A comparative study on the structural, chemical, morphological and electrochemical properties of α-MnO2, β-MnO2 and δ-MnO2 as cathode materials in aqueous zinc-ion batteries

Aqueous zinc-ion batteries (AZIBs) are considered to be highly promising electrochemical energy storage device due to their affordability, inherent safety, large zinc resources, and optimal specific capacity. Among various cathode materials, manganese dioxide (MnO2) stands out for its high voltage, environmental benignity, and theoretical specific capacity. This study systematically investigates the phase formation and structural parameters of alpha-MnO2, beta-MnO2, and delta-MnO2 synthesized via hydrothermal method, employing Rietveld refinement. FTIR and Raman spectroscopy confirms Mn-O and O-H bond formation. BET analysis reveals surface areas, and pore size distribution is calculated with BJH method. High-resolution XPS spectra exhibit a spin energy split of similar to 11.9 eV for Mn 2p confirming the presence of MnO2. Electrochemical studies shows an initial discharge capacities of 230.5, 188.74 and 263.30 mAh g(- 1) at 0.1 A g(- 1) for alpha-MnO2, beta-MnO2 and delta-MnO2. The EIS spectra revealed the capacitive behaviour and electrode reaction kinetics where a R-cT value of 484.14, 327.6, 162.5 ohm for alpha-MnO2, beta-MnO2 and delta-MnO2. These study give insights into relation of various properties of MnO2 with electrochemical performance and its viability in grid storage applications. [GRAPHICS]