Electrolytic Manganese Dioxide Research Articles

The Influence of Residual Acidic and Sulfate Impurities of Electrolytic Manganese Dioxide on the Electrochemistry of LiMn2 O4 Cathode

The Influence of Residual Acidic and Sulfate Impurities of Electrolytic Manganese Dioxide on the Electrochemistry of LiMn₂ O₄ Cathode

Formation of multiporous MnO/N-doped carbon configuration via carbonthermal reduction for superior electrochemical properties

Herein, the multiporous MnO/N-doped carbon (MnO/NC) composite based on the abundant and inexpensive electrolytic manganese dioxide were fabricated through a facile microwave-assisted carbonthermal reduction, combined with a subsequent in-situ polymerization of polydopamine onto MnO along with thermal treatment. As an anode material, it retains a reversible capacity of 770.5mAhg−1 at 300mAg−1 and high Coulombic efficiency of 99% over 500 cycles, superior than those values of the pure multiporous MnO alone. The impressive performance is attributed to the splendid structure stability contributed by well-connected three-dimensional porous configuration and the enhanced reaction kinetics as well as electrical conductivity incurred by N-doped carbon layer with multiple type nitrogen.

Anodic MnO2 deposition on Titanium Electrode Coated with Thermally Prepared Manganese Oxide

Zinc electrowinning uses an acidic zinc sulfate solution prepared from zinc ore, which contains some other metal ions such as Mn2+. The solution after zinc electrowinning goes back to the solution preparation process, in which the zinc concentration is recovered to the appropriate level, while that of Mn2+ is increased, if no Mn2+ is consumed by anodic deposition in electrowinning cell, which is possible with amorphous RuO2-Ta2O5/Ti anodes [1]. Therefore, the situation that Mn2+ concentration becomes high enough to recover Mn2+ as manganese oxide is expected, and it would resemble the commercial production process of EMD (Electrolytic Manganese Dioxide) that is famous as the positive electrode material of some batteries. For such a novel manganese recovering system in zinc electrowinning, the anode for deposition of MnO2 from zinc electrowinning solution is needed, with which MnO2 is deposited on and harvested from the anode that should be durable for the deposition and harvesting cycle. In this study, we prepared the titanium electrode covered with manganese oxide as the catalytic layer for MnO2 deposition from zinc electrowinning solution, and the obtained electrode was characterized by XRD, SEM, and EDX. The polarization measurement and continuous electrolysis of the anode in Mn2+ containing solutions were also performed to examine the obtained product on the anode and the current efficiency. The manganese oxide coated titanium electrode was prepared by thermal decomposition of the precursor solution containing Mn2+ painted on a titanium substrate which had been degreased in acetone and etched in 10% oxalic acid. The obtained electrode was analyzed by XRD, SEM, and EDX. The anodic polarization of the anode in H2SO4 solution with and without Mn2+ was examined by cyclic voltammetry with a conventional three-electrode cell equipped with a platinum plate counter electrode and an Ag/AgCl reference electrode in saturated KCl solution. Constant current electrolysis was also performed to obtain MnO2 on the anode, and the weight of the anode before and after the electrolysis was measured to know the amount of the product which was characterized by XRD. The electrolytic solution was 2 mol/L H2SO4 + MnSO4 and used at a temperature from 40 oC to 75 oC. The catalytic layer prepared by thermal decomposition was found to be Mn2O3 by XRD measurements. Constant current electrolysis with the anode was carried out under different conditions, in which the typical examples are 40 o C or 75 o C as the electrolyte temperature with electrolysis at 5 mA/cm2 for 30 min. For these conditions, the product on the anode was obtained with the increase of the anode’s weight by electrolysis, and the XRD results showed the diffraction pattern corresponding to MnO2, although the diffraction peak intensity was weak for the product obtained at 40 oC compared to that at 75 oC. The current efficiency for MnO2 deposition was calculated with the assumption that no oxygen evolution occurs, and the results were 17.5% at 40 oC and 70.6% at 75 oC. It was also found that the electrolyte was transparent before constant current electrolysis, which was unchanged by the electrolysis at 75 oC, while that became dark red at 40 oC, implying that Mn3 + is generated at 40 oC and the oxidation of Mn2+ to MnO2 is not completed. More detailed results on the effects of the electrolysis conditions on the obtained product and the current efficiency will be shown in this paper. This work was financially supported by “Kyoto Super Cluster Program” of Japan Science and Technology Agency (JST). Reference [1] T. Zhang, Ph.D. Thesis, Doshisha University (2015).

Deconvoluting Capacitive and Pseudo-Capacitive Contributions to Electrochemical Capacitor Electrode Behaviour

Generally the capacitive behaviour of the electrochemical capacitors are associated with electrical double layer at the surface of the electrode, and in some materials pseudo-capacitance, which results from faradaic processes. Several electrochemical methods have been developed for determining the contribution of different charge storage mechanisms such as via the electrical double layer and diffusion-limited processes. This includes using a cyclic voltammetry (CV) data at different scan rates to obtain the relationship between a voltammetric current and scan rate (v). In this method, it can be assumed that the total current response for a particular potential is a summation of the current associated with a capacitive processes and a current associated with a diffusion-limited process. While, the capacitive current is proportional to v, and the diffusion limited current is relative to v1/2 (Conway, et al. 1998). The cyclic voltammetry data also can be applied to determine the relationship between a voltammetric charge and scan rate. The charge attributed to the surface capacitive processes is assumed to be constant with scan rate while, the charge attributed to diffusion-limited processes varies with v-1/2 (Trasatti, et al. 1990). Both approaches have been used widely for characterization of the performance of electrochemical systems. However, these methods have some limitations as the relationship between current and v1/2 and also, between charge and v-1/2 is not always linear in a different range of scan rates. Step potential electrochemical spectroscopy (SPECS) also, has been used to effectively differentiate between different charge storage mechanisms. The SPECS method is based on applying a series of equal magnitude potential steps on a working electrode, with sufficient rest time to allow for equilibrium to be established for each step throughout an applied potential window. This slow scan rate enables an electrode to approach its maximum charge storage capabilities. More importantly, it allows separation of the charge storage mechanisms, such as electrical double layer charge storage and diffusion-limited processes. The aim of this study is to compare these three methods experimentally and also to discuss about their limitations and advantages for interpreting the current data and their ability to distinguish between different charge storage mechanisms. Moreover, the relationship between voltammetric current and scan rate has been modified by introducing the constant parameter of residual current. The modified relationship then, can be used over the entire range of potential scan rate. In this work, the combined CV and SPECS methods have been applied to electrolytic manganese dioxide (EMD) in 0.5 M K2SO4 between 0.0 – 0.8 V (vs SCE). Firstly, EMD electrode was cycled for 250 cycles at different scan rates ranged from 1 to 100 mV/s. Subsequently, the SPECS method was applied using 25 mV potential steps and 300 s equilibration time. Eventually, the contribution of capacitive and diffusion-limited processes were obtained using three techniques which were discussed here. The linear dependence of current to v1/2 and the linear dependence of capacity to v-1/2 have not been observed. However, it can be seen that there is a good agreement between the modified model of the scan rate dependence of current and experimental data. Liu, T. C., Pell, W. G., Conway, B. E., & Roberson, S. L. (1998). Behavior of molybdenum nitrides as materials for electrochemical capacitors comparison with ruthenium oxide. Journal of the Electrochemical Society, 145(6), 1882-1888. Ardizzone, S., Fregonara, G., & Trasatti, S. (1990). “Inner” and “outer” active surface of RuO2 electrodes. Electrochimica Acta, 35(1), 263-267.

Preparation of Chemical Manganese Dioxide by Dilute Sulphuric Acid Pickling of Mn3O4 and Its Application to the Synthesis of LiMn2O4

AbstractChemical manganese dioxide (CMD) was obtained by pickling Mn3O4 with dilute sulfuric acid. Atomic absorption spectroscopy (AAS) showed that S, Na, Ca and Mg impurities in CMD were less than in electrolytic manganese dioxide (EMD). Spinel lithium manganese oxide (LiMn2O4) samples were synthesized using CMD or EMD precursor mixed with Li2CO3 via high temperature solid‐phase reactions. The oxides were applied as the cathode material for lithium ion batteries. X‐ray diffraction (XRD) and scanning electron microscopy (SEM) showed that the crystallinity was high and the size‐distribution was uniform for CMD. The crystallinity of the spinel‐type LiMn2O4 synthesized by the CMD was high as well. Electrochemical tests showed that LiMn2O4 synthesized by the CMD precursor exhibited greater discharge capacity and better rate capability than the sample synthesized by the EMD precursor. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) indicated that LiMn2O4 synthesized by CMD or EMD precursor both showed good kinetics for Li+ ion transport, but LiMn2O4 synthesized by the CMD precursor showed a lower electrochemical impedance. Meanwhile, the synthesis process was simple, cheap, and easy for large‐scale production.

Electrochemical process for electrode material of spent lithium ion batteries

Electrochemical method for recovering cobalt and manganese from electrode materials of spent lithium ion batteries was studied. Electrochemical leaching of cobalt and manganese from electrode material was optimized by varying different process parameters such as time, acid concentration and current density. Both cobalt and manganese could effectively be leached out at a current density of 400A/m2 in 3h using 2M sulphuric acid. In the subsequent study, the metallic cobalt and electrolytic manganese dioxides was recovered from the leach liquor at 200A/m2, pH 2–2.5 and 90°C after removing aluminum. The commercial feasibility of the study was tested in pilot scale. Overall recovery of Co, Cu and Mn was above 96%, 97% and 99%, respectively.

Energy-saving synthesis of electrolytic manganese dioxide using oxygen cathode with Pt/TiO2-CNx nanocatalysts

The awareness of energy, environment, and economy for electrolysis has required the development of new methods to prevent environmental pollution, such as the emission of acid fog, CO2, and SO2. Hence, the use of gas diffusion electrode as a cathode in the electrodeposition of manganese dioxide to save energy and protect the environment is attracting research interest. In this work, a gas diffusion electrode consisting of a mixture of Pt/TiO2-CNx nanocatalysts and two different additive conductor supports that activate carbon and acetylene black were synthesized. The Pt/TiO2-CNx nanocatalysts and Pt/TiO2-CNx gas diffusion electrode were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The Pt/TiO2-CNx nanowire catalyst showed strong interaction between the Pt nanoparticles (~2.21 nm) and TiO2-CNx nanowire support. Results of electrochemical tests in 120 g of MnSO4 + 30 g of H2SO4 at 80 °C show that the Pt/TiO2-CNx gas diffusion electrode used in the electrodeposition of manganese dioxide could save electric energy by approximately 60%. Furthermore, the lifetime of the gas diffusion electrode of Pt/TiO2-CNx nanocatalysts was about twofold longer than that of the gas diffusion electrode of Pt/C and Pt/TiO2 nanocatalysts. The Pt/TiO2-CNx nanowire catalyst exhibited high anti-acid corrosion, activity, and stability, indicating its potential important application in the electrodeposition of manganese dioxide.

PH-Controlled Synthesis of Electrolytic Manganese Dioxide Materials for Alkaline MnO2/Zn Batteries

A systematic study of the effect of electrolysis acid concentration on the physical and electrochemical properties of electrolytic manganese dioxide (EMD) was conducted. High acid concentrations (> 2 M H2SO4), lead to multiphase production of manganese dioxide with poor electrochemical behavior; however, in low to mid-range acidic environments, superior EMD (compared to a commercial product) was obtained. With an electrolysis bath containing 1 M MnSO4 and 2 M H2SO4, the EMD produced had approximately twice the surface area (86.4 m2 gEMD -1) and structural water content (4.4 %) of that of a commercial sample. The aforementioned synthesized EMD furthermore had an improved energy efficiency and an average specific capacity of approximately 65 mAh gEMD -1 after 100 cycles showing about 25 mAh gEMD -1 higher capacity compared to the commercial sample.

Impact of BaSO4 Additive on the Cycling Performance of MnO2/Zn Alkaline Batteries

A detailed electrochemical investigation of BaSO4 as an additive in the electrolytic manganese dioxide (EMD)-based cathode of MnO2/Zn batteries is presented. The addition of BaSO4 appears to have a positive impact on the cycling performance of EMD, but only during the first 50 cycles. The loss of EMD structure and formation of irreversible phases still remain challenging factors in the electrochemical cycling of the EMD materials.

PH-Controlled Electrolysis of Electrolytic Manganese Dioxide (EMD) for Improved Cycle Life of Rechargeable MnO2/Zn Batteries

A systematic study of the effect of acid concentration (0.5–5 M H2SO4) on the electrolysis of electrolytic manganese dioxide (EMD or γ-MnO2) has been performed. All the samples were characterized for their phase and crystallinity, their structural water, the pyrolusitic-to-ramsdellite ratio, BET surface area, pore size range; and were examined for their electrochemical performance. Concentration of the electrolysis acid affects the structural water content and the pyrolusitic-to-ramsdellite ratio of the γ-MnO2 phase as well as the surface area and pore size. The best cycling performance was achieved for the samples prepared with an electrolysis bath containing an acid concentration of about 2 M H2SO4. Electrochemical performance over 100 cycles of the EMD prepared in 2 M H2SO4 has shown higher energy efficiency and improved longer term cycling performance compared to commercial EMD products. Post-mortem analysis of the cycled EMD samples show partial loss of the EMD phase, loss of water content, and growth of irreversible manganese dioxide phases.

Nanometer-Thin Graphitic Carbon Buffer Layers for Electrolytic MnO2 for Thin-Film Energy Storage Devices

In this study, nanometer thin graphitic carbon coatings were applied as an adhesion layer for the growth of submicron to micron thick electrolytic manganese dioxide (EMD) films for thin-film energy storage devices. The graphitic carbon coating served not only as current collector and adhesion layer between the EMD and the substrate, but also prevented the oxidation of the non-noble TiN substrate during the anodic deposition process. The EMD films consisted of a network of interconnected nanometer-size particles with around 50% porosity. The ability to grow a few hundred nanometer thick EMD film with good adhesion to the current collector is critical for reliable thin-film batteries on high aspect ratio microstructured surfaces. Thin EMD films grown on our graphitic carbon coated TiN substrates showed improved reversible Li-ion intercalation kinetics and increased cycle life compared to similar films deposited on noble metal platinum substrates, thus demonstrating the improved interface properties using the graphitic carbon buffer layer.

Electrodeposition of Adherent Submicron to Micron Thick Manganese Dioxide Films with Optimized Current Collector Interface for 3D Li-Ion Electrodes

Three-dimensional (3D) configuration of high-performance energy storage devices has been the subject of ongoing investigations targeting their integration in autonomous microelectronic systems. In this study we demonstrate a route toward the realization of high capacity cathode material for 3D thin-film lithium-ion (Li-ion) batteries. Electrolytic manganese dioxide (EMD) film can be applied as a Li-ion intercalation electrode upon its conversion to lithium manganese dioxide (LiMn2O4 or LMO) by solid-state reaction. The main challenges of depositing thicker EMD film directly on the current collector often lay in achieving a good film adhesion and preventing oxidation of non-noble current collectors such as TiN, Ni. To improve the adhesion of the EMD films we modify the surface of the current collector by means of thin-film or seed layer coatings, which also prevent the oxidation of the underlying current collector substrate during the anodic deposition process. As a result submicron to micron thick EMD films with good adhesion were deposited on various current collectors. The acidity of the electrolyte solutions was varied depending on the type of the surface coating or current collector used. The mechanism of the EMD film growth and morphology on different substrates was examined. Compatibility of the proposed current collector interface modification for the electrodeposition of conformal thick EMD films on high-aspect ratio microstructures was demonstrated. A method of EMD film conversion to LMO at low-temperature on different substrates was shown as the path toward their application in 3D Li-ion batteries.

Impact of cathode additives on the cycling performance of rechargeable alkaline manganese dioxide–zinc batteries for energy storage applications

The impact of chemical additives [e.g., BaSO4, Sr(OH)2·8H2O, Ca(OH)2, and Bi2O3] on the cycling performance of rechargeable alkaline electrolytic manganese dioxide/Zn batteries has been studied. The additives were used in the cathode electrodes consisting of 5 wt% additive, γ-MnO2 (electrolytic manganese dioxide—EMD—80 wt%) and KS44 graphite (15 wt%) in prismatic-type electrode geometries. Powder X-ray diffraction analysis showed the formation of alkaline earth metal carbonates (BaCO3, SrCO3) when the electrodes come into contact with the highly alkaline (pH 15, 9 M KOH) electrolyte. The presence of dissolved carbonate in the electrolyte leads to a double replacement precipitation reaction leading to the formation of these carbonate species. These additives help with the cycle life of the electrolytic manganese dioxide cathode material. The overall energy efficiency of the cells is about 75%. Rate capability studies and equilibrium potential measurements by galvanostatic intermittent titration technique analysis indicate that ohmic polarization plays a significant role in the energy loss and should be improved for high power applications. Rechargeable alkaline batteries with electrolytic manganese dioxide/Zn chemistry provide a low-cost and an environmentally friendly solution for storage of energy. Improvement of this technology would be an important contribution in the area of energy storage applications. The impact of a number of chemical additives (e.g., BaSO4, Sr(OH)2·8H2O, Ca(OH)2 and Bi2O3) on the cycling performance of rechargeable alkaline EMD/Zn batteries has been studied. The additives were used in the cathode electrodes consisting of 5 wt% additive, γ-MnO2 (electrolytic manganese dioxide—EMD—80 wt%) and KS44 graphite (15 wt%) in prismatic-type electrode geometries. Powder X-ray diffraction analysis showed the formation of alkaline earth metal carbonates (BaCO3, SrCO3) when the electrodes come into contact with the highly alkaline (pH 15, 9 M KOH) electrolyte. The presence of dissolved carbonate in the electrolyte leads to a double replacement precipitation reaction leading to the formation of these carbonate species. These additives help with the cycle life of the EMD cathode material. The overall energy efficiency of the cells is about 75%. Rate capability studies and equilibrium potential measurements by galvanostatic intermittent titration technique analysis indicate that ohmic polarization plays a significant role in the energy loss and should be improved for high power applications. Rechargeable alkaline batteries with EMD/Zn chemistry provide a low-cost and an environmentally friendly solution for storage of energy. Improvement of this technology would be an important contribution in the area of energy storage applications.

Electrosynthesis and characterization of nanostructured MnO2 deposited on stainless steel electrode: a comparative study with commercial EMD

The nanostructured MnO2 powder was successfully synthesized by electrodeposition on stainless steel (SS) substrate from hot 0.3 M MnSO4·H2O aqueous solution with pH value adjusted to 2. The electrochemical behavior of synthesized MnO2 was compared to that of the commercial electrolytic manganese dioxide (EMD). The investigation was conducted using a new cell which is manufactured in our laboratory. This gave us the possibility to present a new contribution and an improvement in the study of MnO2 electrochemical behavior. The analysis of the synthesized MnO2 and EMD powders by different techniques: FEG-SEM, EDS, TEM, XRD, and BET revealed the presence of electrodeposited nanostructured γ-MnO2 with high specific surface area of 139.59 m2 g−1 for the nanostructured MnO2 and 46.60 m2 g−1 for EMD. The electrochemical study of these powders conducted by linear voltammetry, electrochemical impedance spectroscopy (EIS) measurements, and Zn/MnO2 battery tests in 0.1 M NH4Cl electrolyte showed that the performance of the synthesized nanostructured MnO2 powder was higher than that of the commercial EMD powder.

PH-Controlled Electrolysis of Electrolytic Manganese Dioxide (EMD) for Improved Rechargeable MnO2/Zn Batteries

Alkaline batteries with the MnO2/Zn chemistry offer a number of advantages over other aqueous batteries (e.g., lead acid) including: a) high energy density, b) lower cost, and c) longer shelf life. The main active material used in the cathode electrode of these batteries is manganese dioxide, which has a low production cost, low toxicity, high specific capacity, low self-drain rate, and is abundant in nature. However, alkaline batteries cannot be easily recharged due to the rapid capacity loss and low energy efficiency of the MnO2 product used. An approach to improving the rechargeability of alkaline batteries may be synthesizing higher quality and/or modified manganese dioxide material. Manganese dioxide is a highly versatile substance that can grow into various crystal structures with different synthesis methods and be used in applications such as lithium-ion batteries, water oxidation electrocatalysts, etc. The preferred manganese dioxide used in alkaline batteries is electrolytic manganese dioxide (EMD) with a crystal structure which is an intergrowth of two different phases, pyrolusite and ramsdellite, which consist of arrays of MnO6 octahedra in 1 x 1 and 1 x 2 tunnels, respectively. The tunnels in the structure allow for the intercalation/deintercalation of protons during the discharge and charge processes. The EMD structure also contains protons (Ruetschi and Coleman protons) in the form of OH- complexes (also referred to as structural water) which provide a proton bridge, thus increasing the rate of proton diffusion into the lattice structure. The structural water content of EMD is an important parameter for the overall performance and has not been thoroughly reported before. Electrodeposition of EMD relies on the oxidation of Mn2+ to Mn4+ on a stable, conductive metal anode (e.g. titanium, nickel, etc.) in an acidic environment (typically H2SO4) which determines the water content. The EMD samples were electrodeposited by electrolysis of MnSO4 onto a titanium anode (4 cm × 14 cm × 2 mm) in an electrolyte solution containing 1.25 M MnSO4 and H2SO4 ranging from 0.5-5 M of H2SO4 at 95 oC using a current density of 115 A m-2. Electrosynthesis was performed for a period of 15 hours, thereafter, the deposits were chipped, grounded, washed, and filtered. The samples were then characterized using Thermogravemetric Analysis (TGA), X-Ray Diffraction (XRD), and Brunauer–Emmett–Teller (BET) surface area analysis techniques. Electrochemical properties of the EMD sample were examined with flat-plate cells using a zinc anode and a 9M KOH electrolyte solution and were cycled at a rate of C/10. Electrochemical impedance spectroscopy analysis was performed using a half-cell set-up using a nickel mesh as the counter electrode and an Hg/HgO reference electrode. The EMD samples synthesized with a manganese salt to acid ratio of 1.25:2 show a structural water content and surface area which are nearly twice that of the commercially available EMD products. Additionally, the ramsdellite fraction of the EMD samples increases by about 40%. EMD samples prepared in 2M acid solution exhibit improved cycling performance (see Figure) and energy efficiency when compared to commercial EMD products. The increase in water content is one possible explanation for the enhancement of the protonic conductivity of the in-house EMD as well as its improved physical characteristics. Synthesis and characterization of EMD samples and their electrochemical results will be presented Figure 1

(Invited) Electrochemical Deposition of Thick and Adherent MnO2 Films for Thin-Film Batteries

Electrolytic manganese dioxide (EMD) is fabricated by anodic electrodeposition typically from acid manganese sulfate baths. After electrodeposition it is peeled from the electrode and ground into powder, hence poor adhesion is required. EMD powder is mainly used for primary alkaline-Zn and Li-ion batteries. EMD allows Li-ion intercalation in the open channels in the γ-MnO2 lattice. In our research group we are interested in adapting the EMD process for bulk batteries to be used for fabrication of thin-film Li-ion batteries. EMD thin films deposition was developed on different substrates. Scanning electron microscopy (SEM) and Rutherford Backscattering Spectrometry (RBS) measurements were performed to extract the film porosity. It was found that all the deposited films have similar porosity values around 50 %. Anodic electrodeposition of EMD films from conventional acid manganese sulfate baths is not possible on easy to oxidize substrates like TiN (passivation) or Ni (dissolution). For this reason a neutral and complexing acetate bath was used. Using this deposition bath thick and adhesive EMD film were deposited on Ni and even on TiN substrates. Up to 1 μm thick film on planar substrate and 600 nm on 50 μm high Si pillar array with 2 μm pillar diameter and 2 μm interpillar spacing. A study of the EMD film deposition in a temperatures range from 5 °C to 50 °C using the neutral acetate deposition bath was performed. The relationship between the morphology and the electrochemical performance of the EMD films deposited at different temperatures were investigated.

Rechargeability of Manganese Dioxide-Zinc Batteries

Primary alkaline batteries use electrolytic manganese dioxide (EMD) as the cathode and zinc as the anode and have been in commercial use for several decades. This chemistry is of great interest because the materials used are inexpensive, environmental friendly, and abundant. In addition, alkaline chemistry offers a better energy density and shelf life than some other aqueous batteries such as lead-acid technology. Rechargeability of EMD, however, is challenging and commercial rechargeable batteries based on this electrochemistry have faced limited success due to the limitation of cycling performance. We have investigated the causes of cycling failures using flatplate-type cathode (MnO2) and anode (Zinc) electrodes which are amenable to large scale production. Electrochemical and physiochemical characterizations were performed and will be presented. Flatplate-type electrodes were prepared by producing paste-like mixtures of cathode and anode materials and applying them onto expanded Ni (cathode) and expanded brass (anode) current collectors. The cathode mixture contained EMD, graphite, additives, SBR binder and CMC gelling agent. Anode mixtures were prepared from zinc, zinc oxide, hydrogen inhibitors, teflon binder and carbapol gelling agent. The alkaline electrolyte (9M) was prepared from DI-water and KOH salt. All the cell hardware used was developed in-house. For the cathode electrode, a number of chemical additives such as BaSO4, Sr(OH)2·8H2O, Ca(OH)2, and Bi2O3were investigated at 5 wt. %. Deep discharge cycling (to 1.1 V) reduces the initial specific capacity of 250 mAh g-1 by 50% after 20 cycles. The specific capacity reduces, although at a slower rate, to about 50 mAh g-1 after 100 cycles. Additives such as BaSO4show marginal improvement in the earlier cycles (cycles 10-50), but beyond cycle 50 no noticeable effect was observed. Deeper cycling can be combined with shallow depths of discharge (1.4 – 1.45 V) to extend the cycle life-time of the batteries. Figure 1 shows the cycling performance of RAM cells for combined deep/shallow depths of discharge at C/2 and C/10 rates. Post-cycling XRD analysis of the cathode electrode shows formation of a todorokite-like phase which could limit the cycling performance. Impedance studies show a rapid increase in the charge transfer resistance, indicating that formation of surface inactive phases also play a role in reducing the capacity upon cycling. Figure 1

(Invited) Novel Method for Conformal LiMn2O4 thin Films Fabrication on Planar and 3D Microstuctured Substrates

In this work we report for the first time on a novel LiMn2O4 (LMO) thin film fabrication method. Using this fabrication method crystalline LMO thin films were prepared on both planar and 3D microstructured Si pillar substrates. The process is based on a solid state reaction between an electrolytic manganese dioxide (EMD) and Li2CO3 stacked-layers upon thermal annealing. The main advantage of using the electrochemical deposition technique to prepare the MnO2 layer is its capability of providing a conformal film deposition on high aspect ratio substrates. Moreover the electrolytic manganese dioxide film shows a high porosity (~50%) which will help later to release the mechanical strain during the Li-ion insertion and extraction process. The Li2CO3 deposition was done either by chemical solution deposition (CSD) or atomic layer deposition (ALD). The temperature dependence of the EMD conversion was investigated. The annealing time was adjusted based on the film thicknesses. Further, different current collector materials such as the noble Pt, Ni and MnO2seed layer on TiN were evaluated for the EMD conversion. The phase and morphology of the prepared LiMn2O4 films were investigated using X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The XRD patterns show the characteristic LMO diffraction peaks confirming the formation of the crystalline phase. SEM images display a continuous and conformal film on both planar and 3D microstructured substrates. The stoichiometry of the fabricated LMO films was evaluated by X-ray photoelectron spectroscopy (surface spectra and depth profile analyses) and elastic recoil detection (ERD) analyses. The results indicate that the fabricated film has a stoichiometry close to the theoretical stoichiometry of LiMn2O4with a homogeneous elements distribution through the layer. In addition, in-situ XRD measurements were performed in order to investigate the conversion mechanism evolution upon annealing and its kinetics. The electrochemical performance of the fabricated films was examined using cyclic voltammetry and charge and discharge measurements. The cyclic voltammogram reveals sharp redox peaks centered around 3 and 4V (vs. Li+/Li) corresponding to Li+ ion insertion/extraction in/from the spinel LiMn2O4. Figure 1.b shows that the converted EMD film shows a similar electrochemical performance to a LiMn2O4 film prepared by RF-sputtering. Also, the lithiation and delithiation curves show the typical LMO potential plateaus. About 100% of the maximum theoretical capacity was reached at 0.1 C. Furthermore, a study of the electrochemical performance of the prepared film based on its annealing time and temperature was done. The LiMn2O4 coated Si Pillar array showed 19 times higher capacity than the film prepared with the same conditions on planar substrate. The relevance of this technique for the fabrication of high rate and high capacity 3D thin-film Li-ion batteries will be discussed. Figure 1

Gradient Morphologies in Electrodeposited Manganese Dioixde and Their Effect on Electrochemical Performance

In this study, the use of current and potential control techniques in production of electrolytic manganese dioxide (EMD) has led to insight into the behaviour of different morphologies of manganese dioxide for a number of chemical storage systems. Further, improvements on industrial milling have been considered. Manganese dioxide has an advantage of existing in a variety of phases, and it has been found that current density greatly influences crystal structure along with deposit densities. Through the manipulation of this factor during the depositing of EMD a variety of morphologically different deposits can be obtained, linking to advantages for a number of industrial applications. Techniques such as chronopotentiometry and chronoamperometry have allowed for insight into the application of step potential ramps, multilayer depositions, and the manipulation of pulse sequences in a series of EMD deposits to be morphologically investigated through techniques such as scanning electron microscope (SEM) and X-ray diffraction (XRD) along with electrochemical performance testing. The objective of this study has been to provide a real world application, and superior performance essentially allowing for an alternative to bulk depositing. The study has considered specialised purposes such as industrial milling i.e. improving fracturing capabilities along with battery/capacitor applications with these deposits aiming to highlight the importance of improved electrolyte transport with regard to cathode interaction.

The Effects of Duty Cycle on the Step Potential Electrochemical Spectroscopy (SPECS) and Electrochemical Impedance Spectroscopy (EIS) Analysis of Manganese Oxides for Electrochemical Capacitors

Step potential electrochemical Spectroscopy (SPECS) and electrochemical impedance spectroscopy (EIS) have been developed for characterising the performance of electrochemical capacitors. However the effects of the different duty cycle on the behaviour and analysis of electrochemical methods still need to be investigated. In SPECS method a small potential step is applied with a sufficient rest time to allow equilibrium between each step throughout an applied potential window. This small scan rate enables an electrode to reach to its maximum charge storage capabilities. More importantly, it allows separation of the charge storage mechanisms such as electrical double layer charge storage and diffusional processes. EIS method also can provide the different information about the electrochemical cell such as double layer capacitance, series resistance, charge transfer resistance and mass transport using a small AC excitation signal. However, the AC excitation signal can be large in magnitude for the electrochemical capacitors due to the cyclability over a large potential window. In this work, the combined SPECS and EIS methods have been applied to electrolytic manganese dioxide (EMD) in 0.5 M Na2SO4 between 0.0 – 0.8 V (vs SCE) at different duty cycles to examine the changes in charge storage mechanisms. Hence, the different scan rates and equilibrium times have been applied for the same electrode ink and electrolyte. Firstly, the same duty cycle with the same effective scan rate has been examined with increasing the step size and equilibrium time which is constituted of the scan rate of 10 mV in 120 s, 25 mV in 300 s and 50 mV in 600 s. Then, the longer duty cycle with slower discharge rate such as 25 mV in 10 min has been applied to compare the results of different duty cycles. So, nine different experiments have been run using the different step size of 10 mV, 25 mV and 50 mV and different equilibrium times ranging of 120 s, 300 s and 600 s. The outcome of this work indicates the systematic effects of different scan rate on the charge storage mechanisms. Also, it can be seen that, the average capacitance of the electrochemical cell from cycling voltammetry (CV), increased with decreasing the scan rate of the duty cycle.