P-induced electronic modulation at the interface boosting p-d orbital coupling for high-performance vanadium flow batteries.

Vanadium flow batteries (VFBs), as a high-safety grid-scale energy storage technology, provide an ideal solution for storing green power generated from intermittent renewable energy sources. However, the sluggish kinetics of the V/V redox reaction at the negative electrode interface limits the development of VFBs toward high-rate performance. Herein, density functional theory (DFT) calculations demonstrate the feasibility of phosphorus (P) atom modulation on the electronic structure at the N, O dual-doped carbon interface. Afterwards, P-modulated polybenzimidazole (PBI)-derived N, O-rich composite electrodes are fabricated via a loading-calcination strategy. The introduction of P atom enhances the adsorption of vanadium ion at the interface and improves the p-d orbital coupling between the electrode and vanadium ion. The VFB with the modified electrode shows an energy efficiency (EE) of 82.27 % at 150 mA cm and maintains stable cycling performance with only 2.4 % EE decay after 2000 cycles at 100 mA cm. This electronic structure modulation strategy provides new insights into the development of next-generation high-performance and long-life VFBs.