Low-temperature aqueous gel electrolyte and preparation method and application thereof

Abstract

The application relates to the technical field of magnesium ion batteries, and discloses a low-temperature aqueous gel electrolyte, which comprises a soluble metal salt, an additive and a solvent, wherein the additive is formamide and SiO2, the volume ratio of the formamide to the solvent is 4: (5-7), and the added amount of the SiO2 is 14%-16% of the total mass of the formamide and the solvent; a preparation method of the low-temperature aqueous gel electrolyte, which comprises the following steps: S1, weighing a certain amount of the soluble metal salt for standby; S2, measuring a certain amount of the formamide, uniformly mixing the formamide with a solvent to prepare a mixed solvent; S3, dissolving the weighed soluble metal salt in the mixed solvent in S2 to prepare an electrolyte; S4, weighing a certain amount of SiO2, adding the SiO2 into the electrolyte prepared in S3 to uniformly mix, and preparing the low-temperature aqueous gel electrolyte. The low-temperature aqueous gel electrolyte is applied to an aqueous ion battery. The technical scheme of the application can solve the performance limitation problem of the aqueous ion battery in a low-temperature environment.

Description

Technical Field

[0001] This invention relates to the field of magnesium-ion battery technology, specifically to a low-temperature aqueous gel electrolyte, its preparation method, and its application. Background Technology

[0002] Against the backdrop of rapid development in energy storage technology, aqueous electrolytes have become an important research direction for aqueous ion batteries due to their significant advantages such as low cost, non-toxicity, non-flammability, and high ionic conductivity. Using water as a solvent, aqueous electrolytes can effectively improve battery safety and environmental friendliness, making them particularly suitable for large-scale energy storage systems. However, the performance limitations of aqueous electrolytes in low-temperature environments have become a major obstacle to their commercialization. Since water's freezing point is 0°C, aqueous electrolytes are prone to freezing at low temperatures, leading to a decrease in ionic conductivity and affecting battery cycle life and energy density. Furthermore, the increased viscosity of the electrolyte at low temperatures further exacerbates the difficulty of ion migration, thus limiting the application of aqueous ion batteries in extremely cold regions.

[0003] To overcome this technological bottleneck, researchers have explored various technical approaches, including high-concentration electrolytes, deep eutectic electrolyte systems, gel electrolyte systems, and co-soluble additives. However, these approaches all have certain limitations. For example, while high-concentration electrolytes can effectively improve low-temperature stability, they are expensive and may lead to salting-out crystallization, affecting the long-term cycle performance of the battery. Although deep eutectic electrolyte systems have some low-temperature adaptability, their ionic conductivity is low, and some components (such as ClO4) are also problematic. - This may corrode the electrodes. While gel electrolyte systems possess advantages such as mechanical flexibility, leak resistance, and non-flammability, the pores of the gel network shrink at extreme temperatures, limiting ion transport. Therefore, synergistic regulation with a low-temperature co-solvent is necessary. Although co-solvent additives are low-cost, require small amounts, and are widely applicable, excessive addition can dilute the ion concentration, reduce battery energy density, and some additives (such as methanol) pose a risk of toxicity or side reactions. Summary of the Invention

[0004] The present invention aims to provide a low-temperature aqueous gel electrolyte, its preparation method and application, in order to solve the performance limitation problem of aqueous ion batteries in low-temperature environments.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: a low-temperature aqueous gel electrolyte, comprising a soluble metal salt, an additive and a solvent, wherein the additive is formamide and SiO2, the volume ratio of formamide to solvent is 4:(5-7), and the amount of SiO2 added is 14%-16% of the total mass of formamide and solvent.

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

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

[0008] Preferably, the soluble magnesium salt is MgCl2.

[0009] Preferably, the working temperature of the electrolyte is -20 to 25°C.

[0010] This invention also provides another technical solution: a method for preparing a low-temperature aqueous gel electrolyte, comprising the following steps:

[0011] S1: Weigh out a certain amount of soluble metal salt for later use;

[0012] S2: Measure a certain amount of formamide, mix it evenly with the solvent, and prepare a mixed solvent;

[0013] S3: Dissolve the soluble metal salt weighed in S1 in the mixed solvent of S2 to prepare an electrolyte;

[0014] S4: Weigh a certain amount of SiO2 and add it to the electrolyte prepared in S3. Mix well to obtain a low-temperature aqueous gel electrolyte.

[0015] The present invention also provides another technical solution, namely, the application of a low-temperature aqueous gel electrolyte in aqueous ion batteries.

[0016] Preferably, the aqueous ion battery is an aqueous magnesium ion battery.

[0017] Preferably, the positive electrode material of the aqueous ion battery includes a vanadium-based positive electrode material containing electrode additives, and the negative electrode material includes PTCDA containing electrode additives.

[0018] Preferably, the preparation process of the electrode additive is as follows: the obtained low-temperature aqueous gel electrolyte is first subjected to low-temperature dehydration treatment at -52 to -48°C, and then ball milled to obtain micron-sized powder, which is the electrode additive.

[0019] Compared with the existing technology, the beneficial effects of this solution are as follows: (1) This solution constructs a dual-mechanism system of "low freezing point co-solution-three-dimensional network conductivity" through the synergistic design of formamide and hydrophilic SiO2. Formamide, as a co-solvent, forms hydrogen bonds with water molecules, lowering the freezing point of the electrolyte to below -20℃, thus solving the problem of freezing at 0℃ in traditional aqueous electrolytes; the silanol groups (Si-OH) on the surface of hydrophilic SiO2 adsorb free ions through hydrogen bonding, forming a continuous ion transport channel. At -20℃, the ionic conductivity can reach 22.73 mS / cm, which is 50% higher than that of 1 mol / L MgCl2 aqueous solution (15.11 mS / cm), breaking through the ion transport bottleneck caused by the low-temperature network shrinkage of existing gel electrolytes.

[0020] (2) SiO2 nanoparticles are uniformly dispersed in the electrolyte to form a three-dimensional network structure, which physically blocks the growth path of MgCl2 crystals through the steric hindrance effect. SEM observation shows that the MgCl2 crystal size in the 4FA electrolyte is 150-200 μm and is severely agglomerated, while the crystal size in the gel electrolyte of this invention is only 10 μm and is uniformly distributed, resulting in better low-temperature cycling stability of the electrolyte. This scheme innovatively combines the "steric hindrance effect" of SiO2 with the "solventization effect" of FA, and improves the low-temperature cycling stability of the electrolyte through the dual effects of physical barrier and chemical solvation.

[0021] (3) This scheme innovatively adopts a "low-temperature dehydration-ball milling" process to convert the quasi-solid FA-SiO2 gel electrolyte into a micron-sized freeze-dried powder additive, which is uniformly dispersed in the positive and negative electrode materials. This electrode additive has both ion conduction and interface stabilization functions: in the vanadium-based positive electrode, it can form a fast ion transport channel, enabling a discharge specific capacity of 214.8 mAh / g at -20℃; in the PTCDA negative electrode, it can suppress interfacial side reactions and improve cycle stability. After 5000 cycles at a current density of 1 A / g, the full cell retains 76.3% of its capacity at -20℃. This scheme innovatively converts the electrolyte material directly into a functional additive, realizing an integrated design of ion conduction and structural stability at the "electrolyte-electrode" interface.

[0022] (4) The electrolyte operates at temperatures ranging from -20°C to 25°C, maintaining its liquid fluidity at -20°C and achieving an ionic conductivity of 71.94 mS / cm at 25°C, thus balancing high-temperature ion transport efficiency with low-temperature stability. It utilizes non-toxic formamide and environmentally friendly SiO2 to replace toxic additives such as methanol. Furthermore, the gel-state electrolyte is non-flammable and has no risk of leakage, making it safer than organic electrolyte systems and meeting the environmental requirements for large-scale energy storage.

[0023] (5) Gel electrolytes have a certain degree of mechanical plasticity, which meets the requirements of flexible devices. The core raw materials MgCl2, formamide and SiO2 have low cost. The preparation process adopts room temperature dissolution and stirring method, which does not require high temperature, high pressure or complicated purification steps, and can realize large-scale production, breaking through the industrialization bottleneck of high cost and complex process of existing low temperature electrolytes.

[0024] This solution achieves multi-level breakthroughs in low-temperature ion conduction, salt precipitation crystal suppression, and interface adaptation through molecular design of composite additives, process innovation of interface regulation, and system reconstruction of functional materials. Compared with existing technologies, it achieves synergistic optimization of "antifreeze-ion conduction-stable interface-low cost", providing a systematic solution for the commercial application of low-temperature aqueous batteries. Attached Figure Description

[0025] Figure 1These are actual state diagrams of the aqueous gel electrolyte prepared in Example 1 of the present invention under conditions of 25°C and -20°C.

[0026] Figure 2 A comparison of the ionic conductivity of the aqueous gel electrolyte prepared in Example 1 of the present invention and the electrolytes prepared in Comparative Examples 1-2 at different temperatures;

[0027] Figure 3 The GCD curves, rate performance, and cycle performance comparison charts of the aqueous gel electrolyte prepared in Example 1 and the electrolyte prepared in Comparative Example 2 are shown.

[0028] Figure 4 Electrochemical performance diagrams of full cells assembled from the aqueous gel electrolyte prepared in Example 1 of this invention and the electrolyte prepared in Comparative Example 2;

[0029] Figure 5 (ab) are SEM images of the electrolyte prepared in Comparative Example 2 of this invention;

[0030] Figure 5 (cd) is a SEM image of the aqueous gel electrolyte prepared in Example 1 of this invention. Detailed Implementation

[0031] The following detailed description illustrates the specific implementation method:

[0032] Example 1

[0033] The volume ratio of formamide to solvent is 4:(5-8), and the amount of SiO2 added is 13%-18% of the total mass of soluble metal salt, formamide and solvent.

[0034] A low-temperature aqueous gel electrolyte comprises a soluble metal salt, an additive, and a solvent. The soluble metal salt is a soluble magnesium salt, specifically MgCl2, with a concentration of 1–5 mol / L. The additive consists of formamide and SiO2, with a formamide to solvent volume ratio of 4:(5-7). The SiO2 is selected as a hydrophilic type, and its concentration is 14%–16% of the total mass of formamide and solvent. The solvent is deionized water. The electrolyte operates at a temperature of -20–25°C. In this embodiment, the MgCl2 concentration is 1 mol / L. The formamide to water volume ratio is 4:6. The hydrophilic SiO2 is manufactured by Shanghai Maclean Biochemical Technology Co., Ltd., and the amount of hydrophilic SiO2 added is 1.5 g.

[0035] A method for preparing a low-temperature aqueous gel electrolyte includes the following steps:

[0036] S1: Weigh 2.033g of MgCl2·6H2O as a soluble metal salt for later use;

[0037] S2: Measure 4 mL of formamide (FA) and mix it with 6 mL of deionized water to prepare a mixed solvent;

[0038] S3: Dissolve the MgCl2·6H2O weighed in S1 in the mixed solvent of S2 to prepare an electrolyte;

[0039] S4: Weigh 1.5g of hydrophilic SiO2 and add it evenly to the electrolyte prepared in S3 in small amounts several times. At the same time, use a magnetic stirrer to stir thoroughly until the entire gel is uniform to obtain a low-temperature aqueous gel electrolyte, denoted as 4FA-SiO2.

[0040] An application of a low-temperature aqueous gel electrolyte is disclosed, which is used in an aqueous magnesium-ion battery. The positive electrode material of the aqueous magnesium-ion battery includes a vanadium-based positive electrode material containing 15 wt% electrode additives, and the negative electrode material includes PTCDA containing 15 wt% electrode additives; wherein the vanadium-based positive electrode material is Mg... x V 10 O 24 • nH2O nanoflower cathode material, denoted as MVOH.

[0041] The preparation process of the electrode additive is as follows: First, the prepared low-temperature aqueous gel electrolyte is placed in a freeze dryer and dehydrated at -52 to -48°C for 12 hours. After dehydration, it is ball-milled into micron-sized powder to obtain the electrode additive. It is important to note that the prepared electrode additive must be stored in a dry environment with humidity less than 10% to prevent moisture absorption and particle agglomeration, which would affect its dispersion characteristics. In this embodiment, the low-temperature dehydration treatment is performed at -50°C.

[0042] Comparative Example 1

[0043] Unlike Example 1, a low-temperature aqueous gel electrolyte comprises MgCl2 and deionized water, contains no additives, and has a MgCl2 concentration of 1 mol / L.

[0044] A method for preparing a low-temperature aqueous gel electrolyte, excluding S3 and S4, wherein in S2, the MgCl2·6H2O weighed in S1 is dissolved in 10 mL of deionized water to prepare a MgCl2 electrolyte, denoted as 0FA.

[0045] Comparative Example 2

[0046] Unlike Example 1, this is a low-temperature aqueous gel electrolyte with formamide as the additive and no hydrophilic SiO2.

[0047] A method for preparing a low-temperature aqueous gel electrolyte, excluding S4, wherein the electrolyte prepared in S3 is denoted as 4FA.

[0048] The performance of the aqueous gel electrolyte prepared in Example 1 and the electrolytes prepared in Comparative Examples 1-2 were tested.

[0049] Performance testing employed both two-electrode and three-electrode systems. Specifically: Two-electrode electrolytic cell: using Pt sheets as both the working and counter electrodes to test ionic conductivity. Three-electrode electrolytic cell: using Mg as the working electrode. x V 10 O 24 ·nH2O, Mg x V 10 O 24 • 15 wt% electrode additive was added to nH2O, with a Pt electrode as the counter electrode and Ag / AgCl as the reference electrode, to test the electrochemical performance of the electrolyte. Full cell testing: A Swagelok battery mold was used, with MVOH as the positive electrode, PTCDA (containing 15 wt% electrode additive) as the negative electrode, and PTCDA containing 15 wt% electrode additive, to evaluate the electrochemical performance of the full cell.

[0050] (1) Test the physical state of the aqueous gel electrolyte prepared in Example 1 and the electrolyte prepared in Comparative Examples 1-2.

[0051] Depend on Figure 1 It can be seen that the electrolyte prepared in Comparative Example 1 freezes at -20℃, while the electrolyte prepared in Comparative Example 2 remains liquid at -20℃. The low-temperature aqueous gel electrolyte prepared in Example 1 still has good fluidity at -20℃ and can be inverted, exhibiting a certain degree of mechanical plasticity. This is because hydrophilic SiO2 has an ultra-high specific surface area and excellent water retention performance. Its surface silanol (Si-OH) groups can adsorb free ions in the electrolyte, giving the electrolyte material good plasticity.

[0052] (2) Electrical conductivity at low temperatures

[0053] A two-electrode electrochemical impedance spectroscopy (EIS) testing system was used, with Pt sheets as the working electrode and counter electrode, to test the ionic conductivity of the aqueous gel electrolyte prepared in Example 1 and the electrolyte prepared in Comparative Examples 1-2 at room temperature (25℃) and low temperature (-20℃).

[0054] Depend on Figure 2It can be seen that at 25℃, the ionic conductivity of the electrolyte prepared in Comparative Example 1 is higher than that of the aqueous gel electrolyte prepared in Example 1 and the electrolyte prepared in Comparative Example 2; however, at -20℃, the ionic conductivity of Comparative Example 1 is only 15.11 mS / cm, which is lower than that of Comparative Example 2 and Example 1. This indicates that adding additives such as formamide and SiO2 to the electrolyte can significantly improve the low-temperature ion transport performance and conductivity of the aqueous gel electrolyte.

[0055] (3) Capacity and cycle performance test

[0056] The low-temperature (-20°C) GCD, rate performance, and cycle performance of the aqueous gel electrolyte prepared in Example 1 and the electrolytes prepared in Comparative Examples 1-2 were tested using a three-electrode system for the vanadium-based cathode material MOVH.

[0057] Depend on Figure 3 It can be seen that, in the three-electrode system, the battery assembled with the aqueous gel electrolyte prepared in Example 1 has a discharge specific capacity as high as 214.8 mAh g⁻¹ at -20°C. -1 Although lower than the battery assembled with the electrolyte prepared in Comparative Example 2, it still showed improvement in 1 Ag. -1 After 500 cycles at the current density, the battery assembled in Example 1 retained 75.6% of its capacity; while the battery assembled in Comparative Example 2 retained only 70.4% of its capacity.

[0058] Full cells were assembled using PTCDA as the negative electrode, MVOH as the positive electrode, and 4FA-SiO2 and 4FA as the electrolytes, respectively, and their electrochemical performance at -20℃ and 25℃ was tested.

[0059] Depend on Figure 4 It can be seen that at -20℃ and 0.2Ag -1 At the specified current density, the discharge specific capacity of the full cell assembled with 4FA-SiO2 as the electrolyte can reach 80.9 mAh g⁻¹. -1 It exhibits excellent rate performance and cycle performance. Tests show that at 1 Ag... -1 After 5000 cycles at a current density, the capacity retention rate was 76.3% at -20°C, while the full cell assembled with 4FA as the electrolyte retained 76.3% at 1Ag. -1 After 5000 cycles at the current density, the capacity retention rate in a -20℃ environment is only 57.7%.

[0060] (4) SEM observation was performed on the aqueous gel electrolyte prepared in Example 1 and the electrolyte prepared in Comparative Example 2.

[0061] To verify whether the three-dimensional composite structure of the 4FA-SiO2 aqueous gel electrolyte can inhibit the crystallization of MgCl2 at low temperatures, the aqueous gel electrolyte prepared in Example 1 and the electrolyte prepared in Comparative Example 2 were separately placed in a freeze dryer at -50°C for 12 hours of dehydration. The resulting powder was then ball-milled to obtain micron-sized powder, which was used to prepare electrode additives. These additives must be stored in a dry environment with humidity less than 10% to prevent moisture absorption and particle agglomeration, which would affect dispersion characteristics. The dried samples were observed using a scanning electron microscope (SEM). Figure 5 It was observed that in the aqueous 4FA electrolyte, the grain size observed by SEM was approximately 150–200 μm, and varied in size. Due to the hygroscopic nature of MgCl2, the grains also agglomerated. In contrast, in the FA-SiO2 gel electrolyte, the silica and FA form a three-dimensional composite structure, which effectively prevents the precipitation of magnesium chloride at decreasing temperatures. After freeze-drying, the gel electrolyte showed numerous fine and uniform grains, approximately 10 μm in size, significantly smaller than the grain size formed after freeze-drying the aqueous 4FA electrolyte. Therefore, the introduction of SiO2 plays a crucial role in suppressing the crystallization process of MgCl2, making it difficult for the MgCl2 grains formed in the electrolyte to continue growing. This ensures that the gel electrolyte can maintain a high ion concentration at low temperatures, resulting in better cycle stability of the FA-SiO2 and enabling stable battery operation at low temperatures.

[0062] The above descriptions are merely embodiments of the present invention, and common knowledge such as specific technical solutions and / or characteristics are not described in detail here. It should be noted that those skilled in the art can make various modifications and improvements without departing from the technical solutions of the present invention, and these should also be considered within the scope of protection of the present invention. These modifications and improvements will not affect the effectiveness of the implementation of the present invention or the practicality of the patent. The scope of protection claimed in this application should be determined by the content of its claims, and the specific embodiments described in the specification can be used to interpret the content of the claims.

Claims

1. An application of a low-temperature aqueous gel electrolyte, characterized in that: For use in aqueous magnesium-ion batteries, the low-temperature aqueous gel electrolyte includes a soluble metal salt, additives, and a solvent. The additives are formamide and SiO2, with a volume ratio of formamide to solvent of 4:(5-7). The amount of SiO2 added is 14%-16% of the total mass of formamide and solvent. The soluble metal salt is MgCl2.

2. The application of the low-temperature aqueous gel electrolyte according to claim 1, characterized in that: The concentration of soluble metal salts is 1–5 mol / L.

3. The application of the low-temperature aqueous gel electrolyte according to claim 2, characterized in that: The electrolyte operates at a temperature of -20 to 25°C.

4. The application of a low-temperature aqueous gel electrolyte according to any one of claims 1-3, characterized in that: Preparation method of low-temperature aqueous gel electrolyte Includes the following steps: S1: Weigh out a certain amount of soluble metal salt for later use; S2: Measure a certain amount of formamide, mix it evenly with the solvent, and prepare a mixed solvent; S3: Dissolve the soluble metal salt weighed in S1 in the mixed solvent of S2 to prepare an electrolyte; S4: Weigh a certain amount of SiO2 and add it to the electrolyte prepared in S3. Mix well to obtain a low-temperature aqueous gel electrolyte.

5. The application of a low-temperature aqueous gel electrolyte according to any one of claims 1-3, characterized in that: The positive electrode material of aqueous ion batteries includes vanadium-based positive electrode materials containing electrode additives, and the negative electrode material includes PTCDA containing electrode additives.

6. The application of the low-temperature aqueous gel electrolyte according to claim 5, characterized in that: The preparation process of the electrode additive is as follows: the low-temperature aqueous gel electrolyte is first dehydrated at -52 to -48℃, and then ball-milled to obtain micron-sized powder, thus obtaining the electrode additive.

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