Surface redox pseudocapacitance-based vanadium nitride nanoparticles toward a long-cycling sodium-ion battery

Structure-stable anodes are essential for achieving long-cycling stability in sodium-ion batteries. However, a large cycled structure/volume change is inevitable in conversion-type or alloying-reaction anodes, which make them intrinsically unsuitable for durable sodium-ion batteries . Here, we synthesized carbon fiber-anchored vanadium nitride nanoparticles (denoted as VN@CF) through a simple molten-salt method without NH3 treatment. The VN@CF anode shows an ultra-stable Na-storage structure with a discharge capacity of 204 mAh/g at 0.1 A/g after 500 cycles. More notably, it shows remarkably long-cycling stability over 6600 cycles without capacity attenuation at 1.0 A/g. Multiple ex-situ characterizations, such as X-ray diffraction and X-ray photoelectron spectroscopy, indicate that the sodium storage behavior of VN@CF is a surface redox-related pseudocapacitive process, which is further supported by theoretical calculations. Such surface pseudocapacitive could not only enhance the sodium-storage structure stability but increase the redox reaction kinetics, which should be the origins of VN@CF's superior electrochemical properties. Our work paves a way for designing structure-stable energy storage materials based on the surface redox pseudocapacitance mechanism.