Covalent Organic Framework Electrolytes for Solid-State Lithium Batteries: Designing Ion Highways for Next-Generation...

Covalent organic frameworks (COFs) are emerging as a programmable platform for solid electrolytes in solid-state lithium batteries, since their crystalline, periodically ordered nanochannels can be engineered to enable directional ion transport. These low-resistance pathways promote directional lithium-ion (Li⁺) migration through a narrower, more spatially ordered distribution of coordination environments, achieved via site-to-site hopping and/or guest-assisted vehicular motion within the channels. This review presents a design-oriented framework linking COF structural descriptors to ion-transport metrics through a cause-effect-performance relationship. We first summarize the Li⁺ transport mechanism in confined COF channels, covering site-to-site hopping along pore walls and guest-assisted vehicular motion in filled channels. We then correlate (i) topology and channel architecture, (ii) pore-wall chemical functionality and framework charge, (iii) crystallinity, stacking registry, and channel alignment, and (iv) hybrid COF architectures with performance indicators including ionic conductivity (σ), activation energy (Ea), lithium-ion transference number (tLi⁺), transport anisotropy, and effective conductivity in working membranes (σeff). Through representative case studies, we highlight cases where high intrinsic channel transport does and does not translate into device-relevant σeff. Finally, we propose standardized reporting practices and device-level benchmarks to accelerate the shift from empirical materials discovery toward predictive ion-highway engineering for next-generation solid-state lithium batteries.