Ultrathin tunable ion conducting nanomembranes for encapsulation of sulfur cathodes

Membranes are of interest for a wide variety of applications such as gas separation, water desalination, fuel cells and batteries. Because the flux across a membrane scales inversely with the membrane thickness, a thick membrane is required to achieve high selectivity, at the expense of permeability. New ultrathin membranes which promise to offer high selectivity and high permeability are highly desirable. Elemental sulfur can provide five times higher capacity than existing Li-ion cathode materials based on transition metal oxides or phosphates. Various problems have hindered the practical use of this highly attractive cathode including the insulating nature of sulfur which retards its reduction and poor electrode stability resulting in an irreversible capacity loss due to polysulfide migration from the cathode to the anode. Here we show the proof of concept for a 5 nm multilayer membrane self-assembled from commercial polyelectrolytes to encapsulate a carbon/sulfur composite and maintain the performance even at discharge rates five times more rapid than its non-encapsulated counterpart.