From Promise to Practice: The Choice of Lithium Reservoir in Lithium Metal Batteries that Balances Cycling and Energy

Abstract Lithium metal batteries (LMBs) are inherently characterized by their high energy density, while the inventory loss of active lithium (Li) and the affected cyclability have been impeding the practical applications. Achieving a balance that simultaneously ensures long cycle life and high energy density is still a challenge. Here different LMB geometries are explored, specifically the anode‐free, anode‐less, and anode‐rich configurations with different Li reservoirs in anode side, to address this trade‐off. An engineered lithiophilic 3D pinchbeck alloy contributing to a suppressed Li inventory loss, a noticeably improved cyclability, and a higher energy density is also applied. By tuning the anode/cathode capacity ratio from anode‐free to anode‐rich of 0–3 using the 3D alloy substrate, from the perspective of balancing cyclability and energy density, a limited excess of Li reservoir (ratio 1–2) tentatively emerges as a more pragmatic choice. Despite a slight reduction in energy density, a significantly improved cycling stability is achieved. This optimized balance elevates battery efficiency and serves as a benchmark for evaluating the tangible effects of diverse architectures on LMB performance. The research underscores the importance of design choices in advancing LMB toward commercial viability, offering valuable insights into how it can be substantially improved for applications.