Low-temperature electrolytes and supercapacitors

Abstract

This application relates to a low-temperature electrolyte and a supercapacitor. This application falls within the field of supercapacitor technology. The technical problem this application aims to solve is: to provide a low-temperature electrolyte and a supercapacitor. The technical solution adopted in this application is: a low-temperature electrolyte comprising a single solvent and a solute dissolved in the solvent; wherein the solvent has a moderate dielectric constant, a low donor number, and an ultra-low melting point; and the solute has a small molecular radius and high electrochemical stability.

Description

Technical Field

[0001] This invention relates to a low-temperature electrolyte and a supercapacitor. It is applicable to the field of supercapacitor technology. Background Technology

[0002] Electrochemical energy storage devices are playing a crucial role in the global energy transition. Among them, supercapacitors, due to their high power density and long-cycle stability, have been widely used in emergency start-up power supplies, primary frequency regulation of power grids, and regenerative braking. However, with the increasing prevalence of extreme temperature applications (≤-65 ℃) such as polar resource development and near-Earth space exploration, the minimum operating temperature (-50 ℃) of commercial supercapacitor electrolytes is no longer sufficient to meet these temperature requirements. This limitation stems from the high melting point and poor low-temperature ion dynamics of commercial electrolytes.

[0003] Specifically, while acetonitrile or propylene carbonate solvents used in commercial electrolytes possess excellent ion dissociation capabilities, the high melting point and high viscosity of these highly polar solvents shorten the liquidus temperature range of the electrolyte and reduce ion transport rates. Furthermore, the high electron donor numbers of acetonitrile and propylene carbonate molecules (15.96 and 16.14, respectively) result in strong binding energies between cations and solvents (cation-acetonitrile binding energy of -1.63 eV and cation-propylene carbonate binding energy of -1.88 eV), significantly hindering the desolvation process of cations and worsening low-temperature capacity retention.

[0004] To address the aforementioned issues, researchers have enhanced the low-temperature performance of mixed electrolytes by introducing co-solvents with ultra-low melting points and low dielectric constants into the main solvent. These low-polarity solvents include short-chain carboxylic esters, fluorocarboxylic esters, and ethers. The binary / multi-component solvent systems they form can effectively broaden the liquidus temperature range of the electrolyte and reduce its viscosity. For example, the electrolyte disclosed in Chinese Patent Publication No. CN110148788A achieves high rate performance at low temperatures by adding carboxylic esters to the main carbonate solvent and specifically limiting their ratio. Similarly, the lithium-ion battery electrolyte disclosed in Chinese Patent Publication No. CN114300750A includes lithium salts and organic solvents. The organic solvents include a main solvent and a co-solvent. The main solvent includes fluorocyclic carbonate compounds, and the co-solvent includes linear carbonate compounds and / or linear carboxylic ester compounds.

[0005] However, these low-polarity cosolvents possess poor ion dissociation capabilities, making it difficult for them to participate in ion-solvated structures and effectively improve the low-temperature conductivity of the electrolyte. Furthermore, these cosolvents still exhibit a high number of electron donors, worsening low-temperature ion dynamics. In addition, binary / multi-component solvent systems increase production process steps and system costs, hindering the economical design of the electrolyte. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a low-temperature electrolyte and a supercapacitor to address the above-mentioned problems.

[0007] The technical solution adopted in this invention is: a low-temperature electrolyte, wherein the electrolyte comprises a single solvent and a solute dissolved in the solvent; The solvent has a moderate dielectric constant, a low donor number, and an ultra-low melting point; the solute has a small molecular radius and high electrochemical stability.

[0008] The solvent is acetone, which has a dielectric constant of 20.9, a donor number of 10.67, and a melting point of -95°C.

[0009] The solute includes N,N-dimethylpyrrolidone tetrafluoroborate.

[0010] The concentration of N,N-dimethylpyrrolidone ontium tetrafluoroborate in the electrolyte is 1.0 mol / kg to 1.2 mol / kg.

[0011] The electrolyte has a conductivity of 20.27 mS / cm - 20.93 mS / cm at room temperature and a conductivity of 2.74 mS / cm - 2.85 mS / cm at -70 °C.

[0012] A supercapacitor having the aforementioned low-temperature electrolyte.

[0013] The supercapacitor is a symmetrical supercapacitor assembled from the low-temperature electrolyte and activated carbon-based electrode sheets.

[0014] The supercapacitor has a minimum operating temperature of -70℃.

[0015] The beneficial effects of this invention are as follows: This invention uses a single solvent with a moderate dielectric constant, low donor number, and ultra-low melting point. The ultra-low melting point of the solvent allows the electrolyte to remain liquid in a low-temperature environment (e.g., -70°C), avoiding low-temperature solidification failure. The moderate dielectric constant effectively dissociates the anions and cations of the solute, enabling the electrolyte to maintain a high bulk ion diffusion rate and low-temperature ionic conductivity even at ultra-low temperatures. The low electron donor number reduces the cation-solvent binding energy, decreases the resistance to the desolvation process of ions, and accelerates the intrapore diffusion process of ions. This invention simplifies the production process and reduces system costs by using a single solvent system.

[0016] In this invention, acetone is used as the solvent. It has a medium dielectric constant (20.9), a low donor number (10.67), and an ultra-low melting point (-95 °C), which can effectively enhance the ion dissociation ability, reduce the desolvation energy barrier of ions, and achieve a wide liquid phase temperature range of the electrolyte.

[0017] The electrolyte provided by this invention has low biotoxicity and is economical; in addition, acetone solvent has a lower production cost than other solvents such as acetonitrile, propylene carbonate and N,N-dimethylformamide.

[0018] In this invention, the solute has a small molecular radius and high electrochemical stability. The small molecular radius reduces the transport resistance of ions in the electrolyte, and combined with the low viscosity of the solvent, it further enhances the low-temperature ion migration rate. The high electrochemical stability ensures that the solute does not decompose in the range of -70℃ to room temperature, avoids electrolyte performance degradation, and ensures long-term stable operation of the supercapacitor.

[0019] The supercapacitor using the electrolyte provided by this invention exhibits excellent ultra-low temperature performance: for example, after cooling from 20 °C to -70 °C, the capacitance retention is as high as 86.85% (at a scan rate of 20 mV / s) and 73.06% (at a scan rate of 50 mV / s); at 20 °C, the energy density of the device can reach 16.45 Wh / kg (at which point the power density is 439 W / kg); even at the ultra-low temperature of -70 °C, the device can still achieve an energy density of 14.29 Wh / kg (at which point the power density is 381 W / kg) and a power density of 1856 W / kg (at which point the energy density is 6.96 Wh / kg).

[0020] The supercapacitor using the electrolyte provided by this invention has a minimum operating temperature of -70 °C. This lower limit of the operating temperature exceeds the temperature limit covered by most current supercapacitors, demonstrating excellent electrochemical performance. Attached Figure Description

[0021] Figure 1 This is a comparison graph showing the capacity of Example 2 and the comparative example at 20, -50 and -70 °C.

[0022] Figure 2 The figure shows the cyclic voltammetry curves of Example 2 at different temperatures.

[0023] Figure 3 This is a capacity graph of Example 2 at different temperatures and scan rates.

[0024] Figure 4 This is a graph showing the relative cell viability of Example 2 and the comparative example. Detailed Implementation

[0025] Example 1: This example is a supercapacitor with a minimum operating temperature of -70°C. It is a symmetrical supercapacitor assembled from a low-temperature electrolyte and an activated carbon-based electrode sheet. The low-temperature electrolyte is composed of a single solvent, acetone, and a solute, N,N-dimethylpyrrolidone onium tetrafluoroborate.

[0026] Acetone has a moderate dielectric constant (20.9), a low donor number (10.67), and an ultra-low melting point (-95 °C), which can effectively enhance ion dissociation ability, reduce the desolvation energy barrier of ions, and achieve a wide liquid phase temperature range for the electrolyte. N,N-dimethylpyrrolidone ontium tetrafluoroborate is a solute with a small molecular radius and high electrochemical stability. The supercapacitor electrolyte composed of the two exhibits excellent ultra-low temperature performance.

[0027] Due to the moderate dielectric constant of acetone, it can achieve effective dissociation of solute anions and cations, allowing the electrolyte to maintain a high bulk ion diffusion rate (4.933 * 10⁻⁶) even at ultra-low temperatures. -11 m 2 / s @ -50 °C, 3.633 * 10 -11 m 2 With a low temperature ionic conductivity (2.85 mS / cm @ -70 °C), acetone exhibits excellent bulk ion migration kinetics. Furthermore, due to its low electron donor number (10.67), acetone has a low ion-solvent binding energy (-1.57 eV) with cations, which effectively reduces the resistance to ion desolvation and accelerates the intrapore diffusion process.

[0028] In this embodiment, the concentration of N,N-dimethylpyrrolidone ontium tetrafluoroborate in the electrolyte is 1.0 mol / kg - 1.2 mol / kg; the conductivity of the electrolyte at room temperature is 20.27 mS / cm - 20.93 mS / cm, and the conductivity of the electrolyte at -70℃ is 2.74 mS / cm - 2.85 mS / cm.

[0029] When the concentration of N,N-dimethylpyrrolidone ontium tetrafluoroborate in the electrolyte is 1.2 mol / kg, the electrolyte has a room temperature conductivity of 20.93 mS / cm and a low-temperature conductivity of 2.85 mS / cm at -70 °C. When the concentration is 1.0 mol / kg, the room temperature and low-temperature conductivity decrease slightly, showing 20.27 mS / cm @ 20 °C and 2.74 mS / cm @ -70 °C, respectively. If the molality of the electrolyte is further reduced to 0.8 mol / kg, the room temperature and low-temperature conductivity deteriorate further, showing 19.44 mS / cm @ 20 °C and 2.66 mS / cm @ -70 °C, respectively.

[0030] Increasing the molality of the electrolyte to 1.4 mol / kg resulted in a slight increase in room temperature conductivity and a significant decrease in low-temperature conductivity, with values ​​of 22.47 mS / cm at 20 °C and 2.22 mS / cm at -70 °C, respectively. When the molality was below 1.0 mol / kg, the electrolyte exhibited an ion-depleted state, leading to decreased conductivity. In this state, ion clusters formed, hindering ion migration channels. When the molality was above 1.2 mol / kg, the low-temperature conductivity decreased significantly. Therefore, a molality between 1.0 mol / kg and 1.2 mol / kg provides a good trade-off between room temperature and low-temperature conductivity.

[0031] Example 2: Acetone (99.0% purity) was dried using a 3 Å molecular sieve for 6 hours under an inert atmosphere and at room temperature (oxygen ≤ 1 ppm, water ≤ 1 ppm). Then, N,N-dimethylpyrrolidone ontium tetrafluoroborate solute was added at a molar concentration of 1.2 mol / kg and mixed thoroughly until clear and transparent to obtain a supercapacitor cryogenic electrolyte, which was then sealed and stored.

[0032] The electrode material used was a commercially available dry-process activated carbon electrode sheet (carbon-coated aluminum foil substrate, 140 μm thick), cut into 11 mm diameter discs. The separator was a commercially available glass fiber separator (540 μm thick), cut into 19 mm diameter discs. The gasket, positive electrode sheet, and separator were sequentially placed into the CR 2032 positive electrode shell, and 260 μL of the electrolyte was slowly and evenly dripped in. Subsequently, the negative electrode sheet, gasket, spring, and negative electrode shell were added, and appropriate mechanical pressure was applied to ensure a complete seal. The CR 2032 supercapacitor button assembly was complete. All the above operations were performed inside a glove box.

[0033] The supercapacitor obtained in this embodiment exhibits excellent low-temperature electrochemical performance. After cooling from 20 °C to -50 °C, the coin capacitor retains a capacitance retention of up to 98.6% and a specific capacitance of up to 65 F / g (at a scan rate of 20 mV / s), with no significant capacitance decay. After cooling from 20 °C to -70 °C, the coin capacitor retains a capacitance retention of up to 86.85% (at a scan rate of 20 mV / s) and 73.06% (at a scan rate of 50 mV / s); and the bulk impedance at the ultra-low temperature of -70 °C is approximately 17 Ω. At 20 °C, the device achieves an energy density of 16.45 Wh / kg (power density of 439 W / kg); at the ultra-low temperature of -70 °C, the device still achieves an energy density of 14.29 Wh / kg (power density of 381 W / kg) and a power density of 1856 W / kg (energy density of 6.96 Wh / kg).

[0034] Comparative Example 1: Acetonitrile (99.0% purity) was dried using a 3 Å molecular sieve for 6 hours under an inert atmosphere and at room temperature (oxygen ≤ 1 ppm, water ≤ 1 ppm). Then, N,N-dimethylpyrrolidone ontium tetrafluoroborate solute was added at a mass molar concentration of 1.2 mol / kg and mixed thoroughly until clear and transparent to obtain the supercapacitor electrolyte, which was then sealed and stored.

[0035] The electrode material used was a commercially available dry-process activated carbon electrode sheet (carbon-coated aluminum foil substrate, 140 μm thick), cut into 11 mm diameter discs. The separator was a commercially available glass fiber separator (540 μm thick), cut into 19 mm diameter discs. The gasket, positive electrode sheet, and separator were sequentially placed into the CR 2032 positive electrode shell, and 260 μL of the electrolyte was slowly and evenly added. Subsequently, the negative electrode sheet, gasket, spring, and negative electrode shell were added, and appropriate mechanical pressure was applied to ensure a complete seal, thus assembling the CR 2032 supercapacitor. All of the above operations were performed inside a glove box.

[0036] The supercapacitor obtained in this comparative example exhibited excellent low-temperature electrochemical performance in the 20–50 °C range, but its electrochemical performance completely failed in the -50–70 °C range. Specifically, after cooling from 20 °C to -50 °C, the button capacitor retained a capacitance of up to 91.8% and a specific capacitance of 53.5 F / g (at a scan rate of 20 mV / s), with no significant capacitance decay. However, upon further cooling to -70 °C, the electrolyte rapidly solidified and underwent a phase transition, resulting in the complete failure of the supercapacitor's electrochemical performance.

[0037] Comparative Example 2: N,N-dimethylformamide (purity 99.0%) was dried using a 3 Å molecular sieve for 6 hours under an inert atmosphere and at room temperature (oxygen ≤ 1 ppm, water ≤ 1 ppm). Then, N,N-dimethylpyrrolidone ontium tetrafluoroborate solute was added at a mass molar concentration of 1.2 mol / kg and mixed thoroughly until clear and transparent to obtain the supercapacitor electrolyte, which was then sealed and stored.

[0038] The electrode material used was a commercially available dry-process activated carbon electrode sheet (carbon-coated aluminum foil substrate, 140 μm thick), cut into 11 mm diameter discs. The separator was a commercially available glass fiber separator (540 μm thick), cut into 19 mm diameter discs. The gasket, positive electrode sheet, and separator were sequentially placed into the CR 2032 positive electrode shell, and 260 μL of the electrolyte was slowly and evenly added. Subsequently, the negative electrode sheet, gasket, spring, and negative electrode shell were added, and appropriate mechanical pressure was applied to ensure a complete seal, thus assembling the CR 2032 supercapacitor. All of the above operations were performed inside a glove box.

[0039] The supercapacitors obtained in this comparative example exhibited significantly decreased low-temperature electrochemical performance across all low-temperature ranges. Specifically, after cooling from 20 °C to -50 °C, the coin capacitor retained only 46.4% of its capacitance and had a specific capacitance of 32.8 F / g (at a scan rate of 20 mV / s), demonstrating significant capacitance decay. Further cooling to -70 °C resulted in a coin capacitor capacitance of only 21.2% of its room-temperature capacitance (at a scan rate of 20 mV / s); the bulk impedance of the device at the ultra-low temperature of -70 °C was approximately 22 Ω.

[0040] Comparative Example 3: Under an inert atmosphere and at room temperature (oxygen ≤ 1 ppm, water ≤ 1 ppm), propylene carbonate (purity 99.0%) was dried using a 3 Å molecular sieve for 6 hours. Then, N,N-dimethylpyrrolidone ontium tetrafluoroborate solute was added at a mass molar concentration of 1.2 mol / kg and mixed thoroughly until clear and transparent to obtain the supercapacitor electrolyte, which was then sealed and stored.

[0041] The electrode material used was a commercially available dry-process activated carbon electrode sheet (carbon-coated aluminum foil substrate, 140 μm thick), cut into 11 mm diameter discs. The separator was a commercially available glass fiber separator (540 μm thick), cut into 19 mm diameter discs. The gasket, positive electrode sheet, and separator were sequentially placed into the CR 2032 positive electrode shell, and 260 μL of the electrolyte was slowly and evenly added. Subsequently, the negative electrode sheet, gasket, spring, and negative electrode shell were added, and appropriate mechanical pressure was applied to ensure a complete seal, thus assembling the CR 2032 supercapacitor. All of the above operations were performed inside a glove box.

[0042] The supercapacitor obtained in this comparative example exhibited a significant decrease in low-temperature electrochemical performance in the 20–50 °C range, and its electrochemical performance completely failed in the -50–70 °C range. Specifically, after cooling from 20 °C to -50 °C, the capacitance retention of the button capacitor was only 32.8%, and the specific capacitance was 24.1 F / g (at a scan rate of 20 mV / s), showing significant capacitance decay. Upon further cooling to -70 °C, the electrolyte rapidly solidified and underwent a phase transition, resulting in the complete failure of the supercapacitor's electrochemical performance.

[0043] Biotoxicity verification of the electrolytes provided in Example 2 and Comparative Examples 1-3: The CCK-8 cytotoxicity test showed that the electrolyte provided by the present invention exhibited the highest relative cell viability (76%), which was superior to commercial acetonitrile-based electrolyte (68%), commercial propylene carbonate-based electrolyte (41%) and common N,N-dimethylformamide-based electrolyte (46%).

Claims

1. A low-temperature electrolyte, characterized in that, The electrolyte comprises a single solvent and a solute dissolved in the solvent; The solvent has a moderate dielectric constant, a low donor number, and an ultra-low melting point; the solute has a small molecular radius and high electrochemical stability.

2. The low-temperature electrolyte according to claim 1, characterized in that, The solvent is acetone, which has a dielectric constant of 20.9, a donor number of 10.67, and a melting point of -95°C.

3. The low-temperature electrolyte according to claim 1, characterized in that, The solute includes N,N-dimethylpyrrolidone tetrafluoroborate.

4. The low-temperature electrolyte according to claim 3, characterized in that, The concentration of N,N-dimethylpyrrolidine ontium tetrafluoroborate in the electrolyte is 1.0 mol / kg to 1.2 mol / kg.

5. The low-temperature electrolyte according to claim 1, characterized in that, The electrolyte has a conductivity of 20.27 mS / cm - 20.93 mS / cm at room temperature and a conductivity of 2.74 mS / cm - 2.85 mS / cm at -70 °C.

6. A supercapacitor, characterized in that, It has the low-temperature electrolyte according to any one of claims 1 to 5.

7. The supercapacitor according to claim 6, characterized in that, The supercapacitor is a symmetrical supercapacitor assembled from the low-temperature electrolyte and activated carbon-based electrode sheets.

8. The supercapacitor according to claim 6, characterized in that, The supercapacitor has a minimum operating temperature of -70℃.

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