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“Dendrites”… This strange word may not mean anything to you, but it’s a pet peeve of all battery developers. These small “peaks” that form on the electrodes can lead to serious malfunctions and loss of efficiency. MIT researchers claim to have found an innovative solution to this problem.
The MIT scientists’ discovery “may finally open the door to the development of a new type of rechargeable lithium battery that is lighter, more compact and safer than current versions and is being sought by labs around the world.” years,” the agency said in a statement.
To lighten and reduce the volume of batteries, the key is the electrolyte. Indeed, between the anode and cathode (terminals + and – of the circuit) there is a conductive substance called electrolyte, in liquid form. The scientists wanted to replace this liquid with a layer of hard ceramic material, thinner and lighter. “This search was marked by a big problem: dendrites,” says the Massachusetts Institute of Technology. Thus, this is the key point that has been solved by scientists.
This is because when the battery is subjected to stress, a metallic coating called electroplating can form. Eventually, dendrites eventually form. Dendrites are small “spikes” formed from deposits that can generate short circuits. Therefore, they develop a bit like branches, hence their Latin name “dendrites”, which comes from “branches”. They cause a lot of trouble for researchers working on battery design.
A new study published in the journal Joule should have addressed this problem directly. Many are looking for solutions. Some innovations use, for example, heating temperature to prevent dendrites. In fact, the MIT researchers made the breakthrough somewhat by accident, they explain, during previous work. Thus, they speak of a “surprising and unexpected” discovery. Namely, that the solid and solid electrolyte material used for a solid-state battery can be permeated with lithium, which is a very soft metal, during the battery charging and discharging process, because lithium ions move between the two sides,” MIT develops.
Dendrites, mechanical problem
They then discovered that the reason for the formation of dendrites was mechanical. Indeed, the reciprocating movement of ions during battery operation changes the volume of the electrodes. The solid electrolyte, which must remain completely in contact with the two electrodes between which it is sandwiched, is then subjected to loads. “In order to deposit this metal, there must be an increase in volume because you are adding new mass,” explains Yet-Ming Chang, one of the study’s authors. “So on the side of the cell where lithium is deposited, there is an increase in volume. And if there are even microscopic defects, it creates pressure on these defects, which can lead to cracks.” Thus, the considered cracks create defects in which dendrites can develop.
Once the problem was solved, they had to find a solution. To counter this mechanical stress, they decided to apply more force, but this time in a calculated and controlled manner. To better understand the effects of mechanical impact, the scientists used a transparent electrolyte, which allowed them to study in detail what was happening inside the battery. “You can see what happens when you apply compression to the system, and you can see if the dendrites behave in a way that corresponds to a corrosion process or a fracture process,” says Cole Fincher, co-author of the study. study.
Diagram representing normal and controlled dendritic spread. © Cole Fincher et al.
In this way, the team demonstrated that they can directly control the growth of dendrites by simply applying and releasing pressure. In other words, they did not stop the growth of the dendrites. On the other hand, they managed to ensure that their development did not harm the battery, in particular, due to the fact that they remained parallel to the two electrodes, and did not cross the electrolyte.
In this experiment, the scientists decided to create pressure by bending the materials. However, they argue that this mechanical stress can manifest itself in more than one way, increasing the possibility of creating batteries in which dendritic growth is controlled. The scientists have no plans to commercialize the concept, but they hope it can be used in industry to produce better batteries. “I would argue that this is an understanding of the failure modes of solid state batteries that we think the industry should be aware of and try to use to develop better products,” concludes Yeat-Ming Chang.