RECHARGEABLE BATTERIES FOR THE ARMYParth Goyal, Sanyam Shah GK3578, GK8803Wayne State University, DetroitAbstractSince the invention of walkie-talkie the electronic usage in the military has ever been increasing with the electronification of the warzone. This also increases the need of continuous power supply, in both energy as well as cost efficient ways. Since the development of different type of equipment’s according to usage and requirements, the rechargeable batteries used for the same purpose have been improved as well.IntroductionIt’s not a hard to accept fact that the job of a military personnel is very difficult, which also means working in extreme environment. This also goes the same for the batteries as well. The batteries need to withstand all the extremities in temperature, altitude, etc. It also need to bear the outside impurities that might damage the electronic structure of the battery itself, rendering the battery less efficient and in some cases even harmful.The development of batteries faced very important challenges. As per the report of 1990, the US military was using 350 different batteries for its equipment and various other applications. Therefore the standardization of batteries was of utmost importance. These batteries were required to last longer than ever. An average mission comprises of 72 hours on the field, this meant the battery needed to have higher charge cycle as well as life cycle. Concluding based on a report, on an average mission, a soldier carries approximately 70lbs of weight at one time out of which, 20lbs was electronic batteries itself, therefore this weight was needed to be reduced efficiently, keeping the charge capacity of the battery on the same or a higher level.Since the improvement in weaponry, the concerns related to safety of soldier also increased. This also brought along the safety of the batteries. These batteries were needed to build rugged and tough enough to survive severe handling and using conditions.The development on the batteries and battery systems also brought with it high cost expenditure. This had to be kept in control as well so as to redirect the funds from not just electronic equipment development but other important aspects as well.The modernization has brought with a broadened scope of electronic uses in many different ways. Some of these uses are: ? Robotics? Advanced Weapons Systems? Electromagnetic Armor (EM Armor)? Starting, Lighting and Ignition (SLI)? Silent Mobility ? Radios & warning Systems? Laser Range finders & GPS systems? Telegraph terminals? Night vision systemsThese important uses have raised even more concerns related to battery and focused us more on battery usage. This includes different battery systems as well as constant improvements in the existing ones, and also looking for more power and energy efficient ways on using these power sources.Past Battery SystemsFigure 1 Batteries in PastSince towards the ending of 17th century, the batteries had expanded uses in the military. Since that period till late 1990’s the below mentioned batteries were used and improved along the timeline:? Lead-acid Batteries? Nickel-Cadmium Batteries? Nickel-Metal Hydride BatteriesThese batteries in various forms and along with various improvements were extensively used by the military.The reasons behind the usage of these batteries were as follows:? Lead-acid batteries were the first commercially usable batteries developed at that point of time.? Scientists were able to construct Nickel-Cadmium Batteries in a robust manner which provided upper hand against damage in the battlefield.? One of the significant improvement over Nickel-Cadmium Battery was done with Nickel-Metal Hydride Battery by adding an additional resettable fuse to the battery system which disconnected in cases of over-charging and overheating, thus preventing any mishaps.Even after many improvements these batteries didn’t prove to be most efficient ones because of the following reasons:? Lead-acid Batteries were highly toxic both to humans and the surroundings. They caused kidney and brain damage and hearing impairment. Also containing Lead as its main constituents, it was very difficult to decompose in nature.? These batteries were also harmed by over-charging, which caused electrolysis in turn leading to internal explosion causing the battery to burn.? Proper disposal was a problem with Nickel-Cadmium Battery as well due to toxic components used for construction. They also suffered memory-effect losses.? Nickel-Metal Hydride Battery also faced problems of over-charging, which caused leakage of Hydrogen-gas, potentially rupturing the cell.Following is a performance comparison between the above three batteries:Table 1 Property Comparison between battery typesProperty Lead-Acid Nickel-Cadmium Nickel Metal HydrideCapacity 0.5 1.2 1.8Voltage 2V 1.2V 1.2VEnergy Density (W/Kg) 35 45 70Cycle Life 400 500 500Life (Years) 1 2 2Charging Time 8 hrs 1.5 hrs 4 hrsSelf-Discharge Rate (%/mo) 20% 30% 35%Safety Good Good GoodHigh Temperature Performance Good Good GoodCold Temp Charge (0 F) Good Fair FairCold Temp. Discharge (0 F) Good Good PoorLithium-ion Batteries Figure 2 Li-ion Battery Configuration A great leap of improvement over batteries was made with the development of Li-ion Batteries. These Lithium-ion Batteries proved to be significant for military usage due to the following reasons:? Li-ion batteries provide lightweight, high energy density power sources for a variety of devices.? Li+ rechargeable batteries have a self-discharge rate typically stated by manufacturers to be 1.5-2% per month.? Li-ion batteries contain less toxic metals than other types of batteries. Therefore safer for the environment.? Performance of manufactured batteries has improved over time. For example, from 1991 to 2005 the energy capacity per price of lithium ion batteries improved more than ten-fold, from 0.3 W·h per dollar to over 3 W·h per dollar. Figure 3 Battery Energy Density TrendsLithium-ion batteries also suffered problems related to overcharging. If overheated or overcharged, Li-ion batteries may suffer thermal runaway and cell rupture. In extreme cases this can lead to leakage, explosion or fire.Apart for minor drawbacks, continuous improvement has been done over Li-ion Batteries and it has showed significant advantages over other battery systems:Table 2 Li-ion Battery PropertiesProperties Li-acid Ni-Cd Ni-MH Li-ionCell Voltage (V) 2 12 12 36Specific Energy 1-60 20-55 1-80 3-100Specific Power <300 150-300 <200 100-1000Energy Density 25-60 25 70-100 80-200Power Density <0.6 0.125 1.5-4 0.4-2Maximum Cycles 200-7-- 500-1000 600-1000 3000Discharge Time Range >1 min 1min -8hr >1min 10s-1hrCost ($kWh) 125 600 540 600Cost ($kW) 200 600 1000 1100Efficiency (%) 75-90 75 81 99Lithium-ion Batteries had the following advantages over previously used batteries:? It was lesser sensitive to higher temperature, therefore improving the performance range of the same.? They did not have deposits every charge/discharge cycle and therefore these batteries had efficiency of approximately 99%.? To achieve any given voltage, as compared to other battery systems, Li-ion batteries required lesser cells in a series.Still a lot of improvements are been done on these batteries to improve its cost, one of its few drawbacks which costs military billions of expenditure cost.Present Research WorkA few of significant commercial advancements that are under work are as follows:? In November 2016, Yasunaga, a Japanese company, revealed that they had developed a special positive electrode surface treatment which would allow the battery to have more than twelve times the cycle life of conventional lithium-ion batteries. Batteries were tested to 60,000 to 102,400 cycles before falling to 70% of the original new capacity, compared to the conventional battery that would only do 5000 to 6000 cycles. This technology also showed 12% reduction in cell resistance. ? In March 2017, American Lithium Energy in California revealed plans for mass marketing of its branded Safe Core technology that was developed for use by the US Department of Defense, Department of Energy and national research labs. The technology was initially devoted to vehicle batteries that would not catch fire if damaged in a crash and led to bullet-safe batteries for troops: a fuse inside the cell, so when something is wrong inside, fuse will kick in and break the current before it reaches a critical temperature.Battery Physics ImprovementsThere is a widening gap between the need for power and the actual availability of that power when the soldier is in the Tier-1 environment, so portable power is an absolute requirement.They’re also a logistical nightmare. With soldiers needing so many batteries, keeping them in supply and keeping them recharged isn’t easy. Worse, there are so many different batteries that recharging them in the field raises compatibility issues. As per a report on the subject, military was using approximately 350-400 different batteries for various requirements.Today the average US soldier carries 20 pounds (9 kg) of batteries on a 72-hour mission. To help lighten the load, the US Army Research facility (CERDEC) has developed a military-grade Universal Battery Charger (UBC) to help soldiers in the field keep their electronics powered up. Figure 4 UBCDeveloped in the 1990s, currently, the Army Standard Battery Charger used by the US military is either a vehicle-mounted or a tabletop unit about the size of a suitcase.The new UBC is an improvement on its predecessor, being the size of a shoe box and weighing only 6 lb. (2.7 kg). It has a built-in solar panel for when no other energy source is available.The UBC is ruggedized and waterproof to survive being hauled over rough terrain in all weather conditions.As “universal” implies, the UBC can charge different kinds of batteries simultaneously. The UBC can charge eight batteries and two USB devices at once. The UBC is also “smart” in that it can “talk” to today’s batteries.Metal Air BatteriesThe lithium-air battery (Li-air) is a metal–air battery chemistry that uses oxidation of lithium at the anode and reduction of oxygen at the cathode to induce a current flow.Most of the current limits in Li-air battery development are at the cathode, which is also the source of its potential advantages. Incomplete discharge due to blockage of the porous carbon cathode with discharge product such as lithium peroxide (in aprotic designs) is the most serious. The effect of pore size and pore size distribution remains poorly understood.Atmospheric oxygen must be present at the cathode, but contaminants such as water vapor can damage it. In current cell designs, the charge overpotential is much higher than the discharge overpotential. Significant charge overpotential indicates the presence of secondary reactions. Thus, electric efficiency is only around 65%.Long-term battery operation requires chemical stability of all cell components. Current cell designs show poor resistance to oxidation by reaction products and intermediates. Many aqueous electrolytes are volatile and can evaporate over time. Stability is hampered in general by parasitic chemical reactions taking place for instance those involving reactive oxygen.The increase in Specific Energy and Energy Density with improvement in batteries is shown below in the graph: Figure 5 Energy Density BenchmarkBattery Road Map Figure 6 Battery RoadmapFuture TechnologiesThere are a few concepts that are under research and further working which are sure to work in exceptional ways:? Wearable Battery? Walking Gear and Sliding Bag? Gravity Light1. Wearable BatteryA common virus to develop improved materials for high performance, rechargeable lithium-ion batteries that could be woven into clothing, such as uniforms or ballistic vests that could provide power to a range of electronic equipment such that each pocket becomes a charging port.Development of new cathodes made from an iron-fluoride material that could soon produce lightweight and flexible batteries with minimal loss of power, performance, or chargeability compared to today’s rechargeable power sources. Figure 7 Wearable BatteryMIT scientists are developing a virus as a template for preparing lithium ion battery anodes and cathodes. The virus, called M13 bacteriophage, an outer coat of protein surrounding an inner core of genes. It infects bacteria and is harmless to people. Using M13 bacteriophage as a template is an example of green chemistry, an environmentally friendly method of producing the battery and these materials, should be less dangerous than those used in current lithium-ion batteries because they produce less heat, which reduces flammability risks.The Belcher Biomaterials group is in the beginning stages of testing and scaling up the virus-enabled battery materials, which includes powering unmanned aerial vehicles for surveillance operations. Making light-weight and long-lasting batteries that could result in rechargeable clothing would have several advantages for both military personnel and civilians. Figure 8 M13 Bacteriophage2. Walking Gear & Sliding BagThe harvester is a light-weight exoskeleton designed to generate electricity from the natural action of walking, in much the same way regenerative braking works in hybrid cars. With every stride, the Instrument’s on-board microprocessors analyze the wearer’s gait to determine precisely when to generate maximum power with the least amount of effort.Figure 9 Flowchart for Walking GearThe PowerWalk is designed to generate electricity from the natural action of walking, in much the same way regenerative braking works in hybrid cars. When we walk, our muscles perform ‘positive’ work to propel us forward. This work is done by the muscles around the ankles and hips.  Our muscles also do ‘negative’ work, acting as brakes to slow down our limbs or absorb impact. The muscles around the knees primarily perform this negative work. The PowerWalk harvests the energy generated by the knee joints during negative work (shown as shaded areas in the graph above), which not only assists the muscles with braking but also generates electricity without noticeably adding to the metabolic cost of the user.  Figure 10 Power Loss while walking In the PowerWalk’s high-efficiency system, a gearbox transmits the power produced to a generator which harvests energy during these regions of the gait. Then, state-of-the-art electronics are employed for power conversion and model-based, gait-phase-detection algorithms intelligently optimize energy harvesting to minimize work from leg muscles. This can reduce fatigue and metabolic effort, and extend the duration and effectiveness of the mission.This works on the electro-magnetic induction law: Figure 11 Electromagnetic InductionHere are the targets that the company aims to achieve by the quadrant:Table 3 Targets for Walking GearParameter Target (Q3 2017)Power (level at 5.0 km/h) 10 WPower (downhill 15% grade) 25 WPower (uphill 15% grade) 4 WSystem Weight 1.8 kgOutput Voltage* 10 – 32 VMax Output Current (into battery) 5AMax Output Current (into power manager) 2ACommunication Protocol SMBus v1.1Acoustic Noise < 40 dBA SPL @ 1mDoffing Time < 5 sTRL six-sevenSealing IP67 / 1m immersionConnectors Glenair Mighty Mouse Series 807? Gravity LightGravityLight is powered by the lift of a weight. As the weight falls it turns a gear train, driving the motor that powers the LEDs.GravityLight doesn't need batteries or sunlight and costs nothing to run. It takes seconds to lift the weight that powers GravityLight, creating 20 minutes of light on its descent. This generates about a tenth of a watt to power the onboard LED and two light LEDs. Together these produce a light more than 5 times brighter than a typical open-wick kerosene lamp.The Benefits of Gravity Light? Instant light, any time? No running costs? No sun or batteries needed? Robust and reliable  Figure  Gravity LightSummaryAfter researching we could concluding a few points regarding the rechargeable batteries with perspective with the army. There are various requirements that a battery system needs to follow to be able to perform well. There have been a few batteries used in the past but have been discontinued because of safety issues or lesser efficiency for longer run. Currently Lithium-ion battery is been used for the purpose.  Many research works are going on the same to improve it better and better to serve the purpose efficiently. A lot of research is also been done on Metal-air batteries and are expected soon to be serving the purpose. On the other hand, a lot of work is also being done on improving the way energy is being provided to the soldier, making the mode of energy more efficient in all terms such as cost, accessibility, etc.  References? U.S. Army's Ground Vehicle  Energy Storage - Laurence M. Toomey, Ph.D. Energy Storage Team Leader, TARDEC (January 29, 2014 )? "Virus-Enabled Synthesis and Assembly of Nanowires for Lithium Ion Battery Electrodes" - Science (print ISSN 0036-8075; online ISSN 1095-9203) is published by the American Association for the Advancement of Science