Enhanced electrochemical performance through the structural core–shell morphological tuning of δ-MnO₂@C@NiSe₂ and realization of asymmetry energy storage devices

This study investigates the synthesis and electrochemical performance of a core–shell architecture comprising amorphous carbon-coated NiSe₂ as the core and birnessite δ-MnO₂ as the shell. Integrating δ-MnO₂, known for its high pseudocapacitance, with a conductive carbon interlayer for efficient electron transport and a stable NiSe₂ core, enables superior energy storage and charge transfer dynamics. Structural and morphological optimization of the hybrid electrode enhances ion diffusion and charge storage, resulting in outstanding energy and power densities. The optimized MnO₂@C@NiSe₂ electrode achieves a remarkable areal capacity of 2236.84 µAh cm⁻² and a specific capacity of 272.24mAh g⁻¹, while demonstrating excellent cyclic stability with 75.8 % capacity retention over 10,000 cycles. The fabricated hybrid asymmetric device exhibits a specific capacitance of 173.2F g⁻¹ at 5 mA cm⁻² and delivers an ultrahigh areal energy density of 213.6 µWh cm⁻² at an areal power density of 21,000 µW cm⁻². Cycling stability shows a 76 % capacitance retention after 20,000 cycles using an aqueous KOH electrolyte. Additionally, a pouch cell device demonstrates practical applicability by maintaining a stable 3 V output, effectively powering electronic displays and LED arrays. This work highlights the MnO₂@C@NiSe₂ core–shell hybrid as a promising candidate for high-performance energy storage and real-world device applications.