Liquid Graphene Oxide Binder and Modified Glass Fiber Separator for Lithium Sulfur Battery with Highly Improved Cycling Performance
Lithium sulfur (Li-S) batteries with high theoretical energy density (~2.5 kWh kg-1) and high theoretical gravimetric capacity (1672 mAh g-1) have drawn great attention as they are promising candidates for large scale energy storage devices. Unfortunately some technical obstacles hinder the practical application of Li-S batteries such as formation of polysulfide intermediates between cathode and anode as well as the insulating nature of sulfur cathode and other discharge products. Glass fiber separators provide some cavities to withstand the volume change of sulfur during cycling leading to long-term cycling stability. Here, application of polar materials with novel liquid graphene oxide (L-GO) binder rather than the standard polyvinylidene fluoride (PVDF) binder as effective coatings on the glass fiber separator of the Li-S cell have been developed to suppress the shuttle effect. The deposition of silicon dioxide (SiO2), titanium dioxide (TiO2) and poly (1,5-diaminoanthraquinone) (PDAAQ) with L-GO binder on the glass fiber separator was investigated with polycarboxylate functionalized graphene (PC-FGF/S) cathode and Li metal anode. The cells with modified coatings and L-GO as an efficient binder could accelerate conversion of long-chain polysulfides to short-chain polysulfides and significantly delayed the growth of lithium dendrites resulted the capacity retention of ~ 1020, 1070 and 1190 mAh g-1 for the cells with SiO2/L-GO, TiO2/L-GO and PDAAQ/L-GO coated separators after 100 cycles. The results demonstrate that ultrathin SiO2, TiO2 and PDAAQ containing coatings with L-GO binder on the glass fiber separator can drastically improve the cyclability of the Li-S cells.