Perspective on the Mechanical Interaction Between Lithium Dendrites and Polymer Separators at Low Temperature

Abstract

This perspective paper underscores the importance of coupled electro-mechanical studies in lithium battery systems with a specific example given of the interaction between temperature-dependent dendrite morphologies and polymer separators. Polymer separators are passive components in lithium battery systems yet play a critical role in cell safety. Separators must maintain dimensional stability to provide electronic isolation of the active electrodes and resist puncture and penetration from lithium dendrites. The polyolefin class of polymers has been used extensively for this application with mixed success. Recent research efforts to characterize lithium dendrite formation and growth have shown distinct temperature-dependent dendrite morphologies: rounded blunt mushroom-shaped, sharp jagged needle-like, and granular particulates. Each of these dendrite morphologies will induce a difference physical interaction with the polymer separator. Anticipating this interaction is difficult since the mechanical properties of the polymer separator itself are largely temperature dependent. This paper describes the anticipated physical interaction of the three different dendrite morphologies listed above as a function of temperature and the local physical properties of the commercial polymer separator. A discussion is also provided on the utility of estimating local mechanical properties in the electrochemical battery environment from traditional mechanical and thermomechanical measurements made in the laboratory.