Phase-Field Modeling of Dead Lithium Formation during Charge/Discharge Cycles

The formation of inactive or "dead" lithium is one of the main reasons for performance decay in lithium batteries, but recent studies find that modified charging protocols can revive this inactive portion of lithium. Thus, the ability to simulate events that lead to the disconnection and reconnection of lithium under experimental conditions can provide a fundamental understanding of the evolution of dead lithium during the charge/discharge cycle. Here, we apply a recently developed quantitative electrochemical phase-field model to study the morphological and topological evolution of lithium during battery operation. We simulate the charge/discharge behavior of lithium metal anodes from the scale of individual dendrites to anodes of relevant experimental size with realistic materials parameters to examine the pathways leading to disconnection and reconnection. Additionally, we quantify the amount of inactive lithium formed during cycling. We discuss the effect of various factors like electrolyte properties, discharge rate, and the assumed reaction kinetics (i.e., Butler-Volmer versus Marcus-Hush) on dead lithium formation. The presented simulation tool can be employed to explore battery design; thus, we will discuss possible ways to optimize the charge and discharge cycles to minimize the amount of dead lithium. Beyond the present application to lithium, the model can also be extended to other metal-anode batteries.