Ionic liquid-based high-voltage fast-charging electrolyte and preparation method thereof

Abstract

The invention discloses an ionic liquid-based high-voltage fast-charging electrolyte and a preparation method thereof, and the preparation method of the electrolyte comprises the following steps: mixing 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, zinc trifluoromethanesulfonate and a trace amount of deionized water to obtain a mixed solution A; and adding tetramethylguanidine hydrochloride, stirring and reacting at 60-80 DEG C, cooling, and continuously stirring and aging to obtain the electrolyte. Wherein based on each milliliter of the ionic liquid, the addition amount of the deionized water is 60-100 microliters, and the concentration of the addition amount of the tetramethylguanidine hydrochloride in the mixed solution is 30-80 mM. Through the synergistic effect of the ionic liquid matrix and the guanidine salt additive, the zinc ion solvation structure is regulated and controlled, and while a wide electrochemical stable window is achieved, the ionic conductivity is remarkably improved, and the interface impedance and zinc deposition overpotential are reduced. The zinc ion battery assembled by the electrolyte has high energy density and excellent rapid charge-discharge capacity and cycling stability, and the preparation process is simple and suitable for large-scale application.

Description

Technical Field

[0001] This invention relates to the field of electrolyte preparation technology, and in particular to an ionic liquid-based high-voltage fast-charging electrolyte and its preparation method. Background Technology

[0002] Aqueous zinc-ion batteries, characterized by high safety, low cost, and environmental friendliness, have attracted widespread attention in recent years as an emerging electrochemical energy storage technology. However, their practical application is limited by energy density, and one of the core bottlenecks is the narrow electrochemical stability window (typically <2.0 V) of aqueous electrolytes. Free water molecules in the electrolyte are prone to initiating side reactions such as hydrogen evolution and oxygen evolution at the electrode interface, severely limiting the operating voltage and energy density.

[0003] To broaden the electrochemical stability window, researchers have proposed novel electrolyte types such as salt-in-water electrolytes and organic molecule crowding electrolytes. Salt-in-water electrolytes significantly increase the content of electrolyte salts in the aqueous solvent, producing a high-concentration salt solution. This effectively reduces the free water content and decreases the activity of water molecules, thereby increasing the electrochemical stability window of the electrolyte. However, the addition of high-concentration salts significantly increases the cost of the electrolyte. Organic molecule crowding electrolytes utilize inexpensive organic molecules as crowding agents to replace part of the electrolyte salt. The hydrogen bonding between the crowding agent and water molecules stabilizes the free water, thus reducing the activity of water molecules. However, due to their high concentration, these electrolytes result in high system viscosity, low ionic conductivity, and significant charge transfer resistance at the electrode / electrolyte interface, leading to slow overall charge transport kinetics. Ultimately, this results in lower battery capacity, lower long-term cycle stability, and lower charge storage efficiency.

[0004] In recent years, ionic liquids have been explored as electrolyte substrates for zinc batteries due to their extremely low volatility, high thermal stability, and wide electrochemical window, potentially breaking through the voltage bottleneck. However, pure ionic liquids or conventional ionic liquid-based electrolytes typically have high viscosity, resulting in slow zinc ion migration and interfacial desolvation processes. This leads to rapid capacity decay at high rates, making it difficult to balance high voltage and fast charging performance. Therefore, developing a novel ionic liquid-based electrolyte that combines a wide voltage window with rapid charge transport kinetics has become a crucial technical challenge for zinc-ion batteries aiming for high energy density and high power density applications. Summary of the Invention

[0005] This application provides an ionic liquid-based high-voltage fast-charging electrolyte and its preparation method, overcoming the technical problems of existing ionic liquid-based zinc electrolytes where it is difficult to simultaneously achieve the desired electrochemical window and ionic conductivity, as well as the large interfacial charge transfer impedance. By introducing specific guanidine salt additives into a highly stable ionic liquid matrix, the solvation structure and interfacial transport process of zinc ions are synergistically regulated. This significantly improves ionic conductivity, reduces interfacial impedance and zinc deposition overpotential while maintaining a wide electrochemical stability window, thereby achieving high-voltage stable operation and fast charge / discharge capability of zinc-ion batteries.

[0006] This application provides a method for preparing an ionic liquid-based high-voltage fast-charging electrolyte, comprising the following steps: Step 1: Mix the ionic liquid, zinc salt and deionized water, and stir evenly at room temperature to obtain mixed solution A; wherein, the ionic liquid is 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, and the zinc salt is zinc trifluoromethanesulfonate; Step 2: Add a certain amount of tetramethylguanidine hydrochloride to the mixed solution A, and stir at 60℃~80℃ for 0.5~2h to obtain mixed solution B; Step 3: After cooling the mixed solution B to room temperature, continue stirring for 8-16 hours to obtain the ionic liquid-based high-voltage fast-charging electrolyte; Specifically, based on the amount of ionic liquid per milliliter, the amount of deionized water added is 60~100μL.

[0007] Preferably, the concentration of the added tetramethylguanidine hydrochloride in the mixed solution is 30–80 mM.

[0008] Preferably, the amount of tetramethylguanidine hydrochloride added is 50 mM.

[0009] This application also provides an ionic liquid-based high-voltage fast-charging electrolyte prepared by any of the above preparation methods.

[0010] This application also provides a zinc-ion battery comprising the above-mentioned ionic liquid-based high-voltage fast-charging electrolyte.

[0011] One technical solution provided in this application embodiment has at least the following technical effects: 1. In this embodiment, the electrolyte obtained by the synergistic effect of the ionic liquid matrix and guanidine salt achieves a synergistic improvement in high voltage window and fast kinetics. Specifically, the electrochemical stability window can reach above 3.07 V, while the ionic conductivity is increased to 7.68 mS / cm, the interfacial charge transfer impedance is as low as 62 Ω, and the zinc deposition overpotential is reduced to 65 mV, thus solving the technical contradiction of "high voltage and slow charging" in traditional ionic liquid electrolytes.

[0012] 2. The electrolyte components in the embodiments of this application are clearly defined, and the preparation process does not require complex equipment. The overall performance can be optimized by adjusting the amount of guanidine salt added (preferred to be 50 mM in Embodiment 1), which facilitates large-scale production and application. Attached Figure Description

[0013] Figure 1 This is an optical image of the FIL-TG-50 electrolyte in Embodiment 1 of the present invention.

[0014] Figure 2 shows the LSV curve of the FIL-TG-50 electrolyte in Example 1 of the present invention. Detailed Implementation

[0015] This application presents an ionic liquid-based high-voltage fast-charging electrolyte and its preparation method. It utilizes highly stable 1-ethyl-3-methylimidazolium trifluoromethanesulfonate as the electrolyte solvent, and employs a highly polar tetramethylguanidine hydrochloride ion compound to regulate the solvation structure of zinc ions in the matrix and alter the desolvation energy of zinc ions. Furthermore, the interfacial electric field generated by the guanidine salt ions drives rapid charge transfer, thereby accelerating the charge transport kinetics of the high-voltage electrolyte. The prepared novel electrolyte exhibits a wide voltage window (3.07 V), high ionic conductivity (7.68 mS / cm), low interfacial charge transfer impedance (62 Ω), and low zinc ion deposition overpotential (65 mV). Moreover, a Zn / / NVP full cell assembled using this electrolyte demonstrates an initial discharge specific capacity of 104.8 mAh / g and high cycle stability of 2500 cycles.

[0016] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods. Example 1

[0017] Mix 1 mL of 1-ethyl-3-methylimidazolium trifluoromethanesulfonate and 0.363 g of zinc trifluoromethanesulfonate in a volumetric flask, then add 80 μL of deionized water and stir at room temperature for 0.5 h to ensure homogeneity.

[0018] Finally, 7.5 mg of tetramethylguanidine hydrochloride (50 mM) was added, and the mixture was stirred at 70 °C for 1 h. After cooling to room temperature, it was stirred for another 12 h to obtain an ionic liquid-based high-voltage fast-charging electrolyte. This electrolyte was named FIL-TG-50. Example 2

[0019] The difference between Example 2 and Example 1 is that tetramethylguanidine hydrochloride was not added. The electrolyte was obtained by stirring directly at 70°C for 1 hour, cooling to room temperature, and then stirring for another 12 hours. This electrolyte was named FIL-TG-0. Example 3

[0020] The only difference between Example 3 and Example 1 is that the 7.5 mg tetramethylguanidine hydrochloride (50 mM) was adjusted to 1.5 mg tetramethylguanidine hydrochloride (10 mM) to obtain the electrolyte. This electrolyte was named FIL-TG-10. Example 4

[0021] The only difference between Example 4 and Example 1 is that the 7.5 mg tetramethylguanidine hydrochloride (50 mM) was adjusted to 4.5 mg tetramethylguanidine hydrochloride (30 mM) to obtain the electrolyte. This electrolyte was named FIL-TG-30. Example 5

[0022] The difference between Example 5 and Example 1 is that the tetramethylguanidine hydrochloride (7.5 mg, 50 mM) was adjusted to 12 mg (80 mM) to obtain the electrolyte. This electrolyte was named FIL-TG-80. Example 6

[0023] The only difference between Example 6 and Example 1 is that the tetramethylguanidine hydrochloride (7.5 mg, 50 mM) was adjusted to 15 mg (100 mM) to obtain the electrolyte. This electrolyte was named FIL-TG-100.

[0024] Zn / / NVP full cells assembled using the electrolytes obtained in Examples 1 to 6 were subjected to performance testing. The voltage window was determined by linear sweep voltammetry (LSV), the ionic conductivity was calculated by electrochemical impedance spectroscopy (EIS), and the interfacial charge transfer impedance and zinc deposition overpotential were tested based on symmetric Zn / / Zn cells. The full cell performance was tested using the Zn / / NaV3(PO4)3(NVP) system at a current density of 2 A / g. All tests were performed at room temperature. The results are shown in Table 1.

[0025] Table 1 Electrolyte name Voltage window (V) Ionic conductivity (mS / cm) Interfacial charge transfer impedance (Ω) Zinc deposition overpotential (mV) Zn / / NVP Initial discharge specific capacity (mAh / g) Capacity retention rate (%) after 2500 cycles FIL-TG-50 3.07 7.68 62 65 104.8 92.8 FIL-TG-0 2.36 5.50 200 120 80.5 60.2 FIL-TG-10 2.65 6.20 150 100 88.3 75.8 FIL-TG-30 2.90 7.20 100 80 98.1 86.5 FIL-TG-80 3.00 7.45 75 72 100.2 88.7 FIL-TG-100 2.88 6.90 110 90 92.4 81.0 As shown in Table 1, the amount of tetramethylguanidine hydrochloride added significantly affects the electrolyte performance. As the addition amount increases from 0 to 50 mM, the electrolyte's voltage window and ionic conductivity gradually increase, while the interfacial impedance and deposition overpotential continuously decrease, indicating that the guanidine salt effectively optimizes the ion solvation structure and interfacial kinetics. However, when the addition amount reaches 100 mM, the performance declines to some extent. This is because excessive guanidine salt ions form large ion clusters in the system, which hinder the free migration of zinc ions and increase the system's microviscosity. Therefore, an addition range of 30–80 mM is preferred to maximize the interfacial regulation effect of the guanidine salt without sacrificing ion conduction.

[0026] Therefore, the results in Table 1 indicate that Example 1 is the best embodiment. Please refer to Table 1. Figures 1-2 , Figure 1 The image shows an optical image of the FIL-TG-50 electrolyte. The FIL-TG-50 electrolyte solution prepared by the method of this invention is homogeneous and stable, and has good flowability. Figure 2 The LSV curve of the FIL-TG electrolyte shows that, compared with the traditional aqueous electrolyte (2.36 V), the FIL-TG-50 electrolyte prepared in this invention has an anodic stability limit of 2.98 V, and its cathode deposition potential electrochemical stability window can reach 3.14 V, which significantly improves high voltage stability and is beneficial for constructing high energy density zinc-ion batteries.

[0027] Comparative Example 1 The difference between this comparative example and Example 1 is that the amount of deionized water added was adjusted to 40 μL, while other conditions remained unchanged. In this comparative example, too little water resulted in incomplete salt dissolution and low conductivity.

[0028] Comparative Example 2 The difference between this comparative example and Example 1 is that the amount of deionized water added was adjusted to 120 μL, while other conditions remained unchanged. Too much water in this comparative example narrowed the electrochemical window and resulted in a loss of high-voltage performance.

[0029] Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including both the preferred embodiments and all changes and modifications falling within the scope of the invention.

[0030] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing an ionic liquid-based high-voltage fast-charging electrolyte, characterized in that, Includes the following steps: Step 1: Mix the ionic liquid, zinc salt and deionized water, and stir evenly at room temperature to obtain mixed solution A; wherein, the ionic liquid is 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, and the zinc salt is zinc trifluoromethanesulfonate; Step 2: Add a certain amount of tetramethylguanidine hydrochloride to the mixed solution A, and stir at 60℃~80℃ for 0.5~2h to obtain mixed solution B; Step 3: After cooling the mixed solution B to room temperature, continue stirring for 8-16 hours to obtain the ionic liquid-based high-voltage fast-charging electrolyte; Specifically, based on the amount of ionic liquid per milliliter, the amount of deionized water added is 60~100μL.

2. The preparation method according to claim 1, characterized in that, The concentration of the added tetramethylguanidine hydrochloride in the mixed solution is 30–80 mM.

3. The preparation method according to claim 2, characterized in that, The amount of tetramethylguanidine hydrochloride added is 50 mM.

4. An ionic liquid-based high-voltage fast-charging electrolyte, characterized in that, It is prepared by the method according to any one of claims 1 to 3.

5. A zinc-ion battery, characterized in that, It contains the ionic liquid-based high-voltage fast-charging electrolyte as described in claim 4.

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