Stabilizing Li_1.3Al_0.3Ti_1.7(PO₄)₃|Li Metal Anode Interface in Solid‐State Batteries by Kevlar Aramid Nanofiber‐Based Protective Coating

Abstract Li_1.3Al_0.3Ti_1.7(PO₄)₃ (LATP) solid‐state electrolyte has garnered considerable interest owing to its competitive room‐temperature Li‐ion conductivity, air stability, and economic nature. Nevertheless, the successful implementation of LATP in next‐generation Li‐metal solid‐state batteries (SSBs) is impeded by its high incompatibility with Li metal. Herein, combining the Kevlar aramid nanofiber (KANF) membrane with a solidified electrolyte (SE) formed via in situ polymerization, the SE@KANF protective layer for LATP can be constructed. Such a protective layer not only effectively prevents Li metal from reducing LATP but also provides intimate interface contact and limits unnecessary electron transport. Consequently, Li symmetric battery incorporating SE@KANF layer enables an ultrahigh critical current density of 1.4 mA cm⁻² and stably cycles for over 2000 h at 0.2 mA cm⁻². Moreover, the full SSB coupling with LiFePO₄ cathode delivers a capacity retention of 95% after 180 cycles at 0.1 C at 30 °C. The present study underscores the importance of the protective interface layer in stabilizing the LATP|Li interface.