Electrolyte for electric double-layer capacitor and electric double-layer capacitor

Abstract

The invention relates to an electrolyte for an electric double-layer capacitor and the electric double-layer capacitor, the electrolyte comprises an organic solvent, an electrolyte and an additive, the electrolyte is quaternary ammonium salt, the organic solvent is a nitrile organic solvent, and the additive comprises fluorinated organic ester containing carbon-carbon double bonds in a molecular structure. According to the invention, the quaternary ammonium salt is used as the electrolyte, the nitrile organic matter is used as the solvent, and the fluorinated organic ester is added as the additive, so that the infiltration effect of the electrolyte for the electric double-layer capacitor is effectively improved, the electrolyte can rapidly and effectively infiltrate the electric double-layer capacitor, the manufacturing time of the electric double-layer capacitor is greatly shortened, the production efficiency is improved, and the cost is reduced. Furthermore, the normal-temperature charge-discharge cycle of the double-electric-layer capacitor is not influenced by selecting proper fluorinated organic ester and proper dosage.

Description

Technical Field

[0001] The present invention relates to an electrolyte for a double-layer capacitor and a double-layer capacitor. Background Art

[0002] From a global perspective, as a new type of energy storage device, double-layer capacitors have continued to grow in market size due to their advantages such as high power density, fast charging and discharging speed, long service life, and safety and pollution-free. The industry needs to improve production efficiency to meet market demand.

[0003] The manufacturing process of double-layer capacitors usually includes winding battery cells, welding, shelling and grooving, vacuum heat treatment, liquid injection and sealing. During the liquid injection process, the electrolyte needs to be fully infiltrated into the interior of the battery cell. If the infiltration is insufficient, the internal interface resistance will increase and affect the transmission of electrons. The commonly used liquid injection method is to first place the double-layer capacitor monomer in a liquid injection device filled with nitrogen and then transfer it to a glove box, first evacuate the vacuum, then inject the electrolyte and pressurize it, and then let it stand to allow the electrolyte to penetrate into the double-layer capacitor core package. This step is repeated at least 4 times. There are problems such as long standing time, many repetitions, and insufficient infiltration during the liquid injection process. Summary of the invention

[0004] The object of the present invention is to provide an electrolyte for an electric double layer capacitor with improved wetting effect, which can effectively reduce the injection time of the electric double layer capacitor and ensure that the electrolyte fully wets the electric double layer capacitor.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] The invention provides an electrolyte for a double-layer capacitor, which comprises an organic solvent, an electrolyte and an additive. The electrolyte is a quaternary ammonium salt, the organic solvent is a nitrile organic solvent, and the additive comprises a fluorinated organic ester containing a carbon-carbon double bond in the molecular structure.

[0007] Preferably, the additive includes one or more of 2,2,3,3-tetrafluoropropyl methacrylate, 2,2,3,3,3-pentafluoropropyl methacrylate, 2,2,3,3-tetrafluoropropyl acrylate, fluoroethylene carbonate, and difluoroethylene carbonate.

[0008] According to some specific embodiments of the present invention, the additive includes at least any one of 2,2,3,3-tetrafluoropropyl methacrylate, 2,2,3,3,3-pentafluoropropyl methacrylate or 2,2,3,3-tetrafluoropropyl acrylate.

[0009] Preferably, the mass of the additive is less than 7% of the sum of the mass of the electrolyte and the organic solvent.

[0010] More preferably, the mass of the additive is 0.5% to 6% of the sum of the mass of the electrolyte and the organic solvent.

[0011] Still more preferably, the mass of the additive is 1% to 5% of the sum of the mass of the electrolyte and the organic solvent, that is, a better wetting effect is achieved and the performance of the electric double layer capacitor is substantially not affected.

[0012] In an embodiment of the present invention, the electrolyte is one or more of tetraethylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, 5,5-spirobispyrrolidinium tetrafluoroborate, N,N-dimethylpyrrolidinium tetrafluoroborate, N,N-methylethylpyrrolidinium tetrafluoroborate, and dimethyldiethylammonium tetrafluoroborate.

[0013] According to some specific embodiments of the present invention, the electrolyte is tetraethylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, 5,5-spirobispyrrolidinium tetrafluoroborate or N,N-dimethylpyrrolidinium tetrafluoroborate.

[0014] In an embodiment of the present invention, the concentration of the electrolyte in the double-layer capacitor electrolyte is 0.5-1.6 mol / L. Too high a concentration will increase the viscosity of the electrolyte, reduce the wetting effect, and also increase the internal resistance of the double-layer capacitor, affecting the performance of the double-layer capacitor.

[0015] In an embodiment of the present invention, the nitrile organic solvent includes one or more of acetonitrile, 3-methoxypropionitrile, succinonitrile, and 3-n-butoxypropionitrile.

[0016] In some embodiments, the organic solvent is acetonitrile.

[0017] In other specific embodiments, the organic solvent is a mixed solvent of 3-methoxypropionitrile, succinonitrile, and 3-n-butoxypropionitrile in a mass ratio of (5-10):1:(1-5).

[0018] In other specific embodiments, the organic solvent is a mixed solvent of acetonitrile and succinonitrile or 3-methoxypropionitrile in a mass ratio of (3-6):1.

[0019] In some further specific embodiments, the organic solvent is a mixed solvent of acetonitrile, succinonitrile, and 3-n-butoxypropionitrile in a mass ratio of (5-10):1:(1-3).

[0020] The present invention also provides a double-layer capacitor, which comprises the above-mentioned electrolyte for the double-layer capacitor.

[0021] In an embodiment of the present invention, the electrode of the double-layer capacitor is an activated carbon porous electrode.

[0022] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0023] The present invention uses quaternary ammonium salt as electrolyte, nitrile organic matter as solvent, and adds fluorinated organic ester as additive, which effectively improves the wetting effect of the electrolyte for double-layer capacitors, enables the electrolyte to quickly and effectively infiltrate the double-layer capacitors, greatly shortens the manufacturing time of the double-layer capacitors, improves production efficiency, and reduces costs. Furthermore, by selecting a suitable fluorinated organic ester and a suitable dosage, it is ensured that the room temperature charge and discharge cycle of the double-layer capacitor is not affected. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the electrolyte climbing speed test curve;

[0025] Figure 2 This is the discharge capacity curve of the double-layer capacitor during the charge and discharge cycle at room temperature. DETAILED DESCRIPTION

[0026] The present invention is further described below in conjunction with the examples, but the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry.

[0027] In the following examples and comparative examples, N,N-dimethylpyrrolidinium tetrafluoroborate was purchased from Hangzhou Feiman Fine Chemical Co., Ltd. with the brand name DMP-BF 4 ; The synthesis method of 5,5-spirobipyrrolium tetrafluoroborate is derived from patent CN104387386B; dimethyldiethylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate and tetraethylammonium tetrafluoroborate were purchased from Shanghai Qidian Chemical; the synthesis method of N,N-methylethylpyrrolidinium tetrafluoroborate is derived from patent CN105448538A; 2,2,3,3,3-pentafluoropropyl methacrylate and 2,2,3,3-tetrafluoropropyl enoate were purchased from MacLean Reagent; 2,2,3,3-tetrafluoropropyl methacrylate was purchased from Myrel Chemical Reagent; fluoroethylene carbonate and bisfluoroethylene carbonate were purchased from Shanghai Yuanye Biotechnology Co., Ltd.

[0028] The technical solution of the present invention is further described below through examples and comparative examples.

[0029] Example 1

[0030] In a glove box with water and oxygen content below 2ppm, 5,5-spirobipyrrolidinium ammonium tetrafluoroborate was added to acetonitrile and stirred to obtain a basic electrolyte solution with an electrolyte salt concentration of 1 mol / L. Then, an additive 2,2,3,3,3-pentafluoropropyl methacrylate was added in an amount equivalent to 5% of the mass of the basic electrolyte solution and stirred to obtain an electrolyte solution for double-layer capacitors.

[0031] Example 2

[0032] In a glove box with water and oxygen content below 2ppm, acetonitrile and succinonitrile were mixed into a mixed solvent at a mass ratio of 8:2, 5,5-spirobipyrrolidinium tetrafluoroborate was added to the mixed solvent, and the mixture was stirred to obtain a basic electrolyte with an electrolyte salt concentration of 1 mol / L. Then, an additive of 2,2,3,3,3-pentafluoropropyl methacrylate was added in an amount equivalent to 5% of the mass of the basic electrolyte, and the mixture was stirred to obtain an electrolyte for a double-layer capacitor.

[0033] Example 3

[0034] In a glove box with water and oxygen content below 2ppm, 3-methoxypropionitrile, succinonitrile and 3-n-butoxypropionitrile were mixed into a mixed solvent in a mass ratio of 7:1:3, N,N-dimethylpyrrolidinium ammonium tetrafluoroborate was added to the mixed solvent, and the mixture was stirred to obtain a basic electrolyte with an electrolyte salt concentration of 0.8 mol / L. Then, an additive of 2,2,3,3,3-pentafluoropropyl methacrylate was added in an amount equivalent to 3% of the mass of the basic electrolyte, and the mixture was stirred to obtain an electrolyte for a double-layer capacitor.

[0035] Example 4

[0036] In a glove box with water and oxygen content below 2ppm, acetonitrile and 3-methoxypropionitrile were mixed into a mixed solvent at a mass ratio of 8:2, triethylmethylammonium tetrafluoroborate was added to the mixed solvent, and the mixture was stirred to obtain a basic electrolyte with an electrolyte salt concentration of 0.8mol / L. Then, 2,2,3,3-tetrafluoropropyl methacrylate, an additive equivalent to 3% of the mass of the basic electrolyte, was added and stirred to obtain an electrolyte for a double-layer capacitor.

[0037] Example 5

[0038] In a glove box with water and oxygen content below 2ppm, tetraethylammonium tetrafluoroborate was added to the acetonitrile solvent and stirred to obtain a basic electrolyte solution with an electrolyte salt concentration of 1 mol / L. Then, an additive 2,2,3,3-tetrafluoropropyl methacrylate was added in an amount equivalent to 2% of the mass of the basic electrolyte solution and stirred to obtain an electrolyte solution for double-layer capacitors.

[0039] Example 6

[0040] In a glove box with water and oxygen content below 2ppm, N,N-dimethylpyrrolidinium ammonium tetrafluoroborate was added to the acetonitrile solvent and stirred to obtain a basic electrolyte with an electrolyte salt concentration of 1 mol / L. Then, 2,2,3,3-tetrafluoropropyl methacrylate, an additive equivalent to 5% of the mass of the basic electrolyte, was added and stirred to obtain an electrolyte for double-layer capacitors.

[0041] Example 7

[0042] In a glove box with water and oxygen content below 2ppm, N,N-dimethylpyrrolidinium ammonium tetrafluoroborate was added to the acetonitrile solvent and stirred to obtain a basic electrolyte solution with an electrolyte salt concentration of 1 mol / L. Then, an additive of 2,2,3,3-tetrafluoropropyl acrylate equivalent to 3% of the mass of the basic electrolyte was added and stirred to obtain an electrolyte solution for double-layer capacitors.

[0043] Example 8

[0044] In a glove box with water and oxygen content below 2ppm, acetonitrile, succinonitrile and 3-n-butoxypropionitrile were mixed into a mixed solvent in a mass ratio of 7:1:2, triethylmethylammonium tetrafluoroborate was added to the mixed solvent, and the mixture was stirred to obtain a basic electrolyte with an electrolyte salt concentration of 1 mol / L. Then, an additive of 2,2,3,3,3-pentafluoropropyl methacrylate was added in an amount equivalent to 1% of the mass of the basic electrolyte, and the mixture was stirred to obtain an electrolyte for a double-layer capacitor.

[0045] Example 9

[0046] In a glove box with water and oxygen content below 2ppm, acetonitrile and succinonitrile were mixed into a mixed solvent at a mass ratio of 8:2, triethylmethylammonium tetrafluoroborate was added to the mixed solvent, and the mixture was stirred evenly to obtain a basic electrolyte solution with an electrolyte salt concentration of 1 mol / L. Then, an additive of 2,2,3,3-tetrafluoropropyl olefinate equivalent to 5% of the mass of the basic electrolyte solution was added, and the mixture was stirred evenly to obtain an electrolyte solution for double-layer capacitors.

[0047] Example 10

[0048] In a glove box with water and oxygen content below 2ppm, tetraethylammonium tetrafluoroborate was added to the acetonitrile solvent and stirred to obtain a basic electrolyte solution with an electrolyte salt concentration of 0.6mol / L. Then, an additive of 2,2,3,3-tetrafluoropropyl acrylate equivalent to 3% of the mass of the basic electrolyte was added and stirred to obtain an electrolyte solution for double-layer capacitors.

[0049] Embodiment 11

[0050] In a glove box with water and oxygen content below 2ppm, N,N-dimethylpyrrolidinium ammonium tetrafluoroborate was added to the acetonitrile solvent and stirred to obtain a basic electrolyte solution with an electrolyte salt concentration of 1.5mol / L. Then, 2,2,3,3-tetrafluoropropyl methacrylate, an additive equivalent to 3% of the mass of the basic electrolyte solution, was added and stirred to obtain an electrolyte solution for double-layer capacitors.

[0051] Example 12

[0052] In a glove box with water and oxygen content below 2ppm, acetonitrile and 3-methoxypropionitrile were mixed into a mixed solvent at a mass ratio of 8:2, 5,5-spirobipyrrolidinium ammonium tetrafluoroborate was added to the mixed solvent, and stirred evenly to obtain a basic electrolyte with an electrolyte salt concentration of 1.3 mol / L. Then, an additive 2,2,3,3-tetrafluoropropyl methacrylate was added in an amount equivalent to 3% of the mass of the basic electrolyte, and stirred evenly to obtain an electrolyte for a double-layer capacitor.

[0053] Embodiment 13

[0054] In a glove box with water and oxygen content below 2ppm, 5,5-spirobipyrrolidinium ammonium tetrafluoroborate was added to the acetonitrile solvent and stirred to obtain a basic electrolyte solution with an electrolyte salt concentration of 1 mol / L. Then, an additive of 2,2,3,3,3-pentafluoropropyl methacrylate equivalent to 7% of the mass of the basic electrolyte was added and stirred to obtain an electrolyte solution for double-layer capacitors.

[0055] Embodiment 14

[0056] In a glove box with water and oxygen content less than 2ppm, N,N-methylethylpyrrolidinium tetrafluoroborate was added to the acetonitrile solvent and stirred to obtain a basic electrolyte with an electrolyte salt concentration of 1 mol / L. Then, 2,2,3,3-tetrafluoropropyl methacrylate equivalent to 3% of the mass of the basic electrolyte and fluoroethylene carbonate equivalent to 2% of the mass of the basic electrolyte were added and stirred to obtain an electrolyte for double-layer capacitors.

[0057] Embodiment 15

[0058] In a glove box with water and oxygen content below 2ppm, dimethyl diethyl ammonium tetrafluoroborate was added to the acetonitrile solvent and stirred to obtain a basic electrolyte with an electrolyte salt concentration of 1 mol / L. Then, 3% of the mass of the basic electrolyte was added with an additive of 2,2,3,3-tetrafluoropropyl methacrylate and 2% of the mass of the basic electrolyte with an additive of bisfluoroethylene carbonate, and stirred to obtain an electrolyte for a double-layer capacitor.

[0059] Comparative Example 1

[0060] In a glove box with water and oxygen contents below 2 ppm, N,N-dimethylpyrrolidinium ammonium tetrafluoroborate was added to acetonitrile solvent and stirred evenly to obtain an electrolyte solution for an electric double layer capacitor with an electrolyte salt concentration of 1 mol / L.

[0061] Comparative Example 2

[0062] In a glove box with water and oxygen content less than 2 ppm, acetonitrile and 3-methoxypropionitrile were mixed into a mixed solvent in a mass ratio of 8:2, 5,5-spirobispyrrolidinium ammonium tetrafluoroborate was added to the mixed solvent, and stirred evenly to obtain an electrolyte for a double-layer capacitor with an electrolyte salt concentration of 0.8 mol / L.

[0063] Performance Testing

[0064] The double-layer capacitor used in the test is a cylindrical double-layer capacitor (cylindrical, 1.5 cm in diameter, 3.0 cm in height), in which the electrode material of the double-layer capacitor is composed of activated carbon (Japan Kuraray Co., Ltd., model: YP-50F), acetylene black (Shenzhen Kejing Zhida Technology Co., Ltd., model: EQ-Lib-AB), and adhesive (PTFE (polytetrafluoroethylene), Shenzhen Kejing Zhida Technology Co., Ltd., model: EQ-Lib-PTFE) in a ratio of 8:1:1, with a thickness of 300 μm. The activated carbon material is coated on aluminum foil using a diaphragm rolling process to make a double-layer capacitor electrode with a designed capacity of 25F.

[0065] The double-layer capacitor electrode is wound into a capacitor core package, and then a double-layer capacitor monomer is obtained by current collector welding, shelling and groove rolling.

[0066] The double-layer capacitor monomer was baked in a vacuum drying oven at 105°C for 8 hours, maintaining a vacuum of -0.09MPa. After baking, nitrogen was introduced for cooling.

[0067] The baked double-layer capacitor monomer is placed in a liquid injection device filled with nitrogen and then transferred to a glove box for liquid injection and sealing to obtain the final double-layer capacitor.

[0068] (1) Test of injection volume:

[0069] In the glove box, put the double-layer capacitor monomer into a vacuum sealing device, first evacuate the vacuum, then inject the double-layer capacitor electrolyte (the electrolyte needs to submerge the capacitor monomer), and then pressurize it. Let it stand for 30 minutes to allow the electrolyte to penetrate into the double-layer capacitor core package. Repeat this step many times until the mass of the double-layer capacitor monomer no longer increases, and then convert the mass of the electrolyte immersed in the double-layer capacitor monomer into volume. The injection volume data is shown in Table 1.

[0070] Table 1

[0071]

[0072] "Unchanged" in Table 1 means that the mass of the electrolyte in the double-layer capacitor monomer no longer increases.

[0073] Electrolyte climbing speed test:

[0074] In the glove box, the double-layer capacitor electrode was cut into 20mm*200mm long strips, and then the electrode was placed vertically in a container with electrolyte (the liquid level was 10mm above the electrode). The climbing height H of the electrolyte in the electrode was recorded at regular intervals, and the corresponding infiltration time t was recorded at the same time. Then, according to the Lucas-Washburn permeation model, the climbing height H and the infiltration time t were plotted. 0.5 relationship diagram. Figure 1 These are the electrolyte climbing speed test results of Example 6, Example 7, Example 8 and Comparative Example 1 and Comparative Example 2.

[0075] Room temperature charge and discharge cycle test:

[0076] The manufactured 25F double-layer capacitor was left to stand at room temperature for 24 hours, and then a room temperature charge and discharge cycle test was performed on a battery test cabinet.

[0077] Test parameter settings: current 75mAd / F, charge cut-off voltage 0.3V, discharge cut-off voltage 0.1V, cycle 40,000 cycles. Figure 2 The data for normal temperature charge and discharge cycles are shown for Example 3, Example 6, Example 7, Example 13, and Comparative Example 1.

[0078] According to Table 1, adding fluorinated organic ester as an additive to a basic electrolyte with nitrile organic matter as solvent and quaternary ammonium salt as electrolyte can significantly reduce the number of injections, shorten the time required for the entire injection process, and improve production efficiency.

[0079] Figure 1 It shows that the climbing rate of the electrolytes of Example 6, Example 7 and Example 8 is significantly improved compared with the electrolytes of Comparative Example 1 and Comparative Example 2.

[0080] Figure 2 It is shown that the normal temperature charge and discharge curves of the capacitors containing the electrolytes of Examples 3, 6 and 7 are very close to the normal temperature charge and discharge curves of the capacitor containing the electrolyte of Comparative Example 1, indicating that the fluorinated organic ester used in the examples as an additive will not affect the performance of the double-layer capacitor. However, the discharge capacity decay of the capacitor containing the electrolyte of Example 13 is slightly greater than that of the capacitor containing the electrolyte of Comparative Example 1, indicating that the addition amount of the above-mentioned fluorinated organic ester is preferably not more than 7% of the mass of the basic electrolyte.

[0081] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. An electrolyte for a double-layer capacitor, comprising an organic solvent, an electrolyte and an additive, characterized in that: The electrolyte is a quaternary ammonium salt, the organic solvent is a nitrile organic solvent, and the additive includes a fluorinated organic ester containing a carbon-carbon double bond in its molecular structure.

2. The electrolyte for electric double layer capacitor according to claim 1, characterized in that The additive includes one or more of 2,2,3,3-tetrafluoropropyl methacrylate, 2,2,3,3,3-pentafluoropropyl methacrylate, 2,2,3,3-tetrafluoropropyl acrylate, fluoroethylene carbonate, and difluoroethylene carbonate.

3. The electrolyte for electric double layer capacitor according to claim 1, characterized in that The mass of the additive is less than 7% of the sum of the mass of the electrolyte and the organic solvent.

4. The electrolyte for electric double layer capacitor according to claim 3, characterized in that The mass of the additive is 0.5% to 6% of the sum of the mass of the electrolyte and the organic solvent.

5. The electrolyte for electric double layer capacitor according to claim 4, characterized in that The mass of the additive is 1% to 5% of the sum of the mass of the electrolyte and the organic solvent.

6. The electrolyte for electric double layer capacitor according to claim 1, characterized in that The electrolyte is one or more of tetraethylammonium tetrafluoroborate, triethylmethylammonium tetrafluoroborate, 5,5-spirobispyrrolidinium tetrafluoroborate, N,N-dimethylpyrrolidinium tetrafluoroborate, N,N-methylethylpyrrolidinium tetrafluoroborate, and dimethyldiethylammonium tetrafluoroborate.

7. The electrolyte for an electric double layer capacitor according to claim 1, characterized in that The concentration of the electrolyte in the electrolytic solution for an electric double layer capacitor is 0.5 to 1.6 mol / L.

8. The electrolyte for an electric double layer capacitor according to claim 1, characterized in that The nitrile organic solvent includes one or more of acetonitrile, 3-methoxypropionitrile, succinonitrile, and 3-n-butoxypropionitrile.

9. An electric double layer capacitor, characterized in that: The electric double layer capacitor comprises the electrolyte for an electric double layer capacitor according to any one of claims 1 to 8.

10. The electric double layer capacitor according to claim 9, characterized in that: The electrodes of the double-layer capacitor are activated carbon porous electrodes.

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