Chloride-promoted formation of octahedral LiNi0.5Mn1.5O4 crystal with greatly enhanced electrochemical performance

Abstract

Two LiNi0.5Mn1.5O4 samples are synthesized by a low-temperature solid-state method using chlorides or acetates as raw materials, and their crystal structure, size, morphology and electrochemical performance are comparatively investigated. The results show that the two samples have the same crystal structure but with different crystal size and morphology. The LiNi0.5Mn1.5O4 prepared from chlorides shows relatively bigger crystals with a well-developed octahedral shape with {111} faces, while the LiNi0.5Mn1.5O4 prepared from acetates displays a quasi octahedral shape whose edges and corners are not fully developed. Such a difference in crystal size and morphology leads to a big difference in their electrochemical performance, and the octahedral LiNi0.5Mn1.5O4 prepared from chlorides has higher capacity, much better rate capability and cycling performance. Our results suggest that the crystal size and morphology difference of the two samples may be associated with the presence of unreacted chloride in the precursor derived from raw materials of chlorides, and the presence of chloride may effectively promote the formation of octahedral LiNi0.5Mn1.5O4 crystal at low temperature via a solid-state reaction (500°C in this work)