Operando Studies of Bismuth Nanoparticles Embedded in N, O‐Doped Porous Carbon for High‐Performance Potassium‐Ion Hybrid Capacitor

Abstract A highly viable alternative to lithium‐ion batteries for stationary electrochemical energy‐storage systems is the potassium dual‐ion hybrid capacitor (PIHC), especially toward fast‐charging capability. However, the sluggish reaction kinetics of negative electrode materials seriously impedes their practical implementation. In this paper, a new negative electrode Bi@RPC (Nano‐bismuth confined in nitrogen‐ and oxygen‐doped carbon with rationally designed pores, evidenced by advanced characterization) is developed, leading to a remarkable electrochemical performance. PIHCs building with the active carbon YP50F positive electrode result in a high operation voltage (0.1–4 V), and remarkably well‐retained energy density at a high‐power density (11107 W kg⁻¹ at 98 Wh kg⁻¹). After 5000 cycles the proposed PHICs still show a superior capacity retention of 92.6%. Moreover, a reversible mechanism of “absorption‐alloying” of the Bi@RPC nanocomposite is revealed by operando synchrotron X‐ray diffraction and Raman spectroscopy. With the synergistic potassium ions storage mechanism arising from the presence of well‐structured pores and nano‐sized bismuth, the Bi@RPC electrode exhibits an astonishingly rapid kinetics and high energy density. The results demonstrate that PIHCs with Bi@RPC‐based negative electrode is the promising option for simultaneously high‐capacity and fast‐charging energy storage devices.