Lithium Dendrite Growth in Glassy and Rubbery Nanostructured Block Copolymer Electrolytes

Enabling the use of lithium metal anodes is a critical step required to dramatically increase the energy density of rechargeable batteries. However, dendrite growth in lithium metal batteries, and a lack of fundamental understanding of the factors governing this growth, is a limiting factor preventing their adoption. Herein we present the effect of battery cycling temperature, ranging from 90 to 120°C, on dendrite growth through a polystyrene-block-poly(ethylene oxide)-based electrolyte. This temperature range encompasses the glass transition temperature of polystyrene (107°C). A slight increase in the cycling temperature of symmetric lithium-polymer-lithium cells from 90 to 105°C results in a factor of five decrease in the amount of charge that can be passed before short circuit. Synchrotron hard X-ray microtomography experiments reveal a shift in dendrite location from primarily within the lithium electrode at 90°C, to primarily within the electrolyte at 105°C. Rheological measurements show a large change in mechanical properties over this temperature window. Time-temperature superposition was used to interpret the rheological data. Dendrite growth characteristics and cell lifetimes correlate with the temperature-dependent shift factors used for time-temperature superposition. Our work represents a step toward understanding the factors that govern lithium dendrite growth in viscoelastic electrolytes.