(354a) Ionic Covalent Organic Frameworks for Solid-State Batteries

One of the recently developed polymers with high porosity and crystallinity, called porous crystalline polymers, includes covalent organic frameworks (COFs). COFs with ionic functional groups can transport ions (e.g., Li⁺, Na⁺, or Zn²⁺) rapidly and reliably. These ionic COFs (iCOFs) are incorporated in energy devices for enhanced transport and safety, outperforming known electrolytes and enabling the next-generation batteries. A key feature of the iCOFs is that they are solid-state single-ion conductors. Utilizing this, we developed new iCOFs, such as the ones bearing hypervalent nodes, redox-active moieties, or three-dimensional network topologies. We proved that the iCOF-based batteries have significantly improved safety while maintaining 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 (J. Am. Chem. Soc. 2023). We recently demonstrated that iCOF/polymer composite can be an excellent all-solid-state electrolyte for LMBs (Adv. Energy Mater. 2024). We demonstrated that composites comprising iCOFs and poly(ionic liquid) (PIL) all-solid-state electrolytes show an exceptional ionic conductivity up to 1.29 × 10⁻³ S cm⁻¹ and a high Li⁺ transference number of > 0.80 at room temperature, outperforming liquid electrolytes. Notably, the Li metal full cells with our iCOF-composite all-solid-state electrolytes and LiFePO₄ (LFP) cathode showed an initial discharge capacity of 141.5 mAh g⁻¹ at r.t. and 1 C, and sustained 87% of the capacity after 800 cycles, meeting the industry standards. Overall, iCOF’s advantageous properties make them the materials for next-generation batteries (Advanced Materials 2021; Advanced Materials 2024).