The inactive lithium islands crawl like worms to reconnect to their electrodes, restoring battery capacity and life.
Researchers from the National SLAC Acceleration Laboratory at the Department of Energy and Stanford University believe they have found a means to revive lithium batteries that can increase the range of electric cars and battery life in next-generation electronic devices.
In a lithium battery cycle, small islands of inactive lithium form between the electrodes, reducing the battery’s ability to hold a charge. However, researchers have found that they can cause this “dead” lithium to crawl like a worm to one of the electrodes until it reconnects, thus partially reversing the unwanted process.
Adding this extra step slowed down the breakdown of their test battery and increased its life by nearly 30%.
“We are currently investigating the potential recovery of lost capacity in lithium-ion batteries using an extremely fast discharge step,” said Stanford doctoral student Fang Liu, lead author of a study published December 22 in nature.
Much of the research is looking at ways to create rechargeable batteries with lighter weight, longer life, improved safety and faster charging speeds than the lithium-ion technology currently used in mobile phones, laptops and electric vehicles. A special focus is on the development of lithium-metal batteries that can store more energy by volume or weight. For example, in electric cars, these next-generation batteries could increase the mileage of a single charge and probably take up less space in the trunk.
Both types of batteries use positively charged lithium ions that move back and forth between the electrodes. Over time, some of the metallic lithium becomes electrochemically inactive, forming isolated lithium islands that no longer bind to the electrodes. This leads to a loss of capacity and is a particular problem for lithium-metal technologies and for fast charging of lithium-ion batteries.
However, in the new study, researchers demonstrate that they can mobilize and restore isolated lithium to extend battery life.
“I’ve always thought insulated lithium was bad because it causes batteries to break down and even catch fire,” said Yi Cui, a professor at Stanford and SLAC and a researcher at the Stanford Institute for Materials and Energy Research (SIMES), who leads research. “But we figured out how to reconnect this ‘dead’ lithium to the negative electrode to reactivate it.”
Creeping, not dead
The idea for the study was born when Qui speculated that applying voltage to the cathode and anode of the battery could cause an isolated lithium island to move physically between the electrodes, a process his team has now confirmed with experiments.
The scientists made an optical cell with a lithium-nickel-manganese-cobalt-oxide (NMC) cathode, a lithium anode and an isolated lithium island between them. This test device allowed them to track in real time what happens to the battery when it is used.
They found that the insulated lithium island was not “dead” at all, but was responding to battery operations. As the cell charged, the island moved slowly toward the cathode; when diluting, it crawled in the opposite direction.
“It’s like a very slow worm that raises its head forward and pulls its tail to move nanometer by nanometer,” Qui said. “In this case, it is transported by dissolving from one end and depositing material at the other end. If we can keep the lithium worm moving, it will eventually touch the anode and reconnect. “
The results, which scientists confirmed with other test batteries and computer simulations, also show how isolated lithium can be recovered in a real battery by modifying the charging protocol.
“We have found that we can move the separated lithium to the anode during discharge, and these movements are faster at higher currents,” Liu said. “So we added a quick high-current discharge step right after charging the battery, which moved the insulated lithium far enough to reconnect it to the anode. This reactivates lithium so that it can participate in battery life. “
She added: “Our findings are also important in the design and development of stronger lithium metal batteries.
This work was funded by the Office of Energy Efficiency and Renewable Energy of DOE, the Office of Vehicle Technology under the Battery Materials Research (BMR) programs, the Battery 500 Consortium and the Extreme Fast Charge Cell Evaluation of Lithium-Ion Batteries ( XCEL).
Reference: “Dynamic Spatial Progression of Insulated Lithium During Battery Operation” by Fang Liu, Rong Xu, Yecun Wu, David Thomas Boyle, Ankun Yang, Jinwei Xu, Yangying Zhu, Yusheng Ye, Zhiao Yu, Zewen Zhang, Xin Xiao , Wenxiao Huang, Hansen Wang, Hao Chen and Yi Cui, December 22, 2021, nature.
DOI: 10.1038 / s41586-021-04168-w