Targeting 100% Lithium Utilization in Lithium Metal Batteries

Anode-free lithium metal batteries (AFLMBs) represent the ultimate solution to mankind's quest for the Holy Grail of batteries, where the cell-level energy density is maximized on the assumption that lithium (Li0) must be fully utilized with near 100% Coulombic efficiency. Although substantial progress has been made since the anode-free concept was first proposed, the challenges presented by the most powerful anode material that can be found on the periodic table still remain unresolved due to its extreme reactive nature, which not only makes it impossible to retain 100% reversibility but also induces inhomogeneity during repeated plating/stripping cycles and persistent capacity loss over a long period of time. The isolated study approaches, emphasizing either individual electrolyte components or interphasial chemistry engineering, but mostly focused on the negative-electrode current collector, hinder insight into issues arising when these components are assembled into cells and forced to interface with each other. In this review, we attempt to examine this high-dimensional topic from a panoramic perspective, with the focus placed on the liquid electrolytes. We first outline the fundamental operating principles of key individual battery components, together with practical perspectives for evaluating lithium utilization and reversibility in AFLMBs. We then discuss how these components interact when assembled into full cells, how such interactions give rise to heterogeneous electrochemical and mechanical behaviors, and how these phenomena can be characterized and regulated. It is also outlined that a hierarchical perspective on lithium behavior, spanning from the nano- to cell-scale, is essential to enable plating, stripping, and recovery in AFLMBs. Finally, we present perspectives from leading researchers actively working on the various elements that constitute AFLMBs and integrate these viewpoints to clarify the future research directions of this field. By providing a system-level framework for understanding AFLMBs, this review aims to guide future research efforts and contribute to addressing the broader challenges of sustainable energy storage.