(684b) Nitrogen-Doped Graphene Paper As Electrodes for High-Performance Lithium/Dissolved Polysulfide Batteries

Graphene sheets with adsorbed polydiallyldimethylammonium chloride can be transformed into nitrogen-doped, free-standing paper (NGP) by high temperature treatment. The NGP are conducting, and can be used as binder-free electrodes for the state-of-the-art Li/dissolved polysulfide batteries.  When tested in the catholyte configuration of soluble polysulfides in a liquid electrolyte, the NGP showed rather stable cycling behaviour and high charge storage capacities, achieving specific capacities of ~1000 mAh/g (based on sulfur) after 100 cycles and coulombic efficiencies >98%. These values were significantly better than undoped graphene papers (GP). The NGP material and the electrochemical cells were characterized with XRD, XPS, TGA, AFM, electron microscopy, and Raman and impedance spectroscopy before and after cycling. The results showed stronger binding of sulfur to NGP relative to GP, which were consistent with modelling results from DFT calculations, which further showed that the pyrrolic and pyridinic N were more effective than quaternary N in interaction with lithium polysulfides. The modelling results were substantiated experimentally by thermal conversion of pyrrolic and pyridinic N into quarternary N with accompanying degradation in battery performance. Reasons for the improved performance of nitrogen-doped material were proposed.