Low-temperature synthesis and electrochemical lithium intercalation behaviour of defect Li-Mn-O spinel oxide

Abstract

Disordered spinel phases with composition Li_{≈ 0.35}MnO_{2 –δ}·nH₂O have been obtained by room-temperature aqueous oxidation of Mn^±2 in LiOH medium. A thermogravimetric study shows that this phase can be dehydrated and reversibly exchanges oxygen in the temperature range 250–500 °C. The anhydrous product obtained by annealing at 300 °C in oxygen is a defect spinel with stoichiometry Li _0.70.Mn₂O₄. Its electrochemical behaviour in lithium cells shows improved capacity retention on charge-discharge cycling compared to high-temperature, stoichiometric LiMn₂O₄. This difference is attributed to the small grain size (in the 0.1 µm scale) and structural disorder, which favour the electrolyte–electrode material contact and lithium diffusion in the low-temperature phase.