Battery tester: This system charges and discharges 60 battery cells and predicts how long they will last.
Jeff Dahn, Dalhousie University
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.
Battery breakthroughs could lower costs and improve performance for electric vehicles and renewable energy storage--but commercializing these new technologies will be challenging.
What about BMS or Full Pack Level Functional Testing?
This article raises the EXTREMELY valid point that full validation and testing of new battery technology is a primary bottleneck in delaying new battery pack designs from getting to the automotive marketplace. For large battery packs like those being developed for hybrid electric vehicles or plug in electric vehicles,
it's important to note that to FULLY evaluate these new complete pack designs, several different styles of testing would need to be performed:
The first level of testing needed is to evaluate the performance of the Lithium Ion cells themselves to evaluate charge/discharge characteristics, energy density, and thermal behavior of a particular cell chemistry. The system Jeff Dahn developed, as described in this article, appears well suited for this task.
The second level of testing is evaluating the BMS, that is, the Battery Management System circuitry that monitors the state (voltages, temperatures, etc) of individual battery cell modules and of the full battery pack as a whole, and handles functions like cell balancing. Correctly performing this these tests involves simulating and controlling all inputs the BMS encounters in normal vehicle operation, subjecting it to any possible conditions it would encounter in the real world, and making sure it responds correctly in all cases.
An example of this approach can be found here:
http://www.dmcinfo.com/Case-Studies/View/ProjectID/236/Battery-Management-System-BMS-Test-Stand-2nd-Generation.aspx
The third level of testing is to validate all functional and performance characteristics of the battery pack as a whole (ie once the cells have been fully assembled into the completed pack that will go in a vehicle). This includes testing the diagnostic (CAN) communications between the pack itself (from the BMS) to the vehicle's Engine Control Unit (ECU) or On Board Diagnostics (OBD) system, testing all internal electrical components and wiring (expected isolation voltages, path resistances, capacitances, etc), and other pack functions like contactor operation, safety interlocks, etc. It also involves performing high power cycling of the pack to simulate actual real world drive profiles to determine qualities like the battery's energy capacity, which in turn is directly related to the vehicle's range it can travel on a single charge. An example of an automated test system for this level of testing can be found here:
http://www.dmcinfo.com/Case-Studies/View/ProjectID/121/Hybrid-Electric-Vehicle-Battery-Test-System.aspx
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Bob Wallace
71 Comments
Thanks, Kevin...
This piece didn't get any discussion, but that shouldn't bear on the importance of this news.
Cutting testing times from years to weeks is extremely important for getting better, cheaper batteries to market quickly.
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tennman
3 Comments
Re: Thanks, Kevin...
I agree, this is particularly important. As a student of reliability and quality engineering, I am constantly amazed at the infancy of the testing in many industries. Before reading this article, I assumed that most testing on these batteries were done at an accelerated pace.
But I also agree with Mr. Mathias. Of course, these accelereated tests can't catch every problem, and often over- or underestimate certain characteristics of the batteries. I definitely see this as an important advancement in testing for these batteries, but perhaps more for quality and production rather than reliability and research. I suppose we'll see in time...
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