Room‐Temperature Anode‐Less All‐Solid‐State Batteries via the Conversion Reaction of Metal Fluorides

All‐solid‐state batteries (ASSBs) that employ anode‐less electrodes have drawn attention from across the battery community because they offer competitive energy densities and a markedly improved cycle life. Nevertheless, the composite matrices of anode‐less electrodes impose a substantial barrier for lithium‐ion diffusion and inhibit operation at room temperature. To overcome this drawback, here, the conversion reaction of metal fluorides is exploited because metallic nanodomains formed during this reaction induce an alloying reaction with lithium ions for uniform and sustainable lithium (de)plating. Lithium fluoride (LiF), another product of the conversion reaction, prevents the agglomeration of the metallic nanodomains and also protects the electrode from fatal lithium dendrite growth. A systematic analysis identifies silver (I) fluoride (AgF) as the most suitable metal fluoride because the silver nanodomains can accommodate the solid‐solution mechanism with a low nucleation overpotential. AgF‐based full cells attain reliable cycling at 25 °C even with an exceptionally high areal capacity of 9.7 mAh cm−2 (areal loading of LiNi0.8Co0.1Mn0.1O2 = 50 mg cm–2). These results offer useful insights into designing materials for anode‐less electrodes for sulfide‐based ASSBs. A room‐temperature anode‐less all‐solid‐state battery is reported by utilizing the conversion reaction of metal fluorides. Silver fluoride is identified as a seed component to induce uniform and reversible lithium plating via a conversion reaction that produces metallic silver nanodomains. These nanodomains, together with the lithium fluoride formed during the conversion reaction, enable sustainable cycling with an extremely high areal capacity.