Separators for Rechargeable Metal Batteries: Design Principles and Evaluation

Abstract Metal anodes exhibit great potential in delivering high capacity and energy density to address modern energy demands. However, the commercialization of these advanced batteries is hindered by metal anode‐related challenges including the fast‐decaying performance and dendrite‐induced safety risks. Though frequently overlooked in cell design, separators can play a critical role in metal anode reactions by actively interacting with both electrolytes and electrodes. This review explores the design principles for separators to achieve safe and stable metal batteries. By analyzing the potential failure modes in each step during the metal electrodeposition process, the key factors of separators that determine the stability of the metal cycling process are discussed. Additionally, the current methods used to evaluate separator effectiveness in suppressing dendrite formation are highlighted and critically examined for their limitations. By enhancing the understanding of separator functionality, this review offers insights into optimizing separator designs, paving the way for the development of safe and efficient metal batteries.