Tris(trimethylsilyl) Phosphite and Lithium Difluoro(oxalato)borate as Electrolyte Additives for LiNi_0.5Mn_1.5O₄‐Graphite Lithium‐Ion Batteries

Abstract

Raising the energy density of lithium‐ion batteries (LIBs) through the operation of high‐voltage cathodes presents a challenge in terms of practical use due to electrolyte degradation. Consequently, it is imperative to explore new materials to circumvent this issue. In this study, a combination of tris(trimethylsilyl) phosphite (TMSPi) and lithium difluoro(oxalato)borate (LiDFOB) is presented as film‐forming additives in a conventional LiPF6‐containing carbonate‐based electrolyte solution in high‐voltage LiNi0.5Mn1.5O4‐graphite full cells. At high voltage, TMSPi oxidizes on the LiNi0.5Mn1.5O4 (LNMO) cathode surface prior to the decomposition of electrolyte solvents, promoting the formation of a stable cathode electrolyte interphase (CEI) layer. In tandem, given that LiDFOB has a lower reduction potential than ethylene carbonate (EC), it has the possibility of forming a solid electrolyte interphase (SEI) on the graphite anode surface. Combining the two additives was found to suppress the degradation of the electrolyte to a large extent. Among the investigated concentration of the additives, the combination of 1 wt. % TMSPi and 2 wt. % LiDFOB added to LP40 electrolyte exhibits improved capacity retention of 80 % after 400 cycles at 0.3 C, compared to the electrolyte with no additive with 67 % capacity retention over the same period. Thereby, the combination of TMSPi with LiDFOB provides an improvement for high voltage LIBs.