In-Situ Construction of Functional Multi-Dimensional MXene-based Composites Directly from MAX Phases through Gas-Solid Reactions.

The weak bonding of A atoms with MX layers in MAX phases not only enables the selective etching of A layers for MXene preparation but brings about the chance to construct A derivatives/MXene composites via in-situ conversion. Here, a facile and general gas-solid reaction systems are elegantly devised to construct multi-dimensional MXene based composites including AlF3 nanorods/MXene, AlF3 nanocrystals/MXene, amorphous AlF3/MXene, A filled carbon nanotubes/MXene, layered metal chalcogenides/MXene, MOF/MXene, and so on. The intrinsic effect mechanism of interlayer confinement towards crystal growth, catalytic behavior, van der Waals-heterostructure construction and coordination reaction are rationally put forward. The tight interface combination and synergistic effect from distinct components make them promising active materials for electrochemical applications. More particularly, the AlF3 nanorods/Nb2C MXene demonstrate bi-directional catalytic activity toward the conversion between Li2S and lithium polysulfides, which alleviates the shuttle effect of lithium-sulfur batteries.

Multifunctional Vanadium Nitride-Modified Separator for High-Performance Lithium-Sulfur Batteries.

Lithium-sulfur batteries (LSBs) are recognized as among the best potential alternative battery systems to lithium-ion batteries and have been widely investigated. However, the shuttle effect has severely restricted the advancement in their practical applications. Here, we prepare vanadium nitride (VN) nanoparticles grown in situ on a nitrogen-doped carbon skeleton (denoted as VN@NC) derived from the MAX phase and use it as separator modification materials for LSBs to suppress the shuttle effect and optimize electrochemical performance. Thanks to the outstanding catalytic performance of VN and the superior electrical conductivity of carbon skeleton derived from MAX, the synergistic effect between the two accelerates the kinetics of both lithium polysulfides (LiPSs) to Li2S and the reverse reaction, effectively suppresses the shuttle effect, and increases cathode sulfur availability, significantly enhancing the electrochemical performance of LSBs. LSBs constructed with VN@NC-modified separators achieve outstanding rate performance and cycle stability. With a capacity of 560 mAh g-1 at 4 C, it exhibits enhanced structural and chemical stability. At 1 C, the device has an incipient capacity of 1052.4 mAh g-1, and the degradation rate averaged only 0.085% over 400cycles. Meanwhile, the LSBs also show larger capacities and good cycling stability at a low electrolyte/sulfur ratio and high surface-loaded sulfur conditions. Thus, a facile and efficient way of preparing modified materials for separators is provided to realize high-performance LSBs.