Rationally designing the composition and phase structure of Ni-Fe-Mn ternary layered oxide system for high-voltage sodium-ion batteries

Sodium-ion batteries are the prominent device for stationary energy storage system and low-speed electric vehicles. However, the practical application is still limited by the unsatisfied performance and high cost of the cathode side, which strictly requires the development of high voltage, high capacity, and earth-abundant cathode material. Ni-Fe-Mn ternary layered oxide has been recognized as one of the most promising standard type of cathodes. However, the composition and phase structure on high-voltage characteristics have not been well investigated. Herein, selecting the typically high-voltage cathode of P2-Na_0.67Ni_0.33Mn_0.67O₂ as a parent material, we fabricate ten Ni-Fe-Mn ternary layered oxides through replacing the Ni, Mn, or both Ni and Mn by Fe. The thermodynamically stable phase diagram for those materials is presented. The electrochemical properties for all the samples are investigated in detail. Three potential Ni-Fe-Mn ternary layered oxides are picked up considering the energy density, cycle stability, kinetics, cost price, and working voltage, which demonstrate great potential for surpassing the performance of lithium iron phosphate. The related electrochemical reaction and fading mechanism are well revealed. This work provides some new foundational Ni-Fe-Mn ternary layered materials for high-voltage sodium-ion batteries. © 2025