Thermal-induced interlayer defect engineering toward super high-performance sodium ion capacitors

Ti-based compounds are considered as attractive anode materials for sodium-ion capacitors (SICs) due to their favorable safety and stability. However, achieving more Na+ intercalated sites and fast sodiation kinetics in Ti-based anodes is still challenging. Herein, a facile strategy to promote the electrochemical properties of H-titanates by regulating their electronic structure and Na+ diffusion kinetics through thermal-induced interlayer defect engineering is developed. The targeted distorted quasi-layered H-titanate (Q-LT) with abundant interlayer defects exhibits superfast and stable cycle performance (97% capacity retention after 10,000 cycles at 25 C) in Na-ion half-cells. Applied in the high-working voltage (1.5-4.5 V) SICs as additive anodes, high energy density (124 Wh kg(-1)) and competitive cycle stability (88% capacity retained after 5000 fast cycles) are achieved. The thermal-induced structure evolution in layered H-titanate has been probed by in-situ X-ray diffraction. First-principles density functional theory calculations demonstrate that the Q-LT is equipped with lower coordinate Ti-O polyhedral, higher delocalized Ti-O environment, narrowed band gap and reduced Na+ migration energies; bond valence sum maps expose the continuous Na+ diffusion pathways within the interlayer of Q-LT. This work may offer a conceptual advance in the understanding of the structure-function-performance relationship of fitanates for energy storage.