Inorganic film-forming electrolyte additives improving the cycling behaviour of metallic lithium electrodes and the self-discharge of carbon—lithium electrodes

Abstract

The beneficial effect of some inorganic electrolyte additives like CO 2, N 2O, CO, CO-complexes and polysulfides S x 2− on self-discharge and cycling behaviour of metallic lithium electrodes as well as of carbon—lithium intercalation electrodes is demonstrated in propylene carbonate (PC) electrolytes. Obviously, the above listed additives promote the formation of thin inorganic films on Li or LIC n , respectively. Films of this kind, being permeable to unsolvated Li + cations and almost impermeable to organic solvent molecules, are also formed in the absence of any additives, however, the additives seem to improve their quality and/or rate of formation. Impedance spectra indicate that the additives decrease in particular low frequency resistances. These low frequency resistances are apparently dominated by diffusion in pores, giving rise to curved Warburg branches. In view of the polymer electrolyte interphase (PEI) model the strong effect of the additives on the low frequency resistances may be related with smaller amounts of polymeric electrolyte decomposition products, i.e., thinner PEI layers. Although the chemical nature of the films formed in the presence of inorganic additives is still unknown, it may be concluded that a variety of material-different inorganic films is characterized by basically similar selective transport properties for Li + ions and organic solvent molecules.