Enhancement of Diffusion-Controlled Pseudocapacity in Biphasic NaMnO ₂ Electrodes for Sodium Batteries by Tailoring...

In this study, we present a biphasic (orthorhombic/monoclinic) NaMnO₂ material synthesized by using cheap and low-temperature sol-gel methods, which presents potential applications as an advanced cathode material for aqueous sodium-ion energy storage. By leveraging its unique structural and morphological properties, our approach optimizes the balance between diffusion-controlled and surface-controlled pseudocapacitive charge storage, significantly enhancing electrochemical performance with capacity values over 100 mAh/g. Electrochemical investigations reveal that the tailored morphology of NaMnO₂ allows for a high pseudocapacitive contribution, with the Na₂SO₄ electrolyte exhibiting the most stable cycling behavior and the highest capacity retention. Ex-situ X-ray diffraction, Raman spectroscopy, transmission electron microscopy, and X-ray photoemission techniques confirm both intercalation and surface pseudocapacitive reactions, highlighting the interplay between intercalation and adsorption processes. The calculated value of diffusion-controlled pseudocapacity contribution of about 55% enables superior charge storage capabilities and rapid charge/discharge rates. These findings establish biphasic NaMnO₂ as a promising, structured, stable electrode material for next-generation, high-performance, and robust sodium energy storage systems.