Higher Power Lithium Batteries
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VOLUME 4 NUMBER 4 EMBEDDED SYSTEMS JUNE 2 008
Is COTS in for a rough landing? Industry execs speak out on tech, trends, future Hardware: Portable power
High-power lithium batteries: Providing more performance, life, and reliability
By Sol Jacobs
Batteries capable of delivering high-rate power to long-life single-use military applications have remained virtually unchanged for decades. Now, a new generation of high-power lithium batteries is available that offers unique performance and features, including higher capacity and energy density, reliability, instantaneous activation, and the COTS advantage.
Driven largely by advancements in em- power, long-life batteries capable of to power long-term single-use military bedded computers and semiconductor providing reliable power for single-use applications; however, high-power lithium fabrication, long-life single-use military/ military applications as a “critical problem” batteries are now an option to consider, too: aerospace systems are rapidly evolving, to address. with new generation products offering Reserve and thermal batteries improved functionality, miniaturization, The search for solutions led to the develop- Silver-zinc batteries and enhanced product reliability, as well ment of new COTS high-power lithium Spin-activated batteries as higher performance expectations. This battery technology featuring exceptionally High-power lithium batteries applies to a wide variety of single-use long shelf life combined with powerful military products, including mortar-guidance performance capabilities previously available A brief review of these competing technologies systems, rockets, missiles, torpedoes, mines, only with reserve or thermal batteries. Design highlights the potential advantages and sonobuoys, unattended ground sensors, engineers are advised to perform appropriate disadvantages of each battery chemistry. UAVs, and dispersed munition sensors, due diligence and compare this new highly among others. reliable COTS lithium battery against older Reserve and thermal batteries battery technologies to ensure that optimum Reserve batteries, traditionally considered Realizing that limitations in battery system performance is achieved. the battery of choice for single-use military performance could create a potential applications, encompass a number of bottleneck that stifles new product devel- Reviewing the options different chemistries, including lithium opment, the U.S. DoD recently identified The first three of the following battery thionyl chloride, silver-zinc, lead-acid, and the need for a new generation of high- chemistries have been commonly utilized thermal.
2 June 2008 Military EMBEDDED SYSTEMS Design engineers have long preferred thermal batteries for their ruggedness, safety, reliability, and extremely long Realizing that shelf life. However, due to the use of limitations in battery squibs and the need to keep the electrolyte A systematic “ continually molten at 400 °C to 700 °C to achieve optimum conductivity, thermal approach to specifying performance could create batteries are inherently bulky, as they must the right battery incorporate insulation layers that serve a dual a potential bottleneck purpose of retaining heat while simultaneously When specifying primary batteries for long-life single-use military appli- protecting nearby components from heat- that stifles new product cations, design engineers need to stay related damage. on top of the latest technology by development, the U.S. DoD reviewing all available battery chem- Silver-zinc batteries istries to ensure that the ideal power recently identified the Single-use military devices can also be management solution is being applied. powered by silver-zinc batteries, which This decision-making process should need for a new generation are relatively complex to manufacture, incorporate: since they require a gas generator, 1. Evaluating anticipated power and of high-power, long-life tubular electrolyte reservoir, manifold, performance requirements battery block, vent, and heating system. batteries capable of As a result, silver-zinc batteries tend to 2. Developing a prioritized checklist be relatively expensive and require long of desired attributes such as: providing reliable power production lead times. These batteries › Voltage, capacity, and size, weight, and/or special also have performance limitations due for single-use military packaging requirements to relatively low energy density of just 260 › Expected energy density, Wh/L. service life, temperature, applications as a and/or environmental issues Spin-activated batteries › Overall cost of ownership “critical problem” to Military fuses and certain marine applications › Considering additional are often powered by spin-activated batteries requirements such as the address. that store the electrolyte inside an ampoule need for instant activation as well as the ability to conduct or bladder. When the projectile is fired, the routine testing for system With reserve batteries,” the electrolyte is stored bladder gets cut open, and the electrolyte readiness separately from other active ingredients, is distributed throughout the cell stack by with a pyrotechnic device typically centrifugal force generated by the spinning 3. Analyzing this checklist to being utilized to initiate the chemical reaction. shell. Spin-activated batteries have also ensure that the optimal technology The active ingredients remain separated, so been manufactured using lithium thionyl is being employed based on overall they stay inert, thus creating the potential chloride chemistry to power minelets or performance criteria for extremely long shelf life of 20+ years. communication jammers. These devices are 4. Performing appropriate tests However, there are significant trade-offs, as propelled by artillery shells equipped with to confirm that the power reserve batteries cannot be tested without being parachutes to ensure a soft landing. management solution fulfills depleted and battery activation is delayed until all necessary performance, a chemical reaction occurs. A common application for spin-activated quality, and safety requirements batteries is Multi-Option Fuses for Artillery in accordance with customer A popular type of reserve battery is the (MOFA) found in 105 mm and 155 mm specifications and applicable third-party certifications thermal battery, which contains a metallic bursting artillery projectiles. Seeking a more salt electrolyte that is inert and non- standardized power management solution, conducting in a solid state and at ambient the U.S. DoD considered various chemistries, temperatures. However, when the selecting lithium oxhalide over lead-acid and metallic salt electrolyte becomes molten, thermal batteries. By comparison, a high- developed that uses widely accepted COTS it quickly transforms into an excellent power lithium battery could deliver over six technology to deliver high current pulses and ionic conductor, yielding high-rate power times the capacity (200 mAh versus 30 mAh), high rate energy, with a storage life up to 20 for relatively short intervals of time over ten times the current (3.5 A versus 325 years and an annual self-discharge rate of less (from a few watts to several kilowatts mA), more stable voltage, and faster activation than 1 percent at room temperature. These depending upon battery size and chemistry). (instantaneous versus a 100 ms delay) versus battery cells are available in three standard The electrolyte is typically activated an equivilent lithium oxhalide battery. cylindrical configurations (AA-size, CR-2 by a pyrotechnic charge delivered by size, and 20 mm length). An example of this a squib. High-power lithium batteries is Tadiran’s AA-size TLM-1550-HP battery, A high-power lithium battery has been which includes a 4.0 V open circuit
Military EMBEDDED SYSTEMS June 2008 3 Hardware: Portable power
voltage and total energy of 2 watt-hours, ODAM 60 mm mortar able to deliver 15 A current pulses as guidance systems: Under DARPA’s well as 5 A maximum continuous current Optically Directed Attack Munitions at 3.2 V. CR-2 sized cells deliver 1 watt- (ODAM) project, BAE Systems under- hour of total energy, while the 20 mm took a development and integration ini- version offers 0.5 watt-hours of total tiative to demonstrate the feasibility of a energy. These cells can be easily configured laser-guided, low-cost 60 mm mortar round. into custom battery packs, leading to faster BAE Systems selected CR-2 sized high- Figure 1 design and manufacturing cycles at reduced power lithium batteries to power the sys- cost due to the use of COTS components. tem’s laser-guided optical seekers. These previously powered by a battery pack batteries were chosen over CR-2 consumer consisting of 19 silver-zinc cells can be Attributes of high-power lithium batter- type batteries because of their ability to oper- converted to a battery pack consisting ies include a wide temperature range (-40 ate in extremely cold environments (-40 °C), of 24 high-power lithium cells. The 24-bat- ºC to +85 ºC) and instant activation with- with up to four times longer shelf life tery pack results in a 30 percent reduction in out the need for squibs or gas generators. (20 years versus 5 years). size, a 75 percent reduction in weight (2.2 The ability to perform periodic testing of Kg versus 0.5 Kg), as well as approximately the battery helps ensure system readiness Unmanned Aerial Vehicles: UAVs are 3.5 times greater energy density. The high- and reduces the number of “duds” in mis- being widely utilized by U.S. armed forces power lithium battery pack achieves further sile guidance systems. When activated, in Iraq and Afghanistan for unmanned reductions in the footprint by eliminating the high-power lithium cells do not produce air reconnaissance. High-power lithium need for the squib, gas generator, and heater high internal temperatures, thus eliminat- batteries are also currently being utilized required by the silver-zinc pack (Figure 2). ing thermal insulation needs. This, in turn, to create weight- and space-saving bat- reduces weight and enables a smaller form tery packs that power emergency recovery New generation of batteries to factor. Size, weight, and cost reductions systems on a UAV. Figure 1 shows a power the future are also achieved by eliminating the need 32 V/480 W battery pack consisting of A new generation of lower-cost COTS for squibs, gas generators, and external heat- 96 AA-size high-power lithium batteries, high-power lithium batteries offers flex- ing elements. capable of delivering up to 120 watt-hours ibility for long-life single-use military at -30 ºC and weighing approximately applications. This includes the potential Sample applications for 2 Kg including its metal enclosure. Since for greater shelf life, increased perfor- high-power lithium batteries COTS technology is employed, the mance, and enhanced COTS product reli- The following examples demonstrate battery pack can be easily reconfigured for ability in challenging environmental con- the potential for high-power lithium other UAV applications. ditions. Design engineers are advised to batteries to enhance performance and COTS carefully evaluate this new technology interoperability of power management sys- Powering missile systems: The guidance against existing battery technologies tems used in single-use military systems. system of an air-to-ground missile when retrofitting existing military equip- ment or developing next-generation military products. Figure 2 Sol Jacobs, VP and general man- ager of Tadiran, holds BSME and MBA de- grees and has been involved in the energy and military industries. He can be reached at: [email protected].
Tadiran 516-621-4980 www.tadiranbat.com
Reprinted with permission from Military Embedded Systems, June 2008,@2008 Open Systems Publishing. All rights reserved. By The Reprint Dept. 800-259-0470 (11146-0708) For Web Posting Only. Bulk Printing Prohibited.