Islands of inactive lithium crawl like worms to reconnect with their electrodes, restoring capacity and battery life.
Researchers in Department of Energy National Accelerator Laboratory SLAC and Stanford University believe they have discovered a means of reviving lithium batteries that can increase the range of electric vehicles and battery life in next-generation electronic devices.
As the cycle of lithium batteries between the electrodes, small islands of inactive lithium are formed, which reduces the ability of the battery to hold charge. However, researchers have found that they can cause this “dead” lithium to crawl like a worm to one of the electrodes until it connects, thus partially reversing the unwanted process.
The addition of this additional step slowed the degradation of their test battery and increased its service life by almost 30%.
“We are currently studying the potential recovery of lost capacity in lithium-ion batteries through an extremely rapid discharge phase,” said Fan Liu, a Stanford Postdoctoral Fellow, lead author of a study published Dec. 22 in Nature.
Numerous studies are looking for ways to produce rechargeable batteries with less weight, longer life, improved safety and higher charging speeds than the lithium-ion technology currently used in mobile phones, laptops and electric vehicles. Particular attention is being paid to the development of lithium-metal batteries that could store more energy by volume or weight. For example, in electric cars, these next-generation batteries can increase mileage on a single charge and possibly take up less space in the trunk.
Both types of batteries use positively charged lithium ions that move between the electrodes. Over time, part of the metallic lithium becomes electrochemically inactive, forming isolated lithium islands that no longer connect to the electrodes. This leads to a loss of capacity and is a particular problem for lithium-metal technologies and for the rapid charging of lithium-ion batteries.
However, in a new study, researchers demonstrated that they can mobilize and restore insulated lithium to extend battery life.
“I have always considered insulated lithium to be bad because it causes the destruction and even ignition of batteries,” said Yi Cui, a Stanford and SLAC professor and researcher at the Stanford Institute for Materials and Energy Research (SIMES) who led the research. “But we figured out how to electrically connect this ‘dead’ lithium to the negative electrode to reactivate it.”
Pause, not dead
The idea for the study was born when Cui suggested that applying voltage to the cathode and anode of the battery could cause an isolated island of lithium to physically move between the electrodes – a process his team confirmed by their experiments.
Scientists have created an optical element with a cathode of lithium-nickel-manganese-cobalt (NMC), a lithium anode and an isolated lithium island between them. This test device allowed them to track in real time what is happening inside the battery during use.
They found that the isolated lithium island was not “dead” at all, but responded to battery life. When charging the cell the island moved slowly to the cathode; when discharged crawled in the opposite direction.
“It’s like a very slow worm moving its head forward and pulling its tail in to move nanometer after nanometer,” Cui said. “In this case, it transports, dissolving at one end and depositing the material at the other end. If we can keep the lithium worm moving, it will eventually touch the anode and restore the electrical connection. ”
Increase service life
The results, which the scientists confirmed with other test batteries and with computer simulations, also demonstrate how insulated lithium can be recovered in a real battery by changing 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 fast, high-precision discharge phase right after charging the battery, which moved the insulated lithium far enough to reconnect it to the anode. It reactivates lithium so it can be involved in battery life. ”
She added: “Our findings are also of great importance for the design and development of more reliable lithium metal batteries.”
This work was funded by the Department of Health’s Office of Energy Efficiency and Renewable Energy, the Office of Automotive Technology in Battery Materials Research (BMR), the Battery 500 Consortium and the Extreme Fast Charge Cell Evaluation of Li-ion Battery (XCEL) programs.
Help: “Dynamic spatial progression of insulated lithium during battery operation” Fang Liu, Rong Xu, Yetsun Wu, David Thomas Boyle, Ankun Yang, Jinwei Xu, Yaning Zhu, Yusheng Ye, Zhao Yu, Zwen Zhang, Xin Xiao, Wenxiao Huang Wang, Hao Chen and Yi Cui, December 22, 2021, Nature.
DOI: 10.1038 / s41586-021-04168-w