Multicomponent (Mo, Ni) metal sulfide and selenide microspheres with empty nanovoids as anode materials for Na-ion batteries

Unique-structured MoS₂-Ni₉S₈-C, MoSe₂-NiSe-C, MoS₂-Ni₉S₈, and MoSe₂-NiSe-NiSe₂ composite microspheres were prepared by pilot-scale spray drying and a subsequent post-treatment process. Dextrin, used as the carbon source, played a key role in the formation of unique-structured multicomponent metal sulfide and selenide microspheres with and without carbon. The empty nanovoids formed by decomposition (or carbonization) of phase-separated dextrin during the spray drying process were uniformly distributed within the multicomponent metal sulfide and selenide composite microspheres. The discharge capacities of MoS₂-Ni₉S₈-C, MoSe₂-NiSe-C, MoS₂-Ni₉S₈, and MoSe₂-NiSe-NiSe₂ for the 80^th cycle at a current density of 0.5 A g^-1 for sodium-ion storage were 366, 386, 459, and 291 mA h g^-1, respectively, and the respective capacity retentions measured from the second cycle were 91, 102, 92, and 64%. The carbon-free MoS₂-Ni₉S₈ microspheres exhibited excellent rate performance and their discharge capacities decreased slightly from 559 to 428 mA h g^-1 as the current densities increased from 0.1 to 3 A g^-1. The MoS₂-Ni₉S₈-C composite microspheres, with high structural stability during repeated sodium-ion insertion and deinsertion, showed extremely long-term cycling performance for 1000 cycles.