Besides the Capacitive and Diffusion Control: Inner‐Surface Controlled Bismuth Based Electrode Facilitating Potassium‐Ion Energy Storage

Abstract One of the major challenges of potassium‐ion hybrid capacitors (PIHCs) is to explore favorable anode materials with fast reaction kinetics to match the cathodes. Here, an “inner‐surface” controlled electrochemistry mechanism based on bismuth electrode is proposed and in‐depth studied, which is different from the capacitive or diffusion controlled electrode. Such inner‐surface controlled electrochemistry performance gives a high K ion diffusion ability under not only room temperature (RT) but also low temperature (LT). In this study, a kind of conjunct‐like bismuth nanoparticle (CBN) is fabricated to model such an advantage. The CBN anode for PIBs displays ultra‐long cycling stability and excellent rate capability, especially with a reversible capacity of 212.9 mAh g −1 at 30 A g −1 after 5000 cycles under RT. At −20 °C, the CBN anode achieves a capacity of 191.9 mAh g −1 at 10 A g −1 after 10 000 cycles. Coupling with activate carbon cathode, the as‐assembled PIHCs deliver high energy/power densities (111.8 Wh kg −1 /412.8 W kg −1 and 29 Wh kg −1 /14 312.6 W kg −1 ), which outperforms those of previously reported PIHCs and other hybrid capacitors. The study provides a new understanding of the energy storage mechanism for bismuth‐based electrodes and accelerates the development of advancing potassium ion storage devices, especially at LT.