Abstract

Single-phase lithium manganese oxide spinels were synthesized in two steps: (1) the preparation of defective spinel precursors with different Li ∶ Mn ratios through lithium insertion into Li-birnessite manganese oxide in a LiNO₃ flux at 400 °C, followed by (2) heat-treatment of the precursors at 750 °C in air. Depending upon the Li ∶ Mn ratio, the precursors yielded three types of single-phase spinels: a lithium-deficient type with lithium and oxygen deficiencies, stoichiometric LiMn₂O₄, and a lithium-rich type with lithium in the 16d-site of space group Fdm but with oxygen deficiency. The electrochemical measurements showed that good rechargeability on cycling between 3–4.3 V could be obtained in all the lithium-rich spinels Li[Li_xMn_{2 − x}]O_{4 − δ}, where 0 < x < 0.33 and δ < 0.2.