High-power lithium batteries: - Military Embedded Systems

Hardware: Portable powerSingle Print OnlyHigh-powerlithium batteries:Providing more performance,life, and reliabilityBy Sol JacobsBatteries capable of delivering high-rate power to long-life single-use militaryapplications have remained virtually unchanged for decades. Now, a newgeneration of high-power lithium batteries is available that offers uniqueperformance and features, including higher capacity and energy density, reliability,instantaneous activation, and the COTS advantage.Photo courtesy of the U.S. Army by Sgt. Timothy KingstonDriven largely by advancements in embeddedcomputers and semiconductorfabrication, long-life single-use military/aerospace systems are rapidly evolving,with new generation products offeringimproved functionality, miniaturization,and enhanced product reliability, as wellas higher performance expectations. Thisapplies to a wide variety of single-usemilitary products, including mortarguidancesystems, rockets, missiles, torpedoes,mines, sonobuoys, unattendedground sensors, UAVs, and dispersedmunition sensors, among others.Realizing that limitations in batteryperformance could create a potentialbottleneck that stifles new product development,the U.S. DoD recently identifiedthe need for a new generation of highpower,long-life batteries capable ofproviding reliable power for single-usemilitary applications as a “critical problem”to address.The search for solutions led to the developmentof new COTS high-power lithiumbattery technology featuring exceptionallylong shelf life combined with powerfulperformance capabilities previouslyavailable only with reserve or thermalbatteries. Design engineers are advisedto perform appropriate due diligence andcompare this new highly reliable COTSlithium battery against older battery technologiesto ensure that optimum systemperformance is achieved.Reviewing the optionsThe first three of the following batterychemistries have been commonly utilizedto power long-term single-use militaryapplications; however, high-power lithiumbatteries are now an option to consider,too:• Reserve and thermal batteries• Silver-zinc batteries• Spin-activated batteries• High-power lithium batteriesA brief review of these competing technologieshighlights the potential advantagesand disadvantages of each batterychemistry.Reserve and thermal batteriesReserve batteries, traditionally consideredthe battery of choice for single-use militaryapplications, encompass a number ofdifferent chemistries, including lithiumthionyl chloride, silver-zinc, lead-acid,and thermal.

“Realizing thatlimitations in batteryperformance could createa potential bottleneckthat stifles new productdevelopment, the U.S. DoDrecently identified theneed for a new generationof high-power, long-lifebatteries capable ofproviding reliable powerfor single-use militaryapplications as a“critical problem” to”address.With reserve batteries, the electrolyte isstored separately from other active ingredients,with a pyrotechnic device typicallybeing utilized to initiate the chemicalreaction. The active ingredients remainseparated, so they stay inert, thus creatingthe potential for extremely long shelf lifeof 20+ years. However, there are significanttrade-offs, as reserve batteries cannotbe tested without being depleted and batteryactivation is delayed until a chemicalreaction occurs.A popular type of reserve battery is thethermal battery, which contains a metallicsalt electrolyte that is inert and nonconductingin a solid state and at ambienttemperatures. However, when the metallicsalt electrolyte becomes molten,it quickly transforms into an excellentionic conductor, yielding high-rate powerfor relatively short intervals of time(from a few watts to several kilowattsdepending upon battery size and chemistry).The electrolyte is typically activatedby a pyrotechnic charge delivered bya squib.Design engineers have long preferredthermal batteries for their ruggedness,safety, reliability, and extremely longshelf life. However, due to the use ofsquibs and the need to keep the electrolytecontinually molten at 400 °C to 700 °Cto achieve optimum conductivity, thermalbatteries are inherently bulky, asthey must incorporate insulation layersthat serve a dual purpose of retainingheat while simultaneously protectingnearby components from heat-relateddamage.Silver-zinc batteriesSingle-use military devices can also bepowered by silver-zinc batteries, whichare relatively complex to manufacture,since they require a gas generator,tubular electrolyte reservoir, manifold,battery block, vent, and heating system.As a result, silver-zinc batteries tend tobe relatively expensive and require longproduction lead times. These batteriesalso have performance limitations dueto relatively low energy density of just260 Wh/L.Spin-activated batteriesMilitary fuses and certain marine applicationsare often powered by spin-activatedbatteries that store the electrolyteinside an ampoule or bladder. Whenthe projectile is fired, the bladder getscut open, and the electrolyte is distributedthroughout the cell stack by centrifugalforce generated by the spinningshell. Spin-activated batteries have alsobeen manufactured using lithium thionylchloride chemistry to power mineletsor communication jammers. Thesedevices are propelled by artillery shellsequipped with parachutes to ensure asoft landing.A common application for spin-activatedbatteries is Multi-Option Fuses for Artillery(MOFA) found in 105 mm and 155 mmbursting artillery projectiles. Seeking amore standardized power managementsolution, the U.S. DoD considered variouschemistries, selecting lithium oxhalideover lead-acid and thermal batteries.By comparison, a high-power lithiumbattery could deliver over six times thecapacity (200 mAh versus 30 mAh),over ten times the current (3.5 A versus325 mA), more stable voltage, and fasteractivation (instantaneous versus a 100 msdelay) versus an equivilent lithium oxhalidebattery.A systematicapproach to specifyingthe right batteryWhen specifying primary batteriesfor long-life single-use military applications,design engineers need to stayon top of the latest technology byreviewing all available battery chemistriesto ensure that the ideal powermanagement solution is being applied.This decision-making process shouldincorporate:Single Print Only1. Evaluating anticipated power andperformance requirements2. Developing a prioritized checklistof desired attributes such as:› Voltage, capacity, and size,weight, and/or specialpackaging requirements› Expected energy density,service life, temperature,and/or environmental issues› Overall cost of ownership› Considering additionalrequirements such as theneed for instant activation aswell as the ability to conductroutine testing for systemreadiness3. Analyzing this checklist toensure that the optimal technologyis being employed based on overallperformance criteria4. Performing appropriate teststo confirm that the powermanagement solution fulfillsall necessary performance,quality, and safety requirementsin accordance with customerspecifications and applicablethird-party certificationsHigh-power lithium batteriesA high-power lithium battery has beendeveloped that uses widely acceptedCOTS technology to deliver high currentpulses and high rate energy, with astorage life up to 20 years and an annualself-discharge rate of less than 1 percentat room temperature. These battery cellsare available in three standard cylindricalconfigurations (AA-size, CR-2 size,and 20 mm length). An example of thisis Tadiran’s AA-size TLM-1550-HP battery,which includes a 4.0 V open circuit

Hardware: Portable powervoltage and total energy of 2 watt-hours,able to deliver 15 A current pulses aswell as 5 A maximum continuous currentat 3.2 V. CR-2 sized cells deliver 1 watthourof total energy, while the 20 mmversion offers 0.5 watt-hours of totalenergy. These cells can be easily configuredinto custom battery packs, leadingto faster design and manufacturingcycles at reduced cost due to the use ofCOTS components.Attributes of high-power lithium batteriesinclude a wide temperature range (-40 ºCto +85 ºC) and instant activation withoutthe need for squibs or gas generators. Theability to perform periodic testing of thebattery helps ensure system readiness andreduces the number of “duds” in missileguidance systems. When activated, highpowerlithium cells do not produce highinternal temperatures, thus eliminatingthermal insulation needs. This, in turn,reduces weight and enables a smaller formfactor. Size, weight, and cost reductionsare also achieved by eliminating the needfor squibs, gas generators, and externalheating elements.Sample applications forhigh-power lithium batteriesThe following examples demonstratethe potential for high-power lithiumbatteries to enhance performance andCOTS interoperability of power managementsystems used in single-use militarysystems.ODAM 60 mm mortarguidance systems: UnderDARPA’s Optically DirectedAttack Munitions (ODAM)project, BAE Systems undertooka development and integrationinitiative to demonstrate thefeasibility of a laser-guided, low-cost60 mm mortar round. BAE Systemsselected CR-2 sized high-power lithiumbatteries to power the system’s laserguidedoptical seekers. These batterieswere chosen over CR-2 consumer typebatteries because of their ability to operatein extremely cold environments (-40 °C),with up to four times longer shelf life(20 years versus 5 years).Unmanned Aerial Vehicles: UAVs arebeing widely utilized by U.S. armed forcesin Iraq and Afghanistan for unmannedair reconnaissance. High-power lithiumbatteries are also currently being utilizedto create weight- and space-saving batterypacks that power emergency recoverysystems on a UAV. Figure 1 shows a32 V/480 W battery pack consisting of96 AA-size high-power lithium batteries,capable of delivering up to 120 watt-hoursat -30 ºC and weighing approximately2 Kg including its metal enclosure. SinceCOTS technology is employed, thebattery pack can be easily reconfiguredfor other UAV applications.Powering missile systems: The guidancesystem of an air-to-ground missileFigure 1previously powered by a battery packconsisting of 19 silver-zinc cells can beconverted to a battery pack consistingof 24 high-power lithium cells. The24-battery pack results in a 30 percentreduction in size, a 75 percent reductionin weight (2.2 Kg versus 0.5 Kg), as wellas approximately 3.5 times greater energydensity. The high-power lithium batterypack achieves further reductions in thefootprint by eliminating the need for thesquib, gas generator, and heater requiredby the silver-zinc pack (Figure 2).New generation of batteries topower the futureA new generation of lower-cost COTShigh-power lithium batteries offers flexibilityfor long-life single-use militaryapplications. This includes the potentialfor greater shelf life, increased performance,and enhanced COTS productreliability in challenging environmentalconditions. Design engineers are advisedto carefully evaluate this new technologyagainst existing battery technologieswhen retrofitting existing military equipmentor developing next-generationmilitary products.Sol Jacobs,VP and generalmanager of Tadiran,holds BSME andMBA degrees andhas been involvedin the energy andmilitary industriesfor more than 28 years. He can bereached at sjacobs@tadiranbat.com.Figure 2Tadiran516-621-4980www.tadiranbat.com© 2008 OpenSystems Publishing. Not Licensed for distribution. Visit opensystems-publishing.com/reprints for copyright permissions.