Yolk–shell carbon microspheres with controlled yolk and void volumes and shell thickness and their application as a cathode material for Li–S batteries

Abstract

Carbon yolk–shell microspheres are ideal sulfur host materials for Li–S batteries because they can accommodate the volume expansion of sulfur during charge–discharge cycles. In this study, yolk–shell structured carbon microspheres are prepared by spray pyrolysis, and their formation mechanism is investigated. SnO₂/carbon–carbon core–shell microspheres, prepared by one-step spray pyrolysis using a solution containing tin(II) oxalate, polyvinylpyrrolidone (PVP), and sucrose, are used as precursor microspheres; the shell and core are formed from PVP and sucrose, respectively. Carbon yolk–shell microspheres with a carbon-void-carbon configuration are prepared by the elimination of SnO₂ using Se under a reducing atmosphere. The carbon yolk–shell microspheres prepared from the solution containing sucrose have more filled yolk than the microspheres prepared from the solution without sucrose. The first discharge and charge capacities of the sulfur infiltrated carbon yolk–shell microspheres with a filled yolk at a current density of 0.1 A g⁻¹ are 1503 and 1368 mA h g⁻¹, respectively. The discharge capacity of the microspheres after the 150th cycle at a current density of 0.5 A g⁻¹ is 602 mA h g⁻¹. The microspheres have high reversible discharge capacities of 817, 735, 626, 513, and 340 mA h g⁻¹ at the current densities of 0.5, 1, 2, 4, and 10 A g⁻¹, respectively. The sulfur-infiltrated carbon yolk–shell microspheres with the filled yolk show superior rate performance compared to the hollow microspheres with negligible yolk.