Stable cycling of lithium sulfide cathodes through strong affinity with multifunctional binders

Background: Rechargeable lithium sulfur batteries have attracted great interest in recent years because of their high theoretical specific energy which is several times that of current lithium-ion batteries. Compared to sulfur fully-lithiated Li2S represents a more attractive cathode material because it enables pairing with safer lithium metal-free anodes. Stanford researchers have designed and tested a new framework for a rational design of stable and high performance Li2S cathodes by using ab initio simulations to elucidate the interaction between Li2S and lithium polysulfides with various functional groups found in macromolecular binders. Using polyvinylpyrrolidone (PVP) as a binder in one embodiment an initial specific capacity of about 760 mAh g-1 of Li2S (~1090 mAh g-1 of S) was achieved at 0.2C with unprecedented capacity retention of about 94% in the first 100 cycles. Even after prolonged cycling over 500 charge/discharge cycles cells retained about 69% of their initial capacity which corresponds to a small capacity decay of about 0.062% per cycle. Technology Description: This invention describes a method to modify the surface of hollow carbon nanofiber by introducing amphiphilic polymers so as to ensure the binding between the sulfur and the conducting carbon matrix. The hollow carbon nanofiber was fabricated using a template synthesis method in which anodized aluminum oxide (AAO) membranes were coated with thin films of carbon. An amphiphilic polymer was then introduced to the carbon channels by soaking the as-fabricated hollow carbon nanofiber in a solution of the polymer. Sulfur was then infused into the carbon nanofiber by heating to 155 degree C. The AAO was then etched away using phosphoric acid to obtain the sulfur cathode. Ab initio calculation was performed to characterize the effect of the polymer in improving the binding between sulfur and carbon surface. Applications: 1) Improved lithium sulfur battery performance for electronics vehicles energy storage 2) Simple approach for modifying lithium sulfide cathode to achieve high energy density and long cycling