Confined seeds derived sodium titanate/graphene composite with synergistic storage ability toward high performance sodium ion capacitors

Sodium ion capacitors (SICs) are increasingly being focused, due to the feature of high energy/power densities derived from the integrated energy storage mechanisms, as well as the ubiquitous sodium sources. Practical anodes with exceptional rate capability can circumvent the kinetic mismatch with cathode, boosting energy/power metrics. Herein, a Na₂Ti₇O₁₅ nanowire/graphene anode is synthesized through an atomic layer deposition (ALD) seeding technique, by which the confined seeds enable Na₂Ti₇O₁₅ with ultra-high aspect ratio and interweaved structure with graphene nanosheets. The composite delivers a superior rate capability of 60 mAh g⁻¹ at a high rate of 17.7 A g⁻¹, and an exceptional cyclic stability of 90% retention after 10 000 cycles even at 8.85 A g⁻¹. It is demonstrated that the morphology, graphene platform, intrinsically low energy diffusion barrier of Na₂Ti₇O₁₅, and associated reaction mechanism synergize the electron transport, sodium ion migration, and surface capacitive contribution, giving rise to such a decent electrochemical performance. The SICs deliver high energy/power densities (82.7 Wh kg⁻¹/97.5 W kg⁻¹, 25 kW kg⁻¹ with 16 Wh kg⁻¹ retained), proving a promise particularly at extremely fast charge/discharge condition. The proposed ALD seeding technique can be developed into a technical strategy for synthesizing high performance energy storage materials.