Investigating Lithium Dendrite Growth
Many things we use daily, like cell phones, electric cars, and power tools come with rechargeable batteries. But there can be problems if you don’t handle them properly. For example, certain types of cell phones are not allowed to be on airplanes because of safety reasons and some electric cars have caught fire due to the delicate nature of their lithium-ion batteries.
Solid-state batteries could be the answer to certain challenges. These batteries use a solid material like ceramic ionic conductors instead of liquid for their core, which is often called an electrolyte. This makes them much sturdier and safer since they’re non-combustible. Plus, they can be miniaturized easily and don’t get affected by temperature changes as much.
Solid-state batteries sound great, but after a few charging cycles they start to have issues. When you first use them, the battery has two sides (positive and negative) that are kept completely separate. But during the charging process lithium dendrites or tiny pieces of lithium slowly start to build up between these two sides until eventually they join together, forming a short circuit and stopping the battery from working anymore. Scientists still don’t know all the details of why this happens, so it’s something they need to research more closely.
A group of scientists led by Rüdiger Berger from Hans-Jürgen Butt’s department used a specific microscope method to answer the question: Where does lithium dendrite growth begin? In other words, do these dendrites spread out like the way stalactites grow from the top and stalagmites arise from the bottom until they meet in the middle (called a “stalagnate” in caves)? As there is no “top or bottom” inside a battery, do these dendrites travel from one pole to another (negative to positive or vice versa), or can they develop alongside each poles at once? Or could it be that some part of the battery helps “trigger” this growth? The researchers are hopeful that after studying this further with their special microscope techniques, they will have an answer.
Rüdiger Berger’s team studied something called “grain boundaries” in ceramic solid electrolyte. Grain boundaries are created during production when the atoms in the ceramic form small, random patterns instead of being arranged perfectly. These imperfect patterns cause line-like structures to appear where they don’t fit properly.
Scientists used an advanced microscopy technique called “Kelvin Probe Force Microscopy” to see the presence of grain boundaries on a surface when they zoom in close. The PhD student, Chao Zhu, says that an electric charge will make these boundaries even more obvious near the negative pole, which suggests that the atoms and electrons around them change as they appear.
When too many negative particles — called electrons — accumulate, positively charged lithium ions in the solid electrolyte can turn into metal lithium. This causes lithium deposits and dendrites (which are like branches) to form. If this same process keeps repeating itself, the dendrite will grow bigger until it connects the battery’s two ends. These beginnings of dendrite growth was only found at the negative side of the battery and nothing happened at the positive side.
Scientists are trying to figure out how lithium solid-state batteries grow, so that they can create a safe way to stop the growth of these batteries where it could be harmful. In turn, this would make it possible to use such batteries in more places.
A new study was recently published which looked into the development of lithium dendrites in materials made up of Li6.25Al0.25La3Zr2O12 grains. Scientists Chao Zhu, Till Fuchs, Stefan A.L Weber and other researchers used special microscopy techniques to look at the evolution of these lithium dendrites and how they form at grain boundaries. The results were published on March 9th, 2023 in Nature Communications with a DOI (digital object identifier) number of 10.1038/s41467-023-36792-7.
