A High-Energy NASICON-Type Na MnTi V (PO ) Cathode Material with Reversible 3.2-Electron Redox Reaction for Sodium-Ion Batteries.

Na superionic conductor (NASICON) structured cathode materials with robust structural stability and large Na diffusion channels have aroused great interest in sodium-ion batteries (SIBs). However, most of NASICON-type cathode materials exhibit redox reaction of no more than three electrons per formula, which strictly limits capacity and energy density. Herein, a series of NASICON-type Na MnTi V (PO ) cathode materials are designed, which demonstrate not only a multi-electron reaction but also high voltage platform. With five redox couples from V (≈4.1 V), Mn (≈4.0 V), Mn (≈3.6 V), V (≈3.4 V), and Ti (≈2.1 V), the optimized material, Na MnTi V (PO ) , realizes a reversible 3.2-electron redox reaction, enabling a high discharge capacity (172.5 mAh g ) and an ultrahigh energy density (527.2 Wh kg ). This work sheds light on the rational construction of NASICON-type cathode materials with multi-electron redox reaction for high-energy SIBs.