Enhanced Electrochemical Stability of Graphite Anodes via Adsorption of Reductively Polymerizable Dibromothiophene in Lithium Ion Batteries

This is the first report showing the improvement of electrochemical stability of a graphite (Gt) anode in lithium ion batteries (LIBs) by using 2,5-dibromothiophene (DBT) as a surface-adsorbent. DBT adsorbed onto Gt underwent reductive electro-polymerization during the first discharge (Li+ intercalation) to form a protective cap over catalytically active sites of Gt. Poly-DBT, thus formed, helped the formation of a compact and thin SEI layer during subsequent Li+ ion intercalation, preventing the continuous formation of SEI layers. The cyclic performance of a half-cell with DBT-adsorbed Gt was compared with half-cells composed of various anode materials (i.e., mere Gt, pyrrole-adsorbed Gt, and thiophene-adsorbed Gt). The adsorption of small amounts of DBT on Gt improved the capacity retention of the half-cells by nearly 7.5% and decreased a fading rate to 0.09 mAh.g(-1).cycle(-1), relative to mere Gt which showed a fading rate of 0.17 mAh.g(-1).cycle(-1). The dissolution of DBT in electrolyte, however, had detrimental effects on cell performance, suggesting that surface-adsorption of DBT is more beneficial. The formation of a compact and thin SEI layer on DBT-adsorbed Gt was confirmed by surface-composition analysis and impedance spectroscopy. (C) 2014 The Electrochemical Society.