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

Materials for Renewable and Sustainable Energy https://doi.org/10.1007/s40243-024-00281-8 (2025) 14:10 ORIGINAL PAPER 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 Basil Chacko1 · Madhuri Wuppulluri2 Received: 24 August 2024 / Accepted: 19 November 2024 © The Author(s) 2024 Abstract 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 α-MnO2, β-MnO2, and δ-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 ~ 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 α-MnO2, β-MnO2 and δ-MnO2. The EIS spectra revealed the capacitive behaviour and electrode reaction kinetics where a RcT value of 484.14, 327.6, 162.5 Ω for α-MnO2, β-MnO2 and δ-MnO2. These study give insights into relation of various properties of MnO2 with electrochemical performance and its viability in grid storage applications. Madhuri Wuppulluri 1 Department of Physics, School of Advanced Sciences, Vellore Institute of Technology, Vellore, Tamil Nadu 632014, India 2 Ceramic Composites Laboratory, Centre for Functional Materials, Vellore Institute of Technology, Vellore, Tamil Nadu 632014, India 13 10 Page 2 of 11 Materials for Renewable and Sustainable Energy (2025) 14:10 Graphical Abstract Keywords Aqueous zinc ion battery · MnO2 · Cyclic voltammetry · GCD · EIS Introduction In the recent years, world has seen a tremendous increase in the usage of energy. According to the reports by international energy agency, the electricity consumption has reached 3.427 MWh / Capita in 2022 which is about 49% increase from 2000 1. Among the total energy sources around 60% of share is from Coal and Oil which are non-renewable energy sources and facing extinction in next few years. Adding to it serious global warming due to the increased CO2 emissions has to be given attention [1]. Power generation is the largest contributor for CO2 which is about 44% of the overall CO2 emissions. Owing to this among the 17 sustainable development goals by United Nations for 2030, Affordable and clean energy, climate action has been given atmost importance. The major focus is to reduce the usage of non-renewable energy sources for energy production and migration to renewable energy sources such as wind, solar 13 etc. These summed up towards the need of sustainable and renewable energy sources with efficient and cost-effective energy storage devices. The primary criteria for designing optimal large-scale energy storage systems include low cost, high reliability, safety, environmental sustainability, high energy efficiency, extended cycle life, and elevated gravimetric energy and power densities [2]. Currently lithiumion batteries are leading the energy storage devices in the market due to their high energy density [3, 4]. But the usage of LIBs in grid energy storage is restricted due to the limited availability of lithium and safety issues due to organic electrolyte, high cost and non eco friendliness is questioning its reliability [5–8]. To address these issues Sodium-ion batteries (SIBs) and potassium-ion batteries (KIBs) due to their reliance on relatively abundant and inexpensive sodium and potassium elements, which exhibit similar chemical properties to lithium [9]. However, they are hindered by low energy Materials for Renewable and Sustainable Energy (2025) 14:10 density, the use of highly toxic and flammable electrolytes, elevated operational costs, and security concerns [9]. The aqueous zinc ion batteries is considered to be a viable alternative for addressing these issues due to the benefits of abundant and inexpensive resources, superior theoretical gravimetric capacity (820 mAh g− 1), volumetric capacity (5851 mAh cm− 3), low redox potential (− 0.76 V vs. standard hydrogen electrode, SHE) [10–13]. Further, The replacement of organic electrolyte with aqueous electrolyte is considered to be an effective way to overcome the safety concerns of LIBs [14–16]. Further the feasibility of manufacturing in normal conditions allow to lower the cost [17]. Moreover, aqueous electrolytes have two orders of magnitude better ionic conductivity than organic electrolytes, which permits higher charging/discharging rates and reduced ohmic polarization [18]. Zinc is substantially more stable in aqueous electrolyte than Li, Na, K, and Al and can be employed directly as the anode in ZIBs due to its relatively higher electrode potential than those of other metals [19]. In ZIBs, cathode materials are linked to the operation voltage, cycle stability, and rate performance of ZIBs. Finding appropriate cathode materials is therefore the main goal in enhancing ZIB performance, including operating voltage, reversible capacity, and lifespan. Reversible Zn-ion storage has been recognized in several host materials, including manganese-based oxides, vanadium-based compounds, and Prussian blue analogues, Organic compounds and polyanionic compounds [20–24]. Vanadium based materials reported high specific capacity but its toxicity and expensive nature limits its application. Prussian Blue analogues has reported higher operating voltage but a comparatively lower discharge capacity and expensive. Manganese-based electrode materials, characterized by low cost, abundant in nature, and significant structural stability, have excellent specific capacity and operating voltage, making them highly attractive for AZIBs [25]. Manganese dioxide (MnO2) is regarded as a potential material for cathode as it is inexpensive, environmentally friendly, and electrochemically active. Manganese atoms can exhibit oxidation states from 0 to + 7. In solid (oxy)(hydr) oxide phases, Mn cations are often present in the + 2, +3, or + 4 oxidation states, coordinated octahedrally by oxygen [26]. The prevalent polymorphs of Mn comprise the α (2 × 2 tunnels), γ (1 × 1 tunnels), R (2 × 1 tunnels), δ (layered), and λ (spinel) configurations [26]. Diverse synthesis routes can yield distinct crystallographic polymorphs of MnO2, specifically α, β, γ, δ, and λ [27, 28]. These MnO2 polymorphs include a one-dimensional tunnel that resembles a chain and a layered structure [29]. Of all the MnO2 polymorphs, α-MnO2 has the (...truncated)