Leo Binder

Effects of direct and pulse current on electrodeposition of manganese dioxide

Abstract The physical and chemical properties of electrolytic manganese dioxide (EMD) are determined predominantly by the conditions employed during the anodic deposition process. There are relationships between deposition parameters, EMD properties and battery performance, as reported in many investigations. This study describes the influence of pulse current and direct current on the electrochemical properties of EMD. The EMD produced at different current conditions is characterized by charge–discharge cycling of various samples in the cathodic mixture of rechargeable alkaline AA cells, whereby the anode composition and the other cell parameters are kept constant. Results have shown that there is a systematic correlation between the pulse parameters and the cycle performance of EMD. The charge–discharge characteristics of test cells indicate an improvement in cycle performance of EMD with increasing duty cycle (i.e. with the approach of pulse current to direct current).

Effect of bath temperature on electrochemical properties of the anodically deposited manganese dioxide

Abstract The effect of bath temperature on the electrochemical properties of electrolytic manganese dioxide (EMD) was studied. EMD was produced by anodic deposition from acidic aqueous solution of manganese sulfate at different bath temperatures in the range of 60–120°C. At temperatures above the boiling point of water, the electrolysis was carried out in an autoclave. The EMD produced at 120°C was of gamma type, identified by X-ray diffraction (XRD). Furthermore, the materials produced at 115 and 120°C were quality-controlled by cycling a sample as cathode mix in small size RAM-cells and by scanning electron microscopy. The results indicated an increase in cyclic charge/discharge performance and an improvement of crystallization conditions of EMD produced at elevated temperature when compared to data of commercially available γ-MnO2.

Synthesis, characterization and application of doped electrolytic manganese dioxides

Abstract Electrolytic manganese dioxides (EMDs) were prepared on the 100 g scale by anodic deposition from acidic aqueous solutions of manganese sulfate. In situ doping with titanium ions was achieved by addition of tetra- n -butoxytitanium to the electrolytic bath. Samples were also doped ex situ by washing the products with aqueous barium hydroxide solution. The EMDs were characterized by electron microscopy studies and BET surface area determinations. Cyclic abrasive stripping voltammetry was successfully applied to evaluate the rechargeability of the newly synthesized undoped and doped EMDs in 9 M KOH. Relative discharge capacities at different depths of discharge (DOD) with respect to the first one-electron reduction of γ-MnO 2 are compared for different EMDs. At about 30% DOD, resulting relative discharge capacities show essentially the same trend as those measured in AA cells from about 10 to 20 discharge/charge cycles onwards. Accordingly, titanium-doped EMD was shown to exhibit superior charge retention and rechargeability when compared to the titanium-free samples.

Production and characterisation of electrolytically doped manganese dioxide

A laboratory batch process for the production of titanium-doped electrolytic manganese dioxide (EMD) in the amount of some hundred grammes is described. The product is characterised by chemical analysis, electrochemical behaviour, X-ray diffraction, and electron microscopy (TEM, ESI) including local electron energy loss spectroscopy (EELS) analysis. Suggestions for possible improvement of the doping process and for the preparation of the product are given.

The effect of the amount of electrolyte in the anode gel on the rechargeability of alkaline manganese dioxidezinc cells

Abstract The zinc-limited anode technology for rechargeable alkaline manganese dioxidezinc cells is well known. Attempts have been made to relate the rechargeability of these cells with the amount of electrolyte available in the anode gel. The rechargeability of the cells is found to increase with the amount of electrolyte up to 35 – 40% of the dry weight of the anode mass. Further increases in the amount of electrolyte were found to be detrimental to the rechargeability of the cells. Analysis of cathodes after running several cycles shows higher amounts of zinc in those from cells with greater amounts of electrolyte. This could be due to haeterolite formation in the cathode which poisons it thus explaining the reduced rechargeability with excess electrolyte.

Mapping the Distribution of Doping Elements in Electrolytically Doped Manganese Dioxide by EFTEM and EELS

Energy-filtering transmission electron microscopy (EFTEM) and electron energy-loss spectrometry (EELS) have been used to measure the distribution of titanium in titanium-doped electrolytic manganese dioxide, which consists of large particle agglomerates of some micrometer diameter. In contrast to previous investigations, where the distribution of the doping elements can only be investigated at the thinnest regions of the agglomerates, we describe an improved procedure which allows to measure the concentration of the dopant not only at the thinner edges of the particle agglomerate, but also in the interior. The titanium distribution maps showed that titanium is enriched on the surface of the agglomerates and in pores penetrating into their interior. Within the agglomerates, titanium is evenly distributed, and in manganese dioxide the titanium concentration could be analyzed quantitatively by EELS spectrometry. Based on these results, suggestions for possible improvements of the doping process and for the preparation of the product are given.