Surface Adaptive Dual-Layer Protection of Li-metal Anode for Extending Cycle-Life of Li–Sulfur Batteries with Lean Electrolyte

Building a lithium–sulfur (Li–S) battery with lean electrolytes is essential to far exceed the energy density of today's Li-ion. However, earlier electrolyte depletion triggered by Li-metal anodes (LMAs) causes sluggish Li–S redox kinetics and poor S utilization, resulting in a short cycle lifespan. To retard the electrolyte loss effectively, sustainable protection of LMAs is necessary against the dynamic interfacial evolution between LMA and protective layers (PLs). This study elucidates two critical parameters in securing the interfacial adaptivity of PLs upon local Li pitting: surface free energy (SFE) and Young's modulus through solid-mechanic simulations and experiments using three different PL models. To alleviate the PL delamination at the early stage, a dual-layer structured, adaptive protective layer (APL) is introduced to adapt the Li pitting-driven structural evolution of the PL|LMA interfaces. The APL consists of a high- SFE polymer as an inner layer, reducing the interfacial energy in contact with LMA surface, and a highly stretchable polymer for outer shield, serving as a physical barrier for the electrolyte and Li polysulfides. APL-coated LMA demonstrates stable cycling of Li–S cells, achieving a twofold extension of cycle-life compared to unprotected LMA, even superior to other single-layer PLs.