Ceramic Felt Separator and Modified Iron (II) Disulfide Cathodes for Lithium Salt Thermal Batteries

Abstract

Ceramic felts as an immobilizing structure for molten salt electrolytes in thermal batteries are shown to be an effective alternative to widely used MgO. One of the major benefits of ceramic felts is their high porosity and low weight. In this work Al2O3 and YSZ ceramic felts with bulk porosity of 97% and 96%, respectively, were investigated. LiCl-KCl eutectic electrolyte was incorporated in ceramic felts at different loading levels and cells’ performance (capacity, specific energy, and charge/discharge behavior) was evaluated. LiSi/FeS2 thermal cells with YSZ and Al2O3 ceramic felt electrolyte/separators reported specific energy of 58.47 ± 0.05 Wh kg-1 and 43.96 ± 0.05 Wh kg-1, respectively, which are 2 times the specific energy for a typical MgO-pellet design thermal cell (22 Wh kg-1).Pellet design pyrite (FeS2) cathodes for thermal batteries usually has low electronic conductivity introducing a large amount of internal ohmic resistance, especially when used in a battery stack with multiple thermal cells. Several alternative materials to pyrite and pellet design alternatives such as tape casting thin film have been introduced, however, due to the simple manufacturing process and their low-cost pyrite pellets are still known as the main type of cathode systems for thermal batteries. By adding chemically compatible and conductive particles into the pyrite powder, the properties of the cathode were modified while the fabrication process remained simple. Iron particles (≤74 µm) as additives for the cathode pellet of thermal batteries were successfully investigated. By adding 11 wt.% Fe particles to the cathode the ohmic polarization was reduced by 17.5 % while the available capacity was increased by 78% over the cell with cathode pellet with no electrically conductive particle additives.