Low‐Cost, Safe, and Ultra‐Long Cycle Life Zn–K Hybrid Ion Batteries

Abstract Zinc‐ion batteries (ZIBs) are viewed as a promising energy storage system for large‐scale applications thanks to the low cost and wide accessibility of Zn‐based materials, the high theoretical capacity of Zn anode, and their high level of safety. However, the practical application of ZIBs is hindered by the rapid performance degradation. Herein, a Zn–K hybrid ion battery design is proposed using a high‐quality Prussian blue cathode and a nonflammable Zn–K hybrid ion electrolyte. The electrochemical process is divided into two parts, with K+ insertion/extraction occurring at the cathode side and Zn2+ plating/stripping occurring at the anode side, which avoids structure destruction caused by Zn2+ insertion in the cathode. The non‐flammable electrolyte not only ensures high safety but also effectively suppresses dendrite growth on the Zn anode. The hybrid cells demonstrate a high capacity of 151.0 mAh g−1, a high voltage of 1.74 V (vs Zn2+/Zn), and an ultra‐long cycle life of 15 000 cycles. Combining the nonflammable nature of the electrolyte, the abundance of raw materials, and good electrochemical performance, the Zn–K hybrid ion battery system promises a promising future for renewable energy storage applications.