Redox flow battery is a large-scale secondary battery energy storage device that stores energy in solution through a redox process. There are many kinds of organic substances, the preparation process is simple and the material structure can be designed. Therefore, the electrochemical properties and solubility of organic compounds can be adjusted, and they can be used as electrode materials or electrolytes to prepare organic redox flow batteries. Organic radicals refer to organic materials containing unpaired electrons, generally organic polymers. In this type of organic matter, it is mainly composed of stable free radical side chains and polymer backbones. The unpaired electrons on the organic radical compound determine the stability of the battery, and nitrogen oxide radicals are generally used. Such batteries have the advantages of high power density, stable cycle performance, structural diversification, designability, sustainable development, and the ability to prepare flexible batteries, and are widely used.
Figure 1. The redox reaction process of nitroxide free radicals
- Electrode material: Organic redox flow batteries using organic radical compounds as electrode materials are a class of rechargeable batteries with good performance. Its working principle is mainly to realize the mutual conversion between electrical energy and chemical energy through the reversible redox reaction of organic freedom during the charging and discharging process. The positive electrode material and negative electrode material of this type of battery generally use p-type radical polymer and n-type radical polymer as active materials, respectively. The p-type radical polymer undergoes oxidation reaction and can be used as a positive electrode material. The n-type radical polymer undergoes a reduction reaction and can be used as a negative electrode material. During the charging process, the free radical undergoes an oxidation reaction at the negative electrode to form a free radical cation, and the free radical undergoes a reduction reaction at the positive electrode to form a free radical anion. The discharge process is the opposite, the radical cation undergoes a reduction reaction at the negative electrode to regenerate neutral free radicals, while the radical anion undergoes an oxidation reaction at the positive electrode to generate neutral free radicals. The extremely fast electron transfer rate of this type of battery during the charging and discharging process endows the organic redox flow battery with excellent rate performance, capacitance and electron diffusion rate, making the organic radical battery widely used.
- Kato M, Senoo K, Yao M. A pentakis-fused tetrathiafulvalene system extended by cyclohexene-1, 4-diylidenes: a new positive electrode material for rechargeable batteries utilizing ten electron redox[J]. Journal of Materials Chemistry A, 2014, 2, 6747-6754.