Unveiling Ion‐Pairing and Anion Dual Charge Carrier in Ca‐Organic Batteries

Abstract Calcium‐organic batteries offer sustainable energy storage with high voltage, yet their reaction mechanisms remain unclear. Here, a hidden dual‐ion charge storage mechanism is unveiled in poly(anthraquinone imide) (PAQI) using Ca(TFSI)₂/ether‐based electrolytes, challenging the conventional Ca²⁺‐only storage model. It is demonstrated that Ca²⁺‐TFSI⁻ ion pairs co‐bind to carbonyl groups during the first electron transfer, followed by TFSI⁻ dissociation to activate adjacent carbonyl sites in the second step—a process reversible upon charging. This mechanism critically depends on electrolyte solvation structures: G4 (tetraglyme) uniquely stabilizes monodentate CaTFSI⁺ contact ion pairs (versus multidentate aggregates in [G1 (monoglyme)/G2 (diglyme)] due to its optimal Ca²⁺ solvation energy, enabling exceptional performance. The PAQI/G4 system achieves a discharge capacity of 114 mAh g⁻¹ at 20 mA g⁻¹ and ultralong cycling (10 000 cycles with 94.5% capacity retention at 1000 mA g⁻¹), surpassing prior calcium‐organic batteries at room temperature. This work redefines cation‐anion interplay in organic electrodes and establishes electrolyte solvation engineering as a pivotal strategy for high‐performance, durable calcium battery systems.