Unraveling the Origin of Enhanced K+ Storage of Carbonaceous Anodes Enabled by Nitrogen/Sulfur Co-Doping

N-doped carbons, as promising anode materials for energy storage, are generally modified by the additional heteroatoms (B, P, and S) doping to further promote the electrochemical performance. However, the promotion mechanism by such additional doping, especially its interplay with N-containing species, remains unclear. Herein, by adopting N/S co-doped carbon as a model system, it is found that S-doping can significantly improve the content of pyridinic-N, i.e., the most energetically favorable N type for K+ storage. Theoretical calculations reveal that such S-induced pyridinic-N improvement possibly originates from its catalytic effect that can facilitate the transition from edge quaternary-N to pyridinic-N. The resultant high content of pyridinic-N, together with the additional S species, ensures abundant active sites for K+ storage. Accordingly, the N/S co-doped carbon anode delivers both a high reversible capacity (422.9 mA h g(-1) at 0.05 A g(-1)) and an impressive cyclic stability (249.6 mA h g(-1) at 1 A g(-1) over 4000 cycles). Moreover, in/ex situ characterizations further verify the merits of N/S co-doped carbon from the perspective of compositional evolution and structural stability. This study unravels the origin of enhanced K+ storage by N/S co-doping, which also helps to understand the synergistic effects of other heteroatoms co-doping systems.

Automated summary

N-doped carbons modified by additional S-doping can enhance the content of pyridinic-N, which is the most favorable N type for K+ storage. The catalytic effect of S induces the transition from edge quaternary-N to pyridinic-N, resulting in abundant active sites for K+ storage. The N/S co-doped carbon anode exhibits high reversible capacity and cyclic stability.