High-efficiency cathode potassium compensation and interfacial stability improvement enabled by dipotassium squarate for potassium-ion batteries

Abstract

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 K_0.5MnO₂ 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 K_0.5MnO₂ 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.