A technique known as cryo-electron microscopy (cryo-EM) won the 2017 Nobel Prize in chemistry and has been used by scientists at Stanford University to capture the first atomic-level images of growths in batteries, which have been one of the largest limitations to developing better batteries.
These crystal growths appear finger-like in nature and contribute to the reason why high-energy batteries fail. Dendrites are serious business because they can cause short circuits and even fires. Although these dendrites have been observed before, they have never been imaged to atomic-level resolution. With these hi-res images, scientists aim to better understand the inner workings of batteries to the most fundamental level and hopefully create better batteries.
These images were taken by a team of scientists at Stanford University using this Nobel Prize winning technique which consists of a flash-freezing process followed by slicing and then imaging. During the flash-freezing phase the sample is dipped into liquid nitrogen which essentially stops the battery in time so that it’s components can be analyzed atom-by-atom. The sample is then sliced and placed under the microscope for investigation.
This process is harmless to the batteries under analysis, whereas, previous methods of imaging such as transmission electron microscopy (TEM) did harm the sample. With TEM, the batteries were prepared for investigation in air which caused corrosion of the lithium. In comparison, the flash-freezing phase of cryo-EM prevents this corrosion. Yuzhang Li, a Stanford graduate student who led the work with fellow graduate student Yanbin Li, explained cryo-EM as ‘focusing sunlight onto a leaf with a magnifying glass. But if you cool the leaf at the same time you focus the light on it, the heat will dissipate and the leaf will be unharmed. That’s what we do with cryo-EM.’
Yi Cui, a member of the Stanford Institute for Materials and Energy Sciences (SIMES) who carried out the research, said, ‘with cryo-EM, you can look at a material that’s fragile and chemically unstable and you can preserve its pristine state – what it looks like in a real battery – and look at it under high resolution’. The video below shows you the difference between the TEM and the cryo-EM techniques. It is evident that the dendrite, magnified by approximately 40,000 times, is harmed during the TEM process however remains intact after cryo-EM.
The team discovered that the lithium dendrites are long, six-sided crystalline nanowires that have a preferred direction of growth. The scientists also examined the coating surrounding the dendrites known as the solid electrolyte interphase (SEI) which is the layer where the dendrite reacts with the surrounding electrolyte. Thus, this area of research will allow scientists to discover the best electrolyte for minimum dendrite growth by being able to analyze the growth at atomic scales. Yanbin Li says, ‘this tool can help us understand what different electrolytes do and why certain ones work better than others.’ Improved battery performance could be seen in the future as a result of this research, so bring on more science. You can check out the findings of Y. Li et. al. in Science here.
Nobel Prize Winning Technique Discovers Reason Behind Battery Fires – Forbes