and the mixture was dried in vacuo at 60 °C for 8 h to obtain 472 mg of [EOE-A-Im][TFSI] ionic liquid powder.

[0061] 2. Preparation of magnesium ion battery electrolyte modified by imidazole ionic liquid

[0062] The preparation of the electrolyte is completed at room temperature in an argon-filled glove box, where the moisture and oxygen content in the glove box is controlled below 0.01 ppm.

[0063] The ionic liquids synthesized above were added to an equal volume of APC electrolyte in a certain proportion, and stirred on a magnetic stirrer at room temperature for 24 hours to fully dissolve them, thereby obtaining ionic liquid electrolytes with different concentrations.

[0064] In order to better understand the present invention, the content of the present invention is further described below with reference to specific examples, but the content of the present invention is not limited to the following examples.

[0065] Example 1:

[0066] Add 1000 μL of APC electrolyte to a reagent bottle. Weigh 5 mg of [EOE-A-Im][TFSI] ionic liquid powder and add it to the APC electrolyte. Stir magnetically at room temperature for 24 hours. The resulting ionic liquid electrolyte has a concentration of 5 mg / mL. This is designated "EAIT-APC-1."

[0067] Example 2:

[0068] Add 1000 μL of APC electrolyte to a reagent bottle. Weigh 10 mg of [EOE-A-Im][TFSI] ionic liquid powder and add it to the APC electrolyte. Stir magnetically at room temperature for 24 hours. The resulting ionic liquid electrolyte has a concentration of 10 mg / mL. This is designated "EAIT-APC-2."

[0069] Example 3:

[0070] Add 1000 μL of APC electrolyte to a reagent bottle. Weigh 15 mg of [EOE-A-Im][TFSI] ionic liquid powder and add it to the APC electrolyte. Stir magnetically at room temperature for 24 hours. The resulting ionic liquid electrolyte has a concentration of 15 mg / mL. This is designated "EAIT-APC-3."

[0071] Comparative Example 1:

[0072] This comparative example is an APC electrolyte without the addition of an ionic liquid. Take 1000 μL of the APC electrolyte for later use. Record this as "APC-control."

[0073] 3. Electrolyte performance test

[0074] In the following examples, the electrolyte performance test method is as follows:

[0075] (1) Reversibility test of magnesium deposition and dissolution in electrolyte

[0076] The reversibility of magnesium deposition and dissolution in the electrolyte was determined by cyclic voltammetry (CV). CV tests were performed using a CHI 660E electrochemical workstation. A CR2032 button cell was used, with a 12 mm diameter copper foil (Cu) as the working electrode and a 14 mm diameter magnesium sheet (Mg) as the counter and reference electrodes. The potential range was set from -1 V to 1.6 V, with a scan rate of 25 mV / s.

[0077] (2) Electrochemical oxidation stability test of electrolyte

[0078] The electrochemical oxidation stability of the electrolyte can be obtained by linear sweep voltammetry (LSV). LSV testing is performed using a CHI 660E electrochemical workstation. LSV testing combined with CV testing can be used to evaluate the oxidation stability potential and electrochemical stability window of the electrolyte. Here, 0.1 mA cm -2 The readout method is used to interpret the electrolyte's oxidation stability potential and electrochemical window. A two-electrode system is assembled, using a 12 mm diameter stainless steel (SS) or copper (Cu) foil as the working electrode and a 14 mm diameter magnesium (Mg) foil as the counter and reference electrodes. The potential range is set to -5 V from the open circuit voltage, with a scan rate of 1 mV / s.

[0079] (3) Ionic conductivity test of electrolyte

[0080] The ionic conductivity of the electrolyte was measured using electrochemical impedance spectroscopy (EIS). Stainless steel foil (SS) with a diameter of 12 mm was used as the working, counter, and reference electrodes of a CR2032 button cell. The frequency range was set to 0.01 Hz to 100 kHz, the test amplitude was 10 mV, and the starting voltage was set at the open circuit potential.

[0081] (4) Coulombic efficiency test of reversible deposition and dissolution of magnesium in electrolyte

[0082] The coulombic efficiency and charge-discharge characteristics of the reversible deposition and dissolution of magnesium in the electrolyte were measured using a Xinwei constant current charge-discharge test system. CR2032 button cells were assembled, using a 12 mm diameter copper foil (Cu) as the working electrode and a 14 mm diameter magnesium sheet (Mg) as the counter and reference electrodes. The current density was set to 0.5 mA cm -2 .

[0083] (5) Polarization performance test of electrolyte

[0084] The polarization properties of the electrolyte were measured using a Xinwei constant current charge and discharge test system. CR2032 button cells were assembled, and magnesium sheets (Mg) with a diameter of 14 mm were used as the working electrode, counter electrode, and reference electrode. The electrolyte was charged and discharged at different current densities (0.1 mA·cm -2 , 0.3mA·cm -2 , 0.5mA·cm -2 , 1mA·cm -2 , 1.5mA·cm -2 , 2mA·cm -2 , 2.5mA·cm -2 、3mA·cm -2 , 4mA·cm -2 , 5mA·cm -2 ) and fixed 0.1 mA·cm -2 When tested at the current density, the charge and discharge time is limited to within 30 minutes.

[0085] 4. Test Results

[0086] The electrolytes prepared in Examples 1 to 3 and the electrolyte in Comparative Example 1 were tested using the above test method. The test results are shown below:

[0087] The test results of the electrolyte prepared in Example 1 are as follows:

[0088] (1) The button cell assembled with the "EAIT-APC-1" electrolyte prepared in Example 1, using copper foil as the working electrode and magnesium sheet as the negative electrode, can achieve reversible deposition / dissolution of magnesium, with a peak current density of 25.5 mA cm at the 100th cycle. -2 , and the overpotential for magnesium deposition / dissolution is also low (see Figure 2 );

[0089] (2) Electrochemical windows (vs. Mg / Mg) of the electrolytes of EAIT-APC-1, EAIT-APC-2, EAIT-APC-3 and APC-control prepared in Example 1, Example 2, Example 3 and Comparative Example 1 on stainless steel (SS) 2+ ) are SS (~4.10V), SS (~2.82V), SS (~2.94V), and SS (~2.79V), respectively. The oxidation stability potential of the "EAIT-APC-1" electrolyte prepared in Example 1 is the highest, indicating that the electrolyte prepared in this scheme has the widest electrochemical window and the best oxidation stability (see Figure 3 );

[0090] (3) The oxidation stability potentials of the "EAIT-APC-1" electrolyte prepared in Example 1 on stainless steel foil and copper foil are SS (4.10 V) and Cu (2.21 V), respectively, indicating that the electrolyte has high oxidation stability and can meet the use requirements (see Figure 4 );

[0091] (4) The ionic conductivities of the electrolytes "EAIT-APC-1" and "APC-control" prepared in Example 1 and Comparative Example 1 were 0.56 mS·cm -1 and 0.23 mS·cm -1 , indicating that the addition of [EOE-A-Im][TFSI] ionic liquid can improve the ionic conductivity of APC electrolyte (see Figure 5 and Figure 6 );

[0092] (5) The Mg / Cu asymmetric battery assembled with the "EAIT-APC-1" electrolyte prepared in Example 1 was -2 The coulombic efficiency of magnesium reversible deposition / dissolution can reach 99.8%, and the cycle can be stable for more than 1200 hours, and the polarization potential remains stable at a low level (see Figure 7 );

[0093] (6) Polarization performance curves of the Mg / Mg symmetrical battery assembled with the "EAIT-APC-1" electrolyte prepared in Example 1 at different current densities. As the current density gradually increases, the voltage increases regularly, and the fluctuation symmetry is good, which indicates that the reaction kinetics of the electrolyte are balanced and the polarization performance is good (see Figure 8 );

[0094] (7) The Mg / Mg symmetrical battery assembled with the "EAIT-APC-1" and "APC-control" electrolytes prepared in Example 1 and Comparative Example 1 was -2 Long-term polarization performance curve under Figure 9 and Figure 10 ).

[0095] The electrochemical test results of the electrolytes prepared in Example 1, Example 2, Example 3 and Comparative Example 1 are shown in Table 1. It should be noted that the average coulombic efficiency in Table 1 is the average coulombic efficiency at the corresponding cycle time of the examples or comparative examples.

[0096] Table 1 shows the electrochemical properties of the electrolytes prepared in Example 1, Example 2, Example 3 and Comparative Example 1.

[0097] Table 1

[0098]

[0099] As shown in Table 1, when the concentration of [EOE-A-Im][TFSI] ionic liquid in the APC electrolyte is too high (Example 3), the peak current density of the cyclic voltammetry is lower than that of Comparative Example 1 due to the increase in electrolyte viscosity. However, when the concentration of the ionic liquid is appropriate (Examples 1 and 2), the peak current density is improved. The peak current density of the EAIT-APC-1 prepared in Example 1 can reach 25.5 mA cm after 100 cycles. -2 . The increase in peak current density indicates that the electrolyte prepared at this time provides a better magnesium ion transmission environment, and has better compatibility between the electrolyte and the electrode interface. After adding the prepared [EOE-A-Im][TFSI] ionic liquid to the APC electrolyte, its ionic conductivity will be improved. The degree of improvement is related to the concentration of the ionic liquid, and the best is achieved when the added concentration is 10 mg / mL (Example 2). When the added concentration of the ionic liquid is 5 mg / mL (Example 1), the electrolyte has the highest oxidative stability, and the electrochemical window on the stainless steel foil can reach SS (~4.10 V), which is greatly improved compared with Comparative Example 1. The electrolytes with three [EOE-A-Im][TFSI] ionic liquid addition concentrations are at 0.1 mA·cm -2The low polarization voltage (0.02V-0.03V) was maintained over long cycles at all current densities, and the voltage fluctuation was more stable than that of the APC electrolyte without the addition of ionic liquid (Comparative Example 1), indicating that ionic liquids can effectively enhance the polarization capability of magnesium-ion battery APC electrolytes. The electrolyte prepared in Example 1 can be stably cycled for more than 1200 hours while maintaining a Coulombic efficiency of 99.8%, demonstrating improved cycling stability compared to the comparative example.

[0100] The above embodiments are only used to specifically illustrate the technical solutions and advantages of the present invention. They are only part of the embodiments of the present invention, not all of the embodiments. Any modification or equivalent replacement of the present invention without departing from the scope of the technical solutions of the present invention is included in the scope of protection of the claims of the present invention.

Claims

1. An imidazole ionic liquid modified magnesium ion battery electrolyte, characterized in that: The invention is obtained by fully dissolving the [EOE-A-Im][TFSI] ionic liquid in the APC electrolyte; wherein [EOE-A-Im][TFSI] is 1-allyl-3-(2-ethoxyethyl)-1H-imidazol-3-ium bis(trifluoromethylsulfonyl)imide, and its chemical structure is shown in Formula I; APC is an all-phenyl complex; 2. The magnesium ion battery electrolyte modified by imidazole ionic liquid according to claim 1, characterized in that The mass concentration of the [EOE-A-Im][TFSI] ionic liquid is 1-15 mg / mL.

3. A method for preparing the magnesium ion battery electrolyte modified with the imidazole ionic liquid according to claim 1 or 2, characterized in that: The following steps are involved: Add [EOE-A-Im][TFSI] ionic liquid into APC electrolyte and stir to fully dissolve it to obtain the product.

4. The method for preparing the magnesium ion battery electrolyte modified by imidazole ionic liquid according to claim 3, characterized in that: Add [EOE-A-Im][TFSI] ionic liquid to APC electrolyte, stir at 500-800 rpm for 24-48 hours at 20-30°C under inert atmosphere and water oxygen content <0.01ppm to fully dissolve it.

5. The method for preparing the magnesium ion battery electrolyte modified by imidazole ionic liquid according to claim 3, characterized in that: The [EOE-A-Im][TFSI] ionic liquid is prepared by the following preparation method, which adopts a two-step synthesis method: S1. 1-allylimidazole and 2-bromoethyl ethyl ether were refluxed in THF under nitrogen protection, and 1-allyl-3-(2-ethoxyethyl)imidazolium bromide intermediate was obtained by vacuum distillation and recrystallization; S2. The 1-allyl-3-(2-ethoxyethyl)imidazolium bromide intermediate is stirred with Mg(TFSI)2 in THF, purified with activated carbon, and dried under reduced pressure to obtain the product; wherein THF is tetrahydrofuran; Mg(TFSI)2 is magnesium bis(trifluoromethylsulfonyl)imide.

6. The method for preparing the magnesium ion battery electrolyte modified by imidazole ionic liquid according to claim 5, characterized in that: In step S1, 1-allylimidazole and 2-bromoethyl ethyl ether are mixed in THF at a molar ratio of 1:1; in step S2, the 1-allyl-3-(2-ethoxyethyl)imidazolium bromide intermediate is mixed with Mg(TFSI)2 at a molar ratio of 1:1 in THF.

7. The method for preparing the magnesium ion battery electrolyte modified by imidazole ionic liquid according to claim 6, characterized in that: In step S1, 1-allylimidazole and 2-bromoethyl ethyl ether are refluxed in THF at 80° C. under nitrogen protection for 2 hours.

8. The method for preparing the magnesium ion battery electrolyte modified by imidazole ionic liquid according to claim 5, characterized in that: In step S1, the reaction of 1-allylimidazole and 2-bromoethyl ethyl ether is carried out in THF solvent, and the amount of THF used is 12 parts by volume of THF for every 2 parts by weight of 1-allylimidazole, wherein parts by weight:parts by volume=g:mL.

9. A magnesium ion battery, characterized in that: A magnesium ion battery electrolyte modified with the imidazole ionic liquid according to claim 1 or 2 is provided with a working electrode, a counter electrode and a reference electrode.

10. Use of the magnesium ion battery electrolyte modified with the imidazole ionic liquid according to claim 1 or 2 in a magnesium ion battery.

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