Significantly Enhancing the Lithium Ionic Conductivity of Metal–Organic Frameworks via a Postsynthetic Modification Strategy

Metal–organic frameworks (MOFs),
due to their possessing
a porous structure, are potential candidates for solid-state ionic
conduction materials. Moreover, uncoordinated carboxylic acid groups
(−COOH) of MOFs can be used as postsynthetic modification sites,
which are favorable for lithium ion exchange. Herein, we synthesized
a unique multiple carboxylic zinc metal–organic framework (Zn-MOF-COOH)
containing uncoordinated carboxylic acid groups. Zn-MOF-COOLi was
synthesized through deprotonation using LiOH via a straightforward
acid–base reaction at room temperature (RT), thereby exhibiting
better good electrochemical properties. The lithium ionic conductivity
(σ) increased from 1.81 × 10–5 to 1.65
× 10–4 S·cm–1, lithium
ion transference number (tLi+) rose from 0.67 to 0.77, and the electrochemical window improved
from 2.0–5.5 to 1.5–6.5 V. This work offers a new strategy
to improve the σ of MOFs and a new perspective toward manufacturing
of high-performance solid-state ionic conduction materials.