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Abstract: Plasticizers of poly(ethylene glycol)-borate (PEG-B) esters are added into lithium-conducting gel polymer electrolyte (GPE) in Li–S cells in order to inhibit the unrestrained migration of polysulfide anions. An improvement of the electrochemical properties of the Li–S cell using GPE is observed upon addition of the plasticizers at room temperature. However, a slow decrease of discharge capacities follows after stable cycles. To understand the origin of the capacity fading, electrochemical impedance spectroscopies (EIS), scanning electron microscopy (SEM), X-ray Diffraction (XRD) and X-ray photoelectron spectra (XPS) are adopted. EIS measurements indicate that the decrease of capacity in the Li–S cell using GPE is related to the increase of interfacial resistance between GPE and anode. SEM studies combined with XRD and XPS measurements reveal the increase of interfacial resistance between GPE and anode is results from Li2S corrosion products. Accordingly, the polysulfide anions precipitate on the anode surface, which leads to a reduction of the cycle life of the Li–S cell using GPE. Li-ion transference number measurement shows an increase of transference number before 20th cycles, and then decreased, which suggests that the GPE using PEG-B esters as plasticizers could inhibit the unrestrained migration of polysulfide anions at some time but not permanently. [Copyright &y& Elsevier]

Lithium-sulfur (Li-S) battery has attracted remarkable attention owing to its high theoretical energy density. However, its commercialization is still hampered by the rapid capacity degradation which mainly originates from the polysulfides shuttle between the anode and cathode. In this paper, a functional multiwall carbon nanotube/sulfonated polyaniline (MWCNT/SPANI) modified separator is designed to enhance the electrochemical performance of the Li-S batteries with high sulfur loading. The MWCNT/SPANI-coated separator is highly permselective to Li + but rejects the transportation of polysulfide anions. Besides, the MWCNT/SPANI coating can also work as an upper current collector and provides channels for electron and ion transport to enhance the sulfur utilization and ensure the reactivation of trapped active materials. With the ion selective MWCNT/SPANI-coated separator, the electrochemical performance of the Li-S batteries based on cathodes with high sulfur loading (5 mg cm −2 ) and high sulfur content (72 wt%) has been significantly improved. It delivers a reversible capacity of 913 mA h g −1 at the current density of 100 mA g −1 after 100 cycles, much higher than that of the cells with pristine Celgard separator. Hence, the ion selective MWCNT/SPANI modified separator is promising for developing high-performance Li-S batteries employing cathodes with high sulfur loading and high sulfur content. [ABSTRACT FROM AUTHOR]

A nitrogen-doped carbyne polysulfide (N-CAS) has been prepared by heating the mixture of nitrogen-doped carbyne analogue (N-CA) and sulfur. The nitrogen-doped carbyne analogue was synthesized by the dehydrochlorination and polymerization of 1, 1, 2-trichloroethane and urea. The XPS characterization indicated that nitrogen atoms have been effectively doped into the carbon skeleton with a nitrogen content of 4.32 wt%, and the obtained N-CAS cathode has a porous structure with uneven pore width. The electrochemical results showed that the N-CAS cathode can deliver a high initial capacity (1570mAh/g at a current density of 200 mA/g) and rate capability (500mAh/g at 2000 mA/g), and after 300 cycles, it displays a reversible capacity as high as 900mAh/g in carbonic ester electrolyte, which are better than that of non-doped carbyne polysulfide. These results suggest that doped nitrogen have electrostatic interaction on the lithium polysulfides to improve electrochemical stability and accelerate redox dynamics. [ABSTRACT FROM AUTHOR]