The Influence of Heat-Treatment Temperature on the Cation Distribution of LiNi[sub 0.5]Mn[sub 0.5]O[sub 2] and Its Rate Capability in Lithium Rechargeable Batteries

Abstract

LiNi[subscript 0.5]Mn[subscript 0.5]O[subscript 2] samples were prepared from NiMnO[subscript 3] and Li[subscript 2]CO[subscript 3] in a range of temperatures from 900 to1050°C . Synchrotron X-ray diffraction analysis combined with X-ray absorption spectroscopy showed that LiNi[subscript 0.5]Mn[subscript 0.5]O[subscript 2]segregated into one major Ni[superscript 2+]O -enriched phase and one minor Li[subscript 2]Mn[superscript 4+]O[subscript 3] -enriched phase, where the extent of segregation decreased with increasing synthesis temperature from 900 to1050°C . Scanning and transmission electron microscopy combined with energy dispersive X-ray spectroscopy revealed that the segregated domains exist in individual particles. Although all of the LiNi[subscript 0.5]Mn[subscript 0.5]O[subscript 2] samples showed comparable specific capacity (∼200mAh/g) and capacity retention at low current densities, the rate capability of LiNi[subscript 0.5]Mn[subscript 0.5]O[subscript 2] of 900°C is lower than that of LiNi[subscript 0.5]Mn[subscript 0.5]O[subscript 2] of 1000°C . As X-ray photoelectron spectroscopy analysis showed that all of the LiNi[subscript 0.5]Mn[subscript 0.5]O[subscript 2] samples had comparable surface chemistry, the higher rate capability of LiNi[subscript 0.5]Mn[subscript 0.5]O[subscript 2] of 1000°C can be attributed to reduced cation segregation of Ni[superscript 2+]O -enriched domains in the layered structure of the major phase, having potentially faster lithium diffusion than that of LiNi[subscript 0.5]Mn[subscript 0.5]O[subscript 2] of 900°C .