Dimethyl Sulfite as a Possible Alternative Electrolyte Solvent for Na-Ion Batteries

Dimethyl sulfite (DMS) is evaluated as an electrolyte single solvent and co-solvent for Na-ion cells. The major motivation for this work was to see if the safety of Na-ion cells with oxide positive electrodes could be improved by switching away from electrolytes based on traditional carbonate solvents. Different additives were tested in the DMS single solvent system in Na-ion pouch cells, with prop-1-ene-1,3-sultone (PES) and methylene methane disulfonate (MMDS) enabling a capacity retention higher than 94% and 91%, respectively, after 900 cycles at 40 °C. When DMS is used as a co-solvent in Na-ion pouch cells, capacity retention can match that of cells with standard carbonate solvents. However, ultra-high precision charger experiments show that cells with DMS have more charge endpoint capacity slippage indicating an additional degradation process. The degradation mechanism present in DMS cells was explored using pouch bag studies and gas analysis. Accelerating rate calorimtery experiments showed exothermic reactions onset at lower temperatures and were more severe as the fraction of DMS in the electrolyte was increased. Therefore, although Na-ion cells with DMS can perform similarly to those with only carbonate solvents, there is neither a performance nor a safety advantage.