Graphene Aerogel-based Free-standing Sulfur Film Cathodes For Long-life Lithium-sulfur Batteries

As a novel electrode material, lithium-sulfur（Li-S） battery have a theoretical specific capacity of 1670 mAh g^-1, which is much higher than that of the traditional transition metal based electrode. At the same time, Li-S battery also possesses several advantages such as high energy density, low cost,low toxicity and its natural abundance. Li-S battery holds great potential in the application including flexible electronics, electric vehicles and grid-level energy storage. However, the practical applications of Li-S battery are restricted by its highly insulating nature and high solubility of lithium polysulfides, which lead to low electron transfer and “shuttle effect”.Due to its high energy density and flexibility, flexible electronic products are considered as a kind of revolutionary invention after notebook computers and mobile phones. However, flexible electrodes are limited by its low conductivity and the ability to withstand repeated deformation under pressure.Based on the analysis mentioned above, a combination of Li-S battery and flexible substrate will attract great attention and can be further explored. In order to address the drawbacks faced in Li-S battery and flexible substrates, the following works were conducted:（1）Polymer-modified Li-S active materials with “core-shell” structure.In order to suppress the polysulfide dissolution and the loss of active materials, polyvinylpyrrolidone（PVP） was used to form a layer of polymer shell. The monodispersed PVP coated sulfur particles are about 1 μm in diameter with large surface area, which allows sufficient electrolyte infiltration. The electrode exhibits excellent cycling stability because of the confinement of PVP shell. The results show that an initial discharge capacity of 1230 mAh g^-1 was delivered at 0.1 C and a capacity retention of 450 mAh g^-1 was achieved even after 500 full cycles at 1 C.（2）Graphene aerogel-based flexible substrate.Graphene is an atom-thick material comprising monolayer hexagonal sp2-hybridized carbons. In recent year, graphene has attracted great attention due to its unique two-dimensional（2D） structure, excellent mechanical properties, high conductivity and great chemical stability. In our experiment, we applied graphene aerogel as conductive and flexible substrate, which eliminate the use of conventional metal-based current collector and binders and improve the energy density of the whole electrode.