High Power Batteries: Enabling Technologies for the Drivetrain
of the Future

Ann Marie Sastry, Ph.D

Arthur F. Thurnau Professor of Mechanical, Biomedical and Materials Science and Engineering
Director, Energy Systems Engineering Program
University of Michigan, Ann Arbor

ABSTRACT: Imminent changes in the world energy portfolio will amplify pressure on development of zero-emission vehicles (ZEV), of which battery-powered vehicles are the nearest-term realization. The anticipated electrification of the drivetrain, and its progenitors in hybrid systems, have intensified research in batteries, an essential component in both fuel cell and gas/hybrid vehicles. Though the basic electrochemistries have been known since Edison, it is their implementation in novel, often nano- structures, which has revolutionized their performance.

Here, we describe some of the technologies, i.e. Li-based batteries, that are anticipated to enable hybrid, or fully-electric drivetrains. Some of these, and a new graduate engineering program developed to enable the transition to electric drivetrains at the University of Michigan, are described. These Li-ion rechargeable cells are used in applications ranging from the biomedical device, defense, computer, hybrid and electrical vehicle, and cellular phone industries. Li-ion technology is often selected over nickel metal hydride (NiMH) or nickel cadmium (NiCd) because of its high specific energy density (100-158 Wh_kg-1), volumetric energy density (245-430 Wh_L-1) and nominal voltage (3.5V). The high reactivity of lithium metal can pose a safety risk in operation; materials selection in present use is a result of rigorous testing to assure safety in operation, and longer lifetimes. These materials include graphite/carbon, lithium-ion intercalated metal oxides, and lithium-ion salts with organic solvents, as anodic, cathodic active materials and electrolyte, respectively. In battery systems, solution of multiphysics problems, incorporating statistical variation in the agglomerates that comprise active materials, is urgently required for optimization of automotive and wireless power systems.

Balancing high energy and power requirements, while meeting constraints on form factor, comprises a challenging engineering and basic science problem. Insertion of new materials technologies, from nanoarchitectured carbons to metallic additives, requires the capability to correctly predict fractions providing high conductivity, for both thin and fully 3D electrode architectures. In our work, we use take a stochastic approach in constructing model materials, so that transport and mechanical properties can be studied at the microscale. We also present results of coupled simulations, for rational design of cells, and higher-level models for design of power systems.

In closing, the continued insertion and scaleup of Li-based, and other technologies, is discussed. The consumption of energy in the U.S., by the approximately 2 billion electronic devices using battery power, has been estimated to be 16TWh/year (16,000GWh/year). Worldwide, the approximately 10 billion electronic devices can be approximated as consuming 80TWh/year. With a U.S. automotive fleet of 220 million vehicles, the total power consumption can be approximated to be 4,700TWh/year (4,700 billion KWh/year); the worldwide automotive fleet of 790 million vehicles (2005) can be assumed to draw around 16,000 TWh/year. Thus, the conversion of the fleet, or even a small portion of it, represents a daunting challenge to scaleups in battery production, and reductions in cost: presently, automobiles consumer comfortably consume more than two orders of magnitude more energy than engineered devices powered by batteries, both worldwide and in the U.S. alone. Both educational, and research needs, for this conversion of the drivetrain, are described.

Bio: Ann Marie Sastry is the Arthur F. Thurnau Professor of Mechanical, Biomedical and Materials Science and Engineering, and Director of the Energy Systems Engineering Program, at the University of Michigan. She is also CEO of Sakti3, Inc. She holds MS and PhD degrees from Cornell University, and a BS from the University of Delaware, all in Mechanical Engineering. She is the recipient of numerous honors for her work, including the 2007 ASME Gustus Larson Award, the University of Delaware Presidential Citation for Outstanding Achievement (2004), the UM College of Engineering 1938E (2000), the University of Michigan Henry Russel Award (1999), and NSF's Presidential Early Career Award for Scientists and Engineers (1997). In 2005, she was honored with a University of Michigan Faculty Recognition Award, acknowledging outstanding contributions as a senior faculty member in research, teaching and service. She has served on three Editorial Boards: the ASME Journal of Engineering Materials and Technologies, Journal of Composite Materials, and as a Founding Associate Editor of the Journal of the Mechanical Behavior of Biomedical Materials. She founded the nation's first graduate degree program in Energy Systems Engineering in 2007 to provide graduate education in advanced energy technologies.

Her research spans the energy/biology interface. She has published over 60 peer-reviewed journal articles and book chapters, and delivered over 50 invited seminars at academic institutions and organizations, including the National Academy of Sciences and the National Institutes of Health. Her work has featured in Nature, Business Week, and other publications. In energy technologies, her laboratory has developed new materials, invented techniques for manufacture and optimization of batteries, and algorithms for optimization of power systems. Her laboratoryʼs work in batteries for the Department of Energy comprises the first coupled mechanical and electrochemical simulation approach to modeling failure initiation in high power battery systems. Her laboratoryʼs projects, sponsored by General Motors, DoE, the Army Research Office, the Air Force Office of Scientific Research, NSF, and the Ford Motor Company, include numerical simulation of performance of Li batteries for electric vehicles, design of microbatteries for implantable systems, creation of biological batteries comprised of cellular organelles coupled with engineered substrates, and modeling of fully integrated structural batteries for realization of multifunctional, composite materials.