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-SiO2), nanoparticulate titania (nm-TiO2), and fumed silica (f-SiO2) 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 LiNO3. The membranes consist of layers of fibers with average fiber diameter of 0.1–0.2 μm. CPEs with f-SiO2 exhibited higher ionic conductivity with a maximum of 1.3 × 10–3 S cm–1 at 25 °C obtained with 10 wt % filler compositions. The optimum CPE based on PVdF-HFP with 10 wt % f-SiO2 exhibited enhanced charge–discharge performance in Li-S cells at room-temperature eliminating polysulfide migration, delivering initial specific capacity of 895 mAh g–1 at 0.1 C-rate and a very low electrolyte/sulfur (E/S) ratios between 3:1 to 4:1 mL.g–1. 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.

Li-Sulfur (Li-S) batteries are emergent next-generation energy storage devices due to their very high specific energy density (~2567 Wh g-1) but are limited by polysulfide dissolution issues. In this work, chemically synthesized sulfur containing non-carbonized metal organic framework (S-MOF) cathodes show initial specific capacities of 1476 mAh g-1 stabilizing at ~609 mAh g-1 with almost no fade for over 200 cycles. Post-cycled separators of the S-MOF cathodes display complete absence of polysulfides after cycle 1, 20 and 200. It was identified that the occurrence of carbonate species in the MOF structure resulted in the formation of C-S bonded species causing retention of polysulfide at the electrode surface ensuring long-term stability. However, this observed capacity drop during the first 10 cycles is attributed to the oxidation of some of the infiltrated sulfur by the MOF as determined by electrochemical and X-ray photoelectron spectroscopy (XPS) analyses. Nevertheless, the negligible fade rate (0.0014% cycle-1) and complete prevention of polysulfide dissolution renders these cathodes most promising candidates for Li-S batteries. Understanding of this transformation behavior in sulfur-containing MOF is essential to engineer chemically-bonded host-structures capable of efficient polysulfide trapping, a key pathway to establishing novel platforms for achieving high power Li-S batteries.

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Lithium–sulfur (Li–S) batteries with high theoretical capacity (≈1650 mAh g−1) and specific energy density (≈2567 Wh g−1) have not achieved commercialization status due to low cycling stability arising from lithium polysulfide dissolution. Herein, sulfur infiltrated noncarbonized noncarbonate containing metal organic complex framework material (CFM) systems; sulfur‐copper‐bipyridine‐CFM (S‐Cu‐bpy‐CFM) and sulfur‐copper‐pyrazine‐CFM (S‐Cu‐pyz‐CFM) are developed as sulfur cathodes for the first time. The S‐Cu‐bpy‐CFM and S‐Cu‐pyz‐CFM show an initial capacity of 1626 and 1565 mAh g−1 with stable capacities of 1063 and 1025 mAh g−1, respectively, after 150 cycles. An X‐ray photoelectron spectroscopy (XPS) analysis after sulfur infiltration reveals the presence of —C—S— bonds arising from the Lewis acid–base interaction of the CFMs with sulfur. The battery separators cycled with the CMF cathodes display complete absence of polysulfides after 150 cycles. These CFM cathodes exhibit an initial fade in capacity during the first ≈25 cycles attributed to the irreversible reaction of nitrogen with sulfur (—N—S—) during cycling. A clear understanding of this chemical interaction between sulfur and nitrogen present in the sulfur‐infiltrated CFMs is essential for engineering nitrogen containing hosts for trapping polysulfides effectively. Understanding reported here will lead to new materials for achieving the high specific energy densities characteristic to Li–S batteries.