The production and characterisation of powder processed silver chloride electrodes for use in the magnesium-silver chloride reserve battery system

Hide, Nicholas Jon (1998) The production and characterisation of powder processed silver chloride electrodes for use in the magnesium-silver chloride reserve battery system. University of Southampton, Doctoral Thesis.

Abstract

Silver chloride is used as the cathode in the magnesium silver chloride reserve battery system. Current wrought processing techniques of the electrode are very costly, limit electrode design and do not allow the inclusion of porosity for efficient high rate battery applications. Powder processing is an ideal alternative for producing components with a minimum of processing steps, allowing complex designs and the incorporation of porosity.

This work investigates the complete processing route from a base powder to a final electrode. Three powder size fractions were produced from agglomerated silver chloride powder and cold pressed over a range of pressing pressures. The morphological, mechanical and electrochemical properties of the electrodes were then assessed to identify the process variables best suited to producing dense, direct wrought replacements and also those producing the most effective high porosity electrodes. The results have been interpreted in terms of the densification mechanisms of silver chloride powder, the interparticle bonding characteristics and electrode porosity morphologies with respect to subsequent mechanical and electrochemical properties.

The research has shown that pressing pressure is the most important process variable in terms of electrode microstructure and subsequent electrochemical performance. At low pressing pressures an open, contiguous pore structure is obtained which is weak and brittle, but allows for rapid electrolyte saturation and enhanced steady electrochemical performance when compared with wrought electrodes. This has been attributed to the large surface area of a porous electrode and the subsequent reduction in current density. However, the initial resistance of these electrodes is high, resulting in long start-up times (c.f. wrought electrode) due to poor electrical inter-particle contacts.

At high pressing pressures, dense electrodes possessing a closed pore structure are produced with steady state electrochemical characteristics that are inferior to high porosity electrodes but comparable with those of wrought electrodes as a result of the near planar surfaces produced. Start-up times are short for dense powder electrodes (when compared with porous electrodes) due to a low initial electrode resistance whilst mechanical strength and ductility characteristics are superior from enhanced bonding between powder particles.

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