High performance all-solid-state lithium-sulfur battery using a Li2S-VGCF nanocomposite

In lithium-sulfur batteries, cyclability is often strongly limited by a high interfacial resistance caused by poor contact between the active material and electron and lithium ion transporting materials. Here, we develop a Li2S-VGCF (Vapor Grown Carbon Fiber) nanocomposite positive electrode for an all-solid-state lithium-sulfur battery that significantly improves cyclability. The Li2S-VGCF nanocomposite is prepared by a solution-based technique with subsequent heat-treatment in order to control the formation of Li2S nanocrystals within the VGCF electron conducting matrix. The small, well-dispersed Li2S nanocrystals offer a large contact area with the solid electrolyte and electron conducting carbon in the composite cathode. To further improve conductivity, the composite cathode employs a multi-dimensional approach with long 1-D VGCF fibers supporting long distance electron transport and 0-D carbon powder enhancing the contact area with the Li2S active material at lower total carbon content. In the all-solid-state batteries, the highest initial capacity of 469 mhA∙g−1 is obtained at conditions of 500 °C during heat-treatment. Activation of Li2S is observed during the first 10 cycles. Subsequently, the capacity gradually increased up to 600 mAh∙g−1 (g of Li2S). The optimized cell exhibits excellent cyclic performance through 20 cycles and a Coulombic efficiency of ∼100%.