Hetero-coating of spherical graphite with sulfide solid electrolytes via the SEED process for all-solid-state lithium batteries

Abstract

Spherical graphite (SG) particles coated with an Li₇P₂S₈I solid electrolyte (SE) were synthesized using a liquid-phase process to fabricate high-performance anode composites for all solid-state batteries. Initially, an Li₂S layer was deposited onto SG, which subsequently combined with an Li₂S–P₂S₅–LiI ethyl propionate solution, forming a uniform Li₇P₂S₈I precursor layer. This process utilized the Li₂S layer as a scaffold to promote homogeneous growth of the Li₇P₂S₈I SE. The resulting SE layers established excellent interfacial contact with SG, enhancing ionic transport efficiency. The obtained anode composite (87 wt % SG and 13 wt % Li₇P₂S₈I) demonstrated favorable charge–discharge performance despite low SE wt %. The microstructure and electrochemical properties of the SE layers were investigated using scanning electron microscopy and electrochemical impedance spectroscopy. To further enhance Li-ion conductivity in the anode layer, ultrathin Li₇P₂S₈I coatings on SG particles were combined with argyrodite-type SE, which is well known for its high ionic conductivity. A composite of 97 wt % SG, 3 wt % Li₇P₂S₈I, and argyrodite-type SE (SG:total SE = 70:30) exhibited excellent cycle performance in a half-cell, maintaining a capacity of 251 mAh g⁻¹ after 100 cycles with a 95 % capacity retention rate.