Nitrogen-doped hierarchically porous carbon architectures coupled with Fe/Fe5C2 nanoparticles as anode materials for alkaline-metal-ion batteries

Abstract

Synthesis of high capacity anode materials for lithium-/potassium-ion batteries (LIBs/PIBs) is still a big challenge. Here we report a highly active electrode material, which is synthesized by heat treatment of mixtures of iron(III)hexacyanoferrate (HCF), dicyanamide (DCA) and SiO2 spheres and then etching engineering. The samples possess three-dimensional (3D) interconnecting carbon architectures coupled with Fe/Fe5C2 and large specific surface area. The highlights can be attributed to three points: (i) as far as we know, the study on Fe/Fe5C2 in carbon hybrids as anodes for LIBs and/or PIBs has not been reported yet, (ii) the strategy using DCA/HCF can increase the amount of N–C/Fe active sites, and can promote the formation of Fe/Fe5C2 and abundant Fe-Nx, and (iii) the results manifest that Fe/Fe5C2 NPs and Fe-Nx-C might also serve as efficient catalysts to activate/promote the formation of the stronger and stabler SEI film on the electrode surfaces in the first cycle. Therefore, 3DM Fe/Fe5C2@NC presents the outstanding lithium/potassium storage properties. As for LIBs, 3DM Fe/Fe5C2@NC exhibits an initial discharge capacity of 1513 mAh g−1 at 0.1 A g−1. At 1 A g−1, it presents the high reversible capacity of 1024 mAh g−1 after 550 cycles and the reversible capacity sustains 839 mAh g−1 (81.9% retention of the maximum capacity) after a long span of 1000 cycles. As for PIBs, 3DM Fe/Fe5C2@NC exhibits high reversible capacity of 460 mAh g−1 at 0.05 A g−1 and high cycling stability of 205 mAh g−1 at 0.5 A g−1 after 1000 cycles with an extremely slow capacity decay of only 0.013% per cycle from the 10th to 1000th cycle. Finally, the strategy to fabricate 3DM Fe/Fe5C2@NC nanocrystal can synthesize other nanocomposites with metallic nanoparticles and abundant active sites as anodes electrodes toward high-performance LIBs/PIBs in future.