Tech Watch: Batteries with Fewer Borders

Ngalula Mubenga has developed a new technology referred to as a “bilevel equalizer.” 

A lithium-ion battery is only as strong as its weakest cell. Since batteries are constructed in a series of cells, one bad cell can disable an entire energy storage system. Balancing the battery load often requires an equalizer consisting of either a passive circuit, which can be inefficient, or an active circuit, which is far more expensive.

Ngalula Mubenga, an electrical engineer at the University of Toledo, has developed a new technology referred to as a “bilevel equalizer.” The device combines the high performance of an active equalizer with the low cost of the passive variety. 

The technology arranges cells into sections where each is balanced by a passive equalizer. The entire section is balanced by an active equalizer. Mubenga said the solution could help electric vehicle batteries hold their charge longer.

"If there are 120 cells in a battery, divide the cells into 10 groups of 12," Mubenga says. "Then you only need nine active equalizer units and 120 passive equalizer units using the bilevel equalizer. With current active equalizers, manufacturers would have to use 120 active equalizers. For manufacturers that can't afford to use only active equalizers, the bilevel equalizer is the solution to the problem."

Mubenga is originally from Democratic Republic of Congo. When she was 17, she waited three days for surgery after her appendix burst because there was no power at the hospital. Her solution is not only relevant to EVs, but grid stations, satellites and other energy storage systems. 

“For three days, my life depended on electricity. I was praying. I could not eat. And decided if I made it out alive, I would work to find a solution so people wouldn't die because of lack of electricity," she says. 

Mubenga, an assistant professor, collaborated on the project with Tom Stuart, professor emeritus in the UT Department of Electrical Engineering and Computer Science, who had the idea for the bilevel equalizer. The UT researchers say they are licensing the hybrid equalizer and retrofit kit to manufacturers.