ANODIC STABILITY OF PROPYLENE CARBONATE ELECTROLYTES AT POTENTIALS ABOVE 4V AGAINST LITHIUM - AN ONLINE MS AND INSITU FTIR STUDY

On-line mass spectroscopy (DEMS) and in situ FTIR spectroscopy provide a valuable extension to classical cyclic voltammetry since they enable the identification of reaction products as a function of applied potential. We have compared the CO2 evolution during the electrooxidation of 0.5 M LiAsF6, 0.5 M LiBF4 and 0.5 M LiClO4/propylene carbonate on platinum combining these techniques. The highest CO2 formation rate was measured for 0.5 M LiClO4/PC and the lowest for 0.5 M LiAsF6, both with an on-set potential at 4.0 V against Li/Li+. On-line MS results in 0.5 M LiBF4/PC show strong evidence for the formation (above 4.7 V) of carbonyl fluoride and other fluorinated species parallel to the CO2 evolution. This indicates an anodic decomposition of BF4- anions interacting with oxidized PC species. The role of the OH- ions on the film formation on platinum at 2.0 V against Li/Li+ was also investigated with in situ FTIR for the three electrolytes.