Confined Cascade Reconstruction of Mn₃O₄ Microstructures for High-Rate and Ultralong-Life Energy Storage

MnO₂ 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 Mn₃O₄ 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 Mn₃O₄, which subsequently enables rapid and spatially confined electrochemical reconstruction into the active MnO₂ 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 MnO₂, 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.