Potential‐Window Engineering Tames Jahn–Teller Distortion in MnO 2 for Ultra‐Stable Aqueous Energy Storage

Abstract The deployment of manganese dioxide (MnO 2 ) in high‐performance aqueous energy storage is frequently hampered by Jahn–Teller (J–T) distortion linked to unstable high‐spin Mn 3+ ions, causing structural degradation and performance decay that conventional static modifications struggle to fully resolve. To overcome these limitations, a potential‐window‐driven in‐situ activation strategy is presented, employing cyclic voltammetry on Mn 3 O 4 precursors, to achieve control over both MnO 2 crystal structure and Mn 3 ⁺ spin states. Optimal in‐situ transformation potential‐window yields MnO 2 within 0–1.0 V (vs SCE) (ATMO‐1.0), featuring significantly suppressed high‐spin Mn 3 ⁺ populations and stabilized low‐spin configurations (), thereby effectively mitigating J–T distortion. Consequently, the optimized ATMO‐1.0 electrode delivers an exceptional areal capacitance of 1876.6 mF cm −2 (at 1 mA cm −2 ) and demonstrates robust stability with 91.9% capacitance retention over 10 000 cycles. When integrated into an asymmetric supercapacitor (ATMO‐1.0//ACCC), it achieves a high energy density of 410.1 mWh cm −2 (at 168.2 mW cm −2 ) and exhibits 86.4% capacity retention over 120 000 cycles. in‐situ and ex‐situ analyses confirm that this potential window engineering strategy enhances [MnO 6 ] octahedral stability and promotes reversible ion intercalation kinetics. This synergistic control over structural integrity and spin‐state offers a powerful new paradigm for designing robust, high‐mass‐loading MnO 2 electrodes, significantly advancing their practical prospects in sustainable energy storage technologies.