Super capacitor low-temperature electrolyte and preparation method thereof

Abstract

The invention belongs to the field of super capacitors, and discloses a super capacitor low-temperature electrolyte and a preparation method thereof, and the low-temperature electrolyte comprises the following components: LiCl, DMF and deionized water; the volume fraction of the DMF is 15 to 50 percent; the concentration of the LiCl is 0.05 mol / L to 5.5 mol / L; economical and practical LiCl is selected as a solute, a mixed solution of deionized water and DMF in different proportions is adopted as a solvent, the freezing point of the electrolyte can be reduced by adding DMF, and the obtained electrolyte is still in a liquid state at the temperature of-60 DEG C and does not solidify. Therefore, DMF is introduced into LiCl to serve as a cosolvent, and the low-temperature performance of the electrolyte can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the field of supercapacitors, and more specifically relates to a supercapacitor low-temperature electrolyte and a preparation method thereof. Background Art

[0002] Supercapacitors are widely used in various fields due to their high power density, fast charge and discharge speed, long service life and excellent low temperature performance. However, without thermal protection, their applications are severely limited when operating in cold seasons and regions, as they will lose most of their capacity and power.

[0003] For some civilian fields, the operating limit temperature is at least -20℃; for some military fields, the operating limit temperature is at least -40℃; for polar scientific research, the operating limit temperature is at least -60℃; for the aerospace field, sufficient energy density is required at least at -100℃. People have put forward higher requirements for the low-temperature performance of energy storage equipment in some special scenarios. It is of great significance to improve the energy density of supercapacitors and broaden the lower limit of operating temperature. The electrolyte is the most important component of supercapacitors. Therefore, developing electrolytes with high ionic conductivity at low temperatures is an important measure to improve the low-temperature performance of supercapacitors.

[0004] Compared with non-aqueous electrolytes, aqueous electrolytes have the advantages of high safety, easy preparation, and high conductivity. However, the high freezing point of water (0°C) is an important factor limiting the low-temperature performance of aqueous batteries. It is generally believed that the hydrogen bonds between water molecules are the cause of the high freezing point. When liquid water freezes into ice, each water molecule forms additional hydrogen bonds. Therefore, breaking the hydrogen bonds between water molecules is an effective way to prevent water from transforming into ice.

[0005] Therefore, how to provide a low-temperature aqueous electrolyte for supercapacitors with good performance at low temperatures is a problem that technicians in this field urgently need to solve. Summary of the invention

[0006] In order to overcome the shortcomings and deficiencies in the prior art, the present invention provides a supercapacitor low-temperature electrolyte. Introducing DMF (N,N-dimethylformamide) as an organic co-solvent in LiCl can effectively improve the low-temperature performance of the electrolyte, have higher conductivity, and the preparation method is simple and easy with low cost.

[0007] In order to achieve the above object, the present invention adopts the following technical solution:

[0008] A supercapacitor low-temperature electrolyte comprises components of LiCl, DMF and deionized water; the volume fraction of the DMF is 15-50%; and the concentration of the LiCl is 0.05-5.5 mol / L.

[0009] Preferably, the volume fraction of the DMF is 20%.

[0010] Preferably, the concentration of LiCl is 4.5-5.5 mol / L.

[0011] Preferably, the concentration of LiCl is 4.5 mol / L.

[0012] The beneficial effect of the above technical solution is that at -60°C, the LiCl aqueous solution solidifies when the concentration is below 5.5 mol / L. When the LiCl concentration is low (<4.5 mol / L), its high freezing point and low ionic conductivity limit its application at low temperatures (-60°C); at the same time, when the LiCl concentration is 4.5-5.5 mol / L, it has a lower freezing point and higher conductivity. The introduction of DMF as a co-solvent can significantly improve its performance at low temperatures, while retaining the advantages of high safety, easy preparation, and high conductivity of aqueous electrolytes. Therefore, the preferred LiCl concentration is 4.5 mol / L.

[0013] The above-mentioned method for preparing a low-temperature electrolyte for supercapacitors comprises the following steps:

[0014] (1) adding DMF to deionized water and stirring thoroughly to mix well to obtain a solvent;

[0015] (2) Add LiCl to the solvent obtained in step (1), and stir thoroughly using a magnetic stirrer to obtain a low-temperature electrolyte.

[0016] The above-mentioned low-temperature electrolyte for supercapacitors is used in symmetrical supercapacitors, wherein the symmetrical supercapacitors use metal Pt as electrodes.

[0017] It can be seen from the above technical solution that, compared with the prior art, the present invention provides a supercapacitor low-temperature electrolyte having the following beneficial effects:

[0018] (1) The present invention selects economical and practical LiCl as the solute, adopts a mixed solution of deionized water and DMF in different proportions as the solvent, and introduces DMF as an organic co-solvent in LiCl, which can effectively improve the low-temperature performance of the electrolyte.

[0019] (2) The addition of DMF can lower the freezing point of the electrolyte. The electrolyte obtained by introducing DMF as a co-solvent in the LiCl aqueous solution is still in a liquid state at -60°C and does not solidify. When the volume fraction of DMF is 20%, the electrolyte has a high conductivity (about 1.143 mS·cm) at -60°C. -1), and at this time its CV curve area reaches the maximum (about 1.43 times when the DMF addition amount is 0%), and the capacitance of the Pt / Pt symmetric supercapacitor is about 244.48μF.

[0020] (3) The preparation method of the present invention is simple and easy to implement, does not require expensive instruments, has a wide range of raw materials, is low in cost, and is suitable for industrial production and commercial applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0022] Figure 1 The solidification point of the LiCl electrolyte obtained in Comparative Example 2-10 and its conductivity curve at -60°C;

[0023] Figure 2 This is a photo of the electrolyte at -60°C;

[0024] Figure 3 Schematic diagram of Pt / Pt symmetric supercapacitor;

[0025] Figure 4 CV curves of various Pt / Pt symmetric supercapacitors at -60°C;

[0026] Figure 5 GCD curves of various Pt / Pt symmetric supercapacitors at -60°C;

[0027] Figure 6 The EIS curves of each Pt / Pt symmetric supercapacitor at -60°C;

[0028] Figure 7 This is an enlarged view of the EIS curve of each Pt / Pt symmetric supercapacitor at -60°C;

[0029] Figure 8 is the capacitance of each Pt / Pt symmetric supercapacitor at different temperatures;

[0030] Fig. 9 Ragone curves of various Pt / Pt symmetric supercapacitors at -60°C;

[0031] Fig.10 The Pt / Pt symmetric supercapacitor cycle performance test curve of Example 2 at -60°C. DETAILED DESCRIPTION

[0032] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Example 1

[0034] A method for preparing a low-temperature electrolyte for a supercapacitor comprises the following steps:

[0035] (1) Accurately measure 8.5 mL of deionized water and 1.5 mL of DMF using a measuring cylinder, transfer them into beaker A, seal them and set aside as solvents;

[0036] (2) Use an electronic balance to accurately weigh 1.90755 g of LiCl as a solute, then add it to beaker A and stir it thoroughly with a magnetic stirrer. After it is fully dissolved, seal it and let it stand for 1 hour to obtain a 4.5 mol / L LiCl electrolyte with a DMF volume fraction of 15%, which is named DMF1.5.

[0037] Two square pieces of metal Pt with a side length of 4 mm are used as electrodes and are completely immersed in the electrolyte obtained in step (2) to form a Pt / Pt symmetrical supercapacitor.

[0038] Example 2

[0039] A method for preparing a low-temperature electrolyte for a supercapacitor comprises the following steps:

[0040] (1) Use a measuring cylinder to accurately measure 8 mL of deionized water and 2 mL of DMF, transfer them into beaker A and seal them for later use as solvents.

[0041] (2) Use an electronic balance to accurately weigh 1.90755 g of LiCl as a solute, then add it to beaker A and stir it thoroughly with a magnetic stirrer. After it is fully dissolved, seal it and let it stand for 1 hour to obtain a 4.5 mol / L LiCl electrolyte with a DMF volume fraction of 20%, named DMF2.

[0042] Two square pieces of metal Pt with a side length of 4 mm are used as electrodes and are completely immersed in the electrolyte obtained in step (2) to form a Pt / Pt symmetrical supercapacitor.

[0043] Example 3

[0044] A method for preparing a low-temperature electrolyte for a supercapacitor comprises the following steps:

[0045] (1) Accurately measure 7.5 mL of deionized water and 2.5 mL of DMF using a measuring cylinder, transfer them into beaker A, seal them and set aside as solvents;

[0046] (2) Use an electronic balance to accurately weigh 1.90755 g of LiCl as a solute, then add it to beaker A and stir it thoroughly with a magnetic stirrer. After it is fully dissolved, seal it and let it stand for 1 hour to obtain a 4.5 mol / L LiCl electrolyte with a DMF volume fraction of 25%, which is named DMF2.5.

[0047] Two square pieces of metal Pt with a side length of 4 mm are used as electrodes and are completely immersed in the electrolyte obtained in step (2) to form a Pt / Pt symmetrical supercapacitor.

[0048] Example 4

[0049] A method for preparing a low-temperature electrolyte for a supercapacitor comprises the following steps:

[0050] (1) Accurately measure 7 mL of deionized water and 3 mL of DMF using a measuring cylinder, transfer them into beaker A, seal them and set aside as solvents;

[0051] (2) Use an electronic balance to accurately weigh 1.90755 g of LiCl as a solute, then add it to beaker A and stir it thoroughly with a magnetic stirrer. After it is fully dissolved, seal it and let it stand for 1 hour to obtain a 4.5 mol / L LiCl electrolyte with a DMF volume fraction of 30%, named DMF3.

[0052] Two square pieces of metal Pt with a side length of 4 mm are used as electrodes and are completely immersed in the electrolyte obtained in step (2) to form a Pt / Pt symmetrical supercapacitor.

[0053] Example 5

[0054] A method for preparing a low-temperature electrolyte for a supercapacitor comprises the following steps:

[0055] (1) Accurately measure 5 mL of deionized water and 5 mL of DMF using a measuring cylinder, transfer them into beaker A, seal them and set aside as solvents;

[0056] (2) Use an electronic balance to accurately weigh 1.90755 g of LiCl as a solute, then add it to beaker A and stir it thoroughly with a magnetic stirrer. After it is fully dissolved, seal it and let it stand for 1 hour to obtain a 4.5 mol / L LiCl electrolyte with a DMF volume fraction of 50%, named DMF5.

[0057] Two square pieces of metal Pt with a side length of 4 mm are used as electrodes and are completely immersed in the electrolyte obtained in step (2) to form a symmetrical supercapacitor.

[0058] Comparative Example 1

[0059] A method for preparing a low-temperature electrolyte for a supercapacitor comprises the following steps:

[0060] (1) Use a measuring cylinder to accurately measure 10 mL of deionized water and transfer it into beaker A, which is sealed for later use as the solvent;

[0061] (2) Use an electronic balance to accurately weigh 1.90755 g of LiCl as a solute, then add it to beaker A and stir it thoroughly with a magnetic stirrer. After it is fully dissolved, seal it and let it stand for 1 hour to obtain a 4.5 mol / L LiCl electrolyte with a DMF volume fraction of 0%, named DMF0.

[0062] Two square pieces of metal Pt with a side length of 4 mm are used as electrodes and are completely immersed in the electrolyte obtained in step (2) to form a Pt / Pt symmetrical supercapacitor.

[0063] Comparative Example 2

[0064] (1) Use a measuring cylinder to accurately measure 10 mL of deionized water and transfer it into beaker A, which is sealed for later use as the solvent;

[0065] (2) Use an electronic balance to accurately weigh 0.021195 g of LiCl as a solute, then add it to beaker A and stir it thoroughly with a magnetic stirrer. After it is fully dissolved, seal it and let it stand for 1 hour to obtain a 0.05 mol / L LiCl electrolyte.

[0066] Comparative Example 3

[0067] (1) Use a measuring cylinder to accurately measure 10 mL of deionized water and transfer it into beaker A, which is sealed for later use as the solvent;

[0068] (2) Use an electronic balance to accurately weigh 0.04239 g of LiCl as a solute, then add it to beaker A and stir it thoroughly with a magnetic stirrer. After it is fully dissolved, seal it and let it stand for 1 hour to obtain a 0.1 mol / L LiCl electrolyte.

[0069] Comparative Example 4

[0070] (1) Use a measuring cylinder to accurately measure 10 mL of deionized water and transfer it into beaker A, which is sealed for later use as the solvent;

[0071] (2) Use an electronic balance to accurately weigh 0.21195 g of LiCl as a solute, then add it to beaker A and stir it thoroughly with a magnetic stirrer. After it is fully dissolved, seal it and let it stand for 1 hour to obtain a 0.5 mol / L LiCl electrolyte.

[0072] Comparative Example 5

[0073] (1) Use a measuring cylinder to accurately measure 10 mL of deionized water and transfer it into beaker A, which is sealed for later use as the solvent;

[0074] (2) Use an electronic balance to accurately weigh 0.4239 g of LiCl as a solute, then add it to beaker A and stir it thoroughly with a magnetic stirrer. After it is fully dissolved, seal it and let it stand for 1 hour to obtain a 1 mol / L LiCl electrolyte.

[0075] Comparative Example 6

[0076] (1) Use a measuring cylinder to accurately measure 10 mL of deionized water and transfer it into beaker A, which is sealed for later use as the solvent;

[0077] (2) Use an electronic balance to accurately weigh 0.8478 g of LiCl as a solute, then add it to beaker A and stir it thoroughly with a magnetic stirrer. After it is fully dissolved, seal it and let it stand for 1 hour to obtain a 2 mol / L LiCl electrolyte.

[0078] Comparative Example 7

[0079] (1) Use a measuring cylinder to accurately measure 10 mL of deionized water and transfer it into beaker A, which is sealed for later use as the solvent;

[0080] (2) Use an electronic balance to accurately weigh 1.4837 g of LiCl as a solute, then add it to beaker A and stir it thoroughly with a magnetic stirrer. After it is fully dissolved, seal it and let it stand for 1 hour to obtain a 3.5 mol / L LiCl electrolyte.

[0081] Comparative Example 8

[0082] (1) Use a measuring cylinder to accurately measure 10 mL of deionized water and transfer it into beaker A, which is sealed for later use as the solvent;

[0083] (2) Use an electronic balance to accurately weigh 1.6956 g of LiCl as a solute, then add it to beaker A and stir it thoroughly with a magnetic stirrer. After it is fully dissolved, seal it and let it stand for 1 hour to obtain a 4 mol / L LiCl electrolyte.

[0084] Comparative Example 9

[0085] (1) Use a measuring cylinder to accurately measure 10 mL of deionized water and transfer it into beaker A, which is sealed for later use as the solvent;

[0086] (2) Use an electronic balance to accurately weigh 1.9076 g of LiCl as a solute, then add it to beaker A and stir it thoroughly with a magnetic stirrer. After it is fully dissolved, seal it and let it stand for 1 hour to obtain a 4.5 mol / L LiCl electrolyte.

[0087] Comparative Example 10

[0088] (1) Use a measuring cylinder to accurately measure 10 mL of deionized water and transfer it into beaker A, which is sealed for later use as the solvent;

[0089] (2) Use an electronic balance to accurately weigh 2.3315 g of LiCl as a solute, then add it to beaker A and stir it thoroughly with a magnetic stirrer. After it is fully dissolved, seal it and let it stand for 1 hour to obtain a 5.5 mol / L LiCl electrolyte.

[0090] Test method:

[0091] The electrolytes obtained in the examples and comparative examples were placed in a high and low temperature alternating test chamber. The temperatures were set to 20°C, 0°C, -20°C, -40°C, and -60°C, and the conductivity was measured at different temperatures.

[0092] Each Pt / Pt symmetrical supercapacitor was placed in a high and low temperature alternating test chamber. The temperatures were set to 20°C, 0°C, -20°C, -40°C, and -60°C. The electrochemical performance at different temperatures was measured using a Shanghai Chenhua CHI660E electrochemical workstation, including cyclic voltammetry, constant current charge and discharge, and electrochemical impedance.

[0093] The results of Comparative Example 1 show that when DMF is not added, the resulting electrolyte solidifies at -60°C and has poor low temperature performance.

[0094] Depend on Figure 1 It can be seen that when the LiCl concentration is below 5.5 mol / L, solidification occurs at -60°C. When the concentration is relatively low, such as 1 mol / L, the solidification point is relatively high (about -8.7°C); when the LiCl concentration is 4.5 mol / L to 5.5 mol / L, its solidification point is about -40°C, and it has relatively good ionic conductivity at -60°C. Therefore, the LiCl concentration is preferably 4.5 mol / L.

[0095] Depend on Figure 4 , 5 , 6, and 7, the electrochemical results show that when the DMF addition amount is 20% (DMF2), the CV curve area reaches the maximum (about 1.43 times that of comparative example 1), the GCD curve is an isosceles triangle, and it has good charge and discharge performance at low current density. The electrochemical impedance spectroscopy results show that the electrolyte has a low internal resistance.

[0096] Depend on Figure 8 , 9 It can be seen that when the DMF addition amount is 20% (DMF2) and at -60°C, the device has the largest capacitance (about 244.48μF) and a higher conductivity (about 1.143mS·cm -1 ), and has a good ragone curve.

[0097] Fig.10 The cycle performance test curve of the Pt / Pt symmetrical supercapacitor of Example 2 at -60°C is shown in Figure 2. The results show that after 1000 tests, the capacitance retention rate reaches 80.48% and the coulombic efficiency is about 100%.

[0098] In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. For the scheme disclosed in the embodiment, since it corresponds to the method disclosed in the embodiment, the description is relatively simple, and the relevant parts can be referred to the method part.

[0099] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A supercapacitor low-temperature electrolyte, characterized in that: The components of the low-temperature electrolyte include: LiCl, DMF, and deionized water; the volume fraction of the DMF is 15-50%; and the concentration of the LiCl is 0.05-5.5 mol / L.

2. A supercapacitor low-temperature electrolyte according to claim 1, characterized in that: The volume fraction of the DMF is 20%.

3. A supercapacitor low-temperature electrolyte according to claim 1, characterized in that: The concentration of LiCl is 4.5-5.5 mol / L.

4. A supercapacitor low-temperature electrolyte according to claim 3, characterized in that: The concentration of LiCl is 4.5 mol / L.

5. The method for preparing a low-temperature electrolyte for supercapacitor according to any one of claims 1 to 4, characterized in that: The steps include: (1) adding DMF to deionized water and stirring thoroughly to mix well to obtain a solvent; (2) Add LiCl to the solvent obtained in step (1), and stir thoroughly using a magnetic stirrer to obtain a low-temperature electrolyte.

6. The use of a supercapacitor low-temperature electrolyte according to any one of claims 1 to 4 in a symmetrical supercapacitor, characterized in that: The symmetrical supercapacitor uses metal Pt as electrode.

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