Fast Ion Transport Pathway Provided by Polyethylene Glycol Confined in Covalent Organic Frameworks

Abstract

Covalent organic frameworks (COFs) with well-tailored channels are able to accommodate ions and offer their conduction pathway. However, due to strong Coulombic interaction and the lack of transport medium, directly including lithium salts into the channels of COFs results in limited ion transport capability. Herein, we propose a strategy of incorporating low-molecular-weight polyethylene glycol (PEG) into COFs with anionic, neutral, or cationic skeletons to accelerate Li+ conduction. The PEG confined in the well-aligned channels retains high flexibility and Li+ solvating ability. The ion conductivity of PEG included in a cationic COF can reach 1.78 × 10–3 S cm–1 at 120 °C. The simplicity of this strategy as well as the diversity of crystalline porous materials holds great promise to design high-performance all-solid-state ion conductors.

Defective 2D Covalent Organic Frameworks for Postfunctionalization

“…The activation energy ( E a ) of these COF‐based electrolytes were calculated by the linear Arrhenius plots with the values of 1.08, 0.81, 0.67, 0.49, 0.41, and 0.28 eV for TPB‐DHTP‐COF@Li, dCOF‐NH 2 ‐60@Li, dCOF‐ImBr‐60, dCOF‐ImTFSI‐20, dCOF‐ImTFSI‐40@Li, and dCOF‐ImTFSI‐60@Li, respectively (Figure b). The relatively lower E a value of dCOF‐ImTFSI‐60@Li compared with other reported COF‐based solid electrolytes reveals the easier lithium‐ion motion across the channel of dCOF‐ImTFSI‐60 (Table S8, Supporting Information) . To reveal the Li‐ion migration behaviors of dCOF based materials, density functional theory (DFT) calculations were employed to simulate the motion in the local structure of dCOFs (Figure S15, Supporting Information).…”

“…As a rule, liquid electrolytes possess low interfacial resistance and high ion conductivity (up to 10 −1 S cm −1 ) and exhibit good performances in Li secondary batteries, but they cannot work safely at high temperature (over 80 °C) . Therefore, exploring all‐solid‐state electrolytes that can be used at high temperature circumstance may provide a new way for developing safer Li secondary batteries.…”

“…The anionic part, bis(trifluoromethylsulfonyl)imide (TFSI − ) anions are highly hydrophobic and less coordinative, which can be integrated better with lithium ion compared with other commonly used anions in imidazolium‐based ILs (such as BF 4 − , PF 6 − ) . COF can be considered as a good candidate materials for electrolytes compared with conventional amorphous polymers owing to their features of structural designability, well‐defined porosity, and suitable pore size distribution, which would beneficial for ion motion and provide pathway for ion transport . Nonetheless, the long side chains of imidazolium‐based ILs are flexible, it seems that direct condensation through imidazolium building blocks and linear monomers to construct defined imidazolium‐containing porous polymers is very difficult .…”

Covalent Organic Frameworks: Chemical Approaches to Designer Structures and Built‐In Functions

“…Similarly, physically loading polyethylene glycol (PEG) into the pores promotes dissociation of the Li ion pairs and accelerates Li + conduction. The Li + conductivities of PEG‐Li + @CD‐COF‐Li (Figure h), PEGLi + @COF‐300 (Figure ), PEG‐Li + @COF‐5 (Figure a), and PEG‐Li + @EBCOF‐ClO 4 (Figure i) are 2.60×10 −5 , 1.40×10 −6 , 3.60×10 −8 , and 1.93×10 −5 S cm −1 at 30 °C, and these values increase to 1.30×10 −4 , 9.11×10 −5 , 3.49×10 −5 , and 1.78×10 −3 S cm −1 , respectively, at 120 °C . COF‐5 (Figure a) and TpPa‐1 COF (Figure c) without polyelectrolyte chains on the pore walls can load 77 mol % Li + and exhibit low conductivities of 2.6×10 −4 and 1.5×10 −4 S cm −1 at room temperature, respectively .…”

Kovalente organische Gerüstverbindungen: chemische Ansätze für Designerstrukturen und integrierte Funktionen

“…1.93×10 −5 S cm −1 bei 30 °C, und diese Werte nehmen bei 120 °C auf 1.30×10 −4 , 9.11×10 −5 , 3.49×10 −5 bzw. 1.78×10 −3 S cm −1 zu . COF‐5 (Abbildung a) und TpPa‐1‐COF (Abbildung c) ohne Polyelektrolytketten an den Porenwänden können 77 mol % Li + laden und zeigen geringe Leitfähigkeiten von 2.6×10 −4 bzw.…”