Evaluation of ceramic papers and tapes for use as separators in thermal batteries.

Abstract

Ceramic tapes and papers were evaluated for potential use as separators in hightemperature thermal batteries. The bulk of the tests involved fiberglass tape and borosilicate filter discs. Quartz (SiO 2) and zirconia (ZrO 2) materials were also examined to a limited extent. In addition, custom-prepared MgO-coated ceramic discs from Inventek Inc. were evaluated as separators. The tapes and paper discs were impregnated with LiCl-KCl eutectic or LiCl-LiBr-LiF electrolytes using three different techniques. Test discs were punched from the tapes and papers, impregnated with electrolyte and evaluated as separators in Li(Si)/FeS 2 single cells at 400 o or 500 o C at a steady-state current of 63 or 125 mA/cm 2. The performance of single cells containing these discs generally improved with increased electrolyte loading for most of the materials in the case of the LiCl-KCl eutectic. Better results were obtained with the paper filter discs than with the tapes. The best results with the paper discs were obtained with Whatman GF/A filter discs. Active lives for cells with these separators were about 85% of standard cells with pressed-powder separators. Good results were obtained in one battery test with the eutectic electrolyte. Mixed results were obtained with the LiCl-LiBr-LiF electrolyte under similar conditions. Higher loadings of electrolyte did not always translate into improved cell performance. Selfdischarge reactions are believed responsible. The best overall results were obtained with the Inventek separators. Based on the results of this study, more work in this technology area is merited.