On the influence of additives in electrolyte solutions on the electrochemical behavior of carbon/LiCoO2 cells at elevated temperatures

In this paper, we studied the influence of some organic additives in electrolyte solutions based on alkyl carbonate mixtures and LiPF6 on the charge–discharge cycling characteristics of Li-ion cells at elevated temperatures (up to 60 °C). These additives were tested in relation to their impact on the electrochemical responses of both lithium–carbon and lithiated cobalt oxide electrodes. The additives chosen belong to organic compounds such as siloxanes, strained olefins, alkoxysilanes, and vinyl ethers. The main findings are as follows: the impedance of carbon and LiCoO2 electrodes is smaller in solutions containing additive AD1 (hexamethyldisiloxane) from the siloxane family. Both Li/LiCoO2 and carbon/LiCoO2 cells exhibited much more stable charge–discharge cycling at 60 °C in the siloxane-containing solutions than in additive-free solutions. XPS analysis of LiCoO2 electrodes cycled in the solution containing the additives indicated that their surface chemistry is strongly modified by the presence of siloxanes, even at low concentration.