Iso-Oriented NaTi₂(PO₄)₃ Mesocrystals as Anode Material for High-Energy and Long-Durability Sodium-Ion Capacitor

Sodium-ion capacitors (SIC) combine the merits of both high-energy batteries and high-power electrochemical capacitors as well as the low cost and high safety. However, they are also known to suffer from the severe deficiency of suitable electrode materials with high initial Coulombic efficiency (ICE) and kinetic balance between both electrodes. Herein, we report a facile solvothermal synthesis of NaTi₂(PO₄)₃ nanocages constructed by iso-oriented tiny nanocrystals with a mesoporous architecture. It is notable that the NaTi₂(PO₄)₃ mesocrystals exhibit a large ICE of 94%, outstanding rate capability (98 mA h g^-1 at 10 C), and long cycling life (over 77% capacity retention after 10 000 cycles) in half cells, all of which are in favor to be utilized into a full cell. When assembled with commercial activated carbon to an SIC, the system delivers an energy density of 56 Wh kg^-1 at a power density of 39 W kg^-1. Even at a high current rate of 5 A g^-1 (corresponds to finish a full charge/discharge process in 2 min), the SIC still works well after 20 000 cycles without obvious capacity degradation. With the merits of impressive energy/power densities and longevity, the obtained hybrid capacitor should be a promising device for highly efficient energy storage systems.