A Quantitative Lithium Inventory Framework for Anode‐Free Lithium Metal Batteries

ABSTRACT Lithium (Li) metal batteries, with their substantially higher specific capacity, have the potential to nearly double the gravimetric energy density of conventional Li‐ion cells, enabling applications that demand exceptional energy‐to‐weight ratios, including electric vehicles, electric vertical takeoff and landing aircraft (eVTOL), and humanoid robots. However, capacity declines arising from Li inventory imbalance, together with safety concerns under extended cycle life, remain major barriers to their practical deployment. A unified and quantitative understanding of how Li redistributes among the cathode, anode, and electrolyte during operation is still lacking. In this work, we use anode‐free batteries as a model system and quantitatively track the Li inventory by combining structural, chemical, and electrochemical analyses. By closing the Li mass balance across multiple cycling stages, we identify three main characteristic regimes of Li evolution and resolve the dominant loss pathways associated with each regime. The resulting Li‐inventory framework clarifies the interplay among cathode lattice Li, inactive Li accumulation, and electrolyte depletion, and identifies cathode optimization as a central design requirement for anode‐free batteries. In addition, the stage‐resolved quantitative dataset generated here provides a structured source of mechanistic insight that can support future data‐driven and physics‐informed modeling efforts.