Neutral Acyl Silanes vs Anion Radical Li Salts as Electrolyte Additives for Lithium-Metal Batteries

Lithium (Li) metal anode and Ni-rich LiNi_xCo_yMn_1-x-yO₂ cathode (NCM) are considered promising candidates for high energy density Li metal batteries. However, lithium dendrite development, HF formation, transition metal dissolution, electrolyte decomposition, and formation of an unstable SEI/CEI layer cause severe electrochemical performance loss. Recently, research has been focused on film-forming organosilicon-derived electrolyte additives for improving the electrochemical activity of Li batteries. In this work, we studied the comparative electrochemical activity of neutral acyl silane with their anion radical Li salt for Li metal anode and nickel-rich, low cobalt, single-crystalline layered oxide cathode (LiNi_0.9Co_0.05Mn_0.05O₂- NCM90). Three pairs of neutral acyl silane and their anion radical Li salt electrolyte additives were synthesized- 1) di-tert-butyl methyl adamantoyl silane (RR^’SiCOAd or <b>1</b>, where R is (tBu)₂, R’ is CH₃ and Ad is 1-Ad) and [RR^’SiCOAd]^●—Li⁺ or [<b>1</b>]^●—); 2) bis(di-tert-butyl methyl silyl ketone) ([(RR^’Si)₂CO] or <b>2</b>) and [(RR^’Si)₂CO]^●—Li⁺ or [<b>2</b>]^●— ; and 3) di-methyl amino di-tert-butyl adamantoyl silane (Me₂NRSiCOAd or <b>3</b>) and [Me₂NRSiCOAd]^●—Li⁺ or [<b>3</b>]^●—. The comparison of the electrochemical performance revealed that the anion radical Li salt additives significantly outperformed their neutral parts.