A team of chemists from New York University and the University of Cambridge has developed a method for examining the inner workings of supercapacitors. Their technique, based on magnetic resonance imaging (MRI), offers a way to monitor and possibly enhance the performance of such devices.
The work, which appears in the latest issue of the journal Nature Communications, focuses on electric double-layer capacitors (EDLCs), which are excellent options for powering systems where fast charging and power delivery are crucial, such as in regenerative braking.
“The MRI method really allows us to look inside a functioning electrical storage device and locate molecular events that are responsible for its functioning,” explains Alexej Jerschow, one of the paper’s senior authors.
“The approach allows us to explore electrolyte concentration gradients and the movement of ions within the electrode and electrolyte, both ultimately a cause of poor rate performance in batteries and supercapacitors,” adds co-author Clare Grey.
Supercapacitors’ ability to store more electrical charge than plain old capacitors is due to an electrical double layer formed at the electrolyte-electrode interface, which serves to trap energy more effectively. However, the exact nature of this charge process remains a subject of debate. Previous research has attempted to understand this process through the synthesis of new electrode materials, simulations of the charging process, and by spectroscopy, rather than by direct imaging of a complete functioning device.
In work published by Nature Materials in 2012, the NYU-Cambridge team developed an MRI-based method of looking inside a battery without damaging it. In the supercapacitor work, the researchers found that MRI could pinpoint the location and estimate the amount of electrolyte ions – crucial data for understanding the energy storage mechanism.
The technique has the potential to analyze functioning devices at different states of charge, providing insights into the microscopic processes responsible for the storage and power capacity of a device. With this non-invasive method, one could rapidly test the properties of different capacitor materials, as well as assessing factors that affect the longevity of the devices.
Next, the team plans to investigate how different ions interact with other molecules in the electrolyte mixture, which may be a key to enhanced performance.