Review of Thin Lithium Metal Battery Anode Fabrication - Microstructure - Electrochemistry Relations

While lithium metal foils used for research may be upward of 250 µm in thickness, anodes for viable lithium metal batteries (LMBs) must be at least one order of magnitude thinner. This review focuses on fabrication approaches that promise to bridge this divide, highlighting the known/unknown processing - microstructure - electrochemical properties interrelations. Four general methodologies are discussed, starting with metallurgical ingot extrusion and rolling, followed by solidification casting, solution-based wet methods, and physical vapor deposition (PVD). Each section begins with an outline of the underlying principles of the approach and how this limits the minimal thickness, morphology, bulk microstructure, and surface chemistry of the resultant anodes. The discussion then moves to specific case studies that illustrate how various state-of-the-art research efforts have overcome these limitations by employing a range of strategies that include alloy and composite metallurgies, functionalized current collector coatings, and liquid-phase additives. It is highlighted that methodologies resulting in planar and conformal lithium films, and subsequently improving electrochemical performance, are fairly consistent across all four fabrication classes. Each section concludes with a critical discussion of the research necessary to advance the field, identifying key outstanding scientific questions and "unknowns."