Scientists explore how to track the internal state of batteries to develop batteries for specific purposes

Future transportation will mainly include electric cars , trucks and airplanes, but a single battery design will obviously not be able to meet complex needs. In the coming decades, batteries may need to be customized according to specific uses, so it is necessary to understand the internal state of various types of batteries as accurately as possible.

(Image source: techxplore)

Every battery works the same way, with ions (atoms or molecules with an electrical charge) transporting an electric current from a negative electrode to a positive electrode and back again through an electrolyte. By understanding exactly how different ions move through different types of electrolytes, researchers can find ways to alter this transport, creating batteries that charge and discharge in a way that's best suited to a particular application.

According to foreign media reports, in a breakthrough discovery, scientists combined multiple techniques to accurately measure the ions moving in the battery. Using the Advanced Photon Source (APS) at Argonne National Laboratory, researchers can not only observe the internal state of the battery while it is running and measure the reaction progress in real time, but also open the door to similar experiments using different types of batteries.

The researchers worked with the Joint Center for Energy Storage Research (JCESR) to come up with this result, detailing the speed at which lithium ions pass through a polymer electrolyte. "By combining different experimental methods to measure speed and concentration and comparing them with theoretical data, we have demonstrated that it is possible and we will now carry out measurements on other systems with different properties," said lead researcher Hans-Georg Steinrück, a professor at Paderborn University in Germany.

These measurements, performed at the APS' 8-ID-I beamline, included using ultrabright X-rays to measure the speed at which ions move through the battery and to measure the concentration of ions in the electrolyte as the model battery discharges. The team then compared the results with a mathematical model and derived an extremely precise number, the ionic conductivity, which represents the current carried by the ions.

Essentially, ionic conductivity (transport number) is the amount of current carried by positively charged ions relative to the total current. The team calculated this number to be about 0.2. The researchers say this new way of measuring ion movement is very sensitive, so the conclusions drawn are different from other methods. "The traditional method is to measure ionic conductivity by analyzing the current. However, it is not clear how much of this current is generated by lithium ions and how much is caused by other factors that you don't want in the analysis," said Professor Michael Toney of the University of Colorado Boulder. "The principle is simple, but we have to make accurate measurements. This is a real proof-of-concept project."

In this experiment, the research team used a solid polymer electrolyte instead of the liquid electrolyte widely used in lithium-ion batteries. This is because polymers are non-flammable and safer. Venkat Srinivasan, one of the researchers, said that in the past, the best way to study the inner workings of a battery was to send current to the battery and then analyze it. Now, scientists can track the movement of ions in real time and find opportunities to change the state of motion to meet the needs of battery design. He said: "We had to connect the dots before, and now we can detect ions directly and clearly."

Eric Dufresne, a physicist in Argonne's X-ray Science Division, said: "In this experiment, the research team used the correlations provided by the APS to obtain results at speeds of just nanometers per second. This is a very thorough and complex study that combines X-ray techniques in a novel way. It is both a great example of this and a step towards developing future applications."

Dufresne and his colleagues note that the experiment will only be possible if the APS upgrades its electron storage ring, increasing the brightness of the X-rays it produces by a factor of 500. "With the APS upgrade, we can push the dynamics studies to better than microseconds," Dufresne said. "We will be able to focus the beam and make finer measurements of thicker materials. The upgrade will give us unique capabilities that will allow us to do more experiments like this."

The research team said the next step will be to analyze more complex polymers and other materials, and eventually move on to studying liquid electrolytes. Toney hopes to explore ions in other types of materials, such as calcium and zinc. Testing a variety of materials is important for achieving the ultimate goal of designing batteries for specific uses. Srinivasan said: "If we want to make high-energy, fast, safe and long-lasting batteries, we need to understand more about ion movement and what is happening inside the battery, and use this knowledge to design new materials."