Inspired by “quenching-cracking” strategy: Structure-based design of sulfur-doped graphite felts for ultrahigh-rate vanadium redox flow batteries

Vanadium redox flow batteries (VRFBs) are perceived as promising candidates for grid-scale energy storage systems. However, limited improvements in electrode structures restrict the operation of VRFBs at high current densities. Herein, finite element simulations are used to guide the construction direction of the electrode structure. Afterwards, a quenching-cracking strategy is ingeniously employed to successfully construct parallel-aligned micron flow channels on electrode fibers in high agreement with the model, and the consistency of the flow channel structure is verified via deep learning technique. The well-constructed flow channels achieve high specific surface areas of electrodes while enabling the smooth flow of electrolyte over the fiber surfaces. Subsequent graphitization and sulfur-doping processes yield hierarchical fibers with highly conductive cores and well-active surfaces. Benefiting from fine structural modulation, the battery equipped with the as-prepared electrodes delivers an energy efficiency of 80.44 % at an ultra-high current density of 500 mA cm−2 and achieves a peak power density of 1.68 W cm−2. Additionally, the battery is consistently cycled for 1000 cycles at 500 mA cm−2 and the average energy efficiency decay is only 0.01032 % per cycle. Notably, finite element simulations are applied to investigate the velocity distribution of electrolyte in the flow channels, and first-principle calculations are employed to reveal the cause for energy efficiency decay of the battery after long-term cycling. Most importantly, the establishment of structure-activity relationships highlights the significance of comprehensive modulation of electrode fiber structures towards enhancing the performance of VRFBs.