Electrolytic Manganese Dioxide Research Articles

Electrochemical characteristics of manganese oxide/carbon composite as a cathode material for Li/MnO 2 secondary batteries

Electrolytic manganese dioxide (EMD) recovered from a simulated leaching solution of spent alkaline batteries using a modified cyclone cell is tested as a cathode material for Li secondary batteries. An EMD/C(Super P) composite heat-treated at 400 °C after high-energy mechanical milling shows better electrochemical performance than that of pure EMD in terms of cycleability and capacity fading. The electrochemical characteristics of the EMD/C(Super P) composite are investigated by various analytical techniques. The irreversible capacity during the first cycle is mainly due to the formation of a Li 2MnO 3 phase. The carbon composite also retards the dissolution of Mn during cycling.

Fabrication and electrochemical characterization of a vertical array of MnO 2 nanowires grown on silicon substrates as a cathode material for lithium rechargeable batteries

A complementary metal-oxide-semiconductor (CMOS) compatible process for fabricating on-chip microbatteries based on nanostructures has been developed by growing manganese dioxide nanowires on silicon dioxide (SiO 2)/silicon (Si) substrate as a cathode material for lithium rechargeable batteries. High aspect-ratio anodized aluminum oxide (AAO) template integrated on SiO 2/Si substrates can be exploited for fabrication of a vertical array of nanowires having high surface area. The electrolytic manganese dioxide (EMD) nanowires are galvanostatically synthesized by direct current (dc) electrodeposition. The microstructure of these nanowire arrays is investigated by scanning electron microscopy and X-ray diffraction. Their electrochemical tests show that the discharge capacity of about 150 mAh g −1 is maintained during a few cycles at the high discharge/charge rate of 300 mA g −1.

Electrolytic Manganese Dioxide Nucleation and Growth on Titanium Substrates

Electrolytic manganese dioxide (EMD) nucleation and growth on titanium substrates from acidic manganese sulfate solutions was studied at 65oC and 90oC at different potentials and sulfuric acid concentrations. Electrochemical experiments allied to SEM examination were performed to characterize the mechanism of nucleation and its evolution with time. The EMD powder produced after a constant charge electrolysis of 448 mA·h was analyzed by SEM, BET, DTA/TG and X-ray diffraction. Results indicated that depending on the experimental conditions nucleation can be either progressive or instantaneous and when three-dimensional nuclei were formed the manganese dioxide deposit presented a higher specific surface area. Surface areas ranging from 51.8 to 168.8 m2/g were obtained under the conditions tested.

Synthesis and electrochemical properties of α-MnO 2 microspheres

We report the synthesis of α-MnO 2 microspheres by a low-temperature hydrothermal method involving no templates or catalysts. The products were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Energy-dispersive X-ray spectrum (EDX), transmission electron microscopy (TEM), Fourier transform infrared spectrum (FT-IR), and Brunauer–Emmett–Teller (BET). The results show that the as-synthesized products are mainly composed of large quantities of α-MnO 2 microspheres having a sea-urchin shape and a few microspheres constructed of small nanorods. Electrochemical characterization indicates that the resulting α-MnO 2 microspheres display promising discharge properties than the commercial electrolytic manganese dioxides (EMD) when used as cathodes in alkaline Zn-MnO 2 batteries.

Surface characterisation of chemically reduced electrolytic manganese dioxide

In this work a titration technique has been used to characterize the amphoteric surface properties of a series of chemically reduced electrolytic manganese dioxide (EMD) samples (MnO 1.97 to MnO 1.50). The surface of the EMD was found to consist of independent acidic and basic hydroxyl groups, which were able to be characterised by their respective equilibrium constants and site concentrations. For this chemically reduced series K b varied from ( 1.81 – 8.43 ) × 10 −10 as reduction proceeded, with the corresponding basic site concentration varying from ( 0.20 – 2.50 ) × 10 −4 mol / m 2 over the pH range considered. K a was ranged from ( 1.23 – 9.23 ) × 10 −6 over the reduction range considered. The increase in K b suggested a weakening of the Mn O bond via the introduction of the larger Mn 3+ ions which will increase the length of this bond. Weakening the Mn O bond results in a corresponding strengthening of the O H bond giving the surface hydroxyl group a basic nature which is supported by the increasing basic site concentration. For the samples with an x in MnO x value above 1.71 the total number of acidic sites decreased which supports the increase in the concentration of basic sites; however, below 1.71, the surface concentration of acidic sites increases slightly, which can be rationalised by the fact that the pyrolusite domains within the EMD (with relatively stronger Mn O bonds) are accessible at this stage of the reduction. The number of surface oxide sites ( N s ) and surface hydroxyl sites ( N s(OH)) were calculated crystallographically, and from the sum of the acid and basic hydroxyl groups determined by titration. Both methods produced data with the same order of magnitude, as well as indicated the expected increase in the number of surface hydroxyl groups with increasing degree of reduction. Electrochemical analysis of the samples in 9 M KOH showed the expected decrease in capacity with an increase in the degree of reduction. It also showed a decrease in the amount of charge contributed to the overall homogeneous reduction by Mn 4+ ions in surface defects and within the ramsdellite domains over the entire x in MnO x range. However, the amount of charge contributed from the pyrolusite domains remained unchanged until after a x in MnO x value of 1.71.

A study around the improvement of electrochemical activity of MnO 2 as cathodic material in alkaline batteries

An optimized combination of reduction by methane and sulfuric acid digestion was developed to improve the electrochemical activity of manganese dioxide at a battery set. Chemical manganese dioxide, CMD, and electrolytic manganese dioxide, EMD, which have been destroyed after discharge cycling process in potential window of 900–1650 mV versus Hg/HgO, were reduced in a furnace with a flow of methane at 300 and 250 °C correspondingly. Thereafter, the reduced samples, CMDr and EMDr, were digested in a solution of sulfuric acid with optimized concentration and temperature. It was found that digested samples, CMDro and EMDro, typically show more stability in cycling, higher capacity and more reversible redox reaction. Alternatively, we reported about the effect of digestion temperature on electrochemical and structural properties of the samples. Digestion at temperatures 60 and 98 °C in 1.5 M sulfuric acid as superior concentration was preferred after comparative experiments in the range 40–98 °C. The samples which were digested in 60 °C (CMDro1 and EMDro1) showed superior electrochemical activity at the early stages of discharge cycling. By contrast, the samples which were obtained at 98 °C (CMDro2 and EMDro2) showed more stability and were superior to the former samples in final stages of discharge cycling process. Afterward, the electrochemical behavior of the pretreated samples was investigated by means of cyclic voltammetry technique and discharge cumulative capacity profiles. Also X-ray diffraction was employed to verify the responses of voltammetric methods. In XRD patterns, peak at 2 θ = 28.6° which is due to β-MnO 2 type was the strongest signal as temperature 98 °C was selected for digestion. After digestion at 60 °C, the characteristic peaks at 2 θ = 38° and 42° were amplified which are attributed to formation of γ-MnO 2. Interestingly enough, the results according to the XRD patterns were in good agreement with the electrochemical approaches.

Manganese metallurgy review. Part I: Leaching of ores/secondary materials and recovery of electrolytic/chemical manganese dioxide

The world rapidly growing demand for manganese has made it increasingly important to develop processes for economical recovery of manganese from low grade manganese ores and other secondary sources. Part I of this review outlines metallurgical processes for manganese production from various resources, particularly focusing on recent developments in direct hydrometallurgical leaching and recovery processes to identify potential sources of manganese and products which can be economically produced.High grade manganese ores (>40%) are typically processed into suitable metallic alloy forms by pyrometallurgical processes. Low grade manganese ores (<40%) are conventionally processed by pyrometallurgical reductive roasting or melting followed by hydrometallurgical processing for production of chemical manganese dioxide (CMD), electrolytic manganese (EM) or electrolytic manganese dioxide (EMD).Various direct reductive leaching processes have been studied and developed for processing low manganese ores and ocean manganese nodules, including leaching with ferrous iron, sulfur dioxide, cuprous copper, hydrogen peroxide, nitrous acid, organic reductants, and bio- and electro-reductions. Among these processes, the leaching with cheap sulfur dioxide or ferrous ion is most promising and has been operated in a pilot scale. The crucial issue is the purification of leach liquors and the selective recovery of copper, nickel and cobalt is often difficult from solutions containing soluble iron and manganese. For treatment of manganese bearing materials including waste batteries, spent electrodes, sludges, slags and spent catalysts, a leaching or reductive leaching step is generally needed followed by various purification steps, which makes the processes less economically viable.It is concluded that the recovery of manganese from nickel laterite process effluents which contain 1–5 g/L Mn offers a growing low cost resource of manganese. Part II of this review considers the application of various solvent extraction reagents and precipitation methods for treating such manganese liquors.

Examining Manganese Dioxide: Graphite Connectivity in Alkaline Electrolytes

Electrochemical impedance spectroscopy has been used to characterize various electrode constructions employing electrolytic manganese dioxide (EMD), the active material used in alkaline manganese dioxide cathodes. The electrodes varied in their access to electrons necessary for reduction. The results suggest that establishing an effective three-phase boundary between EMD, graphite, and the alkaline electrolyte is essential for low impedance behavior. Furthermore, the processes of proton and electron insertion into the structure to cause reduction must occur in close proximity to one another, implying a commercial cathode performance dependence on factors such as mixing, packing, and EMD and graphite particle size. Evidence is also presented to support localization of proton-electron pairs within the structure, rather than delocalization, which is apparent in the literature, as well as the extent to which electrolyte can penetrate into the porous EMD structure.

The Composite Effect of Nanometer MnO 2 Mixed with the Electrolytic MnO 2

The nanometer MnO 2 has outstanding electrochemical performance theoretically, but it is not suitable for actual utilization, which may result in capacity decrease and resource waste. In this study we have utilized the characterizations of the nanometer material, synthesized a type of nanometer α-MnO 2 through KMnO 4 and KNO 3 with hydrothermal method, and mixed the products into micron electrolytic manganese dioxide (EMD) to enhance the electrochemical performance of the electrode. The cyclic voltammogram and galvanostatical discharge measurements of the samples were investigated. It is found that the 50% nanometer MnO 2 mixed electrode has the best electrochemical performance. The electrochemical performance improvement mechanism of the sample nanometer MnO 2 mixed into micron EMD was discussed. With the existence of electrolyte, the nanometer MnO 2 particles filled into the interspaces of the micron EMD particles, the mass and charge transfer conditions of the electrode reaction were improved, and the electrode polarization was diminished.

Discharge rate capabilities of alkaline AgCuO 2 electrode

A series of AgCuO 2 samples are prepared and tested as alkaline cathode materials for primary batteries. AgCuO 2 discharges via four equivalent-charge reduction processes, the rate capabilities of which are determined. At ambient temperature AgCuO 2 displays superior rate capabilities for the two highest voltage processes. For all samples, the rate capability of the two lower voltage processes is always superior to those at higher voltage. This is due to the electrode intrinsically doping itself with elemental silver during discharge as part of the second reduction process. The electrode compares favourably with commercial electrolytic manganese dioxide but is prone to self-discharge, the kinetics of which are also discussed.

Synthesis and Storage Performance of the Doped LiMn2O4 Spinel

A series of spinel-doped lithium manganese oxides, (, , ), (, , , ), (, , , ), have been prepared using the solid-state reaction of a titanium-doped electrolytic manganese dioxide, lithium hydroxide, and doping agents. The oxides have been characterized using several advanced techniques, such as X-ray diffraction, X-ray photoelectron spectroscopy, Fourier transform infrared analysis, Raman spectroscopy, thermogravimetric analysis, differential scanning calorimetry, cyclic voltammograms and charge/discharge cycles. The experimental results show that the sample, prepared at 600°C, showed the best electrochemical performance during the charge/discharge tests and storage process in all samples. In the voltage region of 4.6–, the initial capacities of the fresh, discharge-storage, and charge-storage cell for the sample are 206, 144, and , respectively. In the voltage region of 4.3–, the capacity fade of the sample was 5.3% in 150 cycles. After being doped by titanium ions, the spinel exhibits a lower lattice constant and stronger bond than a pure spinel does.

DSC characterisation of chemically reduced electrolytic manganese dioxide

The thermal decomposition of electrolytic manganese dioxide (EMD), in an inert atmosphere, and the effect of chemical reduction on EMD, using 2-propanol under reflux (82°C), was investigated by differential scanning calorimetry (DSC). This study is an extension of a study investigating the thermal decomposition of EMD and reduced EMD by TG-MS (J. Therm. Anal. Cal., 80 (2005)625)). The DSC characterisation was carried out up to 600°C encompassing the water loss region up to 390°C and the first thermal reduction step. Water removal was observed in two distinct endothermic peaks (which were not deconvolved in the TG-MS) associated with the removal of bound water. For the lower degrees of chemical reduction, thermal reduction resulted in the formation of Mn2O3; for higher degrees of chemical reduction, the thermal reduction resulted in Mn3O4 at 600°C. In the DSC the thermal reduction of the EMD and chemically reduced specimen was observed to be endothermic. The reduced specimens, however, also showed an exothermic structural reorganisation.

Preparation and characterisation of chemical manganese dioxide: Effect of the operating conditions

In this study MnO 2 preparation by chemical methods is investigated for possible applications in dry cell batteries of chemical manganese dioxide (CMD) instead of electrolytic manganese dioxide (EMD). Three preparation procedures were tested: precipitation–oxidation by air plus acid activation (two-step-air), precipitation–oxidation by H 2O 2 plus acid activation (two-step-H 2O 2), precipitation–oxidation by KClO 3 (single-step-ClO 3). Replicated factorial designs and related statistical analysis of experimental data by analysis of variance were performed in order both to obtain a preliminary optimization of the operating conditions and to take into account the intrinsic sample heterogeneity associated to each specific procedure. Comparisons among three different preparations denoted that in the investigated conditions two-step preparations give larger yields of activated solid in comparison with single-step preparation. Preliminary optimized conditions denoted final solid yields (80–86%) for both two-step procedures. The effect of operating conditions on the chemical, structural and electrochemical properties of CMDs produced in preliminary optimised conditions was investigated and compared with those of a commercial EMD sample by acid and acid-reducing leaching for Mn speciation in solid phase, potentiometric titrations, X-ray and IR spectra and cyclic voltammetry. These characterisation tests denoted the significant effect of acid activation in both preparation procedures to obtain CMD samples with high % of Mn(IV)oxides. Potentiometric titrations of solid samples obtained by first and second steps denoted that both procedures gives two CMD samples with the same acid–base properties, which in comparison with commercial EMD present a residual dissociation in the basic pH range (similar structure and proton insertion properties for CMDs and EMD, but different structural defects). X-ray and IR spectra of solid samples by first and second steps denoted highly disordered systems and the presence of Mn 2O 3 in first step products and of γ-MnO 2 in second step product. Voltammetric cycles denoted that CMD samples obtained after acid digestion present similar peaks than commercial EMD but with higher current intensity.

Synthesis of electrolytic manganese dioxide on a heated anode

Synthesis of electrolytic manganese dioxide on a heated anode was studied. The specific energy of chemical power cells fabricated using this dioxide in the Zn-Mn system is as high as 100 W h kg−1.

Synthesis of highly crystalline spinel LiMn 2O 4 by a soft chemical route and its electrochemical performance

Highly crystalline spinel LiMn 2O 4 was successfully synthesized by annealing lithiated MnO 2 at a relative low temperature of 600 °C, in which the lithiated MnO 2 was prepared by chemical lithiation of the electrolytic manganese dioxide (EMD) and LiI. The LiI/MnO 2 ratio and the annealing temperature were optimized to obtain the pure phase LiMn 2O 4. With the LiI/MnO 2 molar ratio of 0.75, and annealing temperature of 600 °C, the resulting compounds showed a high initial discharge capacity of 127 mAh g −1 at a current rate of 40 mAh g −1. Moreover, it exhibited excellent cycling and high rate capability, maintaining 90% of its initial capacity after 100 charge–discharge cycles, at a discharge rate of 5 C, it kept more than 85% of the reversible capacity compared with that of 0.1 C.

Microporosity of heat-treated manganese dioxide

A structural and micro-pore analysis of a series of heat treated electrolytic manganese dioxide (EMD) samples has been conducted. In terms of crystal structure, the original EMD with γ-MnO 2 structure (orthorhombic unit cell) was found to progressively convert to β-MnO 2 (tetragonal unit cell) at elevated temperatures. The structural transition was kinetically limited, with the higher temperatures leading to a greater degree of transformation. The orthorhombic γ-MnO 2 unit cell was found to contract along the a and b axes, while along the c axis an expansion was observed only at the highest heat treatment temperatures. These changes occur as a result of manganese ion diffusion leading to the formation of a denser, more defect free material. The porosity of these heat treated EMD samples was also examined by N 2 gas adsorption combined with various interpretive techniques such as the Kelvin equation, MP method, Dubinin–Radushkevich method, Dubinin–Astakhov method and a more modern density functional theory based approach. Despite shortcomings associated with certain techniques, all clearly indicated that the EMD micro-pore volume decreased and the meso- and macro-pore volume increased as the heat treatment temperature was increased. This was justified as a result of manganese ion movement during the structural rearrangement causing the small pores to be progressively sintered shut, while the larger pores were formed as a result of stress-induced cracking in the denser final product.

Development and utility of manganese oxides as cathodes in lithium batteries

Manganese oxides have a long history of serving as a cathode in charge storage applications. Electrolytic manganese dioxide (EMD) is widely used in alkaline batteries and MnO 2 originally was part of the Leclanché wet cell patented in 1866. Leclanché wet cells used a naturally occurring MnO 2 ore with Zn metal as anode and ammonium chloride electrolyte. While there are a vast number of topics to discuss on manganese oxides, in this short paper, two topics researched at Argonne over the last 12 years are highlighted. First, the addition of lithia (Li 2O) as a stabilizing component in 3 V alpha-MnO 2 is examined. Second, an overview of the evolution of layered–layered composite-structured electrodes derived from the lithium-manganese oxide (Li 2MnO 3) layered rock-salt phase is presented.

New manganese dioxides for lithium batteries

Lithium/manganese dioxide primary batteries use heat treated manganese dioxide (HEMD), a defect pyrolusite structure material as the cathode active material. Ion exchange of the structural protons in electrolytic manganese dioxide (EMD) with lithium before heating results in formation of a lithium containing γ-MnO 2. Increased lithium hydroxide concentration and increased temperature lead to increased lithium levels. At 80 °C with a combination of LiOH and LiBr, almost all of the structural protons in MnO 2 are replaced by lithium resulting in a γ-MnO 2 phase substantially free of protons and containing about 1.8% Li. This highly substituted lithium containing MnO 2 is reduced at between 3.5 and 1.8 V and has a capacity of 250 mAh g −1. There are two reduction processes, one at 3.25 and the other at 2.9 V. TGA studies reveal two processes during heat treatment. Heating the lithium substituted MnO 2 to 350–400 °C results in a partially ordered HEMD-like MnO 2 (LiMD) phase with higher running voltage and superior discharge kinetics. Continued heating of the lithiated manganese dioxide to 450–480 °C under oxygen partial pressure can result in formation of a mixed phase containing both HEMD and a new, ordered MnO 2 phase (OMD). The intimately mixed HEMD/OMD composition has a discharge voltage near 2.9 V with a capacity about 220 mAh g −1. Heating exhaustively lithiated MnO 2 to 350–400 °C results in formation of the partially ordered LiMD MnO 2 phase as with the previous partially lithium substituted MnO 2. Additional heating of the highly lithium substituted MnO 2 to 450–480 °C under oxygen results in formation of the new OMD phase in substantially pure form. Discharge of the new OMD phase shows it has a discharge capacity near 200 mAh g −1 between 3.4 and 2.4 V versus lithium in a single, well-defined discharge process. OMD demonstrated good cycling against Li with no indication of formation of LiMn 2O 4 spinel after 80 deep discharge cycles.

Cycle life improvement of alkaline batteries via optimization of pulse current deposition of manganese dioxide under low bath temperatures

Pulse current electrodeposition (PCD) method has been applied to the preparation of novel electrolytic manganese dioxide (EMD) in order to enhance the cycle life of rechargeable alkaline MnO 2–Zn batteries (RAM). The investigation was carried out under atmospheric pressure through a systematic variation of pulse current parameters using additive free sulfuric acid–MnSO 4 electrolyte solutions. On time ( t on) was varied from 0.1 to 98.5 ms, off time ( t off) from 0.25 to 19.5 ms, pulse frequencies ( f) from 10 to 1000 Hz and duty cycles ( θ) from 0.02 to 0.985. A constant pulse current density ( I p) of 0.8 A dm −2 and average current densities ( I a) in the range of 0.08–0.8 A dm −2 were applied in all experiments. Resultant materials were characterized by analyzing their chemical compositions, X-ray diffractions (XRD) and scanning electron microscopy (SEM). Electrochemical characterizations carried out by charge/discharge cycling of samples in laboratory designed RAM batteries and cyclic voltammetric experiments (CV). It has been proved that specific selection of duty cycle, in the order of 0.25, and a pulse frequency of 500 Hz, results in the production of pulse deposited samples (pcMDs) with more uniform distribution of particles and more compact structure than those obtained by direct current techniques (dcMDs). Results of the test batteries demonstrated that, in spite of reduction of bath temperature in the order of 40 °C, the cycle life of batteries made of pcMDs (bath temperature: 60 °C) was rather higher than those made of conventional dcMDs (boiling electrolyte solution). Under the same conditions of EMD synthesis temperature of 80 °C and battery testing, the maximum obtainable cycle life of optimized pcMD was nearly 230 cycles with approximately 30 mAh g −1 MnO 2, compared to that of dcMD, which did not exceed 20 cycles. In accordance to these results, CV has confirmed that the pulse duty cycle is the most influential parameter on the cycle life than the pulse frequency. Because of operating at lower bath temperatures, the presented synthetic mode could improve its competitiveness in economical aspects.

Effect of the dispersity of components of a cathode mixture on discharge characteristics of a Leclanché cell

The effect of dispersity of electrolytic manganese dioxide and of an electrically conducting additive to the cathode mixture on the discharge capacity of chemical power cells of the manganese-zinc system with a salt electrolyte was studied.