Potassium deficiency and irreversible loss of potassium at the initial cycle of potassium-ion batteries inevitably reduce their energy density and cycle life. Cathode pre-potassiation before battery assembling is an efficient method to address these issues but faces problems such as safety risks and high cost. Herein, we report an economic and facile potassium compensation strategy employing a self-sacrificial agent (i.e., K2C4O4) at cathodes to improve the performances of potassium-ion batteries. We found that with the addition of K2C4O4 in a P3-type K0.5MnO2 cathode, the initial Coulombic efficiency of the electrode can be significantly improved from 53.6% to the reported highest one of 93.5%. Moreover, we demonstrate that the decomposition of K2C4O4 during the charge process contributes to the formation of a thin and F-rich cathode electrolyte interphase layer on the surface of the electrode, benefiting for the improved kinetics and interfacial stability of K0.5MnO2 cathodes. As a result, a K2C4O4-assisted potassium-ion full cell shows about three times higher energy density (220 W h kg−1) and much enhanced capacity retention than the K2C4O4-free cell without any pre-potassiation treatment. The potassium compensation strategy provides an effective approach to overcome the existing technical hurdles for the development of potassium-based energy storage systems.
