Unlocking the energy capabilities of micron-sized LiFePO4

Abstract Utilization of LiFePO 4 as a cathode material for Li-ion batteries often requires size nanonization coupled with calcination-based carbon coating to improve its electrochemical performance, which, however, is usually at the expense of tap density and may be environmentally problematic. Here we report the utilization of micron-sized LiFePO 4 , which has a higher tap density than its nano-sized siblings, by forming a conducting polymer coating on its surface with a greener diazonium chemistry. Specifically, micron-sized LiFePO 4 particles have been uniformly coated with a thin polyphenylene film via the spontaneous reaction between LiFePO 4 and an aromatic diazonium salt of benzenediazonium tetrafluoroborate. The coated micron-sized LiFePO 4 , compared with its pristine counterpart, has shown improved electrical conductivity, high rate capability and excellent cyclability when used as a ‘carbon additive free’ cathode material for rechargeable Li-ion batteries. The bonding mechanism of polyphenylene to LiFePO 4 /FePO 4 has been understood with density functional theory calculations.