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[en] Using conductive interlayers to act as the ‘upper current collector’ is a common strategy to suppress the shuttle effect in lithium-sulfur batteries. However, the current widely used interlayers generally have the disadvantages of poor conductivity and complicated fabrication. Herein, we report a novel carbon paper prepared by simple wet laid method. The as-prepared carbon paper exhibits excellent conductivity of 11.9 S cm−1 and 3D conductive structure. Finally, the carbon paper as an interlayer for lithium-sulfur batteries displays an initial capacity of 1091 mAh g−1 at C/5 rate, and remains 631 mAh g−1 after 200 cycles with a decay rate of 0.21% per cycle. (paper)
[en] Polysulfide shuttling has been the primary cause of failure in lithium-sulfur (Li-S) battery cycling. In this paper, we demonstrate an nucleophilic substitution reaction between polysulfides and binder functional groups can unexpectedly immobilizes the polysulfides. The substitution reaction is verified by UV–visible spectra and X-ray photoelectron spectra. The immobilization of polysulfide is in situ monitored by synchrotron based sulfur K-edge X-ray absorption spectra. The resulting electrodes exhibit initial capacity up to 20.4 mAh/cm2, corresponding to 1199.1 mAh/g based on a micron-sulfur mass loading of 17.0 mg/cm2. The micron size sulfur transformed into nano layer coating on the cathode binder during cycling. Directly usage of nano-size sulfur promotes higher capacity of 33.7 mAh/cm2, which is the highest areal capacity reported in Li-S battery. Finally, this enhance performance is due to the reduced shuttle effect by covalently binding of the polysulfide with the polymer binder.
[en] This review article mainly encompasses on the state-of-the-art electrolytes for lithium–sulfur batteries. Different strategies have been employed to address the issues of lithium–sulfur batteries across the world. One among them is identification of electrolytes and optimization of their properties for the applications in lithium–sulfur batteries. The electrolytes for lithium–sulfur batteries are broadly classified as (i) non-aqueous liquid electrolytes, (ii) ionic liquids, (iii) solid polymer, and (iv) glass-ceramic electrolytes. This article presents the properties, advantages, and limitations of each type of electrolytes. Also, the importance of electrolyte additives on the electrochemical performance of Li–S cells is discussed.
[en] The effect of solvent component on the discharge performance of lithium-sulfur (Li/S) cell and the optimal composition of ternary electrolyte for the improved discharge performance of the cell have been investigated. The capacity value and capacity stability with cycle are dependent on the nature of solvent as well as the composition of mixed solvent. The change trend of discharge performance as a function of content of each solvent component is studied. Capacity value increases as the 1,3-dioxolane (DOX) content decreases. Average discharge voltage shows larger value when the 1,2-dimethoxy ethane (DME) content is small. Finally, we have obtained the optimal solvent composition by using a statistical method
[en] Lithium-sulfur (Li-S) batteries stand as an important candidate for next-generation high-energy secondary batteries due to its high specific capacity, low cost and environmental friendliness. However, practical application of Li-S batteries suffers from low rechargeability, poor rate capability and cycling instability of sulfur cathode, which can be mainly ascribed to the poor conductivity of sulfur and the dissolution of the intermediate polysulfides generated during discharge-charge cycles. In this work, a Nafion/super P-modified dual functional separator is designed to improve the long-term cycle stability and rate capability of the pure sulfur cathode. The electrostatic repulsion between the SO_3"− groups and the dissolved negative S_n"2"− ions, and the trap and reutilizing effect of super P for polysulfides, provide double insurance to confine the polysulfides within the cathode side, leading to great improvement in both reversible capacity and cycling stability of the sulfur cathode as compared to the battery with pristine Celgard separator. With such dual functional separator, a simple elemental sulfur cathode with 70% S content delivers a high initial discharge capacity of 1087 mAh g"−"1 at 0.1C and a long-term cyclability with only 0.22% capacity fade per cycle over 250 cycles at 0.5C.
[en] The protected bis(hydroxyorganyl) polysulfides synthesized have been tested as modifiers of electrolyte of lithium-sulfur rechargeable batteries. The best result (35% increase of the battery capacity at the 50th cycle) was attained using 5 wt.% of 2,2,12,12-tetramethyl-4,10-diphenyl-3,11-dioxa-6,7, 8-trithia-2,12-disilatridecane. Bis(hydroxyorganyl) polysulfides protected at the hydroxyl group have been synthesized for the first time by the reaction of oxiranes with sodium polysulfide (ethanol, NaHCO3, 12 h, 20-25 oC) in yield 21-87%. For the hydroxyl protection in the hydroxy polysulfides, the acetal, tri(methyl)silyloxy or tri(ethoxy)silyl protecting groups were employed.
[en] Highlights: • A new way to analyze textural transformations in Li-S cathodes is proposed. • Redistribution of active sulfur species and pore blocking effects can be identified. • Different pronounced cathode changes can be identified. • Results providing insights in cell mechanism and the role of polysulfide solubility. • Electrolyte properties influence the cathode changes upon cycling decisively. Nitrogen physisorption was used to analyze textural transformations in lithium-sulfur cathodes during cycling for two alternate electrolyte systems. Significant impact of the electrolyte type on the accessible cathode porosity in the charged vs. discharged state was detected, providing important insights in the cells conversion mechanism and the role of polysulfide solubility. The main advantage of the method lies in the resolution of pore accessibility and size distributions. Thus, depending on the state of charge (SoC), the C-rate used for cycling as well as electrolyte properties (i.e. polysulfide solvation), significant differences in the redistribution of active sulfur species as well as pore blocking effects can be identified. This methodology might facilitate interpretation and further optimization to achieve long-term stable lithium-sulfur batteries.
[en] Graphene-mesoporous carbon/sulfur composites (G-MPC/S) were constructed by melt-infiltration of sulfur into graphene-mesoporous carbon which was synthesized by soft template method. The SEM and BET results of the graphene-mesoporous carbon show that the as-prepared sandwich-like G-MPC composites with a unique microporous-mesoporous structure had a high specific surface area of 554.164 m2 · g−1 and an average pore size of about 13 nm. The XRD analysis presents the existence of orthorhombic sulfur in the G-MPC/S composite, which indicates the complete infiltration of sulfur into the pores of the G-MPC. When the graphene-mesoporous carbon/surfur composites (G-MPC/S) with 53.9 wt.% sulfur loading were used as the cathode for lithium–sulfur (Li–S) batteries, it exhibited an outstanding electrochemical performance including excellent initial discharge specific capacity of 1393 mAh · g−1 at 0.1 °C, high cycle stability (731 mAh · g−1 at 200 cycles) and good rate performance (1038 mAh · g−1, 770 mAh · g−1, 518 mAh · g−1 and 377 mAh · g−1 at 0.1 °C, 0.2 °C, 0.5 °C and 1 °C, respectively), which suggested the important role of the G-MPC composite in providing more electrons and ions channels, in addition, the shuttle effect caused by the dissolved polysulfide was also suppressed. (paper)
[en] Recent progress in improving Li–S batteries’ cathodes, anodes, and electrolytes via different approaches is summarized. The poor conductivity of sulfur cathodes, the dissolution of polysulfide intermediates, and the high reactivity of metal Li anodes currently motivate a great deal of research. Urgent challenges concerning Li anodes are also emphasized. (topical review)
[en] A chemical stability between polysulfides and electrolyte is considered to be crucial to achieving good electrochemical performance of lithium–sulfur (Li–S) batteries since long-chain polysulfides which dissolve easily into common electrolyte can trigger substantial electrolyte decomposition due to their nucleophilic nature. In this work, we investigated the chemical reactivity of polysulfides toward carbonate-based electrolytes through a simple probing experimental method and found that the polysulfides react with carbonate-based electrolytes via a nucleophilic addition or substitution reaction leading to a sudden capacity fading of lithium sulfur cells by loss of active sulfur. This study strongly suggests that electrolytes for Li–S system should not possess an electrophilic functionality to avoid undesired chemical reaction with polysulfides. In addition, we show that the methodology developed in this work for the verification of chemical stability between polysulfides and electrolyte can be widely applicable to screening other potential electrolyte candidates