New Highly Stable Ionic Compounds Composed of Multivalent Graphene Quantum Dot Anions and Alkali Metal Cations

Abstract

Developing electrolytes with new chemical structures that simultaneously satisfy excellent ionic conductivity, chemical stability, and thermal stability is an indispensable prerequisite for studying next-generation electrochemical. Herein, we propose a new class of ionic compounds consisting of graphene quantum dots (GQD) polyanions with alkali metal cations. The synthesized solid salts readily dissolve in various solvents ranging from water to carbonates allowing highly conductive liquid electrolytes for electrochemical systems. Molecular dynamics simulation with the electrochemical characterization reveals that the ionic compounds provide highly abundant free metal cations with highly stable GQD polyanions, and negligible ion pairs in solution. The lithium salt (Li-GQD) shows higher lithium transference number than the conventional LiPF6 electrolyte, which improves the interfacial stability of Li metals and leads to a decrease in overvoltage at a high C-rate in battery performance. The Li-GQD electrolyte solution offers a wide electrochemical window of -0.2-5 V, which can reliably apply to various electrode materials (graphite, Li4Ti3O12, and LiCoO2). Prussian blue thin film utilizing K-GQD as electrolyte shows significantly improved electrochromic behaviour and higher K+ cation mobility than other controls using conventional electrolytes. We expect our study on the GQD ionic complex to be another signpost for exploring an innovative electrolyte for electrochemical devices.