Achieving Fully Reversible Conversion in MoO3 for Lithium Ion Batteries by Rational Introduction of CoMoO4.

Electrode materials based on conversion reactions with lithium ions generally show much higher energy density. One of the main challenges in the design of these electrode materials is to improve initial Coulombic efficiency and alleviate the volume changes during the lithiation-delithiation processes. Here, we achieve fully reversible conversion in MoO3 as an anode for lithium ion batteries by the hybridization of CoMoO4. The porous MoO3-CoMoO4 microspheres are constructed by homogeneously dispersed MoO3 and CoMoO4 subunits and their lithiation/delithiation processes were studied by ex situ TEM to reveal the mechanism of the reversible conversion reaction. Co nanoparticles are in situ formed from CoMoO4 during the lithiation process, which then act as the catalyst to guarantee the reversible decomposition of Li2O, thus effectively improving the reversible specific capacity and initial Coulombic efficiency. Moreover, the pores in MoO3-CoMoO4 microspheres also greatly enhance their mechanical strength and provide enough cavity to alleviate volume changes during repeated cycling. Such a design concept makes MoO3 to be a potential promising anode in practical applications. The full cell (LiFePO4 cathode/MoO3-CoMoO4 anode) displays a high capacity up to 155.7 mAh g-1 at 0.1 C and an initial Coulombic efficiency as high as 97.35%. This work provides impetus for further development in electrochemical charge storage devices.