Investigation of Structural Evolution in Anionic-Engineering P2-NaxMnO2 Cathodes

Sodium-ion batteries (SIBs) are receiving increasing attention due to the abundance and wide distribution of sodium resources compared to lithium. Among various sodium storage cathodes, P2-type Na2/3MnO2 (P2-NMO) layered transition metal material stands out as a highly promising candidate due to its straightforward synthesis, cost-effectiveness, high theoretical specific capacity (265 mAh g-1). However, at high state-of-charge (upon deep Na extraction), such materials tend to undergo a phase transition with a volume change and consequent structural degradation in turn leading to a capacity loss over long cycles. Here, we propose a sulfuration approach to stabilize the P2-NMO structure, as sulfur anions are partially integrated into the oxygen sites within the lattice structure. Impressively, the sulfur anions within the internal lattice could reversibly participate in the redox process and improve the integral coordination stability by mitigating undesired manganese migration.