Natural Supra‐Molecular Structure Engineering for High‐Performance Potassium Batteries Separator

Abstract Although potassium batteries (KBs), such as potassium‐metal batteries and potassium‐ion batteries, promise low cost and high‐energy density, specialized separators are not available that can satisfy the KBs operations. In this work, a hierarchical porous cellulose (HPC) separator with high‐performance, by engineering of the natural supra‐molecular structure of cellulose, is reported. The supra‐molecular and hierarchical structure of cellulose provides the separator with high porosity, excellent mechanical properties, superior electrolyte wettability, and stable thermal performance. The incorporation of small pore size (0.64 µm) and suitable tortuosity (1.83) reveal that the separator enables uniform current distribution and inhibits the puncturing of K dendrites. Thus, a lifespan of more than 1000 h for a K//K symmetric cell is achieved without short‐circuiting. Benefiting from the high K⁺ transference number (0.69), graphite//K and Prussian blue (PB)//K cells with HPC separators exhibited pre‐eminent cycling stability (400 and 200 cycles, respectively) and high‐rate performance. Moreover, the PB//graphite full cell with HPC separator is shown to deliver a reversible capacity of 86 mAh g⁻¹ with 100 cycles. This novel HPC separator provides a possibility for the sustainable development of KBs and other energy storage systems by the rational structural modification of plants.