Foldable potassium-ion batteries enabled by free-standing and flexible SnS2@C nanofibers

Potassium-ion batteries (PIBs) have been regarded as promising alternatives to lithium-ion batteries in large-scale energy storage systems owing to the high abundance and low cost of potassium. However, the large radius of the K-ion hinders the development of suitable electrode materials. In this work, we confine SnS2 in N,S co-doped carbon nanofibers as anode materials for PIBs with high reversible capacity (457.4 mA h g−1@0.05 A g−1), remarkable cycling stability (1000 cycles@2.0 A g−1), and superior rate capability (219.4 mA h g−1@5.0 A g−1), overmatching most of the reported studies. The origin of the high reversible capacity is revealed by in situ XRD techniques. The combined capacitive and diffusion-controlled behaviors are disentangled through consecutive CV measurements. Combining the Randles–Sevcik equation and dQ/dV plots, correlations between the K-ion storage behaviors and diffusion kinetics at various potassiation depths are constructed. Theoretical calculations on K adsorption affinities at various N,S co-doped sites illuminate the synergistic effects of the N,S co-doping strategy in boosting the K-ion transport kinetics. Moreover, foldable potassium-ion full cells are successfully assembled with stable cycling performance, showing application potential in flexible electronic devices. These findings will boost the rational design and mechanistic understanding of anode materials in PIBs and related energy storage devices.