A pomegranate-structured sulfur cathode material with triple confinement of lithium polysulfides for high-performance lithium–sulfur batteries

Abstract

High-performance lithium–sulfur batteries are widely and intensively pursued, owing to their projected high energy density and low cost. However, realizing the stable cycling of a sulfur cathode with good discharging/charging rate capability under high sulfur content and high sulfur loading conditions remains a major challenge. Confining the dissolvable lithium polysulfide intermediates while addressing the intrinsic low electrical conductivity of sulfur is a key approach toward solving the problem. This work presents the design of a pomegranate-structured sulfur cathode material with high electrochemical performance. To synthesize the material, mesoporous carbon particles with ferrocene decoration are infiltrated with sulfur and then wrapped into secondary particles by dendrimer-linked graphene oxide. In the designed structure, the mesoporous carbon serves as a conductive matrix and porous host for sulfur species; ferrocene provides polar sites to bind lithium polysulfides chemically; the dendrimer-linked graphene oxide encapsulation layers further confine leaching of polysulfides and ferrocene into the electrolyte. With the three components providing triple confinement of the polysulfides, the material with a high sulfur content of 75.7 wt% exhibits excellent cycling stability and good rate capability. A capacity of 826 mA h g⁻¹ can be delivered at 1.0C with an average decay of only 0.010% per cycle over 1200 cycles. With a high S mass loading of 4 mg cm⁻², the cathode can still be cycled at 0.5C for 300 cycles with a capacity decay as low as 0.038% per cycle.