Structure-electrochemical property relationships in monophasic and biphasic layered oxide cathodes for Na-ion batteries

Abstract

The field of energy storage has witnessed significant advancements, with a growing focus on sustainable and efficient battery materials. Amidst global resource constraints and the demand for renewable energy solutions, sodium-ion batteries (SIBs) are emerging as a promising alternative to lithium-ion batteries due to the abundance and low cost of sodium. However, achieving high energy density, structural stability, and energy efficiency in SIBs presents notable challenges, particularly concerning cathode materials [1]. Layered oxide materials, commonly composed of sodium-transition metal oxides like NaₓMeO₂, exhibit varying phase structures such as P2, P3, and O3. These phases refer to different atomic arrangements within the material, each influencing electrochemical properties like ion mobility and capacity retention. In terms of electrochemical properties, the P2 type frameworks show higher ionic conductivity and structural stability but suffer from low specific capacities. In contrast, O3 type materials exhibit relatively higher specific capacities but are known to undergo O3 to P3 phase transformations during desodiation, limiting their cyclability. P3 type compounds, on the other hand, have properties similar to P2 phases. These are known to have good Na+ transport properties and form at lower calcination temperatures, which makes it easier to synthesize [2].