Grafting polyethyleneimine on electrospun nanofiber separator to stabilize lithium metal anode for lithium sulfur batteries

High-energy-density lithium sulfur (Li-S) batteries are suffering several seemingly insurmountable barriers, including lithium dendrite formation and polysulfides shuttling. Functional separator, which bridges anode, electrolyte and cathode together, has the potential to offer a perfect solution to these concerns. Herein, we develop a functional ammoniated polyacrylonitrile (PAN) nanofiber separator (APANF) which can simultaneously inhibit Li dendrite formation and polysulfides shuttling. Branched polyethyleneimine (PEI) are fixed on the electrospun PAN nanofiber mat via a chemical grafting to provide amino groups. Such strongly polar separator can well regulate the uniform Li ions distribution and induce the formation of the Li3N-rich SEI layer, resulting in an interesting 3D spherical and dendrite-free Li deposit pattern. The coulombic efficiency of resulting Li anode can be improved up to 98.8% with a low overpotential of 15 mV. Meanwhile, the separator can also serve as a block for polysulfides shutting due to the strong chemical adsorption capability of PEI, thus facilitating the capacity retention of sulfur cathode. This work provides an easy and scalable alternative to conventional polyolefin separators for solving problems in both anode and cathode of Li-S battery.