Foldable Solid‐State Batteries Enabled by Electrolyte Mediation in Covalent Organic Frameworks

Solid-state electrolytes with high Li+ conductivity, flexibility, durability, and stability offer an attractive solution to enhance safety and energy density. However, meeting these stringent requirements poses challenges to the existing solid polymeric or ceramic electrolytes. Here, an electrolyte-mediated single-Li+ -conductive covalent organic framework (COF) is presented, which represents a new category of quality solid-state Li+ conductors. In situ solidification of a tailored liquid electrolyte boosts the charge-carrier concentration in the COF channels, decouples Li+ cations from both COF walls and molecular chains, and eliminates defects by crystal soldering. Such an altered microenvironment activates the motion of Li+ ions in a directional manner, which leads to an increase in Li+ conductivity by 100 times with a transference number of 0.85 achieved at room temperature. Moreover, the electrolyte conversion cements the ultrathin COF membrane with fortified mechanical toughness. With the COF membrane, foldable solid-state pouch cells are demonstrated.