Piperazine-Linked Phthalocyanine Covalent Organic Frameworks for Efficient Anodic Lithium Storage

Organic anode materials have been considered as promising electrodes for achieving low-cost and sustainable lithium-ion batteries (LIBs). However, organic materials face challenges, such as inadequate cycling stability and sluggish reaction kinetics, leading to an unsatisfactory LIB performance. Covalent organic frameworks (COFs) possess a porous and designable structure coupled with exceptional stability, making them promising candidates for anode electrodes in LIBs to address the challenges. Herein, two piperazine-linked conjugated phthalocyanine-based COFs (named CoPc-BTM-COF and CoPc-DAB-COF) were fabricated from reacting hexafluorophthalocyanine cobalt(II) (CoPcF₁₆) with 1,2,4,5-benzenetetramine (BTM) and 3,3'-diaminobenzidine (DAB), respectively. Powder X-ray diffraction and electron microscopy analyses in combination with theoretical simulation reveal their crystalline nature with sql net and AA arranged stacking pattern. The pore sizes of these two Pc-COFs are 1.62 and 1.90 nm according to theoretical simulation and N₂ sorption measurement, which facilitates their rapid transport of Li⁺ ions. The immersion experiments disclose their remarkable stability. These advantages, together with their conjugated nitrogen-rich skeletal structures, lead to outstanding anodic Li⁺ storage capabilities, exceptional rate performance, and favorable cycling stability. In particular, both Pc-COFs exhibit high capacities of 877 and 669 mAh g^-1 at 100 mA g^-1, superior to most reported organic LIB anodes, showing promising application potential in high-performance LIBs.