## 3 Results and Discussion
### Extended Cycling Performance  
Figure 7a-c represents the lithiation/delithiation specific capacity and corresponding coulombic efficiency of all SiCN-S composites. Besides the initial lithiation capacity, the reversible capacity after 50 cycles, the coulombic efficiency and capacity retention of all SiCN-S composites are listed in Table 2. As shown in Figure 7a,b, both the lithiation and delithiation capacity of the sample SiCN-S-900 are the lowest in the first four cycles. Nevertheless, after the fourth cycle, its specific capacity surpasses that of the sample SiCN-S-1100. After 12 cycles, the sample SiCN-S-900 even surpasses that of the SiCN-S-800 and remains the highest capacity until the 50 th cycle. The lowest performance is registered for the sample SiCN-S-1100. In the end, after 50 cycles, the sample SiCN-S-900 exhibits the highest lithiation retention of 22%. The enhancement of the electrochemical performance of sample SiCN-S-900, in comparison to that of SiCN-S-800, is mainly due to the enhanced conductivity resulted from the increasing of the degree of graphitization of the free carbon. Although the SSA of the sample SiCN-900 is lower, its total pore volume V\({}_{\mathrm{t}}\) changed little, in comparison with the sample SiCN-800, and it reveals more mesopores, in comparison to SiCN-1100 (results of BET). The presence of mesopores is of advantage for stabilization of sulfur electrochemical behavior [27; 40; 41], which can explain the best electrochemical performance of SiCN-S-900 among measured samples. Even though SiCN-S-1100 contains more organized free carbon phase and thus reveals higher electronic conductivity, SiCN-S-900 outperforms it in prolonged cycles stability. It is known that the \"shuttle effect\" originating from the diffusion of soluble polysulfides usually leads to a coulombic efficiency higher than 100% [11; 33; 42]. This phenomenon was also discussed in our previous work. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Samples**} & **Initial Lithiation** & **Reversible Capacity** & **Initial Coulombic** & **Capacity** \\  & **Capacity (mAh/g)** & **after 50 Cycle (mAh/g)** & **Efficiency (\%)** & **Retention (\%)** \\ \hline SiCN-S-800 & 934 & 158 & 85 & 17 \\ SiCN-S-900 & 885 & 195 & 85 & 22 \\ SiCN-S-1100 & 1040 & 118 & 82 & 11 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Electrochemical parameters of the sulfurized SiCN samples. During delithiation process, the long-chain soluble polysulfides pass through the membrane and migrate to Li anode, redox reaction happens, and short chain polysulfides are formed; then, the short-chain polysulfides migrate back and are re-oxidized to long-chain polysulfides, resulting in long delithiation process and excessive coulombic efficiency over 100% [27]. Hence, the level of coulombic efficiency can reflect the degree of the \"shuttle effect\". While, in addition to the remarkable initial coulombic efficiency of all SiCN-S composites, in the first 14 cycles, all samples keep the state where the coulombic efficiency is not growing rapidly (lower than 110%). In the subsequent cycles up to the 50 th cycle, all samples except SiCN-S-900 exhibit a coulombic efficiency around 110%. This finding in turn demonstrates that that the lowest extent of a \"shuttle effect\" is observed for SiCN-S-800 and SiCN-S-1100. As for the sample SiCN-S-900, its coulombic efficiency, growing from 110% to 130%, is a sign of a progressing polysulfides diffusion (\"shuttle effect\"), visible also in an excessive anodic polarization of the cyclic voltammetry curve shown in Figure 6b. Figure 6: Cyclic voltammograms of samples SiCN-S-800, SiCN-S-900, and SiCN-S-1100 at a scan rate of 0.02 mV/s. The first cycle (**a**) and the fifth cycle (**b**). temperature, more ordered free carbon phase is present, however a pore diameter increase, resulting in lower capacity retention.