NiCo₂O₄@TiN Core-shell Electrodes through Conformal Atomic Layer Deposition for All-solid-state Supercapacitors

Ternary transition metal oxides such as NiCo₂O₄ show great potential as supercapacitor electrode materials. However, the unsatisfactory rate performance of NiCo₂O₄ may prove to be a major hurdle to its commercial usage. Herein, we report the development of NiCo₂O₄@TiN core-shell nanostructures for all-solid-state supercapacitors with significantly enhanced rate capability. We demonstrate that a thin layer of TiN conformally grown by atomic layer deposition (ALD) on NiCo₂O₄ nanofiber arrays plays a key role in improving their electrical conductivity, mechanical stability, and rate performance. Fabricated using the hybrid NiCo₂O₄@TiN electrodes, the symmetric all-solid-state supercapacitor exhibited an impressive stack power density of 58.205 mW cm^-3 at a stack energy density of 0.061 mWh cm^-3. To the best of our knowledge, these values are the highest of any NiCo₂O₄-based all-solid-state supercapacitor reported. Additionally, the resulting NiCo₂O₄@TiN all-solid-state device displayed outstanding cycling stability by retaining 70% of its original capacitance after 20,000 cycles at a high current density of 10 mA cm^-2. These results illustrate the promise of ALD-assisted hybrid NiCo₂O₄@TiN electrodes within sustainable and integrated energy storage applications.