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

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.