Lithium Sulfide (Li₂S)/Graphene Oxide Nanospheres with Conformal Carbon Coating as a High-Rate, Long-Life Cathode for Li/S Cells

Abstract

In recent years, lithium/sulfur (Li/S) cells have attracted great attention as a candidate for the next generation of rechargeable batteries due to their high theoretical specific energy of 2600 W·h kg^–1, which is much higher than that of Li ion cells (400–600 W·h kg^–1). However, problems of the S cathode such as highly soluble intermediate species (polysulfides Li₂S_<i>n</i>, <i>n</i> = 4–8) and the insulating nature of S cause poor cycle life and low utilization of S, which prevents the practical use of Li/S cells. Here, a high-rate and long-life Li/S cell is proposed, which has a cathode material with a core–shell nanostructure comprising Li₂S nanospheres with an embedded graphene oxide (GO) sheet as a core material and a conformal carbon layer as a shell. The conformal carbon coating is easily obtained by a unique CVD coating process using a lab-designed rotating furnace without any repetitive steps. The Li₂S/GO@C cathode exhibits a high initial discharge capacity of 650 mA·h g^–1 of Li₂S (corresponding to the 942 mA·h g^–1 of S) and very low capacity decay rate of only 0.046% per cycle with a high Coulombic efficiency of up to 99.7% for 1500 cycles when cycled at the 2 C discharge rate