Multiple Active Sites: Lithium Storage Mechanism of Cu‐TCNQ as an Anode Material for Lithium‐Ion Batteries

Abstract

Recently, carboxylate metal‐organic framework (MOF) materials were reported to perform well as anode materials for lithium‐ion batteries (LIBs); however, the presumed lithium storage mechanism of MOFs is controversial. To gain insight into the mechanism of MOFs as anode materials for LIBs, a self‐supported Cu‐TCNQ (TCNQ: 7,7,8,8‐tetracyanoquinodimethane) film was fabricated via an in situ redox routine, and directly used as electrode for LIBs. The first discharge and charge specific capacities of the self‐supported Cu‐TCNQ electrode are 373.4 and 219.4 mAh g−1, respectively. After 500 cycles, the reversible specific capacity of Cu‐TCNQ reaches 280.9 mAh g−1 at a current density of 100 mA g−1. Mutually validated data reveal that the high capacity is ascribed to the multiple‐electron redox conversion of both metal ions and ligands, as well as the reversible insertion and desertion of Li+ ions into the benzene rings of ligands. This work raises the expectation for MOFs as electrode materials of LIBs by utilizing multiple active sites and provides new clues for designing improved electrode materials for LIBs.

Improve the Conductivity of CuBTC by in‐situ Reduction to Core‐Shell CuTCNQ@CuBTC

“…The concentric rings revealed the polycrystalline structure of the shell layer of CuTCNQ@CuBTC, and the inside ring corresponding to the interplanar spacing of 3.1 Å was indexed to the (120) plane of CuTCNQ (phase I), with a 2θ angle of 28.8° in the powder X‐ray diffraction pattern [25] . The second ring of the SAED pattern should be designated to a plane with a 2θ higher than 46°, which exceeded the reported PXRD angle range of CuTCNQ (phase I) [12,25] …”

“…[25] The second ring of the SAED pattern should be designated to a plane with a 2θ higher than 46°, which exceeded the reported PXRD angle range of CuTCNQ (phase I). [12,25] The effect of reaction time on CuTCNQ@CuBTC…”

“…For example, CuBTC and CuBTC-derived composite materials are widely applied in the adsorption and removal of poluttant, [7][8] and Cu-based organic reaction catalysts. [9][10][11] Recently, MOFs and their derivatives are investigated as active materials for electrochemical applications such as batteries, [12] supercapacitors, [13] and electrocatalysts. [14] The large specific surface area of MOFs is conducive to electrochemical reactions, and transition metal ions with multiple valence and organic ligands can provide abundant active sites for the chemical reaction.…”

Strategies to Optimize the Lithium Storage Capability of the Metal‐Organic Framework Copper‐1,3,5‐Trimesic Acid (Cu‐BTC)

“…It was well proved that the organic moiety (including the carboxylate groups and the benzene ring) of MOFs played important roles in the lithium storage capability. [46][47][48] However, whether the coordinated transition metal ions participated in the lithiation process of MOF was elusive. [24,47] To further determine the role of Cu 2 + , the high-resolution XPS measurement was carried out to investigate the fresh Cu-BTC powder and fully-discharged Cu-BTC (Figure 5d).…”

“…Above all, both copper species and organic ligands of Cu-BTC took part in the redox chemistry contributing to the lithium storage capability, like other conventional MOFs. [24,46]…”