A High Rate and Long Cycling Performance NaTi₂(PO₄)₃ Core–Shell Porous Nanosphere Anode for Aqueous Sodium-Ion Batteries

NASICON-type material NaTi₂(PO₄)₃ has a suitable working potential (−0.87 V vs saturated calomel electrode) in aqueous sodium-ion cells. Nevertheless, the inherent electronic conductivity in the internal core and external shell limits its rate and cycling performance. Herein, a carbon-coated porous nanosphere NaTi₂(PO₄)₃ material is synthesized by the solvothermal method. This structure effectively improves the electrical conductivity, enlarges the contact area with the electrolyte, and facilitates the rapid intercalation/deintercalation of Na⁺. It delivers an excellent rate behavior of 123.59, 113.55, 102.81, 90.85, and 60.95 mAh g⁻¹ at 0.2, 0.5, 1, 2, and 5 A g⁻¹, respectively. Improved long cyclability under a 5 A g⁻¹ high current density is also demonstrated by a capacity retention of 70.2% over 500 cycles and an average Coulombic efficiency of 98%. As-prepared core–shell porous nanosphere NaTi₂(PO₄)₃ exhibits potentially practical applications in a new type of aqueous sodium-ion battery system.