A Flexible Potassium-Ion Hybrid Capacitor with Superior Rate Performance and Long Cycling Life

Potassium-ion batteries are promising candidates for large-scale energy storage applications owing to their merits of abundant resources, low cost, and high working voltage. However, the unsatisfying rate performance and cycling stability caused by sluggish K+ diffusion kinetics and dramatic volume expansion hinder the development of potassium-ion batteries. In this study, we design a flexible potassium-ion hybrid capacitor (PIHC) by combining the K-Sn alloying mechanism on the Sn anode and the fast capacitive behavior on the AC cathode with high surface area and mesoporous structure. After optimization, the fabricated Sn parallel to AC PIHC achieves both a high energy density of 120 W h kg(-1) and high power density of 2850 W kg(-1), much better than other similar hybrid devices. Moreover, a gel polymer electrolyte with a 3D porous structure and high ionic conductivity was employed to improve the structural stability of the Sn anode, which not only realizes good flexibility but also achieves long cycling stability with a capacity retention of nearly 100% for 2000 cycles at a high current density of 3.0 A g(-1).