Suppressing high-voltage phase transition in layered oxide positive electrodes toward stable cycling for sodium ion batteries

Intercalation-type layered oxides are the most promising positive electrodes for next-generation sodium-ion batteries due to their high energy density, low cost, and tunable chemistry. However, these materials are often subjected to substantial phase transitions and lattice changes when cycled at high voltage, leading to fast capacity decay. In this work, we demonstrate a strategically performed low-temperature heat treatment of the desodiated electrode for mitigating the pernicious structural changes in layered P2-type Na2/3Ni1/3Mn2/3O2 electrode. An intergrowth framework forms and consists of a primary layered structure and secondary disordered rock-salt-like nano domains. This intergrowth structure manifests significant enhancement in cycling stability with negligible electro-chemo-mechanical changes due to small lattice variation. Our study demonstrates an effective approach for performance improvements through a straightforward heat treatment and provides insights into the ability to nanoengineering and interface engineering in intergrowth structures.