Na-ion batteries are considered to be environmentally favourable alternatives to Li-ion batteries, particularly in the extremely large-scale application of grid storage, given the abundance of Na. Among them, sodium layered oxides are very important cathode materials with good sodium mobility and high specific capacity. Layered transition metal oxides Na_XMeO₂ consist of layers of MeO₆ octahedra to preserve 2D transport channels for direct Na ion diffusion. For metal selections, Me can be Fe, Mn, Co, Cr, Ni, Ti, V and their combinations. Interestingly, single transition metal oxides show worse battery performance than binary or ternary transition metal systems, making composition studies imperative. Metal combinations can achieve tuneable properties with structure, electrochemical performance, and cycling stability.

In this application note, air/moisture stability is effectively and systematically investigated with XPS, paving the way for material stability to be modified through rational design.