Achieving a Zn-ion battery-capacitor hybrid energy storage device with a cycle life of more than 12,000 cycles

Prussian blue is considered as a promising zinc ion battery material because of its advantages such as stable structure, large lattice gap and simple preparation process. However, the poor conductivity seriously hinders the application of Prussian blue electrode materials. Herein we report a simple and interesting strategy to grow Prussian blue nanoparticle on expanded graphite electrode through a facile electrochemical method. Thanks to the synergy between Prussian blue analogue nanoparticles and self-supporting graphite flakes, the composite electrode with unique architectural structure possess both battery and capacitor characteristics. What's even more interesting is that the defects of Prussian blue crystals are gradually reduced during the extraction and insertion of zinc ions, and then the increasingly perfect crystal structure result in excellent cycling performance (120% capacitance retention after 12,000 cycles).