Texas Engineers have discovered a new phenomenon in modern batteries, one that could be used to improve their life cycles.
Battery performance suffers over time, like when a phone needs to be charged more frequently after years of use. A thin film that forms on the metal anode when the battery is charging and discharging plays a part in that issue. This film has benefits, but its roughness gradually wears the battery down.
Researchers have discovered a temporary version of this film that appears at rapid discharge speeds and dissolves back into the battery when the process finishes. This transient solid-electrolyte interphase (T-SEI) promotes a smoother surface of the metal anode than the permanent version, offering protection while avoiding harmful abrasiveness and resulting long-term issues.
This research, published in the Proceedings of the National Academy of Sciences, could significantly improve the performance and safety of everyday devices, from smartphones to electric cars, and enhance the potential of batteries as a viable option for large-scale energy storage.
"By controlling this transient interphase, we can design batteries that perform better under high-demand conditions, last longer and are less prone to failure," said Stephen T. Fuller, a Ph.D. student in the Cockrell School of Engineering's McKetta Department of Chemical Engineering, fellow of the National Defense Science and Engineering Graduate Program and the lead author of the research.
Much of the attention in the battery community typically goes to the recharge process, when an external power source jolts electrons from the cathode to the anode to give power to the battery. This new information came from closely studying the discharge process, indicating that this area could lead to further breakthroughs that improve battery performance.
"Before I joined UT, I spent my entire career looking at the recharge process in batteries, but I wanted to study the other side of the equation," said Kent Zheng, an assistant chemical engineering professor who came to UT in 2023 and was recently named to Forbes' 30 Under 30 Science list. "The battery discharge process has largely been overlooked in our community."
For this project, the researchers used an aqueous battery, which features an electrolyte solution made primarily of water. This solution shuttles ions through the battery to facilitate charging and discharging.
Aqueous batteries have tremendous potential for large-scale grid energy storage, storing renewables like wind and solar energy until they need to be deployed. They are less flammable and rely on lower-cost and more sustainable materials than other types of batteries. However, this technology still needs refinement before it can be defined at large scales.
State-of-the-art electroanalytical systems, including a rotating disk electrode and in operando visualization, were critical to discovering the formation and behavior of T-SEI. The film forms from supersaturation, which leads to salt deposition on the electrode.
The transient interface dissolves completely when the battery rests, leaving a clean and flat surface. The formation of the T-SEI layer during cycling reduced surface roughness by 42%, improving battery efficiency and durability.
The researchers plan to apply this discovery to other types of batteries to see if the T-SEI also appears in them. Harnessing this phenomenon could help researchers decrease or eliminate the formation of dendrites, irregular structures that develop over many charge-discharge cycles that can short a battery or cause reduced performance over time.
