A Novel Pentanary Metal Oxide Cathode with P2/O3 Biphasic Structure for High‐Performance Sodium‐Ion Batteries

Abstract The rapid capacity loss suffered by P2‐type Mn‐based layered oxide cathode materials, caused by deleterious high‐voltage phase transformations and the dissolution of active materials, greatly limits their application in large‐scale sodium‐ion battery installations. In this study, a novel P2/O3 biphasic cathode is developed using a multi‐element (Fe, Mg, and Li) co‐substitution strategy. The results of ex situ X‐ray diffraction analyses and the absence of significant voltage plateaus in the charge–discharge profiles of cells featuring the proposed cathode indicate that deleterious phase transformations and concomitant lattice mismatch in the high‐voltage region are effectively suppressed because of the topotactic intergrown structure of the resulting cathode. The optimized cathode also demonstrates improved structural stability and enhanced Na + diffusion kinetics, owing to the incorporation of stabilizing dopant pillars and suppressed metal‐ion dissolution. Hence, the resulting Na half cell demonstrates a high initial capacity of 170.5 mA h g −1 at 0.1 C and excellent rate capability (106.6 mA h g −1 at 10 C). Furthermore, the resulting Na full cell, featuring a hard carbon anode, displays excellent cycling stability (72.1% capacity retention after 400 cycles), demonstrating its practical viability. This study presents the design and optimization of high‐performance Mn‐based cathodes.