Synthesis and Electrochemical Properties of ZnO-coated LiNi0.5Mn1.5O4 Spinel Materials on Elevated Temperature Cycling for Lithium Secondary Batteries

초록

Spinel LiMn2O4 is one of the most promising cathode materials due to low cost, abundance, and nontoxicity. However, the spinel LiMn2O4 electrode shows good stability during cycling at room temperature but a poor cycling behavior at elevated temperature, e.g. 50-80℃. Recently, some research groups have reported that transition metal-substituted spinel materials (LiMxMn2-xO4, M = Cr, Co, Fe, Ni) showed a higher voltage plateau at around 5 V. In larger scale batteries for zero emission vehicles, the cathode materials with the high energy density are a critical issue for development. Although the liquid electrolyte oxidation at the electrode surface is a barrier for practical use for 5 V cathode materials, improved electrolytes have recently made it possible to explore the cathode materials with the potential range to ca. 5 V. The capacity and 5 V plateau in Li/LiMxMn2-xO4 cells strongly depend on the kind of transition metals (M) and their concentration. It has been well known that the 5 V plateau is originated from oxidation of substituted transition metals (M), while 4 V plateau is associated with Mn3+ to Mn4+. There are no reports that have been studied the cycling performance of 5 V cathode materials at elevated temperature so far. In this paper, we study the effect of sol-gel coating of ZnO on LiNi0.5Mn1.5O4 particle surface on the electrochemical cycling behavior of the electrode in the 5 V region at elevated temperature. Also structural change of host materials after cycling was characterized by means of charge/discharge experiments, X-ray diffraction (XRD).