High‐rate sodium‐ion storage of vanadium nitride via surface‐redox pseudocapacitance

Vanadium nitride (VN) electrode displays high-rate, pseudocapacitive responses in aqueous electrolytes, however, it remains largely unclear nonaqueous, Na+-based electrolytes. The traditional view supposes a conversion-type mechanism for Na+ storage VN anodes but does not explain the phenomena of their size-dependent specific capacities and underlying causes charge behaviors. Herein, we insightfully reveal anode exhibits surface-redox as demonstrated by kinetics analysis, experimental observations, first-principles calculations. Through ex situ X-ray photoelectron spectroscopy semiquantitative analyses, is characterized redox reactions occurring with V5+/V4+ to V3+ at surface particles, which different from well-known conversion reaction mechanism. performance enhanced through nanoarchitecture design via oxidized vanadium states surface. optimized VN-10 nm delivers sodium-ion capability 106 mAh g−1 high current 20 A g−1, excellent cycling 5000 cycles negligible capacity losses. This work demonstrates emerging opportunities utilizing realizing high-rate applications.