Confined Cascade Reconstruction of Mn 3 O 4 Microstructures for High‐Rate and Ultralong‐Life Energy Storage

ABSTRACT MnO 2 has garnered attention for pseudocapacitive energy storage owing to its high theoretical capacitance and tunable microstructures; however, its application remains severely constrained by the inherent trade‐off between activity and stability. Here, taking Mn 3 O 4 as a starting model, we propose a confined cascade reconstruction strategy that synergistically combines thermochemical and electrochemical reconstruction to break this limitation. Specifically, a polyurethane‐mediated interfacial thermochemical reconstruction tailors a defect‐rich carbon layer and introduces abundant oxygen vacancies into Mn 3 O 4 , which subsequently enables rapid and spatially confined electrochemical reconstruction into the active MnO 2 phase. Theoretical calculations indicate that the N/O co‐doped carbon and oxygen vacancy interface substantially lowers the kinetic barrier for *OH dissociation, thereby accelerating the reconstruction kinetics. Concurrently, interfacial electronic coupling increases the Mn extraction energy of MnO 2 , effectively stabilizing the reconstructed structure and overcoming the intrinsic activity‐stability trade‐off. Accordingly, the electrode achieves a volumetric capacitance of 100 F cm −3 and a gravimetric capacitance of 180 F g −1 at an ultrahigh current density of 150 A g −1 , while retaining 83.6% of its initial capacitance after 50 000 cycles. Moreover, at a commercial‐level mass loading of 7.6 mg cm −2 , high volumetric and areal capacitances of up to 168 F cm −3 and 1557 mF cm −2 are achieved.