Recently, Li Xianfeng, a researcher of the Energy Storage Technology Research Department of the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, cooperated with Fu Qiang, a researcher of the Nanometer and Interface Catalysis Research Center of the State Key Laboratory of Catalysis Foundation, and made progress in the research of halogen water system batteries. A multi electron transfer anode based on bromine and iodine was developed, with a specific capacity of more than 840 ampere hours/liter, and an energy density of more than 1200 watt hours/liter on the positive side in the full battery test.
Energy density and safety are important standards for measuring secondary batteries. Traditional non-aqueous lithium-ion batteries have high energy density, but the organic electrolyte they use is flammable and safety issues are difficult to ensure. Water based batteries use water as a solvent, which is safe. However, due to issues such as low electrolyte solubility and low battery voltage, the energy density of water-based batteries is generally low, meaning that the battery stores less electricity per unit volume. For example, traditional water-based batteries such as all vanadium flow batteries and zinc bromide flow batteries have energy densities of approximately 30 watt hours/liter and 60 watt hours/liter, respectively, making them only suitable for large-scale fixed energy storage.
In order to improve the energy density of aqueous batteries, Li Xianfeng's team used a mixed halogen solution of iodine ions and bromine ions as the electrolyte to construct a multi electron transfer reaction from iodine ions to elemental iodine and then to iodate ions. During the charging process, iodine ions generate iodate ions at the positive electrode, and the accompanying hydrogen ions are conducted from the positive electrode to the negative electrode side; During the discharge process, hydrogen ions conduct from the negative electrode to the positive electrode, and iodate ions are reduced to iodide ions. The team utilized the intermediate state of bromide formed during the charging and discharging process to optimize the reaction pathway, improve the activity and reversibility of electrochemical reactions, and developed a multi electron transfer positive electrode with a specific capacity of 840 ampere hours per liter. The positive electrode and metal cadmium form a full battery, based on an energy density of over 1200 watt hours per liter on the positive electrode side.
Research has found that bromine ions added to the electrolyte can generate polar iodine bromide during battery charging, which is beneficial for reacting with water to form iodate ions, thereby increasing the reaction rate and reducing the charging voltage. During the discharge process, iodate reacts with bromine ions to generate bromine, participating in electrochemical reactions to achieve reversible and rapid discharge of iodate ions. This not only increases the discharge voltage of the battery, but also enhances the reduction rate of iodate ions. In the optimized electrolyte, bromide acts as a bridge for redox reactions, improving the efficiency and reaction rate of the battery. The research team demonstrated the above reaction process through in-situ optical microscopy, Raman spectroscopy, and other means.
This study is expected to broaden the research avenues for high-energy density water-based batteries and provide new ideas for the design of high-energy density water-based batteries. In addition, this study has expanded the application scope of water-based batteries, such as power batteries, providing technical support for environmental protection and energy structure upgrading.
The related achievements are titled "Reversible multielectron transfer I −/IO3 − catalyst enabled by a hetero harmonic energy for high energy density acute batteries" and published in Nature Energy. The research work has received support from the National Natural Science Foundation of China and others.
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