Abstract:

Vanadium flow battery (VFB) is imperative long-term energy storage technology for the development of low-carbon power systems. Developing high-power stacks is an important way to promote the scale application of VFB. Electrode, as a crucial material in a VFB power unit, is the key to realize high-power battery technology. To enhance the electrochemical performance of commercial carbon felt electrodes, two thermal treatment activation strategies are proposed in this work: low-temperature long-time treatment and high-temperature short-time treatment. Specifically, in the air atmosphere, pristine carbon felts are activated by adjusting the processing temperature and time. Physical, chemical, and electrochemical properties of activated electrodes are characterized using scanning electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, contact angle measurement, cyclic voltammetry, electrochemical impedance spectroscopy and single-cell charge-discharge tests. Results indicate that low-temperature long-time treatment controllably increases carbon felt fiber roughness, and preserves mechanical stability while introducing oxygen functional groups with minimal impact on the graphite crystal structure. After thermal treatment at 450 °C for 6 h, the activated carbon felt exhibits the best electrochemical activity for VO²⁺/VO₂⁺ and V²⁺/V³⁺ and V2+/V3+ reactions. The BET surface area increases to 1.75 m²g^-1, and the content of oxygen functional groups on the surface increases to 10.38 at.%. Optimized activated carbon felt electrodes exhibit 77.8% energy efficiency at 300 mA cm^-2, surpassing pristine carbon felt. This study offers practical guidance for activating commercial carbon felt electrodes. It is of great practical significance for the development of high power VFB.

Key words: all-vanadium flow battery, electrode, carbon felt, thermal treatment, activation