Surface‐Engineered Black Niobium Oxide@Graphene Nanosheets for High‐Performance Sodium‐/Potassium‐Ion Full Batteries

Abstract Nanoscale surface‐engineering plays an important role in improving the performance of battery electrodes. Nb 2 O 5 is one typical model anode material with promising high‐rate lithium storage. However, its modest reaction kinetics and low electrical conductivity obstruct the efficient storage of larger ions of sodium or potassium. In this work, partially surface‐amorphized and defect‐rich black niobium oxide@graphene (black Nb 2 O 5− x @rGO) nanosheets are designed to overcome the above Na/K storage problems. The black Nb 2 O 5− x @rGO nanosheets electrodes deliver a high‐rate Na and K storage capacity (123 and 73 mAh g −1 , respectively at 3 A g −1 ) with long‐term cycling stability. Besides, both Na‐ion and K‐ion full batteries based on black Nb 2 O 5− x @rGO nanosheets anodes and vanadate‐based cathodes (Na 0.33 V 2 O 5 and K 0.5 V 2 O 5 for Na‐ion and K‐ion full batteries, respectively) demonstrate promising rate and cycling performance. Notably, the K‐ion full battery delivers higher energy and power densities (172 Wh Kg −1 and 430 W Kg −1 ), comparable to those reported in state‐of‐the‐art K‐ion full batteries, accompanying with a capacity retention of ≈81.3% over 270 cycles. This result on Na‐/K‐ion batteries may pave the way to next‐generation post‐lithium batteries.