Slow surface diffusion on Cu substrates in Li metal batteries

Abstract

Dendrite growth on the lithium metal anode still obstructs a widespread commercialization of high energy density lithium metal batteries. In this work, we investigate how the crystal structure of the copper foil current collector influences the morphology of the lithium anode and the mobility of lithium on the anode using density functional theory and molecular dynamics simulations. We have developed an adaptive Common Neighbour Analysis, surface adaptive Common Neighbour Analysis, that provide insights into the surface crystal structure of the lithium anode and its impact on the surface diffusion barrier of lithium. The surface diffusion barrier is in turn used as an descriptor for dendrite formation. Our analyses reveal that the mobility of lithium on the anode is drastically enhanced when the lithium anode inherits the close-packed fcc crystal structure of the copper foil current collector; the surface diffusion barrier is reduced by more than six times compared to a copper-free lithium anode. However, the large lattice mismatch between lithium and copper creates vacancies and disorder in the lithium anode, which reduce the mobility of lithium. The results provide an atomistic explanation for the lithium dendrite growth observed on copper current collectors as well as a guideline to find alternate anode current collectors that can reduce the formation of dendrites.