Dead-Potassium Activation Reconstructing Stabilized Interface Enables Stable Anode-Free Potassium Metal Batteries

Anode-free high-energy-density potassium metal batteries (AFPMBs) are critically constrained by the irreversible accumulation of dead potassium (K) and severe dendrite growth. These issues stem from sluggish interfacial kinetics and the continuous fracture of the solid electrolyte interphase (SEI). A multifunctional electrolyte engineering strategy is proposed by incorporating bismuth iodide (BiI3) into a carbonate-based system to simultaneously regulate the bulk K+ solvation sheath, reconstruct the interfacial solvation structure, and reactivate dead K. Experimental and theoretical analyses reveal that the iodide/triiodide (I-/I3-) species weaken the coordination of K+ with solvents and FSI- in the bulk electrolyte, generating a weakly coordinated solvation structure, which facilitates K+ desolvation. At the electrode interface, Bi-derived sites preferentially recruit and selectively adsorb free FSI- over carbonate solvents and promote their enrichment toward the inner Helmholtz layer, thereby reconstructing an anion-rich interfacial solvation structure that directs the formation of a robust inorganic-rich SEI. In parallel, the reversible I-/I3- redox couple can reactivate dead K. Benefiting from the synergistic suppression of dendrite growth, reduction of irreversible K loss, and enhancement of interfacial kinetics, the symmetric cells demonstrate stable cycling for over 1300 h at 0.5 mA cm-2 and 0.5 mAh cm-2. AFPMBs also demonstrate markedly improved cycling stability and capacity retention in the carbonate-based electrolyte. This work provides a foundation for designing advanced electrolyte additives to enhance electrochemical stability in AFPMBs.