Free-standing sulfide/polymer composite solid electrolyte membranes with high conductance for all-solid-state lithium batteries

Bulk-type all-solid-state lithium batteries (ASSLBs) with high theoretical capacity and good safety are considered to be promising candidates as future energy storage devices. The ASSLBs with inorganic electrolytes usually have a thick electrolyte layer (more than 1 mm), which significantly reduces the cell-based energy density; therefore, a free-standing high-conductance electrolyte layer with a low thickness is essential for high-performance ASSLBs. In this work, we prepare free-standing 78Li₂S–22P₂S₅ glass-ceramic (7822gc) composite solid electrolyte membranes reinforced with polymer electrolytes with a thickness of 120 μm through a liquid-phase method and systematically investigate the effects of solvents and polymer electrolytes on the microstructure and electrochemical properties of the 7822gc/polymer composite membranes. The sulfide/PEO and sulfide/PVDF composite electrolytes without lithium salt show an ionic conductivity of 2–4 × 10⁻⁴ S cm⁻¹ at room temperature, while the conductivity of those with lithium salt is enhanced to 4–7 × 10⁻⁴ S cm⁻¹. With such a high conductivity and low thickness, an ultra-high areal conductance of 59.0 mS cm⁻² is obtained for the composite electrolyte membranes, which is ~2.7 times of that of pure 7822gc electrolyte pellets. All-solid-state lithium-sulfur batteries (ASSLSBs) with a sulfur/carbon nanotube composite cathode and a Li–In alloy anode are prepared. The cell-based energy density is as high as 87.0 Ah L⁻¹. A discharge capacity of 725.1 mA h g⁻¹ at 0.176 mA cm⁻² after 100 cycles and a high capacity retention of 93.2% are achieved for the cells with 7822gc/polymer composite electrolyte membranes.