Electrolyte based on fluorine-containing polynitrile compound and high-voltage supercapacitor

Abstract

The invention discloses an electrolyte based on a fluorine-containing polynitrile compound and a high-voltage supercapacitor, and belongs to the field of energy storage materials. The electrolyte comprises a fluorine-containing polynitrile compound, an organic solvent and electrolyte salt; the structure of the fluorine polynitrile compound is as follows: Fm-A-(CN) n, wherein A is C1-C10 alkyl, C6-C14 aryl or a heteroatom-containing linking group, m is greater than or equal to 1, and n is greater than or equal to 2. By introducing the Fm-A-(CN) n structure compound and utilizing the synergistic effect of fluorine atoms and cyano groups, a stable interfacial film is formed on the surface of an electrode, so that the working voltage of the electrolyte is increased to 3-3.2 V. The capacitance decay rate of the electrolyte in the range of 60-80 DEG C is lt; the method is suitable for the fields of vehicle-mounted energy storage, power grid frequency modulation and the like.

Description

Technical Field

[0001] The present application relates to an electrolyte and a high-voltage supercapacitor based on fluorinated polynitrile compounds, belonging to the field of energy storage materials. Background Art

[0002] As a high-performance energy storage device, supercapacitors have broad application prospects in new energy vehicles, aerospace, grid frequency modulation, and other fields due to their rapid charge and discharge capabilities and high power density. However, traditional supercapacitor electrolytes (such as acetonitrile-based and carbonate-based) have problems such as a limited voltage window (≤2.7V) and easy decomposition at high voltages, which restricts the improvement of their energy density and the expansion of their application scenarios.

[0003] Among them, acetonitrile is the most widely used organic supercapacitor solvent with low viscosity (0.34cp) and high dielectric constant (37.5). Its strong polarity can dissociate the electrolyte salt well, making the electrolyte have high conductivity. However, as the working voltage increases, acetonitrile (AN)-based organic electrolyte will produce a large amount of gas when it is used at high voltage (>3.0V) and high temperature (>60℃), which will cause the gas inside the device to expand, thus causing serious safety hazards. Fluorinated electrolytes have strong electronegativity and weak polarity of fluorine atoms, and the chemical stability of fluorinated solvents is excellent, which has great potential in the application of high-voltage electrolytes. For example, patent CN202410119917 provides a single-component lithium battery electrolyte composed of a fluorinated carboxylic acid ester solvent and a solute. Through molecular structure design, the antioxidant stability of the electrolyte is effectively improved, especially at high voltage, it can promote the formation of a stable interface on the positive electrode surface and improve compatibility with the high-voltage positive electrode. Patent CN109273767 covers chain fluorinated carbonate compounds, which increase the oxidative decomposition voltage of the electrolyte and optimize the electrode interface, thereby improving the high-temperature and high-voltage stability of lithium batteries. However, fluorinated solvents, due to their weak polarity, have insufficient ability to dissociate electrolyte salts, resulting in low ionic conductivity of the electrolyte.

[0004] Therefore, it is of great practical significance to develop a new high-voltage electrolyte that has both high ionic conductivity and good antioxidant properties to break through the existing technological bottleneck. Summary of the Invention

[0005] The present invention aims to solve the problems of existing supercapacitor electrolytes such as easy decomposition at high voltage and narrow voltage window, and to provide a high-voltage supercapacitor electrolyte and its application to meet the needs of high-performance energy storage devices.

[0006] According to a first aspect of the present application, an electrolyte based on a fluorine-containing polynitrile compound is provided.

[0007] An electrolyte based on a fluorinated polynitrile compound, the electrolyte comprising a fluorinated polynitrile compound, an organic solvent, and an electrolyte salt;

[0008] The structure of the fluorocarbon nitrile compound is as follows:

[0009] F m -A-(CN) n

[0010] Wherein, A is a C1-C10 alkyl group, a C6-C14 aryl group or a heteroatom-containing linking group, m≥1, and n≥2.

[0011] Optionally, the fluorine-containing polynitrile compound is selected from at least one of 2-fluoroadiponitrile, 2,2-difluorosuccinonitrile, perfluorosuccinonitrile (CF2(CN)-CF2(CN)), tetrafluoroterephthalonitrile (C6F4(CN)2), tetrafluoroterephthalonitrile (C8F4N2), fluorotetracyanoethylene (F2C=C(CN)2-CF3), 1,3-bis(trifluoromethyl)-1,3-propanedinitrile (CF3-CN-CH2-CN-CF3), fluorocyclohexane tetranitrile (C6F4(CN)4), and fluorobenzodinitrile (C6F2(CN)2).

[0012] The molecules of the fluorinated polynitrile compounds contain multiple nitrile groups (-CN) and fluorine atoms. This type of compound combines the strong polarity of the nitrile group with the unique properties of the fluorine atom (such as high electronegativity and strong electron-withdrawing effect). As an electrolyte additive or co-solvent, it has both high salt dissociation ability and antioxidant properties through the fluorine-nitrile synergistic effect. In addition, it forms a stable fluorine-cyanide synergistic interface film on the electrode surface, effectively widening the voltage window and inhibiting the decomposition of the electrolyte. Furthermore, the fluorine atoms in the fluorinated polynitrile compounds contribute as follows: 1) Antioxidation: The high electronegativity of fluorine can stabilize the electrolyte molecules and inhibit the oxidative decomposition of the electrolyte under high pressure; 2) Thermal stability: The CF bond energy is high (~485kJ / mol), which improves safety at high temperatures (>60°C). The nitrile group (-CN) in the fluorinated polynitrile compounds contributes as follows: dissolving electrolyte salts, the strong polarity of the nitrile group can coordinate with the quaternary ammonium salt cation to promote salt dissociation, and the polynitrile group improves ionic conductivity.

[0013] Optionally, the fluorine-containing polynitrile compound is used in an amount of 0.05-15 wt %.

[0014] Optionally, the fluorine-containing polynitrile compound is used in an amount of 2-8 wt %.

[0015] Optionally, the organic solvent is a nitrile solvent or a mixed system of a carbonate solvent and a nitrile solvent;

[0016] Optionally, the nitrile solvent is selected from at least one of acetonitrile, propionitrile and butyronitrile;

[0017] The carbonate solvent is selected from at least one of propylene carbonate, ethylene carbonate and ethyl acetate.

[0018] Optionally, the electrolyte salt is selected from at least one of tetraethylammonium tetrafluoroborate (TEABF4), triethylmethylammonium tetrafluoroborate (TEMABF4), and spirobispyrrolidinium tetrafluoroborate (SBPBF4).

[0019] Optionally, the electrolyte further comprises an ionic liquid;

[0020] Optionally, the ionic liquid is selected from 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4), 1-butyl-3-methylimidazolium hexafluorophosphate (BMIPF6), N-butyl-N-methylpyrrolidine bis(trifluoromethanesulfonyl)imide (PYR 14 At least one of TFSI).

[0021] Optionally, the mass ratio of the ionic liquid to the fluorinated polynitrile compound is 1:0.5-1:2.

[0022] Optionally, the mass ratio of the ionic liquid to the fluorinated polynitrile compound is 1:0.5-1:1.

[0023] According to a second aspect of the present application, a high-voltage supercapacitor is provided.

[0024] A high-voltage supercapacitor comprises a positive electrode, a negative electrode, a diaphragm and the electrolyte described above.

[0025] Optionally, the operating voltage is ≥3V.

[0026] Optionally, the high voltage supercapacitor is an asymmetric supercapacitor, such as activated carbon / / Li4Ti5O 12 system.

[0027] The beneficial effects of this application include:

[0028] The electrolyte and high-voltage supercapacitor based on fluorinated polynitrile compounds provided in this application have the following advantages:

[0029] 1) Voltage window improvement: The introduction of fluorinated polynitrile compounds increases the electrolyte operating voltage from the conventional 2.5-2.7V to 3-3.2V;

[0030] 2) Extended high-voltage cycle life: Capacity retention is ≥90% after 5,000 cycles at 3.2V, compared to 82% for the fluorinated polynitrile system;

[0031] 3) Enhanced high temperature adaptability: capacitance attenuation rate is less than 15% (5000 cycles) in the range of 60-80°C.

[0032] In short, by introducing F m -A-(CN) n The structural compound utilizes the synergistic effect of fluorine atoms and cyanide groups to form a stable interfacial film on the electrode surface, increasing the electrolyte operating voltage to 3-3.2 V. The electrolyte exhibits a capacitance decay rate of less than 15% in the temperature range of 60-80°C, making it suitable for applications in areas such as on-board energy storage and grid frequency modulation. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a supercapacitor performance test curve of Comparative Example 1 (30°C and 80°C);

[0034] Figure 2 This is a supercapacitor performance test curve diagram of Example 1 (30°C and 80°C);

[0035] Figure 3 This is a supercapacitor performance test curve diagram of Example 2 (30°C and 80°C). DETAILED DESCRIPTION

[0036] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0037] Unless otherwise specified, the raw materials and catalysts in the examples of this application were purchased from commercial sources.

[0038] Unless otherwise specified, conventional methods were used for testing, and instrument settings were those recommended by the manufacturer.

[0039] Comparative Example 1

[0040] At 25°C, tetraethylammonium tetrafluoroborate (TEABF4) was added to acetonitrile solvent with a TEABF4 concentration of 1 M. The mixture was stirred at 500 rpm for 2 hours until completely transparent, forming a basic electrolyte similar to a commercial electrolyte.

[0041] The prepared electrolyte is injected into the electrode assembly of the supercapacitor to assemble a complete supercapacitor device.

[0042] Example 1

[0043] The fluorine-containing polynitrile compound 2-fluoroadiponitrile was added to the basic electrolyte at a ratio of 5 wt %, and the mixture was stirred until it was completely dissolved to obtain a high-voltage electrolyte.

[0044] The prepared electrolyte is injected into the electrode assembly of the supercapacitor to assemble a complete supercapacitor device.

[0045] Example 2

[0046] The fluorine-containing polynitrile compound 2-fluoroadiponitrile was added to the basic electrolyte at a ratio of 5 wt %, and the mixture was stirred until it was completely dissolved to obtain a high-voltage electrolyte.

[0047] Add ionic liquid BMIBF4 and adjust the mass ratio of BMIBF4 to the fluorinated polynitrile compound to 1:0.5, and stir evenly.

[0048] The prepared electrolyte is injected into the electrode assembly of the supercapacitor to assemble a complete supercapacitor device.

[0049] Examples 3 to 5

[0050] The operation is the same as that of Example 1, except that the fluorinated polynitrile compounds are tetrafluoroterephthalonitrile, fluorotetracyanoethylene, and fluorocyclohexanetetranitrile, respectively, to obtain a high-voltage electrolyte.

[0051] The electrical properties of the high-voltage electrolytes of Comparative Example 1 and Examples 1 and 2 were tested as follows:

[0052] (1) Assembly of supercapacitors: Take a number of commercial activated carbon electrode sheets (cut into round pieces with sizes matching the button battery shell), place them in the order of positive electrode shell, electrode, diaphragm, electrode, gasket, and spring, add a certain amount of electrolyte, generally enough to fully soak the electrode and diaphragm; align the negative electrode shell and the positive electrode shell of the battery shell, use a dedicated button battery sealing device, and seal the battery shell tightly according to a certain pressure and method. After the packaging is completed, the assembled button supercapacitor can be left at room temperature for one day to allow the electrolyte to fully soak the electrode and diaphragm, and to allow the electrochemical system inside the capacitor to reach a relatively stable state.

[0053] (2) Electrochemical test of supercapacitors: The assembled supercapacitors were placed on a battery tester and subjected to constant current charge and discharge cycle tests. The charge and discharge current density was set to 0.2 A / g and the charge cut-off voltage was set to 2.7-3.2 V.

[0054] Figure 1 This is the supercapacitor performance test curve of comparative example 1 (30℃ and 80℃). It can be seen that the upper limit of the stable voltage of the supercapacitor is 2.7V. As the temperature increases from 30℃ to 80℃, the charging curve of the supercapacitor is significantly deformed, indicating that the supercapacitor begins to undergo oxidation side reactions at 80℃ and cannot work stably.

[0055] Figure 2This is a supercapacitor performance test curve diagram of Example 1 (30°C and 80°C). At a high operating voltage of 3V, even if the temperature increases from 30°C to 80°C, the supercapacitor discharge curve maintains an ideal symmetrical triangle, indicating its ideal capacitance behavior.

[0056] Figure 3 This is a supercapacitor performance test curve diagram of Example 2 (30°C and 80°C). At a high operating voltage of 3.2V, even if the temperature increases from 30°C to 80°C, the supercapacitor discharge curve maintains an ideal symmetrical triangle, indicating its ideal capacitance behavior.

[0057] The result data of the operating voltage, specific capacity at 30°C, capacity attenuation rate after 10,000 cycles, capacity retention rate of 1000h float charge at 70°C, and capacity attenuation rate after 10,000 cycles of Comparative Example 1 and Examples 1-4 are shown in Table 1.

[0058] Table 1

[0059]

[0060] As can be seen from Table 1, the maximum operating voltage and high-temperature stability of the comparative example are limited, while the addition of fluorinated polynitrile compounds increases the oxidation decomposition voltage of the electrolyte, thereby improving the high-temperature resistance and high-voltage stability of the supercapacitor.

[0061] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. An electrolyte based on a fluorinated polynitrile compound, characterized in that: The electrolyte comprises a fluorinated polynitrile compound, an organic solvent and an electrolyte salt; The structure of the fluorocarbon nitrile compound is as follows: F m -A-(CN) n Wherein, A is a C1-C10 alkyl group, a C6-C14 aryl group or a heteroatom-containing linking group, m≥1, and n≥2.

2. The electrolyte according to claim 1, characterized in that The fluorine-containing polynitrile compound is at least one selected from 2-fluoroadiponitrile, 2,2-difluorosuccinonitrile, perfluorosuccinonitrile, tetrafluoroterephthalonitrile, tetrafluoroterephthalonitrile, fluorotetracyanoethylene, 1,3-bis(trifluoromethyl)-1,3-propanedinitrile, fluorocyclohexane tetranitrile, and fluorobenzodinitrile.

3. The electrolyte according to claim 1, characterized in that The usage ratio of the fluorine-containing polynitrile compound is 0.05-15 wt %.

4. The electrolyte according to claim 1, characterized in that The organic solvent is a nitrile solvent or a mixed system of a carbonate solvent and a nitrile solvent; Preferably, the nitrile solvent is selected from at least one of acetonitrile, propionitrile and butyronitrile; The carbonate solvent is selected from at least one of propylene carbonate, ethylene carbonate and ethyl acetate.

5. The electrolyte according to claim 1, characterized in that The electrolyte salt is selected from at least one of tetraethylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, and spirobispyrrolidinium tetrafluoroborate.

6. The electrolyte according to claim 1, characterized in that The electrolyte further comprises an ionic liquid; Preferably, the ionic liquid is selected from BMIBF4, BMIPF6, PYR 14 At least one of the TFSIs.

7. The electrolyte according to claim 6, characterized in that The mass ratio of the ionic liquid to the fluorine-containing polynitrile compound is 1:0.5-1:

2.

8. A high voltage supercapacitor, characterized in that: The electrolyte comprises a positive electrode, a negative electrode, a separator and the electrolyte according to any one of claims 1 to 7.

9. The high voltage supercapacitor according to claim 8, characterized in that: Working voltage ≥3V.

10. The high voltage supercapacitor according to claim 8, characterized in that: The high voltage supercapacitor may also be an asymmetric supercapacitor.

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