Preparation of LiNi0.5Mn1.5O4 spinel as 5 V cathode material by molten salt method

Abstract

Recently, some research group have reported that transition metal-substituted spinel materials (LiMxMn2-xO4, M=Cr, Co, Fe, Ni, Cu) showed high voltage plateau at around 5 V [1-4]. The capacity and voltage plateau in Li/LiMxMn2-xO4 cells strongly depend on the kind of transition metals (M) and their content. Among those materials, LiNi0.5Mn1.5O4 received many attention for its dominant plateau at around 4.7 V while other materials exhibited two plateau at 4.0 V and ca. 5 V [3]. In general, LiNi0.5Mn1.5O4 material was prepared by a conventional solid state method. However, it involves many problems such as inhomogeneity, irregular morphology, and long synthetic time. Molten salt method is reported to be one of the simplest techniques for preparing ceramic powders including mixed oxides. Yang et al. prepared lithium manganese oxides by molten salt synthesis using LiCl, LiNO3, Li2SO4, and LiOH as flux [5]. Han et al. synthesized LiCoO2 using LiCl-Li2CO3 composite flux [6]. In this work, we prepared LiNi0.5Mn1.5O4 material with LiCl flux by molten salt method. The LiNi0.5Mn1.5O4 powders were characterized by X-ray diffraction, charge/discharge cycling, and scanning electron microscope (SEM). Figure 1 shows XRD pattern of the LiNi0.5Mn1.5O4 powder obtained by molten salt synthesis. All the peaks indicated a well-defined cubic spinel structure without any impurities. Figure 2 shows charge and discharge curves of Li/ LiNi0.5Mn1.5O4 cell between 3.5-5 V at a rate of 0.2 mA/cm2 (20mA/g). LiNi0.5Mn1.5O4 electrode delivers a discharge capacity of 138 mAh/g.