Researchers at Northwestern University have discovered a new method for stabilizing the performance of record-high-capacity batteries. Based on lithium manganese oxide cathodes, the innovation could more than triple the power of smartphones and electric vehicles.

"This battery electrode has reached the capacity of one of the highest ever recorded transition metal oxide-based electrodes. It has more than twice the capacity of your current cell phone or computer."

Christopher Wolverton, a professor of materials science and engineering at Northwestern University's McCormick School of Engineering, said.

"The high capacity of this electrode indicates a huge advance in its target for lithium-ion batteries in electric vehicles," added Christopher.

The research was reported online May 18 in the journal Science Advances.

Lithium-ion batteries work by migrating lithium ions back and forth between the positive and negative electrodes. The positive electrode is made from a compound containing lithium ions, transition metals and oxygen. Transition metals, usually cobalt, efficiently store and release electrical energy as lithium ions migrate back and forth between the positive and negative electrodes. The cathode capacity is thus limited by the number of electrons in the transition metal participating in the reaction.

A French research team first identified the properties of high-capacity lithium manganese oxides in 2016. By replacing traditional cobalt with lower-cost manganese, the researchers have developed a cheaper electrode with twice the previous capacity. But it's not flawless either. Scientists don't think it can be applied to the market because the battery's performance is greatly diminished during the first two cycles. At the same time, they do not fully understand the chemical roots of battery degradation and its high capacity.

After drawing a comprehensive picture of the positive electrode where atoms are connected, Wolverton's team discovered the reason behind the material's high performance: It drives oxygen to the reaction process. By using oxygen and transition metals to store and release electrical energy, batteries have greater capacity to store and utilize more lithium.

The Northwestern team then turned their R&D focus to how to stabilize the battery's performance and stop its rapid decay.

"Aided by the theory of the charging process, we used high-speed computing to thoroughly search the periodic table to find ways to alloy this compound containing other elements to enhance the performance of the battery."
Zhenpeng Yao, a former doctoral student in Wolverton's lab and co-first author of the paper, said.

Calculations identified two potentially useful elements: vanadium and chromium. The research team predicts that mixing lithium manganese oxide with one of these will result in a stable compound that maintains the unparalleled high performance of the cathode. These theoretical compounds will then be tested experimentally in the laboratory by Wolverton and his partners.

The research was supported by the Center for Electrochemical Energy Science, part of the Energy Frontiers Research Center funded by the U.S. Department of Energy's Office of Science, under its Fundamental Energy Science Program (Program Code: DE-AC02-06CH11357). Yao, a postdoctoral researcher at Harvard, and Soo Kim, a postdoctoral researcher at MIT, both former members of the Wolverton lab, are co-first authors on the paper.