The Effect of Decalin and Perfluorodecalin on Dendrite Formation at Metallic Lithium Anodes during Their Operation

In this work, we studied the effect of additions of decahydronaphthalene (decalin) and its derivative, perfluorodecalin (octadecafluorodecalin) on the lithium metal deposition and dissolution, in particular, the dendrite formation, at the anodes of lithium secondary power sources in an electrolyte based on lithium hexafluorophosphate in the mixture of ethylene carbonate and diethyl carbonate. The study was carried out using the methods of current transients and electrochemical impedance. The results showed that, in contrast to traditional cationic surfactants cetyltrimethylammonium bromide and hexadecylpyridinium bromide, which we have studied earlier, the decalin and perfluorodecalin demonstrated specific interaction with the surface of the lithium electrode. Moreover, the interaction with decalin is so strong that it actually blocks the processes of both lithium deposition and anodic dissolution at the surface of the lithium electrode. The interaction of perfluorodecalin with the lithium surface turned out to be weaker. As a result, perfluorodecalin does not interfere with the cycling of the lithium-metal anode, but at the same time shows an inhibitory effect on the dendrite formation. In the electrolyte added with perfluorodecalin, the lithium anode was able to undergo more than 80 charging–discharging cycles with a Coulomb efficiency of 70–80%, while without the additive, the number of cycles was less than 40, and the Coulomb efficiency was 60% or lower.