High Thermal Conductivity Carbon-Carbon Composites for Sodium Sulfur Batteries

Filament wound carbon-carbon (C-C) composites exhibit excellent strength and thermal conductivity, routinely exceeding 160 watts/mK. In addition, by depositing carbon by CVD, the C-C composites can be made impervious. High thermal conductivity and stability of C-C composites in highly corrosive atmospheres is the motivation behind this proposed application in sodium-sulfur batteries as a container material. The state-of-the-art sodium-sulfur batteries use chromized mild steel containers for the sulfur electrode. This has three drawbacks: (1) attack of mild steel due to defects in chromized layer shortens cell life. (2) heat dissipation during charge-discharge is a limitation due to low thermal conductivity. (3) Higher specific gravity of mild steel lowers the specific energy density (energy/weight). C-C composites are ideally suited as they are superior to chromized mild steel in all three aspects. In addition, due to the additional step of chromizing that is a must with mild steel containers, the projected cost of C-C composites is not expected to be a limitation. It is proposed that C-C composite tubes will be acquired from Hercules, Inc. The issue of attachment of steel collar to the tube to form a hermetic seal will be addressed. Two sodium-sulfur cells using Na- "-alumina solid electrolyte tubes, sodium anode and sulfur-impregnated carbon felt cathode will be assembled and tested in charge-discharge mode and peak power mode. The cells will be thermally cycled and technical feasibility of using C-C composites for sodium-sulfur cells will be evaluated. The two cells will be delivered to Air Force at the conclusion of Phase I. In Phase II, lifecycle testing and cost-effective cell fabrication, including C-C composites will be addressed. OPTION: None submitted.