Structure and Electrochemical Characterization of LiNi0.5Mn1.5-xTixO4 prepared by Solid-state Reaction Method

초록

The effect of Ti substitution for Mn on the structure and electrochemical properties of the LiNi0.5Mn1.5-xTixO4 was studied. The LiNi0.5Mn1.5-xTixO4 (x=0~1.0) was successfully synthesized at 900℃ by solid-state reaction method. Additional annealing was used for the ordering of transition metals in octahedral sites. X-ray diffraction (XRD) and selected-area electron diffraction (SAED) study clearly showed that Ti substitution leads to the disordering of the transition metals and consequently lowers the symmetry from primitive simple cubic structure (P4332) to face-centered spinel (Fd3m). Electron diffraction patterns of the LiNi0.5Mn1.5-xTixO4 showed stacking faults which operating voltages, faster lithium ion diffusion, and better rate capability than Ti-free LiNi0.5Mn1.5-xTixO4 confirmed by electrochemical tests including GITT measurement. In addition, ex-situ XRD data of the delithiated LiNi0.5Mn1.5-xTixO4 LiNi0.5Mn1.5-xTixO4 (x=0, 0.3, and 0.5) showed that phase transition was suppressed with increasing Ti content. A large amount of Ti substitution in LiNi0.5Mn1.5-xTixO4, however, exhibited low discharge capacity, which would be due to the blocking migration pathway of electrons by the Ti4+(d0) ions in octahedral sites.