High‐Performance Quasi‐Solid‐State Calcium‐Ion Batteries from Redox‐Active Covalent Organic Framework Electrolytes

Quasi‐solid‐state calcium‐ion batteries (QSSCIBs) employing redox‐active covalent organic frameworks (COFs) based electrolytes are developed. The COFs’ crystalline porous structures, featuring aligned carbonyl groups, enabled high Ca2⁺ conductivity, supported by molecular dynamics simulations of the ion transport mechanism. The fabricated QSSCIBs demonstrate competitive capacity and stability over reported gel/polymer‐based counterparts, as validated by post‐cycling analysis. Abstract Calcium ion batteries (CIBs) are promising for energy storage with volumetric capacity and reduction potential comparable to lithium, while richer in earth abundance. However, sluggish cation transport and unstable cycling performance primarily due to anode surface passivation remain vital challenges for realizing high‐performance CIBs. Herein, two kinds of redox covalent organic frameworks (PT‐COFs and PQ‐COFs) with different‐density carbonyl groups are prepared as quasi‐solid‐state electrolytes (QSSEs) to address those challenges. In particular, PT‐COFs exhibit ionic conductivity of 0.46 and 5.05 mS cm−1 at room temperature and 80 °C, respectively, and Ca2+ transference number of 0.532. Due to the efficient ionic conduction and intrinsic stability of PT‐COFs structure, the prepared full calcium ion cell with PT‐COFs demonstrates the highest reversible specific capacity of 155.9 mAh g−1 at 0.15 A g−1 (1 C), and stable cycle performance (capacity retention over 74.6% at 1 A g−1 after 1000 cycles). This work shows the effectiveness of the redox COFs and their promising potential as SSE for the development of high‐performance CIBs. Quasi-solid-state calcium-ion batteries (QSSCIBs) employing redox-active covalent organic frameworks (COFs) based electrolytes are developed. The COFs’ crystalline porous structures, featuring aligned carbonyl groups, enabled high Ca 2 ⁺ conductivity, supported by molecular dynamics simulations of the ion transport mechanism. The fabricated QSSCIBs demonstrate competitive capacity and stability over reported gel/polymer-based counterparts, as validated by post-cycling analysis. Abstract Calcium ion batteries (CIBs) are promising for energy storage with volumetric capacity and reduction potential comparable to lithium, while richer in earth abundance. However, sluggish cation transport and unstable cycling performance primarily due to anode surface passivation remain vital challenges for realizing high-performance CIBs. Herein, two kinds of redox covalent organic frameworks (PT-COFs and PQ-COFs) with different-density carbonyl groups are prepared as quasi-solid-state electrolytes (QSSEs) to address those challenges. In particular, PT-COFs exhibit ionic conductivity of 0.46 and 5.05 mS cm −1 at room temperature and 80 °C, respectively, and Ca 2+ transference number of 0.532. Due to the efficient ionic conduction and intrinsic stability of PT-COFs structure, the prepared full calcium ion cell with PT-COFs demonstrates the highest reversible specific capacity of 155.9 mAh g −1 at 0.15 A g −1 (1 C), and stable cycle performance (capacity retention over 74.6% at 1 A g −1 after 1000 cycles). This work shows the effectiveness of the redox COFs and their promising potential as SSE for the development of high-performance CIBs. Advanced Science, EarlyView.