ZIF-12-derived N-doped Fe/Co/S/@C nanoparticles as high-performance composite anode electrode materials for lithium-ion batteries

Different sulfide species of both iron and cobalt metals (FeS2, FeS, CoS, and FeCoS2) are composed together in N-doped porous carbon (NPC) for the synthesis of composite anode materials (labeled as Fe/Co/S@NPC-T hereafter, T = 700, 800, 900) by sulfurization and pyrolysis of Fe/Co-based zeolitic imidazolate framework (ZIF-12). Their structural properties are investigated by XRD, FTIR, SEM, TEM, BET and XPS analysis, and Fe/Co/S@NPC-T composite materials, heat treated at different temperatures, are used as anode materials in rechargeable lithium-ion batteries. According to XRD results, the heat treatment of the Fe/Co@ZIF-12/S heat treated at 900 °C leads to the formation of the FeCoS2 phase (66 %) along with CoS (33 %) phase impurity. The heat treatment of the Fe/Co@ZIF-12/S heat treated at 800 °C causes the formation of the main phase of FeCoS2 with minor impurity phases of CoS and FeS2. However, pyrolysis of the Fe/Co@ZIF-12/S heat treated at 700 °C leads to the formation of the FeCoS2, CoS, FeS, and FeS2 phases. Among the samples, the highest BET surface area is 53.4 m2/g for the Fe/Co/S@NPC-900 sample. The CV analysis of the battery cell shows anodic and cathodic redox peaks, which belong to the redox reaction of CoS, FeS2, and FeS. The first discharge capacities of the cells for Fe/Co/S@NPC-700, Fe/Co/S@NPC-800 and Fe/Co/S@NPC-900 are 395, 963, 574 mA h/g at 300 mA/g, and 229, 835 and 1024 mA h/g at 1000 mA/g, respectively.