Electrochemical performance of nano-sized ZnO-coated LiNi0.5Mn1.5O4 spinel as 5 V cathode materials at elevated temperatures

Abstract

In view of the economic and environmental advantage, spinel LiMn2O4 has been demonstrated to be the most promising positive electrode material for lithium-ion batteries because they are cheaper, less toxic, and easier to prepare than their alternatives (LiCoO2 and LiNiO2). An important problem prohibiting them from wider use as a cathode for lithium-ion batteries is structual instability from acidic HF attack on the spinel particles at elevated temperatures. The poor cycling performance could be much improved by cation and anion substitution, and surface treatment of electrode active materials. Recently, some research groups have reported that transition metal-substituted spinel materials (LiMxMn2-xO4, M=Cr, Co, Fe, Ni, Cu) exhibit a higher voltage plateau at around 5 V. The capacity and voltage plateau in Li/LiMxMn2-xO4 cells strongly depend on the nature and the concentration of transiton metals (M). It has been well known that the 5 V plateau originates from the oxidation of the substituted transition metals (M), while the 4 V plateau is associated with Mn3+ to Mn4+ transition. In this study, we examined the effect of the amount of ZnO-coating on the electrochemical performance and structural stability of the LiNi0.5Mn1.5O4 electrode in the 5 V region at elevated temperature. The 1.5 wt% ZnO-coated Li1.06Ni0.5Mn1.5O4 electrode delivers an initial discharge capacity of 137 mAh g-1 without any capacity loss even after 50 cycles at 55 ℃