Trimethylsiloxy based metal complexes as electrolyte additives for high voltage application in lithium ion cells

Imholt L, Röser S, Börner M, Streipert B, Rezaei Rad B, Cekic-Laskovic I, Winter M

Abstract

Previous studies have shown that electrolyte additives based on metals and semimetals (LiBOB, Mg(TFSI)2, Al(TFSI)3) as well as additives containing trimethylsiloxyl (TMS) groups as ligands can have positive impact on the cycling performance of lithium ion battery cells due to solid electrolyte interphase (SEI) and/or cathode electrolyte interphase (CEI) film forming properties and/or scavenging properties towards acidic impurities. In this study, both active functionalities (metal core and trialkylsiloxy based ligands) were combined into one using Al, Ti and B as metal cores combined with TMS ligands (M(TMS)x). All investigated additives M(TMS)x were able to improve the cycling performance regarding Coulombic efficiency, energy efficiency and capacity retention of LiNi1/3Co1/3Mn1/3O2 (NCM111)/Li half-cells and NCM111/graphite full-cells at high potentials (>4.3V vs. Li/Li+). The formed CEI was studied by means of electrochemical impedance spectroscopy, scanning electron microscopy and X-ray photoelectron spectroscopy. The obtained results indicate that the investigated additives are either actively incorporated into the formed CEI layer (in case of Al, Ti as metal core) or interacting with decomposition products (in case of B as metal core) resulting in lower charge-transfer impedance and hence improved long-term cycling behavior.