IN-SITU INVESTIGATION OF THE ELECTROCHEMICAL REDUCTION OF CARBONATE ELECTROLYTE-SOLUTIONS AT GRAPHITE-ELECTRODES

The reductive decomposition of carbonate electrolyte solutions contain ing lithium ions was studied by differential electrochemical mass spec trometry (DEMS) and subtractively normalized interfacial Fourier trans form infrared spectroscopy (SNIFTIRS). The influence of the compositio n of the negative electrode on its electrochemical behavior was invest igated by varying the graphite/binder ratio and using nongraphitic mat erials. The effect of different electrolyte salts was studied in a 1:1 ethylene carbonate (EC)/dimethyl carbonate (DMC) mixture. In addition , EC/DMC-based electrolyte solutions containing different amounts of w ater were used to investigate the influence of H2O on the performance of graphite electrodes. Ethylene and hydrogen were the volatile decomp osition products monitored by DEMS. Ethylene evolution is restricted t o a potential region between about 0.8 and 0.3 V vs Li/Li+ and occurs only during the first cycle. Hydrogen begins to evolve at about 1.3 V vs Li/Li+ in the first cycle and the amount of gas decreases' with inc reasing cycle number. The experimental results are discussed in terms of proposed reaction mechanisms.