Development of asymmetric polysulfone membrane for the application in tropicalized lead acid battery

Abstract

The objectives of this research are to develop asymmetric polysulfone membrane for the application in lead acid battery and to investigate the effect of fabrication conditions on the performance of the membrane-assisted lead acid battery and its morphology. The function of the membrane is to prevent electrolyte losses by minimizing the rate of vaporized electrolyte disposed into the atmosphere. Lead acid batteries in tropical countries normally face the problem of water decomposition, caused by the combine factors of the charge-discharge process and the heat accumulation caused by hot tropical climate and heat generated from engine compartment. This causes unpleasant setbacks such as corrosion of parts inside the car bonnet and having to top up the electrolyte whenever it reduces. The membrane will be functioning as a water-retaining device when applied onto the battery vent holes by delaying the permeation of hydrogen, oxygen and traces of water vapor during charge-discharge processes. Effects of polymer concentration and casting shear rate were investigated in order to produce the most suitable membrane. The prepared membranes were tested on lead acid battery during charging process to evaluate their performance in retaining electrolyte as well as minimizing pressure build up. Results showed that decreasing polymer concentration in casting solution decreases compactness of the polymer matrixes in the membrane structure, therefore decreases pressure build-up in battery casing during charging process. Increasing shear rate resulted in a decrease of skin layer thickness and in turn, lowers the pressure build-up during battery charging process. Membrane with 13 wt/wt % Polysulfone (PSF) and 87 wt/wt % of N-N-dimethylformamide (DMF) and at shear rate of about 233.33 s-1 was found to be the most suitable membrane to be applied on the maintenance free battery. At room temperature, the electrolyte losses of a membrane-assisted lead acid battery is about 6.67 grams per hour, while for conventional battery is about 26.67 grams per hour. During charging process at temperature about 80oC, membrane assisted lead acid battery can save up to 40% of electrolyte losses compared to the conventional battery. Membrane characterization using Scanning Electron Microscopy (SEM) and Raman Spectroscopy were also carried out to investigate the structure of the membrane and to differentiate the components of the permeated electrolytes from both membrane-assisted and conventional batteries. Based on SEM images, it can be observed that the membrane cast at the shear rate of about 233.33s-1 has the most suitable skin layer thickness. The membrane is permeable enough to minimize the pressure build up inside the battery and sufficiently selective enough to minimize the electrolyte losses. In the Raman spectrometer analysis, it was proven that with the application of membrane, the intensities of hydrogen and oxygen gases in the permeated vaporized electrolyte had been suppressed to about 50-60% and 10-30% respectively. Therefore this research is considered as a revolutionary step in the establishing a new age of maintenance free battery with the application of membrane technology into lead acid battery.