Covalent Organic Frameworks for High-Performance Lithium Metal Batteries

Polymers are ubiquitous in our daily life—plastic bags, clothes, house furniture, electronic devices, vehicles, etc. The number of applications is countless. One of the recently developed polymers with high porosity and crystallinity, called porous crystalline polymers, includes covalent organic frameworks (COFs). The unique features of those porous polymers, permanent porosity, and crystallinity make them essential in energy engineering applications. COFs with ionic functional groups can transport ions (e.g., Li⁺, Na⁺, or Zn²⁺) rapidly and reliably. Those ionic COFs (iCOFs) are incorporated in energy devices for enhanced transport and safety, outperforming known electrolytes and enabling the next-generation batteries. A primary focus is to make solid-state and single-ion-conducting iCOFs for all-solid-sate Lithium metal batteries. For this goal, we developed new iCOFs, such as the ones bearing hypervalent nodes, redox-active moieties, or three-dimensional network topologies. We proved that the iCOFs-based batteries have significantly improved safety while keeping the same high performance as those with liquid electrolytes. The iCOFs we have developed showed the highest Li⁺ conductivity of 9.8 mS cm^–1 at r.t. and a transference number of 0.92. The solid-state batteries with iCOFs installed cells showed 188 mAh g^–1 at 0.25 C. These findings demonstrate the promise of using redox-active anionic COFs for electrochemical energy storage devices. Adopting such all-solid-state rechargeable batteries will render electric vehicles more robust, safe, and affordable, ultimately leading to improved environmental conditions (<i>Advanced Materials</i> <b>2021</b>; <i>J. Am. Chem. Soc.</i> <b>2023</b>; <i>Advanced Energy Materials</i> <b>2024</b>). Overall, porosity, periodicity, tailorability, and modularity advantages make them the next-generation materials for sustainable energy engineering.