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.