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. Nb₂O₅ 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 Nb₂O_5−x@rGO) nanosheets are designed to overcome the above Na/K storage problems. The black Nb₂O_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 Nb₂O_5−x@rGO nanosheets anodes and vanadate-based cathodes (Na_0.33V₂O₅ and K_0.5V₂O₅ 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.