If you've ever wondered what challenges lie in the path of developing next-generation lithium-ion batteries, one major hurdle is the formation of 'lithium dendrites'. These tiny, tree-like structures can grow during the battery's charging process and pose significant performance and safety risks.
Lithium metal is a prime candidate for anodes in future batteries due to its high energy capacity and ability to boost battery voltage. However, during charging, lithium ions can deposit unevenly on the anode surface, leading to dendritic growth. These dendrites can eventually pierce the battery's separator, creating a path for electrical current that can cause short circuits or even fires.
Traditionally, imaging the intricate details of dendritic structures inside a battery in real-time has been challenging. Techniques like X-ray tomography and various forms of microscopy have been used, but they either lack sufficient resolution or require invasive methods that could alter the battery's behavior.
Using MRI, particularly using the hydrogen (1H) signals from the battery's electrolyte, is a recent approach that has changed how we can visualize these structures non-destructively. Unlike direct lithium imaging, which struggles with sensitivity and resolution, MRI of the electrolyte offers a clever workaround. By focusing on how the dendrites displace and affect the surrounding electrolyte, MRI can provide detailed 3D images of dendritic growth without directly imaging the lithium itself. This method has also revealed their volume and growth patterns over time during the battery charging process.
In a recent study, Peklar R et al explored how different configurations of battery cells affect dendrite formation. They tested single cells and multiple cells arranged in parallel & series circuits. It turns out that the arrangement of cells has a significant impact on how dendrites grow. In series configurations, where the same current passes through each cell, dendritic growth was found to be uniform. Conversely, in parallel configurations, cells can experience different current flows, leading to uneven growth. Thus, the series configuration appears to be potentially safer & more stable.
What's particularly fascinating is the ability of MRI to track these changes in real-time. The study involved sequential MRI scans during the battery charging process, allowing the researchers to see how dendrites formed and evolved. They used a technique called thresholding to differentiate between areas of electrolyte and dendrites, which helped quantify the volume of dendrites accurately.
These findings are crucial for battery manufacturers and researchers, as they offer insights into designing safer and more efficient batteries.