Boosting the electrochemical performance and moisture stability of O3-type NaNi1/3Fe1/3Mn1/3O2 cathodes using novel Na2MoO4 coatings prepared via a polyvinylpyrrolidone-anchored complex coating process

Abstract

O3-type layered oxides are considered highly promising cathode materials for sodium-ion batteries owing to their notable specific capacities, high theoretical energy densities, and low costs. However, the applications of O3-type layered oxides are limited owing to their structural degradation during charge–discharge cycles and poor moisture stability, which negatively affect their performance and durability. Notably, surface modifications of these materials play a crucial role in mitigating these challenges by providing a protective layer safeguarding the cathode material. In this study, Na₂MoO₄ (NMO) was successfully coated onto the surface of Na(Ni_1/3Fe_1/3Mn_1/3)O₂ (NFM) using a polyvinylpyrrolidone (PVP)-assisted wet chemical method. Despite their low costs and good electrical conductivities, Mo-based coatings are yet to be explored as potential coating materials for O3-type layered oxide cathodes. Here, the main PVP chain facilitates the formation of a uniform NMO coating layer by effectively anchoring Mo⁶⁺ ions onto the surface of the (Ni_1/3Fe_1/3Mn_1/3)C₂O₄·xH₂O ((NFM)C₂O₄) precursor. The presence of the NMO nanocoating layer on the NFM surface was confirmed via various characterization techniques. The NMO-coated NFM exhibited notable improvements in electrochemical performance compared to pristine NFM. In addition, the NMO-coated NFM exhibited superior moisture stability. This study presents an effective strategy to simultaneously improve the electrochemical performance and moisture stability of O3-type layered cathodes for sodium-ion batteries.