Impact of 2-Vinylpyridine as Electrolyte Additive on Surface and Electrochemistry of Graphite for C∕LiMn[sub 2]O[sub 4] Li-Ion Cells

Abstract

For lithium-ion batteries of C/spinel Li-Mn-O, severe capacity loss occurs after storage of the battery at 50C. According to our previous studies, this occurrence is predominantly attributable to degradation of the carbon anode, which was induced by electroreduction of MnII dissolved from the spinel; this step is followed by the irreversible electrochemical reaction at the graphite/Mn deposits/electrolyte interface. 2-Vinylpyridine VP used as an additive in the electrolyte suppressed this degradation; therefore, improving the battery performances. During the first "charge," the electrochemical reductive polymerization of VP monomers at about 0.9 V vs. Li/Li + resulted in the film formation of poly2-vinylpyridine on the graphite surface. The quantity of charge passed for the polymeric film formation depends on the amount of VP addition. Surface analyses using X-ray photoelectron spectroscopy and electron microscopy confirmed that the electrodeposited film blocked the electroreduction of dissolved MnII on the graphite electrode.