A model cathode for mechanistic study of organosulfide electrochemistry in Li-organosulfide batteries

Organosulfides offer new opportunities for high performance lithium-sulfur(Li-S)batteries because of materials abundance,versatile structures and unique properties.Yet,their redox kinetics as well as cycling performance need to be further improved.Employing redox mediators is a highly effective strategy to address above challenges.However,the underlying mechanism in this chemistry is so far insufficiently explored.Here,phenyl disulfide(Ph S–SPh)and phenyl diselenide(Ph Se–Se Ph)are used as a model system for mechanistic understanding of organosulfide electrochemistry,particularly the rate acceleration.Profiling the reaction thermodynamics and charge-discharge process reveals redox of both S–S and C–S bonds,as well as that the coupling between radical exchange and electrochemical redox is the key to enhance the sulfur kinetics.This study not only establishes a basic understanding of orgaonsulfide electrochemistry in Li-S batteries,but also points out a general strategy for enhancing the kinetics of sulfur electrodes in electrochemical devices.

Two-dimensional Supramolecular Structure of a Mercury(Ⅱ) Iodide Complex with Organosulfide

A mercury（Ⅱ） iodide complex with organosulfide [Hg（pymt）（pymtH）I] 1 （pymt = the anion of pyrimidine-2-thiolate） has been synthesized by slow evaporation of the solution at room temperature and structurally characterized by single-crystal X-ray diffraction. Basic ideas and data collected are given. X-ray diffraction analysis reveals that complex 1 is mononuclear. Crystallographic data： C8H7HgIN4S2, Mr = 550.79, monoclinic system, space group P21/c, a = 11.218（4）, b = 9.551（3）, c = 15.877（4） A^°, β = 129.697（15）°, V = 1308.9（7） A^°^3, Z = 4, Mr = 550.79, Dc = 2.795 g/cm^3, F（000） = 995, μ（MoKa） = 14.415 mm^-1, 2（MoKa） = 0.71073 A^°, T= 293（2） K, 2θmax = 54.9°, GOOF= 1.053, the final R = 0.0310 and wR = 0.0742 for 2547 observed reflections with I 〉 2σ（I） （refinement on F^2）. Complex 1 is connected through hydrogen bonds to give a one-dimensional supramolecular chain structure. Furthermore, π-π interactions are also found between the pyrimidine rings with the center-to-center distances of 3.439（4） and 3.603（4） A^°, so complex 1 expands the chains into a two-dimensional network.

P(VDF-HFP)-poly(sulfur-1,3-diisopropenylbenzene) functional polymer electrolyte for lithium–sulfur batteries

Lithium–sulfur(Li–S)battery as a high-energy density electrochemical energy storage system has attracted many researchers’attention.However,the shuttle effect of Li–S batteries and the challenges associated with lithium metal anode caused poor cycle performance.In this work,the organosulfide poly(sulfur-1,3-diisopropenylbenzene)(PSD)was prepared as cathode material and additive of P(VDFHFP)polymer electrolyte(P(VDF-HFP)).It was verified that P(VDF-HFP)polymer electrolyte with 10%PSD(P(VDF-HFP)-10%PSD)showed a higher ionic conductivities than that of liquid electrolyte up to2.27×10-3 S cm-1 at room temperature.The quasi-solid-state Li-S batteries fabricated with organosulfide cathode material PSD and P(VDF-HFP)based functional polymer electrolyte delivered good cycling stability(780 m Ah g-1 after 200 th cycle at 0.1 C)and rate performance(613 m Ah g-1 at 1 C).The good cycling performance could be attributed to the synergistic effect of components,including the interaction between polysulfides and polymer main chain in the organosulfide cathode,the sustained organic/inorganic hybrid stable SEI layer formed by polymer electrolyte additive PSD,the improved cathode/electrolyte interface and the good affinity between P(VDF-HFP)based functional polymer electrolyte and Li metal surface.This strategy herein may provide a new route to fabricate high-performance Li–S batteries through the organosulfide cathode and functional polymer electrolyte.

Nitrogen-rich azoles as trifunctional electrolyte additives for high-performance lithium-sulfur battery

Rechargeable lithium-sulfur(Li-S)batteries are considered one of the most promising energy storage techniques owing to the high theoretical energy density.However,challenges still remain such as the shuttle effect of lithium polysulfides(LPSs)and the instability of lithium metal anode.Herein,we propose to use nitrogen-rich azoles,i.e.,triazole(Ta)and tetrazole(Tta),as trifunctional electrolyte additives for Li-S batteries.The azoles afford strong lithiophilicity for the chemisorption of LPSs.The density functional theory and experimental analysis verify the presence of Li bonds between the azoles and LPSs.The azoles can also interact with lithium salt in the electrolyte,leading to increase ionic conductivity and lithiumion transference number.Moreover,the azoles render particle-like lithium deposition on the lithium metal anode,leading to superlong cycling of a Li symmetric cell.The Li-S batteries with Ta and Tta exhibit the initial discharge capacity of 1425.5 and 1322.2 m Ah g^(-1),respectively,at 0.2 C rate,and promising cycling stability.They also enable enhanced cycling performance of a Li-organosulfide battery.