Lean-solvent solid electrolytes for safer and more durable lithium batteries: a crucial review†

Pursuing safer and more durable electrolytes is imperative in the relentless quest for lithium batteries with higher energy density and longer lifespan. Unlike all-solid electrolytes, prevailing quasi-solid electrolytes exhibit satisfactory conductivity and interfacial wetting. However, excessive solvent (>60 wt%) as a plasticizer triggers safety concerns and questionable electrode compatibility. Recent studies have underscored that minimizing the liquid solvent content below 20 wt% can improve battery safety and cyclability. Unfortunately, this emerging “lean-solvent” system is often, and somewhat misleadingly, categorized under all-solid electrolytes, thereby obscuring the presence of liquid components. In this Review, we provide unprecedented comprehensive insight into the unique solvation structure, interfacial behavior, and fundamental properties of lean-solvent solid electrolytes (LSEs), including lean-solvent polymer electrolytes (polymer-LSEs), lean-solvent porous electrolytes (porous-LSEs), and lean-solvent inorganic electrolytes (inorganic-LSEs). Finally, we elucidate the dominant challenges in developing safe and durable LSE-based batteries, providing a perspective for future research and technological breakthroughs.