Pyridine-based benzoquinone derivatives as organic cathode materials for sodium ion batteries

Herein, we describe the design of two molecules connecting two benzoquinone (BQ) groups by the electron-withdrawing pyridines: 2,6-bis(p-benzoquinonyl) pyridine (QPQ-1) and 2,5-bis(p-benzoquinonyl) pyridine (QPQ-2). Structurally, the conjugation of the whole molecule gets expanded in the two compounds, and QPQ-2 is hardly dissolved in the electrolyte, which gives the electrode good stability. Moreover, the introduced pyridine also enhances the operating voltage (2.71 V/2.26 V). The QPQ-2 shows a high reversible capacity of 214 mA h g(-1), and could maintain 93% of its initial value even after 100 cycles at a rate of 0.1 C, and exhibits a capacity of 160.3 mA h g(-1) in the first cycle, with a good capacity retention of 82.7% over 1000 cycles at a rate of 1 C. The QPQ-1 shows a relatively lower performance due to serious polarisation and its slight solubility in the electrolyte. This work demonstrates that the rational molecular design of organic electrode materials is important for achieving high performance rechargeable batteries.