Macroscale Inhomogeneity in Electrochemical Lithium‐Metal Plating Triggered by Electrolyte‐Dependent Gas Phase Evolution

Abstract

Promoting homogeneous electrode reactions is crucial for mitigating premature electrode degradation and achieving enhanced cycle stability. This is particularly important for lithium‐metal electrodes that undergo drastic morphological change during electrochemical cycles, as their failure can result in dendritic lithium growth and safety hazards. Extensive prior studies have focused on managing the nano‐/micro‐scale dendritic lithium formations, and proposed the importance of the electrolyte engineering in tailoring the solid‐electrolyte interphase. Herein, this study demonstrates, for the first time, that the macroscale inhomogeneity during lithium plating, comparable to the size of electrode, is also governed by the electrolyte, but, strikingly, this phenomenon stands independent of the propensity of the electrolyte to promote growth of nano‐/micro‐scale lithium dendrites. In situ probe reveals that this electrode‐level inhomogeneity, which occurs irrespective of lithium dendrite formation, is triggered by gas‐generating reactions influenced by the electrolyte composition, and the subsequent gas‐phase (i.e., bubble) evolution causes localized lithium growth. The restricted lithium‐ion mass transport through these bubbles increases the overpotential, which exacerbates the macroscale inhomogeneity, as supported by experimental results and continuum model simulations. The observation of electrolyte‐dependent macroscale lithium inhomogeneity highlights the importance of adopting a multi‐scale perspective when considering control strategies for achieving homogeneity during lithium deposition/stripping processes.