Tailoring covalent triazine frameworks anode for superior Lithium-ion storage via thioether engineering

The development of high-performance lithium-ion capacitors (LICs) requires the use of electrode materials with higher energy/power density, faster charging, and longer cycle-life. Herein, by taking the merit of the strong designability of covalent triazine frameworks (CTFs), two tailor-made thioether-functionalized CTFs (S-CTF-Et and S-CTF-Me) with tunable properties are designed and synthesized as anodes for LICs. Due to the rich redox active sites and highly accessible specific surface area of the S-CTF-Et anode, which delivers a very large reversible capacity up to 1334 mAh g−1 at 0.1 A g−1, good rate capability (520 mAh g−1 at 2 A g−1) and cycling stability. After being comprehensively studied via ex-situ FT-IR, ex-situ XPS analyses, and theoretical calculations, it is found that the lithium-storage mechanism involves multi-electron redox reactions of benzene and triazine rings and coordination of thioether-groups by the accommodation of Li+. As proof of the new concept, an all CTF-related LIC device is assembled with S-CTF-Et anode and CTF-derived porous carbon (CTF-800) cathode for the first time, which delivers competitive energy and power densities (179.3 Wh kg−1 and 10.7 kW kg−1) and a capacity retention of 81 % after 10 000 cycles at a large current density of 2 A g−1.