Iron nanoparticles surface decorated MXene via molten salts etching as selenium host for ultrafast sodium ion storage.

Sodium-selenium (Na-Se) batteries have gained attention due to their high energy density and power density, resulting from the liquid-liquid reaction at the interface in the dimethoxyethane electrolyte. Nevertheless, the pronounced shuttle effect of polyselenides causes low coulomb efficiency and inadequate cycling stability for Na-Se batteries. Herein, the iron nanoparticles surface modified accordion-like Ti3C2Tx MXene (MXene/Fe) synthesized via the molten salt etching is utilized as the host of Se species for high-performance Na-Se battery cathode. Benefiting from the layered structure and chemical adsorption of accordion-like MXene, the shuttle effect of the cathode is effectively inhibited. Simultaneously, electrochemical kinetics is boosted due to the catalytic effect of Fe nanoparticles, which facilitate the transformation of polyselenide from long-chain to short-chain, contributing to pseudocapacitive capacity. Consequently, the Se-based cathode delivers a steady capacity of 575.0 mA h g-1 at 0.2 A/g, and even a high capacity of 500 mAh/g at 50 A/g based on the mass of Se@MXene/Fe electrode, indicating the ultrafast Na+ ion storage. Most notably, this structure demonstrated remarkable long-term cycling stability for 5000 cycles with a high capacity retention of 97.4 %. The electrochemical energy storage mechanism is further revealed by in situ Raman. Herein, the confinement-catalysis structure shines light on inhibiting shuttling and facilitating ultrafast ion storage.

Encapsulation of Se into Cu-decorated MXene nanosheets with superior electrochemical performance for advanced Na-Se batteries.

Sodium-selenium (Na-Se) batteries are promising energy storage systems with high energy density, high safety, and low cost. However, the huge volume change of selenium, the dissolution shuttle of polyselenides, and low selenium loading need to be solved. Herein, Cu nanoparticles decorated MXene nanosheets composite (MXene/Cu) are synthesized by etching Ti3AlC2 using a molten salt etching strategy. The Se-loaded MXene/Cu (Se@MXene/Cu) electrode delivers superior electrochemical performance even with a high Se loading of ∼74.3 wt%, owing to the synergistic effect of the two-dimensional (2D) confined structure and catalytic role of the unique MXene/Cu host. Specifically, the obtained electrode provides a reversible capacity of 587.3 mAh/g at 0.2 A/g, a discharge capacity as high as 511.3 mAh/g at a high rate of 50 A/g, and still maintains a capacity of 471.9 mAh/g even after 5000 cycles based on the mass of Se@MXene/Cu. With such excellent electrochemical kinetic properties, this study highlights the importance of designing various MXene-based composites with synergistic effects of 2D confined structure and Cu catalytic center for the development of high-performance alkali metal-chalcogen battery systems.

MoP quantum dots based multifunctional efficient electrocatalyst for stable and long-life flexible lithium-sulfur batteries.

The commercialization of lithium-sulfur (Li-S) batteries is challenging, owing to factors like the poor conductivity of S, the 'shuttle effect', and the slow reaction kinetics. To address these challenges, MoP quantum dots were decorated on hollow carbon spheres (MoPQDs/C) in this study and used as an efficient lithium polysulfides (LiPSs) adsorbents and catalysts. In this approach polysulfides are effectively trapped through strong chemisorption and physical adsorption while simultaneously facilitating LiPSs conversion by enhancing the reaction kinetics. MXene serves as a flexible physical barrier (MoPQDs/C@MXene), further enhancing the confinement of LiPSs. Moreover, both materials are conductive, significantly facilitating electron and charge transfer. Additionally, the flexible MoPQDs/C@MXene-S electrode offers a large specific surface area for sulfur loading and withstand volume expansion during electrochemical processes. As a result, the MoPQDs/C@MXene-S electrode exhibits excellent long-term cyclability and maintains a robust specific capacity of 992 mA h g-1 even after 800cycles at a rate of 1.0C (1C = 1675 mA g-1), with a minimal capacity decay rate of 0.034 % per cycle. This work proposes an efficient strategy to fabricate highly efficient electrocatalysts for advanced Li-S batteries.