Advanced primary portable power requirements in next-generation military applications

Story

December 09, 2010

Eric Lind

Contour Energy Systems

A new generation of carbon fluoride batteries is stepping onto the front lines to power soldier-carried and unmanned aerial applications, thanks to much-increased volumetric and gravimetric energy densities.

The ideal battery would deliver ample power for the application, provide long shelf and service lives, withstand environmental extremes, and be safe to handle and use. The problem is the trade-offs required to achieve these different desirable operating characteristics. Delivering ample power in next-generation military applications requires higher energy and power densities than currently available in the batteries typically used in consumer electronics. Some military batteries, for example, employ toxic or hazardous chemicals to achieve a higher energy density, making them unsuitable for certain applications. Others may be able to deliver safe operation over a long service life, but only for low-amperage applications.

The following discussion examines the issue of energy density, both gravimetric and volumetric, and how existing primary lithium batteries stack up in next-generation military applications for soldiers and unmanned aircraft systems. The exclusive focus here on primary batteries – including sulfur dioxide, manganese dioxide, polycarbon monofluoride, and carbon fluoride – is not meant to diminish the growing importance of rechargeable batteries; rather, it is to limit the scope of the topic to one that can be covered in sufficient depth.

Lightening the load

The burden on today’s soldier to carry an increasing amount of high-tech equipment, such as advanced soldier systems, next-generation radios, and imaging and sensing systems, is great and growing. Depending on the mission, the total weight of a soldier’s gear ranges from 28 to more than 70 kilograms (kg), or 60 to more than 130 pounds. The batteries needed to power the electronic equipment can often constitute approximately 15 to 30 percent of the total load. And because the batteries must last an entire mission, soldiers often need to carry spares (or a charging system when rechargeable batteries are used).

A similar situation exists for a small or micro Unmanned Aerial System (UAS) where the battery needs to power the motor, controls, radio, and imaging equipment. As with the soldier, the battery must last the full duration of the mission. The allowable weight for the battery varies by the type of vehicle, of course, but is normally set to enable mission durations of between 30 minutes and two hours with existing types of batteries.

The solution to these weight and battery duration limitations is to use a lighter battery. By doubling the energy density, the weight of the battery pack needed for a mission of given duration can be cut in half. Alternatively, the same size and weight in battery pack(s) with double the energy density could double any mission’s duration. This would be particularly valuable in remote reconnaissance and surveillance, in addition to target acquisition missions, where being aloft longer could make the difference between success and failure.

Doubling the energy density is, of course, far easier said than done, which is why this goal has remained elusive for the two most popular types of Commercial Off-the-Shelf batteries used in military applications today: Lithium/Sulfur Dioxide (Li/SO2) and Lithium/Manganese Dioxide (Li/MnO2). While these batteries have similar energy densities of 200-250 Watt-hours/kilogram (Wh/kg), their volumetric energy densities are different at 350-450 Watt-hours/liter (Wh/l) and 500-650 Wh/l, respectively. Note that because energy densities vary with the different form factors used for different applications, the ranges used here depict typical values for cells in applications requiring moderate to high rates of amperage.

In applications where the weight is a significant design consideration, the similar gravimetric energy densities shared by sulfur dioxide and manganese dioxide batteries gives neither an advantage. But manganese dioxide batteries are increasingly preferred owing to other reasons, including their enhanced safety over pressurized sulfur dioxide batteries. And in applications where the space available for the battery is limited, the manganese dioxide battery has an even greater advantage with its 40 percent improvement in volumetric energy density.

In a BA-5X90/U battery pack, for example, manganese dioxide’s increased volumetric energy density delivers about 11.5 Amp-hours (Ah) of service compared to about 7.5 Ah with sulfur dioxide. But the problem remains: the 11.5 Ah battery in this example is significantly heavier than the 7.5 Ah battery (at about 1.35 kg or 48 ounces compared to 1.0 kg or 36 ounces) because the gravimetric energy densities of both are similar. Table 1 compares and contrasts sulfur dioxide and manganese dioxide batteries, in addition to polycarbon monofluoride and carbon fluoride batteries, which will be discussed in the following section. (The table additionally shows Thionyl Chloride (Li/SOCI2) batteries, also used in some military applications.)

Table 1: A comparison of the four types of batteries covered in this discussion – sulfur dioxide, manganese dioxide, polycarbon monofluoride, and carbon fluoride – in addition to Lithium/Thionyl Chloride (Li/SOCl2), which is also used in some military applications.

(Click graphic to zoom by 1.9x)

Advanced carbon fluoride batteries

Lithium/Polycarbon Monofluoride or Li/(CF)n batteries have been around since the 1970s and were traditionally used for high-energy, low-power applications, such as memory backup systems. In the never-ending quest for a better battery, however, a new technology has emerged as an off-shoot of traditional Li/(CF)n batteries: the Lithium/Carbon Fluoride (Li/CFx) battery. Carbon fluoride batteries maintain the benefits of high energy and power densities, wide operating temperature range and long shelf life found in sulfur dioxide batteries, while employing a solid cathode (with no heavy metals or other toxic materials) to eliminate the safety and environmental concerns (see again Table 1). In addition, the carbon fluoride battery possesses none of the operational problems exhibited by some other batteries, such as passivation.

Most important is the carbon fluoride battery’s higher gravimetric and volumetric energy densities of >600 Wh/kg and 700-1000 Wh/l, respectively, as compared to the other batteries discussed herein. As shown in Figure 1, the gravimetric and volumetric energy density improvements may be even greater in some configurations than the conservative estimates provided earlier.

Figure 1: This comparison of gravimetric and volumetric energy densities for different types of batteries (in addition to alkaline) demonstrates the advantage that carbon fluoride provides.

(Click graphic to zoom by 1.5x)

In BA-5X90/U battery packs commonly used in military radios and other systems, a carbon fluoride version of this popular battery should be able to more than double the operating time of this battery – while weighing about the same as a traditional sulfur dioxide version of this product.

An additional major advantage of the carbon fluoride battery is its ability to exceed manganese dioxide and polycarbon monofluoride batteries, among others, in both power density and maximum safe current draw. The laboratory test results in Figure 2 demonstrated up to an 8x improvement in high-current applications and a nearly 2x improvement in low-current applications. This makes the carbon fluoride battery particularly well suited for applications that require high sustained or pulse currents.

Figure 2: These test results of available capacity at three different rates of discharge (to 2.0 V) for three different 2016 size coin cells quantify the carbon fluoride battery’s improvements in power density at low, moderate, and high discharge rates.

(Click graphic to zoom by 1.6x)

Like the other lithium-based primary batteries, carbon fluoride batteries can be packaged in a variety of form factors, including coin, cell, film, or prismatic. This enables carbon fluoride batteries to accommodate both standard sizes and customized packs (which combine cells in series and/or in parallel to satisfy specific needs for operation in the typical military range of 6 to 30 V).

Additional “weighty” design considerations

How does the carbon fluoride battery stack up against the other battery types in other respects? As mentioned, Table 1 lists the details important in most applications. The use of only solid materials and a nontoxic electrolyte makes the carbon fluoride batteries safer than sulfur dioxide batteries, especially in those applications drawing a high, sustained current where sulfur dioxide batteries might overheat and fail. Solid materials eliminate the need for pressurized cans that can vent or leak corrosive or noxious gases, making carbon fluoride batteries safe even when mishandled or damaged or when subjected to a short-circuit condition. This is obviously of particular concern for the soldier, but even the batteries used in weapons and unmanned vehicles must still be handled during transport and replacement.

Operating temperature range is not a factor for the soldier, but can be for weapon and surveillance systems. And here, too, the carbon fluoride battery technology has made improvements over both manganese dioxide and sulfur dioxide. Indeed, the operating temperature range of carbon fluoride batteries such as Contour Energy Systems’ advanced Fluorinetic batteries far exceeds the requirements of today’s military applications.

Not only that, with their higher gravimetric and volumetric energy densities and other attributes described in this discussion, Contour Energy Systems’ carbon fluoride Fluorinetic batteries provide a longer service life than both manganese dioxide and sulfur dioxide batteries. Just as significantly, these battery systems also afford a longer shelf life – up to 50 percent longer than either manganese dioxide or sulfur dioxide batteries.

Eric Lind is VP of Business Development at Contour Energy Systems. Before joining Contour Energy Systems, he was VP/General Manager of Ultralife Corporation’s Commercial Business. Prior to that, Eric was the Director of Business Development in ConocoPhillips’ Emerging Technology group. He started his career at Duracell, where he spent eight years in various engineering and management positions. Eric is a graduate of Duke University with a double major in Biomedical Engineering and Electrical Engineering, and holds an MBA from the University of Connecticut with a concentration in Marketing. He can be contacted at [email protected].

Contour Energy Systems 626-620-0660 www.contourenergy.com