Structural, electronic structure, and electrochemical correlations in Mn2O3 and LiMn2O4 for an advanced symmetric supercapacitor device

Abstract

Manganese oxide (Mn2O3) and lithium manganese oxide (LiMn2O4) compounds were prepared using a chemical-precipitation method, and their structural, morphological, electronic, and electrochemical properties were investigated for supercapacitor applications. X-ray diffraction (XRD) patterns, combined with Rietveld refinement, confirmed the formation of pure Mn2O3 and LiMn2O4 compounds with crystallite sizes of 44.6 nm and 68.6 nm, respectively. Fourier transform infrared (FTIR) spectroscopy revealed characteristic Mn–O vibrational bands in both samples. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) investigations demonstrated the polyhedral morphology of LiMn2O4. The LiMn2O4 samples showed a larger specific surface area and a wider pore size distribution (25–100 Å) compared to Mn2O3. X-ray absorption near-edge structure (XANES) spectroscopy, at Mn K-edge, confirmed the presence of Mn3+ ions in Mn2O3 and, mixed, Mn3+/Mn4+ ions in LiMn2O4. Electrochemical characterization revealed pronounced pseudocapacitive behaviour, as evidenced by redox-rich cyclic voltammograms (CV) and non-linear galvanostatic charge–discharge (GCD) curves. High specific capacitances of approximately 853 F g−1 (for Mn2O3) and 936 F g−1 (for LiMn2O4) were obtained at a 5 mV s⁻¹ scan rate, with ≥ 95% retention of the initial capacitance after 5000 cycles, demonstrating their promise for pseudocapacitor energy storage applications. The symmetric supercapacitor device was tested for the LiMn2O4 sample. The symmetric supercapacitor offered an exceptional energy density of 204 Wh kg−1 (at a 3919 W kg−1 power density) and a maximum power density of 19,500 W kg−1 (at a 90 Wh kg−1 energy density).