Patent Application
20240021887
This application claims priority to Korean Patent Application No. 10-2022-0086525 filed on Jul. 13, 2022 in the Korean Intellectual Property Office (KIPO), the entire contents of which are hereby incorporated by reference.
Example embodiments of the present inventive concept relates to an electrolyte for an aqueous battery and an aqueous battery including the same, and more particularly, to an electrolyte for an aqueous zinc-bromine battery, including a bromine complexing agent and a metal ion additive, and an aqueous zinc-bromine non-flow battery, including the same.
As an alternative to environmental problems caused by the use of fossil fuel, research using renewable energies such as solar light and wind power is being conducted, but it is difficult to secure the stability of power supply because natural energy with high variability is used. Accordingly, a large-scale energy storage system (ESS) that can address unstable power supply and increase the efficiency of power consumption is attracting attention.
Currently, a lithium ion battery-based ESS with high energy efficiency is mainly used, but there is a risk of ignition because it uses a flammable organic electrolyte and a lithium-based material. Accordingly, a non-flammable aqueous battery, which uses water as an electrolyte that can block overheating and lower the risk of fire, is attracting attention as a next-generation ESS.
As a representative aqueous battery, there is a zinc-bromine redox battery. The zinc-bromine redox battery is inexpensive and has a high driving voltage and a high energy density. However, a crossover phenomenon in which the charged positive electrode active materials, Br2 and Brn−, diffuse to a negative electrode to react with Zn to generate a self-discharge reaction occurs. In addition, during charging, zinc ions are locally electrodeposited on a specific area on the surface of a zinc negative electrode and thus a dendrite is formed, decreasing the lifetime and efficiency of the battery. Accordingly, there is a need for a technology that can uniformly electrodeposit/release a metal to prevent a crossover phenomenon by fixing a positive electrode active material to an electrode and the dendrite formation of the zinc negative electrode.
Example embodiments of the present inventive concept provide an electrolyte for a zinc-bromine aqueous battery, which includes zinc bromide (ZnBr2) salt, a bromine complexing agent and a metal ion additive.
Example embodiments of the present inventive concept also provide an aqueous zinc-bromine non-flow battery, which includes the electrolyte.
In some example embodiments, an electrolyte for a zinc-bromine aqueous battery, which includes ZnBr2, a bromine complexing agent and a metal ion additive, is provided. A salt containing manganese, which is a metal ion that has a standard reduction potential of less than −0.76 V and a standard oxidation potential of more than 1.08 V, may be used as the metal ion additive.
In other example embodiments, an aqueous zinc-bromine non-flow battery in which the electrolyte described above is charged in a space between a positive electrode formed by disposing carbon graphite felt on a positive electrode conductive plate and a negative electrode formed by disposing a zinc metal layer on a negative electrode conductive plate is provided.
Example embodiments of the present inventive concept will become more apparent by describing in detail example embodiments of the present inventive concept with reference to the accompanying drawings, in which:
While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.
Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
Hereinafter, example embodiments of the present inventive concept will be described in further detail with reference to the accompanying drawings.
The bromine complexing agent is one or more selected from the group consisting of 1-ethylpyridinium bromide ([C2Py]Br,1-EpBr), 1-methylpyrrolidin-1-ium hydrobromide ([HMP]Br), 1-ethyl-1-methylpyrrolidin-1-iumbromide ([C2MP]Br)(=[MEP]Br), 1-n-butyl-1-methylpyrrolidin-1-iumbromide ([C4MP]Br), 1-n-hexyl-1-methylpyrrolidin-1-iumbromide ([C6MP]Br), 1-ethyl-1-methylmorpholin-1-iumbromide ([C2MM]Br)(=[MEM]Br), 1-n-butyl-1-methylmorpholin-1-iumbromide ([C4MM]Br), pyridin-1-ium hydrobromide ([HPy]Br), 1-n-butylpyridin-1-iumbromide ([C4Py]Br), 1-n-butylpyridin-1-iumchloride ([C4Py]Cl), 1-n-hexylpyridin-1-iumbromide ([C6Py]Br), 1-n-hexylpyridin-1-iumchloride ([C6Py]Cl), 4-methylpyridine hydrobromide ([H4MPy]Br), 1-ethyl-4-methylpyridine hydrobromide ([C24MPy]Br), 1-n-butyl-4-methylpyridine hydrobromide ([C44MPy]Br), 1-n-hexyl-4-methylpyridine hydrobromide ([C23MPy]Br), 3-methylpyridine hydrobromide ([H3MPy]Br), 1-ethyl-3-methylpyridinebromide ([C23MPy]Br), 1-n-butyl-3-methyl-pyridinebromide ([C43MPy]Br), 1-n-hexyl-3-methyl-pyridinebromide ([C63MPy]Br), 3-methylimidazol-1-ium hydrobromide ([HMIm]Br), 1-ethyl-3-methylimidazol-1-iumbromide ([C2MIm]Br), 1-ethyl-3-methylimidazol-1-iumchloride ([C2MIm]Cl), 1-n-propyl-3-methylimidazol-1-iumbromide ([C3MIm]Br), 1-n-butyl-3-methyl-imidazol-1-iumbromide ([C4MIm]Br), 1-n-butyl-3-methyl-imidazol-1-iumchloride ([C4MIm]Cl), 1-n-hexyl-3-methylimidazol-1-iumbromide ([C6MIm]Br), 1-n-hexyl-3-methylimidazol-1-iumchloride ([C6MIm]Cl), 1-methylpiperidin hydrobromide ([HMPip]Br), 1-ethyl-1-methylpiperidinbromide ([C2MPip]Br), 1-n-butyl-1-methylpiperidinbromide ([C4MPip]Br), 1-n-hexyl-1-methylpiperidinbromide ([C6MPip]Br), 1,1,1-trimethyl-1-n-tetradecylammoniumbromide ([MTA]Br), 1,1,1-trimethyl-1-n-hexadecylammoniumbromide ([CTA]Br), tetraethylammoniumbromide ([TEA]Br), tetra-n-butylammoniumbromide ([TBA]Br), tetra-n-octylammoniumbromide ([TOA]Br), tetra-n-octylammoniumchloride ([TOA]Cl), (polysorbate)n-1R1-2R2-3R3 imidazolium bromide, and (polysorbate)n-1R1-3R3 imidazolium bromide, in which each of R1, R2 and R3 independently has a functional group with 1 to 4 carbon atoms. As the bromine complexing agent, 1-EpBr is preferably used. As the 1-EpBr forms a complex with bromine to allow bromine to remain in the carbon graphite felt 40, a crossover phenomenon in which bromine in an electrolyte moves to a negative electrode is inhibited without a membrane. Since the crossover phenomenon is inhibited, dendrite formation caused by the reaction of bromine and zinc and self-discharge may be prevented.
The bromine complexing agent may have a molarity of 0.1 to 1.5 M, preferably 0.1 to 1.0 M. The molarity of the bromine complexing agent is more preferably 0.1 to 0.6 M, and even more preferably 0.4 to 0.6 M. When the molarity is less than 0.1 M, bromine may not be properly captured, and when the molarity is more than 1.5 M, as the concentration increases, the ionic conductivity in the electrolyte decreases, and thus the bromine concentration in the electrolyte becomes excessively low. Accordingly, battery performance may not be good.
The metal ion additive may induce an electrostatic shielding phenomenon on the surface of a zinc electrode.
The metal ion additive preferably includes metal ions having a standard reduction potential of less than −0.76 V and a standard oxidation potential of more than 1.08 V.
Br2+2e−↔2Br−
Zn2++2e−↔Zn [Formula 1]
The standard oxidation potential of bromine in Formula 1 is 1.08 V, and the standard reduction potential of zinc in Formula 1 is −0.76 V. Accordingly, the metal ions of the metal ion additive have to be materials that do not cause redox reactions at −0.76 V to 1.08 V to prevent a battery from reacting during battery operation. Metal ions satisfying the condition outside the range of −0.76 V to 1.08 V are lithium, sodium, potassium, and manganese. Although chromium is a metal ion having the same cycle as potassium and manganese, it is not suitable for use as a metal ion additive because it is reduced from Cr3+ to Cr2+ at approximately −0.407 V within the above range. When chromium is used as a metal ion additive, compared to the case in which only ZnBr2 is used as an electrolyte, or 1-EpBr is additionally included, the voltage rapidly decreased after approximately 45 hours of discharging. Accordingly, it is difficult to use chromium as a metal ion additive because self-discharge is induced by a reaction of chromium in a battery over time and thus the voltage drops greatly.
The metal ion additive preferably includes Mn, and is one selected from the group consisting of MnSO4, MnCl2, Mn(NO3)2, Mn3(PO4)2, and Mn(CH3CO2)2. More preferably, as the metal ion additive, MnSO4 is used. The standard reduction potential of Mn2+ is approximately −1.18 V, which is not included in the above range, and the standard oxidation potential of Mn2+ is approximately 1.4 V, which is not included in the above range. When a metal ion additive including manganese is used, compared to metal ion additives including lithium sodium and potassium, fewer dendrites are formed, and excellent coulombic efficiency is obtained up to 700 cycles.
The metal ion additive may have a molarity of 0.05 M to 0.1 M, preferably 0.05 M. When the molarity of the metal ion additive is less than 0.05 M or more than 0.1 M, the performance of the battery may not be excellent because the coulombic efficiency drops below 90%.
The molarity of ZnBr2 may be 2.0 M to 3.0 M, and preferably 2.25 M to 2.8 M. When the molarity of ZnBr2 is less than 2.0 M, it is disadvantageous in terms of energy density because the amount of an active material in the electrolyte is reduced. In addition, since the salt concentration in the electrolyte is lowered, ionic conductivity is lowered. When the molarity of ZnBr2 exceeds 3.0 M, the pH of the electrolyte decreases, so a hydrogen evolution reaction (HER) becomes active. Accordingly, the pressure in a cell increases due to hydrogen generated in the cell, causing the problem of an insufficient electrolyte.
An electrolyte was prepared by inputting 2.25 M ZnBr2, 0.1 M 1-EpBr and 0.5 M MnSO4 to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.25 M ZnBr2 and 0.1 M 1-EpBr to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.25 M ZnBr2, 0.1 M 1-EpBr, and 0.05 M MnSO4 to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.25 M ZnBr2 and 0.05 M MnSO4 to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.25 M ZnBr2, 0.1 M 1-EpBr, and 0.1 M MnSO4 to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.8 M ZnBr2 and 0.1 M 1-EpBr to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.8 M ZnBr2 and 0.2 M 1-EpBr to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.8 M ZnBr2 and 0.3 M 1-EpBr to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.8 M ZnBr2 and 0.4 M 1-EpBr to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.8 M ZnBr2 and 0.5 M 1-EpBr to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.8 M ZnBr2 and 0.6 M 1-EpBr to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.8 M ZnBr2, 0.5 M 1-EpBr, and 0.05 M MnSO4 to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.8 M ZnBr2, 0.5 M 1-EpBr, and 0.1 M MnSO4 to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.8 M ZnBr2, 0.5 M 1-EpBr, and 0.2 M MnSO4 to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.25 M ZnBr2 to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.25 M ZnBr2, 0.1 M 1-EpBr, and 0.025 M Na2SO4 to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.25 M ZnBr2, 0.1 M 1-EpBr, and 0.025 M Li2SO4 to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.25 M ZnBr2, 0.1 M 1-EpBr, and 0.025 M KaSO4 to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.25 M ZnBr2 and 0.05 M CrCl3 to DI water and stirring the resulting solution for 1 hour.
An electrolyte was prepared by inputting 2.25 M ZnBr2, 0.1 M 1-EpBr, and 0.05 M CrCl3 to DI water and stirring the resulting solution for 1 hour.
Experiments were performed by preparing unit cells including electrolytes of Preparation Examples 1 to 14 and Comparative Examples 1 to 6, respectively. In the unit cell, a current collector was placed on the end plate, the positive electrode was placed on the current collector, a chamber including the electrolyte was placed on the positive electrode, and a negative electrode were disposed in a symmetrical structure based on the chamber and fastened. The positive electrode used herein is 4T graphite felt, and the negative electrode is 0.25 T Zn foil.
Table 1 shows the values of average coulombic efficiency according to the type of electrolyte. Comparative Example 1 which does not include 1-EpBr as a bromine complexing agent and MnSO4 as a metal ion additive has an average coulombic efficiency of 88.1%, which is the lowest among Comparative Example 1, Preparation Example 2 and Preparation Example 3, and becomes irreversible due to dendrites formed at approximately 100 cycles. In contrast, Preparation Examples 2 and 3 maintain coulombic efficiency for 300 cycles or more, and exhibit excellent performance with an average coulombic efficiency of 98% or more. In Preparation Example 2 in which 1-EpBr as a bromine complexing agent is added, dendrites start to form after 200 cycles, resulting in a decrease in coulombic efficiency. However, in Preparation Example 3 in which MnSO4 as a metal ion additive is added, MnSO4 induces the electrodeposition and release of zinc to inhibit dendrite formation and prevent decreased coulombic efficiency, resulting in improving electrochemical performance.
Referring to
Referring to
Referring to Table 3, the coulombic efficiency of Preparation Example 10 is the highest at 96.38%. Accordingly, a preferable 1-EpBr concentration according to the average coulombic efficiency is 0.1 M to 0.6 M. However, when 1-EpBr is used alone, referring to
Referring to Table 4, MnSO4 has a coulombic efficiency of 90% or more in Preparation Examples 12 and 13. Compared to Experimental Example 4, as the current density decreases from 20 mAcm−2 to 10 mAcm−2, and the electrostatic repulsion force decreases, and thus in Preparation Example 13 including 0.1 M MnSO4, excellent coulombic efficiency is shown. In addition, referring to
Accordingly, under the above conditions, the optimal concentration range of MnSO4 in an electrolyte is 0.05 M to 0.1 M, and the performance of Preparation Example 13 is the highest.
As the present inventive concept uses a metal ion additive, an electrostatic shielding phenomenon may occur in a positive electrode to induce uniform electrodeposition/release of zinc, thereby inhibiting the growth of dendrites. Accordingly, reversibility is secured and thus electrochemical performance is improved. By using a metal ion additive with a higher standard reduction potential than that of zinc and a lower standard oxidation potential than that of bromine, the metal ion may not react during battery operation, resulting in maintenance of battery performance.
The present inventive concept may prevent a crossover phenomenon of bromine using a bromine complexing agent, and thus bock a reaction with zinc as a negative electrode active material. Due to this, dendrite formation may be inhibited, and as a result, self-discharge of the electrolyte may be inhibited during charging.
Since the present inventive concept provides an aqueous non-flow zinc-bromine battery, there is no need to use an additional electrolyte tank, so the problem of pipe corrosion may not occur.
In the present inventive concept, as a commercially-available metal ion additive and bromine complexing agent are added to an electrolyte, and a membrane and a tank are not used, a manufacturing process may be simplified, and production costs may be reduced.
Example embodiments of the present inventive concept can inhibit dendrite growth by inducing uniform electrodeposition/release of zinc due to an electrostatic shielding phenomenon occurring at a negative electrode by using a metal ion additive. Accordingly, reversibility is secured to improve electrochemical performance. In addition, by using a metal ion additive which has a higher standard reduction potential than that of zinc and a lower standard oxidation potential than that of bromine, the metal ions do not react during battery operation, so battery performance can be maintained.
Example embodiments of the present inventive concept can prevent a crossover phenomenon of bromine using a bromine complexing agent without a membrane, preventing a reaction with zinc, which is a negative electrode active material. Accordingly, coulombic efficiency can be increased by inhibiting dendrite formation, resulting in inhibition of self-discharge of the electrolyte during charging.
Example embodiments of the present inventive concept relate to an aqueous non-flow zinc-bromine battery, and thus, there is no need to additionally use an electrolyte tank, so the problem of piping corrosion does not occur.
Example embodiments of the present inventive concept can simplify a manufacturing process and reduce costs by inputting a commercially-available metal ion additive and bromine complexing agent to an electrolyte without using a membrane and a tank.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2022-0086525 | Jul 2022 | KR | national |
