Understanding the degradation mechanism of rechargeable lithium/sulfur cells: a comprehensive study of the sulfur–graphene oxide cathode after discharge–charge cycling

Abstract

Degradation mechanism of rechargeable lithium/sulfur-graphene oxide cell was studied using scanning electron microscopy and X-ray spectroscopy.

Leaf‐Like Graphene‐Oxide‐Wrapped Sulfur for High‐Performance Lithium–Sulfur Battery

“…Notably, the peak intensity from 171.1 to 165.0 eV assigned to polythionate (≈168.2 eV) and thiosulphate(≈167.2 eV), respectively becomes much stronger, while the peaks corresponding to active S species with C—S bond and O—S bond from 164.0 to 160.0 eV have weakened. The result indicates that some of the active S species has been converted into the polythionate and thiosulphate during cycling 48. The as‐formed polythionate and thiosulphate species during cycling can serve as highly efficient polysulfide mediator to limit the diffusion of lithium polysulfides, which is confirmed by recent report 49…”

“…All the capacity retention and capacity degradation are calculated from the third cycle after achieving stabilized capacity. The achieved cycling ability in Figure 5c,d is much better than that of most previous reports 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 48. Only very recently, Cui and co‐workers51 successfully demonstrated that the TiO 2 /S yolk–shell composites can be cycled over 1000 times with a capacity decay of 0.033% per cycle.…”

“…The battery delivers a reversible discharge capacity of 1250 mAh g −1 at current rate of 0.1 C that slowly reduced to 1130 mAh g −1 at 0.2 C , 930 mAh g −1 at 0.5 C , 753 mAh g −1 at 1 C , and 685 mAh g −1 at 2 C . Even at high rate of 4 C (6680 mA g −1 ), the leaf‐like GO/S cathode still can deliver a capacity of 468 mAh g −1 , which is almost the best rate performance of C/S composite cathode 8, 10, 11, 12, 14, 15, 16, 17, 18, 19, 20, 21, 22, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 45, 46, 48, 51, 52, 53…”

“…Figure 4a,b exhibits the S 2 p XPS spectrum for leaf‐like GO/S before cycling (Figure 4a) and leaf‐like GO/S after cycling for 20 times (Figure 4b). As shown in Figure 4a, a strong peak at ≈163.6 eV is observed, which can be assigned to active S species with the C—S and S—S bond, while the shoulder peak at ≈164.8 eV can be fitted by three peaks, which is assigned to C—S bond and O—S bond respectively 48. Furthermore, the peak at ≈168.4 eV can be assigned to the O—S bond arising from the sulphate species formed by oxidation of S in air 48.…”

“…It can be identified the presence of C—S and O—S bonds in the S 2 p XPS spectrums. These chemical bonds between leaf‐like GO and S can largely trap the S on the surface of GO and limit diffusion of lithium polysulfide into the electrolyte 48. Figure 4b exhibits the S 2 p XPS spectrums after cycling for 20 times.…”