Cracking the code on solid-state batteries

University of Missouri researchers may have a solution. Assistant Professor Matthias Young and team are figuring out how to use solid electrolytes instead of liquids or gels to make solid-state batteries, which are safer and more energy efficient.

"When the solid electrolyte touches the cathode, it reacts and forms an interphase layer that's about 100 nanometers thick -- 1,000 times smaller than the width of a single human hair," said Young, who has joint appointments in Mizzou's College of Engineering and College of Arts and Science. "This layer blocks the lithium ions and electrons from moving easily, increasing resistance and hurting battery performance."

Understanding this issue with solid-state batteries -- and how to overcome it -- has vexed scientists for more than a decade.

Young's team tackled the problem by better understanding the root cause.

Using four-dimensional scanning transmission electron microscopy (4D STEM), the researchers examined the atomic structure of the battery without taking it apart -- a revolutionary breakthrough for the field. This novel process allowed them to gain a fundamental understanding of the chemical reactions happening inside batteries, ultimately determining that the interphase layer was the culprit.

A potential solution

From electric vehicles to wireless earbuds, traditional lithium-ion batteries power our daily lives as they charge fast and store plenty of energy. However, they rely on a solution known as liquid electrolyte, which can catch on fire if damaged or overheated.

University of Missouri researchers may have a solution. Assistant Professor Matthias Young and team are figuring out how to use solid electrolytes instead of liquids or gels to make solid-state batteries, which are safer and more energy efficient.

"When the solid electrolyte touches the cathode, it reacts and forms an interphase layer that's about 100 nanometers thick -- 1,000 times smaller than the width of a single human hair," said Young, who has joint appointments in Mizzou's College of Engineering and College of Arts and Science. "This layer blocks the lithium ions and electrons from moving easily, increasing resistance and hurting battery performance."

Understanding this issue with solid-state batteries -- and how to overcome it -- has vexed scientists for more than a decade.

Young's team tackled the problem by better understanding the root cause.

Using four-dimensional scanning transmission electron microscopy (4D STEM), the researchers examined the atomic structure of the battery without taking it apart -- a revolutionary breakthrough for the field. This novel process allowed them to gain a fundamental understanding of the chemical reactions happening inside batteries, ultimately determining that the interphase layer was the culprit.

A potential solution

Young's lab specializes in thin-films formed by a vapor-phase deposition process known as oxidative molecular layer deposition (oMLD). Now, he plans to test whether his lab's thin-film materials can form protective coatings to prevent the solid electrolyte and cathode materials from reacting with each other.

"The coatings need to be thin enough to prevent reactions but not so thick that they block lithium-ion flow," he said. "We aim to maintain the high-performance characteristics of the solid electrolyte and cathode materials. Our goal is to use these materials together without sacrificing their performance for the sake of compatibility."

This carefully engineered approach at the nanoscale level will help ensure these materials work together seamlessly -- making solid-state batteries one step closer to reality.

"Understanding Cathode-Electrolyte Interphase Formation in Solid State Li-Ion Batteries via 4D-STEM" was published in Advanced Energy Materials. Co-authors are Nikhila C. Paranamana, Andreas Werbrouck, Amit K. Datta and Xiaoqing He at Mizzou.