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

Nanoscale surface-engineering plays an important role in improving the performance of battery electrodes. Nb₂ O₅ 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 Nb₂ O_{5- x} @rGO) nanosheets are designed to overcome the above Na/K storage problems. The black Nb₂ 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 Nb₂ O_{5- x} @rGO nanosheets anodes and vanadate-based cathodes (Na_0.33 V₂ O₅ and K_0.5 V₂ O₅ 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.