Formation and characterization of a new monoclinic lithium manganese oxide: m-type LixMnO2

Abstract

A new lithium manganese oxide with formula Li_xMnO₂ (x = 0.20.3), denoted as m-phase, has been identified and isolated. First noticed as an intermediate phase during the early steps of the solid-state synthesis of Li–Mn–O spinels at low temperature, it can be isolated by extended annealing and grinding mixtures of finely divided β-MnO2 and LiOH or Li₂CO₃ at 150 °C. Its X-ray pattern can be indexed as primitive monoclinic with a = 938, b = 565.5, c = 490.6 pm and β = 102.2 °. Thermogravimetric and X-ray investigations show that it is stable up to ca. 550 °C. The m-phase structure appears to be rather rigid. It allows only limited lithium extraction in acidic medium and limited electrochemical lithium intercalation, with maximum reversible capacity Δx = 0.25 Li per formula unit. These properties confirm that it is a new oxide, with a rather different behaviour from that of known spinel-type or layered Li–Mn–O compounds.