Linker length-dependent lithium storage of pyrene-4,5,9,10-tetraone-based conjugated organic polymer cathodes

Conjugated organic polymers (COPs) have been emerged as a class of cathode materials for lithium-ion batteries (LIBs) because of the rigid structural units and tunable properties. Nonetheless, their applications are still limited due to the poor conductivity and low cycling life. Herein, we design a series of pyrene-4,5,9,10-tetraone-based COPs (P(PTODB)-1, P(PTODB)-2, P(PTODB)-3), containing different number of benzene rings as linking units. Consequently, prolonging the linker lengths could effectively improve structural stability and extend pi-conjugation, leading to the enhanced charge-storage capability. When tested as cathode materials for LIBs, the P (PTODB)-2 electrode delivers a better electrochemical performance with high capacity of 203 mA h g-1 after 100 cycles at 0.1 A g-1 (coulombic efficiency almost 100%) and excellent rate performance (150 mA h g-1 at 5 A g-1). In addition, the Li+ storage mechanism was carried out by ex situ Fourier transform infrared (FT-IR) and X-ray photoelectron spectroscopy (XPS) analysis. Eventually, our study brings forward the appropriately extended linker lengths to fabricate COP cathodes with high electrochemical properties.