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. For the plug-in hybrid application the Toyota Prius is also being used as the test bed. The bipolar battery consists of six modules containing 7.5 kWh of energy storage, and gives the vehicle an all-electric range of approximately 25 miles.
Through programs with the Department of Energy and Sandia National Laboratories, and collaborations with utility companies, EEI has successfully built high voltage power and energy battery systems and integrated them with existing UPS and inverter systems. EEI's unique safety/control system allows relatively seamless integration with existing applications. By monitoring cell pressures and module temperatures, the individual battery strings within systems containing multiple parallel strings can be controlled and dropped in and out as necessary, resulting in safe operation and limited down time. EEI has already developed and demonstrated a 500 V / 100 kVA inverter system and a high energy 600 V, 35 kWh, 20 kW UPS system. Plans are underway to build and integrate 600 V, 100-200 kWh, 100 kW systems, with the intention of using multiple systems in parallel to provide MW discharge rates.
In this paper, EEI will discuss the different configurations and design features of automotive and utility battery systems, of which EEI is in the process of establishing high volume manufacturing capabilities based on the bipolar nickel metal hydride design.