Biphasic interfacial engineering of lithium metal anode using zinc nitrate for sulfide-based all-solid-state batteries

Sulfide-based all-solid-state lithium batteries (ASSLBs) are promising candidates for high-energy-density energy-storage systems, but their practical implementation is strongly limited by interfacial instability between lithium metal and sulfide solid electrolytes. Here, we report a simple ex situ surface treatment of lithium metal using zinc nitrate to construct a biphasic protective interphase for sulfide-based ASSLBs. Multi-scale structural and chemical analyses using SEM-EDS, XRD, XPS, and ToF-SIMS show that the modified interphase is compositionally differentiated, consisting of an N-rich outer region containing reduced Li N species and a LiZn-rich inner region adjacent to the Li substrate. Symmetric-cell measurements reveal that the treated Li exhibits more stable plating/stripping behavior and lowers interfacial resistance growth compared with bare Li, indicating mitigation of continuous interfacial degradation. Post-cycling analysis on the electrolyte side further confirms that the treated Li markedly suppresses sulfide-electrolyte decomposition. When applied to Li 6 PS 5 Cl-based full cells with a high-loading Ni-rich layered oxide cathode (4 mAh cm −2 ), the treated Li anode delivers stable rate capability and markedly improved cycling durability under demanding conditions. In particular, the interface-treated full cell retains more than 98% of its capacity over 100 cycles at 1C, whereas the bare-Li counterpart shows abnormal charge-capacity inflation and early shorting. These results demonstrate that a chemically simple yet functionally differentiated biphasic interphase can effectively stabilize the Li/sulfide-electrolyte interface and provide a practical interfacial-engineering strategy for sulfide-based lithium-metal ASSLBs.