Highly Conductive\nTwo-Dimensional FeTHBQ/Graphene\nNanocomposite as the Cathode Material for Lithium-Ion Batteries

Constructing high-performance coordination polymer (CP)\ncathodes\nfor lithium-ion batteries based on the redox reactions of both high-potential\ntransition metal ions and high-capacity organic ligands has attracted\nextensive attention. However, CP cathodes suffer from structural degradation,\nlow electrical conductivity, and sluggish diffusion kinetics, resulting\nin poor cycling stability and inferior rate capability. Herein, the\nultrafine FeTHBQ (THBQ = tetrahydroxy-1,4-benzoquinone) CP nanoparticles\nin situ grew on both sides of graphene nanosheets to form the uniform\ntwo-dimensional (2D) FeTHBQ/Graphene nanocomposite with a sandwich\nstructure via a one-pot solvothermal method. The highly conductive\ngraphene skeleton promotes the electronic conduction and structural\nstability for the 2D FeTHBQ/Graphene nanocomposite. Besides, compared\nwith bulk FeTHBQ, the primary FeTHBQ nanoparticles in the FeTHBQ/Graphene\nnanocomposite have smaller particle sizes with larger specific surface\nareas. This not only shortens the Li<sup>+</sup> diffusion distance\nin the FeTHBQ crystal but also benefits Li<sup>+</sup> transfer between\nthe electrolyte and the electrode. In the FeTHBQ/Graphene nanocomposite,\nthe active material of FeTHBQ manifested multiple redox centers of\ntransition metal ions (Fe<sup>3+</sup>/Fe<sup>2+</sup>) and carbonyls\n(CO/C–O<sup>–</sup>) in THBQ ligands. Owing\nto the enhancements of structural stability, electronic conduction,\nand Li<sup>+</sup> diffusion kinetics, the 2D FeTHBQ/Graphene nanocomposite\npresented a high lithium-ion storage capacity of 217.2 mA h g<sup>–1</sup> at 50 mA g<sup>–1</sup>, a fast rate capability\nof 79.1 mA h g<sup>–1</sup> at 5000 mA g<sup>–1</sup>, and a stable cycling performance of 87.2 mA h g<sup>–1</sup> at 500 mA g<sup>–1</sup> after 100 cycles. This work sheds\nlight on the great opportunity for optimizing the electrochemical\nperformances of CP-based functional electrode materials by combining\nwith conductive substrates.