Electrolyte Covalent Organic Frameworks for Exceptional Potassium Ion Conduction

In this research we report the concept and strategy of electrolyte covalent organic frameworks for high-rate low-activation-energy potassium ion conduction. One-pot polymerization of monomers with oligo(ethylene oxide) chains of different lengths creates crystalline porous electrolyte frameworks with discrete electrolyte interfaces in pores. Integration of potassium salts to the pores develops potassium ion-electrolyte networks, offering pathways for potassium ion transport. Notably, the frameworks with well-developed electrolyte interfaces improve ion conductivity, which is not a simple numeric summation of electrolyte chains but shows an exponential correlation. The materials operate over temperatures from 40°C to 190°C under anhydrous conditions and achieve an ion conductivity as high as 3.2 × 10-3 S cm-1 with a low activation energy of 0.2 eV. Notably, under humid conditions, the conductivity further increases to 2.1 × 10-1 S cm-1 with an activation energy of only 0.04 eV, suggesting a frictionless ion conduction. Remarkably, potassium ion batteries show a stable and wide voltage window of -6 - 6 V, with a high potassium ion transference number of 0.76. Our results pave a way to exceptional potassium ion conduction through molecular design of electrolyte frameworks and show their promise for various types of energy storages under solid-state and aqueous conditions.