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Batteries/Reserve 060706
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At the 42nd Power Sources Conference...
Reserve Batteries, New Possibilities for Old Applications
by Donald Georgi

...Performance and Aging Study... (Session 2.5) Rather unique to the military world is the need for a standby battery which may not be needed for up to twenty years of storage. We might think of it as a ‘Rip Van Winkle’ battery. A cannon shell  or missile with electronics may be packed in inventory for many years and then be called upon to perform a one time role. As a piece of smart ordinance, the ‘smarts’ require electric power which will be provided by the reserve battery.

The ordinary forms of reserve batteries are maintained in either a low conductive or inactive condition by such means as having to add strong electrolytes when asked to perform. An alternative was presented which reviewed the performance of the  Energizer L91 AA (Li/FeS2) commercial-off-the-shelf (COTS) production battery available in most retail stores. Company data has predicted the batteries to have 26 year life at ambient temperatures and shelf life of 7 years at 600 C. With an operational temperature range of -400 C to +630 C, here is a cell which may meet some reserve battery applications with low cost.

Adobe Photoshop ImageAdobe Photoshop ImageThe Energizer L 91 AA cell has shown such good shelf life that it has attracted military attention  as a possible replacement for some reserve batteries which are very expensive and may not have power on capability while stored. Low temperature testing and sealing are challenges yet to be resolved. (Photo from www.Energizer.com)

As a replacement for an ordinary reserve battery which may not provide electricity until it is activated for final use, the L91 battery is always active and provides a power capability to carry out routine diagnostics for the stored munitions and is available to provide an indication of state-of-charge or state-of-health.

To simulate 20 year aging, a test quantity of the cells was stored at 430 C, 530 C and 630 C for 6 months. Then elevated humidity testing was performed and discharge profiles obtained at - 400 C, 230 C and 600 C. Leak testing was also investigated to determine if thermal shock would compromise the crimp seal. Performance was good at the higher temperatures, but at - 400 C there was  a large drop in performance. Packaging improvements are suggested to attain better performance.

Reserve Thermal Battery Alternatives... (Session 4.6) Following in the mode of using  commercial cells for otherwise high cost thermal batteries, Tadiran has combined a Lithium thyonyl chloride cell with a capacitor demonstrating 45% loss in 10 years. The cell alone may not have sufficient power density to perform the short term power pulses of a pyrotechnic device, so the capacitor provides the needed high current pulses. Again because the cell is always active, the state of  charge is always available, and there is power for checking internal parts of the device.

Bimodal Lithium... (Session 2.1) One variation of the conventional Lithium-oxyhalide reserve batteries is the ‘Bimodal Battery’ which has a neutral electrolyte during the storage phase and is able to provide low currents. It is injected with a high molecular concentration of acid to activate the battery for high currents. Injecting the acid from fractured ampoules or from a piston driven reservoir is being considered. Development is ongoing.

Corrosion Resistance... (Session 2.2) While new electrolytes can increase the performance of Lithium-thyonyl chloride batteries, the need to verify the ability to contain the electrolytes over a period of years must be demonstrated. In this work, the standard 304 L SS and MP35 N alloys were exposed to a variety of the new electrolytes, with results showing suitability between the electrolytes and containment materials.

...High Rate and high Power Lithium Oxyhalide... (Session 2.3) Demonstrating that incremental improvements can be significant, this work verified the increased Voltage by 200 mV and capacity by 40% with the addition of metal macacrocyclic complex catalysts.

A Pressure Tolerant... Power source... (Session 2.4) A battery’s pressure environment can be its limiting condition and when subjected to undersea pressures, a proven Lithium-thyonyl chloride battery will upon discharge produce products which are denser than the reactants, resulting in voids which could lead to crushing. In this work, a new disk shaped vessel which provided pressure compensation for the battery was built and tested to 500 psi. At pressure, the cell performed as required, supporting the conclusion that such a simple, disk shaped housing without a complicated auxiliary electrolyte container could be used.

For other Power Sources 2006 Primary Lithium overviews, see “ Lithium Primary Continues to Evolve”          
BD