Tunable pseudocapacitive contribution in nanosheet-constructed titania hierarchical tubes to achieve superior lithium-storage properties by phase control

Abstract

Nanostructured materials have been extensively investigated as high-rate lithium-storage materials due to their high surface area and shortened charge-transport length. The pseudocapacitive effect plays a considerable role in electrochemical lithium storage when the electrochemically active materials approach nanoscale dimensions but has received limited attention. Herein, phase-composition-controlled anatase TiO₂/TiO₂-B nanosheet-assembled hierarchical tubes (denoted as TONS-HTs) were prepared by a hydrothermal reaction, followed by calcination in air. The unique tubular hierarchical structure composed of nanosheet building blocks is beneficial for the penetration of the electrolyte throughout the entire electrode and avoiding the aggregation of nanomaterials. Moreover, rationally modulating the phase composition of the TiO₂ hierarchical tubes can contribute to tuning the crystal size and grain boundaries, thus maximizing the pseudocapacitive contribution to achieve high rate capability. The optimum TONS-HT product presents high rate capability (172 mA h g⁻¹ at 10 A g⁻¹) and excellent charge–discharge durability (145 mA h g⁻¹ at 6 A g⁻¹ after 1000 cycles). Further, the as-assembled asymmetric hybrid lithium-ion supercapacitor delivers an outstanding power density of ∼6 kW kg⁻¹ when a high energy density of 40 W h kg⁻¹ is achieved. This work offers an approach to tune the lithium-storage properties of TiO₂ by nano-engineering and phase modulation and gives insights into the enhancement of pseudocapacitance-assisted lithium-storage capacity.