Efficient Regulation of Polysulfides by MoS2 /MoO3 Heterostructures for High-Performance Li-S Batteries.

The notorious shuttle effect and sluggish conversion of polysulfides seriously hinder the practical application of Lithium-sulfur (Li-S) batteries. In this study, a novel architecture of MoS2 /MoO3 heterostructure uniformly distributed on carbon nanotubes (MoS2 /MoO3 @CNT) is designed and introduced into Li-S batteries via decorating commercial separator to regulate the redox reactions of polysulfides. Systematic experiments and theoretical calculations showed that the heterostructure not only provides sufficient surface affinity to capture polysulfides and acts as an active catalyst to promote the conversion of polysulfides, but also the highly conductive CNT enables rapid electron/ion migration. As a result, Li-S batteries with the MoS2 /MoO3 @CNT-PP separator deliver an impressive reversible capacity (1015 mAh g-1 at 0.2 A g-1 after 100 cycles), excellent rate capacity (873 mAh g-1 at 5 A g-1 ), and low self-discharge capacity loss (94.6% capacity retention after 7 days of standing). Moreover, even at an elevated temperature of 70 °C, it still exhibits high-capacity retention (800 mAh g-1 at 1 A g-1 after 100 cycles). Encouragingly, when the sulfur load is increased to 8.7 mg cm-2 , the high reversible areal capacity of 6.61 mAh cm-2 can be stably maintained after 100 cycles, indicating a high potential for practical application.

Covalent Organic Framework-Coated Polyimide Ion-Track-Etched Separator with High Thermal Stability for Developing Lithium-Ion Batteries with Long Lifespans.

Separators play a crucial role in inhibiting thermal runaway in lithium-ion batteries (LIBs). In this study, the doctor blade coating method and heavy-ion track etching technology were used to prepare a polyimide-based covalent organic framework (PI_COF) separator with excellent thermal stability and a long cycle life. Specifically, COF300 was simply coated on the surface of a polyimide-based track-etched membrane (PI_TEM) with straight through holes, which provided a rigid framework and high-temperature stability at 300 °C. These features were conducive to inhibiting thermal runaway, while porous COF300 with large holes increased the wettability of the electrolyte, facilitating lithium-ion migration and suppression of lithium dendrite growth; consequently, LIBs with an excellent cycling performance and a high rate capacity were obtained. The cell with the PI_COF separator delivered a high capacity of 90.0 mA h g-1 after 1000 cycles. The PI_COF separator with high thermal stability exhibited a long cycle life in LIBs. These features are beneficial for improving the safety characteristics of LIBs as well as for accelerating the practical application process of the PI_COF separator.

Sheet-Like Stacking SnS2/rGO Heterostructures as Ultrastable Anodes for Lithium-Ion Batteries.

SnS2-based materials have attracted considerable attention in energy storage and conversion owing to their high lithium activity and theoretical capacity. However, the practical application is severely limited by the low coulombic efficiency and short cycle life due to irreversible side reactions, low conductivity, and serious pulverization in the discharge/charge process. In this study, sheet-like stacking SnS2/reduced graphene oxide (rGO) heterostructures were developed using a facile solvothermal method. It was found that the composites between SnS2 nanoplates and rGO nanosheets are closely coupled through van der Waals interactions, providing efficient electron/ion paths to ensure high electrical conductivity and sufficient buffer space to alleviate volume expansion. Therefore, the SnS2/rGO heterostructure anode can obtain a high capacity of 840 mA h g-1 after 120 cycles at a current density of 200 mA g-1 and maintain a capacity of 450 mA h g-1 after 1000 cycles at 1000 mA g-1. In situ X-ray diffraction tests showed that SnS2/rGO undergoes typical initial intercalation, conversion, and subsequent alloying reactions during the first discharge, and most of the reactions are dealloying/alloying in the subsequent cycles. The galvanostatic intermittent titration technique showed that the diffusion of lithium ions in the SnS2/rGO heterostructures is faster in the intercalation and conversion reactions than in the alloying reactions. These observations help to clarify the reaction mechanism and ion diffusion behavior in the SnS2 anode materials, thus providing valuable insights for improving the energy efficiency of lithium-ion batteries.

Sandwich-like SnS2/graphene multilayers for efficient lithium/sodium storage.

2D materials have attracted extensive attention in energy storage and conversion due to their excellent electrochemical performances. Herein, we report utilization of monolayer SnS2 sheets within SnS2/graphene multilayers for efficient lithium and sodium storage. SnS2/graphene multilayers are synthesized through a solution-phase direct assembly method by electrostatic interaction between monolayer SnS2 and PDDA (polydimethyl diallyl ammonium chloride)-graphene nanosheets. It has been shown that the SnS2/graphene multilayer electrode has a large pseudocapacity contribution for enhanced lithium and sodium storage. Typical batteries deliver a stable reversible capacity of ∼160 mA h g-1 at 2 A g-1 after 2000 cycles for lithium and a stable reversible capacity of ∼142 mA h g-1 at 1 A g-1 after 1000 cycles for sodium. The excellent electrochemical performances of SnS2/graphene multilayers are attributed to the synergistic effect between the monolayer SnS2 sheets and the PDDA-graphene nanosheets. The multilayer structure assembled by different monolayer nanosheets is promising for the further development of 2D materials for energy storage and conversion.