Interactions between Lithium Growths and Nanoporous Ceramic Separators

To enable lithium (Li) metal anodes with high areal capacity that can match advanced cathodes, we investigate the growth mechanisms and the tendency of the deposited metal to penetrate nanoporous ceramic separators across a range of practical current densities. Our results from realistic sandwich cells and special transparent junction cells suggest the existence of three growth modes of lithium, due to the competing reactions of lithium deposition and the solid electrolyte interphase formation. A critical current density (6 mA cm⁻²), ∼30% of the system-specific limiting current density, is identified as a practical safety boundary for battery design and operation, under which root-growing lithium whiskers are the dominant structure of electrodeposition and can be blocked by the nanoporous ceramic separator. Our operando experiments reveal that metal penetration of the separator does not lead to zero voltage immediately, but rather to sudden, small voltage drops, which should not be treated as benign soft shorts.