It’s not unusual for a cellphone battery to die unexpectedly, and generally it isn’t life-threatening. But an electric vehicle can’t run out of charge without warning on a busy freeway.
This is just one of the concerns that Mo-Yuen Chow, an electrical engineer at North Carolina State University, is working to solve. Chow recently coauthored a study on improving estimates of how much charge remains in a battery as part of his work on electric vehicles.
How did this research come about?
Many of us have the experience where we thought [our laptop] battery would last three hours, but we use the laptop for 30 minutes, and then the indicator just all of a sudden drops down to only 25 percent left. This cannot happen for vehicles. Say that we want to take a trip for 120 miles. The battery indicator says yes we can drive 120 miles, but once we hit the road, after 30 minutes it says now we only have 20 miles of battery energy left. We need a much more accurate indicator for recording state of charge of the battery.
What are the limitations of battery technology and do you think it can perform in the way we need it to?
Actually, battery technology has had a huge growth in the last 10 to 20 years … and today many electronics use lithium ion batteries. Of course, there is the cost issue, there is a safety issue, there’s a power density issue, there’s an energy density issue. Lithium ion still has a lot of room to grow, and we also work on lithium polymer, which is a little bit more expensive but has some better characteristics.
Can electric vehicles fit into the existing gas station model somehow?
Right now many of the companies [that] developed charging stations made them look very much like gasoline pumps. We can just drive our car into a charging station and then … plug it into the connector.
But it takes so much longer to charge a battery than fill up the tank, right? How can we overcome that time obstacle?
Yes, currently there are [batteries that] take around eight to 10 hours that we usually charge at home overnight. Then the fast-charging batteries, they’re usually 20 minutes, so it still doesn’t make too much sense to wait 20 minutes to charge it. There are some solutions called battery swapping, where the car pulls into a station and then there’s a robot that takes your battery out and puts another fully charged battery in. Different approaches have different pros and cons, in terms of reliability, in terms of liability and so on. People continue to do fast charging and fast charging is a problem, [because] for certain kinds of batteries it really reduces the battery life. They need to make better, more robust batteries to stand fast charging. I think all those things can be solved technically. Right now it’s just a matter of growing pains, and once it becomes a very profitable market, then we will be amazed at what technology can do.