An exceptionally large energy cathode with the K–SO4–Cu conversion reaction for potassium rechargeable batteries

Abstract

Although layered-type cathode materials for lithium-ion batteries (LIBs) have received great attention due to their large gravimetric energy density, those for potassium rechargeable batteries (PRBs) just deliver small and limited energy density due to the large structural change and phase transition during de/intercalation of K⁺ ions with a large ionic size. Thus, a new approach is required for achieving high energy densities. A cathode material that results in ultrahigh energy density for potassium rechargeable batteries (PRBs) based on the conversion reaction of K–SO₄–Cu in the system was developed. To maximize the electrochemical performance, a copper-sulfate/carbon nanocomposite (hereafter denoted as N-CSO/C) was prepared using a simple high-energy ball-milling process. At a current density of 12 mA g⁻¹, the conversion reaction of K–SO₄–Cu in the PRB system resulted in a specific capacity of ∼240 mA h g⁻¹ with an average operating voltage of ∼2.8 V (vs. K⁺/K). This capacity and the resulting energy density are larger than those of other cathode materials for PRBs reported to date. After 200 cycles at 360 mA g⁻¹, N-CSO/C retained ∼70% of the initial capacity. The overall reversible reaction mechanism of K–SO₄–Cu in N-CSO/C in the PRB system was investigated through combined studies using first-principles calculation and various experimental techniques.