Lithium surface protection by polyacetylene in situ polymerization

Direct acetylene polymerization at ambient temperature on a Li metal surface and polyolefin separator with Ziegler–Natta catalyst was developed. Thin conducting polyacetylene films with strong adhesion to Li or polyolefin surface was formed and studied by electrochemical methods. AC impedance measurements and charge/discharge tests were applied for prepared coin cells with LiCoO2 as a cathode material in the presence of 1 M LiPF6 in dimethyl carbonate, ethylene carbonate, propylene carbonate (5:3:2 vol) electrolyte. Three kinds of polyolefins were used to prepare composite separators with polyacetylene: polypropylene (PP), polyethylene (PE) and three-layer type: PP–PE–PP.The polyacetylene film thickness on Li metal or polyolefin separator was easily controlled by catalyst concentration and polymerization time. It was shown that high ionic conductivity (7.5 × 10−5 S cm−1) might be achieved due to higher porosity of a polyethylene separator. Li–polyacetylene electrodes showed highest ionic conductivity and stability in charge/discharge tests.