Thermally Engineered Rock‐Salt Surface Nanolayer for Environmentally Stable P2‐Type Sodium‐Ion Battery Cathodes

Abstract Layered manganese (Mn)‐based oxides have garnered significant attention for use in high‐performance sodium‐ion batteries. However, the interfaces of these materials are prone to atmospheric and electrochemical corrosion, which leads to a decline in their electrochemical performance and precludes their commercial viability. In this study, a mechanically robust rock‐salt nanolayer (≈4 nm) is reconstructed on a layered manganese‐based cathode formed through precise heat treatment. The layer demonstrates lattice compatibility with the bulk layered structure and significantly enhances the chemical and electrochemical stability of the cathode surface. During electrochemical cycling, this heat‐induced rock‐salt nanolayer effectively suppressed transition‐metal dissolution and electrolyte corrosion. As a result, the interface‐engineered electrode exhibited excellent cycling performance, maintaining 92.3% of its capacity after 800 cycles, compared with only 55.4% for the untreated electrode. Furthermore, the rock‐salt nanolayer mitigated the moisture‐induced degradation, as evidenced by the structural integrity of the interface‐engineered electrodes. This cost‐effective and scalable strategy offers a promising path for the development of precisely engineered cathode materials for Na‐ion storage.