Synergistic modulation of bulk and interface structures in Ni-Mn-based O3-type cathodes via dual-Y strategy for highly stable sodium-ion batteries

The practical application of O3-type layered oxide cathode materials in sodium-ion batteries is limited by their insufficient structural stability and poor interfacial compatibility, especially under high-voltage operation. In this work, a thin Y 2 O 3 coating is applied to the surface of Na 0.9 Cu 0.12 Ni 0.33 Mn 0.42 Ti 0.13 O 2 (CNMT). During high-temperature annealing, partial diffusion of Y 3+ ions into the CNMT lattice results in an expansion of the interlayer spacing within the sodium layer and a reduction in lattice oxygen vacancies. Owing to the stabilized Y 2 O 3 -modified interface and improved structural integrity, the CNMT modified with 2 wt% Y 2 O 3 (CNMT-2Y) demonstrates superior cycling performance in the voltage range of 2.2–4.3 V. Specifically, in a half-cell configuration, CNMT-2Y delivers an initial discharge capacity of 130.9 mAh g −1 and maintains 94.35 % of its capacity after 100 cycles at a current density of 100 mA g −1 . After being exposed to ambient air for 10 days, the material still retains 89.62 % of its capacity over 100 cycles under the same conditions, significantly outperforming the pristine CNMT (83.54 %). In a full-cell setup with hard carbon (HC) as the anode, CNMT-2Y provides an initial discharge capacity of 119.5 mAh g −1 and retains 77.14 % of its capacity after 150 cycles at 100 mA g −1 within 1.5–4.2 V. This facile dual-modification strategy shows promising potential for promoting the commercialization of O3-type layered oxide cathode materials.