Thermal Battery with Low Internal Operating Temperatures for Missle Applications

Thermal batteries use a number of halide-based electrolytes, such as LiCl-KCl eutectics, that have an operational temperature range from 350°C to over 550°C. Such high temperatures can be unacceptable if there are temperature-sensitive electronics adjacent to the battery. In a Phase I SBIR effort we have identified and tested battery systems with operational temperatures in the 120°C to 228.5°C range. The most promising system uses tetra-alkyl bis(oxalato)borate(BOB)electrolyte. The salt is very stable toward both the anode and cathode materials, i.e., it possesses a wide electrochemical voltage window. One system uses substituted imidazolium salts with LiBOB as a passivating agent for the lithium and lithium-alloy anodes. Other lower-melting halide-based systems (one melting at 151°C, for example)can be achieved by forming a pentanary eutectic. A candidate battery has been successfully tested at Sandia Labs in a 5 cell configuration. Alternative electrolytes that show promise are based on nitrates melting at 124.5°C. This electrolyte system can be tested in a 5-cell configuration. All of the above systems show promise. It is proposed that the above candidate systems be further evaluated in 5-cell battery tests. Prior to carrying our these tests, single-cell tests will be conducted to characterize each system and to select those that show the most promise. Following the result of successful 5-cell battery tests, the most promising candidates would then be built into full-sized hermitically sealed,15 cell batteries using standard hardware. Testing will be subjected to acceptance, stand-life and simulated qualification testing. Selecting an initiation source has been already established in earlier work at Sandia Labs. However, additional pyrotechnic development will be necessary if the nitrate candidate is selected, but recent research at Sandia has identified carbonyl iron as a suitable material for moderating the burn rate and heat output for the standard Fe/KClO4 pyrotechnic.