Phenothiazine Derivatives as Small-Molecule Organic Cathodes with Adjustable Dropout Voltage and Cycle Performance

Compared with conventional inorganic materials, organic electrodes are competitive candidates for secondary battery cathodes due to their resourcefulness, environmental friendliness, and cost-effectiveness. Much effort is devoted at the level of chemical structure, while ignoring the impact of molecular aggregation on battery behavior. Herein, this work designs a series of organic molecules with two electrochemically active phenothiazine groups linked by different lengths of alkyl chain to regulate molecular symmetry and crystallinity. The results emphasize the equally important role of molecular aggregation and chemical structure for battery performance. Among them, 2PTZ-C7H14|Li cell exhibits the most impressive cycle and rate performance. At the high rate of 50 C, it can still deliver a capacity of 63.4 mA h g-1 and 74.5% capacity retention after 10 000 cycles. Besides, the dropout voltage of 2PTZ-C9H18|Li cell is only 52 mV, which is among the lowest reported for lithium-organic batteries to the best of the author's knowledge. This work connects microstructure and macroscopic properties via molecular aggregation, and for the first time summarizes the relationship among molecular structure, molecular aggregation, and electrochemical properties. With the extension of alkyl chain, the dropout voltage exhibits "odd-even effect", and the cycle stability presents "alkyl chain length effect", providing valuable guidance for the further development of this field. image