Dual-Layer Li Metal All-Solid-State Battery Based on an Argyrodite-type Li ₆ PS ₅ Cl Catholyte and a Garnet-type Li ₇ La ₃ Zr ₂ O ₁₂ Separator

The integration of argyrodite-type Li₆PS₅Cl (LPSCl) solid-state electrolytes (SSEs) in solid-state batteries faces significant challenges due to their chemical reactivity with lithium metal, which precludes the direct use of lithium metal as an anode alongside LPSCl. In this study, we propose a compelling solution to this issue based on a dual solid-state electrolyte battery architecture. This design combines argyrodite-type LPSCl on the cathode side with a reductively stable garnet-type Li₇La₃Zr₂O₁₂(LLZO) SSE paired with a lithium metal anode. Through in situ synchrotron X-ray diffraction, cyclic voltammetry, and X-ray photoelectron spectroscopy, we confirmed the chemical compatibility of LPSCl and LLZO. Further validation of their electrochemical compatibility using symmetric and full-cell configurations revealed that Li/LLZO/LPSCl/LLZO/Li symmetrical cells maintain cycling stability over 330 cycles at a current density of 0.1 mA cm^–2and an areal capacity of 0.5 mAh cm^–2. The measured interfacial resistance between the LLZO and LPSCl layers was 341 Ω cm². When paired with a LiNi_0.8Mn_0.1Co_0.1O₂(NMC811) cathode active material, the proposed dual-layer Li–metal all-solid-state battery demonstrated high initial charge-storage capacities of 184 mAh g_NMC^–1and Coulombic efficiency (>99.8%) over 375 cycles at a 0.2 C rate under a minimal applied stack pressure of 1 MPa and a temperature of 75 °C.