CF@rGO/PPy-S Hybrid Foam with Paper Window-like Microstructure as Freestanding and Flexible Cathode for the Lithium–Sulfur Battery

The lithium–sulfur (Li–S) battery is one of the most promising energy-storage systems due to its high energy density. However, the insulation of sulfur and the “shuttle effect” hinder the exertion of its capacity. Rational structure design and functionalization of host materials are crucial for the high-performance Li–S battery. Herein, the carbon foam (CF), whose fiber surface is decorated with polypyrrole (PPy)-modified reduced graphene oxide (rGO) flakes, is chosen as a 3D freestanding matrix to achieve a multifunctional framework with paper window-like microstructure. Acting as both sulfur host and current collector of cathode, the interconnecting carbon fibers of CF afford an integrated flexible conductive network to accelerate electronic transport; additionally, the rGO/PPy attached to carbon fibers not only improve the sulfur loading due to the large specific surface of rGO but also inhibit the “shuttle effect” because of chemisorption to polysulfides from PPy. Thanks to these advantages, the resulting flexible and freestanding electrode displays a high initial discharge capacity (1437 mAh g–1 at 0.1 C, 1 C = 1675 mA g–1) and excellent capacity retention at 1 C with average capacity loss of only 0.044% every cycle for over 100 cycles, suggesting that this rational structure design has the potential to be applied in the flexible, stable, and energy-dense Li–S battery.