Comparative Study of Tris(trimethylsilyl) Phosphate and Tris(trimethylsilyl) Phosphite as Electrolyte Additives for Li-Ion Cells

The effects of tris(trimethlysilyl) phosphate (TTSP) and tris(trimethlysilyl) phosphite electrolyte (TTSPi) additives with and without VC in Li[Ni1/3Mn1/3Co1/3]/graphite (NMC/graphite) pouch cells were studied using the Ultra High Precision Charger at Dalhousie University and electrochemical impedance spectroscopy. The coulombic efficiency of NMC/graphite cells was improved when TTSPi was added to the electrolyte. TTSP and TTSPi both reduce the cell impedance significantly. The addition of vinylene carbonate (VC) to NMC/graphite cells containing TTSP or TTSPi improves the coulombic efficiency and decreases the charge end point capacity slippage. However, when VC was added the impedance of cells containing either TTSP or TTSPi increased. In the presence of VC, the TTSPi additive decreased the rate of parasitic reactions, reduced the charge end point capacity slippage and also the reduced impedance of NMC/graphite cells compared to cells with TTSP and VC. These results demonstrate that TTSPi is a better additive than TTSP when added to control electrolyte and to electrolyte containing VC for NMC/graphite cells.