The ultrathin two-dimensional nanosheets of layered transition-metal dichalcogenides (TMDs) have attracted great interest as an important class of materials for fundamental research and technological applications. Solution-phase processes are highly desirable to produce a large amount of TMD nanosheets for applications in energy conversion and energy storage such as catalysis, electronics, rechargeable batteries, and capacitors. Here, we report a rapid exfoliation by supercritical fluid processing for the production of MoS2 and MoSe2 nanosheets. Atomic-resolution high-Angle annular dark-field imaging reveals high-quality exfoliated MoS2 and MoSe2 nanosheets with hexagonal structures, which retain their 2H stacking sequence. The obtained nanosheets were tested for their electrochemical performance in a hybrid Mg-Li-ion battery as a proof of functionality. The MoS2 and MoSe2 nanosheets exhibited the specific capacities of 81 and 55 mA h g-1, respectively, at a current rate of 20 mA g-1.