The effect of binders on the performance and degradation of the lithium/sulfur battery assembled in the discharged state

Capacity fading on cycling of lithium/sulfur batteries may result from at least four processes: increase of SEI thickness resistance, loss of cathode capacity (precipitation of sulfur species outside the cathode), agglomeration and thickening of sulfur species and increase in cell impedance as a result of reduction of the electrolyte. A very important issue that has not been properly addressed up to now is the influence of the type and content of the cathode binder on the cell parameters and on the electrochemical performance of lithium/sulfur batteries. We present here a detailed analysis and discussion of the electrochemical behavior, during prolonged cycling, of Li2S-based cathodes containing five different binders. The binders under investigation are: poly(vinylidene fluoride) (PVDF-HFP), polyvinylpyrrolidone (PVP), mix of PVP with polyethylene imine (PEI), polyaniline (PANI) and lithium polyacrylate (LiPAA). Sulfur utilization in the cathode follows the order of LiPAA > PVP:PEI > PVP > PVDF-HFP > PANI. Depending on the type of binder, cells provide 500 to 1400 mAh/g (S), 94.6-98.0% faradaic efficiency and enable more than 500 reversible cycles.