Salen-based porous aromatic frameworks with multi-active sites as anode materials for lithium-ion batteries

Porous organic polymers are considered as excellent candidates for the electrode materials in rechargeable battery due to their desirable properties including porosity, customizable structure, and intrinsic chemical stability. Herein a Salen-based porous aromatic framework (Zn/Salen-PAF) is synthesized through a metal directed method and further used as efficient anode materialfor lithium-ion battery. Attributing to the stable functional skeleton, Zn/Salen-PAF delivers a reversible capacity of 631 mAh·g^-1 at 50 mA·g^-1, a high-rate capability of 157 mAh·g^-1 at 20.0 A·g^-1 and a long-term cycling capacity of 218 mAh·g^-1 at 5.0 A·g^-1 even after 2000 cycles. Compared to the Salen-PAF without metal ions, Zn/Salen-PAF possesses better electrical conductivity and more active sites. X-ray photoelectron spectroscopy (XPS) investigation indicates that the coordination of Zn²⁺ with N₂O₂ unit not only improves the conjugation of the framework but also contributes to the in situ cross-sectional oxidation of the ligand during reaction, which results in the electron redistribution of oxygen atom and the formation of CO bonds.