2005 年 73 巻 10 号 p. 874-882
Two lithium iron oxides have been synthesized at low temperatures by the conventional solid-state method. Orthorhombic LiFeO2 has been synthesized using LiOH and γ-FeOOH at 150°C was composed of orthorhombic LiFeO2 and small amount of spinel LiFe5O8 phases. A Li/LiFeO2 cell showed not only a fairly high initial discharge capacity of over 150 mAh g−1 but also a good cycle retention rate at room temperature. It was found that the orthorhombic phase of the LiFeO2 underwent a structural change to the LiFe5O8 spinel phase in the first cycle. Especially, it showed a severe structural change during the first discharge process, which might be the main reason for the capacity loss of the Li/LiFeO2 system. An amorphous-like LixFeyOz has been synthesized using LiOH and α-FeOOH at 200°C consisted of three kinds of structures, LiFe5O8, Li5FeO4, and a trace of cubic α-LiFeO2 A Li/LixFeyOz cell showed a very high initial discharge capacity (215 mAh g−l) as well as an excellent cycle retention rate (95%) from the 11th to the 50th cycle. It was found that LixFeyOz material was transformed into the spinel LiFe5O8 and tetragonal β-LiFeO2 phases after long-term cycling.