Hydroxide/Selenide Heterostructures With Built‐In Electric Fields Enabling Reconstruction for Advanced Quasi‐Solid‐State Supercapacitors

ABSTRACT The construction of heterostructures is regarded as an effective strategy to enhance the reaction kinetics of battery‐type electrodes for hybrid supercapacitors (HSCs). However, the pre‐designed heterointerfaces often undergo inevitable phase transformations and eventually disappear during electrochemical operation, obscuring the true operating mechanism of the original interfaces. Herein, NiCoSe@Ni(OH) 2 heterostructures are constructed via an in situ embedded strategy to manipulate the electrochemical reconstruction behavior. These tailored interfaces induce charge redistribution and establish a built‐in electric field (BIEF), significantly enhancing OH − adsorption kinetics and interfacial electron transfer, thereby facilitating more complete electrochemical activation. Notably, the initial heterointerfaces ultimately transform into a uniform amorphous phase during activation. In situ Raman and theoretical calculations confirm an accelerated phase transition to defect‐rich active oxyhydroxides during potentiostatic activation. The activated a‐NiCoSe@Ni(OH) 2 cathode delivers an exceptional specific capacity of 4.7 C cm −2 at 1 mA cm −2 , superior rate capability, and enhanced cycling stability, far exceeding that of the pristine a‐NiCoSe. Furthermore, the assembled quasi‐solid‐state HSC demonstrates remarkable rate performance, extended cycling life, and high mechanical robustness under bending and pressure conditions. This work elucidates the critical role of heterointerface engineering in facilitating electrochemical reconstruction and provides a strategic pathway for designing advanced energy storage materials.