Electrochemical properties of Li[Ni0.5Mn1.5]O4 cathode materials for lithium secondary batteries prepared by ultrasonic spray pyrolysis method

Abstract

The spinel LiMn2O4 has been extensively investigated as the most promising a cathode material for lithium secondary batteries because of its low cost and environmental advantage1. Many researchers reported that substituted manganese spinel compounds Li[Mn2-xMx]O4 (M= Cr, Co, Ni, Fe, etc)2,3. Recently, it has been reported by Wakihara et al. that doped lithium manganese spinel by ultrasonic spray pyrolysis4,5. In this work, 5V spinel Li[Ni0.5Mn1.5]O2 powders have been prepared by ultrasonic spray pyrolysis method. The particle characteristics, such as crystallite size, particle morphology, size distributions, structural and electrochemical properties are investigated. Shown in Figure 1 are X-ray diffraction (XRD) patterns of the Li[Ni0.5Mn1.5]O4 powders with various synthesis temperature. The XRD analysis indicates that all samples are identified as a single-phase spinel with a space group Fd3m in which the lithium ions occupy the tetrahedral (8a) sites and the transition metal ions reside at the octahedral (16d) sites. Sharp (400) peak of all the samples reveals that highly crystallized manganese oxides were synthesized over 900 oC calcination temperature. Figure 2 show SEM photographs of the powders prepared at the 1000 oC temperature as same condition of Fig. 1(c). The particles are shaped into a well-developed octahedral structure and have size distribution, ranging from approximately to 1-3 ㎛. Figure 3 shows the discharge capacity with number of cycles for the Li[Ni0.5Mn1.5]O4 materials. The charge/discharge current density was 0.2 mA/cm2 (1/6 C) with a cut-off voltage of 3.5 to 5.0 V. Li/Li[Ni0.5Mn1.5]O4 cell delivers an initial discharge capacity of 135 mAh/g with excellent cycling property.