Bi nanoparticles encapsulated in nitrogen-doped carbon as a long-life anode material for magnesium batteries

Bismuth has garnered significant interest as an anode material for magnesium batteries(MBs) because of its high volumetric specific capacity and low working potential. Nonetheless, the limited cycling performance(≤100 cycles) limits the practical application of Bi as anode for MBs. Therefore, the improvement of Bi cycling performance is of great significance to the development of MBs and is also full of challenges. Here, Bi nanoparticles encapsulated in nitrogen-doped carbon with single-atom Bi embedded(Bi@NC) are prepared and reported as an anode material for MBs. Bi@NC demonstrates impressive performance, with a high discharge capacity of 347.5 mAh g^(-1) and good rate capability(206.4 mAh g^(-1)@500 mA g^(-1)) in a fluoride alkyl magnesium salt electrolyte. In addition, Bi@NC exhibits exceptional long-term stability, enduring 400 cycles at 500 mA g^(-1). To the best of our knowledge, among reported Bi and Bi-based compounds for MBs, Bi@NC exhibits the longest cycle life in this work. The magnesium storage mechanism of Bi@NC is deeply studied through X-ray diffraction, transmission electron microscopy and X-ray photoelectron spectroscopy. This work provides some guidance for further improving the cycling performance of other alloy anodes in MBs.

Bottom-up synthesis of 2D heterostructures enables effective polysulfides inhibition and conversion

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)(Ti_(3)C_(2)T_(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 Ti_(3)C_(2)T_(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.