Functional interlayer of PVDF-HFP and carbon nanofiber for long-life lithium-sulfur batteries

Abstract

In the present work, we develop 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 achieving a three-dimensional (3D) structural design. The CNF network is used as the current collector and S holder to overcome the insulating nature and volume expansion of S, while the composite membrane comprises a gel polymer poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), and CNF additive is used as an interlayer to trap polysulfides and recycle the remaining S species, leading to a 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, an outstanding cycle stability was also achieved at even higher current densities (1.0 to 2.0 °C), indicating its good potential for practical applications of Li-S batteries.