Empirical Understanding of Li‐Ion Transport Through Hetero‐Grain Boundaries Within Li‐Electrolyte Interface for Stable Li Metal Anodes

ABSTRACT Understanding the Li‐ion transport mechanism across the Li/electrolyte interface (LEI) is fundamental for stabilizing Li‐metal batteries (LMBs). In particular, hetero‐grain boundaries (h‐GBs) such as Li 2 O/LiF or Li 2 CO 3 /LiF are theoretically recognized to provide favorable Li‐ion pathways within inorganic LEI; however, experimental verification of h‐GB‐mediated Li‐ion transport remains elusive. In this study, we provide experimental evidence for favorable Li‐ion transport associated with h‐GBs using a tailored h‐GB‐rich MgO/MgF 2 heterostructure (MgO/F). Multifaceted analyses indicate that the MgO/MgF 2 heterointerfaces establish a favorable Li‐ion transport environment through coupled interfacial effects, with the enhanced defect population potentially contributing to increased Li‐ion carrier availability. Furthermore, upon contact between the Li substrate and the MgO/F layer acting as the LEI, the MgO/F layer spontaneously constructs a dual‐interfacial architecture: an inorganic‐rich solid electrolyte interphase abundant in h‐GB‐rich Li 2 O/LiF and a Li/substrate interphase consisting of a Li–Mg alloy with rapid Li surface migration. This synergistic interfacial architecture maximizes the practical efficacy of h‐GB‐rich MgO/F for stabilizing Li metal anodes. Consequently, the h‐GB‐rich MgO/F demonstrates exceptional electrochemical stability, significantly outperforming bare Li in both symmetric and full cells. This study provides experimental insight into the role of h‐GBs in inorganic interfaces and provides a strategic blueprint for designing highly stable LMBs.