Due to the high theoretical capacity and energy density, lithium-sulfur (Li-S) batteries have good commercial prospects. However, shuttle effect of soluble lithium polysulfides (LiPSs) formed by sulfur reduction has severely limited the further development of Li-S batteries. In this work, the two-dimensional (2D) MXene-metal–organic framework (MOF) (Ti₃C₂T_x-CoBDC (BDC: 1,4-benzenedicarboxylate)) heterostructures were employed to modify the separator to inhibit the shuttle effect and facilitate the conversion of the soluble polysulfides. Firstly, a bottom-up synthesis strategy was adopted to synthesize the 2D MXene-MOF heterogeneous layered structure. With high specific surface area, in which the catalytic metal atoms not only restrain the shuttle effect of polysulfides but also exhibit excellent redox electrocatalytic performance. The cell with Ti₃C₂T_x-CoBDC@PP (PP: polypropylene) separator has a high initial capacity of 1255 mAh·g⁻¹ at 0.5 C. When the current density is 2 C, the battery has a capacity retention rate of 94.4% after 600 cycles, with the fading rate of only 0.01% per cycle. Besides, with a sulfur loading of 7.5 mg·cm⁻², the battery shows the discharge capacity of 1096 mAh·g⁻¹ at 0.2 C and exhibits excellent cycling stability. This work offers novel insights into the application of MOF and MXene heterostructures in Li-S batteries.

The separator is of great significance to alleviate the shuttle effect and dendrite growth of lithium-sulfur batteries. However, most of the current commercial separators cannot meet these requirements well. In this work, a dense metal-organic-framework (MOF) modification layer is in-situ prepared by the assistant of polydopamine on the polypropylene separators. Due to the unique structure and synergistic effect of polydopamine (PDA) and zeolitic imidazolate framework-8 (ZIF-8), the functional separator can not only trap the polysulfides effectively but also promote the transport of lithium ions. As a result, the battery assembled with the functional separator exhibits excellent cycle stability. The capacity remains 711 mAh·g⁻¹ after 500 cycles at 2 C, and the capacity decay rate is as low as 0.013% per cycle. The symmetrical battery is cycled for 1,000 h at 2 mA·cm⁻² (2 mAh·cm⁻²) with the plating/stripping overpotential of 20 mV. At the same time, the modification separator shows a higher lithium ion transference number (0.88), better thermal stability and electrolyte wettability than the unmodified separator.

As a promising candidate for next generation energy storage devices, lithium sulfur (Li-S) batteries still confront rapid capacity degradation and low rate capability. Herein, we report a well-architected porous nitrogen-doped carbon/MnO coaxial nanotubes (MnO@PNC) as an efficient sulfur host material. The host shows excellent electron conductivity, sufficient ion transport channels and strong adsorption capability for the polysulfides, resulting from the abundant nitrogen-doped sites and pores as well as MnO in the carbon shell of MnO@PNC. The MnO@PNC-S composite electrode with a sulfur content of 75 wt.% deliveries a specific capacity of 802 mAh·g^-1 at a high rate of 5.0 C and outstanding cycling stability with a capacity retention of 82% after 520 cycles at 1.0 C.

Planar micro-supercapacitors show great potential as the energy storage unit in miniaturized electronic devices. Asymmetric structures have been widely investigated in micro-supercapacitors, and carbon-based materials are commonly applied in the electrodes. To integrate different metal oxides in both electrodes in micro-supercapacitors, the critical challenge is the pairing of different faradic metal oxides. Herein, we propose a strategy of matching the voltage and capacitance of two faradic materials that are fully integrated into one high-performance asymmetric micro-supercapacitor by a facile and controllable fabrication process. The fabricated micro-supercapacitors employ MnO₂ as the positive active material and Fe₂O₃ as the negative active material, respectively. The planar asymmetric micro-supercapacitors possess a high capacitance of 60 F·cm^-3, a high energy density of 12 mW·h·cm^-3, and a broad operation voltage range up to 1.2 V.