Modulation of solid electrolyte interphase of lithium-ion batteries by LiDFOB and LiBOB electrolyte additives

Solid-electrolyte interphase (SEI) layer is an organic–inorganic composite layer that allows Li ⁺ transport across but blocks electron flow across and prevents solvent diffusing to electrode surface. Morphology, thickness, mechanical and chemical properties of SEI are important for safety and cycling performance of lithium-ion batteries. Herein, we employ a combination of in-situ AFM and XPS to investigate the effects of two electrolyte additives namely lithium difluoro(oxalate)borate (LiDFOB) and lithium bis(oxalato)borate (LiBOB) on SEI layer. LiDFOB is found to result in a thin but hard SEI layer containing more inorganic species (LiF and LiCO ₃ ); meanwhile LiBOB promotes formation of a thick but soft SEI layer containing more organic species such as ROCO ₂ Li. Findings from present study will help development of electrolyte additives that promote formation of good SEI layer.