C3-symmetric trimeric imidazole naphthoquinone derivative with dual redox-active sites for high-performance cathodic lithium storage

Organic lithium-ion batteries (LIBs) are among the most promising energy storage systems owing to their high energy density, low-cost and excellent sustainability. Although many organic materials with preferable redox centers and π-conjugated structure have been utilized as the cathodes, they often have unsatisfactory properties, such as low practical capacity, poor rate capability and short cycle life as well as high production complexity, which hindered the large-scale development of organic LIBs. Herein, a novel trimeric imidazole naphthoquinone derivative (2,2′,2′'-(benzene-1,3,5-triyl)tris(1H-naphtho [2,3-d]imidazole-4,9-dione, BTNID) with a highly π-extended conjugation backbone has been achieved by directly introducing quinone moieties from initial reactants and forming imidazole unit in-situ via Schiff base condensation. Exploited as organic cathode materials for LIBs, the BTNID delivers a specific capacity of up to 483 mAh g−1 at 0.2 A g−1 with an average discharge potential of ∼ 2.0 V, thus realizing an impressive energy density of ∼ 966 Wh kg−1. Moreover, the BTNID cathode shows remarkable rate capability (245 mAh g−1 at 10 A g−1) and excellent cycling stability (74.8% capacity retention after 3000 cycles at 10 A g−1), much higher than most of the so far reported results, which are mainly attributed to unique trigonal geometrical shape and extended π-conjugated backbone of BTNID molecule that allows electrons of redox-active quinone and imidazole moieties to delocalize through the π-π orbital interactions.