Constructing multi-functional composite separator of PVDF-HFP/h-BN supported Co-CNF membrane for lithium–sulfur batteries

The functional design of separators has been proved to be one of the most efficient methods to improve the electrochemical performance of lithium–sulfur batteries. In this work, a multifunctional separator with gradual changes to four aspects was constructed by integrating a PVDF-HFP/h-BN membrane with a Co-doped carbon nanofiber. The architecture has four gradations, which offers multifold advantages. First, in terms of density, there is a transition from loose to dense, which results in a higher electrolyte uptake rate, reduces the amount of free electrolyte and further suppresses the shuttle effect. Additionally, in terms of composition, a transition from inorganic to organic is designed, which allows the inorganic and organic components to bind closely and reduces the interfacial resistance. Meanwhile, there is a transition from high electronic conductivity to insulation. The change in electronic conductivity leads to effective conversion of the polysulfide. Finally, in terms of ionic conductivity, there is a transition from low to high, which gives the separator better ability to conduct lithium ions. As a consequence, a battery with the as-constructed multifunctional separator performs with good capacity stability, which demonstrates a new concept for high-performance lithium–sulfur battery design.