Towards high-performance anthraquinone-derived cathode material for lithium-ion batteries through rational molecular design

Organic electrode materials are considered to be one of promising alternatives for next-generation lithium-ion batteries, yet they often suffer from problem of severe dissolution in electrolytes, which inhibits their practicability. Herein, a rational molecular design strategy through constructing redox-active molecules with nonfused ring but planar structure was proposed. To validate our ideas, 1,4-bis(9,10-anthraquinonyl)pyrazine (BAQP) was synthesized by connecting two AQ units to 2,5-positions of pyrazine via C-C bond. Density functional theory calculation reveals that BAQP is a planar structure because of reduction of hydrogen atoms adjacent to bonding sites. Comparative experiments show that solubility of BAQP is significantly reduced. Electrochemical tests demonstrate BAQP electrode for lithium-ion batteries displays prominently enhanced cycle performance (90.7% retention after 100 cycles at 0.2 C) and rate capability (capacity at 5 C is 79.8% of capacity at 0.2 C), which is much better than that of its control molecule, 1,4-bis(9,10-anthraquinonyl)benzene (BAQB, corresponding retentions are 40.2% and 53.5%, respectively). Importantly, the BAQP electrode also shows an excellent long cycle life of 1000 cycle with high retention of 70.0%, which is among the best long-term cycle performance in the literature about AQ-derived small molecule electrode materials. These results manifest that the molecular design concept of fabricating non-fused ring but planar structure is effective to develop highperformance organic electrode materials.