Interfacial engineering for high-performance garnet-based lithium metal batteries: A perspective on lithiophilicity and lithiophobicity

The research and development of energy storage devices has witnessed a paradigm shift towards the realization of solid-state lithium metal batteries owing to the high theoretical capacity of the lithium metal anode (LMA). Among all types of solid-state electrolytes (SSEs), garnet-based solid electrolytes are one of the most promising candidates which developed due to their relatively high ionic conductivity (10^–4 to 10^–3 mS cm^–1), wide electrochemical stability window (0–6 V vs. Li⁺/Li), and, most importantly, thermodynamic stability with lithium. Applying suitable interfacial engineering solutions is crucial for solid-state lithium metal batteries, especially for garnet-solid electrolytes due to their brittle nature, which cannot withstand high stack pressure. In this review, we focus on the recent developments in interface engineering solutions and broadly classify them based on the interface modification approach/fabrication routes using various classes of materials. Certain vital electrochemical performance parameters have been compared closely, which gives an appropriate estimation of what types of interlayers will be suitable along with the possible mechanistic route. Moreover, the role of lithium affinity at the interface in terms of lithiophilicity and its importance, along with the presence of lithiophobic phases, is discussed as it amplifies the critical current density of the anode/solid-electrolyte interface and reduces the area-specific resistance. This article comprehensively analyzes the anode-solid-state electrolyte interface in garnet-based lithium metal batteries. It aims to provide a clear perspective on lithiophilicity and lithiophobicity to achieve high-performance batteries.