N-Heteroaromatic Hydrocarbon π-Conjugated Porous Polymers for High-Rate-Performance Sodium-Ion Batteries

As one type of promising material, porous organic polymers (POPs) have been widely used in sodium-ion battery (SIB) electrodes on account of their environmental friendliness and adjustable pore diameter. However, their capacity and rate performance require further improvement. Herein, a conjugated porous polymer (PQ-POP), containing an azaacene-deficient electron-deficient system, was synthesized by a simple condensation reaction. The conjugated and N-containing heteroaromatic structure improves the conductivity, charge-transfer efficiency, and physicochemical stability. Also, the porous polymeric framework shows a large specific surface area and high porosity, providing a large contact area with electrolytes and reducing the diffusion distance. Therefore, PQ-POP exhibits very good electrochemical properties. Besides its superior reversible specific capacity of 245 mAh g^-1, PQ-POP also shows remarkable cycling stability, maintaining almost 100% after 1000 cycles at 4 A g^-1. At 10 A g^-1, its capacity holds steady at 202 mAh g^-1, outperforming many similar materials. The sodium ion storage mechanism of PQ-POP was confirmed by in situ FTIR and XPS experiments. In order to broaden the application of PQ-POP in SIBs, the electrochemical performance of PQ-POP as the negative electrode and Na₃V₂(PO₄)₃ as the positive electrode were employed to assemble a full cell, where, even at 3 A g^-1, the full cell based on PQ-POP//Na₃V₂(PO₄)₃ maintained 101 mAh g^-1 of the capacity with nearly 100% coulomb efficiency, highlighting its potential in energy storage applications and providing perspectives into designing advanced POP electrodes for SIBs.