Selenium (Se) is potential as a promising alternative cathode material for high-energy batteries because of its comparable theoretical volumetric capacity density (3240mAhcm−3) to sulfur (3467mAhcm−3) and a much higher electronic conductivity (1×10−3 Sm−1) than sulfur (5×10−28 Sm−1). In this work, we developed a novel Se composite confined within porous carbon nanospheres (Se/PCNs) as cathode for advanced Li–Se battery. A Se loading as high as 70.5wt% is attained in such composite. The Se/PCNs cathode shows high volumetric capacity density of 3150mAh/cm3 and excellent rate capability (retains 57% of the theoretical capacity at 20C). Remarkably, it exhibits impressive cycling stability over 1200 cycles with a capacity decay as low as ~0.03% per cycle. The superior overall battery performance can be ascribed to high loading of active material, effective protective film formed on the surface of the active material, and strong adsorbing ability of Se/Li2Se x provided by the micropore-rich carbon structure.