Solution-recrystallization mechanism of g-C3N4 and its inhibitory effect on polysulfide shuttling through cross-linked porous network structure with carbon nanotubes

Abstract

Lithium-sulfur batteries have the advantages of high specific capacitance density and high theoretical capacity, which are attracting more and more attention in the field of energy storage. However, in practice, there are still many difficulties, such as the poor conductivity of sulfur, the large volume expansion of sulfur, and the shuttle effect of polysulfides, which lead to rapid capacity degradation and poor cycling stability. Here, we utilize g-C3N4 which is soluble in concentrated H2SO4 and has a good solution-recrystallization reversible property, alcohol was used as deprotonation solvent, the g-C3N4/CNT composites were prepared by the method of solution-recrystallization as sulfur host. The dissolution and precipitation mechanism of g-C3N4 in concentrated sulfuric acid and the composite mechanism with CNT were revealed. The g-C3N4/CNT/S cathode exhibit excellent electrochemical properties. The capacity of SPCNT11 can still be maintained to 1013 mAh·g−1 after 200 cycles at 0.2 C, with a capacity retention rate of 73.2%. Even at rate of 4C, the SPCNT11 material still has a capacity of 547 mAh·g−1 after 450 cycles. The first-principle calculation results further reveal that the interaction between g-C3N4 and CNT produces conjugated effect, the constrain of g-C3N4 to electrons is weakened, enhances its conductivity, and thus realizes the effect of promoting polysulfide transformation.