FeCo alloy modified and carbon nanotube linked hollow carbon nanocages as efficient sulfur hosts for Li-S batteries

Although lithium-sulfur batteries have a high theoretical energy density, the lithium polysulfide (Li2Sn, n = 4 ∼ 8) shuttle effect and slow electrochemical reaction kinetics always arouse the poor rate performance, fast capacity decay and low Coulombic efficiency. Therefore, efficiently adsorption and timely catalytic conversion of Li2Sn by sulfur host is critical to overcome the above challenges of lithium sulfur batteries. In this work, an FeCo alloy modified and carbon nanotube linked hollow carbon nanocages host (CoFe-CHC-X) is constructed by in situ transformation of Fe and Co elements doped Zn-based metal-organic frameworks and melamine. Moreover, the catalytic properties of the CoFe-CHC-X with different Fe and Co ratios are investigated. The results reveal that both small and excessive amounts of Co metal nanoparticles in CoFe-CHC-1 and CoFe-CHC-2 composites are not conducive to the adsorption and conversion of Li2Sn. In contrast, the separated and uniformly dispersed FeCo alloy nanoparticles in CoFe-CHC-3 composite not only can effectively adsorb Li2Sn, but also reduce it conversion reaction energy barriers, accelerate conversion kinetics and inhibit shuttle effects. Meanwhile, the hollow carbon nanocages linked by carbon nanotube can facilitate the transport of electrons on the cathode and physical adsorption Li2Sn. Benefiting from these synergistic modulations, the Li-S batteries assembled by S@FeCo-CHC-3 cathode can stably cycle for 700 cycles at 1.0 C. During cycle, the Coulombic efficiency is maintained at about 98%, and the capacity decay is as low as 0.052% per cycle.