Automotive Electronics

Industry, Academia, and Government Working to Extend Battery Life in EVs

In what could propel electric vehicles (EVs) miles down the road toward commercial viability, GE researchers, in partnership with Ford Motor Company</b< and the University of Michigan, will develop a smart, miniaturized sensing system that has the potential to significantly extend the life of car batteries over conventional battery systems used in electric vehicles today.

"The car battery remains the greatest barrier and most promising opportunity to bringing EVs mainstream." said Aaron Knobloch, principal investigator and mechanical engineer at GE Global Research. "Improvements in the range, cost and life of the battery will all be needed for EVs to be competitive. With better sensors and new battery analytics, we think we can make substantial progress at increasing battery life. This, in turn, could help bring down its overall cost and the cost entitlement of buying an electric car."

To improve the life and reduce the lifecycle cost of EV batteries, GE will combine a novel ultrathin battery sensor system with sophisticated modeling of cell behavior to control and optimize battery management systems. Today’s sensors on EVs and plug-in hybrid vehicles (PHEVs) measure the health of the battery by looking at factors such as its temperature, voltage, and current. However, these measurements provide a limited understanding of a battery’s operation and health. The goal of the ARPA-E project will be to develop small, cost effective sensors with new measurement capabilities. Due to their small size, these sensors will be placed in areas of the battery where existing sensor technologies cannot be currently located. The combination of small size and ability to measure new quantities will enable a much better understanding of battery performance and life.

A group of scientists from the University of Michigan, led by Anna Stefanopoulou, a professor of mechanical engineering, will use the data generated by GE sensors to verify advanced battery models. They will ultimately create schemes that use instantaneous sensor data to predict future battery-cell and battery-pack behavior.

"Ensuring a battery’s health over many cycles requires taking frequent snapshots of its condition as it ages. Control systems on cars have to be able to use this vast amount of data quickly and efficiently. Information provided by advanced sensors will allow us to create and verify finely resolved physical models to underpin battery management schemes," said Charles Monroe, a chemical engineering professor on the University of Michigan team. He added, "The big challenge is to make battery management programs adapt and work fast."

The use of sensors in conjunction with real-time models will enable novel algorithms that optimize how the battery system is managed to extend its life. To demonstrate the capabilities of the sensor system and analytics, Ford will integrate them into one of their vehicles for validation.

Tony Philips, Senior Technical Leader, Vehicle Controls, Research and Engineering, Ford Motor Company, said. "This collaboration brings together a diverse set of experts on sensor technology, controls and modeling, and automotive engineering to innovate on some of the most critical elements of battery technology. Ultimately, through this collaboration we anticipate being able to deliver more cost effective and durable battery system solutions to our customers."

The goal of this 3-year / $3.1 million program is to demonstrate a working sensing system in an actual electric vehicle.

The Department of Energy (DOE) announced that a team of engineers at Washington University in St. Louis will receive $2 million to design a battery management system for lithium-ion batteries that will guarantee their longevity, safety and performance.

The project is one of 12 that won funding from the DOE’s Advanced Research Projects Agency-Energy (ARPA-E) under the new AMPED program that focuses on innovations in battery management and storage to advance electric vehicle technologies and to help improve the efficiency and reliability of the electrical grid.

"This initiative is part of a broader effort to strengthen the university’s expertise in energy-related technologies," says Pratim Biswas, PhD, chair of the Department of Energy, Environmental & Chemical Engineering in the School of Engineering & Applied Science. "While this grant targets car batteries," he says, "the technology is also directly applicable to intermittent sources of energy such as solar that produce energy that may need to be buffered rather than plugged directly into electrical grid."

The AMPED award goes to the Modeling, Analysis and Process-control Laboratory for Electrochemical systems (MAPLE) in the Department of Energy, Environmental & Chemical Engineering, led by Venkat Subramanian, PhD, associate professor.

Lithium-ion batteries are what are called secondary cells, because the electrochemical reactions that create a current are reversible and the battery can be recharged. The more familiar primary cells, in contrast are used once and thrown away. The lithium is stored in metallic (uncharged) form inside the particles of a graphic electrode, explained Subramanian. During discharge the lithium comes to the electrode’s surface, where it is ionized, creating a current that travels to the cathode. At the cathode, typically a lithium-based alloy, the ions are neutralized and enter electrode particles as metallic lithium. The battery is recharged by forcing a current to flow in the opposite direction, moving the lithium back into the anode.

Lithium-ion batteries hold great promise for applications such as electric vehicles because they have high energy density (energy stored per unit volume) and lose charge very slowly when not in use. No battery is perfect and lithium-ion batteries, like all batteries, have drawbacks. If the batteries are charged too fast, they can heat up and may explode. To avoid catastrophic failure, manufacturers overdesign the batteries and use only part of their energy capacity per cycle, Subramanian said.

"The goal of the AMPED program is to push the current technology to 100-percent efficiency, while making sure battery lifetime is not compromised," Subramanian said. This would ultimately reduce the weight of the car and improve its energy efficiency.

"If you can predict what will happen inside the battery, you can push the battery to do more per cycle," Subramanian says. "Currently empirical (experience based) models that have no predictive capability are used to manage the batteries. This is why manufacturers over-stack the material; they have no idea what’s happening inside."

There are physics-based models of lithium-ion batteries but they are computationally intensive and can’t be solved in real time by the usual methods. This is where the MAPLE lab comes in. The engineers plan to use a class of simulation techniques called spectral methods aided by mathematical analysis to solve a physics-based model’s differential equations. Spectral methods should allow them to cut down on the model’s computational demands so that it runs faster.

The Battery Management System (BMS), MAPLE lab develop will keep the battery operating optimally, enabling maximum utilization of energy at all times.

More news and information regarding the latest developments in Smart Grid electronics can be found at Darnell’s SmartGridElectronics.Net.

Washington University in St. Louis , US Department of Energy , University of Michigan , GE Global Research , Ford Motor Co.
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