High graphitized N-doping porous carbon combined with bifunctional separator for the synergistic adsorption/conversion of polysulfides in Li–S batteries

Inferior conductivity of sulfur and inevitable shuttle effect of polysulfides are major obstacle of commercial application for Li–S batteries. Balancing the relation between adsorption effect and polysulfides synchronous conversion on the surfaces of metal oxides is crucial. Herein, a combination strategy with graphitized porous carbon and bifunctional separator is proposed for the multiple suppression of shuttle effect by the synergistic adsorption and synchronous conversion of polysulfides. Silk cocoon derived in-situ N-doping porous carbon and nano-TiO 2 /Super P decorated bifunctional separator are prepared by simultaneous activation/carbonization and surface coating approach, respectively. The unique lamellar porous carbon and nano-TiO 2 effectively encapsulate active sulfur and immobilize polysulfides by the physical/chemical synergetic adsorption. The density functional theory calculations effectively testify that TiO 2 with exposed (101) plane shows high chemical affinity toward polysulfides. Especially the as-prepared porous carbon shows an ultrahigh degree of graphitization that enhances the electronic conductivity . The TiO 2 /Super P-coated conductive bifunctional separator not only accelerates the electron transmission but also synchronously facilitates the redox conversion of polysulfides adsorbed on the TiO 2 surface. Benefiting from the above structure merits, the optimized battery delivers high initial discharge capacity of 1311 mAh g −1 at 0.2C and good cycling stability with a low capacity decay of 0.037% per cycle at 1.0C as well as excellent rate capacity of 977 mAh g −1 at 2.0C. Even with 4.2 mg cm −2 , the discharge capacity of 697 mAh g −1 is still retained after 70 cycles at 0.1C. This combination strategy exploits a novel way for the design and preparation of advanced lithium-sulfur batteries.