P2-phase Fe1/2Mn1/2 and Ni1/4Mn3/4 manganese-based system materials for advanced sodium-ion batteries: Quo Vadis?

Driven by the growing demand for efficient energy storage in renewable systems, sodium batteries have triggered extensive attention for scaled applications due to their rapid ion kinetics, exceptional cycling stability, and cost-effectiveness. Among the cathode candidates, manganese-based layered oxides emerge as particularly promising owing to their economic viability and high theoretical capacity, with Fe-Mn and Ni-Mn binary systems demonstrating remarkable synergistic effects. In this study, focusing on the Fe1/2Mn1/2 and Ni1/4Mn3/4 Mn-based oxide systems with specific stoichiometric ratios, we systematically reviewed the research progress of key modification strategies, such as bulk phase doping and surface coating, and revealed the mechanism of the transition metal coordination reconstruction on the diffusion kinetics of sodium ions. Based on the in-depth analysis of the function mechanism of the material, the study further points out that the construction of a new type of multifunctional composite cathode through multi-scale structural design is an important way to realize the synergistic enhancement of high energy density and high cycling stability, in which the optimization of the electronic structure of the bulk phase and the enhancement of the interfacial stability are especially critical. This paper not only provides a theoretical basis for the rational design of manganese-based oxide cathode, but also points out the direction of technological breakthrough for the development of the next-generation sodium energy storage system that can be adapted to the extreme working conditions.