A Dithiin‐Linked Covalent Organic Polymer for Ultrahigh Capacity Half‐Cell and Symmetric Full‐Cell Sodium‐Ion Batteries

Abstract Sodium ion‐batteries (SIBs) are considered as a class of promising alternatives to lithium‐ion batteries (LIBs) to overcome their drawbacks of limited sources and safety problems. However, the lack of high‐performance electrode materials hinders the wide‐range commercialization of SIBs. Comparing to inorganic counterparts, organic electrode materials, which are benefitted from flexibly designable structures, low cost, environmental friendliness, and high theoretical gravimetric capacities, should be a prior choice. Here, a covalent organic polymer (COP) based material (denoted as CityU‐9) is designed and synthesized by integrating multiple redox motifs (benzoquinone and thioether), improved conductivity (sulfur induction), and intrinsic insolubility (rigid skeleton). The half‐cell SIBs exhibit ultrahigh specific capacity of 1009 mAh g−1 and nearly no capacity drop after 650 cycles. The first all‐COP symmetric full‐cell shows high specific capacity of 90 mAh g−1 and excellent rate capability. This work can extend the selection of redox‐active moieties and provide a rational design strategy of high‐performance novel organic electrode materials.