In Situ TEM Observation of Local Phase Transformation in a Rechargeable LiMn2O4 Nanowire Battery

Abstract

We developed a “nanobattery” consisting of LiMn2O4 nanowires, ionic liquid electrolyte, and Li4Ti5O12 crystals and performed in situ transmission electron microscope observation during charge and discharge cycles. The LiMn2O4 nanowire was found to be changed into the tetragonal phase at the interface region with electrolyte during the discharge process of the 4 V reaction (vs Li/Li+). This result is explained by the lithium accumulation due to the different local lithium diffusion rates: the lithium ions were inserted into the nanowire at a higher rate than they diffused toward the bulk side of the nanowire. We also found that the LiMn2O4 nanowire cathode was restored to be cubic phase without any fracture in the charge process. No fracture during the cubic-tetragonal transition is promising for the long-lifetime battery with LiMn2O4 nanowire cathode.