Membrane-free dual-phase zinc-bromine battery capable of realizing extremely low self-discharge and electrolyte of membrane-free dual-phase zinc-bromine battery

Abstract

The invention relates to a membrane-free double-phase zinc-bromine battery capable of realizing extremely low self-discharge and an electrolyte thereof, the membrane-free double-phase zinc-bromine battery comprises a positive electrode, a negative electrode, a battery container and a double-phase electrolyte, the positive electrode and the negative electrode are placed in the battery container, the double-phase electrolyte is added into the battery container, the double-phase electrolyte comprises a water-phase negative electrode electrolyte and a non-water-phase positive electrode electrolyte, and the water-phase negative electrode electrolyte and the non-water-phase positive electrode electrolyte are connected with the battery container. The aqueous-phase negative electrode electrolyte comprises water and an active substance, and the non-aqueous-phase positive electrode electrolyte comprises a non-aqueous solvent and a positive electrode supporting electrolyte salt. The novel membrane-free battery and the electrolyte thereof are adopted, so that the extremely low self-discharge rate and the cross-quarter storage capacity of the battery are realized.

Description

Technical Field

[0001] The invention relates to a membraneless two-phase zinc-bromine battery and an electrolyte. Technical Background

[0002] Ion exchange membranes, such as Nafion, Fumasep, Selemion, etc., are commonly used in redox flow batteries, which can effectively inhibit the crossover of redox species and reduce self-discharge. However, in practice, irreversible reactions caused by the transport of redox active species through ion exchange membranes, as well as low Coulombic efficiency and capacity decay are still one of the main decay mechanisms of redox flow batteries. Even though great efforts have been made in the development of high-performance ion exchange membranes in the past few years, no considerable progress has been made. On the other hand, current ion exchange membranes are expensive (accounting for 20% of the total battery cost) and their lifespan is difficult to meet the needs of long-term energy storage in energy storage systems. Recently, in order to solve the above problems, the concept of membraneless batteries has been proposed, including water-based two-phase systems, unmixed systems, etc. They eliminate the ion exchange membranes inherent in battery systems, reduce the cost of energy storage systems, and are one of the most promising technologies for achieving large-scale energy storage.

[0003] However, although the liquid-liquid interface of the biphasic battery has the ability to select ions similar to that of an ion exchange membrane and can ensure that the active molecules will be confined to their respective phases, limiting crossover, the current biphasic technology is still insufficient in suppressing the crossover of redox substances. The long storage time record of membraneless biphasic batteries is still less than 100 hours, and long-term storage is not possible. This situation affects the application and development of biphasic batteries. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings of existing liquid batteries in terms of redox species cross-diffusion, and to provide a membrane-free two-phase zinc-bromine battery with low self-discharge. In the two-phase zinc-bromine battery, zinc bromide as a redox species is completely present in the water phase to eliminate the self-discharge caused by the cross-diffusion of redox species. In addition, N-methyl-N-ethylpyrrolidone bromide (MEPBr) is added to the organic solvent as a bromine complexing agent, tetrabutylammonium bromide (TBABr), which complexes with the charging product bromine in the organic solvent to generate hydrophobic polybromine. This unique electrolyte design can greatly inhibit the diffusion of polybromine, reduce self-discharge, and enable the battery to be stored for a long time at a high charge state (90%).

[0005] The present invention is achieved through the following technical solutions.

[0006] The present invention aims to provide a membraneless two-phase zinc-bromine battery with extremely low self-discharge and its electrolyte, comprising a positive electrode, a negative electrode, a battery container and a two-phase electrolyte, wherein the battery container is provided with a positive electrode and a negative electrode, and the battery container is filled with a two-phase electrolyte, wherein the two-phase electrolyte comprises an aqueous negative electrode electrolyte and a non-aqueous positive electrode electrolyte, wherein the negative electrode electrolyte comprises water and an active substance, and the positive electrode electrolyte comprises a non-aqueous solvent and a positive electrode supporting electrolyte salt.

[0007] The first electrolyte is applied to the above-mentioned extremely low self-discharge membraneless two-phase zinc-bromine battery, wherein the negative electrode active material is zinc bromide, the concentration is 0.1 to 6 mol / L (preferably 0.5 to 3 mol / L), the non-aqueous solvent is dichloromethane, and the positive electrode supporting electrolyte salt is N-methyl-N-ethylpyrrolidone bromide (MEPBr) with a concentration of 0.1 to 2.5 mol / L (preferably 0.5 to 2.5 mol / L).

[0008] The second electrolyte used in the above-mentioned extremely low self-discharge membraneless two-phase zinc-bromine battery, wherein the negative electrode active material is zinc bromide, the concentration is 0.1 to 6 mol / L (preferably 0.5 to 3 mol / L), the non-aqueous solvent is dichloromethane, and the positive electrode supporting electrolyte salt is tetrabutylammonium bromide (TBABr) with a concentration of 0.1 to 2.5 mol / L (preferably 0.5 to 2.5 mol / L).

[0009] The third electrolyte used in the above-mentioned extremely low self-discharge membraneless two-phase zinc-bromine battery, the negative electrode active material zinc bromide, the concentration is 0.1 to 6 mol / L (preferably 0.5 to 3 mol / L), the non-aqueous solvent is acetonitrile, and the positive electrode supporting electrolyte salt is N-methyl-N-ethylpyrrolidone bromide (MEPBr) with a concentration of 0.1 to 2.5 mol / L (preferably 0.5 to 2.5 mol / L).

[0010] The third electrolyte used in the above-mentioned extremely low self-discharge membraneless two-phase zinc-bromine battery is that the negative electrode active material is zinc bromide with a concentration of 0.1 to 6 mol / L (preferably 0.5 to 3 mol / L), the non-aqueous solvent is acetonitrile, and the positive electrode supporting electrolyte salt is tetrabutylammonium bromide (TBABr) with a concentration of 0.1 to 2.5 mol / L (preferably 0.5 to 2.5 mol / L).

[0011] The graphite felt used in the negative electrode is treated with acid by soaking in 3M sulfuric acid for 12 to 28 hours.

[0012] Advantages of the present invention:

[0013] By using a bromine complexing agent in an organic solvent for the first time, a membraneless biphasic zinc-bromine battery is assembled using raw materials that are easily obtained using simple methods. A reasonable electrolyte design is used to fix the hydrophobic complex product of the complexing agent and bromine in the organic phase in the form of a solute, avoiding the irreversible capacity loss caused by the diffusion of bromine to the negative electrode, greatly reducing the battery self-discharge, and improving the battery coulomb efficiency and cycle stability. And compared with other membraneless batteries, it has a higher energy density. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 Schematic diagram of the composition of a membraneless two-phase zinc-bromine battery.

[0015] Figure 2 It is a statistical chart of the coulombic efficiency, voltage efficiency, energy efficiency and cycle number of the battery in Example 2.

[0016] Figure 3 It is a statistical chart of the coulombic efficiency, voltage efficiency, energy efficiency and cycle number of the battery in Example 4. DETAILED DESCRIPTION

[0017] Example 1

[0018] The membraneless two-phase zinc-bromine battery of this embodiment has a graphite felt electrode and a graphite felt electrode wrapped with zinc sheets as the positive and negative electrodes, respectively. 2M MEPBr in ethylene oxide is used as the organic phase, and 2M zinc bromide in deionized water is used as the aqueous phase. The battery is assembled by mixing the two electrolytes together and then naturally layering. The battery is charged to a 50% state of charge at a current density of 2mA / cm2, and then charged and cycled at the same current density, with a cut-off voltage of 0 to 2.1V.

[0019] Example 2

[0020] The membraneless two-phase zinc-bromine battery of this embodiment has a graphite felt electrode as the positive and negative electrodes and a graphite felt electrode wrapped with zinc sheets. 2M TBABr in ethylene oxide is used as the organic phase, and 2M zinc bromide in deionized water is used as the aqueous phase. The battery is assembled by mixing the two electrolytes together and then naturally layering. The battery is charged to 50% of the state of charge at a current density of 2mA / cm2, and then charged and cycled at the same current density, with a cut-off voltage of 0 to 2.1V. The statistical chart is as follows Figure 2 As shown, the coulombic efficiency after 500 cycles is above 99.99%, no capacity decay is observed, and the energy efficiency is greater than 70%.

[0021] Example 3

[0022] The membraneless two-phase zinc-bromine battery of this embodiment has a graphite felt electrode and a graphite felt electrode wrapped with zinc sheets as the positive and negative electrodes, respectively. 2M MEPBr in acetonitrile is used as the organic phase, and 2M zinc bromide in deionized water is used as the aqueous phase. The battery is assembled by mixing the two electrolytes together and then naturally layering. The battery is charged to a 50% state of charge at a current density of 4mA / cm2, and then charged and cycled at the same current density, with a cut-off voltage of 0 to 2.1V.

[0023] Example 4

[0024] The membraneless two-phase zinc-bromine battery of this embodiment has a graphite felt electrode and a graphite felt electrode wrapped with zinc sheets as the positive and negative electrodes, respectively. 2M TBABr in acetonitrile is used as the organic phase, and 2M zinc bromide in deionized water is used as the aqueous phase. The two electrolytes are mixed together and then naturally layered to assemble the battery. The battery is charged to 50% of the charge state at a current density of 4mA / cm2, and then charged and cycled at the same current density, with a cut-off voltage of 0 to 2.1V. The statistical chart is as follows Figure 3 As shown, the coulombic efficiency after 256 cycles is above 99.99%, no capacity decay is observed, and the energy efficiency is greater than 60%.

Claims

1. A membraneless two-phase zinc-bromine battery and its electrolyte for achieving extremely low self-discharge, characterized in that: The invention comprises a positive electrode, a negative electrode, a battery container and a biphasic electrolyte. The positive electrode and the negative electrode are arranged in the battery container. The biphasic electrolyte is filled in the battery container. The biphasic electrolyte comprises an aqueous phase negative electrode electrolyte and a non-aqueous phase positive electrode electrolyte. The negative electrode electrolyte comprises water and an active substance. The positive electrode electrolyte comprises a non-aqueous solvent and a positive electrode supporting electrolyte salt.

2. A membraneless two-phase zinc-bromine battery with extremely low self-discharge according to claim 1, characterized in that The negative electrode active material zinc bromide has a concentration of 0.1 to 6 mol / L (preferably 0.5 to 3 mol / L), the non-aqueous solvent is acetonitrile, propylene carbonate, ethylene oxide, dichloromethane and chloroform, and the positive electrode supporting electrolyte salt is N-methyl-N-ethylpyrrolidone bromide (MEPBr) with a concentration of 0.1 to 2.5 mol / L (preferably 0.5 to 2.5 mol / L).

3. A membraneless two-phase zinc-bromine battery with extremely low self-discharge according to claim 1, characterized in that The negative electrode active material is zinc bromide, with a concentration of 0.1 to 6 mol / L (preferably 0.5 to 3 mol / L), the non-aqueous solvent is acetonitrile, propylene carbonate, ethylene oxide, dichloromethane and chloroform, and the positive electrode supporting electrolyte salt is tetrabutylammonium bromide (TBABr) with a concentration of 0.1 to 2.5 mol / L (preferably 0.5 to 2.5 mol / L).

4. A membraneless two-phase zinc-bromine battery with extremely low self-discharge according to claim 1, characterized in that The negative electrode (graphite felt) is acid-treated by soaking in 3 mol / L sulfuric acid for 12 to 28 hours.

5. A membraneless two-phase zinc-bromine battery with extremely low self-discharge according to claim 1, characterized in that The charging product bromine generated in the organic phase reacts with the supporting salts TBABr and MEPBr to form hydrophobic polybromides, which inhibit bromine diffusion and realize a membraneless liquid-liquid biphasic battery with extremely low self-discharge and long-term storage.

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