PVDF-HFP + Carbon Nanofiber as a Functional Interlayer for Long-Life Lithium-Sulfur Batteries

Recently, lithium-sulfur (Li-S) battery has become increasingly attractive due to the high theoretical specific capacity (1675 mAh g^-1) and energy density (2567 Wh kg^-1). In addition, the cost can also be reduced dramatically because S is abundant in the Earth crust. In the present work, we have developed a scalable and inexpensive design for lithium-sulfur (Li-S) batteries by capping a flexible gel polymer / carbon nanofiber (CNF) composite membrane onto a free-standing and binder-free CNF + Li₂S₆ cathode, thus forming a three-dimensional (3D) structural design. While the CNF network was used as the current collector and S holder to overcome the insulating nature and volume expansion of S, the composite membrane composed of a gel polymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) and CNF additive was used as an interlayer to trap polysulfides and recycle remaining S species, leading to high specific capacity and long cycle life. This 3D structure enables excellent cyclability for 500 cycles at 0.5 C with a small capacity decay of 0.092% per cycle. Furthermore, outstanding cycle stability has also been achieved at even higher current densities (1.0 C - 2.0 C), indicating the great promise for practical applications of Li-S batteries.