Transformation of vulnerable imine bond into aromatic in 3D COF for ultrastable lithium-ion batteries

Abstract

About half of the thus far reported covalent organic frameworks (COFs) are of imine-linked 2D and 3D structures, which usually suffer from relatively low working stability due to the vulnerable easily nucleophile-attacked C = N bond nature. Herein, an imine-linked 3D COF, TAM-DMPZD-COF, was constructed by reaction between 4-connected T_d 4,4′,4′',4′''-methanetetrayltetraaniline and 2-connected 5,10-methyl-5,10-dihydrophenazine-2,7-dicarbaldehyde. Addition of S₈ into the above mentioned reaction leads to the transformation of imine bond into an aromatic thiazole moiety in the framework, affording the thiazole-linked 3D COF, TAM-DMPZD-COF-S. This result in significant enhancement over the ultrahigh cycling stability of the TAM-DMPZD-COF-S-based LIBs cathode, with the thus far reported highest 50,000 cycles and 0.00016 % capacity decay per cycle at 10 A g^-1, in good contrast to only 55 % capacity retention after 5000 cycles at 10 A g^-1 for TAM-DMPZD-COF-based LIBs cathode. Nevertheless, transformation of imine bond into an aromatic thiazole moiety in the 3D framework also induces an increase in the redox active sites for both Li⁺ and PF₆^- ions, resulting in enhanced ion storage capacity and energy density of TAM-DMPZD-COF-S (325 mA h g^-1 and 736 W h kg⁻¹ at 0.1 A g^-1), surpassing those for traditional inorganic cathodes and all the thus far reported COFs-based electrodes.