Functionalized Double Side Coated Separator for Lithium-Sulfur Batteries with Enhanced Cycle Life

Lithium-sulfur batteries are increasingly being investigated due to their high theoretical energy density in comparison to lithium-ion batteries. However, their performance is hindered by the dissolution of polysulfides in liquid electrolytes causing the shuttle effect, which then leads to capacity fading due to loss of active material. Here we report glass fiber separators with both sides coated and doped to suppress the shuttle effect thus restrain the capacity fading and achieve long cycle life. Cathode-facing side is coated with potassium functionalized graphene nanoplates doped with Poly 1,5 diaminoanthraquinone, titanium dioxide, or cyltrimethylammonium bromide, while anode- facing side is coated with potassium functionalized graphene nanoplates (K-FGF) doped with Poly 1,5 diaminoanthraquinone (PDAAQ). Liquid graphene oxide and PVDF binder in NMP solvent are used as a binder alternatively. Electrochemical performances of the batteries with these double side coated separators are tested and compared. It is found that the battery with titanium dioxide(TiO2) doped K-FGF coated separator on the cathode-facing side exhibits high capacity retention of 1191 mAh g−1 and 1237 mAh g−1 after 200 cycles at 1 C and 0.5 C rates respectively. The cell with cyltrimethylammonium bromide (CTAB) doped K-FGF coated separator on the cathode-facing side displays capacity retention of 1189 and 1011 mAh g−1 over 200 cycles for 0.5 C and 1 C respectively. In both cases liquid graphene oxide (L-GO) is used as a binder in the cathode-facing side and PVDF binder in NMP solvent is added at the anode-facing side.