A team at Cornell University has used ice-templating to synthesize hierarchical porous carbons (HPCs) with extremely high surface areas of up to 2340 m 2 g −1 with total pore volume of up to 3.8 cm 3 g −1 as supports for sulfur for electrodes in Li–S batteries.

Ice-templating (or freeze-casting) uses the controlled freezing of colloids to template designed porosity in materials. The porosity is basically a replica of the ice crystals, produced by freezing the suspension and subsequently removing the ice crystals by sublimation.

For the electrodes, the hierarchical structure of the carbon originating from interconnected large mesopores (10–50 nm), small mesopores (2–10 nm) and micropores (<2 nm) makes the total available surface area highly accessible, resulting in excellent kinetics.

At high C-rates of 2 C and 5 C, large specific capacities of 647 mA h g−1 and 503 mA h g−1, respectively, were obtained after 200 cycles. In addition, the Cornell team also showed that the cyclic stability is independent of the size of the pores in which the sulfur is initially confined when LiNO 3 is used as the electrolyte additive. This indicated, they said, that capacity fade due to polysulfide shuttle is effectively eliminated and that it is not related to pore size.

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