Military: Batteries and Fuel Cells C Cremers, J Tu ¨ bke, and M Krausa, Fraunhofer-Institute for Chemical Technology, Pfinztal, Germany & 2009 Elsevier B.V. All rights reserved. Introduction In order to ensure their own leadership capability, sustainability, supportability, mobility, or survivability, modern armed forces are becoming increasingly depen- dent upon having a reliable supply of electrical energy. Consequently, electrochemical power sources are be- coming increasingly important as a means to guarantee this reliable power supply. As this concerns quite a broad field of applications, the potential solutions using elec- trochemical power sources are also quite different. This article focuses on one specific sector, that of portable applications. In fact, most nonportable applications such as stationary power supply for military bases, in the form of power generation or backup power, or mobile power supply for traction of military land, sea, or air vehicles are not very different from corresponding civil appli- cations, so the reader should have a fir st insight into these topics by reading chapters related to civil applications. Still the portable applications discussed here cover a broad range of energy and power demands star ting from a few watts over long periods of time for remote sensors to about 1 kW for portable rechargers for batteries used by entire squads. Also, the duration over which the electrical energy needs to be supplied varies and, therefore, the required energy content or density of the electrochemical power source also varies. Finally, in many applications, the power demands vary with time so that no single type of power source is fully suitable but hybrid solutions combining different types of power sources will be required. Such hybrid solutions may end up in energy networks worn by the soldier, allowing harvesting of energy from any power source that might be available and to dedicate power to whichever appli- ance is in need of it. Batteries General Considerations Batteries are still the most important source of portable electric power in military applications and these are ex- pected to continue to play an important role in future power supply scenarios. Today, quite a broad range of batteries are used in the military sector as can be seen from the fact that the generic standard for batteries in the United Kingdom DEF STAN 61-21 currently has about 50 supplements describing the different batteries used in the UK army. In part, this is due to the fact that each appliance such as radio, night sight, and g lobal positioning system (GPS) device has its own battery. However, certain trends can be found. One important trend is an increasing use of lithium- based technology for both primary and secondary bat- teries. For example, the most used type of primary battery in the US Army today, the BA-5590, is a lithium–sulfur dioxide battery. Alternative primary battery technologies comprise lithium–manganese dioxide and lithium–thionyl chloride. In the field of rechargeable batteries, nickel– metal hydride batteries are currently being replaced by lithium-ion batteries. Another important trend is a greater use of secondary batteries. This w ill become necessary as the increasing demand for electrical energy causes severe logistic problems if only primary batteries are used to fulfill the demand. Further on, rechargeable batteries offer a higher flexibility as part of hybrid systems or energy networks, as will be shown later. An exce ption to this trend toward secon dary batteries are metal–air batteries, which are increasingly used for special applications demanding a long-term supply of energy at lower power densities where they compete with small fuel cells. As with all military equipment, batteries for military applications need to be able to operate under quite harsh conditions. So usually temperature endurance from À 40 to þ 701C, high humidity resistance, and resistance against shock and vibrations are required. A further constraint is the required ability to operate at high alti- tudes up to at least 2500 m. For most primary and sec- ondary batteries, this is not an issue but all air-consuming types of power sources such as fuel cells or air–metal batteries are likely to suffer from the reduced oxygen partial pressure at these conditions. Common Military Primary Batteries For the most part, the batteries used during combat op- erations are primary batteries. Although primary bat- teries offer the highest capacity, the problem is that they are often replaced after each mission, even thoug h many of those discarded batteries would still have had sufficient capacity. This results in high battery usage costs, which could be lowered by a built-in state of charge indicator or the usage of secondary (rechargeable) batteries. There are about 13 different types of lithium batteries, which are the most used type of military primary 13 . Military: Batteries and Fuel Cells C Cremers, J Tu ¨ bke, and M Krausa, Fraunhofer-Institute for Chemical Technology, Pfinztal,. such as fuel cells or air–metal batteries are likely to suffer from the reduced oxygen partial pressure at these conditions. Common Military Primary Batteries For the most part, the batteries. secondary batteries. This w ill become necessary as the increasing demand for electrical energy causes severe logistic problems if only primary batteries are used to fulfill the demand. Further