In-situ coating strategy to synthesize ultra-soft sulfide solid-state electrolytes for dendrite-free lithium metal batteries

High energy density lithium metal batteries play a crucial role in future energy storage. High ionic conductivity argyrodite-type Li5.5PS4.5Cl1.5 is a promising candidate for future lithium metal all-solid-state batteries. However, under cold pressing conditions, the combination of high electronic conductivity and high porosity significantly accelerates the growth of lithium dendrites, resulting in low capacity and a short lifespan. In this study, we combined a simple wet ball milling and in-situ polymerization process to fabricate a polyvinylene carbonate-coated sulfide composite solid electrolyte. The ultra-soft particle, when cold-pressed without binders, completed a tightly packed and void-free internal structure. This electrolyte, combined with a stable LiF-rich interface layer on lithium metal, held a higher critical current density of 2.0 mA cm-2 than 0.65 mA cm-2 of uncoated argyrodite and a 2000-hour stable cycle at 0.5 mA cm-2 in lithium symmetric cells. The unique coating structure also mitigated the chemomechanical failure between electrolyte and electrode, preventing the rapid increase of interface impedance and achieving a high initial capacity of 173.5 mAh g-1 without a short circuit for 300 cycles in LiNi0.6Co0.2Mn0.2O2//Li cells.