3D stress mapping reveals the origin of lithium-deposition heterogeneity in solid-state lithium-metal batteries

Solid-state lithium-metal batteries possess intrinsic advantages in terms of both safety and energy density. However, the fundamental origin of electrochemical lithium deposition heterogeneity in solid-state batteries is much less understood than that in lithium-metal batteries using a liquid electrolyte, partly due to the difficulties of directly mapping lithium-deposition reaction fronts and the associated changes in local stress of the solid-state electrolyte. Here, we trace the evolution of three-dimensional microscopic stress and demonstrate that the stress distribution is rather broad in a garnet solid-state electrolyte during processing and battery cycling using confocal Raman spectroscopy. We further discuss the effect of local stress variations on the overpotential of lithium deposition as the most likely origin of lithium-deposition heterogeneity in garnet systems. The ex situ stress-mapping tool developed in this work provides a strong basis for understanding the electromechanical effects, a prerequisite to fully unlock the potential of solid-state lithium-metal batteries.