Synthesis and electrochemical characteristics of lithium iron oxides(LixFeyOz) for Lithium secondary batteries

초록

The first row (3d) transition metal oxides have become attractive candidates as cathodes for lithium secondary batteries due to their light weight. Among them, various iron compounds have been evaluated for potential use as cathode active materials in lithium secondary batteries due to their environmental advantage, abundance and low cost. Unfortunately, Lithium iron oxide prepared by solid-state reaction at low temperature is difficult to synthesize because of its instability. Therefore other groups are reported that ion exchange of the layered α-NaFeO2 with LiOH·H2O under hydrothermal condition and molten salts method. The recent synthesis has being studied by alcohol H+/Li+ ion-exchange which is complex process. In this work, Lithium iron oxides(LixFeyOz) were synthesized by solid-state reaction and sol-gel method at low temperature. Powder X-ray diffraction (Rigaku, Rint-2000) using CuKα radiation was used to identify the structure properties of as-prepared powders and cycled electrodes. We have obtained various structure of LixFeyOz such as spinel-like phase, cubic LiFeO2 and tetragonal LiFeO2. The sample has nanocrystalline with 10∼30 nm size. The material calcined exhibits discharge capacity of 170 mAh/g after 50th cycles in the range 1.5-4.5 V. On the other hand, material calcined at higher temperatures exhibit much lower discharge capacity.