A lithium secondary battery, in which electrolyte impregnation capability is improved, even in the case of a high-density electrode assembly, by forming a bottom insulator plate with a structure to facilitate the impregnation of the electrode assembly with an electrolyte. The bottom insulator plate may be formed with a plurality of holes in the form of a mesh, and the holes are defined by a plurality of protrusions with differing heights to improve the electrolyte impregnation capability. Alternatively, the bottom insulator plate may be formed with a central hole and a plurality of peripheral holes radially arranged around the central hole in an aperture ratio to improve the electrolyte impregnation capability.