Hybrid pseudocapacitance/co-intercalation mechanisms of TiO2/graphite anodes for rapid sodium-ion storage

Abstract

Developing anode materials with high specific/volumetric capacities, high-rate capability, long-term cycles and low cost is significant for advanced sodium-ion storage. Herein, we report the hybrid TiO₂/graphite (TiO₂/G) anodes for fast (dis)charging sodium-ion storage. Taking advantage of the rapid pseudocapacitive surface-redox on anatase TiO₂ nanoparticles (NPs) and fast [Na(diglyme)_x]⁺ co-intercalation into graphite, the hybrid anodes display excellent rate capabilities. Additionally, the TiO₂ NPs are able to fill into the interspaces among graphite flakes and the graphite provides continuous electron pathways, which largely boosts the volumetric capacities and rate performance. Benefitting from the synergistic effects, the hybrid electrodes display excellent comprehensive electrochemical performance. At the thick-film electrodes (a single-side mass loading of 10 mg·cm⁻²), the hybrid TiO₂/G anode, in a ratio of 40/60 by weight, exhibits high gravimetric and volumetric capacities (71 mAh·g⁻¹/152 mAh·cm⁻³) at a high current density of 20 mA·cm⁻² (2 A·g⁻¹), which are higher than those of the graphite (61 mAh·g⁻¹/121 mAh·cm⁻³), TiO₂ NPs (37 mAh·g⁻¹/72 mAh·cm⁻³) and hard carbon (19 mAh·g⁻¹/23 mAh·cm⁻³) anodes. The TiO₂/G hybrid anodes with excellent comprehensive electrochemical performance display promising potential for high-power sodium-ion batteries and capacitors.

Graphical abstract