Mechanism-Guided Design of Conductive and Stable Interlayers for NASICON-Based Solid-State Lithium Batteries

High Resolution Image Download MS PowerPoint Slide NASICON-type Li 1.5 Al 0.5 Ge 1.5 (PO 4 ) 3 (LAGP) suffers from severe interfacial instability against lithium metal due to Ge reduction and insulating interphase formation. Herein, a thin (∼8 µm) composite polymer electrolyte (CPE) is introduced as an interfacial layer to decouple LAGP from direct contact with Li and to regulate interfacial Li + transport. The CPE comprises Ta-doped garnet Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 and succinonitrile embedded in a polyethylene oxide matrix, delivering a room-temperature ionic conductivity of 1.6 × 10 −4 S cm −1 . With this interlayer, Li|CPE|LAGP|CPE|Li symmetric cells exhibit stable cycling for over 300 h with a low overpotential of ∼75 mV, and all-solid-state full cells retain 90% of their capacity after full-cell cycling. Molecular dynamics simulations reveal that garnet fillers promote Li salt dissociation via anion adsorption while simultaneously moderating interfacial Li + mobility through polymer immobilization and interfacial energy barriers, explaining the improved interfacial stability observed experimentally.