|GM is exploring combining supercapacitors for power with high-energy lithium-ion batteries for a next-generation energy storage system for the E-Flex EREVs. Click to enlarge.|
General Motors is actively exploring the concept of combining supercapacitors and lithium-ion batteries in a next-generation energy storage system (ESS) for its E-Flex series of extended range electric vehicles (EREVs).
Although the primary objective of the project is to explore using supercapacitors for peak shaving the power capacity requirements of the lithium-ion battery pack, such a combination of ESS technologies also has the benefit of addressing the low-temperature performance issues of lithium-ion batteries, said Dr. Mark Verbrugge, Director, Material and Process Labs at GM’s Tech Center, during a presentation at the Advanced Automotive Battery Conference (AABC) this week in Tampa, FL.
The concept is especially suited for the EREV vehicles—such as the Volt—because of the combined requirement for high energy and high power. This is not for the coming Volt in 2010, Verbrugge stressed, “but we’re thinking beyond.”
|Some initial results of the supercap-Li-ion combo (in green) compared to two conventional Li-ion chemistries. The upper grouping is plotted against the left vertical axis; the bottom three against the right vertical axis. Click to enlarge.|
To keep the system complexity down, they are eliminating the DC/DC converter. The initial system being explored, partly as a way of developing and validating the method for subsequent work—consists of 6 100F Nesscap supercapacitors and two Kokum high-energy lithium-ion batteries.
Initial results show augmented power delivery for the ESS, at lower battery surface temperatures, with a slight sacrifice in energy density. GM has not yet evaluated the effect of the lower battery temperature on cycle life (higher battery temperatures degrade the performance of the cells)—a potential positive trade-off against the decreased energy density.
We’re running the Volt power versus time profile through this combination with and without the supercaps. We wanted to show it [the early work], perhaps it will be compelling to those who want to provide ESS to the automotive industry.—Mark Verbrugge
Supercapacitor manufacturer Maxwell Technologies and Argonne National Laboratory are investigating the potential of combinations of the two types of storage technologies for hybrid and plug-in hybrid vehicles as well. (Earlier post.)