Lithium-ion Batteries Could Hold the Key to 100-MPG Hybrids

	At Argonne's Advanced Photon Source (APS), researchers load a lithium-ion battery pouch into an insertion device x-ray beamline in order to evaluate the electrode material structure stability during charging and discharging. The APS and Electron Microscopy Center are valuable research tools for Argonne’s battery R&D. Shown here are Christopher Johnson (foreground) and Jeremy Kropf (background).

Argonne National Laboratory is using its expertise as a top lithium-ion battery R&D organization to help the Department of Energy advance technology for plug-in hybrids — hybrid electric vehicles that let consumers recharge batteries by plugging into a wall outlet.

Hybrid electric vehicles (HEVs) are no longer cars of the future. As the price of gasoline has gone up, so has the demand for HEVs. Interest is growing in HEVs that can recharge from wall-plug energy (plug-in HEVs, or PHEVs) because of their high fuel economy (up to 100 miles per gallon) and the ability take advantage of off-peak electricity, which offers power generation efficiency and environmental benefits.

There are substantial technical challenges associated with PHEVs. Although they can be built today (concept prototypes include General Motors' Chevrolet Volt car, DaimlerChrysler's Sprinter van, Hymotion's plug-in retrofit for Toyota's Prius automobile, Ford's Escape sport utility vehicle [SUV], and Mercury's Mariner SUV hybrids), current battery technology is a "show stopper" in terms of energy, life, and cost.

Lithium-ion Batteries are the Way to Go

Lithium-ion batteries are a promising alternative to the nickel metal hydride batteries used in current-generation HEVs. Lithium-ion NiMH batteries pack more power and energy into a smaller battery package. The volume and weight savings (about 60%) over a NiMH battery means less weight and more room for comfort in the vehicle. But there's work to do before lithium-ion batteries are ready for commercialization in this market.

Under the Department of Energy's Advanced Technology Development (ATD) Program, Argonne has been working with battery developers to overcome lithium-ion battery limitations and increase battery performance, life, and tolerance to abusive conditions (such as overcharge), while reducing cost. Argonne's work under this program provides a rich background for studying the particular requirements of batteries for plug-ins.

Similar technical challenges apply, but because PHEVs would utilize the all-electric mode more extensively than HEVs, there would be different demands on the batteries. For example, today's HEV batteries are used intermittently and typically discharge less than 5% before recharging. The PHEV duty cycle would include daily deep discharges of up to 75%, and battery life likely would be affected.

Argonne is focusing on developing advanced lithium-ion battery materials and cell chemistries that can meet the demands of PHEV use, and on simulating how batteries made with these new chemistries would perform under conditions typical for a PHEV.

Argonne's Approach

Argonne will study prototype lithium-ion batteries of the type being used in the DaimlerChrysler Sprinter van program, which is targeted at demonstrating a PHEV van for use in fleet applications. Argonne will use two of the batteries in hardware-in-the-loop testing as part of breadboard vehicle systems. Another battery will be tested in Argonne's Electrochemical Analysis and Diagnostics Laboratory to characterize its performance and cycle life, as well as establish its capabilities and limitations for use in PHEVs.

Experts agree that a battery's ability to store and deliver energy at low cost is key to making PHEV technology viable. Argonne has discovered high-capacity cathode materials that exhibit capacity densities of ~270 mAh/g compared with the 150 mAh/g capacity density for state-of-the-art cathode materials. These materials are excellent candidates for lithium-ion batteries to power PHEVs, and research efforts are focused on increasing the rate capability and particle density of these materials, as well as making them more stable for longer battery life and enhanced safety, while reducing battery size.

Argonne's lithium-ion battery research is funded by the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, FreedomCAR and Vehicle Technologies Program.

TransForum Vol. 7 No. 1 (March 2, 2007 )