Encapsulation of Se in dual-wall hollow carbon spheres: Physical confinement and chemisorption for superior Na–Se and K–Se batteries

Sodium-Se (Na–Se) and potassium-Se (K–Se) batteries are prospective candidates for energy storage systems with high theoretical specific capacity and low cost. However, some intractable problems need to be overcome, such as the shuttle effect of polyselenide and the low Se loading, which lead to poor cyclic performance and low capacity. Herein, dual-wall hollow carbon spheres (DWHCSs) modified with cetyltrimethylammonium bromide (CTAB) were designed to be served as a host material (C-DWHCSs) for the load of Se to construct the Se electrode material (C-DWHCSs/Se). Dual-wall hollow structure with satisfactory specific surface area greatly increased the load capacity of Se, which effectively improved the battery capacity. In terms of physical confinement, the gap between two carbon walls provided a buffer space for the volume expansion of Se and prevented the escape behavior of electrode material after expansion pulverization. Based on the chemisorption strategy, the polyselenides were immobilized by CTAB functionalized graphite carbon through the Lewis acid-base interaction, which was demonstrated by theoretical calculation. As a consequence, C-DWHCSs/Se in Na–Se batteries delivered an outstanding cycling performance (∼331 mAh g−1 at 2 C after 1000 cycles). For K–Se batteries, they also exhibited a splendid cycling stability (∼292 mAh g−1 at 0.5 C after 500 cycles). [Display omitted]