A Quicker Test for Electric Car Batteries
Promising battery technologies often get bogged down in long experiments–a new test could set them loose.
It takes years to verify that a new battery technology will last for the life of a hybrid or electric car. That means battery materials that might cost less and store more energy than today’s batteries are languishing on lab benches.
A new way to test lithium-ion batteries could cut that time to a few weeks instead of a few years, eliminating a key bottleneck that’s keeping battery costs high and storage capacities low.
By accurately measuring how efficiently experimental batteries store and deliver an electrical charge, Jeff Dahn of Dalhousie University can predict how many times battery cells can be charged and discharged–known as the cycle life of the battery. Dahn, a professor of physics and chemistry, is also trying to demonstrate that the method can predict how long a battery will last on the shelf–known as calendar life.
Together, cycle life and calendar life determine how long a battery will be useful. They’re essential for determining, for example, how big the battery pack needs to be to store the advertised amount of energy throughout the life of the car.
The technique has caught the attention of automakers, which are trying to validate and use it, particularly as a tool for predicting cycle life. It could also allow academics, who have fewer resources than automakers, to develop battery materials with real commercial potential. “We think this technique could be very useful,” says Masaki Matsui, manager of the materials research department at Toyota Research Institute of North America. He says it will identify problems with materials very early in battery development, allowing researchers to quickly sort through combinations of battery electrodes and electrolytes.
A panoply of things can go wrong in a battery. The key insight of Dahn’s approach is that many such snags can show up in a single test–the measurement of the difference between the amount of charge that goes into a battery during charging and the amount that comes out when it’s discharged (also called coulombic efficiency). If less charge comes out than goes in, that energy is being wasted by unwanted reactions within the battery. These losses add up: with successive cycles, the battery returns less and less charge until eventually it isn’t usable.
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