High performance all-solid-state lithium-sulfur battery using a Li₂SVGCF nanocomposite

Abstract

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 furthet improve conductivity, the composite cathode employs a multi-dimensional approach with long 1-D VGCF fibers supporting long distance electron transport and O-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%.