**4. Conclusions**

The present article provided significant insight into the underlying mechanisms that give rise to the capacity fade of SnS materials during cycling. Although it has been suggested that SnS undergoes a conversion mechanism upon lithiation, its morphological consequences have not been examined. The microscopy observations herein indicate that lithiation of SnS/C leads to the formation of free-standing Sn and SnS nanoparticles that are dispersed throughout the electrolyte/SEI layer on the electrode surface. As a result, the Sn and SnS become inactive and isolated from the current collector, leading to continuous capacity fade. The microstructural observations are in accordance with the electrochemical cycling results, which indicate that, after 120 cycles, the capacity had dropped to that of the pure carbon matrices, suggesting the SnS was not participating in the reactions. Furthermore, EIS showed that increasing the SnS content increased the interface resistance, as the content of Sn and SnS in the inactive layer increased. Hence, in order to commercialize SnS electrodes, which have the ability to offer a capacity greater than other Sn-based anodes, it is necessary to inhibit such dissolution of Sn and SnS into the electrolyte. Approaches similar to those followed for S–C electrodes (for Li–S batteries), which "trap" S in highly porous carbon substrates, may be appropriate [1]. However, the goal of the present study was to provide insight into the capacity fade of SnS, not fabricate a promising new anode.

**Author Contributions:** Conceptualization: K.A., T.S. and H.D.; methodology, K.A., T.S., A.Y. and H.D.; validation, K.A., H.D., T.S., A.Y. and T.H.; data curation, K.A., H.D., A.Y., T.S. and T.H.; writing review and editing, K.A, H.D., A.Y. and T.S.; All authors have read and agreed to the published version of the manuscript.

**Funding:** This research was initially funded by K.A., A.Y., T.S., T.H., grant number ERC-MINATRAN 211166.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Acknowledgments:** This work began with the support of ERC-MINATRAN 211166 (K.A., A.Y., T.S., T.H.). Many of the present results were included in the PhD thesis of H.D.

**Conflicts of Interest:** The authors declare no conflict of interest.
