Synergistic Coupling of Ether Electrolyte and 3D Electrode Enables Titanates with Extraordinary Coulombic Efficiency and Rate Performance for Sodium-Ion Capacitors

Sodium-ion capacitors (SICs) have attracted increasing attention for sustainable energy utilization owing to their low cost and similar intercalation electrochemistry with lithium-ion capacitors. However, the practical application of SICs is seriously hindered by the low initial coulombic efficiency (ICE) and limited redox kinetics at the battery electrode side. Herein, taking a layered sodium titanate battery anode as an example, this study reports on the synergistic combination of ether electrolyte and binder-free array architecture to simultaneously achieve superior ICE and ultrafast Na+ intercalation. The resulting Na2Ti2O5 nanosheet array anode delivers extraordinary ICE (91%), high cycle CE (approximate to 100%), and outstanding rate performance (66% capacity retention at 120 C). The key to the superior performance lies in the synergistic promotion between electrolyte and 3D electrode architecture, which ensures a very thin and stable solid-electrolyte interphase, largely reduced resistances, and fully accessible interlayers for Na+. Moreover, a SIC device is assembled with an Na2Ti2O5 array anode and a commercial activated carbon cathode, exhibiting high ICEs (80-90%) at various current densities, high energy densities (54.5 Wh kg(-1); 17.2 mWh cm(-3)), and ultralong cycling stability (>10 000 cycles). This work presents an advanced concept for designing high-CE and high-rate battery electrodes for a variety of sodium ion energy storage systems.