|The battery pack of the i MIEV. Click to enlarge.|
At the Advanced Automotive Battery Conference and Symposium 2008 in Tampa, Florida (12-16 May), Takuha Miyashita from Mitsubishi described the characteristics of the lithium-ion battery pack that Mitsubishi, in partnership with GS Yuasa, developed for the i MiEV (earlier post).
The i MiEV is powered by a compact 47 kW motor that develops 180 Nm (133 lb-ft) of torque and a 330V, 16 kWh lithium-ion battery pack. Top speed is 130 kph (81 mph), with a range of up to 160 km (100 miles) under Japanese 10-15 cycle driving conditions.
GS Yuasa Corporation, Mitsubishi Corporation (MC) and Mitsubishi Motors Corporation (MMC) launched a joint venture—Lithium Energy Japan—last December to manufacture large-capacity and high-performance lithium-ion batteries. (Earlier post.)
Battery-maker GS Yuasa is the majority shareholder with 51%; MC holds 34% and MMC holds the remaining 15%. Initial production is targeted at 200,000 cells in fiscal year 2009.
The 16 kWh i MiEV battery pack is installed under the base floor. The pack consists of 22 cell modules connected in series at the nominal voltage of 330 V—the high voltage helps deliver high power. There are two types of modules to enable efficient use of the limited space. Two 4-cell modules are vertically placed at the center of the pack and 10 8-cell modules are placed horizontally.
|Specifications of the i MiEV Li-Ion Cell|
|Dimensions||43.8W x 113.5H x 171D [mm]|
|Rated capacity||50 Ah|
|Specific energy||109 Wh/kg|
|Energy density||218 Wh/L|
(60-sec pulse at 25°C and 50% SOC)
|Max output current @ 25°C||300A|
Mitsubishi and GS Yuasa developed the cell for both high specific energy and high rate discharge. The newly developed prismatic cell used in the i MiEV pack has a specific energy of 109 Wh/kg and specific power of 550 W/kg. Energy density is 218 Wh/L. The entire pack has a specific energy of 80 Wh/kg.
The cell—and pack—feature high capacity retention at constant current discharges. Capacity at the high current of 200A is slightly less than at the lower rates (93.9% of capacity).
When discharged with an ambient temperature of 25° C, the pack is capable of delivering the maximum power from 80% DOD. Even at 0°C, the pack can deliver the maximum power from 70% DOD and enough power for propulsion from 90% DOD.
|Pack capacities at 25°C. Click to enlarge.||60-sec pulse power of pack. Click to enlarge.|
Mitsubishi tested the cycle life of the pack under standard (50 A) and quick charge (120 A) conditions using the JC08 driving pattern and found that the pack retained 84% of capacity with quick charging and 83% with standard charging after 1,000 cycles.
Development of the i MiEV EV concept began in 2005, and Mitsubishi is currently field testing units in Japan in cooperation with electric utilities, with market introduction slated for 2010. The company is also targeting market introduction in Europe and North America.