Exploration of structural and electrochemical characterization of niobium substituted alpha Na1.1MnO2 as sodium-ion battery cathodes

Sodium-ion batteries (SIBs) are growing as attractive alternatives to lithium-ion batteries due to the wide availability and affordability of sodium. In this study, it was investigated the structural and electrochemical characteristics of niobium-doped α-Na1.1MnO2 as a cathode material for SIBs. A series of Na1.1Mn1−xNbxO2 compositions (x = 0.03 to 0.50) were synthesized through a solid-state reaction method accompanied by rapid cooling. The structural characterization such as X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS), proved the effective doping of Nb into the crystal lattice, resulting in phase transformation and lattice expansion. The morphological and surface data disclosed that Nb doping altered morphology, increased grain size, and minimized porosity. The electrochemical tests, including redox behavior, impedance, and galvanostatic charge-discharge cycling, showcased enhanced electrochemical performance for Nb concentrations (x = 0.03 to 0.10). The findings revealed that enhanced Na-ion diffusion, reduced charge transfer resistance, and good cycling stability were demonstrated by x = 0.30, achieving capacity retention of ~ 85% over 100 cycles. On the other hand, increasing Nb doping (x ≥ 0.40) led to increased polarization and capacity fading, which were attributed to structural distortions. These outcomes concluded that boosting the stability and performance of α-Na1.1MnO2 through controlled Nb incorporation makes it a promising cathode candidate for next-generation SIBs.