We live in a world of electric devices, some as sophisticated as a computer and others as basic as a battery. We rarely spend much time pondering how they work, but we do know that they fail on a regular basis and are a recurring cost in our budget. So the question is, how to make a device, such as a battery, perform better with higher efficiency and a lower cost during its lifetime?
Matthew Starr, a material science graduate student at the University of Wisconsin-Madison, thinks he may have an answer. He has been looking at a class of materials that generate electricity when they are stressed by bending, compressing and stretching. He thinks these piezoelectric materials could serve as a more efficient and cheaper conductor in an electric device, such as the two terminals of a battery. These materials may someday offer an alternative for conventional conductors.
“This can be turned into cheaper batteries, capacitors and solar cells with higher performance,” says Starr, “because piezoelectric materials are generally cheap.”
If his idea holds up, Starr anticipates it would open a new area combining the advanced studies of electricity, chemistry, and physics.
Usually, a conductor is made of metal or other materials whose the conducting properties are stable. For example, a battery’s conductors are its two terminals called electrodes. In a lithium battery, one electrode uses the lithium (Li) metal to exchange electric charge with the other electrode, both dipped in a solution called electrolyte, to create and conduct electricity. During the whole process, the lithium’s conducting property won’t change.
Thus comes the difference of piezoelectric materials: they change. When given mechanic stress from outside, like pushing or pulling, piezoelectric materials can create electric energy by themselves and enhance their conducting properties.
Starr believes this could make piezoelectric materials better electrodes for batteries, as well as other conductors that run a device, at a lower cost. He has tested some of these piezoelectric materials, such as zinc oxide.
The idea behind the experiments is complicated, yet its core contains three basic steps: First, compress and stretch the material, which has been soaked in a solution to produce electric energy.
Second, the electric energy generated can drive an electrochemical reaction within the solution, which will undergo the gain and loss of electrons. This is like how the battery electrodes interact in the electrolyte. By giving and getting electrons between each other, the two electrodes create a flow of electric charge inside the battery.
Next, if the solution is just water, the reaction will split it into hydrogen and oxygen gases.
The good new is that the experiments yielded positive results, which gave off hydrogen and oxygen from the solution. This means the tested piezoelectric material was working in a predicted way.
“People may have been using them (piezoelectric materials) in many ways, but they don’t take the advantage of their (piezoelectric) properties,” says Starr.
Due to their ability to produce electric energy by mechanically deforming, piezoelectric materials have long been used as sources of high electrical power. The best-known application would be the electric cigarette lighter. By pressing the button we hit its piezoelectric crystal, which produces electric current high enough to ignite the gas when it flows by the small spark.
But the idea to extend the function of piezoelectric materials beyond electricity production to the electrochemical reactions within a battery has not been well considered. This inspired Starr to look at the intersections of the fields where piezoelectric materials can be utilized.
Starr is now building a theory on the new use of piezoelectric materials, based on his experiments. Once the theory is done, the next step will be testing the theory with more piezoelectric materials.
If the result supports the theory, applications will be started as well as further development of the theory. But Starr isn’t in a rush to push his research into the applied world. “My job is just doing the studies,” Starr says, “The project is more on the basic side of science, not the applied thing.”
He has coauthored a paper on the result of his experiments with his advisor, Xudong Wang, and another colleague.
Experiments are conducted with tiny, sensitive equipment, in which the tested material is the size of a kernel of corn. “We need to measure things in a very low concentration,” says Starr. “The amount of the experiment byproducts is very small. Measuring them is very difficult.”
Yet this tiny “kernel” shows a promising likelihood to make up a complicated electrical system. “I think the study is very interesting,” Starr adds. By bending, straining and stretching these materials, “they can be used in the components of devices that people use every day.”