Insights into the heteroatom-incorporated storage mechanism of hierarchically interconnected porous conjugated polymer networks for extremely stable potassium-ion storage

Conjugated microporous polymers (CMPs) with enhanced electrical conductivity and insolubility against liquid electrolytes are receiving increasing attention as promising organic anode materials for rechargeable batteries. However, the poor electronic conductivity and restricted-access active sites limit the specific capacity and cycling stability of CMPs and the potassium-storage mechanism in hetero-incorporated CMPs not well understood. Herein, a highly conjugated polymer network with hierarchically interconnected porous structure was deliberately constructed by selecting 4,7-dibromo-2,1,3-benzothiadiazole (BT) and 1,3,5-triacetylene benzene as the acceptor and donor, respectively. The good planarity and high pi-electron delocalization of BT units lead to an enhanced conductivity of BT-CMP. Ex-XPS analysis and DFT calculations reveal that the synergistic coupling of S and N enables a prompt complexation and release of K+ ions and improves the coordination activity of the C--N active sites. More importantly, the hierarchically interconnected porous networks make active sites facilely accessible and accommodate the volumetric expansion effectively, enabling highly stable storage of K-ions. Therefore, the as-prepared BT-CMP anode displays a high specific capacity (462 mAh/g- 1 at 30 mA g-1 after 100 cycles) and ultra-long stability (226.2 mAh g-1 at 1000 mA g-1 after 2000 cycles without significant attenuation) in potassium-ion storage.