Co₄N Nanosheet Assembled Mesoporous Sphere as a Matrix for Ultrahigh Sulfur Content Lithium–Sulfur Batteries

High utilization and loading of sulfur in cathodes holds the key in the realization of Li–S batteries. We here synthesized a Co₄N mesoporous sphere, which was made up of nanosheets, <i>via</i> an easy and convenient method. This material presents high affinity, speedy trapping, and absorbing capacity for polysulfides and acts as a bifunctional catalysis for sulfur redox processes; therefore it is an ideal matrix for S active material. With such a mesoporous sphere used as a sulfur host in Li–S batteries, extraordinary electrochemistry performance has been achieved. With a sulfur content of 72.3 wt % in the composite, the Co₄N@S delivered a high specific discharge capacity of 1659 mAh g^–1 at 0.1 C, almost reaching its theoretic capacity. Also, the battery exhibited a large reversible capacity of about 1100 mAh g^–1 at 0.5 C and 1000 mAh g^–1 at 1 C after 100 cycles. At a high rate of 2 C and 5 C, after 300 cycles, the discharge capacity finally stabilized at 805 and 585 mAh g^–1. Even at a 94.88% sulfur content, the cathode can still deliver an extremely high specific discharge capacity of 1259 mAh g^–1 with good cycle performance

Electrolyte Optimization for Enhancing Electrochemical Performance of Antimony Sulfide/Graphene Anodes for Sodium-Ion Batteries–Carbonate-Based and Ionic Liquid Electrolytes

The electrolyte is a key component in determining the performance of sodium-ion batteries. A systematic study is conducted to optimize the electrolyte formulation for a Sb₂S₃/graphene anode, which is synthesized via a facile solvothermal method. The effects of solvent composition and fluoroethylene carbonate (FEC) additive on the electrochemical properties of the anode are examined. The propylene carbonate (PC)-based electrolyte with FEC can ensure the formation of a reliable solid-electrolyte interphase layer, resulting in superior charge–discharge performance, compared to that found in the ethylene carbonate (EC)/diethyl carbonate (DEC)-based electrolyte. At 60 °C, the carbonate-based electrolyte cannot function properly. At such an elevated temperature, however, the use of an <i>N</i>-propyl-<i>N</i>-methylpyrrolidinium bis­(fluorosulfonyl)­imide ionic liquid electrolyte is highly promising, enabling the Sb₂S₃/graphene electrode to deliver a high reversible capacity of 760 mAh g^–1 and retain 95% of its initial performance after 100 cycles. The present work demonstrates that the electrode sodiation/desodiation properties are dependent significantly on the electrolyte formulation, which should be optimized for various application demands and operating temperatures of batteries

Electrolyte Optimization for Enhancing Electrochemical Performance of Antimony Sulfide/Graphene Anodes for Sodium-Ion Batteries–Carbonate-Based and Ionic Liquid Electrolytes

The electrolyte is a key component in determining the performance of sodium-ion batteries. A systematic study is conducted to optimize the electrolyte formulation for a Sb₂S₃/graphene anode, which is synthesized via a facile solvothermal method. The effects of solvent composition and fluoroethylene carbonate (FEC) additive on the electrochemical properties of the anode are examined. The propylene carbonate (PC)-based electrolyte with FEC can ensure the formation of a reliable solid-electrolyte interphase layer, resulting in superior charge–discharge performance, compared to that found in the ethylene carbonate (EC)/diethyl carbonate (DEC)-based electrolyte. At 60 °C, the carbonate-based electrolyte cannot function properly. At such an elevated temperature, however, the use of an <i>N</i>-propyl-<i>N</i>-methylpyrrolidinium bis­(fluorosulfonyl)­imide ionic liquid electrolyte is highly promising, enabling the Sb₂S₃/graphene electrode to deliver a high reversible capacity of 760 mAh g^–1 and retain 95% of its initial performance after 100 cycles. The present work demonstrates that the electrode sodiation/desodiation properties are dependent significantly on the electrolyte formulation, which should be optimized for various application demands and operating temperatures of batteries

Conductive Lewis Base Matrix to Recover the Missing Link of Li₂S₈ during the Sulfur Redox Cycle in Li–S Battery

Sulfur and polysulfides play important roles on the environment and energy storage systems, especially in the recent hot area of high energy density of lithium–sulfur (Li–S) batteries. However, the further development of Li–S battery is still retarded by the lack of complete mechanistic understanding of the sulfur redox process. Herein we introduce a conductive Lewis base matrix which has the ability to enhance the battery performance of Li–S battery, via the understanding of the complicated sulfur redox chemistry on the electrolyte/carbon interface by a combined in operando Raman spectroscopy and density functional theory (DFT) method. The higher polysulfides, Li₂S₈, is found to be missing during the whole redox route, whereas the charging process of Li–S battery is ended up with the Li₂S₆. DFT calculations reveal that Li₂S₈ accepts electrons more readily than S₈ and Li₂S₆ so that it is thermodynamically and kinetically unstable. Meanwhile, the poor adsorption behavior of Li₂S_<i>n</i> on carbon surface further prevents the oxidization of Li₂S_<i>n</i> back to S₈ upon charging. Periodic DFT calculations show that the N-doped carbon surface can serve as conductive Lewis base “catalyst” matrix to enhance the adsorption energy of Li₂S_<i>n</i> (<i>n</i> = 4–8). This approach allows the higher Li₂S_<i>n</i> to be further oxidized into S₈, which is also confirmed by in operando Raman spectroscopy. By recovering the missing link of Li₂S₈ in the whole redox route, a significant improvement of the S utilization and cycle stability even at a high sulfur loading (70%, m/m) in the composite on a simple super P carbon