Ultrathin Li Metal Anodes: Quantitative Design Principles and Manufacturability Across Liquid and Solid‐State Batteries

Li metal anode shows significant potential for advancing high-energy-density and commercially viable lithium batteries due to its high specific capacity and low electrochemical potential. However, thinning Li metal encounters serious challenges owing to its mechanical stickiness and fragility during the mechanical rolling process, which severely restricts its practical utilization. Consequently, most current Li metal batteries rely on excessively thick Li foils, leading to substantial resource waste and undermining the pursuit of high energy density. This review highlights the quantitative design principles of ultrathin Li metal (≤15 µm) and elucidates its critical roles in realizing the true potential of Li metal batteries. Emerging strategies for the fabrication of ultrathin Li metal, followed by a critical evaluation of recent advances and persistent challenges in their deployment for both liquid and solid-state batteries, are summarized. A perspective on future directions for ultrathin Li metal is also presented. Ultrathin Li metal anodes are poised to deliver transformative improvements in energy density, unlocking new opportunities for advanced energy storage systems.