Resolving Current-Dependent Regimes of Electroplating Mechanisms for Fast Charging Lithium Metal Anodes

Poor fast-charge capabilities limit the usage of rechargeable Li metal anodes. Understanding the connection between charging rate, electroplating mechanism, and Li morphology could enable fast-charging solutions. Here, we develop a combined electroanalytical and nanoscale characterization approach to resolve the current-dependent regimes of Li plating mechanisms and morphology. Measurement of Li+ transport through the solid electrolyte interphase (SEI) shows that low currents induce plating at buried Li parallel to SEI interfaces, but high currents initiate SEI-breakdown and plating at fresh Li parallel to electrolyte interfaces. The latter pathway can induce uniform growth of {110}-faceted Li at extremely high currents, suggesting ion-transport limitations alone are insufficient to predict Li morphology. At battery relevant fast-charging rates, SEI-breakdown above a critical current density produces detrimental morphology and poor cyclability. Thus, prevention of both SEI-breakdown and slow ion-transport in the electrolyte is essential. This mechanistic insight can inform further electrolyte engineering and customization of fast-charging protocols for Li metal batteries.

Automated summary

This study reveals the plating mechanisms and morphologies under low and high currents by measuring the transport of lithium ions at the solid electrolyte interface. Under fast-charging rates, the breakdown of the solid electrolyte interface can lead to detrimental morphologies and poor cyclability in lithium metal batteries.