  Following the successful utilization of LiFePO4 as a novel cathode material
for rechargeable lithium batteries, interest and efforts have grown in the
research of another olivine structured material LiMnPO4 due to its higher
operating potential voltage and energy density. However, high rate performance
for LiMnPO4-based cathode materials has been challenging due to its extremely
low electrical and ionic conductivities. Here, we develop a synthesis of
Fe-doped LiMnPO4 (LiMn0.75Fe0.25PO4) nanorods directly bonded on graphene
sheets (reduced from graphene oxide) to render LiMn0.75Fe0.25PO4 nanorods
superior electrical conductivity. The LiMn0.75Fe0.25PO4 nanorod morphology is
unique to materials grown on graphene over those grown in free solution, and is
ideal for fast Li+ diffusion with the diffusion path of [010] crystallographic
axis along the short radial direction (~20-30nm) of the nanorods. These
together lead to ultrafast discharge within ~30-40 seconds without using a high
carbon content. With high columbic efficiency above 99.5% at a high operating
voltage, our LiMn0.75Fe0.25PO4 nanorods/graphene hybrid exhibits the best rate
performance among all doped LiMnPO4 cathode materials for Lithium ion
batteries.
