Tetrathiafulvalene Carboxylate-Based Anode Material for High-Performance Sodium-Ion Batteries.

Organic electrode materials are promising to be applied in sodium ion batteries (SIBs) due to their low cost and easily modified molecular structures. Nevertheless, low conductivity and high solubility in electrolytes still limit the development of organic electrodes. In this work, a carboxylate small molecule (BDTTS) based on tetrathiafulvalene is developed as anode material for SIBs. BDTTS has a large rigid π-conjugated planar structure, which may reduce solubility in the electrolyte, meanwhile facilitating charge transporting. Experimental results and theoretical calculations both support that apart from the four carbonyl groups, the sulfur atoms on tetrathiafulvalene also provide additional active sites during the discharge/charge process. Therefore, the additional active sites can well compensate for the capacity loss caused by the large molecular weight. The as-synthesized BDTTS electrode renders an excellent capacity of 230 mAh g-1 at a current density of 50 mA g-1 and an excellent long-life performance of 128 mAh g-1 at 2 C after 500 cycles. This work enriches the study on organic electrodes for high-performance SIBs and paves the way for further development and utilization of organic electrodes.