Tailoring heterogeneous interfacial chemistry enables long-term cycling of all-solid-state lithium-metal batteries

The application of poly(ethylene oxide) (PEO)-based polymer electrolytes has been impeded due to extremely low room-temperature ionic conductivity and inevitable Li penetration. Herein, FeF3·3H2O is demonstrated to be a valid additive in PEO to improve the Li+ transfer dynamics as well as manipulate profitable interface chemistry on Li metal surface at the molecular level. Combining experimental and theoretical investigations, we find that the Fe3+ ions could accelerate the mobility of Li+ ions due to the strong coordination with ether oxygen and anions. More impressively, the inorganic-organic bilayer heterogeneous SEI interphase triggered by the strong coordination effect of Fe3+ ensures dendrite-free anode during long cycling. Consequently, the Fe3+-integrated PEO electrolytes deliver a remarkable critical current density of 1.3 mA cm−2. Coupled with its high anodic stability, the competitive all-solid-state Li||Li and Li||LiFePO4 cells endow unprecedented lifespan over up to 1000 cycles at 0.2 mA cm−2 and 800 cycles at 0.5 C, respectively. Intriguingly, tailoring heterogeneous interfacial chemistry by FeF3·3H2O is further demonstrated with the LiFePO4-based pouch cells, providing the pioneering levels for practical all-solid-state batteries.