A research team from Tokyo University of Science recently conducted a pioneering study to gain insights into solid-electrolyte interphases (SEI) formation and their properties in water-in-salt electrolyte-based potassium-ion batteries (KIBs).
In a paper published in the journal Angewandte Chemie International, the scientists explain that water-in-salt electrolytes (WISE) are used in KIBs to make them more stable thermally and chemically.
However, the prevention of hydrogen evolution at the negative electrode for its stabilization is a major challenge in high-voltage aqueous batteries. While solid-electrolyte interphases that form between these electrodes and the electrolyte solution help stabilize the electrodes in LIBs by preventing electrolyte decomposition and self-discharge of the batteries, they have been scarcely researched in the context of KIBs.
To address this lack of knowledge, the researchers employed two advanced analytical techniques—scanning electrochemical microscopy and operando electrochemical mass spectrometry—to observe how SEI forms and reacts in real-time during the operation of a KIB with a 3,4,9,10-perylene tetracarboxylic diimide negative electrode and a water-in-salt electrolyte developed by the team in a previous study.
The experiments revealed that solid-electrolyte interphases form a passivating layer in WISE akin to that seen in LIBs, with slow apparent electron transfer rates, helping suppress hydrogen evolution. This can ensure stable performance and higher durability of potassium-ion batteries. However, the researchers observed that the coverage of the SEI layer was incomplete at higher operating voltages, leading to hydrogen evolution.
Taken together, the results reveal the need to explore potential avenues to enhance solid-electrolyte interphase formation in future aqueous batteries.
“While our results reveal interesting details on the properties and stability of SEI found in one particular WISE, we should also focus on reinforcing the SEI network to achieve improved functionality,” Shinichi Komaba, lead author of the study, said in a media statement. “SEI could perhaps be improved by the development of other electrolytes that produce unique SEIs, but also through the incorporation of electrolyte additives or electrode surface pretreatment.”
Komaba noted that the development of aqueous batteries such as KIBs will be instrumental for sustainable societies in the future since they could replace the expensive and hazardous LIBs currently used in electric vehicles, smart grids, renewable energy systems, and marine applications.