Intercalation pseudocapacitance of sodium-ion storage in TiO2(B)

Abstract

Compared to the well-investigated Li⁺ intercalation into layered TiO₂(B), the Na⁺ storage properties of TiO₂(B) remain relatively unexplored. Herein, an insight into the Na⁺ storage mechanism of TiO₂(B) is gained by simultaneously investigating the structural evolution and reaction kinetics of the nanosheets (NSs) and nanowires (NWs) with different specific surface areas. Based on ex situ characterizations, the Na⁺ (de)intercalation into layered TiO₂(B) follows a solid-solution reaction with negligible lattice changes. Detailed kinetic analysis reveals the intercalation pseudocapacitance of sodium-ion storage in TiO₂(B), with a high capacitive contribution of ∼90% for both the NSs and NWs electrodes. The Na⁺ storage capacities and capacitive dominant responses of TiO₂(B) anodes are independent of their specific surface area and morphology, demonstrating the intrinsic intercalation pseudocapacitance of sodium-ion storage in TiO₂(B). Density functional theory (DFT) calculations reveal different storage sites in TiO₂(B) for the accommodation of Na⁺ and Li⁺ ions, leading to the lower Na⁺ storage capacity of 120 mA h g⁻¹ than that of Li⁺ storage. Due to the advantages of intercalation pseudocapacitance, the TiO₂(B) anode displays excellent high-rate capability and long-term cycling stability for Na⁺ storage.