Electrolyte Engineering for Lithium Metal Batteries Under Extreme Operating Conditions

ABSTRACT The practical deployment of high‐specific‐energy lithium metal batteries (LMBs) demands stable operation under conditions of high voltage, fast charging, a wide temperature range, high cathode loading, lean electrolyte, and thin lithium. These conditions intensify the coupling among ion transport, interfacial reactions, and the limited inventories of electrolyte and active lithium, leading to transport polarization, unstable electrode‐electrolyte interphases, and irreversible material loss. Although electrolyte design has evolved from empirical formulation optimization to coordinated regulation across solvation, molecular, interfacial, and system levels, systematic links between condition‐specific failure mechanisms and corresponding design strategies remain incomplete. This review elucidates dynamic Li + solvation dynamics, multiscale transport, interphase evolution, and electrolyte and active‐lithium consumption govern cycling stability under extreme conditions. Representative strategies, including solvation and transport regulation, molecular and interfacial reaction engineering, polymer/gel electrolytes, and spatially differentiated electrolytes, are summarized with emphasis on their operating windows and trade‐offs. Finally, we propose that electrolyte design under extreme conditions should identify the dominant condition‐specific limitation and coordinate solvation, transport, interfacial reactions, and the consumption of electrolyte and active lithium accordingly, thereby establishing an integrated “application conditions–failure mechanisms–key descriptors–electrolyte engineering–practical validation” framework for practical high‐specific‐energy LMBs.