Facile Room Temperature Synthesis and Directable Self-Assembly of Ultrasmall Antimony (III) Sulfide Nanoparticles for Li⁺/Na⁺ Batteries

Nano-assemblies of Antimony (III) sulfide have the potential to be an extremely important class of material in thermoelectric, photovoltaic, and electrochemical energy systems. The amorphous phase of Sb₂S₃ is especially useful for electrochemical systems where the high defect concentration improves its already impressive ion transport capabilities. Engineering the size and morphology of the amorphous phase, however, is particularly challenging due to its instability relative to the bulk orthorhombic phase. To this end, we demonstrate the first synthetic pathway to amorphous ultrasmall antimony (III) sulfide nanoparticles by developing a scalable room temperature and open-atmosphere procedure that uses commonly available chemicals. The synthesis is made possible by the immediate self-assembly of the seeds, that we also characterize using small angle X-ray scattering (SAXS), which halts growth by segregating the particles into a stable mesophase. This mesophase exhibits rod-like hexagonal close packing which is unexpected in an amorphous system lacking crystallographic registry between zero dimensional particles. We provide experimental evidence that elucidates the fundamental driving forces of the assembly and demonstrate that the superstructure is directable via simple compositional changes to the solvent environment. The ligands, which are chemically related short-chain alkyl molecules, that direct the assembly of our Sb₂S₃ nanoparticles also carry their influence forward into the performance of electrodes prepared from the particles for Li⁺ and Na⁺ battery systems. Integration of these materials yields impressive rate and cyclability results. With this study we illustrate the impressive battery performance of our ultrasmall Sb₂S₃ nanoparticles and with it, justify the need for more fundamental examination in this and similar colloidal self-assembly systems for electrochemical applications.