Potential-Window Engineering Tames Jahn-Teller Distortion in MnO₂ for Ultra-Stable Aqueous Energy Storage

The deployment of manganese dioxide (MnO₂) in high-performance aqueous energy storage is frequently hampered by Jahn-Teller (J-T) distortion linked to unstable high-spin Mn³⁺ 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 Mn₃O₄ precursors, to achieve control over both MnO₂ crystal structure and Mn³⁺ spin states. Optimal in-situ transformation potential-window yields MnO₂ within 0-1.0 V (vs SCE) (ATMO-1.0), featuring significantly suppressed high-spin Mn³⁺ populations and stabilized low-spin configurations ( $t_{2g}^4{e}_g^0$ ), 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 [MnO₆] 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 MnO₂ electrodes, significantly advancing their practical prospects in sustainable energy storage technologies.