Lithium Difluoro(dioxalato) Phosphate as an Electrolyte Additive for NMC811/Graphite Li-ion Pouch Cells

Lithium difluoro(dioxalato)phosphate (LiDFDOP) has been systemically studied as an electrolyte additive singly and in combination with co-additives fluoroethylene carbonate (FEC) and vinylene carbonate (VC) in LiNi0.8Mn0.1Co0.1O2 (NMC811)/artificial graphite (AG) pouch cells. Long-term cycling tests at room and elevated temperatures (20 degrees C, 40 degrees C, and 55 degrees C) with different upper cutoff voltages (4.06 V and 4.20 V) were performed. These results were combined with ultra-high precision coulometry (UHPC), ex-situ gas measurements, and automatic cell storage tests to reveal multiple aspects of cell performance. A density functional theory (DFT) calculation has also been performed and compared to formation data to reveal the mechanistic aspects of LiDFDOP reduction. Radar plots and a figure-of-merit (FOM) approach were further utilized to summarize results and rank additive and additive combination performance for the NMC811/AG cells. This work highlights an effective additive and suitable co-additives for use in NMC811/graphite cells and gives important insights for future electrolyte additive studies.

Automated summary

In this study, the effectiveness of LiDFDOP as an electrolyte additive, both singly and in combination with co-additives, was systematically investigated in NMC811/AG cells. Through long-term cycling tests and various analyses, the study revealed multiple aspects of the additive's impact on cell performance. The results provide important insights for future electrolyte additive studies.