Formamide and MgCl2-based low-temperature aqueous electrolyte and preparation method and application thereof

Abstract

The invention relates to the technical field of battery electrolyte materials, and discloses a formamide and MgCl2-based low-temperature aqueous electrolyte, which comprises a solvent, a soluble metal salt and an additive, the additive is formamide, and the volume ratio of the formamide to the solvent is (2-8): 10. The preparation method comprises the following steps: S1, weighing a certain amount of soluble metal salt for later use; s2, measuring a certain amount of additive, and uniformly mixing the additive with the solvent to prepare a mixed solvent; and S3, dissolving the soluble metal salt weighed in the step S1 into the mixed solvent in the step S2 to prepare the low-temperature aqueous electrolyte based on formamide and MgCl2. The low-temperature aqueous electrolyte based on formamide and MgCl2 is applied to an aqueous ion battery. According to the technical scheme, dual breakthrough of low-temperature performance and electrochemical stability is achieved through the synergistic effect of the formamide and the dihydrogen bonds of MgCl2.

Description

Technical Field

[0001] The present invention relates to the technical field of battery electrolyte materials, and in particular to a low-temperature aqueous electrolyte based on formamide and MgCl2, and a preparation method and application thereof. Background Art

[0002] Magnesium has a high volumetric capacity (3832 mAh / cm 3 Aqueous magnesium-ion batteries (Mg-ion batteries) exhibit significant potential for large-scale energy storage due to their inherent advantages, including a relatively negative redox potential (-2.37 V vs. SHE), and high abundance in the Earth's crust. However, traditional aqueous electrolytes are limited by water's intrinsic freezing point (0°C), which typically exceeds -20°C. They easily freeze in low-temperature environments, blocking ion transport channels and hindering the improvement of battery energy density. This has become a key bottleneck in the commercialization of this technology.

[0003] In recent years, in response to the bottlenecks faced by aqueous magnesium-ion battery electrolytes under extreme conditions, researchers have actively explored high-concentration electrolytes, deep eutectic electrolytes, co-soluble additives and gel electrolyte systems. However, existing research methods have certain limitations: First, high-concentration electrolytes improve low-temperature performance by increasing the salt concentration to >20moL / L, but this leads to a significant increase in raw material costs, and at the same time, the viscosity of the electrolyte increases significantly (>100mPa・s). At low temperatures, ion migration is severely hindered, and salting out crystallization is very likely to occur, and the long-term cycle stability is poor; second, some deep eutectic system electrolytes have the problem of low ionic conductivity (<5mS / cm), and some components (such as ClO4 - ) may also cause corrosion to the electrode. In addition, the eutectic ratio optimization process is complex and difficult to achieve large-scale preparation; thirdly, although the gel electrolyte system has mechanical flexibility and is suitable for flexible devices, its solid-state properties can avoid the risk of leakage and it is inherently non-flammable. It can also achieve self-repair and anti-dehydration functions through dynamic bonds such as hydrogen bonds and ionic cross-linking, and can work normally at lower temperatures. However, at extreme temperatures, the shrinkage of the gel network pores will severely limit ion transport, and it needs to be combined with anti-low-temperature co-solvents for synergistic regulation; fourthly, although co-solvent additives have the advantages of low cost and small dosage, they can synergistically improve low-temperature performance through hydrogen bond regulation and solvation optimization, and have good compatibility with various salt systems such as Li / Na / K / Zn / Mg, and have strong universality, but excessive addition will dilute the effective ion concentration, thereby reducing the energy density. Some additives (such as methanol) also have the risk of toxicity or causing side reactions. Summary of the Invention

[0004] The present invention aims to provide a low-temperature aqueous electrolyte based on formamide and MgCl2, and its preparation method and application, in order to solve the problems of insufficient low-temperature performance of existing electrolytes and limitations of various optimization schemes.

[0005] To achieve the above-mentioned purpose, the present invention adopts the following technical solution: a low-temperature aqueous electrolyte based on formamide and MgCl2, comprising a solvent, a soluble metal salt and an additive, wherein the additive is formamide, and the volume ratio of formamide to solvent is (2-8):10.

[0006] Preferably, the soluble metal salt is a soluble magnesium salt.

[0007] Preferably, the concentration of the soluble metal salt in the electrolyte is 1-5 mol / L.

[0008] Preferably, the operating temperature of the electrolyte is -20°C to 25°C.

[0009] The present invention also provides another technical solution, a method for preparing a low-temperature aqueous electrolyte based on formamide and MgCl2, comprising the following steps: S1: Weigh a certain amount of soluble metal salt for use; S2: taking a certain amount of additives and mixing them evenly with the solvent to prepare a mixed solvent; S3: The soluble metal salt weighed in S1 is dissolved in the mixed solvent in S2 to prepare a low-temperature aqueous electrolyte based on formamide and MgCl2.

[0010] The present invention also provides another technical solution, an application of a low-temperature aqueous electrolyte based on formamide and MgCl2, which is applied to aqueous ion batteries.

[0011] Preferably, the aqueous ion battery is an aqueous magnesium ion battery.

[0012] Preferably, the positive electrode material of the aqueous ion battery includes a vanadium-based positive electrode material, and the negative electrode material includes PTCDA.

[0013] Preferably, the vanadium-based positive electrode material is a multivalent magnesium vanadate compound.

[0014] Compared with the existing technology, the beneficial effects of this solution are: the low-temperature aqueous electrolyte based on formamide and MgCl2 and the preparation method thereof provided by the present invention achieve a dual breakthrough in low-temperature performance and electrochemical stability through molecular design and solvation structure regulation.

[0015] First, a breakthrough in low-temperature performance: This invention constructs a double hydrogen bond system between formamide (FA) and MgCl2 through molecular design: the carbonyl oxygen (C=O) of formamide forms a hydrogen bond with water molecules, and the amino hydrogen (NH) forms a hydrogen bond with Cl - O in the hydration layer - Form hydrogen bonds and synergistically destroy Mg 2+This mechanism reduces the freezing point of the electrolyte from -15°C (without formamide) to -43°C (with 4 mL formamide). When the amount of formamide added reaches 8 mL, there is no obvious freezing point in the range of -60°C to 10°C. This breaks through the technical barrier of traditional aqueous electrolytes freezing below -20°C, expands the operating temperature to -20°C to 25°C, and provides a liquid electrolyte solution for low-temperature energy storage scenarios.

[0016] Second, optimization of electrochemical performance: Formamide reconstructs Mg through double hydrogen bonding 2+ Solvation sheath, forming [Mg(H2O) m (FA) n ] 2+ The efficient transport structure enables the ionic conductivity to reach 30.98mS / cm at -20°C, which is significantly improved compared to the system without formamide. In the three-electrode system, the discharge capacity reaches 260mAh / g at a current density of 0.05A / g at -20°C. After 500 cycles at a current density of 1A / g, the capacity retention rate is 70.4%. The full battery uses PTCDA as the negative electrode and MVOH as the positive electrode. With this electrolyte, the discharge capacity can reach 82.9mAh / g at a current density of 0.2A / g at -20°C, showing excellent rate performance and cycle stability. After 5000 cycles at a current density of 1A / g, the capacity retention rate at -20°C is 57.7%, solving the problem of "rapid attenuation at low temperatures" of traditional electrolytes.

[0017] Thirdly, this solution has achieved a double breakthrough in safety and cost control: formamide is non-flammable and non-toxic, and compared with ClO4 - The deep eutectic system eliminates the risk of electrode corrosion. The Tafel test shows a positive shift in the hydrogen evolution potential, and the side reaction inhibition effect is significant. The MgCl2 concentration is only 1-5 mol / L, and the formamide addition amount is 20%-80% of the solvent volume. The raw material cost is significantly lower than that of traditional high-concentration electrolytes. The preparation process only requires dissolution at room temperature, and does not require complex eutectic ratios or gel synthesis. It solves the problems of high viscosity and salting-out crystallization in existing high-concentration systems and has the potential for large-scale production.

[0018] Fourth, theoretical breakthrough in the mechanism of action: This invention proposes for the first time the theory of "double hydrogen bond coordinated regulation": the C=O of FA forms hydrogen bonds with water molecules, and NH with Cl - O in the hydration layer - Forming hydrogen bonds, the dual effect makes Mg 2+ The desolvation energy barrier is significantly reduced, and the overpotential of the hydrogen evolution reaction is increased. In the NaClO4-FA system, FA only relies on a single C=O…HO hydrogen bond with Na + Weak coordination, unable to trigger Cl -Under the same FA concentration conditions, the freezing point drop of the MgCl2-FA system is significantly higher than that of the NaClO4-FA system, which highlights the synergistic effect of MgCl2-FA system. 2+ Specific optimization of high charge density (2.0e / nm³). By establishing a "charge density-hydrogen bond strength" correlation model, it is confirmed that Mg 2+ Because the charge density is higher than that of Na + , stronger hydrogen bonds are required to destroy the solvation sheath, providing a theoretical paradigm for the design of high charge density ion battery electrolytes.

[0019] In summary, this solution achieves multi-technology chain innovation in dimensions such as low-temperature performance, cycle stability, safety and cost control through precise design of intermolecular forces. It breaks through existing technical bottlenecks such as the high cost of high-concentration electrolytes, low conductivity of deep eutectic systems, and limited low-temperature transmission of gel electrolytes. It provides a solution with both theoretical innovation and engineering value for the commercial application of aqueous magnesium-ion batteries in extreme scenarios such as polar energy storage and wide-temperature electronic devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Graph showing the actual states of the electrolytes prepared in Examples 1-2 and Comparative Examples 1-3 of the present invention at 25°C and -20°C; Figure 2 A comparison chart of the freezing points of the electrolytes prepared in Examples 1-2 and Comparative Examples 1-3 of the present invention; Figure 3 This is a comparison chart of the ionic conductivities of the electrolytes prepared in Examples 1-2 and Comparative Examples 1-3 of the present invention at different temperatures; Figure 4 GCD curves of the electrolytes prepared in Examples 1-2 and Comparative Examples 1-3 of the present invention; Figure 5 This is a comparison chart of the rate performance and cycle performance of the electrolytes prepared in Examples 1-2 of the present invention and Comparative Examples 1-3 at -20°C; Figure 6 Electrochemical performance diagram of a full battery assembled with the electrolyte prepared in Example 1 of the present invention; Figure 7 A safety performance comparison chart of the electrolytes prepared in Example 1 of the present invention and Comparative Example 1; Figure 8 This is a DFT theoretical calculation diagram of the electrolyte prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0021] The following is further described in detail through specific implementation methods: Example 1 A low-temperature aqueous electrolyte based on formamide and MgCl₂ comprises a solvent, a soluble metal salt, and an additive. The solvent is deionized water; the soluble metal salt is a soluble magnesium salt, specifically MgCl₂, and the concentration of MgCl₂ in the electrolyte is 1-5 mol / L; the additive is formamide, and the volume ratio of formamide to solvent is (2-8):10. In this embodiment, the concentration of MgCl₂ in the electrolyte is 1 mol / L, and the volume ratio of formamide to deionized water is 4:6.

[0022] A method for preparing a low-temperature aqueous electrolyte based on formamide and MgCl2 comprises the following steps: S1: Weigh 2.033 g of MgCl2·6H2O as a soluble metal salt; S2: Measure 4 ml of formamide (FA) as an additive, add deionized water to make up to 10 ml, and mix well to prepare a mixed solvent; S3: Dissolve the MgCl2·6H2O weighed in S1 in the mixed solvent in S2, add a magnetic stirrer and transfer to a magnetic stirrer, and stir for 10 minutes until completely dissolved to prepare a low-temperature aqueous electrolyte based on formamide and MgCl2, which is recorded as 4FA.

[0023] A low-temperature aqueous electrolyte based on formamide and MgCl2 is used in aqueous ion batteries. The aqueous ion battery is an aqueous magnesium ion battery. The positive electrode material of the aqueous ion battery includes a vanadium-based positive electrode material, and the negative electrode material includes PTCDA. The vanadium-based positive electrode material is a multivalent magnesium vanadate compound, and the multivalent magnesium vanadate compound is specifically Mg x V 10 O 24 nH2O nanoflower cathode material, denoted as MVOH.

[0024] Example 2 Different from Example 1, a low-temperature aqueous electrolyte based on formamide and MgCl2 is used, and the volume ratio of formamide to deionized water is 2:8.

[0025] A method for preparing a low-temperature aqueous electrolyte based on formamide and MgCl2 comprises: in S2, measuring 2 ml of formamide (FA) as an additive, adding deionized water to make the volume to 10 ml, and mixing evenly to prepare a mixed solvent; the low-temperature aqueous electrolyte based on formamide and MgCl2 prepared in S3 is recorded as 2FA.

[0026] Comparative Example 1 Different from Example 1, a low-temperature aqueous electrolyte based on formamide and MgCl2 is used, and the volume ratio of formamide to deionized water is 6:4.

[0027] A method for preparing a low-temperature aqueous electrolyte based on formamide and MgCl2 comprises: in S2, measuring 6 ml of formamide (FA) as an additive, adding deionized water to make the volume to 10 ml, and mixing evenly to prepare a mixed solvent; the low-temperature aqueous electrolyte based on formamide and MgCl2 prepared in S3 is recorded as 6FA.

[0028] Comparative Example 2 Different from Example 1, a low-temperature aqueous electrolyte based on formamide and MgCl2 is used, and the volume ratio of formamide to deionized water is 8:2.

[0029] A method for preparing a low-temperature aqueous electrolyte based on formamide and MgCl2 comprises: in S2, measuring 8 ml of formamide (FA) as an additive, adding deionized water to make the volume to 10 ml, and mixing evenly to prepare a mixed solvent; the low-temperature aqueous electrolyte based on formamide and MgCl2 prepared in S3 is recorded as 8FA.

[0030] Comparative Example 3 Different from Example 1, a low-temperature aqueous electrolyte based on formamide and MgCl2 includes a solvent and a soluble metal salt, does not contain additives, and the volume of the solvent is 10 mL.

[0031] A method for preparing a low-temperature aqueous electrolyte based on formamide and MgCl2, excluding S2. In S3, the MgCl2·6H2O weighed in S1 is dissolved in 10 mL of deionized water, a magnetic stirring bar is added, and the mixture is transferred to a magnetic stirrer and stirred for 10 minutes until completely dissolved to prepare a MgCl2 electrolyte, which is recorded as OFA.

[0032] The performance of the electrolytes prepared in Examples 1-2 and Comparative Examples 1-3 was tested.

[0033] The two-electrode system and the three-electrode system were used in the performance test, specifically: two-electrode electrolytic cell: Pt sheet was used as the working electrode and counter electrode to test the ionic conductivity. Three-electrode electrolytic cell: the working electrode was Mg x V 10 O 24 nH2O, a Pt counter electrode, and an Ag / AgCl reference electrode are used to test the electrochemical performance of the electrolyte. Full-cell testing: Using a Swagelok cell mold, MVOH as the positive electrode and PTCDA as the negative electrode, the full-cell electrochemical performance is evaluated.

[0034] (1) Freezing point test of electrolyte Depend on Figure 1It can be seen that at 25°C, the electrolytes prepared in Examples 1-2 and Comparative Examples 1-3 are all liquid; at -20°C, the electrolyte prepared in Comparative Example 3 freezes, while the electrolytes prepared in Examples 1-2 and Comparative Example 1-2 remain liquid, indicating that the addition of FA can significantly lower the freezing point of the electrolyte.

[0035] The freezing point of the electrolytes prepared in Examples 1-2 and Comparative Examples 1-3 was tested by differential scanning calorimetry (DSC). Figure 2 It can be seen that the freezing point of the electrolyte without FA addition is -15°C, which shows that although magnesium chloride can lower the freezing point, the effect is relatively limited. With the gradual addition of FA, the low-temperature performance of the electrolyte is significantly improved: when the FA addition amount is 2mL, the freezing point of the electrolyte drops to -31°C; when the addition amount is increased to 4mL, the freezing point further drops to -43°C; when the addition amount reaches 6mL, the freezing point is as low as -56°C; and when the FA addition amount is 8mL, no obvious freezing point is detected in the test temperature range of -60°C to 10°C, indicating that the electrolyte has now formed a highly stable low-temperature liquid structure and can maintain fluidity under extremely cold conditions.

[0036] The significant decrease in the freezing point has greatly broadened the low-temperature application range of aqueous electrolytes, allowing them to remain liquid in environments of -20°C and below, making it possible for aqueous ion batteries to be used in low-temperature scenarios. The reason is that FA forms hydrogen bonds with water molecules that are stronger than the intermolecular forces of water molecules, destroying and reorganizing the original hydrogen bond network of water molecules, thereby effectively lowering the freezing point of the electrolyte and inhibiting the hydrogen evolution reaction. In addition, FA as an electrolyte additive can regulate the solvation sheath structure, promoting the 2+ The H2O molecules in the solvation sheath are more easily replaced by FA molecules, thereby optimizing the solvation structure and transmission environment of magnesium ions and further enhancing the low-temperature stability of the electrolyte.

[0037] (2) Low-temperature conductivity of electrolyte A two-electrode electrochemical impedance spectroscopy (EIS) test system was used, with Pt sheets as the working electrode and the counter electrode, to test the ionic conductivities of the electrolytes prepared in Examples 1-2 and Comparative Examples 1-3 at room temperature (25°C) and low temperature (-20°C).

[0038] from Figure 3 It can be seen that at room temperature of 25°C, the electrolyte without FA addition has the highest ionic conductivity. As the amount of FA added increases, the electrolyte ionic conductivity continues to decrease, which shows that at room temperature, FA mainly has a "negative" effect and will have an adverse effect on ionic conduction.

[0039] In a low-temperature environment of -20°C, the electrolyte without FA freezes, the ion transmission channel is blocked, and the ion conductivity is only 15.11mS / cm. As FA is gradually added, the ionic conductivity of the electrolyte shows a trend of first increasing and then decreasing. When the amount of FA added is 4mL, the ionic conductivity reaches a peak of 30.98mS / cm, which is significantly higher than the case without FA addition. This change reflects that FA has a "two-way" effect on the ionic conductivity of the electrolyte under low-temperature conditions: when added in a low proportion, FA forms hydrogen bonds with water molecules, regulates the solvation structure of magnesium ions, lowers the freezing point of the electrolyte, optimizes the ion transmission environment, and thus effectively improves the ionic conductivity; but when the amount of FA added exceeds a certain threshold, the negative effect begins to become prominent, causing the ionic conductivity to decrease.

[0040] (3) Capacity and cycle performance test Using a three-electrode system, the electrolytes prepared in Examples 1-2 and Comparative Examples 1-3 were applied to the vanadium-based positive electrode material MOVH, and the constant current charge and discharge (GCD), rate performance, and cycle performance were tested at a low temperature of -20°C.

[0041] Depend on Figure 4-5 It can be seen that in the three-electrode system, when the amount of FA added is 4 mL, at -20 ° C and 0.05 Ag -1 Under current density conditions, the battery discharge capacity can reach 260mAhg -1 , and showed excellent rate performance and cycle performance. -1 After 500 cycles at the same current density, the capacity retention rate reached 70.4% at -20°C. Compared to the battery without FA (0FA), the battery with 4mL of FA (4FA) showed a significant improvement in discharge specific capacity, with better rate and cycle performance. However, as the FA addition level continued to increase (e.g., 6FA and 8FA), the battery's discharge specific capacity continued to decline, and its rate and cycle performance deteriorated simultaneously. When the FA addition level reached 8mL, the battery's discharge specific capacity dropped to its lowest level.

[0042] A full battery was assembled with PTCDA as the negative electrode, MVOH as the positive electrode, and 4FA as the electrolyte, and its electrochemical performance was tested at -20℃ and 25℃. Figure 6 It can be seen that at -20℃, 0.2Ag -1 At the current density, the discharge capacity reaches 82.9 mAh g -1 , the rate and cycle performance are excellent, after testing, with 1Ag -1 After 5000 cycles at a current density of 1.544 nm, the capacity retention rate at -20°C and the capacity retention rate at 25°C were 85.14%, and 57.78%, respectively, indicating that the system has excellent long-cycle stability. Although it is slightly inferior to room temperature at low temperatures, the attenuation is small, making it suitable for long-life and wide-temperature range application scenarios.

[0043] (4) Test the safety performance of the electrolyte The safety of the electrolytes prepared in Example 1 and Comparative Example 1 was evaluated by combustion experiments and Tafe polarization curves. Figure 7 It can be seen that by dipping a certain amount of electrolyte in 4FA and pure FA with a glass fiber diaphragm and burning it for several seconds with an ignition torch, it can be found that after 5 seconds of combustion, the ignition torch is turned off and neither pure FA nor 4FA electrolytes continue to burn. This shows that FA electrolyte is non-flammable and has a certain degree of safety. The Tafel corrosion test of FA electrolyte shows that its corrosion potential increases from -0.453 V to 0.333 V, and the corrosion current also increases from 4.368 nA cm -2 Reduced to 0.549 nAcm -2 The more positive corrosion potential and smaller corrosion current indicate that the addition of FA additives inhibits the corrosion of the electrolyte to the metal, thereby protecting the battery shell and current collector and improving the stability of the battery system.

[0044] (5) The electrolyte system prepared in Example 1 was calculated based on DFT theory. Depend on Figure 8 It can be seen that the binding energy of the water dimer H2O-H2O is -0.142eV, which is 0.035eV smaller than the binding energy of H2O-FA and 0.035eV smaller than the binding energy of H2O-Cl - The binding energy is 0.11eV smaller. Therefore, the higher binding energy of H2O-FA is conducive to the formation of hydrogen bonds between H2O and FA molecules, resulting in the destruction and reorganization of the original hydrogen bonds between water molecules, which can effectively lower the freezing point of the electrolyte and inhibit the hydrogen evolution reaction. It was also found that the binding energy of FA-FA is slightly stronger than that of H2O-FA, but from the previous spectral characterization, it seems that this smaller energy difference does not inhibit the formation of hydrogen bonds between H2O molecules and FA molecules, that is, there is a dynamic process in the formation and dissociation of FA-FA and H2O-FA. Calculation of Mg 2+ With FA, H2O and Cl - The binding energy between Mg and Mg in FA electrolyte system is explored. 2+ The solvation structure of Mg 2+ The binding energy of -H2O is -1.155eV, while Mg 2+ The binding energy of -FA is -1.370eV, which is 0.255eV larger than the former, indicating that the binding energy of FA molecules to Mg 2+ The coordination ability of H2O molecules is better than that of Mg 2+ Therefore, the above results can show that FA as an electrolyte additive can regulate the structure of the electrolyte solvation sheath, so that the Mg 2+The H2O molecules in the solvation sheath are more likely to be replaced by FA molecules. The DFT results further prove that the addition of FA not only destroys the original hydrogen bond network between water molecules in the electrolyte, but also affects the solvation structure of magnesium ions in the electrolyte, possibly transforming the solvation structure of magnesium ions into [Mg(H2O) m (FA) n ] 2+ Therefore, the low-temperature application range of aqueous electrolytes is broadened and the hydrogen evolution reaction caused by water molecules generated during the desolvation process of magnesium ions is reduced, thereby optimizing the performance of magnesium ion batteries. 2+ With Cl - The formamide molecule can be combined with Cl through the above mentioned - The interaction competes with water and other solvent molecules to bind Cl - From the binding energy, Mg 2+ −Cl - The binding energy of formamide and Cl is −1.615 eV. - The binding energy is −0.224 eV. Although the value is small, the binding energy of formamide to Cl - The solvation effect can weaken the Mg 2+ With Cl - inter-ionic bond, promoting Cl - Detached Mg 2+ .

[0045] The above is only an embodiment of the present invention, and the common knowledge such as the specific technical solutions and / or characteristics in the solution are not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several variations and improvements can be made, which should also be regarded as the scope of protection of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the description can be used to interpret the content of the claims.

Claims

1. A low-temperature aqueous electrolyte based on formamide and MgCl2, characterized in that: The method comprises a solvent, a soluble metal salt and an additive, wherein the additive is formamide, and the volume ratio of formamide to the solvent is (2-8):

10.

2. A low-temperature aqueous electrolyte based on formamide and MgCl2 according to claim 1, characterized in that: The soluble metal salt is a soluble magnesium salt.

3. A low-temperature aqueous electrolyte based on formamide and MgCl2 according to claim 2, characterized in that: The concentration of soluble metal salts in the electrolyte is 1-5 moL / L.

4. A low-temperature aqueous electrolyte based on formamide and MgCl2 according to claim 3, characterized in that: The working temperature of the electrolyte is -20℃~25℃.

5. A method for preparing a low-temperature aqueous electrolyte based on formamide and MgCl2, characterized in that: The following steps are involved: S1: Weigh a certain amount of soluble metal salt for use; S2: taking a certain amount of additive and mixing it evenly with the solvent to prepare a mixed solvent; S3: The soluble metal salt weighed in S1 is dissolved in the mixed solvent in S2 to prepare a low-temperature aqueous electrolyte based on formamide and MgCl2.

6. An application of a low-temperature aqueous electrolyte based on formamide and MgCl2, characterized in that: Used in aqueous ion batteries.

7. The use of a low-temperature aqueous electrolyte based on formamide and MgCl2 according to claim 6, characterized in that: The aqueous ion battery is an aqueous magnesium ion battery.

8. The use of a low-temperature aqueous electrolyte based on formamide and MgCl2 according to claim 7, characterized in that: The positive electrode material of the aqueous ion battery includes a vanadium-based positive electrode material, and the negative electrode material includes PTCDA.

9. The use of a low-temperature aqueous electrolyte based on formamide and MgCl2 according to claim 8, characterized in that: The vanadium-based positive electrode material is a polyvalent magnesium vanadate compound.

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