Sb-Doped Biphasic P2/O3-Type Mn-Rich Layered Oxide Cathode Material for High-Performance Sodium-Ion Batteries

Mn-rich P2-type layered oxide cathode materials suffer from severe capacity loss caused by detrimental phase transition and transition metal dissolution, making their implementation difficult in large-scale sodium-ion battery applications. Herein, we introduced a high-valent Sb⁵⁺ substitution, leading to a biphasic P2/O3 cathode that suppresses the P2-O2 phase transformation in the high-voltage condition attributed to the stronger Sb-O covalency that introduces extra electrons to the O atom, reducing oxygen loss from the lattices and improving structural stability, as confirmed by first-principle calculations. Besides, the enhanced Na⁺ diffusion kinetics and thermodynamics in the modified sample are associated with the enlarged lattice parameters. As a result, the proposed cathode delivers a discharge capacity of 142.6 mAh g^-1 at 0.1C between 1.5 and 4.3 V and excellent performance at a high mass loading of 8 mg cm³ with a specific capacity of 131 mAh g^-1 at 0.2C. Furthermore, it also possesses remarkable rate capability (90.3 mAh g^-1 at 5C), specifying its practicality in high-energy-density sodium-ion batteries. Hence, this work provides insights into incorporating high-valent dopants for high-performance Mn-rich cathodes.