Electrolyte additives for enhanced thermal stability of the graphite anode interface in a Li-ion battery

The influence of electrolyte additives on the thermal stability of graphite anodes in a Li-ion battery has been investigated. The selected additives are: ethyltriacetoxysilane, 1,3 benzoldioxole, tetra (ethylene glycol) dimethylether and vinylene carbonate. These compounds were added in 4% to an electrolyte consisting of 1 M LiBF4 ethylene carbonate (EC/diethyl carbonate (DEC) solvent mixture. Differential scanning calorimetry (DSC) was used to investigated the thermal stability. The electrochemical performance was investigated by galvanostatic cycling and the formed solid electrolyte interphase (SEI) was characterised by photoelectron spectroscopy (PES) using Al Ka and synchrotron radiation /SR). The onset temperature for the thermally activated reactions was found to increas for all electrodes cycled with additives compared to electordes cycled without additives. The onset temperature in creased in the order: no additive < tetra (ethylene glycole) dimethyl ether < 1,3-benzoldioxole < ethyl-triacetoxysilane < vinylene carbonate. Feature in the PES spectra found to be associated with high onset temeratures for thermally activated reactions are: (i) no discernible graphite peak, (ii) small amount of salt species of the type LiF and LixBFyOz and (iii) larger amounts of organic compounds preferably with a high oxygen content.