High-pressure synthesis and electrochemical properties of tetragonal LiMnO 2 .

Tetragonal structured LiMnO 2 (t-LiMnO 2 ) samples were synthesized under pressures above 8 GPa and investigated as a positive electrode material for lithium-ion batteries. Rietveld analyses based on X-ray diffraction measurements indicated that t-LiMnO 2 belongs to a γ-LiFeO 2 -type crystal structure with the I 4 1 / amd space group. The charge capacity during the initial cycle was 37 mA h g -1 at 25 °C, but improved to 185 mA h g -1 at 40 °C with an average voltage of 4.56 V vs. Li + /Li. This demonstrated the superiority of t-LiMnO 2 over other lithium manganese oxides in terms of energy density. The X-ray diffraction measurements and Raman spectroscopy of cycled t-LiMnO 2 indicated an irreversible transformation from the γ-LiFeO 2 -type structure into a Li x Mn 2 O 4 spinel structure by the displacement of 25% of the Mn ions to vacant octahedral sites through adjacent octahedral sites.