Wide potential window supercapacitor ionic liquid hybrid electrolyte and preparation method thereof

Abstract

The application discloses a kind of wide potential window's supercapacitor ionic liquid mixed electrolyte, by one organic solvent and two ionic liquids, two ionic liquids are dissolved in organic solvent, organic solvent is triethyl phosphate, two ionic liquids are respectively 1-ethyl-3-methyl imidazole double trifluoromethanesulfonyl imidate, 1-ethyl-3-methyl imidazole tetrafluoroboric acid salt, two ionic liquids are mixed in different proportions.The beneficial effects of the application: construct ionic rearrangement system, obtain the electrolyte with wide potential window, high energy density and low self-discharge, while having excellent rate performance, stable cycle performance.By optimizing the electrolyte component, effectively widen the use temperature range of supercapacitor, compared with pure ionic liquid and common carbonate electrolyte, has wider use temperature, can work normally in-20~80 ℃ temperature range, can meet the use requirements of supercapacitor under extreme temperature conditions.

Description

Technical Field

[0001] This invention relates to the field of new energy materials and devices, specifically to a wide potential window supercapacitor ionic liquid mixed electrolyte and its preparation method. Background Technology

[0002] As a high-efficiency energy storage device, supercapacitors achieve energy storage through the electrostatic charge adsorption at the interface between the electrodes and the electrolyte via their double-layer energy storage mechanism. They have outstanding advantages such as high power density, long cycle life, and fast charging and discharging speed, and play an irreplaceable role in fields such as frequency regulation of smart grids, braking energy recovery of rail transit, and instantaneous power compensation of industrial equipment.

[0003] However, existing technologies face three major bottlenecks: First, poor adaptability to operating temperatures. Conventional aqueous electrolytes are prone to freezing at low temperatures, hindering ion migration; organic electrolytes decompose at high temperatures, generating gas and causing expansion failure; and while ionic liquids possess high thermal stability, their excessively high viscosity at low temperatures leads to a sharp drop in interfacial charge transport efficiency. Second, low energy density. Limited by the double-layer physical energy storage mechanism and the electrochemical window of the electrolyte, it is difficult to overcome the order-of-magnitude gap with battery systems. More prominent is the self-discharge problem. Due to the thermal motion of ions in the electrolyte and the internal micro-currents caused by redox impurities, the voltage decays severely when the device is stationary, restricting long-term energy storage applications. These defects essentially stem from the inherent contradiction between the thermodynamic properties and electrochemical stability of the electrolyte system. For example, increasing the voltage window requires electrolytes with high decomposition potentials, but such materials often suffer from high viscosity and poor wettability.

[0004] Therefore, constructing a novel electrolyte system that combines a wide electrochemical window, a low viscosity temperature coefficient, and high interfacial stability to fundamentally coordinate the competitive relationship between energy density, temperature adaptability, and self-discharge characteristics is of great significance for the development of supercapacitors. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a wide-potential-window ionic liquid hybrid electrolyte for supercapacitors and its preparation method. This electrolyte, through a strategy of ionic component regulation and synergistic optimization with organic solvents, ultimately improves the performance of supercapacitors and expands their application boundaries.

[0006] The specific technical solution adopted in this invention is as follows: a supercapacitor ionic liquid mixed electrolyte with a wide potential window, which is composed of an organic solvent and two ionic liquids, wherein the two ionic liquids are dissolved in the organic solvent and the total molar concentration is 0.25 to 4 mol / L.

[0007] Preferably, the total molar concentration of the two ionic liquids is 1 mol / L.

[0008] Preferably, the organic solvent is triethyl phosphate (TEP).

[0009] Preferably, the two ionic liquids are 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIm][TFSI]) and 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF4]). The two ionic liquids are mixed in different proportions to form a two-component liquid phase system, namely A / B. The molar fraction is used as the control parameter and is adjusted in an equal gradient within the range of 0 to 100%. Eleven characteristic samples are prepared at 10% molar fraction intervals, namely A:B = 10:0, 9:1, ..., 0:10.

[0010] Preferably, the molar ratio of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIm][TFSI]) to 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF4]) is 7:3.

[0011] Preferably, the preparation method of the wide potential window supercapacitor ionic liquid mixed electrolyte is as follows: in a glove box filled with protective gas, the ionic liquid is transferred into a volumetric flask using a pipette, and an organic solvent is transferred to make up the volume. After taking it out, it is placed on a magnetic stirrer and stirred until it is evenly mixed to obtain the electrolyte.

[0012] Preferably, the protective gas is high-purity argon.

[0013] Preferably, the present invention provides a supercapacitor, wherein the electrolyte of the supercapacitor is the preferred electrolyte described above.

[0014] Preferably, the supercapacitor is a double-layer symmetric supercapacitor in the form of a 2032 button cell, comprising a positive electrode, a negative electrode, an electrolyte, and a separator. The positive and negative electrodes are both made of YP50F activated carbon material, and the separator is a Whatman GF / D glass fiber separator.

[0015] Preferably, the supercapacitor operates at a temperature of -20℃ to 80℃ and a voltage of 0 to 3.2V.

[0016] The beneficial effects of the present invention are as follows: (1) The present invention constructs an ion rearrangement system, which yields an electrolyte with a wide potential window, high energy density and low self-discharge, while also having excellent rate performance and stable cycling performance. (2) The present invention effectively broadens the operating temperature range of supercapacitors by optimizing the electrolyte composition. Compared with pure ionic liquids and common carbonate electrolytes, it has a wider operating temperature range and can operate normally within the temperature range of -20 to 80℃, which can meet the requirements of supercapacitors under extreme temperature conditions. Attached Figure Description

[0017] Figure 1 The Ragone curves of the button supercapacitors assembled using the electrolytes of Examples 1, 2, and 3 are shown at room temperature and at current densities of 0.2–10 A / g, illustrating the energy density and power density of the supercapacitors.

[0018] Figure 2 The images show Raman spectral data for the electrolytes of Examples 1, 2, 3 and Comparative Examples 2, 3.

[0019] Figure 3 The figure shows the cyclic voltammetry curves of the button supercapacitor assembled using the electrolyte of Example 2 at room temperature, ranging from 10 to 200 mV / s.

[0020] Figure 4 The graph shows the constant current charge-discharge curves of the button supercapacitor assembled using the electrolyte of Example 2 at room temperature, ranging from 0.2 to 10 A / g.

[0021] Figure 5 The cyclic voltammetry curves of the button supercapacitor assembled using the electrolyte of Example 2 at an operating temperature of -20 to 80°C and a speed of 50 mV / s are shown.

[0022] Figure 6 The cyclic voltammetry curves of the button-type supercapacitor assembled using the electrolyte of Comparative Example 4 at an operating temperature of -20 to 80°C and a speed of 50 mV / s are shown.

[0023] Figure 7 The cyclic voltammetry curves of the button-type supercapacitor assembled using the electrolyte of Comparative Example 5 at an operating temperature of -20 to 80°C and a speed of 50 mV / s are shown.

[0024] Figure 8 The graph shows the constant current charge-discharge curves of the button supercapacitor assembled using the electrolyte of Example 2 at an operating temperature of -20 to 80°C and a constant current of 1 A / g.

[0025] Figure 9 The graph shows the 10,000-cycle long-cycle curve of the button supercapacitor assembled using the electrolyte of Example 2 at an operating temperature of -20 to 80°C and a current density of 5 A / g.

[0026] Figure 10 The diagram shows the leakage current of the button supercapacitor assembled using the electrolytes of Examples 1, 2, 3 and Comparative Example 1 after being charged to the operating voltage and kept at a constant potential for 2 hours. Examples 1, 2, and 3 are charged to 3.2V, and Comparative Example 1 is charged to 2.5V.

[0027] Figure 11This is a schematic diagram showing the voltage decay of button supercapacitors assembled using the electrolytes of Examples 1, 2, 3 and Comparative Example 1 after being charged to the working voltage, kept at a constant potential for 2 hours, and then kept at an open circuit potential for 20 hours. Examples 1, 2, and 3 are charged to 3.2V, and Comparative Example 1 is charged to 2.5V. Detailed Implementation

[0028] This invention provides a method for preparing an ionic liquid mixed electrolyte for a supercapacitor with a wide potential window. Unless otherwise specified, the materials or reagents used in this invention are commonly used in the field and can be obtained from commercially available products. The specific implementation process of this invention is described in detail below to more clearly illustrate the invention, but the scope of protection of this invention is not limited thereto.

[0029] like Figures 1-11 As shown, the following examples and comparative examples all use electrolytes, which are placed in capillary tubes for Raman testing and assembled into supercapacitors for electrochemical testing. The supercapacitor is a double-layer symmetric supercapacitor, in the form of a 2032 coin cell, including a positive electrode, a negative electrode, an electrolyte, and a separator. Both the positive and negative electrodes are made of YP50F activated carbon material, and the separator is a Whatman GF / D glass fiber membrane. The electrochemical tests were performed using a DH7000 electrochemical workstation.

[0030] The innovations of this invention are twofold: 1. Ion composition regulation: By selecting [EMIM][BF4] with theoretically smallest anions and [EMIM][TFSI] with large anions to construct an ion rearrangement system, the spontaneous formation of the electric double layer structure is promoted, providing an efficient charge storage architecture. By regulating the spatial arrangement of anions, the ion migration rate is optimized, and the traditional concentration gradient-driven adsorption mode is broken through, enhancing the adsorption capacity of anions on graphite electrodes. This provides theoretical guidance for obtaining supercapacitors with high specific capacitance and low self-discharge. 2. Synergistic optimization of organic solvents: Based on the ion rearrangement system, non-flammable and low-toxicity triethyl phosphate is used to dilute the ionic liquid, successfully developing an intrinsically non-flammable electrolyte. This results in an electrolyte system with both low-temperature and high-temperature adaptability, and its application potential in wide-temperature-range supercapacitors is systematically verified.

[0031] Example 1:

[0032] This embodiment provides a single ionic liquid electrolyte based on triethyl phosphate, and its preparation method is as follows:

[0033] Transfer 2.576 mL of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIm]TFSI) to a 10 mL volumetric flask, dilute to volume with triethyl phosphate (TEP), remove and place on a magnetic stirrer to mix evenly to obtain the electrolyte with an ionic liquid concentration of 1 mol / L.

[0034] Example 2:

[0035] This embodiment provides a binary ionic liquid electrolyte based on triethyl phosphate, and its preparation method is as follows:

[0036] 1.803 mL of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIm]TFSI) and 0.459 mL of 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF4]) were transferred to a 10 mL volumetric flask and diluted to volume with triethyl phosphate (TEP). The flask was then placed on a magnetic stirrer and stirred until homogeneous to obtain the electrolyte. The molar ratio of the two ionic liquids was 7:3, and the total concentration was 1 mol / L.

[0037] Example 3:

[0038] This embodiment provides a single ionic liquid electrolyte based on triethyl phosphate, and its preparation method is as follows:

[0039] Transfer 1.530 mL of 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF4]) to a 10 mL volumetric flask, dilute to volume with triethyl phosphate (TEP), remove and place on a magnetic stirrer to mix evenly to obtain the electrolyte with an ionic liquid concentration of 1 mol / L.

[0040] Comparative Example 1:

[0041] This comparative example provides a commercial electrolyte, the preparation method of which is as follows:

[0042] Weigh 2.171 g of tetraethylammonium tetrafluoroborate (TEATFB), add it to a 10 mL volumetric flask, dilute to volume with acetonitrile (ACN), remove it and place it on a magnetic stirrer to stir until it is mixed evenly, thus obtaining the electrolyte with a concentration of 1 mol / L.

[0043] Comparative Example 2:

[0044] This comparative example provides a pure ionic liquid electrolyte, the preparation method of which is as follows:

[0045] The pure ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIm]TFSI) was directly used as the electrolyte;

[0046] Comparative Example 3:

[0047] This comparative example provides a pure ionic liquid electrolyte, the preparation method of which is as follows:

[0048] The pure ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF4]) was directly used as the electrolyte;

[0049] Comparative Example 4:

[0050] This comparative example provides a binary ionic liquid electrolyte, the preparation method of which is as follows:

[0051] 1.803 mL of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIm]TFSI) and 0.459 mL of 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF4]) were transferred and stirred on a magnetic stirrer until they were mixed evenly to obtain the electrolyte. The molar ratio of the two ionic liquids was 7:3.

[0052] Comparative Example 5:

[0053] This comparative example provides a binary ionic liquid electrolyte based on acetonitrile, and its preparation method is as follows:

[0054] 1.803 mL of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIm]TFSI) and 0.459 mL of 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF4]) were transferred to a 10 mL volumetric flask and diluted to volume with acetonitrile (ACN). The flask was then placed on a magnetic stirrer and stirred until homogeneous to obtain the electrolyte. The molar ratio of the two ionic liquids was 7:3, and the total concentration was 1 mol / L.

[0055] Test 1:

[0056] The energy density and power density of the supercapacitors assembled in Examples 1, 2, and 3 above were compared through constant current charge-discharge tests. The operating voltage was 0–3.2V, the current density was 0.2–10A / g, and the operating temperature was room temperature. The comparison figures are shown below. Figure 1 As shown. The results indicate that Example 2 at 302.1 W kg -1 It exhibits a power density as high as 42.43 Wh / kg. -1 The energy density, even at 16.2 kW kg -1 Even at a power density of [value missing], it still has a high efficiency of 28.71 Wh / kg. -1 The energy density of Example 2 is significantly improved compared to Examples 1 and 3.

[0057] Test 2:

[0058] The electrolytes of Examples 1, 2, and 3, and Comparative Examples 2 and 3 were analyzed using Raman spectroscopy. The results showed that the addition of TEP dissociated the ion pairs of the ionic liquid, forming solvated ions, which would increase the ionic conductivity of the electrolyte and reduce its viscosity.

[0059] Test 3:

[0060] The coin-type supercapacitor assembled using the electrolyte of Example 2 was analyzed by cyclic voltammetry testing at a scan rate of 10–200 mV / s and an operating temperature of room temperature. Figure 3 As shown. These curves clearly show the effect when the scan rate starts from 10 mV / s. -1 Increased to 200mV s -1 The quasi-rectangular shape and negligible distortion indicate that it has good capacitance characteristics and fast speed capability.

[0061] Test 4:

[0062] The button-type supercapacitor assembled using the electrolyte of Example 2 was analyzed by constant current charge-discharge testing. The current density was 0.2–10 A / g, and the operating temperature was room temperature. Figure 4 As shown in the figure. The results indicate that, under different current densities, the curve exhibits an approximately symmetrical triangular capacitive behavior, demonstrating high coulombic efficiency.

[0063] Test 5:

[0064] The coin-type supercapacitor assembled using the electrolyte of Example 2 was analyzed by cyclic voltammetry testing at a scan rate of 50 mV / s and an operating temperature range of -20 to 80°C. Figure 5 As shown in the figure. The results show that the curves maintain an approximately rectangular shape regardless of whether the temperature is low (-20℃) or high (80℃), indicating ideal capacitive behavior. The current density changes very little, indicating that the electrolyte has good wide temperature adaptability.

[0065] Test 6:

[0066] The coin-type supercapacitor assembled using the electrolyte of Comparative Example 4 was analyzed by cyclic voltammetry testing at a scan rate of 50 mV / s and an operating temperature range of -20 to 80℃. Figure 6 As shown in the figure. The results indicate that the supercapacitor based on pure ionic liquids suffers from slow ion transport due to the excessively high viscosity of the electrolyte, resulting in a sharp decrease in current density at -5℃ and failure to function properly at -20℃.

[0067] Test 7:

[0068] The coin-type supercapacitor assembled using the electrolyte of Comparative Example 5 was analyzed by cyclic voltammetry testing at a scan rate of 50 mV / s and an operating temperature range of -20 to 80℃. Figure 7 As shown in the figure. The results indicate that it has good performance at low and room temperature. When the temperature is below 60℃, all curves maintain a good rectangular shape. However, as the temperature continues to rise to 80℃, the current shows obvious polarization, which indicates that the electrolyte is unstable and decomposes at high temperature, leading to an increase in current.

[0069] Test 8:

[0070] The coin-type supercapacitor assembled using the electrolyte from Example 2 was analyzed by constant current charge-discharge testing. The current density was 1 A / g, and the operating temperature was -20 to 80°C. Figure 8 As shown in the figure. The results indicate that the curves exhibit an approximately symmetrical triangular capacitive behavior at different operating temperatures, demonstrating high coulombic efficiency and indicating that the electrolyte has good wide-temperature adaptability.

[0071] Test 9:

[0072] The coin-type supercapacitor assembled using the electrolyte from Example 2 was analyzed by constant current charge-discharge testing. The current density was 5 A / g, the operating temperature was -20 to 80°C, and it underwent 10,000 cycles. Figure 9 As shown in the figure, the results indicate that the capacitance retention rates after 10,000 cycles are 87.4%, 85.6%, and 78.4% at temperatures of 25℃, -20℃, and 80℃, respectively, demonstrating excellent long-term cycling stability. Furthermore, the coulombic efficiency of the supercapacitor remains close to 100% throughout the long-term cycling process at different temperatures, indicating good reversibility.

[0073] Test 10:

[0074] The leakage current of the coin-type supercapacitors assembled using the electrolytes of Examples 1, 2, 3, and Comparative Example 1 after being charged to the operating voltage and kept at a constant potential for 2 hours, and the voltage decay after being kept at an open-circuit potential for 20 hours were analyzed by self-discharge testing. The results are as follows: Figure 10 , 11 As shown, the operating temperature was room temperature. Examples 1, 2, and 3 were charged to 3.2V, while Comparative Example 1 was charged to 2.5V. The results show that after charging to 3.2V, the open-circuit potential of the supercapacitor based on the electrolyte of Example 2 decreased to 2.16V after 20 hours, with a corresponding voltage drop of approximately 32.5%. This is superior to the supercapacitors using Example 1 (voltage drop to 1.83V, voltage drop of 42.8%) and Example 3 (voltage drop to 1.36V, voltage drop of 57.5%). Meanwhile, the leakage currents corresponding to the supercapacitors based on Examples 2, 1, and 3 stabilized at 5.9, 8.4, and 13.5 μA g, respectively. -1This is consistent with their voltage drop during self-discharge. The self-discharge test results of Examples 1, 2, and 3 are significantly better than those of the supercapacitor in Comparative Example 1, which uses commercial electrolyte (voltage drop to 1.05V, voltage drop of 58.0%, leakage current of 15.1 μA g). -1 This proves that it has practical application value.

Claims

1. A supercapacitor ionic liquid mixed electrolyte with a wide potential window, characterized in that: It consists of one organic solvent and two ionic liquids, with the two ionic liquids dissolved in the organic solvent, and the total molar concentration is 0.25~4 mol / L; The organic solvent is triethyl phosphate; The two ionic liquids are 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and 1-ethyl-3-methylimidazolium tetrafluoroborate salt, respectively. The two ionic liquids are mixed in different proportions to form a two-component liquid phase system, namely A / B. The molar fraction is used as the control parameter and is adjusted in an equal gradient within the range of 0 to 100%. Nine characteristic samples are prepared at 10% molar fraction intervals, that is, A:B = 9:1 to 1:

9.

2. The wide potential window supercapacitor ionic liquid mixed electrolyte according to claim 1, characterized in that: The total molar concentration of the two ionic liquids is 1 mol / L.

3. The wide potential window supercapacitor ionic liquid mixed electrolyte according to claim 1, characterized in that: The molar ratio of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt to 1-ethyl-3-methylimidazolium tetrafluoroborate is 7:

3.

4. A method for preparing a wide potential window supercapacitor ionic liquid mixed electrolyte according to any one of claims 1 to 3, characterized in that: In a glove box filled with protective gas, use a pipette to transfer the ionic liquid into a volumetric flask, transfer the organic solvent to make up to volume, remove the flask and place it on a magnetic stirrer to stir until it is evenly mixed, thus obtaining the electrolyte.

5. The method for preparing the wide potential window supercapacitor ionic liquid mixed electrolyte according to claim 4, characterized in that: The protective gas is high-purity argon.

6. The application of the wide potential window supercapacitor ionic liquid mixed electrolyte according to any one of claims 1 to 3, characterized in that: A supercapacitor is provided, wherein the electrolyte of the supercapacitor is a supercapacitor ionic liquid mixed electrolyte with a wide potential window.

7. The application of the wide potential window supercapacitor ionic liquid mixed electrolyte according to claim 6, characterized in that: The supercapacitor is a double-layer symmetric supercapacitor in the form of a 2032 button cell, comprising a positive electrode, a negative electrode, an electrolyte, and a separator. The positive and negative electrodes are both made of YP50F activated carbon material, and the separator is a Whatman GF / D glass fiber separator.

8. The application of the wide potential window supercapacitor ionic liquid mixed electrolyte according to claim 7, characterized in that: The supercapacitor operates at a temperature of -20℃ to 80℃ and a voltage of 0 to 3.2 V.

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