Electrostatic interfacial engineering of MXene@Cobalt niobate heterostructures with accelerated charge transport kinetics for ultra-long-life lithium-ion hybrid capacitors

The practical application of lithium-ion hybrid capacitors (LIHC) is limited by the poor cycling and structural degradation of battery-type anodes. Hence, designing structurally stable anodes with enhanced ionic/electronic conductivity is crucial. Metal niobates have recently gained considerable attention as lithium storage materials due to their “zero-strain” columbite structure, which supports intercalation-conversion reactions and fast ion diffusion. However, low intrinsic electrical conductivity and volume expansion during cycling restrict their practical utilization. Herein, we report an electrostatically coupled Nb 2 C MXene@CoNb 2 O 6 (NCNO) heterostructure as an anode for high-performance LIHCs. The optimized NCNO (1:2) anode provides enhanced interfacial structural stability and abundant active sites for Li + storage. Consequently, it exhibits a reversible capacity of 250 mAh/g after 25 cycles at 0.1 A/g and retains 44% of this value even at 1.5 A/g. Also, after 1000 cycles at 1 A/g, it maintains ~224 mAh/g, indicating excellent long-term durability. Ex-situ XPS and in-situ EIS analyses reveal enhanced reaction kinetics and stable interfacial charge transport. Moreover, the assembled NCNO (1:2)//porous carbon LIHC delivers a maximum energy density of 132 Wh/kg with 78% capacity retention after 18,000 cycles. Additionally, low self-discharge (~3.04 V after 100 h) highlights the strong potential of these heterostructures for advanced lithium storage applications.