STUDYING LONG TERM LI-ION ELECTROLYTE DEGREDATION USING LITHIUM ION DIFFERENTIAL THERMAL ANALYSIS

Abstract

Lithium ion cells contain liquid electrolytes that degrade over the lifetime of the cell. Though the results of this degradation are well understood, the pathways are not. Lithium ion differential thermal analysis (Li-ion DTA) is a non-destructive in-situ method for probing the state of an electrolyte in a cell. This functions by controlled cooling and heating through the freezing point of the electrolyte. The temperature signal of the cell will then show phase transitions that can be associated with the components of the electrolyte. This thesis discusses several experiments using this method. These are: a proof of concept of the creation of salt-solvent diagrams, a long term study of the effects of cycling on standard electrolytes, a short term test, that examines the effects of high voltage on electrolyte composition. These experiments have resulted in the creation of a method to study electrolyte molarity in situ.