Inverse vulcanization of bismaleimide and divinylbenzene by elemental sulfur for lithium sulfur batteries

A novel approach to fabricate sulfur rich thermosets as materials for Li-S batteries is described. For this purpose, polybismaleimide copolymers were synthesized by reacting bismaleimide (BMI) monomer and elemental sulfur at 180 °C. Parameters such as monomers and feed ratios on the polymerization were studied. Divinylbenzenes were also used in the formulation to increase sulfur feed ratios up to 70 wt%. The thermal stability of the copolymers was also investigated by using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). BMI based copolymers had shown excellent thermal stability and yielded up to 40% char yield at 800 °C. The obtained insoluble copolymers were used in Li-S battery applications. Thus, galvanostatic discharge-charge experiments were carried out to evaluate the electrochemical performance of these materials. Both 30% sulfur containing, poly(S-BMI)30%, and 70% sulfur containing, Poly(S-BMI-DVB)70%, composites exhibited a staircase voltage profile which is typical for Li-S batteries. These materials, as Li-S battery cathodes, demonstrated around 400 mA h/g specific capacities at 50 cycles.