by Jack Rosebro
|Nissan has been running extended field testing of its new Li-ion batteries in a fleet of Tino hybrids in the US. Click to enlarge.|
Nissan Motor has been field-testing a fleet of 20 Tino hybrids equipped with its next-generation Li-ion battery packs for the last three years in the US, with up to 240,000 km (150,000 miles) accumulated on one of the vehicles. Nissan made a limited introduction of the Tino hybrid in Japan in 2000.
Toshio Hirota of Nissan outlined the program and provided some insight into the automaker’s lithium-ion battery research in a presentation at the 2008 SAE Hybrid Vehicle Technology Symposium this week in San Diego.
Nissan started R&D on Li-ion batteries for automobiles in 1992, and introduced a variety of EV and HEVs with Li-ion packs from 1997 through 2000. During that period, Nissan switched from using a cylindrical battery format to the laminated type represented in the testing.
Nissan Motor, NEC and NEC TOKIN began developing Li-ion rechargeable batteries for automotive applications in about 2000. NEC group had been working with Fuji Heavy Industries Ltd. to develop lithium-ion automotive batteries through a joint-venture: NEC Lamilion Energy Ltd. This partnership was dissolved in March 2006 when Fuji Heavy, the maker of Subaru vehicles, moved under Toyota’s umbrella.
In 2007, Nissan Motor, NEC Corporation, and NEC TOKIN Corporation, signed an agreement to establish a joint-venture company—Automotive Energy Supply Corporation (AESC)—to develop and market lithium-ion batteries for wide-scale automotive application by 2009, including applications such as hybrids, plug-in hybrids, hydrogen fuel cell vehicles and electric vehicles. (Earlier post.)
The real-world results of the Li-ion packs has proven to be very close to predictive simulations. The prototype battery packs have also proven to be more efficient than comparable nickel-metal hydride (NiMH) packs.
Of particular note is the charge and discharge power restriction frequency, as expressed in a percentage. This metric refers to the amount of time that the powertrain computer requests a given amount of current from the battery pack, but is instead provided with a somewhat lower amount to protect the pack. Hirota reported that the frequency of such events was 44.2% for NiMH, and 2.2% for Li-Ion.
|Charge/Discharge Efficiency of Nissan Li-ion vs. NiMH|
|SOC Range %||30-85||39-80|
|Average Effective Power kW||4.28||4.25|
|Battery Temperature deg. C||49||52|
|Ah Efficiency %||98.8||90.7|
|Wh Efficiency %||95.1||83.4|
|Charge/Discharge Power Restriction Frequency %||2.2||44.2|
Although Nissan is looking at all lithium-ion chemistries, the company currently favors a manganese anode with a spinel structure, enabling the battery to remain stable even under abnormal thermal conditions. The laminated cell structure enables higher cooling performance, and enables a more flexible layout with a thin structure.
According to Hirota, Nissan’s goal is to reduce the CO2 output of new vehicles to 70% of 2000 levels by 2050, and has a long-term focus on electric vehicles and fuel cell vehicles powered by hydrogen from renewable sources. The company also sees plug-in hybrids as a potential mechanism to reduce CO2 output in the shorter term.
However, Hirota noted, the company has concerns about PHEVs, including battery cost, market demand, and the CO2 intensity of electricity.