S/N Co-Doped Ultrathin TiO₂ Nanoplates as an Anode Material for Advanced Sodium-Ion Hybrid Capacitors

Anatase titanium dioxide (TiO₂) has emerged as a potential anode material for sodium-ion hybrid capacitors (SICs) in terms of its nontoxicity, high structure stability and cost-effectiveness. However, its inherent poor electrical conductivity and limited reversible capacity greatly hinder its practical application. Here, ultrathin TiO₂ nanoplates were synthesized utilizing a hydrothermal technique. The electrochemical kinetics and reversible capacity were significantly improved through sulfur and nitrogen co-doping combined with carbon coating (SN-TiO₂/C). Sulfur and nitrogen co-doping generated oxygen vacancies and introduced additional active sites within TiO₂, facilitating accelerated Na-ion diffusion and enhancing its reversible capacity. Furthermore, carbon coating provided stable support for electron transfer in SN-TiO₂/C during repeated cycling. This synergistic strategy of sulfur and nitrogen co-doping with carbon coating for TiO₂ led to a remarkable capacity of 335.3 mAh g^-1 at 0.1 A g^-1, exceptional rate property of 148.3 mAh g^-1 at 15 A g^-1 and a robust cycling capacity. Thus, the SN-TiO₂/C//AC SIC delivered an impressive energy density of 177.9 W h kg^-1. This work proposes an idea for the enhancement of reaction kinetics for energy storage materials through a synergistic strategy.