(226i) X-Ray Microtomography of Lithium Dendrite Growth through Polystyrene-Block-Poly(ethylene oxide) Copolymer Electrolyte Membranes

High modulus block copolymer electrolytes have the ability to lengthen the cycle lifetime of rechargeable batteries by slowing lithium dendrite growth. However, batteries made with these polymer electrolyte membranes still eventually fail via dendritic short circuit. Hard X-ray microtomography was used to image dendrite growth in situ in symmetric lithium/polymer electrolyte/lithium samples. Each symmetric cell contained many dendrites. The volume of the dendrites was measured as a function of the charge passed through the electrolyte in order to determine the rate of dendrite growth in these systems. The dendrites appear to form on crystalline contaminants at the lithium metal electrode/electrolyte interface and then slowly grow in the electrode before protruding into the electrolyte. Further experiments were performed to determine the effect of temperature and depth of discharge on dendrite morphology and growth rate. The dendrites have a “foam-like” structure where the interior of the foam cells is lithium metal and the exterior consists of elements from the lithium, polymer electrolyte, and salt. The size of the “cells” in the dendrite is correlated to the amount of lithium ions moved per cycle. These experimental results are compared with theoretical models for the growth of dendrites in high modulus polymer electrolyte systems.