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Energy storage devices are needed for applications requiring very high power over short periods of time. Such devices have various military (rail guns, electromagnetic launchers, and DEW) and commercial applications, such as hybrid electric vehicles, vehicle starting (SLI), and utility peak shaving. The storage and delivery of high levels of burst power can be achieved with a capacitor, flywheel, or rechargeable battery. In order to reduce the weight and volume of many systems they must contain advanced state-of-the-art electrochemical or electromechanical power sources. There is an opportunity and a need to develop energy storage devices that have improved high power characteristics compared to existing ultra capacitors, flywheels or rechargeable batteries. Electro Energy, Inc. has been engaged in the development of bipolar nickel metal hydride batteries which may fulfill the requirements of some of these applications. This paper describes a module rated at 300 V (255 cells) / 6 Ah.

The increasingly wide range of small devices that consume stored electrical energy, has placed additional demands for secondary batteries which have improved power/energy, while retaining long cycle life. An additional facet to the demands are an increasingly blurred distinction between batteries and the devices that use them. This is especially true of emerging microelectonics, particularly those which are intended to be autonomous; i.e. those which have their own power supply. Batteries must have minimal volume, while being able to deliver pulses of power that can last from ms – seconds. Additionally, they must often absorb recharge at high rates. Electrode and cell designs must be altered, to minimize cell degradation under the strenuous demands of miniature electronics. We report design concepts for accomplishing these goals, and the factors which affect the life of two types of battery designs under pulsed charge and discharge.

EEI bipolar nickel metal hydride batteries and cells were tested under various conditions relevant to consumer and aerospace pulse power applications, with differing power and discharge pulse time requirements. A generic hybrid vehicle specification required that a full scale battery obtain 300,000 life cycles, while being able to deliver 25 kW discharge power after 18 seconds and 30 kW recharge power after 2 seconds. This corresponds to 15 years of normal use. Using this testing procedure, over 300,000 life cycles were obtained (using 25 Wh energy swings, scaled) on single full-capacity cells, with less than 10-15% pulse power capability loss measured. The projected full-sized battery mass was 40 kg and volume was 20 L. Testing of selected cells is continuing. Another test related to an automotive application demonstrated that a 6 Ah cell starting at 50% SOC was capable of being discharged at 200 A for 10 seconds (33C), with an end voltage of 0.945 V.

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.

Most aircraft in the U. S. Air Force inventory currently use vented nickel-cadmium (Ni-Cd) batteries for the main aircraft d.c. electrical power system and emergency power as well as other functions such as powering lights and instruments prior to engine starting/ignition. The major concerns of todays users are the high maintenance requirements, low reliability of vented NiCd battery systems and lack of a built-intest capability to check the battery state of health prior to flight. This paper will summarize efforts by the Wright Research and Development Center to develop maintenance free battery technologies for current and future aircraft applications.