For electric cars to run as long as possible, their batteries need to be powerful. One of the viable options for this would be lithium metal batteries with a key component made of lightweight elements. This gives them more storage capacity than commonly used lithium-ion batteries made from the same component graphite. Although lithium-metal batteries can store more energy than lithium-ion batteries of the same size, they also degrade faster, limiting how many times they can charge and discharge. But researchers have found a new charging technique that can restore damaged material, significantly extending the life of the battery. As a rechargeable lithium-based battery is charging and discharging, lithium ions move back and forth between the positively charged cathode and the negatively charged anode. But over time, small pieces of reactive material cannot be locked into the body of the anode. Inside the battery, the missing pieces form tiny "islands" of lithium that until now most researchers thought were inactive. Stanford University researchers discovered that these isolated bits can respond electrically by physically moving back and forth as the battery charges and discharges.
The scientists discovered that the islands wiggle just enough to re-establish an electrical connection between the isolated lithium and the anode. They realized that they could reassemble the material by immediately discharging a small amount of electricity once the battery was fully charged. "This is how we encourage the growth of [lost lithium] toward the anode to re-establish the electrical connection," says Fang Liu, lead author of the study and Stanford materials scientist. When a lithium metal test battery is charged using this protocol, it can perform more charge cycles, lasting 29 percent longer than a standard charged battery. Princeton University electrochemistry and materials scientist Kelsey Hatzell, who was not involved in the study, says the finding adds to the fundamental understanding of lithium metal batteries. "The dynamics of isolated lithium metal are very difficult to observe," he says, adding that the researchers "designed many interesting experiments to begin to decompose the mechanisms." He notes, however, that practical applications may be far away; these batteries are still short of the thousands of charge cycles that rechargeable batteries have to endure.
Stanford researchers hope to further refine their charging methods to maximize lithium metal battery life. They are also working on a charging protocol that will increase the usability of lithium-ion batteries. "I will consider [this work] a major discovery for the battery field—lithium-ion, lithium-metal," says Yi Cui, senior author, and Stanford materials scientist.
Reference:
https://www.scientificamerican.com/article/new-charging-technique-puts-crumbling-batteries-back-together/
