Aqueous electrolyte and its application in alkaline zinc-based flow battery

Abstract

The present invention discloses an aqueous electrolyte and its application in an alkaline zinc-based flow battery, belonging to the field of electrochemical energy storage technology. A mixed electrolyte is formed by adding an appropriate amount of an amine organic solvent to an aqueous solution of a zinc salt, which effectively alleviates electrolyte migration without affecting the electrolyte ion conductivity, and optimizes the solvation state of zinc ions in the electrolyte, thereby improving the zinc deposition morphology and improving the cycle stability. The mixed electrolyte can also be applied to other zinc-based flow batteries and has broad application prospects.

Description

Technical Field

[0001] The present invention belongs to the technical field of electrochemical energy storage, and in particular relates to an aqueous electrolyte and an application thereof in an alkaline zinc-based liquid flow battery. Background Art

[0002] With the development of society, human demand for energy is gradually increasing, but non-renewable energy such as fossil energy is gradually depleting, while renewable energy such as wind energy, solar energy, tidal energy, etc., have received widespread attention due to their renewability and environmental friendliness. However, the discontinuity, instability, and unpredictability of renewable energy generation have seriously hindered its widespread application, and energy storage technology is an important support for achieving safe and stable power supply of renewable energy. There are physical and chemical energy storage in energy storage technology, among which chemical energy storage is more widely used, and electrochemical energy storage is the most common energy storage device in chemical energy storage. In electrochemical energy storage, liquid flow battery energy storage technology has broad application prospects in the field of large-scale energy storage due to its independent energy density and power density, flexible design, safety and reliability, environmental friendliness, and small geographical restrictions. Zinc-based liquid flow batteries have received widespread attention in the field of energy storage due to their abundant resources, low price, and high kinetics. Alkaline zinc-based liquid flow batteries have good development prospects in the field of energy storage due to their high open circuit voltage, high power density, and low electrolyte cost.

[0003] At present, the zinc salt or / and zinc oxide on the negative electrode side of the alkaline zinc-based flow battery dissolves in a strong base to generate Zn(OH)4 2- Then, an electrochemical reaction of deposition and dissolution occurs on the electrode, and the positive electrode is Fe(CN)6 3- / Fe(CN)6 4- The electrolyte has the advantages of low cost, low viscosity, high ion conductivity, etc. The open circuit voltage of the battery can reach 1.77V, it can operate at room temperature and pressure, has good safety, and the system is environmentally friendly. However, the migration of the electrolyte in the zinc-based flow battery and the growth and shedding of the negative zinc dendrites reduce the cycle stability and restrict its further application. Summary of the invention

[0004] In order to solve the above technical problems, the present invention aims to provide an aqueous electrolyte and its application in the zinc negative electrode of alkaline zinc-based flow battery. By adding an appropriate amount of amine organic solvent to the aqueous solution of zinc salt to form a mixed electrolyte, the electrolyte migration is effectively alleviated without affecting the electrolyte ion conductivity, and the solvation state of zinc ions in the electrolyte is optimized, thereby improving the zinc deposition morphology and improving the cycle stability. On this basis, the mixed electrolyte can also be extended to other zinc-based flow batteries.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A water-based electrolyte, wherein the solute of the electrolyte is zinc ions, and the additive is an amine organic solvent, wherein the amine organic solvent is selected from any one of hydroxyethylethylenediamine, N-isobutylethylenediamine, triethanolamine, and N,N,N'N'-tetrahydroxyethylethylenediamine, or a mixture of two or more thereof; preferably, it is any one of N,N,N'N'-tetrahydroxyethylethylenediamine and triethanolamine, or a mixture of two or more thereof.

[0007] Furthermore, the concentration of the additive in the electrolyte is 0.005-0.1 mol L -1 , preferably 0.005-0.015 mol L -1 .

[0008] Furthermore, the concentration of zinc ions in the electrolyte is 0.1-2.0 mol L -1 , preferably 0.3-1.0 molL -1 .

[0009] Furthermore, the source of the zinc ion includes zinc oxide, zinc sulfate, zinc chloride, zinc nitrate, zinc acetate, zinc phosphate, zinc trifluoromethanesulfonate, zinc bistrifluoromethanesulfonyl imide, zinc tetrafluoroborate, zinc hexafluorophosphate, zinc bisoxalate borate, preferably zinc oxide.

[0010] Another aspect of the present invention provides use of the aqueous electrolyte and / or additive in an alkaline zinc-based flow battery or an alkaline zinc-based secondary battery.

[0011] Furthermore, the aqueous electrolyte and / or additive is applied to the negative electrode electrolyte of the alkaline zinc-based flow battery, which can reduce the migration of the electrolyte of the zinc negative electrode of the alkaline zinc-based flow battery.

[0012] Furthermore, the alkaline zinc-based liquid flow battery is mainly composed of a positive electrode, an ion conductive membrane and a zinc negative electrode.

[0013] Furthermore, the electrode materials of the positive electrode and the negative electrode are selected from graphite felt or carbon felt, preferably carbon felt.

[0014] Furthermore, the ion-conducting membrane is selected from an ion exchange membrane and a porous membrane, preferably an ion exchange membrane.

[0015] Furthermore, the alkaline zinc-based secondary battery includes zinc-iron battery, zinc-nickel battery, zinc-manganese battery, and zinc-silver battery.

[0016] The beneficial effects of the present invention compared with the prior art are as follows:

[0017] 1. The aqueous electrolyte provided by the present invention has a high ionic conductivity, maintains the excellent performance of the battery and can better alleviate the migration of the electrolyte and the growth of zinc dendrites, effectively improving the cycle stability of the battery.

[0018] 2. As the cycle progresses, the electrolyte migration phenomenon becomes more serious, the negative electrode electrolyte decreases, resulting in insufficient active substances and increased battery polarization. When the cycle time is greater than 90 hours, the battery is basically unable to operate. In comparison, adding a small amount of N,N,N'N'-tetrahydroxyethylethylenediamine or triethanolamine additives to the commonly used negative electrode electrolyte can significantly alleviate the electrolyte migration and level the zinc negative electrode deposition morphology, maintaining the excellent performance of the battery and improving the battery cycle stability.

[0019] 3. The aqueous electrolyte provided by the present invention can form a new hydrogen bond network with water due to the introduction of amine molecules, break the original hydrogen bond network between water, and alleviate the migration of the electrolyte.

[0020] 4. Due to the introduction of amine molecules in the aqueous electrolyte provided by the present invention, the solvation structure of zinc ions is optimized, and the adsorption effect on the carbon felt surface is enhanced, so that the zinc ions are deposited on the carbon felt more densely and evenly, reducing the formation of zinc dendrites.

[0021] 5. The amine organic matter such as N,N,N'N'-tetrahydroxyethylethylenediamine added to the aqueous electrolyte provided by the present invention is low in cost and environmentally friendly and safe. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention, the drawings related to the embodiments are briefly introduced below.

[0023] Figure 1 : CV of the mixed electrolyte of Comparative Example 1 and Examples 1-3.

[0024] Figure 2 : Change in electrolyte volume of the mixed electrolyte of Comparative Example 2 and Examples 4-6.

[0025] Figure 3 : Charge and discharge curves of the mixed electrolyte of Comparative Example 2 and Example 4.

[0026] Figure 4 : Infrared spectra of mixed electrolytes of Comparative Example 4 and Examples 10-12.

[0027] Figure 5 : Chronoamperometry of the mixed electrolyte of Comparative Example 3 and Examples 7-9.

[0028] Figure 6: The zinc deposition morphology of the mixed electrolyte of Comparative Example 2 and Examples 4-6, wherein a and a' are Comparative Example 2, b and b' are Example 4, c and c' are Example 5, and d and d' are Example 6.

[0029] Figure 7 : Initial battery performance of the mixed electrolyte of Comparative Example 2 and Examples 4-6.

[0030] Figure 8 : Cycling performance of mixed electrolyte of Comparative Example 2 and Example 4. DETAILED DESCRIPTION

[0031] The present invention is described in detail below with reference to the embodiments, but the embodiments of the present invention are not limited thereto. Obviously, the embodiments described below are only partial embodiments of the present invention. For those skilled in the art, other similar embodiments obtained without creative labor all fall within the protection scope of the present invention.

[0032] Comparative Example 1

[0033] Prepare 0.1 molL -1 Zn(OH)4 2- +3.2molL -1 OH - The electrolyte adopts a three-electrode system, in which the working electrode and the counter electrode are both graphite, the reference electrode is Hg / HgO, the test range is -0.9V–-1.7V, and the electrolytic cell is an H-type three-mouth cell.

[0034] Comparative Example 2

[0035] Prepare 0.4 molL -1 Zn(OH)4 2- +3.8molL -1 OH - Negative electrolyte, 0.8 molL -1 Fe(CN)6 4- +3molL - 1 OH - The positive electrode electrolyte, the positive and negative electrodes are carbon felt, the positive and negative electrolyte volumes are 80mL each; the battery adopts constant current charge and discharge mode, at 80mA cm -2 The current density was 80 mA cm-1 and the charge was carried out for about 20 min. Then the voltage was cut off and the charge was carried out for about 20 min. -2 The battery was discharged to 0.1 V under the condition of current density of . When the battery was charged to the end of the fourth cycle, the battery was disassembled, the carbon felt on the negative electrode side was taken out, and it was rinsed with water several times to remove the salt on the surface of the carbon felt, and then it was freeze-dried in a vacuum freeze dryer and sealed for storage.

[0036] Comparative Example 3

[0037] Prepare 0.4 molL -1 Zn(OH)4 2- +3.8molL -1 OH - The positive and negative electrolytes are carbon felt, the volume of the positive and negative electrolytes is 80 mL each, and a zinc symmetrical battery is assembled; the battery adopts a constant voltage charge and discharge mode, and is charged for about 400s at a potential of -200mV.

[0038] Comparative Example 4

[0039] Prepare 0.1 molL -1 Zn(OH)4 2- +1.2molL -1 OH - Electrolyte, KBr pellet method was used to measure Fourier transform infrared, the test range was 400–4000 cm -1 .

[0040] Example 1

[0041] Prepare 0.1 molL -1 Zn(OH)4 2- +0.01molL -1 THEED+3.2molL -1 OH - The electrolyte adopts a three-electrode system, in which the working electrode and the counter electrode are both graphite, the reference electrode is Hg / HgO, the test range is -0.9V–-1.7V, and the electrolytic cell is an H-type three-mouth cell.

[0042] Example 2

[0043] Prepare 0.1 molL -1 Zn(OH)4 2- +0.05molL -1 THEED+3.2molL -1 OH - The electrolyte adopts a three-electrode system, in which the working electrode and the counter electrode are both graphite, the reference electrode is Hg / HgO, the test range is -0.9V–-1.7V, and the electrolytic cell is an H-type three-mouth cell.

[0044] Example 3

[0045] Prepare 0.1 molL -1 Zn(OH)4 2- +0.1molL -1 THEED+3.2molL -1 OH -The electrolyte adopts a three-electrode system, in which the working electrode and the counter electrode are both graphite, the reference electrode is Hg / HgO, the test range is -0.9V–-1.7V, and the electrolytic cell is an H-type three-mouth cell.

[0046] Example 4

[0047] Prepare 0.4 molL -1 Zn(OH)4 2- +0.01molL -1 THEED+3.8molL -1 OH - Negative electrolyte, 0.8 molL -1 Fe(CN)6 4- +3molL -1 OH - The positive electrode electrolyte, the positive and negative electrodes are carbon felt, the positive and negative electrolyte volumes are 80mL each; the battery adopts constant current charge and discharge mode, at 80mA cm -2 The current density was charged for about 20 min, and then the voltage was cut off at 80 mA cm -2 The battery was discharged to 0.1 V under the condition of current density of . When the battery was charged to the end of the fourth cycle, the battery was disassembled, the carbon felt on the negative electrode side was taken out, and it was rinsed with water several times to remove the salt on the surface of the carbon felt, and then it was freeze-dried in a vacuum freeze dryer and sealed for storage.

[0048] Example 5

[0049] Prepare 0.4 molL -1 Zn(OH)4 2- +0.05molL -1 THEED+3.8molL -1 OH - Negative electrolyte, 0.8 molL -1 Fe(CN)6 4- +3molL -1 OH - The positive electrode electrolyte, the positive and negative electrodes are carbon felt, the positive and negative electrolyte volumes are 80mL each; the battery adopts constant current charge and discharge mode, at 80mA cm -2 The current density was charged for about 20 min, and then the voltage was cut off at 80 mA cm -2 The battery was discharged to 0.1 V under the condition of current density of . When the battery was charged to the end of the fourth cycle, the battery was disassembled, the carbon felt on the negative electrode side was taken out, and it was rinsed with water several times to remove the salt on the surface of the carbon felt, and then it was freeze-dried in a vacuum freeze dryer and sealed for storage.

[0050] Example 6

[0051] Prepare 0.4 molL-1 Zn(OH)4 2- +0.1molL -1 THEED+3.8molL -1 OH - Negative electrolyte, 0.8 molL -1 Fe(CN)6 4- +3molL -1 OH - The positive electrode electrolyte, the positive and negative electrodes are carbon felt, the positive and negative electrolyte volumes are 80mL each; the battery adopts constant current charge and discharge mode, at 80mA cm -2 The current density was charged for about 20 min, and then the voltage was cut off at 80 mA cm -2 The battery was discharged to 0.1 V under the condition of current density of . When the battery was charged to the end of the fourth cycle, the battery was disassembled, the carbon felt on the negative electrode side was taken out, and it was rinsed with water several times to remove the salt on the surface of the carbon felt, and then it was freeze-dried in a vacuum freeze dryer and sealed for storage.

[0052] Example 7

[0053] Prepare 0.4 molL -1 Zn(OH)4 2- +0.01molL -1 THEED+3.8molL -1 OH - The positive and negative electrolytes are carbon felt, the volume of the positive and negative electrolytes is 80 mL each, and a zinc symmetrical battery is assembled; the battery adopts a constant voltage charge and discharge mode, and is charged for about 400s at a potential of -200mV.

[0054] Example 8

[0055] Prepare 0.4 molL -1 Zn(OH)4 2- +0.05molL -1 THEED+3.8molL -1 OH - The positive and negative electrolytes are carbon felt, the volume of the positive and negative electrolytes is 80 mL each, and a zinc symmetrical battery is assembled; the battery adopts a constant voltage charge and discharge mode, and is charged for about 400s at a potential of -200mV.

[0056] Example 9

[0057] Prepare 0.4 molL -1 Zn(OH)4 2- +0.1molL -1 THEED+3.8molL -1 OH -The positive and negative electrolytes are carbon felt, the volume of the positive and negative electrolytes is 80 mL each, and a zinc symmetrical battery is assembled; the battery adopts a constant voltage charge and discharge mode, and is charged for about 400s at a potential of -200mV.

[0058] Example 10

[0059] Prepare 0.1 molL -1 Zn(OH)4 2- +0.01molL -1 THEED+1.2molL -1 OH - Electrolyte, KBr pellet method was used to measure Fourier transform infrared, the test range was 400–4000cm -1 .

[0060] Embodiment 11

[0061] Prepare 0.1 molL -1 Zn(OH)4 2- +0.05molL -1 THEED+1.2molL -1 OH - Electrolyte, KBr pellet method was used to measure Fourier transform infrared, the test range was 400–4000cm -1 .

[0062] Example 12

[0063] Prepare 0.1 molL -1 Zn(OH)4 2- +0.1molL -1 THEED+1.2molL -1 OH - Electrolyte, KBr pellet method was used to measure Fourier transform infrared, the test range was 400–4000cm -1 .

[0064] Figure 1 This is the CV of the mixed electrolyte of Comparative Example 1 and Examples 1-3, with a scan rate of 15 mV / s. When a small amount of the additive THEED is added, there is basically no effect on the peak current of the active material, indicating that adding a small amount of THEED can still maintain the excellent performance of the battery.

[0065] Figure 2 The volume change of the electrolyte of the mixed electrolyte of Example 2 and Examples 4-6 is shown in Figure 2. From the volume change of the electrolyte, it can be seen that at 80 mA cm -2At the current density of , the negative electrode electrolyte of Comparative Example 2 decreased by 30mL after 50 cycles, indicating that the electrolyte migrated by 30mL after 50 cycles, while the number of cycles required for Examples 4-6 to migrate substantially the same electrolyte volume was greater than that of Comparative Example 2, indicating that the addition of the additive THEED can effectively alleviate the migration of the electrolyte, wherein the addition of 0.01molL - 1 THEED has the most obvious effect in alleviating migration.

[0066] Figure 3 The charge and discharge curves of the mixed electrolyte of Comparative Example 2 and Example 4. Figure 3 ) can be seen that at 80mA cm -2 Under the current density of , the polarization of the charge and discharge curve of the battery in Comparative Example 2 gradually increases. When the cycle time is greater than 70 hours, the charging voltage gradually increases, up to about 2.3V, indicating that the positive and negative active materials are insufficient due to the migration of the electrolyte and the formation and shedding of zinc dendrites, which increases the polarization of the battery and reduces the performance. However, after running for about 120 hours, the charging voltage of the battery in Example 4 remains stable without obvious polarization, indicating that adding a small amount of THEED can reduce the polarization of the battery and improve the cycle stability of the battery.

[0067] Figure 4 The infrared spectrum of the mixed electrolyte of comparative example 4 and examples 10-12. From the Fourier transform infrared analysis, it can be seen that after the addition of the additive THEED, the vibration peak of water is red-shifted. After the addition of THEED, the electron-withdrawing groups on THEED will form new hydrogen bonds with water, thereby breaking the original hydrogen bond network between water, reducing the amount of water clusters, and increasing the electron cloud density of protons, so the vibration peak of water is red-shifted. By forming a new hydrogen bond network and reducing the amount of water clusters, the migration of the electrolyte can be effectively alleviated.

[0068] Figure 5 The chronoamperometry of the mixed electrolyte of comparative example 3 and examples 7-9 was used to study the primary nucleation of zinc. Figure 5 It can be seen that with the addition of the additive THEED, the initial stage of zinc nucleation can enter the three-dimensional diffusion mode faster, thereby inducing the generation of zinc at the three-dimensional level and reducing the accumulation of zinc nuclei on the surface. Therefore, the zinc deposition morphology is effectively improved, thereby inhibiting the growth of zinc dendrites and achieving uniform and dense zinc deposition.

[0069] Figure 6The zinc deposition morphology of the mixed electrolyte of comparative example 2 and examples 4-6. The zinc deposition morphology at the end of the fourth cycle charge shows that the zinc deposition morphology of comparative example 2 is a typical moss-like morphology, which is conducive to the formation of zinc dendrites. After the addition of THEED, zinc is induced to grow in a layered direction, thereby inhibiting the formation of zinc dendrites. Moreover, as the concentration of the additive THEED increases, the zinc deposition morphology becomes more uniform and dense.

[0070] Figure 7 The initial performance of the mixed electrolyte of Comparative Example 2 and Example 4. Figure 7 It can be seen that adding a small amount of THEED will not reduce the performance of the battery. As the concentration increases, the voltage efficiency decreases slightly. This may be because when more THEED is added, the viscosity of the electrolyte increases, the resistance of the electrolyte increases, and thus the voltage efficiency decreases.

[0071] Figure 8 The cycle performance of the mixed electrolyte of Comparative Example 2 and Example 4 is shown. Figure 8 It can be seen that adding a small amount of THEED can effectively improve the stability of the battery, and can stably run for 200 cycles, and the capacity is basically not decayed. However, the battery capacity of Comparative Example 2 gradually decayed after running for 140 cycles. This shows that adding a small amount of THEED can effectively improve the long-cycle performance of the battery.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An aqueous electrolyte is used in an alkaline zinc-based flow battery or an alkaline zinc-based secondary battery, characterized in that: The solute of the aqueous electrolyte is zinc ion, and the additive is an amine organic solvent, wherein the amine organic solvent is selected from any one of hydroxyethylethylenediamine, N-isobutylethylenediamine, triethanolamine, and N,N,N'N'-tetrahydroxyethylethylenediamine or a mixture of two or more thereof.

2. The use according to claim 1, characterized in that: The amine organic solvent is any one of N,N,N'N'-tetrahydroxyethylethylenediamine and triethanolamine or a mixture of the two.

3. The use according to claim 1, characterized in that: The concentration of the additive in the aqueous electrolyte is 0.005-0.1 mol L -1 .

4. The use according to claim 3, characterized in that: The concentration of the additive in the aqueous electrolyte is 0.005-0.015 mol L -1 .

5. The use according to claim 1, characterized in that: The concentration of zinc ions in the aqueous electrolyte is 0.1-2.0 mol L -1 .

6. The use according to claim 5, characterized in that: The concentration of zinc ions in the aqueous electrolyte is 0.3-1.0 mol L -1 .

7. The use according to any one of claims 1 to 6, characterized in that: The sources of the zinc ions include zinc oxide, zinc sulfate, zinc chloride, zinc nitrate, zinc acetate, zinc phosphate, zinc trifluoromethanesulfonate, zinc bistrifluoromethanesulfonyl imide, zinc tetrafluoroborate, zinc hexafluorophosphate, and zinc bisoxalate borate.

8. The use according to claim 7, characterized in that: The source of the zinc ions is zinc oxide.

9. The use according to claim 1, characterized in that: The aqueous electrolyte is applied to the negative electrode electrolyte of the alkaline zinc-based liquid flow battery, and can reduce the migration of the electrolyte of the zinc negative electrode of the alkaline zinc-based liquid flow battery.

10. The use according to claim 1, characterized in that: The alkaline zinc-based liquid flow battery is mainly composed of a positive electrode, an ion conductive membrane and a zinc negative electrode.

11. The use according to claim 10, characterized in that: The electrode materials of the positive electrode and the negative electrode are selected from graphite felt or carbon felt.

12. The use according to claim 11, characterized in that: The electrode materials of the positive and negative electrodes are carbon felt.

13. The use according to claim 10, characterized in that: The ion conducting membrane is selected from an ion exchange membrane and a porous membrane.

14. The use according to claim 13, characterized in that The ion conducting membrane is an ion exchange membrane.

15. The use according to claim 1, characterized in that: The alkaline zinc-based secondary batteries include zinc-iron batteries, zinc-nickel batteries, zinc-manganese batteries, and zinc-silver batteries.

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