Electrode Edge Effects and the Failure Mechanism of Lithium-Metal Batteries

The very high specific capacity of Li metal makes it an ideal anode for high-energy batteries. However, Li dendrite growth and the formation of isolated (or "dead") Li during repeated Li plating/stripping processes leads to a low coulombic efficiency (CE). In this work, we discovered, for the first time, that electrode edge effects play an important role in the failure of Li-metal batteries. The dead Li formed on the edge of Cu substrate was systematically investigated through SEM, energy-dispersive X-ray (EDX) spectroscopy, and 2D X-ray photoelectron spectroscopy (XPS). To minimize the Li loss at the edge of the Cu exposed to pressure-free space, a modified Li∥Cu cell configuration with a Cu electrode smaller than Li metal is preferred. It was clearly demonstrated that using an electrode configuration with a minimal open space or pressure-free space across electrodes can reduce accumulation of dead Li during cycling and increase Li CE. This phenomenon was also verified in Li-metal batteries (Li∥LiNi_1/3 Mn_1/3 Co_1/3 O₂ ) and should be considered in the design of practical Li-metal batteries.