A yolk-shell-structured material (16, 59, 59a, 74) is disclosed as including a plurality of silicon nano-particles (12, 54, 54a, 62) and a cavity (16, 60, 80, 84) enclosed by a micron-sized shell (18, 72) made of carbon nano-particles (14, 56, 58). A method of forming a yolk-shell-structured material with silicon nano-particles (12) and a cavity (16) enclosed by a micron-sized shell (18) made of carbon nano-particles (14) is disclosed as including (a) providing a micron-sized cornstarch core (10), (b) forming a layer of nano silicon-particle (12) on the cornstarch core (10), (c) forming a micron-sized shell (18) of carbon nano-particles (14) on the layer of nano silicon-particle (12), and (d) removing the cornstarch core (10) by heating.