No abstract

Nitrogen-containing carbon spheres with hollow core and mesoporous shell (NHCS), capable of confining Se at levels as high as 72 wt % has been demonstrated to exhibit appreciable electrochemical behavior with 52 and 61 wt % Se loading. In particular, 52 wt % Se confined NHCS cathode exhibits 265 mAh/g at 10C rate and retains 75% of initial capacity at 2C rate up to 10 000 cycles with an insignificant decay of 0.0025% per cycle, which is an ever first report on the extended cycle life of Li-Se batteries. Due to the negligible difference found between the transport kinetics of Se and that of LiSe, irrespective of the cycling rate, 52 wt % Se @ NHCS performs better at high rates. Furthermore, capacity is governed by the extent of utilization of confined Se and cycle life by the extent of mitigation of volume expansion. Accordingly, rate capability studies recommend 52 wt % Se loaded cathode above 2C rate and 61 wt % Se loading up to 2C rate. Furthermore, NHCS/Se-52 cathode demonstrates suitability for Na-Se batteries by exhibiting 339 and 219 mAh/g of capacity at rates of C/5 and 2C rates, respectively. NHCS with select Se concentration could thus be exploited for multifunctional cathode behavior in Li-Se and Na-Se systems.

No abstract

An attempt made to improve sulfur loading in a template free porous carbon to the extent of 70 wt. % has inferred two interesting observations, viz., 60 wt. % sulfur loading exhibits superior electrochemical properties in the S@C composite form and an enhanced 73 wt. % sulfur loading leads to the formation-cum-stabilisation of sulfur in its monoclinic phase. Carbon aerogel with tunable properties, derived from the catalyst aided cross linki ng of resorcinol and formaldehyde, possessing a specific surface area of 1395 m 2 /g and pore volume of 1.423 cm 3 /g has been exploited for sulfur loading to form series of S@C composites. Interestingly, carbon aerogel prepared in the present study offers multifarious advantages such as conducting additive, potential host to accommodate higher concentration of sulfur and better polysulfide confining matrix. The 60 wt. % sulfur loaded carbon aerogel composite exhibits an appreciable specific capacity of 600 mAh/g at C/10 rate up to 100 cycles, 480 mAh/g at 1C and 422 mAh/g at 2C rate. Hence, the capability of carbon aerogel, synthesized through the present study in accommodating higher concentration of sulfur, effective management of polysulfide shuttle and provision of favorable electrode-electrolyte interface to facilitate extended cycling possibilities at different current densities has been demonstrated.