Developing complex nanostructured materials with amorphous phases remains an important challenge and such materials are potentially valuable for achieving highly efficient electrochemical energy storage. Here, a facile surfactant-free strategy is developed to synthesize size-controllable Ni-Co-Mn sulfide spheres with an amorphous and yolk-shell structure. In the absence of surfactant, monodispersed Ni-Co-Mn glycerate solid spheres with diameters ranging from 650 to 1100 nm are controllably synthesized by regulating the amount of Mn(NO3)2, and subsequently transformed into yolk-shelled amorphous Ni-Co-Mn sulfide spheres via an anion-exchange reaction. Benefitting from compositional and structural advantages, the optimized electrode displays an outstanding specific capacity of 1204 C g-1 at 2 A g-1 with a long cycling lifetime. A hybrid supercapacitor, fabricated with the yolk-shelled amorphous Ni-Co-Mn sulfide spheres as the positive electrode material and activated carbon as the negative one, achieves superior cyclic stability with a high energy density of 71.86 Wh kg- 1 at 793.56 W kg -1, demonstrating their potential application for high-performance hybrid supercapacitors.