Synthesis and structural changes of LixFeyOz material prepared by a solid-state method

Lithium iron oxides (LixFeyOz) have been synthesized using LiOH and α-FeOOH by a solid-state method at various temperatures (200–800 °C). The lithium iron oxide obtained at 200 °C is composed of three types of structure namely, α-LiFe5O8, β-LiFe5O8, and a trace of cubic α-LiFeO2. It exhibits not only a high initial discharge capacity 215 mAh g−1, but also excellent cycling retention from the 11th to the 50th cycle (95%) between 1.5 and 4.5 V. On the other hand, the powder obtained at 800 °C has a well-developed, single α-LiFeO2 phase and gives a very poor cycle performance below 5 mAh g−1under the same test conditions. It is also found that lithium iron oxide obtained at 200 °C is first transformed into the spinel LiFe5O8 phase and is then converted into the tetragonal LiFeO2 phase after a long-term cycling. It is suggested that the tetragonal LiFeO2 phase might assist the stabilization of the original lithium iron oxide structure on cycling.