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The AFRL, Electrochemistry and Thermal Sciences Branch has evaluated numerous aircraft battery designs and chemistries since the 1960s. Recent experiments on advanced battery chemistries have shown poor performance at ultra low temperatures below −20° C. Aircraft battery designs stress low weight and volume and maximum capacity. One design concept uses lower capacity cells in a series parallel configuration to reduce overall battery resistance and should also improve ultra low temperature performance. Our organization has begun experiments with series-parallel cell designs to evaluate the concept and to solve low temperature performance issues. Progress, observations on the effect of different chemistries, and the impact on aircraft battery characteristics are discussed.

The Air Force Research Laboratory (AFRL), Energy Storage and Thermal Sciences (PRPS) Branch has been developing nickel-metal hydride (Ni-MH) rechargeable batteries as an environmental replacement for existing valve regulated lead-acid (VRLA) and vented/sealed nickel-cadmium (VNC/SNC) batteries since 1995 and has evaluated cylindrical, prismatic and bipolar designs for this application. Recent advances in cell chemistry and design have resulted in a significant improvement in ultra low temperature performance indicating the suitability of these batteries for military aircraft applications over the temperature range from -40 °C to +65 °C. Results of the latest in-house tests of developments in bipolar and prismatic cell and battery designs indicate the current prismatic cell formulations are limited to temperatures above -25 °C while those used in bipolar designs operate over the full military aircraft temperature regime.

Electro Energy, Inc. (EEI) has developed a bipolar Ni-MH wafer cell design that has the advantages of reduced weight, with increased capacity, high power and low temperature capabilities over conventional Ni-MH and competing technologies. These advantages make the EEI bipolar Ni-MH the battery of choice to replace the present F16/F18 and other military aircraft batteries. EEI's present F-16 battery has 10% reduced weight in the same volume as the existing lead-acid battery, while having 2½ times the capacity. EEI's design of parallel stacks of thin wafer cells results in increased electrode surface area leading to improved high-rate and low temperature capability. The design has shown to be capable of operating at the Air Force minimum temperature requirement of -40°C. This has been achieved by optimizing each of the following variables: 1) metal-hydride alloy; 2) electrode capacity and surface area relationship; and 3) electrolyte composition. Supported by U.S.

The Air Force Research Laboratory, Energy Storage and Thermal Sciences Branch conducted performance tests of 22 Ah nickel-metal hydride (Ni-MH) cell packs containing four prismatic sealed design cells over the operational temperature range for a modern fighter aircraft at the C/2, C and 2C rates. Capacity tests indicated satisfactory performance at the C/2 and C rates down to -30 °C and at the 2C rate down to -20 °C. Self discharge tests at elevated temperatures up to +60 °C were also conducted. Test results will be presented and implications for further development of an environmental main aircraft battery will be discussed.

Electro Energy Inc. has been developing their wafer cell bipolar nickel-metal hydride battery for aircraft applications. The design consists of individual sealed wafer cells that are stacked in series to make a multi-cell, multi voltage battery pack. Each individual wafer cell consists of one positive electrode, a separator material and a negative electrode contained in an outer envelope so that the faces of the wafer cell represent the positive and negative contact of the cell. The perimeter of the cell is sealed to contain battery gases and electrolyte, making a fully sealed cell. To construct a multi-cell battery, identical cells are stacked one on top of the other, such that, the positive face of one cell makes contact with the negative face of an adjacent cell to make a series connection. Multi-cell stacks are held in compression for physical integrity and to ensure good cell-to-cell contact.

As the maintenance and disposal costs of aircraft batteries have risen, it has become critical to increase battery lifetime and to reduce maintenance cycles. This has led to the development of charging techniques designed to increase battery life while continuing to satisfy battery performance requirements. However, the cost of battery chargers accounts for 60% to 80% of the battery/charger system cost. AFRL/PRPB has initiated an in-house project to evaluate F-16 batteries using the existing F-16 charger. The objective is to determine which batteries can pass all F-16 performance and lifetime requirements using this charger. Several batteries were procured from several sources and two F-16 chargers are on loan to us from Sacramento/ALC. Depending on the outcome of this phase the project may be extended to include other aircraft and other chemistries such as Nickel-Metal Hydride and Lithium-Ion. Results to date and future plans will be discussed in this paper.

The USAF in conjunction with NASA and the Jet Propulsion Laboratory established the DoD/NASA joint program to competitively develop high power, lithium ion battery technology and to establish North American domestic sources for lithium ion batteries. The program was initiated in FY97 to meet DoD and NASA requirements not addressed by commercial battery developments. Four contracts were awarded for cylindrical and prismatic cell and battery systems development. Technical and program management advisory groups were established to coordinate program management and to verify and validate test results from individual contractors. Specific applications, contract deliverable items and the overall schedule are presented.

The development of new environmentally friendly commercial batteries that offer rechargeable alternatives to lead-acid and Ni-Cd vented batteries has resulted in consideration of these new batteries for military aircraft applications. Existing vented batteries must be replaced with sealed, maintenance free or reduced maintenance batteries to meet USAF operational requirements and environmental policy guidance. Viable near term candidates for these replacements are the SLA, AMFABS, Ni-MH and the Lithium-ion batteries. The status of the technology and the development programs to implement these batteries along with the operational aircraft requirements are discussed.