Unanticipated Mechanism of the Trimethylsilyl Motif in Electrolyte Additives on Nickel-Rich Cathodes in Lithium-Ion Batteries

Abstract

School of Energy and Chemical Engineering (Battery Science and Technology)Various electrolyte additives containing trimethylsilyl (TMS) motif have been reported to remove HF formed by the decomposition of LiPF6-based electrolyte and suppress dissolving transition metal from the cathode in Li-ion batteries (LIBs). Among them, tris(trimethylsilyl)phosphite (TMSP) was used as a multi-functional additive that increases the cycle performance of LIBs by forming a stable cathode electrolyte interphase (CEI) layer by decomposing before the electrolyte as well as scavenging HF which present in electrolytes. However, we found that TMSP-containing electrolyte exhibited poor performance compared to baseline electrolyte that does not have a TMS motif on 80% Ni-containing LiNixCoyMnzO2 (NCM) electrodes. At this, we compared the cycle performance of TMSP-containing electrolyte using not only NCM electrode with 80% Ni content but also 60% electrode and LiCoO2 (LCO) cathode with 80% nickel content. In addition, we propose the causes and mechanism of deterioration of additives with TMS motifs using NMR, SEM, and TEM analysis.ope