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Electro Energy Inc.'s (EEI's) patented bipolar nickel-metal hydride battery design, based on flat wafer cells, has resulted in high power and energy densities. This design approach leads to increased capacity at a reduced weight and volume, when compared to other rechargeable batteries and energy storage devices. These advantages make the bipolar NiMH a logical choice for Army Silent Watch applications, where it is essential to maximize energy and minimize weight and volume. Through programs with Army Cecom EEI has successfully built a high energy battery system that would replace existing lead acid batteries and provide silent watch operation for an extended period of time. In addition, the bipolar Silent Watch battery offers reduced volume and weight over fuel cells considered for this application. EEI's internal safety/control system allows the battery to serve as a drop-in replacement for many applications requiring silent watch operation.

Electro Energy Inc. (EEI) has been developing its patented bipolar version of nickel metal hydride rechargeable batteries since the company was founded in 1992. The design of the battery is based on flat wafer cells, resulting in high power and energy densities, and leading to reduced weight and costs as well as increased performance over existing rechargeable battery technologies and other competing energy storage devices. Using this design approach, Electro Energy Inc. is developing and demonstrating batteries for multiple transportation applications including electric scooters, peaking batteries for hybrid electric vehicles, and high energy batteries for plug-in hybrids and various configurations of electric buses. For the hybrid peaking battery application the Toyota Prius was used as the test bed. The EEI bipolar battery is approximately 20% smaller in volume and is predicted to be more than 25% less costly than the OEM Prius NiMH battery.

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.

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 Nickel Metal Hydride Battery system has emerged as the battery of choice for portable computers, cell phones and other small electronic applications. It also is a leading candidate to serve as the energy storage source for electric and hybrid electric vehicles. The Nickel Metal Hydride battery eliminates the use of highly toxic chemicals which is a major consideration for environmental issues. The battery also exhibits higher energy density than Lead-Acid and Nickel-Cadmium batteries along with excellent power capabilities. These features make this battery a viable candidate for aircraft applications and that is the subject of this presentation.

Electro Energy, Inc. (EEI) is developing high power, long life, bipolar nickel-metal hydride batteries for aerospace applications. Bipolar nickel-metal hydride designs allow for high energy and high power designs with a 25 percent reduction in both weight and volume as compared to prismatic and/or cylindrical Ni-MH designs. Utilizing a sealed wafer cell design Electro Energy has demonstrated a 1.2 kW/kg power capability. Prototype designs have achieved 70 Wh/kg. Designs studies show 80 Wh/kg are achievable with EEI’s state-of-the-art technology. The sealed wafer-cell is the building block for EEI’s high power and high voltage bipolar batteries making the assembly easy and significantly lower in cost. Satellite and aircraft batteries are being developed which provide high power and long life. Sealed cells now show excellent rate capability and life. Cells tested in a low earth orbit (LEO) cycle have reached 9,000 cycles and continue on test.

An account of the work at Electro Energy, Inc. involving the development of a battery for NASA's Crew Rescue Vehicle (CRV) is given. Test data is presented both at the sub-stack level (6V) as well as the full module level (30 V). Based on these results, a design for the full-sized battery is described along with improvements at the cell level intended to enhance cycle life.