Lithium-sulfur batteries have attracted increasing attention as one of the most promising candidates for next-generation energy storage systems. However, the poor cycling performance and the low utilization of sulfur greatly hinder its practical applications. Here we report the improved performance of lithium-sulfur batteries by coating TiCT MXene nanosheets (where T stands for the surface termination, such as -O, -OH, and/or -F) on commercial "Celgard" membrane. In favor of the ultrathin two-dimensional structure, the TiCT MXene can form a uniform coating layer with a minimum mass loading of 0.1 mg cm and a thickness of only 522 nm. Owing to the improved electric conductivity and the effective trapping of polysulfides, the lithium-sulfur batteries with MXene-functionalized separators exhibit superior performance including high specific capacities and cycling stability.

Rechargeable aqueous zinc-ion batteries have attracted extensive interest owing to their low cost and high safety. Herein, oxygen-defective potassium vanadate/amorphous carbon nanoribbons (C-KVO|O d) is successfully synthesized through a one-step solid-state sintering process as a high performance cathode material for zinc-ion batteries. This unique 3D interconnected network structure can not only act as continuous conductive path, but also decreases aggregation and provide more adsorption sites for zinc ions. The as-prepared C-KVO|O d exhibites a high capacity of 385 mAh g-1 at 0.2 A g-1 , superior rate performance (166 mAh g-1 even at 20 A g-1) and an outstanding cycling stability with a 95% capacity retention over 1000 cycles. Density functional theory calculations elucidated that the oxygen defects in the C-KVO|O d remarkably reduced Zn 2+ ion adsorption Gibbs free energy and Zn 2+-diffusion barriers. Meanwhile, the amorphous carbon networks enable the rapid electron transfer and provide additional active sites for Zn 2+ storage. This work could facilitate the development of high-performance zinc-ion batteries for large-scale energy storage.

Poor electrical conductivity and mechanical instability are two major obstacles to realizing high performance of MnO2 as pseudocapacitor material. The construction of unique hierarchical core-shell nanostructures, therefore, plays an important role in the efficient enhancement of the rate capacity and the stability of this material. We herein report the fabrication of a hierarchical α-MnO2 nanowires@ultrathin δ-MnO2 nanosheets core-shell nanostructure by adopting a facile and practical solution-phase technique. The novel hierarchical nanostructures are composed of ultrathin δ-MnO2 nanosheets with a few atomic layers growing well on the surface of the ultralong α-MnO2 nanowires. The first specific capacitance of hierarchical core-shell nanostructure reached 153.8 F g(-1) at the discharge current density of as high as 20 A g(-1), and the cycling stability is retained at 98.1% after 10,000 charge-discharge cycles, higher than those in the literature. The excellent rate capacity and stability of the hierarchical core-shell nanostructures can be attributed to the structural features of the two MnO2 crystals, in which a 1D α-MnO2 nanowire core provides a stable structural backbone and the ultrathin 2D δ-MnO2 nanosheet shell creates more reactive active sites. The synergistic effects of different dimensions also contribute to the superior rate capability.

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