A Dual-Functional Electrolyte Additive for High-Performance Potassium Metal Batteries

Potassium metal batteries (KMBs) coupled with layered transition metal oxides as cathode materials are a promising energy−storage technology owing to low cost and high capacity. However, uncontrollable dendritic growth in the K−metal anode and chemical reactivity of the layered transition metal oxide cathode against the electrolyte solution cause KMBs to suffer from low Coulombic efficiency, rapid capacity fading, and critical safety issues. In this study, an electrolyte engineering strategy is introduced by introducing adiponitrile (ADN) as a dual−functional electrolyte additive containing an electron−rich nitrile group (C≡N) in its molecule structure. Thus, the addition of 1 wt.% ADN can alter the chemical properties of the electrolyte solution, thereby improving the anode−electrolyte and cathode−electrolyte interfacial stabilities in KMBs. The formation of a potassiophilic compound with C≡N in the solid electrolyte interphase layer can guide the uniform electrodeposition of K and suppress the dendritic growth in the K−metal. Moreover, C≡N forms a strong coordination bond with the oxidized transition metal, leading the reversible redox reactions by mitigating the undesirable disproportionation reaction and improving the thermal stability of the layered transition metal oxide cathode. Computational calculations and experimental characterizations are used to verify the role of ADN additive in enhancing the electrochemical properties of KMBs.