Stable calcium metal batteries enabled by ionic covalent organic framework artificial protection layers

Abstract Calcium metal batteries (CMBs), utilizing calcium (Ca) as anodes, offer great potential for next‐generation high‐energy density battery technologies. However, Ca plating/stripping at room temperature (r.t.) is severely impeded by the formation of ion‐insulating passivation layers. Constructing artificial protective layers that can effectively transport Ca 2+ on Ca metal is crucial for realizing practical CMBs. Nonetheless, identifying a suitable candidate that is both highly ionic conductive (>10 −4 S cm −1 at r.t.) and electrically insulating remains a formidable challenge. Ionic covalent organic frameworks (iCOFs) represent a distinctive class of porous, crystalline polymers containing ionic moieties to facilitate ion conduction in batteries. In this study, we introduce, for the first time, single‐ion conductive sulfonate iCOFs with a Ca 2+ transference number of 0.95 and ionic conductivity of 2.23 × 10 −4 S cm −1 at r.t. as artificial protective layers for the Ca metal anode. This iCOF protective layer promotes uniform Ca deposition and effective anticorrosion of modified anodes. As a result, full cells equipped with iCOF‐protective Ca anodes and polyaniline cathodes demonstrated stable operation up to 75 cycles with high energy density. Our work facilitates the attainment of high‐performance CMBs by the construction of iCOF protective layers. image