Researchers identify optimal lithium metal battery stack pressure to significantly improve performance

According to foreign media reports, a research team composed of material scientists and chemists has determined the optimal stack pressure that lithium metal batteries (LMBs) need to withstand during battery operation to produce optimal performance. The research team members are mainly from the University of California San Diego, Michigan State University, Idaho National Laboratory and General Motors Research and Development Center.

(Image credit: University of California, San Diego)

Replacing graphite with lithium metal as the negative electrode of batteries is the ultimate goal of some battery research and development fields. These lithium metal batteries will have the potential to double the performance of the current best lithium-ion technology. For example, electric vehicles using lithium metal batteries can have twice the range of lithium-ion batteries with the same battery weight.

Despite these advantages, LMBs are not favored because of their short lifespan and safety risks, especially short circuits caused by lithium dendrite growth. Researchers and technicians have found that subjecting LMBs to partial stress during battery cycling can improve performance and stability, thereby solving the lifespan problem. But the reason behind this is still unknown.

"We not only answered the scientific question, but also determined the optimal pressure required," said Shirley Meng, a professor in the UC San Diego Department of Nanoengineering. "In addition, we proposed new testing protocols to obtain maximum LMB performance."

Using a variety of characterization and imaging techniques, the researchers studied the LMB morphology and quantified the performance of the battery at different pressures. They found that using higher pressure levels, about 350 kPa, forced the lithium particles to deposit in neat columns without any porous spaces in between. In contrast, batteries subjected to lower pressures exhibited porous spaces and lithium particles were deposited in a disordered manner, allowing dendrites to have room to grow.

The researchers also showed that the process does not affect the solid electrolyte interface (SEI) structure of the battery electrolyte. But to apply this new technology, LMB's manufacturing facilities must be modified.

Another way to improve performance is to not fully discharge the battery when it is cycled. Instead, the researchers leave a reservoir of lithium for re-nucleation to occur. The discovery was demonstrated at GM's R&D center in Michigan.

In addition, INL researchers used molecular dynamics simulations to understand the stack pressure range in this project, which is much smaller than expected based on macroscopic mechanical models. The researchers also shed light on the mechanical origins of this unique process.