Spinel LiNi0.5Mn1.5O4 as superior electrode materials for lithium-ion batteries: Ionic liquid assisted synthesis and the effect of CuO coating

The LiNi0.5Mn1.5O4 with different morphologies have been successfully prepared through co-precipitation route in mixed solution containing 1-dodecyl-3-methylimidazolium bromide ([C12mim]Br) and H2O with different mass ratios and followed by a solid reaction at high temperature. The morphology of LiNi0.5Mn1.5O4 varies with the increasing ratio of [C12mim]Br. These samples synthesized at three kinds of concentrations present flake-like morphology, agglomerated flake-like structure and polygon particles with size about 700 nm, respectively. The as-prepared LiNi0.5Mn1.5O4 with polygon structure presents the highest discharge capacity. The optimal LiNi0.5Mn1.5O4 sample was modified with 1, 3 and 5 wt.% CuO, respectively. The electrochemical testing results demonstrate 3 wt.% CuO-modified material had the capacity retention of higher than 95% after 100 cycles, and high capacity of 98.7 mAh g−1 at 10 C rate, in comparison with the capacity retention of 83% and capacity of 63.6 mAh g−1 for the pristine one. The remarkably improved rate performance and cycling stability can be attributed to CuO coating, which acts as an effective lithium-ion conductor and a protective material against corrosion from electrolyte.