Sodium-ion batteries (SIBs) can develop cost-effective and safe energy storage technology for substantial energy storage demands. In this work, we have developed manganese oxide (α-MnO₂) nanorods for SIB applications. The crystal structure, which is crucial for high-performance energy storage, is examined systematically for the metal oxide cathode. The intercalation of sodium into the α-MnO₂ matrix was studied using the theoretical density functional theory (DFT) studies. The DFT studies predict Na ions’ facile diffusion kinetics through the MnO₂ lattice with an attractively low diffusion barrier (0.21 eV). When employed as a cathode material for SIBs, MnO₂ showed a moderate capacity (109 mAh·g^–1 at C/20 current rate) and superior life cyclability (58.6% after 800 cycles) in NaPF₆/EC+DMC (5% FEC) electrolyte. It shows a much higher capacity of 181 mAh·g^–1 (C/20 current rate) in NaClO₄/PC (5% FEC) electrolyte, though it suffers fast capacity fading (11.5% after 800 cycles). Our findings show that high crystallinity and hierarchical nanorod morphology of the MnO₂ are responsible for better cycling performance in conjunction with fast and sustained charge-discharge behaviors.