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Reprinted from COTS Journal, May 2002When lives depend on battery-powered devices, batteries must meet the key safety, capacity, weight and performance issues unique to military apps. By Mark Warner Marketing Manager for Government Programs Ultralife Batteries It is a common goal of the military to use COTS technology wherever possible. However some COTS components such as batteries aren’t designed to survive the harsh environmental demands of military applications. Batteries for the military call for special requirements that add cost to their development. Most military batteries hold a lot of energy and can be dangerous if not handled and used properly. Special handling is also required in the manufacturing of these batteries. At the top of the performance curve are lithium batteries, the most common non-rechargeable batteries used by the military. Because lithium reacts with water, the first stage of the manufacturing process requires a factory that is completely environmentally controlled. Battery cells are therefore assembled in a dry room, which is maintained at two percent or less relative humidity, 24 hours a day, seven days a week. Once the cells are sealed they can be further processed in normal room conditions. Special precautions for product handling and testing also have to be in place throughout the manufacturing process, and, unlike most consumer batteries, this type of production can be expensive.  While devices like cellular phones operate on one 4.2-Volt battery, most military devices operate at between six and 24 Volts.Military devices also require a lot more power than cellular phones, especially devices like satellite communications, weapon sighting and targeting systems. These devices require amps of power versus the milliamps needed in consumer applications. Meeting the Demand with Safer Batteries Demands for portable power for military applications in the field require a special breed of high-performance batteries. Over the last twenty years lithium/sulfur dioxide (Li/SO2) primary (nonrechargeable) battery technology met the needs for many of these applications. That technology serves the military well and it performs at the wide temperature ranges currently required. But Li/SO2hasn’t been without problems and challenges. Some of the challenges facing battery manufacturers who supply the military are safety, weight, capacity and cost. Battery safety tops the list of concerns in military organizations. Battery cells in today’s Li/SO2 batteries used in military portable devices use pressurized cylindrical cans. Though many of these are rectangular batteries, the cells inside are cylindrical. These cans pose a hazard if abused. That’s of special concern to the soldier, because these batteries can explode when punctured. Among the steps battery manufacturers are taking to make batteries safer and have more energy density is incorporating non-pressurized, non-toxic, lithium/manganese dioxide (Li/MnO2) cells into the existing military battery cases. Li/MnO2 cells are built with a solid lithium metal anode, solid MnO2 cathode and liquid electrolyte. Hazardous gasses venting from a battery are also a serious safety issue. The U.S. Army has replaced the Li/SO2 cells in most electro-optical type devices, such as night vision goggles, with Li/MnO2 cells. That avoids the possibility of the battery venting corrosive and noxious sulfur dioxide gas into the face of the device user in the event of short circuit or overheating conditions. Another safety improvement now being implemented into Li/MnO2 cells is a fusible safety separator. This is a separator between the anode and cathode of the cell. It shuts the battery down (reduces ion-flow) when overheated, either due to short circuit or over-current conditions, which prevents venting of electrolyte. Using this type of separator is not possible with Li/SO2 cells. More Capacity Means Longer Missions  As more portable electronic devices are fielded, the demand for longer battery life increases. Designers regularly ask battery manufacturers to make batteries lighter, thinner and longer lasting. This challenge is being addressed by the move toward the Li/MnO2 system, which has higher capacity than Li/SO2, and by using the entire battery cavity. An example of this is the U.S. Army’s Li/SO2 BA-5590/U battery; the most widely used portable lithium battery in the Defense Department inventory. Its primary use is in the SINCGARS (single-channel ground and airborne radio system), but it is also used in over 60 other portable communications devices and weapons systems.The Li/MnO2 version of this battery, the BA-5390/U, provides up to 50 percent more capacity and operating time than the Li/SO2 battery it replaces (Figure 2). Efforts are underway to develop and manufacture Li/MnO2 cells into a rectangular pouch package, which allows full use of a rectangular battery cavity. These (BA-7590) batteries will have capacities at or above 12 Amphours. Naturally, the weight of the batteries is critical, especially to a soldier who must carry them all day. Every ounce counts. The implementation of lithium batteries significantly reduced the weight when compared to the battery technologies preceding it, such as alkaline and carbon-zinc. Now the challenge for battery manufacturers is to take the next step in weight reduction.  One approach is to increase the energy density in existing battery compartments. The introduction of Li/MnO2 does just that. Though the weight of this battery may be slightly higher than a Li/SO2 battery, the Li/MnO2 battery provides 30 to 50 percent more energy, enabling it to last longer throughout the mission. The demand for longer running, lighter, safer and thinner batteries are some of the challenges facing battery manufacturers in programs such as the U.S. Army’s Land Warrior system (Figure 3).Another market that needs lightweight batteries is the Aerospace industry. Most of the applications in this market, such as satellites and reusable launch vehicles, require rechargeable technology. Several battery manufacturers are developing and building batteries for these applications. In such applications, every pound saved in batteries represents thousands of dollars in added payload. Some of the particular challenges they face are the extreme conditions of space, such as temperature. Battery manufacturers are addressing these challenges through the continued development and improvement of lithium-ion polymer rechargeable cells and batteries. Lithium-ion polymer technology has a higher specific energy, as measured in Watt-hours per kilogram, than other rechargeable chemistries such as liquid electrolyte lithium-ion technology. The development of complicated charge control electronics for large, highvoltage, multi-cell batteries is yet another challenge. Efforts to improve the temperature performance of those electronics are similar to those of the primary batteries. The efforts include continued research and development on electrolyte and continuous development and improvement of the cell packaging. For the development of control electronics many battery manufacturers are partnering with battery electronics designers and manufacturers to create custom circuitry to meet specific application requirements. Reducing Cost and Improving Performance Not only do battery manufacturers need to make batteries safer, lighter, smaller, more powerful and able to be stored for years, they must also make these batteries cost effective. This is a significant challenge, especially as the electronic devices become “smart,” the need for a smarter battery is on the rise. Examples of this are the increasing need for state-of-charge indicators and battery-to-device “Smart Bus” communications. For example, the latest version of the Ultralife Batteries Land Warrior LM11 battery uses the SmBus 1.1 communications protocol. Though these smart electronics add to the cost of the battery, the value of the battery is increased and the lifecycle cost is improved. This is because with stateof- charge indicators and smart communications the user knows how much energy is left in the battery and it can be used completely. Production volume factors into reducing the cost of batteries as well. As more U.S. military equipment is used world wide, the need for batteries increases, and as the demand and quantities increase the price decreases. Other ways to reduce the cost of military batteries is to increase quantities via usage in commercial products that require long storage capability, high power on demand and the ability to operate at wide temperature ranges. Applications such as sonobuoys, emergency location transmitters and heart defibrillators are a few which require this type of battery. Military organizations around the world have begun to realize the benefits and cost savings of using rechargeable technology. This technology is especially desired in training. In the past, rechargeable batteries have had low energy density when compared to primary technology, and they were heavy. Battery manufacturers have made considerable improvements in both energy density and weight in the last few years by the development and improvement of lithium-ion and lithium polymer rechargeable technology. As this technology continues to improve, it may be considered for missions other than training. Recharging these in the field is an issue that still needs refinement. Manufacturing batteries for the military has its challenges: Continuous quality inspections and delivery deadlines, pressure to reduce cost and rigorous operating conditions. However, historically, the military has driven cuttingedge technology. Overlooked Batteries Batteries are often overlooked, under-appreciated and are often an afterthought design. Unfortunately, in some instances design engineers find that their device needs too much power with too little room available for the battery. High-performance batteries for military applications are an essential part of today’s high-tech military. Batteries are a vital component contributing to the technological advantage that the U.S. military has today. Development programs underway for fuel cells and micro-generators hope to someday replace batteries, but that’s not likely to happen for many years. It’s probable that rechargeable batteries will be an important part of fuel cell technology. Most likely, hybrid systems will emerge as they have with electric vehicles that use both rechargeable batteries and gasoline engines. Batteries are a fact of life in today’s military and they won’t be going away anytime soon. |
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