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 Ca²⁺ 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 Ca²⁺ 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.

Keywords

artificial protective layer / Ca metal batteries / ionic covalent organic frameworks

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