Abstract
Utilization of LiFePO4 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 LiFePO4, 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 LiFePO4 particles have been uniformly coated with a thin polyphenylene film via the spontaneous reaction between LiFePO4 and an aromatic diazonium salt of benzenediazonium tetrafluoroborate. The coated micron-sized LiFePO4, 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 LiFePO4/FePO4 has been understood with density functional theory calculations.
Highlights
Utilization of LiFePO4 as a cathode material for Li-ion batteries often requires size nanonization coupled with calcination-based carbon coating to improve its electrochemical performance, which, is usually at the expense of tap density and may be environmentally problematic
Carbon coatings on LiFePO4 produced by heat treatment tend to be irregular, which does not provide a good connectivity for the particles and the expected performance for battery applications[16]
Powder X-ray diffraction (PXRD), scanning electron microscopy (SEM)/ transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) characterizations (Supplementary Figs 3–5) showed that the micron-sized LiFePO4 is of pure phase and contains no adventitious impurities such as Li2CO3 and LiOH
Summary
Utilization of LiFePO4 as a cathode material for Li-ion batteries often requires size nanonization coupled with calcination-based carbon coating to improve its electrochemical performance, which, is usually at the expense of tap density and may be environmentally problematic. Considerable efforts have been devoted to overcoming the intrinsically low electrical conductivity of LiFePO4, a drawback that hinders its direct use in Li-ion cells[5,6]. Several strategies, such as doping with foreign metal ions, have been explored[7,8,9]. The calcination-based strategies are often energy intensive and can be environmentally unfriendly because of the emission of harmful volatile organic compounds from the thermal decomposition of organic precursors[15]
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