Phase Transition Mechanism for Crystalline Aromatic Dicarboxylate in Li⁺ Intercalation

Abstract

Crystalline aromatic dicarboxylate, also known as intercalated metal–organic frameworks, electrodes can be used in sustainable lithium-ion batteries owing to their low resource risks and eco-friendly syntheses via CO2 sequestration. However, little consideration has been given to understanding the phase transition mechanism during electrochemical charge–discharge processes. Here, we report a comparative study on the phase transition mechanism and associated Li+ diffusivity (DLi) in crystalline aromatic dicarboxylate lithium salts with naphthalene and biphenyl frameworks by electrochemical techniques and energy-state analyses using synchrotron radiation. The naphthalene framework, with a strong Li+ interaction and two stable Li+-intercalated structures, forms an energetically stable Li+-storage state through a metastable state, predominantly providing a two-phase reaction, and, at the end of charge and discharge, a solid-solution reaction with low DLi of 10–14–10–12 cm2 s–1. In contrast, the biphenyl framework, weakly interacting with Li+, forms an energetically unstable Li+-storage state, providing a solid-solution reaction with high DLi of 10–12–10–8 cm2 s–1 over the entire region. These findings contribute toward superior stability and high-rate capability in organic electrodes.