Improved Reversibility of Fe 3+ /Fe 4+ Redox Couple in Sodium Super Ion Conductor Type Na 3 Fe 2 (PO 4 ) 3 for Sodium-Ion Batteries.

The methodology employed here utilizes the sodium super ion conductor type sodium iron phosphate wrapped with conducting carbon network to generate a stable Fe3+ /Fe4+ redox   couple, thereby exhibiting higher operating voltage and energy density of sodium-ion batteries. This new class of sodium iron phosphate wrapped by carbon also displays a cycling stability with >96% capacity retention after 200 cycles.