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 I4(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.