Accelerating ion and charge transfer of hybrid titanium niobium oxides through interface engineering for high-performance lithium ion capacitors

Titanium niobium oxides have garnered significant attention as potential anode materials for lithium ion capacitors (LICs) due to their open ionic channels and high safety. However, the sluggish ion and charge transfer kinetics impede their rate capability. Hereby, we have investigated the phases evolution process of titanium niobium oxides by simple optimizing Nb/Ti ratio in the precursor, leading to the successful construction of hybrid TiO₂/TiNb₂O₇ with active interface. Density functional theory (DFT) calculations manifest the low Li⁺-diffusion barrier and the formation of built-in electric fields, resulting in the accelerated interfacial charge separation/transfer and Li⁺ diffusion. In-situ XRD results reveal the highly reversible structural changes of TiO₂/TiNb₂O₇ during charging/discharging process. Accordingly, hybrid TiO₂/TiNb₂O₇ demonstrates much reinforced rate capability, which could retain a specific capacity of 205.1 mAh g⁻¹ at high current density of 10 A g⁻¹ compared to 300.3 mAh g⁻¹ at 0.1 A g⁻¹. Moreover, the assembled TiO₂/TiNb₂O₇//AC LIC displays high energy density of 149.6 W h kg⁻¹ (at 200 W kg⁻¹). Overall, this work emphasizes the critical role of interface engineering in promoting ion and charge transfer of nanomaterials for superior energy storage and beyond.