Drexel University elucidates electrochemical energy storage mechanisms in batteries and supercapacitors

According to foreign media reports, researchers at Drexel University have developed a new technology that can quickly identify the exact electrochemical mechanisms occurring in batteries and supercapacitors of different compositions. This breakthrough could help accelerate the design of high-performance energy storage devices.

(Image source: Drexel University)

The team combined two well-established scientific research methods, one is to determine the composition of a compound by its ability to absorb visible light, and the other is to measure the current flow of energy storage devices such as batteries and supercapacitors. By conducting these tests simultaneously, researchers can track ion transfer within the device in a more precise manner, revealing the complex electrochemical processes that produce usable electricity.

Danzhen Zhang, a researcher at the school, said that it is extremely difficult to quantify and observe complex electrochemical systems in a meaningful way during operation. The challenge is that it is impossible to see ions (charged atomic particles). These particles enter the device when charging and create an electrical current through their movement, powering the device, but are too small and move too fast.

Because you can't see how the ions are arranged inside, on top of, and between the electrodes, rational design to maximize the energy storage area and promote orderly entry and exit of ions is quite challenging. "It's like opening the pantry door with your eyes closed and smelling it to see if there's enough room for a few more cans of soup," said researcher John Wang.

The three most common ways for ions to accumulate on an electrode is within its atomic layer, on its surface, or on top of other ions on its surface. Each of these arrangements has advantages and disadvantages in terms of battery or supercapacitor performance. Embedding the electrode material layer can store more energy; attaching and detaching from the material surface, called surface redox reaction, can quickly release energy; staying on the surface ion layer with solvent molecules, which is a double electric layer reaction, Slightly greater discharge power can be achieved, but with less energy.

Researchers can observe how long it takes for a storage device to discharge and recharge, or test electrode materials at the beginning and end of a discharge cycle to better understand the dominant storage mechanism. But recent research suggests that these energy storage mechanisms may not always occur in orderly, discrete reactions. Many reactions occur in mixed or intermediate mechanisms. Therefore, distinguishing and fundamentally understanding these mechanisms is of great significance for improving the performance of energy storage devices.

By precisely quantifying and tracking the ions within the electrodes as they cycle through charge and discharge, researchers can better understand all the reactions that occur. It is important to identify parasitic side effects that may hinder device performance. Based on this information, designers can better tailor electrode materials and electrolytes to improve performance and slow degradation.

The team's new method can monitor the location and movement of ions from the electrolyte to the electrodes in energy storage devices. This method combines ultraviolet-visible (UV-vis) spectroscopy, which determines the chemical composition of a compound by the way it absorbs light, and a method of measuring electrical current during charge-discharge cycles, called cyclic voltammetry (CV). Danzhen said: "Previously, researchers used UV-vis to qualitatively distinguish energy storage mechanisms, but never quantified redox activity. The new UV-vis method can quantify the number of electron transfers and use optical signals to directly monitor changes in electrode materials. Furthermore, derivative calculations in this UV-vis method help to further eliminate inaccuracies when using traditional electrochemical characterization.

Applications of this method are currently limited to the transparency of electrode materials, but the researchers believe this method could be a low-cost alternative to X-ray absorption spectroscopy. Research leader Yury Gogotsi said: "Finding the precise combination of electrode material and electrolyte from countless possibilities requires rapid assessment and classification of the electrochemical behavior of the materials used. Using this method, it helps to discover better energy storage materials and equipment to avoid mistakes.”

The team plans to continue its work using this method to test new electrolyte and electrode material combinations and investigate more complex electrochemical energy storage systems.