Where to go for the chemical designs of P2 phase Mn-based sodium cathodes?

P2 Mn based cathode materials has become one of the most promising candidate cathode materials due to its high specific capacity, suitable operating voltage and low-cost advantages, but its practical application is still limited by challenges such as high-voltage phase transition, Jahn-Teller effect, Na + /vacancy ordering and air sensitivity. So far, a comprehensive summary study of the corresponding mechanisms and design principles for modification design is still lacking. Based on the multi-scale ontological relationship analysis, this review firstly constructs the systematic research framework of P2 Mn based cathode materials, elucidates the constitutive relationship between the transition metal interlayer slip barrier-oxygen stacking sequence and the thermodynamic origins of the irreversible phase transition, and reveals the influence of the lattice doping-surface passivation synergistic regulation strategy on the dynamic coupling mechanism of the coordination distortion and the lattice oxygen activation in Mn 3+ . At the same time, it provides the theoretical support for deciphering the degradation of the air stability. In addition, this work examines the direction of elemental doping and surface/interfacial engineering to overcome the limitations in capacity and cycling stability, as well as the optimized design of low temperature cathode/electrolyte interface, aiming to summarize the design principle, mechanism and electrochemical performance. Finally, the modified design of such cathode materials is summarized, the existing key scientific issues of these materials are pointed out, and the direction of development in the near future is proposed. This review presents a systematic framework for P2-Mn-based cathodes in sodium-ion batteries, detailing challenge, structural changes and modifying strategy design, especially synergistic optimization of the cathode-electrolyte interface at extreme temperatures. • The thermodynamic origin of irreversible phase transitions was revealed, linking TM sliding barriers with oxygen stacking sequences. • The mechanism of the bulk-surface synergy strategy on coordination distortion and lattice oxygen activation was elaborated. • The consolidation of material and electrolyte design, and perspectives on practical application obstacle are innovatively proposed.