Multi-faceted highly crystalline LiMn2O4 and LiNi0.5Mn1.5O4 cathodes synthesized by a novel carbon exo-templating method

LiMn2O4 and LiNi0.5Mn1.5O4 powders have been synthesized by a novel cost-effective carbon exo-templating process. It has been observed that controlled nucleation in the pores of highly surface active carbon produces a distinct effect on the powder morphology and crystallinity. Quantitative X-ray phase analyses show single phase spinel structure having Fd3m symmetry for both samples. Field emission electron microscopy reveals particles of size 0.5–1.0 µm with well defined multi-faceted crystals. Cyclic voltammetry results show well separated distinct redox peaks at 4.05/3.92 and 4.17/4.08 V for LiMn2O4/Li and 4.91/4.61 V for LiNi0.5Mn1.5O4/Li coin cells indicating good crystallinity and reversibility of the cathodes compared to that of pristine LiMn2O4 synthesized by conventional combustion process. The LiMn2O4/Li and LiNi0.5Mn1.5O4/Li cells deliver an initial discharge capacity of 110 mA h/g and 122 mA h/g respectively at a current density of 0.05 mA/cm2 and when cycled at 0.2 mA/cm2, the cells maintain 81% and 96% of their initial discharge capacity respectively even after 20 cycles. On the other hand, at the same current density, LiMn2O4 synthesized by conventional combustion process suffers from severe capacity fading (only 37.5% capacity retention after the 25th cycle). The capacity fading rate is found to be very less even at further higher current densities (0.4–0.8 mA/cm2) for both LiMn2O4/Li and LiNi0.5Mn1.5O4/Li cells synthesized by the templating process. The present study reveals that high crystallinity along with multi-faceted morphology shows a remarkable enhancement in capacity as well as rate performance of pristine LiMn2O4 and its Ni derivative.