Defect‐Driven Reconstruction of Na‐Ion Diffusion Channels Enabling High‐Performance Co‐Doped TiO2 Anodes for Na‐Ion Hybrid Capacitors

Abstract Na‐ion hybrid capacitors (NICs) are known for their potential to integrate high power and energy density along with superior lifespan into a single energy storage device. However, the practical implementation of NICs is delayed due to their inadequate energy densities (<100 Wh kg −1 ), which is a result of the lack of anodes with rapid Na‐ion diffusion kinetics to match the cathodes. To accelerate Na‐ion diffusion kinetics, cobalt‐doped TiO 2 (Co x Ti 1−x O y ) nanosheet anodes with reconstructed low‐energy barrier channels for Na‐ion transfer are designed. Crystal defects, including nanointerfaces, Ti interstitials, and oxygen vacancies, are intentionally introduced to the Co x Ti 1−x O y structure to improve its conductivity and induce pseudocapacitive‐type Na‐ion storage. Moreover, these crystal defects subtly alter the Na‐ion transfer pathways in the bulk Co x Ti 1−x O y and reduce the energy barrier, as confirmed by density functional theory (DFT) simulations. Rapid Na‐ion diffusion kinetics can minimize the kinetics discrepancy between anodes and cathodes, presenting great potential for achieving high‐performance anodes for NIC applications. When integrated with activated carbon/reduced graphene oxide composite (AC/rGO) cathodes, the fabricated NICs demonstrate remarkable energy density (164 Wh kg −1 at 31 W kg −1 ), power density (8307 W kg −1 at 56 Wh kg −1 ), and an ultralong lifespan (83% capacity retention after 15000 cycles).