A High-Energy NASICON-Type Na3.2MnTi0.8V0.2(PO4)3 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 Na3+xMnTi1-xVx(PO4)(3) cathode materials are designed, which demonstrate not only a multi-electron reaction but also high voltage platform. With five redox couples from V5+/(4+) (approximate to 4.1 V), Mn4+/3+ ( approximate to 4.0 V), Mn3+/2+ (approximate to 3.6 V), V4+/3+ (approximate to 3.4 V), and Ti4+/3+ (approximate to 2.1 V), the optimized material, Na3.2MnTi0.8V0.2-(PO4)(3), realizes a reversible 3.2-electron redox reaction, enabling a high discharge capacity (172.5 mAhg(-1)) and an ultrahigh energy density (527.2 Whkg(-1)). This work sheds light on the rational construction of NASICON-type cathode materials with multi-electron redox reaction for high-energy SIBs.