Impact of Shape Defects in LLZO on Premature Cell Shorting

Dendritic growth of lithium upon charging is a leading failure mode of batteries with lithium metal anodes coupled with solid-state electrolytes. With the development of stabilizing interlayers between the Li metal anode and LLZO solid electrolyte, high critical current densities (>2.5 mA cm–2) can be realized. However, achieving similar current densities consistently across a large number of cells with thin LLZO membranes (<100 μm thick) has proven challenging. The origin of variation in the rate of success is generally attributed to manufacturing defects in the LLZO separator. Here, with the aid of the dendrite location detection method and other characterization techniques, we report shape defects on an otherwise flat surface as an additional origin for crack formation and concomitant dendrite growth. A combination of experimental work and simulations reveals that shape defects act as a stress riser during the operation of the cell. Once the stress on LLZO reaches a critical threshold, it is expected that LLZO will fracture, with rapid growth of lithium dendrites along the crack, leading to rapid shorting of the cell. This finding has shed light on a defect which is critical for the commercial manufacturing of LLZO separators.