Organic Cationic Pillars Boosting Calcium Storage Kinetics and Structural Stability in Layered MnO ₂ for Aqueous Calcium‐Ion Pouch Cell

ABSTRACT Aqueous calcium‐ion batteries (ACIBs) emerge as promising post‐lithium energy storage systems due to their low cost and high safety. However, the strong electrostatic interactions and large ionic radius of Ca ²⁺ cause most cathode materials to exhibit inferior rate performance and cycling stability. Herein, a strategy involving the pre‐intercalation of tetramethylammonium cations (TMA ⁺ ) into MnO ₂ interlayers is employed to simultaneously enhance its structural integrity and Ca ²⁺ diffusion kinetics. This strategy expands the interlayer spacing from 0.71 to 0.98 nm to physically mitigate steric constraints. The inserted TMA ⁺ functions as structural pillars, effectively stabilizing the layered framework of MnO ₂ . Consequently, the TMA ⁺ ‐intercalated MnO ₂ (TMAMnO ₂ ) demonstrates exceptional durability (98.9% retention after 1000 cycles) and high‐rate capability (72.8 mAh g ⁻¹ at 4.0 A g ⁻¹ ). The single‐phase solid‐solution Ca ²⁺ storage mechanism and the origin of enhanced diffusion kinetics in TMAMnO ₂ are elucidated through in situ/ex situ characterizations and theoretical calculations. The assembled aqueous calcium‐ion full cell exhibits a long‐life of 1000 cycles and wide‐temperature operation capability (‐20 °C to 25 °C). The stable operation of the fabricated pouch cells for over 100 cycles underscores the practical potential of TMAMnO ₂ . This study offers key insights into the rational design of high‐stability and high‐rate cathode materials for next‐generation multivalent‐ion batteries.