Evaluating high-boiling binary carbonate mixtures for enhanced lithium-ion battery safety

This study outlines how an optimized electrolyte selection can be made from a matrix of organic carbonates (dipropyl carbonate, ethylene carbonate, propylene carbonate, dibenzyl carbonate, diphenyl carbonate, 1,2-butylene carbonate, fluoroethylene carbonate) and selected conductive salts (LiBF4, lithium bis (trifluoromethanesulfonyl)imide, lithium bis(oxalato)borate, lithium difluoro oxalatoborate). An optimized electrolyte design was thus achieved with a focus on electrolyte safety and electrolyte performance. For this purpose, physicochemical methods (solubility, phase ransitions, density measurement, conductivity measurement, viscosity measurement) and electrochemical methods (cyclic voltammetry, corrosion tests, lithium mobility, cell tests) are presented, which were used to select the electrolyte in a reasonable and meaningful way. Finally, three electrolyte systems were identified and evaluated against a standard reference electrolyte(ethylene carbonate/dimethyl carbonate + LiPF6). It was found that the electrolytes exhibit comparable performance at low to medium currents and have a significantly improved flash point. However, the self-ignition temperature is in a similar range to that of the standard electrolyte. The novel electrolyte formulations can thus help to improve cell safety by delaying the flammability of the electrolyte in the event of a spark. In addition, automatic electrolyte optimization, which isbecoming increasingly important today, can benefit from the selection process, which shows how individual measurements will influence the selection.