Synthesis and Electrochemical Behavior of Bare and ZnO-coated LiFeO2-LixMnO2 materials

Abstract

It is well known that many research groups have tried many interactive improvements to the performance of lithium secondary batteries. In the case of cathode materials, layered LiMO2 (M=Co, Ni, Mn, Fe...) compounds were focused on � 새 their cost, thermal safety, and environmental aspects. Among them, the LiFeO2 compound is one of the best candidate from the viewpoint of cost because iron is the most abundant and cheapest metal in the world. Recently, we reported that two kinds of LiFeO2 materials, orthorhombic LiFeO2 obtained at low temperature (150oC) and LixFeyOz obtained at high temperature (800oC). However, many problems still remained; such as a lower operating voltage, no electrochemical activity, and a poor cycle characteristic during the cycling test. In order to solve this problem, we tried to synthesize the LiMnxFe1-�2 and Mn-substituted LiFeO2 materials for improving the electrochemical characteristics of LiFeO2 including the problem of the low operating voltage. Although some research groups have been investigating the role and meaning of the reaction of Fe3+/4+ in the LiCo1-xFexO2 and LiNi1-xFexO2 systems, we believe that it is the first trial in which the cycling and electrichemical performances of LiFeO2 system were improved by substituting Mn in this study, because previous studies were conduced on the LiCoO2 and LiNiO2 main systems. Furthermore, Tabuchi et al. recently reported that the Fe-substituted Li2MnO3 system as a 4V cathode materials. They suggested that it showed a high possibility for use as a new cathode material in the 4V region, because it presented a unique Fe3+/4+ redox at 4V and could form an electrochemically active phase of LiFeO2 and Li2MnO3. However, one different thing in this study versus the above report was that the orthorhombic LiFeO2 material made by our group exhibited a fairly good cycle performance, which was the starting point to develop a new type of Fe-based materials, because they believed that the conventional and some layered LiFeO2 materials, which were used in their study, are inactive and impossible to undergo insertion/extraction of lithium ions inti the FeO2 layers. We report here the powder property and electrochemical behavior of a new type of Fe-based material, a solid solution type of LiFeO2 and LixMnO2, which showed an excellent cycle performance using ZnO-doping technique at room and high temperatures.