Electrolyte-assisted dissolution-recrystallization mechanism towards high energy density and power density CF cathodes in potassium cell

Fluorinated carbons are reported to have the highest energy density as Li primary cell cathodes. While it has poor rate performance and the electrochemical reaction mechanism is still unclear. In this work, fluorinated graphite CF0.88 as K cell cathode is studied. It demonstrates a better rate performance, higher operational voltage, and higher energy density than that of Li cell. Without modification, the micro-size fluorinated graphite demonstrates a specific energy density of 805 Wh kg−1 at 2C (1C corresponding to 821 mA g−1) in K cell vs. 776 Wh kg−1 in Li cell. A dissolution-recrystallization mechanism is proposed for CF cathodes for discharge process. A high K ion diffusion coefficient and an early KF nucleation ascribe to its good performance. After discharge, amorphous CF0.88 transforms to ordered graphite and KF crystals. KF particles nuclear and grow on the electrode surface. Electrolyte plays not only a role as K+ conductor, but also a solution medium to dissolve-aggregate KF. Moreover, electrolyte salt concentration determines particle size of discharge product KF.