Hierarchical MoSe₂ yolk-shell microspheres with superior Na-ion storage properties.

Yolk-shell-structured MoSe₂ microspheres were prepared via a simple selenization process of MoO₃ microspheres. The yolk-shell-structured MoSe₂ and MoO₃ microspheres delivered initial discharge capacities of 527 and 465 mA h g(-1) in the voltage range of 0.001-3 V vs. Na/Na(+) at a current density of 0.2 A g(-1), respectively, and their discharge capacities after 50 cycles were 433 and 141 mA h g(-1), respectively. The yolk-shell-structured MoSe₂ microspheres also exhibited outstanding high rate capabilities. The hierarchical yolk-shell structure comprised of wrinkled nanosheets facilitated fast Na-ion and electron kinetics, and buffered the large volume changes encountered during cycling.