A fluorinated covalent–organic framework-based quasi-solid-state electrolyte enables low-temperature lithium-ion batteries

Abstract

Maintaining stable operation over a wide temperature range (−40–110 °C) still constitutes a critical challenge for quasi-solid-state electrolytes (QSSEs), particularly under extreme cold conditions. Here, a series of covalent triazine frameworks have been obtained, among which COF-TA_0.5TF_0.5 featuring multi-component functionalities of CN linkages, triazine cores, –F atoms and rich channels has been proposed as a promising solution to the aforementioned challenge, realizing a significant improvement in wide-temperature-range electrochemical performance. Notably, the ionic conductivity of the COF-TA_0.5TF_0.5 QSSE can be maintained up to 10⁻³ S cm⁻¹ from −40 to 110 °C (1.07 × 10⁻³ to 9.11 × 10⁻³ S cm⁻¹), and the transference number is as high as 0.91 and 0.87 at room temperature and −40 °C respectively, revealing outstanding prospects for low-temperature applications. Furthermore, COF-TA_0.5TF_0.5 features excellent cycling stability and lithium dendrite inhibition capacity over 1600 h under 0.1 mA cm⁻² and a coulombic efficiency retention rate of 99.80% after 100 cycles at 0.1 C and −20 °C. Density functional theory (DFT) calculations reveal that COF-TA_0.5TF_0.5 with rich lithiophilic sites and stronger adsorption binding energy for PF₆⁻ is conducive to facilitating lithium salt dissociation and Li⁺ transport. This work opens a new avenue to broaden the wide-temperature-range application of COF-based quasi-solid-state lithium-ion batteries.