Aqueous magnesium ion battery electrolyte, preparation method and application thereof

Abstract

The application belongs to the technical field of magnesium ion batteries, and discloses a kind of aqueous magnesium ion battery electrolyte and its preparation method and application, the mixed electrolyte for aqueous magnesium ion battery is composed of magnesium salt, organic solvent and deionized water;Wherein, the organic solvent is tetramethyl urea (TMU), and tetramethyl urea and deionized water jointly constitute the mixed solvent of the mixed electrolyte, and the volume percentage of tetramethyl urea in the mixed solvent is 10%~50%, and the volume percentage of deionized water is 90%~50%;Magnesium salt is dissolved in the mixed solvent.The application improves the components of electrolyte, the mixed electrolyte with TMU as cosolvent and accurate control of TMU volume fraction, solves the problem of narrow electrochemical stability window (ESW) of aqueous magnesium ion battery, serious interface side reaction leads to the poor cycle life, and the electrolyte has the advantages of simple preparation, environmental friendliness and low cost, which provides a new way for improving the energy density and cycle life of aqueous magnesium ion battery.

Description

Technical Field

[0001] This invention belongs to the field of magnesium-ion battery technology, and more specifically, relates to an aqueous magnesium-ion battery electrolyte, its preparation method and application. The solvent used in this aqueous magnesium-ion battery electrolyte is a mixed solvent of TMU and water, with tetramethylurea (TMU) as the organic co-solvent. Background Technology

[0002] Aqueous-based ion batteries have shown broad application prospects in large-scale energy storage due to their advantages such as high safety, low cost, and environmental friendliness. Among them, aqueous magnesium-ion batteries utilize divalent magnesium ions (Mg²⁺). 2+ Magnesium, as a charge carrier, theoretically has a higher volumetric energy density than lithium ions. Moreover, magnesium resources are widely distributed and inexpensive, giving it a significant cost advantage over lithium-ion batteries, and thus it has attracted much attention.

[0003] However, the inherent limitations of aqueous electrolytes restrict their further development in the field of magnesium-ion batteries: (1) Narrow electrochemical stability window (ESW): The theoretical thermodynamic decomposition voltage window of water molecules is narrow (about 1.23 V). Hydrogen evolution by reduction (HER) is prone to occur in the low potential region and oxygen evolution by oxidation (OER) is prone to occur in the high potential region, which seriously restricts the working voltage and energy density of the battery. (2) Electrode-electrolyte interface compatibility problem: Even if a non-metallic magnesium-intercalated anode is used, water molecules are still prone to triggering hydrogen evolution side reactions on the anode surface, which not only causes electrode corrosion and pulverization, but also is accompanied by by-products and pH fluctuations, accelerating the degradation of electrode structure, resulting in a decrease in coulombic efficiency and rapid capacity decay, making it difficult to meet the requirements of long-term energy storage for cycle stability. In order to solve the above problems, broaden the ESW and suppress side reactions, existing research mainly focuses on two types of electrolyte modification strategies: one is to use a high-concentration electrolyte strategy ("Water-in-Salt"), which reduces the free water content by ultra-high salt concentration (>20 mol / kg), which can extend the ESW to above 3.0 V. However, such systems suffer from problems such as a sharp increase in viscosity, a decrease in ionic conductivity, deterioration in low-temperature performance, and excessively high raw material costs, which limit their large-scale application. Another approach is to introduce organic additives to reconstruct the solvated structure through water miscibility. For example, polyethylene glycol (PEG) binds free water through hydrogen bonding, partially inhibiting HER, but it has a negative effect on Mg... 2+ The primary solvation sheath control capability is weak, and the ESW extension is limited (usually not exceeding 3.0 V). Moreover, high addition amounts (>50 vol%) lead to a sharp drop in ion mobility. In addition, current research focuses on common organic solvents such as dimethyl sulfoxide (DMSO) and acetonitrile (AN). These additives not only have limited effects on improving ESW, but may also have poor interfacial compatibility issues.

[0004] Therefore, for magnesium-ion batteries, if a novel aqueous hybrid electrolyte can be developed, it can be systematically optimized using a non-protic polar solvent with excellent coordination ability, effectively reducing free water activity at relatively low salt concentrations, thereby significantly broadening the ESW. This is not only the key to suppressing side reactions and improving cycle stability, but also the core to achieving a balance between the three objectives of "free water suppression – ion transport – interface compatibility".

[0005] On the other hand, although aqueous zinc-ion batteries (AZIBs) can provide insights for the design of aqueous electrolytes (e.g., by using organic cosolvents to broaden the window), those skilled in the art are well aware that magnesium ions (Mg... 2+ ) and zinc ions (Zn 2+ They differ fundamentally in ionic radius, charge density, solvation energy, and interfacial reaction kinetics. Mg 2+ Higher charge density results in stronger polarization, making it more prone to water molecule decomposition and electrode interface passivation. Therefore, directly applying mature electrolyte formulations from AZIBs (such as acetonitrile and PEG) to magnesium-ion systems is not only ineffective but may even exacerbate performance degradation due to uncontrollable side reactions. The technological barriers between aqueous magnesium-ion and aqueous zinc-ion batteries mean that the development of efficient organic cosolvents for both systems tends to be independent; currently, there is a lack of efficient organic cosolvents suitable for aqueous magnesium batteries. Summary of the Invention

[0006] To address the aforementioned deficiencies or improvement needs of existing technologies, the present invention aims to provide an aqueous magnesium-ion battery electrolyte, its preparation method, and its applications. By improving the electrolyte composition, using tetramethylurea (TMU) as a co-solvent in a mixed electrolyte and precisely controlling the TMU volume fraction (10%~50%), the problems of narrow electrochemical stability window (ESW) and poor cycle life caused by severe interfacial side reactions in aqueous magnesium-ion batteries are solved. TMU molecules reshape Mg through strong coordination. 2+ The solvated sheath structure significantly suppresses free water activity, extending the ESW to above 3.4 V. This electrolyte combines the advantages of simple preparation, environmental friendliness, and low cost, requiring no changes to existing production processes and better meeting the requirements of large-scale industrial applications. It provides a new approach to improving the energy density and cycle life of aqueous magnesium-ion batteries.

[0007] To achieve the above objectives, according to one aspect of the present invention, a mixed electrolyte for an aqueous magnesium-ion battery is provided, characterized in that it comprises a magnesium salt, an organic solvent, and deionized water; wherein the organic solvent is tetramethylurea (TMU), the tetramethylurea and the deionized water together constitute the mixed solvent of the mixed electrolyte, the volume percentage of the tetramethylurea in the mixed solvent is 10% to 50%, and the volume percentage of the deionized water in the mixed solvent is 90% to 50%; the magnesium salt is dissolved in the mixed solvent.

[0008] As a further preferred embodiment of the present invention, the volume percentage of the tetramethylurea in the mixed solvent is 30% to 50%, and the volume percentage of the deionized water in the mixed solvent is 70% to 50%.

[0009] As a further preferred embodiment of the present invention, the tetramethylurea has a volume percentage of 40% in the mixed solvent, and the deionized water has a volume percentage of 60% in the mixed solvent.

[0010] As a further preferred embodiment of the present invention, the magnesium salt is magnesium trifluoromethanesulfonate (Mg(OTf)2).

[0011] As a further preferred embodiment of the present invention, the concentration of the magnesium salt in the mixed electrolyte is 1 to 4 mol / L.

[0012] As a further preferred embodiment of the present invention, the concentration of the magnesium salt in the mixed electrolyte is 1 mol / L.

[0013] According to another aspect of the present invention, the present invention provides a method for preparing the above-mentioned mixed electrolyte for aqueous magnesium-ion batteries, characterized by comprising the following steps: S1: Mix tetramethylurea (TMU) and deionized water at a volume ratio of (10~50):(50~90), stir, and obtain a uniform mixed solvent; S2: Add magnesium salt to the mixed solvent and stir until completely dissolved to obtain a mixed electrolyte for aqueous magnesium ion batteries.

[0014] According to another aspect of the present invention, the present invention provides the application of the above-described mixed electrolyte for aqueous magnesium-ion batteries as an electrolyte in aqueous magnesium-ion batteries.

[0015] According to another aspect of the present invention, an aqueous magnesium-ion battery is provided, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that the electrolyte is the above-mentioned mixed electrolyte for aqueous magnesium-ion batteries.

[0016] As a further preferred embodiment of the present invention, the negative electrode of the aqueous magnesium ion battery uses a non-metallic intercalated material as the active material. Preferably, the negative electrode of the aqueous magnesium ion battery uses intercalated sodium titanate (Na2Ti2O5) as the active material. The positive electrode of the aqueous magnesium ion battery uses layered manganese oxide as the active material; preferably, the positive electrode of the aqueous magnesium ion battery uses hydrated manganese oxide-type layered manganese dioxide (δ-MnO2) as the active material.

[0017] Compared with the prior art, the present invention uses tetramethylurea (TMU) as an organic co-solvent, which is mixed with water to form a mixed solvent, and together dissolves magnesium salts to form a mixed electrolyte for aqueous magnesium-ion batteries. The TMU molecule contains a -C=O polar group, which can react with Mg... 2+ Strong interactions are formed, and the large-sized -N(CH3)2 groups repel water molecules through steric hindrance.

[0018] Specifically, the present invention can achieve the following beneficial effects: (1) Significantly broadened electrochemical stability window (ESW): This invention innovatively introduces TMU as an organic co-solvent. TMU molecules have an extremely high donor number (DN value) and react with Mg. 2+ Ions generate strong coordination interactions, and Mg is controlled through electrolyte composition optimization. 2+ The solvation structure of the ions replaces and repels water molecules in the solvated sheath, while effectively disrupting the hydrogen bond network between water molecules through strong hydrogen bonding between the co-solvent polar groups and water molecules, thereby inhibiting the hydrogen evolution / oxygen evolution reaction. Experimental data show that the electrolyte (TMU40) of this invention can significantly increase the ESW to ~3.4 V, providing a possibility for high-voltage aqueous batteries.

[0019] (2) Significantly improves electrode-electrolyte interface compatibility: The aqueous magnesium-ion battery electrolyte obtained in this invention can be specifically matched with the intercalated sodium titanate anode, exhibiting a unique interface matching effect and producing a synergistic effect. The TMU constructs a highly efficient ion-conducting electrode-electrolyte interface layer in situ, significantly inhibiting Mg 2+ Side reactions during ion insertion / extraction. With an optimized TMU ratio of 40%, the battery retained 88.5% of its capacity after 200 cycles, achieving a reversible specific capacity of 153.9 mAh g. -1 This invention solves the problems of interfacial side reactions and poor cycle stability, achieves synergistic effect between electrolyte and electrode, and obtains a low-cost and high-safety electrolyte system with wide ESW and stable interfacial phase. It is the best NTO effect reported in the current technology, and provides a new path to solve the technical bottleneck of current aqueous magnesium ion batteries.

[0020] This invention is the first to discover a specific matching effect between TMU-modified electrolyte and intercalated sodium titanate (NTO) anode in aqueous magnesium-ion battery systems. Addressing the long-standing challenge of a lack of non-metallic anode materials and poor interfacial compatibility in this system, the introduction of TMU can construct a stable interface layer (SEI) with high ion conductivity in situ on the NTO surface. This effectively suppresses side reactions and water decomposition during magnesium ion intercalation / deintercalation, thereby improving the battery's cycle stability. This specific matching strategy effectively solves the problem of incompatibility between highly active components and electrode interfaces in aqueous magnesium-ion batteries, resulting in excellent cycle performance (e.g., capacity retention of 113.1% after 100 cycles and 88.5% after 200 cycles).

[0021] Currently, research on non-metallic anode materials for aqueous magnesium-ion batteries is still in the exploratory stage, with relevant reports (such as vanadium oxides (VO2, NaV8O)) being relatively limited. 20 The availability of suitable materials for aqueous magnesium-ion batteries (such as organic materials like PTCDA) is very limited. Compared to these existing technologies, the aqueous magnesium-ion battery electrolyte obtained in this invention can be used in conjunction with intercalated sodium titanate anodes. Intercalated sodium titanate exhibits a more negative discharge voltage platform in aqueous magnesium-ion batteries and is compatible with the modified electrolyte of this invention, demonstrating excellent electrochemical performance. The aqueous magnesium-ion battery electrolyte obtained in this invention expands the range of anode materials that can be selected for aqueous magnesium-ion batteries. Furthermore, given the applicability of NTO anode materials, which possess a more negative discharge voltage platform, the electrolyte system obtained in this invention will inevitably have broad compatibility and adaptability advantages for most anode materials.

[0022] In summary, this invention overcomes the core shortcomings of existing aqueous magnesium-ion battery electrolytes, such as narrow electrochemical window, poor compatibility with electrode materials, and poor cycle life. Through the core innovation of a specific TMU / H2O volume ratio, a novel hybrid electrolyte system for aqueous magnesium-ion batteries is constructed. Its formulation and preparation method are simple, while also achieving a wide electrochemical stability window. Furthermore, this hybrid electrolyte exhibits a significant and specific matching effect with intercalated electrodes, effectively broadening electrode material compatibility and improving battery cycle stability. Based on this invention, the solvation structure regulation of the electrolyte and electrode interface modification engineering can be combined, potentially making low-cost, high-safety, and environmentally friendly aqueous magnesium-ion batteries an important choice for next-generation electrochemical energy storage devices. Attached Figure Description

[0023] Figure 1 This is a comparison of linear sweep voltammetry (LSV) curves of electrolytes with different TMU volume ratios prepared in Comparative Example 1 and Examples 1-5 of this invention; wherein, Figure 1 In this context, 'a' corresponds to a potential of -2V to 2V (vs. SCE). Figure 1The image shows a magnified view of the potential corresponding to b in the range of -1.7V to -0.9V (vs. SCE).

[0024] Figure 2 This is a comparison chart of the cycle performance and coulombic efficiency of half-cells composed of the electrolytes prepared in Comparative Example 1 and Examples 1-5 of this invention, respectively, and matched with intercalated sodium titanate (NTO) negative electrodes; wherein, Figure 2 In this context, 'a' represents the loop performance. Figure 2 In this context, b represents the Coulomb efficiency.

[0025] Figure 3 These are the test results of the cyclic voltammetry (CV), long-cycle performance, rate performance, and charge-discharge curve (GCD) of the half-cell composed of the electrolyte of Example 4 (TMU40) and the intercalated sodium titanate (NTO) negative electrode; wherein, Figure 3 In this context, 'a' corresponds to the cyclic voltammetry curve. Figure 3 In this context, 'b' corresponds to long-cycle performance. Figure 3 In this context, 'c' corresponds to the rate performance. Figure 3 The d in the figure corresponds to the charge-discharge curve.

[0026] Figure 4 This is a cycle performance test diagram of a full cell composed of the electrolyte of Example 4 (TMU40) of this invention, matched with an intercalated sodium titanate (NTO) negative electrode and a layered manganese dioxide (δ-MnO2) positive electrode. Detailed Implementation

[0027] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0028] This invention proposes an aqueous magnesium-ion battery hybrid electrolyte. Accordingly, subsequent examples aim to provide a series of aqueous hybrid electrolytes with improved electrochemical performance and to explore the optimal addition ratio of the organic co-solvent tetramethylurea (TMU, ≥99.5%). The preparation methods for Examples 1-5 are the same, differing only in the volume ratio of TMU to deionized water; they are named TMU10, TMU20, TMU30, TMU40, and TMU50, respectively. The specific ratios are shown in the table below:

[0029] The preparation process will be described in detail using Example 4 (TMU40) as an example: S1. Preparation of mixed solvent: At room temperature and pressure, accurately measure 40 mL of TMU organic solvent and 60 mL of deionized water using a graduated cylinder, and stir rapidly for 10 minutes using a magnetic stirrer to obtain 100 mL of uniform and transparent TMU / H2O mixed solvent.

[0030] S2. Salt dissolution: While stirring, slowly add 32.244 g of precisely weighed magnesium trifluoromethanesulfonate (Mg(OTf)2, 98% purity) salt to the above mixed solvent.

[0031] S3. Continue stirring: Continue stirring for 12 hours to ensure that the salt is completely dissolved and a uniform and clear 1 M Mg(OTf)2in TMU / H2O (4:6 v / v) mixed electrolyte is obtained.

[0032] S4. Let stand and age: Seal the prepared electrolyte and let it stand for 24 hours before use.

[0033] The preparation methods of Examples 1-3 and Example 5 are the same as those of Example 4, except that the volume of TMU and deionized water is adjusted.

[0034] Comparative Example 1 This comparative example provides a conventional 1 M magnesium trifluoromethanesulfonate (Mg(OTf)2, 98% purity) aqueous electrolyte for performance comparison with the mixed electrolyte provided by this invention. It is named BE.

[0035] The preparation method is as follows: Under normal temperature and pressure, 32.244g of magnesium trifluoromethanesulfonate was weighed and dissolved in 100ml of deionized water. The solution was magnetically stirred until the salt was completely dissolved to obtain an aqueous solution of Mg(OTF)2 with a concentration of 1mol / L. This clear and transparent solution was used as the electrolyte for aqueous magnesium ion batteries.

[0036] This invention also relates to the application of aqueous electrolytes in magnesium-ion batteries, wherein the intercalated negative electrode material is Na2Ti2O5 (named NTO), the positive electrode material is layered δ-MnO2, and the electrolytes are those prepared in the above-mentioned examples and comparative examples. The electrode preparation process is as follows: the negative electrode is prepared by mixing NTO active material, conductive carbon black (Super P), and polytetrafluoroethylene (PTFE) binder in a mass ratio of 8:1:1, adding an appropriate amount of isopropanol, and grinding into a uniform electrode sheet. Then, it is pressed onto a titanium mesh current collector using a tablet press at a pressure of 5 MPa; after vacuum drying at 100 °C for 12 hours, the active material loading is approximately 1.0 mg cm⁻¹. -2 The positive electrode preparation process is similar to that of the negative electrode, except that the active material is replaced with δ-MnO2 instead of NTO, and the active material loading is approximately 1.2 mg cm⁻¹. -2 .

[0037] The electrochemical performance tests described later, including linear cyclic voltammetry (LSV), cyclic voltammetry (CV), and galvanostatic charge-discharge curves (GCD), were all performed on an electrochemical workstation (KOSTAR CS2350H) to obtain electrochemical performance information such as the electrochemical stability window (ESW), CV curves, cycle life, and rate performance.

[0038] Test Example 1 Figure 1 Examples 1-5 (named TMU10, TMU20, TMU30, TMU40, and TMU50) and Comparative Example 1 (named BE) of the aqueous electrolyte of the present invention were tested using linear cyclic voltammetry (LSV), with a scan potential range of -2.0 to 2.0 V (vs. SCE) and a scan rate of 1 mV / s. -1 This is used to determine the electrochemical stability window of an electrolyte. Figure 1 It can be seen that, compared with Comparative Example 1 (BE), the electrochemical window of the aqueous electrolyte of the present invention in Examples 1-5 shows an increasingly wider trend, which can be seen from the magnified details of the negative potential region (e.g. Figure 1 As shown in b), this corresponds to the reduction decomposition of the electrolyte at the negative electrode and the hydrogen evolution side reaction of water molecules. Among them, Comparative Example 1 (BE) begins to undergo vigorous hydrogen evolution at about -1.3 V (vs. SCE), while Example 4 has a negative electrode side window potential of about -1.5 V (vs. SCE) and an electrochemical stability window width of about 3.4 V, proving that it can effectively suppress water decomposition.

[0039] Test Example 2 Figure 2 Three-electrode tests were conducted using the electrolytes of Comparative Example 1 (BE) and Examples 1-5 (TMU10, TMU20, TMU30, TMU40, TMU50) with intercalated sodium titanate (NTO) negative electrodes. The NTO electrode served as the working electrode, the platinum sheet as the counter electrode, and the calomel electrode as the reference electrode. Using a KOST electrochemical testing workstation (CS2350H), at room temperature and a voltage range of -0.6 to -1.5 V (vs. SCE), at a concentration of 2 A g... -1 Constant current charge-discharge test was performed on the current density.

[0040] The results show that the half-cell using the electrolyte of this invention exhibits significantly better cycle stability than the half-cell using the electrolyte of Comparative Example 1 (BE). The half-cell corresponding to the electrolyte in Example 4 (TMU40) demonstrates the highest average coulombic efficiency (92.8%) and the best cycle life (capacity of 128.7 mAh g⁻¹ after 100 cycles). -1The capacity retention rate of the half-cell using the electrolyte of Example 1 (TMU10) was as high as 113.1%, far exceeding that of Comparative Example 1 (BE). The capacity retention rates of Comparative Example 1 and Examples 1-5 after 100 cycles were 34.5%, 32.6%, 60.2%, 89.0%, 113.1%, and 100.5%, respectively, with average coulombic efficiencies of 62.6%, 74.6%, 70.7%, 80.5%, 92.8%, and 90.4%, respectively. Although the half-cell using the electrolyte of Example 1 (TMU10) had a slightly lower capacity retention rate after 100 cycles than the half-cell using the electrolyte of Comparative Example 1 (BE), the average coulombic efficiency was significantly improved, and the overall performance was still superior to that of the half-cell using the electrolyte of Comparative Example 1 (BE).

[0041] Surprisingly, when the TMU content was 40% (Example 4), the battery's overall performance showed a clear extreme point, with a cycle retention rate (113.1%) far exceeding that of groups with higher (50% TMU) or lower (10% TMU) TMU contents. This indicates that the performance improvement is not a simple linear function of TMU content, but rather that there exists an optimal ratio range. Therefore, based on this invention, the TMU content in the mixed solvent can preferably be controlled at 30 vol% to 50 vol%, especially 40 vol% to 50 vol% (of course, 40 vol% yields the best results).

[0042] Test Example 3 Figure 3 Taking the electrolyte of Example 4 (TMU40) as an example, a half-cell was assembled with an intercalated sodium titanate (NTO) electrode, wherein the electrode preparation and testing environment were the same as in Test Example 2 above. Within the potential range of -0.4 to -1.55 V (vs. SCE), at 1 mVs... -1 Cyclic voltammetry (CV) tests were performed at a scan rate of 2Ag. The potential range was -0.4 to -1.55 V (vs. SCE). -1 Constant current charge-discharge tests were performed at different current densities (e.g., 2, 3, 4, 5, 6, 8 A g). -1 The rate performance was tested under these conditions.

[0043] Figure 3 Figure 'a' shows the cyclic voltammetry (CV) curve. A pair of distinct oxidation / reduction peaks can be observed at approximately -1.2 V / -1.5 V in the CV curve, indicating that the intercalated NTO anode exhibits reversible electrochemical insertion / extraction of Mg. 2+ Ionic properties.

[0044] Figure 3 Figure b shows the long-cycle performance curve, which reveals that the electrolyte of Example 4 (TMU40) paired with an intercalated NTO anode exhibits a performance of 173.9 mAh g⁻¹.-1 It exhibits a high initial specific capacity, and retains a reversible specific capacity of 153.9 mAh g⁻¹ after 200 cycles. -1 The capacity retention rate was 88.5%, and the average coulombic efficiency was 92.6%, demonstrating the excellent cycling performance of the electrolyte-electrode combination.

[0045] Figure 3 The value of 'c' in the figure represents the rate performance. It can be seen that this battery exhibits excellent rate performance at 2 A g. -1 Below is 183.3 mAh g -1 The initial specific capacity, even at 8 A g -1 Even under high current, it can still maintain 111.1 mAh g. -1 The reversible capacity. When the current density recovers to 2 A g. -1 At that time, the capacity can be restored to 170.0 mAh g. -1 It exhibits good structural stability.

[0046] Figure 3 Figure d shows the charge-discharge curve, which can be seen to have a clear voltage plateau and small polarization, reflecting the presence of Mg. 2+ Excellent ion insertion / extraction kinetics.

[0047] Test Example 4 Figure 4 Taking the electrolyte of Example 4 (TMU40) as an example, a full cell was assembled with an intercalated NTO negative electrode and a layered δ-MnO2 positive electrode. The electrode preparation and testing environment were the same as in Test Example 2 above. The voltage range was 0.01~2.4 V, and the current density was 2 A g. -1 The long-cycle test was conducted below. Figure 4 It can be seen that the full battery exhibits excellent long-cycle stability, with a first-cycle discharge specific capacity of 30.3 mAh g⁻¹. -1 After 150 cycles, the capacity retention rate remained as high as 86.9%, and the average coulombic efficiency was 92.5%. This fully demonstrates that the mixed electrolyte with 40 vol% TMU co-solvent provided by this invention has extremely high application value in practical battery devices.

[0048] It is evident that the TMU electrolyte obtained based on this invention exhibits an excellent and unique interface matching effect when matched with intercalated sodium titanate (NTO), a non-metallic layered anode. We hypothesize that TMU, through its strong coordination ability and hydrophobic properties, forms a more stable interface layer on the NTO anode surface, effectively suppressing Mg... 2+ Side reactions during the insertion / extraction process significantly improve cycle life. This "TMU-NTO" combination is reported for the first time in this invention.

[0049] In summary, for aqueous magnesium-ion batteries, this invention significantly broadens the electrochemical stability window of the electrolyte and improves the electrode / electrolyte interface by introducing a specific proportion of TMU organic co-solvent into the aqueous electrolyte, thereby greatly improving the cycle life and rate performance of the aqueous magnesium-ion battery. Among these, the overall performance is optimal when the TMU volume percentage is 40% (Example 4).

[0050] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An aqueous magnesium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte, characterized in that, The electrolyte is a mixed electrolyte with a wide electrochemical stability window for aqueous magnesium-ion batteries; The electrolyte is composed of a magnesium salt, an organic solvent, and deionized water; wherein the organic solvent is tetramethylurea (TMU), and the tetramethylurea and the deionized water together constitute the mixed solvent of the mixed electrolyte, with the volume percentage of tetramethylurea in the mixed solvent being 40% and the volume percentage of deionized water in the mixed solvent being 60%; the magnesium salt is dissolved in the mixed solvent, and the concentration of the magnesium salt in the mixed electrolyte is 1 mol / L; and the electrochemical stability window of the mixed electrolyte is above 3.4 V. The magnesium salt is magnesium trifluoromethanesulfonate Mg(OTf)2; The negative electrode of the aqueous magnesium-ion battery uses a non-metallic intercalated material as the active material; the positive electrode of the aqueous magnesium-ion battery uses layered manganese oxide as the active material. The negative electrode of the aqueous magnesium-ion battery uses intercalated sodium titanate (Na2Ti2O5) as the active material.

2. The aqueous magnesium-ion battery as described in claim 1, characterized in that, The positive electrode of the aqueous magnesium-ion battery uses layered manganese dioxide δ-MnO2 of the sodium manganese ore type as the active material.

3. The aqueous magnesium-ion battery as described in claim 1, characterized in that, The method for preparing the mixed electrolyte with a wide electrochemical stability window for aqueous magnesium-ion batteries includes the following steps: S1: Mix tetramethylurea (TMU) and deionized water at a volume ratio of 40:60, stir, and obtain a homogeneous mixed solvent; S2: Add magnesium salt to the mixed solvent and stir until completely dissolved to obtain a mixed electrolyte for aqueous magnesium ion batteries.

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