In a surprising revelation that challenges prevailing assumptions, researchers have uncovered a counterintuitive phenomenon in electric vehicle (EV) batteries – cracks in the cathodes may actually enhance charging speeds. This discovery challenges the approach of many EV manufacturers who aim to minimize cracks in batteries to extend their lifespan.
Yiyang Li, an assistant professor of materials science and engineering at the University of Michigan and the corresponding author of the study published in the journal Energy and Environmental Sciences, explains, “Many companies are interested in making ‘million-mile’ batteries using particles that do not crack. Unfortunately, if the cracks are removed, the battery particles won’t be able to charge quickly without the extra surface area from those cracks.”
Li further emphasizes the significance of rapid charging, stating, “On a road trip, we don’t want to wait five hours for a car to charge. We want to charge within 15 or 30 minutes.”
This groundbreaking insight applies to a considerable portion of EV batteries where the positive electrode, or cathode, consists of countless microscopic particles, commonly composed of lithium nickel manganese cobalt oxide or lithium nickel cobalt aluminum oxide.
The research challenges the conventional understanding of the relationship between cathode particle size and charging speed. While smaller particles were believed to charge faster due to their higher surface area relative to volume, prior methods could only measure the average charging properties of all particles within the cathode.
To delve deeper, the researchers adopted a unique approach by measuring the charging speed of individual cathode particles. They used a custom-designed chip with microelectrodes, similar to arrays employed in neuroscience to study brain cell electrical signals. By placing cathode particles on the electrodes and conducting simultaneous charging and discharging experiments, the researchers found that the charging speed was not determined by particle size.
Jinhong Min, a doctoral student in materials science and engineering involved in the study, highlights, “We find that the cathode particles are cracked and have more active surfaces to take in lithium ions—not just on their outer surface, but inside the particle cracks.”
This unexpected behavior suggests that larger cracked particles may mimic the behavior of smaller particles when they crack, potentially due to rapid lithium ion movement in the grain boundaries of cathode particles.
The implications of cracked cathodes extend beyond rapid charging. As the electric vehicle industry aims to design long-lasting batteries with single-crystal particles, understanding the benefits of cracked materials could lead to innovative strategies. Li suggests that smaller particles may be necessary to enable fast charging with single-crystal cathodes. Alternatively, exploring different materials with enhanced lithium ion mobility could be a solution, although potential limitations in metal supply or energy density need to be considered.
The research, funded by LG Energy Solution, Battery Innovation Contest, and the University of Michigan College of Engineering, was conducted at the Lurie Nanofabrication Facility and studied at the Michigan Center for Materials Characterization. This revelation opens up new avenues for optimizing battery design and charging efficiency in the rapidly evolving world of electric vehicles.
By Impact Lab
