A low-temperature aqueous electrolyte, its preparation method and application

Abstract

This application discloses a low-temperature aqueous electrolyte, its preparation method, and its application, belonging to the technical field of aqueous electrolytes. The low-temperature aqueous electrolyte provided by this application comprises a metal salt, an additive, water, and a co-solvent; the metal salt is selected from one or more of lithium chloride, lithium nitrate, lithium perchlorate, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, sodium chloride, sodium hexafluorophosphate, sodium tetrafluoroborate, sodium nitrate, potassium chloride, potassium nitrate, magnesium chloride, magnesium perchlorate, zinc perchlorate, and zinc chloride; the additive is calcium chloride; and the co-solvent is ethylene glycol. The aqueous electrolyte provided by this application uses ethylene glycol, which has low toxicity, as a co-solvent, achieving excellent low-temperature performance while reducing the lithium salt concentration in the aqueous electrolyte, and also possesses advantages such as being environmentally friendly, relatively inexpensive, and safe and flame-retardant.

Description

Technical Field

[0001] This application belongs to the field of aqueous electrolyte technology, and particularly relates to a low-temperature aqueous electrolyte, its preparation method and application. Background Technology

[0002] Aqueous batteries and capacitors have gained popularity among researchers due to their low cost, intrinsic safety, and environmental friendliness. However, water freezes below zero degrees Celsius, leading to significant performance degradation in aqueous batteries and devices at low temperatures. Therefore, broadening the electrochemical stability window of aqueous electrolytes and lowering their freezing point are crucial for developing high-performance aqueous batteries and capacitors at low temperatures.

[0003] Currently, various low-temperature aqueous electrolytes have been designed and prepared in the literature. For example, Wu Zhongshuai (National Science Review, DOI:10.1093 / nsr / nwac024) developed a low-temperature resistant, safe, and environmentally friendly aqueous electrolyte (20m LiCl). MXene-based supercapacitors constructed using this electrolyte can operate stably for extended periods at -40℃. However, the high cost is due to the large amount of lithium salt used. To overcome the drawbacks of high salt concentration, researchers have begun to try adding additives to reduce the salt concentration while improving low-temperature performance. For instance, Li Xianfeng et al. (Energy & Environmental Science, DOI:10.1039 / d0ee01538e) designed an aqueous electrolyte (composed of water, zinc sulfate, and ethylene glycol). Aqueous zinc-ion capacitors and zinc-ion batteries constructed using this electrolyte exhibit excellent electrochemical performance at -20℃. However, current research in this area is still limited, and there is still significant room for development. Summary of the Invention

[0004] To address the aforementioned technical problems, this application provides a low-temperature aqueous electrolyte, its preparation method, and its application. The low-temperature aqueous electrolyte is inexpensive and has a wide voltage window. It uses ethylene glycol, which has low toxicity, as a co-solvent, and the concentration of lithium salt used is relatively low, making it more environmentally friendly.

[0005] To achieve the above-mentioned objectives, this application provides the following technical solution:

[0006] On the one hand, this application provides a low-temperature aqueous electrolyte, which includes a metal salt, an additive, water, and a co-solvent;

[0007] The metal salt is selected from one or more of lithium chloride, lithium nitrate, lithium perchlorate, lithium hexafluorophosphate, lithium bis(trifluoromethanesulfonyl)imide, sodium chloride, sodium hexafluorophosphate, sodium tetrafluoroborate, sodium nitrate, potassium chloride, potassium nitrate, magnesium chloride, magnesium perchlorate, zinc perchlorate, and zinc chloride.

[0008] The additive is calcium chloride;

[0009] The co-solvent is ethylene glycol.

[0010] Optionally, the low-temperature aqueous electrolyte is composed of a metal salt, additives, water, and a co-solvent.

[0011] Optionally, the molar ratio of the metal salt to the additive is 1:0.125 to 8, wherein the molar amount of the metal salt is calculated as the molar amount of the substance itself, and the molar amount of the additive is calculated as the molar amount of the substance itself.

[0012] Optionally, the molar ratio of the metal salt to the additive is independently selected from any value of 8:1, 6:1, 4:1, 2:1, 1:1, 1:2, 1:4, 1:6, 1:8 or any range between the two.

[0013] Optionally, the molar ratio of the metal salt to the additive is 1:2 to 6, wherein the molar amount of the metal salt is calculated as the molar amount of the substance itself, and the molar amount of the additive is calculated as the molar amount of the substance itself.

[0014] Optionally, the molar ratio of the metal salt to the additive is independently selected from any value of 1:2, 1:3, 1:4, 1:5, 1:6 or any range between two of them.

[0015] Optionally, the volume ratio of water to co-solvent is 0.1 to 9:1.

[0016] Optionally, the volume ratio of water to co-solvent is independently selected from any value of 9:1, 6:1, 4:1, 1:1, 1:3, 1:9 or any range between two of them.

[0017] Optionally, the volume ratio of water to co-solvent is 1 to 9:1.

[0018] Preferably, the volume ratio of water to co-solvent is 2 to 7:1.

[0019] Optionally, the final concentration of the metal ions in the metal salt in the low-temperature aqueous electrolyte is 1 to 5 mol / kg.

[0020] Optionally, the final concentration of the metal ions in the metal salt in the low-temperature aqueous electrolyte is independently selected from any value of 1 mol / kg, 2 mol / kg, 3 mol / kg, 4 mol / kg, 5 mol / kg, or any range between the two.

[0021] Optionally, the electrochemical window of the aqueous electrolyte is 2.5–4.5 V.

[0022] Optionally, the electrochemical window of the aqueous electrolyte is independently selected from any value of 2.5V, 3V, 3.5V, 4V, 4.5V or a range between any two.

[0023] Secondly, this application provides a method for preparing the aforementioned low-temperature aqueous electrolyte, comprising the following steps:

[0024] The metal salt, additives, water, and co-solvent are mixed to obtain the low-temperature aqueous electrolyte.

[0025] Thirdly, this application provides the application of the aforementioned low-temperature aqueous electrolyte in the preparation of aqueous high-voltage energy storage devices.

[0026] Optionally, the water-based high-voltage energy storage device includes a water-based high-voltage battery and / or a water-based high-voltage capacitor.

[0027] Compared with the prior art, this application has the following advantages:

[0028] (1) The aqueous electrolyte provided in this application uses ethylene glycol, which has low toxicity, as a co-solvent, and at the same time reduces the concentration of lithium salt in the aqueous electrolyte. It has the advantages of being green and environmentally friendly, relatively low in price, and safe and flame-retardant.

[0029] (2) The method for preparing aqueous electrolyte provided in this application produces products with high quality, good performance, and wide application range.

[0030] (3) Compared with traditional aqueous electrolytes, the aqueous electrolyte provided in this application has significantly broadened the electrochemical stability window and has excellent low-temperature performance. It is also characterized by low cost and environmental friendliness. Attached Figure Description

[0031] Figure 1 Linear sweep voltammetry (LSV) tests were performed on the electrolytes prepared in Comparative Examples 1-3 and Example 2 of this application, using glassy carbon electrodes as working electrodes.

[0032] Figure 2 Linear sweep voltammetry (LSV) was performed on the electrolytes prepared in Comparative Example 1 and Examples 1-3 of this application, using glassy carbon electrodes as working electrodes.

[0033] Figure 3Cyclic voltammetry tests (at different cutoff voltages) were conducted on the electrolyte prepared in Example 2 of this application in an AC / electrolyte / AC capacitor.

[0034] Figure 4 Cyclic voltammetry tests (at different scan rates) were conducted on the electrolyte prepared in Example 2 of this application in an AC / electrolyte / AC capacitor.

[0035] Figure 5 The electrolyte prepared in Example 2 of this application was used to calculate the surface capacitance of the capacitor at different temperatures by measuring the constant current charge-discharge (GCD) curves at the same current density at different temperatures in an AC / electrolyte / AC capacitor using a formula.

[0036] Figure 6 The electrolyte prepared in Example 2 of this application was subjected to a long-cycle test (-40°C) in an AC / electrolyte / AC capacitor. Detailed Implementation

[0037] The present application is further illustrated below with reference to specific embodiments. The following descriptions are merely a few embodiments of the present application and are not intended to limit the present application in any way. Although the present application discloses preferred embodiments as follows, they are not intended to limit the present application. Any modifications or variations made by those skilled in the art without departing from the scope of the technical solution of the present application using the disclosed technical content are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

[0038] Unless otherwise specified, the raw materials used in the embodiments of this application are all purchased commercially and used directly without any special treatment.

[0039] Unless otherwise specified, the analytical methods in the embodiments all adopt conventional instrument or equipment settings and conventional analytical methods.

[0040] The following examples and comparative examples were analyzed using a Chenhua 760E electrochemical workstation for cyclic voltammetry and constant current charge-discharge analysis.

[0041] Example 1

[0042] Add 0.038 mol of anhydrous calcium chloride and 0.01 mol of lithium chloride to a sample vial containing 10 mL of a mixed solution of ethylene glycol and water (volume ratio 1:9), stir well, and obtain the electrolyte.

[0043] Example 2

[0044] Add 0.038 mol of anhydrous calcium chloride and 0.01 mol of lithium chloride to a sample vial containing 10 mL of a mixed solution of ethylene glycol and water (volume ratio 3:7), stir well, and obtain the electrolyte.

[0045] Example 3

[0046] Add 0.038 mol of anhydrous calcium chloride and 0.01 mol of lithium chloride to a sample vial containing 10 mL of a mixed solution of ethylene glycol and water (volume ratio 1:1), stir well, and obtain the electrolyte.

[0047] Example 4

[0048] Add 0.038 mol of anhydrous calcium chloride and 0.01 mol of lithium nitrate to a sample vial containing 10 mL of a mixed solution of ethylene glycol and water (volume ratio 3:7), stir well, and obtain the electrolyte.

[0049] Example 5

[0050] Add 0.038 mol of anhydrous calcium chloride and 0.01 mol of zinc chloride to a sample vial containing 10 mL of a mixed solution of ethylene glycol and water (volume ratio 1:1), stir well, and obtain the electrolyte.

[0051] Comparative Example 1

[0052] Add 0.038 mol of anhydrous calcium chloride and 0.01 mol of lithium chloride to a sample bottle containing 10 mL of water, stir well, and obtain the electrolyte.

[0053] Comparative Example 2

[0054] Add 0.01 mol of lithium chloride to a sample bottle containing 10 mL of water, stir well, and obtain the electrolyte.

[0055] Comparative Example 3

[0056] Add 0.01 mol of lithium chloride to a sample vial containing 10 mL of a mixed solution of ethylene glycol and water (volume ratio 3:7), stir well, and obtain the electrolyte.

[0057] Experimental Example 1

[0058] Electrochemical tests were performed on the electrolytes prepared in Comparative Examples 1-3 and Examples 1-5. The test methods were cyclic voltammetry, constant current charge-discharge test, and electrochemical window test.

[0059] Typical test results are as follows Figure 1 As shown, the electrolytes prepared in Examples 1-3 and Example 2 are compared. Figure 1 It can be seen that the addition of calcium chloride and ethylene glycol significantly broadened the electrochemical window.

[0060] Typical test results are as follows Figure 2 As shown, the electrolytes prepared in Examples 1 and 1-3 are corresponding to those in Examples 1-3. Figure 2 It can be seen that the voltage window of the CaCl2-EG3 aqueous electrolyte is 3.5V.

[0061] Typical test results are as follows Figure 3 As shown, this corresponds to the electrolyte prepared in Example 2. (The text abruptly ends here.) Figure 3 It can be seen that the assembled capacitor does not exhibit obvious polarization when operating at 0–1.6V.

[0062] Typical test results are as follows Figure 4 As shown, this corresponds to the electrolyte prepared in Example 2. (The text abruptly ends here.) Figure 4 It can be seen that the assembled capacitors exhibit ideal double-layer effect at 0–1.6V and scan rates of 2–20mV / s.

[0063] Typical test results are as follows Figure 5 and 6 As shown, the electrolyte prepared in Example 2 was subjected to charge-discharge tests at different temperatures in an AC / electrolyte / AC capacitor system, and a long-cycle test at -40°C. Figure 5 and Figure 6 It is known that the electrolyte of this application has a higher capacity retention rate at low temperatures compared to at room temperature, and can operate stably and normally at low temperatures for a long time.

[0064] The above description is merely a few embodiments of this application and is not intended to limit this application in any way. Although this application discloses preferred embodiments as described above, it is not intended to limit this application. Any changes or modifications made by those skilled in the art without departing from the scope of the technical solution of this application using the disclosed technical content are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A low-temperature aqueous electrolyte, characterized in that, The low-temperature aqueous electrolyte is composed of metal salts, additives, water, and a co-solvent. The metal salt is lithium chloride; The additive is calcium chloride; The co-solvent is ethylene glycol; The molar ratio of the metal salt to the additive is 1:2 to 6, wherein the molar amount of the metal salt is calculated as the molar amount of the substance itself, and the molar amount of the additive is calculated as the molar amount of the substance itself. The volume ratio of water to co-solvent is 1~9:1; The final concentration of the metal ions in the metal salt in the low-temperature aqueous electrolyte is 1~5 mol / kg.

2. The low-temperature aqueous electrolyte according to claim 1, characterized in that, The electrochemical window of the aqueous electrolyte is 2.5~4.5V.

3. A method for preparing a low-temperature aqueous electrolyte according to any one of claims 1 to 2, characterized in that, Includes the following steps: The metal salt, additives, water, and co-solvent are mixed to obtain the low-temperature aqueous electrolyte.

4. The application of the low-temperature aqueous electrolyte according to any one of claims 1 to 2 in the preparation of aqueous high-voltage energy storage devices.

5. The application according to claim 4, characterized in that, The water-based high-voltage energy storage device includes a water-based high-voltage battery and / or a water-based high-voltage capacitor.

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