Experimental Measurement of the Local Current Density in the Vicinity of a Lithium Protrusion: Plating and Stripping

Abstract

Successful prevention of lithium dendrite growth would enable the use of lithium metal as an anode material in next-generation secondary batteries. Mechanically stiff solid polymer electrolytes have been shown to prolong the life of lithium metal cells by partially suppressing lithium dendrite growth. However, we lack fundamental knowledge about the nature of lithium electrodeposition and stripping as a function of time, as direct observation of this phenomenon is non-trivial. Synchrotron X-ray microtomography was used observe lithium metal plating and stripping through these solid polystyrene-block-poly(ethylene oxide)-LiTFSI electrolyte membranes in the vicinity of lithium protrusions. Local current density was calculated from these experimental measurements and mapped on the top and bottom electrode under conditions of lithium metal plating and stripping. Local current density at one electrode was correlated to local current density at the other electrode and to electrode thickness. We show quantitatively how lithium protrusions are stripped at a faster rate than planar lithium and gain insight into the lithium ion transport governing protruding lithium growth in a cycled lithium metal electrode.