Hierarchical Sulfur-Based Cathode Materials with Long Cycle Life for Rechargeable Lithium Batteries



Composite materials of porous pyrolyzed polyacrylonitrile–sulfur@graphene nanosheet (pPAN–S@GNS) are fabricated through a bottom-up strategy. Microspherical particles are formed by spray drying of a mixed aqueous colloid of PAN nanoparticles and graphene nanosheets, followed by a simple heat treatment with elemental sulfur. The pPAN–S primary nanoparticles are wrapped homogeneously and loosely within a three-dimensional network of graphene nanosheets (GNS). The hierarchical pPAN–S@GNS composite shows a high reversible capacity of 1449.3 mAh g−1sulfur or 681.2 mAh g−1composite in the second cycle; after 300 cycles at a 0.2 C charge/discharge rate the capacity retention is 88.8 % of its initial reversible value. Additionally, the coulombic efficiency (CE) during cycling is near 100 %, apart from in the first cycle, in which CE is 81.1 %. A remarkable capacity of near 700 mAh g−1sulfur is obtained, even at a high discharge rate of 10 C. The superior performance of pPAN–S@GNS is ascribed to the spherical secondary GNS structure that creates an electronically conductive 3D framework and also reinforces structural stability.