The key role of molecular aggregation in rechargeable organic cathodes

Summary

Rechargeable organic cathodes have reignited widespread research interest in lithium batteries. Most research attention is currently paid to their molecular chemistry to increase the specific capacity or operating voltage. Nevertheless, the redox reaction of organic cathodes inevitably leads to changed molecular aggregation, which is mostly ignored. Herein, we clarify how the molecular aggregation of organic cathodes fundamentally determines their electrochemical properties. Results show that the flexible and centrosymmetric molecular conformation of phenothiazines effectively regulates the molecular aggregation states and reduces the adverse effects of molecular deformation during charge/discharge cycles, contributing to an excellent capacity retention of 85% after 500 cycles at 5C and rate capability of 78 mAh g⁻¹ at 10C. In contrast, for phenothiazines with slight differences in molecular chemistry but large differences in molecular aggregation, the characterized collapse of the crystal leads to a rapid capacity decay at prolonged cycling and rate tests.