Morphology engineering of covalent organic frameworks: boosting the electrochemical performance of quasi-solid-state electrolytes for wide-temperature battery applications.

Solid-state lithium-ion batteries are promising for safe energy storage, yet their performance remains limited by temperature-dependent ion transport and interfacial instability. Herein, a morphology engineering strategy is employed to regulate the ion transport behavior of covalent organic frameworks (COFs) and improve interfacial contact for the preparation of quasi-solid-state electrolytes (QSSEs) suitable for a wide temperature range. By controlling the emulsion polymerization process, a spherical e-TpPa-COF and a bowl-shaped b-TpPa-COF are obtained. The e-TpPa-COF-based QSSEs exhibit superior electrochemical performance over a wide temperature range (-20 to 100 °C), achieving a conductivity of up to 8.14 × 10-3 S cm-1 at elevated temperatures, maintaining an ionic conductivity of 9.95 × 10-4 S cm-1 and a Li+ transport number of 0.75 at -20 °C. In addition, the e-TpPa-COF demonstrated stable lithium plating/stripping behavior, maintaining a low overpotential of 15 mV during 1500 hours of cycling. After 130 cycles at a current density of 1C, the discharge capacity remained exceptionally stable and the average coulombic efficiency reached 92.15%. This work highlights the critical role of morphology in regulating ion transport and interfacial behavior, providing an effective strategy for developing high-performance QSSEs under wide temperature conditions.