Electrochemical Analysis of Li-Ion Cells Containing Triphenyl Phosphate

The development and subsequent incorporation of flame retardant additives (FRAs) has become a priority for Li-Ion battery research and development. Triphenyl phosphate (TPP) was studied to ascertain the safety benefits and electrochemical performance when incorporated into a LiPF6/ethylene carbonate (EC)/ethyl methyl carbonate (EMC) electrolyte system. The flammability of electrolytes containing TPP was investigated via self-extinguishing time and flash point analysis. The electrochemical stability was studied by cyclic voltammetry (CV), battery cycling in graphite/LiNi0.8Co0.2O2 cells, electrochemical impedance spectroscopy (EIS) and Tafel polarization. In order to better understand the role of TPP, ex-situ surface analysis of the cycled electrodes was conducted with X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). Incorporation of TPP results in a moderate decrease in the flammability of the electrolyte with relatively minor detrimental effects on the performance of the cells and thus is a promising additive for lithium ion batteries.