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 MnO2-Zn batteries (RAM). The investigation was carried out under atmospheric pressure through a systematic variation of pulse current parameters using additive free sulfuric acid-MnSO4 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 (theta) 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 degrees C, the cycle life of batteries made of pcMDs (bath temperature: 60 degrees C) was rather higher than those made of conventional dcMDs (boiling electrolyte solution). Under the same conditions of EMD synthesis temperature of 80 degrees C and battery testing, the maximum obtainable cycle life of optimized pcMD was nearly 230 cycles with approximately 30 mAh g(-1) MnO2, 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. (c) 2006 Elsevier B.V. All rights reserved.