Flame Retardant Co-Solvent Incorporation into Lithium-Ion Coin Cells with Thin-Film Si Anodes

Abstract

Flame retarding co-solvents triphenyl phosphate (TPP) and dimethyl methylphosphonate (DMMP) were incorporated into a standard binary LiPF6/ethylene carbonate (EC)/Ethyl methyl carbonate (EMC) electrolyte with and without the anode solid electrolyte interface (SEI) film forming additive, lithium bis(oxalato)borate (LiBOB). Thin-film silicon/Li cells were cycled with the different electrolytes. The standard electrolyte has poor cycling performance losing ∼ 50% of the initial capacity during the first 50 cycles. Electrolytes containing TPP and DMMP show comparable cycling performance to the standard electrolyte. Incorporation of LiBOB into the standard electrolyte or the standard electrolyte containing flame retarding co-solvents results in improved cycling efficiency and capacity retention. Ex-situ analysis via X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) provides insight into the role of LiBOB in the improved cycling performance and SEI structure and composition.