Uniform Polypyrrole Layer-Coated Sulfur/Graphene Aerogel via the Vapor-Phase Deposition Technique as the Cathode Material for Li–S Batteries

The practical application of Li–S batteries is hampered because of their poor cycling stability caused by electrolyte-dissolved lithium polysulfides. Dual functionalities such as strong chemical adsorption stability and high conductivity are highly desired for an ideal host material for the sulfur-based cathode. Herein, a uniform polypyrrole layer-coated sulfur/graphene aerogel composite is designed and synthesized using a novel vapor-phase deposition method. The polypyrrole layer simultaneously acts as a host and an adsorbent for efficient suppression of polysulfide dissolution through strong chemical interaction. The density functional theory calculations reveal that the polypyrrole could trap lithium polysulfides through stronger bonding energy. In addition, the deflation of sulfur/graphene hydrogel during the vapor-phase deposition process enhances the contact of sulfur with matrices, resulting in high sulfur utilization and good rate capability. As a result, the synthesized polypyrrole-coated sulfur/graphene aerogel composite delivers specific discharge capacities of 1167 and 409.1 mA h g–1 at 0.2 and 5 C, respectively. Moreover, the composite can maintain a capacity of 698 mA h g–1 at 0.5 C after 500 cycles, showing an ultraslow decay rate of 0.03% per cycle.