Can an Electrolyte for Lithium-Ion Batteries Be Too Stable?

A new differential scanning calorimeter (DSC) sample cell has allowed for the analysis of lithium-ion battery electrolytes at high temperatures. These welded stainless-steel sample tubes contain any decomposition gases that typically leak from conventional hermetically sealed DSC sample pans. Electrolytes of in ethylene carbonate, diethyl carbonate at various concentrations were found to be less thermally stable than electrolytes based on lithium imide-type salts. When these electrolytes were added to portions of the samples containing the lithium imide [including and electrolytes were surprisingly less thermally stable than those with the electrolyte. In the electrolyte, polyethylene-oxide-like polymer forms from the reaction between the solvent and HF impurities, which are generated by the reaction of water (from the combustion of solvent by with Polymer is not produced in the imide electrolytes. The polymer deposits on the surface of the particles and hinders the release of oxygen, resulting in a more controlled decomposition and a more thermally stable sample. Therefore, even though the imide electrolytes are more thermally stable than electrolytes, in the presence of they react more strongly, because the polymer is absent. © 2002 The Electrochemical Society. All rights reserved.