Activating Forbidden Intercage‐Ionic‐Diffusivity by Anion‐Gradient‐Disordered Interphase for Ultrastable Argyrodite‐Based All‐Solid‐State Lithium Metal Batteries

Lithium argyrodite sulfide electrolytes show great potential in all‐solid‐state lithium metal batteries (ASSLMBs) due to their high ionic conductivity and ductile feature, among which Li6PS5I presents the most promising stability with Li metals but a low ionic conductivity (≈10−6 S cm−1). It is because of the absence of S2−/I− disorder and thus the forbidden Li+ ion intercage migrations. Herein, argyrodite particles with iodine‐gradient‐disordered interphase were designed that opened up the proscribed Li+ ion intercage jumps and synergistically blocked the interfacial electron leakage for ultrastable ASSLMBs. Density functional theory calculations and 7Li spin‐lattice relaxation NMR experiments prove the activated and even accelerated intercage Li+ conduction with reduced migration barrier. Electrostatic potential profiles also certify the electron transition‐shielding interphase as the origin of parasitic‐reaction‐free Li interface. Gathered evidence of, other characterizations demonstrated the combination of high ionic conductivities (cold press 5.7 mS cm−1), low electron conductivity (1.5×10−8 S cm−1), improved critical current density (1.65 mA cm−2), excellent stability with Li metal (over 1,500 h) and prominent cycling and rate performance. This study provides insights on novel interphase design to fulfill the cooperatively high ionic conductivity and high Li metal‐compatibility for high‐performance ASSLMBs.