Designing high-performance P3-type Na2/3[Ni1/3Mn2/3]O2 cathodes for Na-ion batteries

Abstract

P3-type layered oxide materials, where Na⁺ ions occupy prismatic sites and layers stack in an ABBCCA sequence, have received relatively limited attention as positive electrode materials for Na-ion batteries (NIBs) due to their low temperature synthesis and poor structural stability. Unlike widely studied O3- and P2-type analogues, conventional P3-type materials often suffer from low crystallinity and mechanical fragility, leading to rapid degradation upon cycling in a non-aqueous Na cell. In this study, we report successful design of high-performance P3-type Na_2/3Ni_1/3Mn_2/3O₂ positive electrode materials synthesized via a novel pathway using spinel-type NiMn₂O₄ precursors. The resulting P3-phase exhibits distinct physicochemical features, including high crystallinity, large particle size, dispersed NiO buffer domains within the bulk, unique axis ordering, and surface exposure of {100} facets, as well as unintended compositional shifts. These attributes effectively suppress phase transitions, surface side reactions, and particle cracking, enabling superior electrochemical performances such as cycling stability and rate capability in Na cells, even without any modifications including elemental doping and surface coating. Our findings highlight the practical potential of P3-type materials through tailored synthesis, addressing key limitations and expanding the design space for next-generation NIB positive electrodes.