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 Li₂O/LiF or Li₂CO₃/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/MgF₂ heterostructure (MgO/F). Multifaceted analyses indicate that the MgO/MgF₂ 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 Li₂O/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.