CoNb<sub>2</sub>O<sub>6</sub> embedded in graphene nanosheets as an advanced intercalation anode for high-energy lithium-ion capacitors

Intercalation anode materials are promising candidates for hybrid lithium-ion capacitors (LICs) owing to their excellent lithium storage capacity and cycling stability. In this study, a composite of CoNb2O6 embedded in graphene nanosheets (CoNb2O6@G) was synthesized via a two-step hydrothermal method and demonstrated for the first time as an intercalation anode material for lithium storage. The graphene sheets form a three-dimensional porous framework that provides abundant binding sites for the CoNb2O6 particles, effectively miti­gating particle agglomeration and volume expansion during charge-discharge cycles. The composite with the optimal graphene content of 100 mg (CoNb2O6@G-100mg) exhibited a remarkable reversible capacity of 508.5 mA h g-1 at a current density of 50 mA g-1. Furthe­rmore, the CoNb2O6@G-100mg//activated carbon (AC) LIC, in which CoNb2O6@G-100mg and AC are used as the anode and cathode, respectively, exhibited an energy density of 94.1 W h kg-1 and a maximum power density of 8750 W kg-1 within the voltage range of 0.0 to 3.5 V. The device demonstrated outstanding cycling stability, with negligible capacity loss (0.00255% per cycle) over 10,000 charge-discharge cycles. These results demonstrate the potential of CoNb2O6@G as a high-performance anode material for energy-storage devices, particularly in power-oriented applications.