Covalent Organic Framework-Based Electrolytes for Fast Li⁺ Conduction and High-Temperature Solid-State Lithium-Ion Batteries

Abstract

It has been a long-standing challenge to design and fabricate high Li+ conductive polymer electrolytes at the atomic level with superior thermal stability for solid-state lithium-ion batteries. Covalent organic frameworks (COFs) with tailor-made 1D nanochannels provide a potential pathway for fast ion transport, but it remains elusive. In this work, three crystalline thiophene-based imine-linked COFs were constructed and explored as Li+-conducting composite electrolytes by doping ionic liquids into their 1D nanochannels. The COF–IL composite electrolytes exhibited excellent thermal stability (up to 400 °C) and high Li+ conductivity (up to 2.60 × 10–3 S/cm at 120 °C, one of the highest values of doped porous organic materials). Furthermore, the COF–IL composite electrolytes exhibited stable cycling in a LiFePO4–Li full cell with a high initial discharge specific capacity of 140.8 mA·h/g at 100 °C, more stable than common poly­(ethylene oxide)-based electrolytes, indicating great potential application under a high-temperature operation. This work opens a new avenue for the development of fast Li+-conducting COF-based electrolytes for high-temperature solid-state lithium-ion batteries.

Branched Poly(ethylene glycol)-Functionalized Covalent Organic Frameworks as Solid Electrolytes

“…N 2 gas sorption experiments at 77 K were performed to investigate the details of the surface area of these samples. Much lower than that of non-PEG-modified COF-43 (400 cm 2 g −1 ), 23 the BET amounts are 16.15, 2.95, and 3.0 cm 2 g −1 for COF-PEG-B1, COF-PEG-B3, and COF-PEG-B6, proving the crowded situation of these COFs (Figure 2b). After introducing LiTFSI, the BET amounts drop obviously and are 2.60, 1.69, and 2.56 cm 2 g −1 for COF-PEG-B1-Li, COF-PEG-B3-Li, and COF-PEG-B6-Li (Figure S4).…”

“…For these complex and inevitable results, it is a challenge to investigate the ionic conduction in PEG-based electrolytes systematically. In our previous contributions, grafting a PEG chain into COFs can accomplish solid PEG-based COF electrolytes and high ionic conductivity. − The regular pore architectures not only remain solid state at high temperature but also offer compatible space for lithium-ion coupled segment motion and Li-ion movement, bringing about a remarkable conductivity. Nonetheless, being a facilitator for Li-ion conduction, the elevated temperature will promote anionic migration as well, which may exacerbate the problem of low Li + transference number.…”

Foldable Solid‐State Batteries Enabled by Electrolyte Mediation in Covalent Organic Frameworks

“…[14][15][16][17][18] Such stable pore channels are of great interest for nanofluidic ion transport. [19][20][21][22][23][24][25] Nevertheless, the real solid-state ion conduction is far from a practical requirement, [15] even with the most attractive SIC-type COFs (Figure 1c). This is because in the solid state, diffusion of closely associated Li ions occurs mainly along the pore walls of lithiated COFs (Figure 1f).…”

Covalent Organic Framework for Rechargeable Batteries: Mechanisms and Properties of Ionic Conduction

“…In addition, the devised nanochannels wall could also impart the host-guest interaction, which is favorable to the introduction of benign ion-conducting materials into COF channels. [33,34] The synergistic effect between the periodic structure of COFs and the ionic conduction ability of guests can intensify the ion conducting ability. Third, the intrinsic insolubility supports COFs to be used in liquid batteries.…”