Pit-Controllable Lithium Metal Protection in Lithium–Sulfur Batteries

As promising lightweight battery, practical Li–sulfur (Li–S) cells require lean electrolyte and thin Li metal anodes (LMAs). In these cell designs, parasitic reactions between LMAs and the electrolyte induce electrolyte depletion, severely limiting the cycling lifespan of Li–S cells. Protective layers (PLs) have therefore been used as physical barriers to reduce direct electrolyte contact with LMAs. However, Li stripping during the initial discharge generates localized pits, dynamically destabilizing the PL/LMA interface. In this talk, we present a pit-responsive PL strategy that addresses pit-induced interfacial failure in practical Li–S cells. Motivated by pit-driven PL failure, a pit-adaptive dual-layer PL composed of a PEO inner layer and a PVDF-HFP outer layer was rationally designed to maintain interfacial contact while suppressing electrolyte and polysulfide penetration. Although structural optimization can improve PL adaptivity, irregular pit formation during Li stripping remains unavoidable. At high Li utilization, localized deep pits still deform and damage the PL, while repeated stripping/plating gradually embeds the PL within a pulverized Li/SEI interphase. These limitations motivate a new strategy that actively regulates Li stripping from the outset, promoting uniformly distributed shallow pits before localized damage can accumulate. Beyond pit adaptivity, a “pit-controllable” PL (PCPL) was designed by incorporating a pit-selective shielding (PSS) agent into the Li-facing inner layer. PSS-mediated Li₂O dissolution and repassivation generate local resistance feedback at newly formed pits, suppressing persistent pit deepening and redistributing Li stripping into dispersed shallow pits. This PCPL can induce uniform stripping-to-plating behavior, preserving PL integrity and thereby enabling stable cycling of Li–S and Li–SPAN cells under practical conditions. Our results suggest that controlling pit evolution, rather than merely accommodating it, is essential for durable Li metal protection in high-energy Li–S batteries.