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Liquid Ammonia Reserve Batteries for Electronic Fuzing

Description:

TECHNOLOGY AREA(S): Weapons 

OBJECTIVE: The objective of this topic is to investigate the liquid ammonia system in a reserve battery format as a viable power source for current and future electronic fuzing applications, in particular those developed for medium-caliber (30- and 40-mm) projectiles. 

DESCRIPTION: For the past decade, ARDEC fuze developers have been working to add radar proximity fuzing capability to several medium-caliber projectiles, for both lethal and non-lethal applications. These programs include Airburst Non-Lethal Munition (ANLM), Lightweight 30 (LW30), and Increased Range Anti-Personnel (IRAP) grenade. To meet the typical 20-year shelf-life requirement, efforts were launched to develop very small (0.23-0.63 cm3) reserve batteries to power the fuze electronics. Because these are direct-fire weapons, flight times are short (10-20 seconds) and the batteries must activate and reach full power in a very short amount of time (100-200 ms) even at the cold temperature operating extreme (typically -45 degrees F). To date, battery development efforts have achieved very limited success, with the primary hurdle being meeting the cold temperature activation time requirement. Over the past two decades, the lithium/oxyhalide electrochemistry has become the dominate, and essentially only, system used in fuze batteries because of its high working voltage (nominally 3 volts), high energy density, and generally good low-temperature performance. However, this battery system has not shown itself to be capable of reliably meeting the requirements of the noted fuze programs. It is believed that, at low operating temperatures, the increased viscosity of the electrolyte inhibits wetting of the cathode during activation, and the decreased conductivity of the electrolyte reduces discharge rate capability. In combination, these effects slow activation time unacceptably. To address the needs of the fuze developers, this topic seeks to reopen investigation into an alternative battery chemistry, the liquid ammonia system, which had been used in several Army mine applications but was eventually out-competed by the lithium systems. The liquid ammonia system was recognized for its ability to activate very quickly at temperatures as low as -65 degrees F due to the high conductivity, low viscosity, and high vapor pressure of its electrolyte. However, at its present state of development, the nominal voltage of the liquid ammonia system is around 2.2 volts, which is below the 3 volts required by the targeted fuze applications. (As electronic fuze design and componentry have advanced over the years, the voltage levels required have steadily decreased. At present, because of the ubiquity of the lithium/oxyhalide system, the effort has been made to develop the key electronic components so they can run reliably at voltages as low as the 3-volt level typically provided by that system. Lower supplied voltage may require additional components in an already-crowded space for munitions of this scale, or further engineering advancements in key custom components.) Therefore, one of the primary areas for investigation under this topic is the identification of an electrode pair that can achieve a working voltage of at least 3 volts over the entire operating temperature range (-45 to +145 degrees F) of the applications. In the intervening years since the commercialization of the lithium systems led to the demise of the liquid ammonia battery, a tremendous amount of cathode work has been done to further the advance of the lithium systems. It is believed that some of this work could be applied to the ammonia system, to push voltage levels to 3 volts and possibly beyond. Additional investigative efforts might include optimizing the processing of the identified electrode materials, and designing an appropriate mechanical package for the resultant battery system. 

PHASE I: Investigate appropriate candidate anode and cathode materials to meet the desired performance targets and for storage stability. In particular, explore electrode pairings that may increase the working cell voltage to 3 volts or higher, at a current density of 40 mA/cm2, for a discharge time of 15 seconds, at -45 degrees F. Demonstrate the performance of the selected materials in laboratory cells. 

PHASE II: Develop optimized compositions and fabrication processes for the electrode materials that were selected as the result of Phase I activities. Design and fabricate prototype battery hardware appropriate to the IRAP fuze application. The IRAP application requires a reserve-type battery that is 0.350” in diameter and 0.400” in length. The battery must be able to provide 40 mA of current at a minimum of 3 volts within 100 milliseconds of being activated, at temperatures down to -45 degrees F. Discharge life must equal or exceed 20 seconds. The battery must survive and function properly while experiencing setback forces up to 20,000 G and continuous rotation at 3600 revolutions per minute. Produce prototype IRAP batteries and conduct laboratory performance validation testing of the prototype design. 

PHASE III: Successful completion of the preceding efforts will make the developed technology applicable to the three medium-caliber Army fuze programs mentioned previously (ANLM, LW30, and IRAP). In addition, the liquid ammonia system may also be applicable to large-caliber fuzing applications, as it can sustain significantly higher discharge rates than the lithium/oxyhalide system with the benefit of improved safety. As such, it might be inserted into an application such as the Navy’s Multi-Function Fuze (MFF) which also had activation time requirements that the lithium system was greatly challenged to meet. Therefore, the developer shall pursue resources to commercialize this technology internally, or offer it to a qualified manufacturer, such as a member of the existing fuze battery industrial base, as the required material processing and device fabrication and testing would likely be not too dissimilar from what is currently being done with the existing fuze battery systems. Unfortunately, it has historically been very challenging to identify commercial (consumer) applications for fuze-type batteries, where design trade-offs are made to enhance their use as single-use, moderate-to-high power, short-lived devices, capable of operating in extreme physical environments, characteristics which are quite different from those sought by the consumer market. Typically, cost alone would make these types of batteries unappealing for non-military uses. 

REFERENCES: 

1: J. C. Daley, "FC-2 Liquid Ammonia Reserve Battery, Status of Prototype Study," Naval Ordnance Laboratory Corona Report 655, 1 November 1966.

2:  Printz, "Pursuit Deterrent Munition Reserve-Cell Ammonia Battery Redesign Analysis," U.S. Army Armament Research, Development, and Engineering Center, Picatinny Arsenal, NJ, Technical Report ARFSD-TR-91009, April 1991.

3:  D. Linden, "Reserve Batteries," Chapter 16, Handbook of Batteries, Third Edition, 2002.

KEYWORDS: Liquid Ammonia, Fuze, Projectile, Reserve Battery 

CONTACT(S): 

Jeffrey Swank 

(301) 394-3116 

jeffrey.a.swank4.civ@mail.mil 

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