The many cells that make up a lithium battery pack are not all the same; some will degrade and fail faster than others. In view of this, Stanford University in the United States pointed out in a new study that if each battery is charged separately, the life of the entire battery will be greatly extended. 

There are a number of reasons why individual cells in a battery pack might degrade faster than others, the researchers note. Maybe there are differences in manufacturing or materials, or maybe some cells are exposed to more heat sources than others, or are located in locations that are harder to cool. However, the average life of a single battery is generally longer than that of a battery pack. 

"If not handled properly, cell-to-cell heterogeneity can compromise the lifespan, health, and safety of battery packs, and induce Group's early failure." 

Rapid charging and discharging are notoriously stressful for battery cells, and while they are designed to withstand this stress, the weaker cells tend to be damaged and degrade the fastest during these moments. So the Stanford team wondered whether the standard technique of charging all battery cells at the same rate would accelerate battery damage.

To do this, the researchers devised a computer model and performed extensive simulations. They compared standard and charging methods at different rates to test their idea. The theory here is that only the "strongest" batteries can withstand the highest stress; batteries that have begun to degrade prematurely should be treated more gently, hopefully extending their life. 

The team found that by individually setting the charge rate for each battery, they could minimize temperature rise and battery degradation, allowing the packs to last at least 20 percent longer than standard-charged batteries. The research results have recently been published in "IEEE Control Systems Technology Transactions" on.

The researchers say their charging model could be easily rolled out to existing EV designs, or used to guide the development of next-generation battery management systems. 

They also suggest that the same model could be applied to the discharge cycle, requiring less of the weaker cells and more of the stronger cells to further improve the life of the battery pack. 

"Lithium-ion batteries have changed the world in many ways," Onori said, "and it's important that we reap as many benefits as possible from this transformative technology and its successors."