Technical progress with the advanced battery systems Nickel Metal Hydride (NiMH) and Lithium-Ion (Li-lon) is regarded as essential for the future of Hybrid Electric Vehicles (HEV). Power performance and energy efficiency are crucial for the fuel saving potential of these vehicles. Cost and life endurance are the key issues for their economical and ecological aspects. Modern NiMH sub-module concepts enable performance data of more than 1300 W/kg in terms of specific power and power densities of up to 2500 W/I. This allows for building highly efficient battery systems. New technical achievements have brought about considerable improvements in low temperature discharge capability, mainly by changes in the anode material composition. NiMH product lines used for current HEV passenger cars include two different design approaches : cylindrical shaped cells and prismatic multi-cell modules. A comparison of both shows advantages for either of them depending on the system integration into the vehicle. The Lithium-Ion battery system is regarded as an important option for the future of hybrid electric vehicles. The main advantage over NiMH batteries is the chance of drastic weight saving. With specific power data exceeding 2.000 W/kg and a specific energy of 80 Wh/kg modern systems are already showing off these advantages. Also advantages with respect to service life will be realised on a longer term. A more than 10 years life is the objective. The system reliability and potential misbalance of the cell stack is enhanced last but not least due to the high open circuit voltage of 3.6V reducing the number of cells by 2/3 compared to NiMH (OCV = 1.25V). High energy Li-Ion cells with specific energy content may become interesting for future vehicle electric supply systems at 14V system voltage level as well as a power source for special electric vehicles. With its potential for very high specific power, Li-lon will enable weight and volume reductions in automotive application up to 40% compared to NiMH. The system will also show a lower cost impact on the volatile raw material commodity price. At the current state, development activities in the industry focus on designing safety concept (on cell and battery level incl. electronic control strategy) and the calendar life time to comply with automotive specifications.
Advances in NiMH and Li lon batteries for full hybrids
Fortschritt auf dem Gebiet der NiMH- und Lithiumion-Batterien für Vollhybridfahrzeuge
2005
10 Seiten, 7 Bilder, 1 Tabelle
(nicht paginiert)
Conference paper
English
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