Advanced metal anodes and their interface design toward safe metal batteries: A comprehensive review

Metal batteries have attracted significant interest due to their higher energy density compared to state-of-the-art metal-ion batteries. However, the combination of a metal anode and flammable organic electrolyte results in safety issues, which has motivated the exploration of solid-state electrolytes (SSEs) and aqueous electrolytes (AEs). SSEs and AEs have been widely considered as 'enablers' of metal anodes for safe metal batteries (SMBs) with improved energy density. Nevertheless, detrimental interfacial side reactions and undesirable dendrite growth at the anode side have slowed the path to practical application. This review aims to combine fundamental science and engineering perspectives to seek rational design parameters for practical SMBs. Firstly, the kinetics and thermodynamics explaining interfacial side reactions and dendrite growth are reviewed. Then, current research hotspots relying on structural design, interface modification, and innovation of both SSEs and AEs for improving safety are discussed. Following that, advanced characterization techniques and theoretical analysis for the mechanisms of SMBs are highlighted. To pave the way for practical application, key parameters that affect the energy density of SMBs will be systematically analyzed and shine a light on the gap between fundamental research and practical application. Lastly, potential future directions and prospects in engineering SMBs are explored.