Optimization of Structure and Porosity of Nitrogen Containing Mesoporous Carbon Spheres for Effective Selenium Confinement in Futuristic Lithium–Selenium Batteries

A series of nitrogen containing mesoporous carbon spheres (NCS), possessing a range of hollow to nonhollow core structures to confine Se, are prepared using an easily tunable silica template and exploited as cathodes in Li–Se batteries. Nonhollow spheres with 400 nm average size accommodate 70% Se in the amorphous state in its higher pore volume of 1.72 cm3/g, whereas hollow spheres accommodate 60% Se in their 20–30 nm shell. Detailed electrochemical studies of different amounts of Se containing carbon spheres infer that hollow spheres outperform by 50% Se compared to nonhollow spheres by delivering an initial capacity of 585 mAh/g with 90% retention up to 500 cycles at the C/5 rate and exhibit superior capacity of 155 mAh/g at the 10C rate. Besides, nonhollow NCS/Se-60 exhibits a capacity of 421 mAh/g and retains 344 mAh/g up to 500 cycles at the C/5 rate. Long-term cyclability of 50% Se loaded hollow and nonhollow NCS exhibits 344 and 231 mAh/g, respectively, up to 3000 cycles at the 1C rate. The study demonstrates (1) the requirement of hollow structure of NCS for effective and high rate utilization of Se along with the maintenance of structural integrity against volume changes and (2) porosity dependent cycle life of 60% Se.