Ion-transporting channel-embedded MOF-in-COF structures as composite quasi-solid electrolytes with highly enhanced electrochemical properties

Abstract

Covalent organic framework (COF) materials have demonstrated significant potential as solid-state electrolytes (SSEs) in advanced energy storage systems. However, a limitation of COF-based electrolytes lies in their restricted ion-conducting ability within the COF pores. To overcome this challenge, numerous researchers have introduced ionic liquid (IL) into COF frameworks, resulting in the creation of a quasi-solid-state electrolyte known as COF-IL (QSSE). This incorporation of IL improves the mobility of lithium ions, but there are still some limitations in terms of electrochemical performance. To address this issue, in this work, metal organic frameworks (MOFs) are additionally employed to control and optimize the properties of COF pores. This leads to the formation of a MOF-in-COF (MC) structure that can more effectively accommodate IL, creating an exceptionally effective pathway for lithium-ion transportation. The IL-incorporated MC (IL@MC) solid electrolyte displays a notably high ionic conductivity of 1.5 × 10⁻³ S cm⁻¹ at room temperature and a lithium-ion transference number of 0.26 at 60 °C. This performance improvement can be attributed to the functionalization of the COF pores with MOFs, which act as selective gates for transporting cations.