The cells that make up a lithium ion battery pack are not all the same. There are some that will inexorably degrade faster than others. Now, a research from Stanford University has discovered the battery would have a longer useful life if each cell receives an individualized charge treatment.
There are many reasons why individual cells in a pack degrade sooner. From differences in manufacturing or in materials to the fact that some are more exposed to heat, or located in an area that is difficult to cool. In any case, a single battery cell lasts longer than a battery pack… as weak cells drag down the rest.
Rapid charges and discharges are stressful on battery cells. Despite being designed to withstand these moments, weak cells suffer and deteriorate more quickly. Hence, the team of researchers from Stanford University wondered if charging all the cells of a battery at the same rate could speed up the death of the battery.
The first thing was to create a computer model, with a simulation at an unprecedented level of detail. They represented the physical and chemical state of the battery and the changes that can occur throughout its life, from those that occur in seconds to others that can take years to happen.
Building on that model, they compared standard fixed charges to other approaches in which the capacity of each cell served as an indicator of how much charge it could take. While the strongest cells were subjected to the highest stresses, those that had already begun to degrade were treated more carefully, hoping to slow their deterioration.
And… Bingo! The team found that by individually configuring each cell’s charge rate, they could minimize temperature rise and degradation. Packets could complete at least 20% more charge/discharge cycles than charging normally.
Should we change the way we charge batteries?
It is great to increase the useful life of the batteries, but those of us who have charged an electric car or a mobile phone want them to charge as quickly as possible so that they can be used again. And based on this research, some of the cells would not charge as fast as they normally would. But given the lithium shortage, getting longer battery life is good for everyone…and may not mean drastic changes from users when charging their cars.
On a nice note, the researchers say this charging model can be easily implemented in existing electric vehicles, as well as guiding the development of next-generation batteries. And beware, the same model could be applied to the discharge cycle, demanding less from the weaker cells and more from the stronger ones, for more benefit in the lifespan of any battery pack that is subjected to high stress loads.
Via: IEEE Transactions on Control Systems Technology.