Exploration of the NaxMoO2 phase diagram for low sodium contents (x ≤ 0.5)

Abstract

The phase diagram of the layered Na_xMoO₂ system for low sodium contents (x ≤ 0.5) was explored using electrochemical (de)intercalation in a sodium ion battery from the Na_2/3MoO₂ composition which is the only one obtained by solid state reaction at high temperature. This study was realized using electrochemistry combined with in situ X-ray diffraction for sodium contents x below 0.5. For the first time, four single phase domains (x = 0.5, 0.4 ≤ x ≤ 0.42, x = 0.37, and x = 0.33) were evidenced during the cycling of the Na_xMoO₂ based battery in the 0.25 ≤ x ≤ 0.5 composition domain. All structural phase transitions are fully reversible. The existence of a superstructure was observed for the Na_0.5MoO₂ and Na_0.33MoO₂ compositions, attributed to the regular arrangements of both the sodium and molybdenum cations.