Entropy‐Driven Ultrafast Ion Conduction Via Confining Organic Plastic Crystals in Ordered Nanochannels of Covalent Organic Frameworks

• Published in: Small (Weinheim an der Bergstrasse, Germany) Vol. 19; no. 17; pp. e2207831 - n/a
• Main Authors: Wang, Jing, Liu, Lili, Liu, Yukun, Zhang, Xian‐Ming, Li, Juan
• Format: Journal Article
• Language: English
• Published: Germany Wiley Subscription Services, Inc 01.04.2023
• Subjects: Anions; Cations; Confining; covalent organic frameworks; Ion diffusion; Ion migration; Ions; Lithium; lithium ion conductors; Low conductivity; Low temperature; Molten salt electrolytes; Nanochannels; Nanotechnology; NMR; NMR spectroscopy; Nuclear magnetic resonance; organic ionic plastic crystals; Photoelectrons; Porous materials; Solid electrolytes; solid state electrolytes; Spectrum analysis; X ray photoelectron spectroscopy; organic ionic plastic crystals; covalent organic frameworks; solid state electrolytes; lithium ion conductors
• DOI: 10.1002/smll.202207831
• ISSN: 1613-6810

Low conductivity over a wide temperature region due to ultra‐slow ion migration dynamics is a key issue in the field of solid‐state electrolytes (SSE), which needs to be solved and improved. Covalent organic frameworks (COFs), a rapidly growing class of porous crystalline materials, emerge as a new research hotspot in the field of SSEs. This is due to their homogeneously dispersed sites and well‐defined pathways for ion diffusion, demonstrating great advantages over conventional non‐porous solids. Herein, a composite solid electrolyte by confining organic ionic plastic crystal (OIPC) in the 1D ordered nanochannels of COFs as the host matrix for solid‐state lithium‐ion conduction, is reported. Due to the loss of coupling between PBu4+ cations and TFSI− anions, the cation–anion interaction is weakened; and thus, the lithium‐ion transportation is facilitated. As a result, the COF‐confining OIPC SSEs show ultra‐high lithium‐ion conductivity of 0.048 S cm−1 at 30 °C and 0.021 S cm−1 at the extremely low temperature of −30 °C. The dynamic origin of this fast ion conduction is characterized by differential scanning calorimetry (DSC), X‐ray photoelectron spectroscopy (XPS), and variable temperature solid‐state nuclear magnetic resonance (NMR) spectroscopy. Entropy‐driven ultrafast ion conduction is achieved. Via confinement effect of the nanochannels of covalent organic frameworks, organic ionic plastic crystals (OIPCs) exhibit higher entropy and lower enthalpy of solid–solid phase transition than bulky OIPCs, giving lithium, sodium, and potassium ions a material basis for their highly flexible migration.