Realizing Three‐Electron Redox Reactions in NASICON‐Structured Na 3 MnTi(PO 4 ) 3 for Sodium‐Ion Batteries

Developing multielectron reaction electrode materials is essential for achieving high specific capacity and high energy density in secondary batteries; however, it remains a great challenge. Herein, Na 3 MnTi(PO 4 ) 3 /C hollow microspheres with an open and stable NASICON framework are synthesized by a spray‐drying‐assisted process. When applied as a cathode material for sodium‐ion batteries, the resultant Na 3 MnTi(PO 4 ) 3 /C microspheres demonstrate fully reversible three‐electron redox reactions, corresponding to the Ti 3+/4+ (≈2.1 V), Mn 2+/3+ (≈3.5 V), and Mn 3+/4+ (≈4.0 V vs Na + /Na) redox couples. In situ X‐ray diffraction results reveals that both solid‐solution and two‐phase electrochemical reactions are involved in the sodiation/desodiation processes. The high specific capacity (160 mAh g −1 at 0.2 C), outstanding cyclability (≈92% capacity retention after 500 cycles at 2 C), and the facile synthesis make the Na 3 MnTi(PO 4 ) 3 /C a prospective cathode material for sodium‐ion batteries.