A research team from Stanford University has investigated dendrite formation to further improve lithium-metal batteries.
A novel mathematical model combining physics and chemistry to develop highly promising lithium-metal batteries has presented scientists with credible, fresh solutions to a problem that has been previously known to cause degradation and failure.
This study was recently published in the Journal of The Electrochemical Society.
Building better, safer lithium-metal batteries
Currently, rechargeable lithium-ion cells are widely utilised in portable electronics and electric cars. In comparison, it has been observed that lithium-metal batteries hold tremendous promise as next-generation energy storage devices. This is because, compared to lithium-ion devices, lithium-metal batteries hold more energy, charge up faster, and weigh considerably less.
However, it has been observed by researchers that the commercial use of rechargeable lithium-metal batteries has been limited. A primary explanation for this is the formation of ‘dendrites’, which are thin, metallic, tree-like structures that grow as lithium metal accumulates on electrodes inside the battery. This dendrite formation in batteries considerably degrades battery performance and ultimately leads to failure which, in some instances, can even dangerously ignite fires.
Approaching the dendrite problem from a theoretical perspective
Approaching this issue with a theoretical perspective meant that the research team developed a mathematical model that combines the physics and chemistry involved in dendrite formation.
This model provided the insight that swapping in new electrolytes – the medium through which lithium ions travel between the two electrodes inside a battery – with certain properties could slow or even completely stop dendrite growth.
“Our study’s aim is to help guide the design of lithium-metal batteries with a longer life span,” explained Weiyu Li, lead author of the study and a PhD Student in Energy Resources Engineering. “Our mathematical framework accounts for the key chemical and physical processes in lithium-metal batteries at the appropriate scale.”
“This study provides some of the specific details about the conditions under which dendrites can form, as well as possible pathways for suppressing their growth,” added Tchelepi, co-author of the study and a Professor of Energy Resources Engineering at Stanford’s School of Earth, Energy & Environmental Sciences.
Interpreting the results: Understanding batteries’ internal electric fields
Scientists have attempted to understand the factors leading to dendrite formation for decades. However, the laboratory work is labour-intensive, and results from relevant experiments have proven difficult to interpret. To address this issue, the research team created a mathematical representation of the batteries’ internal electric fields and transport of lithium ions through the electrolyte material, as well as other relevant mechanisms.
With the results of the study in hand, scientists can concentrate on physically plausible material and architecture combinations. “Our hope is that other researchers can use this guidance from our study to design devices that have the right properties and reduce the range of trial-and-error, experimental variations they have to do in the lab,” Tchelepi said.
The innovative strategies for electrolyte design that have emerged include pursuing materials that are anisotropic, which means that they exhibit different properties in different directions. A classic example of an anisotropic material is wood, which is stronger in the direction of the grain, visible as lines in the wood, versus against the grain.
In the case of anisotropic electrolytes, these materials could finetune the complex interplay between ion transport and interfacial chemistry, thwarting build-up that proceeds dendrite formation. Researchers observed that some liquid crystals and gels display these desired characteristics.
Additionally, another approach identified by this study involves battery separators, which are membranes that prevent electrodes at opposite ends of the battery from touching and short-circuiting. Brand new kinds of separators could be designed, which feature pores that cause lithium ions to pass back and forth through the electrolyte in an anisotropic manner.
Manufacturing devices that rely on new electrolyte formations
Researchers are excited to see other scientists consider and expand upon the ‘leads’ identified in their study. Those next steps will involve manufacturing real devices that rely on experimental new electrolyte formulations and battery architectures, then testing which might prove effective, scalable, and economical.
“An enormous amount of research goes into materials design and experimental verification of complex battery systems, and in general, mathematical frameworks like that spearheaded by Weiyu have been largely missing in this effort,” observed co-author Tartakovsky, a Professor of Energy Resources Engineering at Stanford.
Following through on these latest results, Tartakovsky and colleagues are working on constructing a fully-fledged virtual representation – known as a ‘digital avatar’ – of lithium-metal battery systems, or DABS.
“This study is a key building block of DABS, a comprehensive ‘digital avatar’ or replica of lithium-metal batteries that are being developed in our lab,” concluded Tartakovsky. “With DABS, we will continue to advance the state of the art for these promising energy storage devices.”
