Novel
Composite Polymer Electrolytes of PVdF-HFP Derived by Electrospinning
with Enhanced Li-Ion Conductivities for Rechargeable Lithium–Sulfur
Batteries
Composites
of poly(vinylidene fluoride-co-hexafluoro propylene) (PVdF-HFP) incorporating
10 wt % bis(trifluoromethane)sulfonimide lithium salt (LiTFSI) and
10 wt % particles of nanoparticulate silica (nm-SiO<sub>2</sub>),
nanoparticulate titania (nm-TiO<sub>2</sub>), and fumed silica (f-SiO<sub>2</sub>) were prepared by electrospinning. These membranes served
as host matrix for the preparation of composite polymer electrolytes
(CPEs) following activation with lithium sulfur battery electrolyte
comprising 50/50 (vol %) dioxolane/dimethoxyethane with 1 M LiTFSI
and 0.1 M LiNO<sub>3</sub>. The membranes consist of layers of fibers
with average fiber diameter of 0.1–0.2 μm. CPEs with
f-SiO<sub>2</sub> exhibited higher ionic conductivity with a maximum
of 1.3 × 10<sup>–3</sup> S cm<sup>–1</sup> at 25
°C obtained with 10 wt % filler compositions. The optimum CPE
based on PVdF-HFP with 10 wt % f-SiO<sub>2</sub> exhibited enhanced
charge–discharge performance in Li-S cells at room-temperature
eliminating polysulfide migration, delivering initial specific capacity
of 895 mAh g<sup>–1</sup> at 0.1 C-rate and a very low electrolyte/sulfur
(E/S) ratios between 3:1 to 4:1 mL.g<sup>–1</sup>. The CPEs
also exhibited very stable cycling behavior well over 100 cycles (fade
rate ∼ 0.056%/cycle), demonstrating their suitability for Li-S
battery applications. In addition, the interconnected morphological
features of PVdF-HFP result in superior mechanical properties (200–350%
higher tensile strength). Higher Li-ion conductivity, higher liquid
electrolyte uptake (>250%) with dimensional stability, lower interfacial
resistance, and higher electrochemical stability are some of the attractive
attributes witnessed with these CPEs. With these improved performance
characteristics, the PVdF-HFP system is projected herein as suitable
polymer electrolytes system for high-performance Li–S rechargeable
batteries