Synthesis of LiMnO2 with α ‐ NaMnO2‐Type Structure by a Mixed‐Alkaline Hydrothermal Reaction

A metastable form of LiMnO 2 with α-NaMnO 2 -type structure (layered-LiMnO 2 ) was synthesized directly from Mn 2 O 3 by hydrothermal reaction at 220°C using aqueous mixed-alkaline solutions such as LiOH.H 2 O-KOH or LiCl-KOH. Relatively highly crystallized samples could be obtained by a one-step process, compared with that of an ion-exchanged sample obtained previously. Magnetization data between 83 and 500 K show that manganese ions are present as 3+ in high-spin state and a broad maximum is observed ca. 250 K, suggesting a yield of antiferromagnetic ordering below room temperature. Preliminary electrochemical tests using coin-type cells in which lithium metal was used as negative electrode material show that about 100 mAh/g specific capacity remained at the eighth cycle between 2.0 and 4.3 V, whereas the initial charge capacity reached ca. 210 mAh/g up to 4.3 V.