MRS Bulletin recently featured a paper co-authored by Regina García-Méndez, an assistant professor of materials science and engineering and core researcher with the Ralph O’Connor Sustainable Energy Institute (ROSEI), focusing on the future of solid-state batteries (SSB) in the electric vehicle (EV) industry.

In “Recent progress and challenges for manufacturing and operating solid‑state batteries for electric vehicles,” García-Méndez and her co-author Eric Kazyak, an assistant professor of mechanical engineering at the University of Wisconsin-Madison, outlined several challenges that need to be addressed before SSB can become widely adopted in the EV industry. This contrasts with lithium-ion batteries (LIB), which are the current norm.

Regina García-Méndez

“Metal-based SSB are ideal for portable applications like electric vehicles, by offering longer ranges, lower weight, faster charging, and enhanced safety than standard lithium-ion batteries. They can also enhance consumer electronics with better battery life and reliability,” García-Méndez said. “Despite significant progress, plenty of challenges remain, which this paper highlights, along with emphasizing the importance of scalable and sustainable processing for the commercial success of SSB technology.”

One major difference between SSB and lithium-ion batteries is the presence of liquids: SSB lacks any liquids, while LIBs contain them. The liquid electrolyte in LIBs can fill voids, enhancing contact between components and promoting uniform ionic transport. However, SSBs make use of pressure to ensure contact between components.

García-Méndez said that a key challenge in SSB is managing “stack pressures”—the force per unit area used to hold together different layers within the components of batteries upon operation. The charge must move from one battery component to the other, so the goal is to optimize materials properties and operating variables to enable such phenomenon

“We must figure out how to minimize such stack pressure if SSB is going to become viable for EVs,” she said.

Another challenge involves understanding the behavior of composite cathodes, which are the positively charged electrodes through which electrons and ions enter an electrical device upon discharge. When a battery is discharged, the active material in the cathode first expands and then contracts when the battery starts being charged. Those volume changes create stresses within the materials. García-Méndez notes that there is still a lot of work to be done to find the correct material composition and architecture to accommodate the repeated expansion and contraction of the materials in the cathode.

“Sometimes these stresses are high enough that they fracture adjacent materials, then they disconnect affecting the amount of charge you can store,” García-Méndez said. “It’s complex because we have so many interfaces and materials to consider. We need to figure out how different material properties affect the performance of the entire component. Batteries are somewhat of a black box, but advanced characterization techniques could allow us to better understand these mechanisms.”

On the manufacturing side of things, García-Méndez suggests that developers aim to produce SSB similar to LIB production. This will ensure that potential migration from one battery type to the other is as seamless as possible.

“Realistically, you need to make the transition easy, or companies likely won’t do it. They’ll stick with their old practices out of convenience unless there is a step change in performance that justifies such changes,” she said.

The paper highlights the ongoing research that García-Méndez has been pursuing since joining Hopkins in September 2023 and will continue to do so. SSB technology is a popular focus research area, with major automakers backing startups to figure out how to make SSB work in electric vehicles. In fact, the issue of MRS Bulletin that featured García-Méndez’s work was dedicated to materials for EVs and included a webinar in which she presented her findings.

“This area is currently a highly active field of research, with significant advancements anticipated in the coming years,” García-Méndez said.