## 3 Results and Discussion
### Electrochemical Characterization
The decrease of the particle size led to an increase of the initial capacity equal to more than twice: The greater the specific surface, the higher the amount of material involved in the lithium sulfides formation process. However, since smaller particle size means higher exposed surface, the dissolution of the high order sulfides [39] in the electrolyte during the cycling was observed as well. The problem may then be solved by producing a core-shell type structure. In fact, in this case it is possible to see as the percentage decrease of the capacity of the third discharge sweep, respect to the first one, was only about 7.7%, although also in this case the capacity tended to decrease for the first 20 cycles and then it stabilized to a value higher than in the two previous cases. Since EDX analysis suggested that the coating was not homogeneous, it is possible that part of the active material in the poorly covered zones still slowly dissolved, while where the core-shell was well formed there was a good retention of capacity. Moreover, most likely, after the first few cycles, the continuous variations of cathode volume caused the destruction of initial morphology of material. In particular, the strong expansion of elemental sulfur during the discharge process also involves the breaking of titanium dioxide rigid shell which surrounds the particles. However, since it forms a mechanical limit to polysulfide mobility, TiO\({}_{2}\) can absorb these ions preventing their spread within the electrolyte [40]. In Figure 12a,b, the curves for the first, third, fifth and tenth charge and discharge sweep, respectively, are shown for core-shell S-TiO\({}_{2}\) materials. With particular reference to the first discharge cycles, the capacity was 1395 mAh/g, namely about 83% of the sulfur theoretical value. The cell showed a value of 1290 mAh/g and 1270 mAh/g respectively during the third and fifth cycles, and around 1120 mAh/g at the end of tenth cycle. The loss of capacity was 18% of the initial value. In Figure 13 discharge and charge curves related to the thirteenth, seventeenth, fiftieth and hundredth cycle, are shown. It is possible to notice that the capacity measured after 50 cycles was 460 mAh/g, a value that remains, as said before, unchanged during subsequent cycles. The trend of capacity as a function of cycle number is presented in Figure 14. The cell, after the twentieth cycle, lost 63% of the initial value, even if it maintained a capacity of about 450 mAh/g at the end of the 100 cycles. The results obtained demonstrate the effectiveness of core- shell configuration in multi-functional design of a sulfur-based cathode. In particular, the high capacity observed during the first few cycles are attributable to the small size of particles which allows an almost total use of active material. Moreover, the presence of TiO\({}_{2}\) shell represents a barrier against polysulfides diffusion [21]. Although the material is still unable to deliver a capacity near the theoretical one, the results obtained in term of capacity are bigger with respect to the traditional cathodic material used nowadays in lithium-ion batteries. Figure 12: (**a**) Charge curves obtainedat C/10 for first, third, fifth and tenth cycle and (**b**) discharge curves obtained for first, third, fifth and tenth cycle for core–shell S–TiO\({}_{2}\) materials.