Top row: top view and cross sections of deposited lithium at 70 kilopascal (kPa) (less than one atmosphere). Bottom row: top view and cross sections of deposited lithium at 350kPa, or 3.5 atmospheres. The higher pressure causes the lithium particles to deposit in neatly stacked columns, which increases the volume of lithium deposited and prevents porosity. Image: University of California San Diego.A team of materials scientists and chemists has determined the proper stack pressure that lithium metal batteries (LMBs) need to be subjected to during battery operation in order to produce optimal performance. The team, which included researchers from the University of California (UC) San Diego, Michigan State University, Idaho National Laboratory and the General Motors Research and Development Center, reports its findings in a paper in Nature Energy.
Replacing the graphite in battery anodes with lithium metal is the ultimate goal for part of the battery R&D field, as LMBs have the potential to double the capacity of today’s best lithium-ion technologies. For example, electric vehicles powered by LMBs would have twice the range of vehicles powered by lithium-ion batteries, for the same battery weight.
Despite this advantage over lithium-ion batteries, LMBs are not currently considered a viable option for powering electric vehicles or electronics, because of their short lifespan and potential safety hazards, particularly short circuits caused by the growth of lithium dendrites.
Researchers and technologists had noticed that subjecting LMBs to pressure during battery cycling increases performance and stability, helping to solve this lifespan challenge. But the reasons behind this were not fully understood.
“We not only answered this scientific question, but also identified the optimum pressure needed,” said Shirley Meng, a professor in the UC San Diego Department of NanoEngineering and the paper’s senior author. “We also proposed new testing protocols for maximum LMB performance.”
Meng and her colleagues used several characterization and imaging techniques to study LMB morphology and quantify performance when the batteries were subjected to different pressures. They found that higher pressure levels force the lithium particles to deposit in neat columns, without any porous spaces in between. The pressure required to achieve this result is 350 kilopascal (roughly 3.5 atmospheres).
In contrast, batteries subjected to lower levels of pressure are porous and the lithium particles deposit in a disorderly fashion, leaving room for dendrites to grow. The researchers also showed that the high pressure doesn’t affect the solid electrolyte interphase (SEI) structure of the batteries’ electrolytes. However, manufacturing facilities for LMBs would have to be retooled for this new technique to be applied at industrial scales.
Another way to boost performance is not to discharge the battery completely while it cycles. Instead, the researchers kept a reservoir of lithium where re-nucleation can occur.
The researchers’ findings were validated at the General Motors Research and Development Center in Michigan. Separately, researchers at Idaho National Laboratory used molecular dynamics simulations to understand the stack pressure range used in this work, which is much less than expected from macroscopic mechanical models. The researchers were also able to explain the mechanistic origin of this unique process.
“Research institutions should keep collaborating with national laboratories and industries to solve practical problems in the battery field,” said Chengcheng Fang, the paper’s first author, who earned her PhD in Meng’s research group and is now on faculty at Michigan State University.
This story is adapted from material from the University of California, San Diego, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.