Structural and Electrochemical Analyses on the Transformation of CaFe(2)O(4)-Type LiMn(2)O(4) from Spinel-Type LiMn(2)O(4)

[Image: see text] Lithium manganese oxides have received much attention as positive electrode materials for lithium-ion batteries. In this study, a post-spinel material, CaFe(2)O(4)-type LiMn(2)O(4) (CF-LMO), was synthesized at high pressures above 6 GPa, and its crystal structure and electrochemical properties were examined. CF-LMO exhibits a one-dimensional (1D) conduction pathway for Li ions, which is predicted to be superior to the three-dimensional conduction pathway for these ions. The stoichiometric LiMn(2)O(4) spinel (SP-LMO) was decomposed into three phases of Li(2)MnO(3), MnO(2), and Mn(2)O(3) at 600 °C and then started to transform into the CF-LMO structure above 800 °C. The rechargeable capacity (Q(recha)) of the sample synthesized at 1000 °C was limited to ∼40 mA h·g(–1) in the voltage range between 1.5 and 5.3 V because of the presence of a small amount of Li(2)MnO(3) phase in the sample (=9.1 wt %). In addition, the Li-rich spinels, Li[Li(x)Mn(2–x)]O(4) with x = 0.1, 0.2, and 0.333, were also employed for the synthesis of CF-LMO. The sample prepared from x = 0.2 exhibited a Q(recha) value exceeding 120 mA h·g(–1) with a stable cycling performance, despite the presence of large amounts of the phases Li(2)MnO(3), MnO(2), and Mn(2)O(3). Details of the structural transformation from SP-LMO to CF-LMO and the effect of Mn ions on the 1D conduction pathway are discussed.