Anodic Decomposition of Trimethylboroxine as Additive for High Voltage Li-Ion Batteries

Trimethylboroxine (TMB) is used as an additive in the electrolyte for improving the performance of LiCoPO4 (LCP) in Li-ion batteries. In this work, the role and behavior of TMB are investigated by cyclic voltammetry (CV), impedance spectroscopy (EIS) and on line electrochemical mass spectroscopy (OEMS). It was found that TMB oxidizes from 4.6 V and a low amount in the electrolyte is necessary to obtain good performance. On one hand, its oxidation produces boron trifluoride (BF3), phosphorylfluoride (POF3) and carbanion (CH3‑) linked to a huge increase in impedance. Based on these results, a complete oxidation mechanism is proposed. The catalytic effect of the TMB decomposition products on carbonate polymerization could enhance the performance of LCP. On the other hand, an unexplained water and/or HF release was detected. Further experiments need to be done.