Electrochemically-driven formation of Intermetallic Cu3ZnLi2 alters Li-transport in nanostructured bimetallic battery anode

The role of Li-based batteries in the electrification of society cannot be understated, however their operational lifetime is often limited by the formation of dendrites, i.e. the localised deposition of Li that can cause shorts between the two electrodes leading to the failure of the battery. Nanocrystalline bimetallic current collectors can be used for anode-free Li-metal batteries, with improved Li plating and limited or suppressed formation of dendrites. Here, we demonstrate that the microstructure of an α-Brass current collector, Cu 63% Zn 37%, used in an anode-free Li-metal battery evolves during cycling. It initially had a nanocrystalline deformation layer approximately 80 nm in thickness after polishing. After 100 cycles, the initial deformed brass layer was partially converted to a ternary Laves phase Cu 3 ZnLi 2 within a nanocrystalline brass matrix that grew to 200 – 250 nm in thickness. Upon Li stripping, the phase partially decomposes electrochemically, but what remains can sequester Li, thus forming “dead Li” thereby contributing to capacity loss. We propose a mechanism for the microstructural evolution including dynamic recrystallization and phase formation. Since this ternary Laves phase emerges during electrochemical cycling alone, binary alloy current collectors must be assessed for metastable ternary phase formation under different cycling conditions to either stabilize and exploit such phases or electrochemically fully strip them. • Mechanically polished CuZn current collector formed thin nanocrystalline layer. • Stable Cu 3 ZnLi 2 ternary Laves phase observed after 100 cycles in Li-metal half cell. • Initial nanocrystalline layer converted and continued growing into brass. • Phase is retained after electrochemical stripping. • Ternary phase formation effects capacity retention.