Manganese doubles capacity of lithium batteries
Based on a lithium-manganese-oxide cathode, the analysis could double enable smart phones and battery-powered automobiles to last more than twice as long between charges by adding vanadium and chromium .
“This battery electrode has realized one of the highest-ever reported capacities for all transition-metal-oxide-based electrodes. It’s more than double the capacity of materials currently in your cell phone or laptop,” said Christopher Wolverton, the Jerome B. Cohen Professor of Materials Science and Engineering in Northwestern’s McCormick School of Engineering, who led the study. “This sort of high capacity would represent a large advancement to the goal of lithium-ion batteries for electric vehicles.”
Lithium-ion batteries work by shuttling lithium ions back and forth between the anode and the cathode. The cathode is made from a compound that comprises lithium ions, a transition metal and oxygen. The transition metal, typically cobalt, effectively stores and releases electrical energy when lithium ions move from the anode to the cathode and back. The capacity of the cathode is then limited by the number of electrons in the transition metal that can participate in the reaction.
A French research team first reported the large-capacity lithium-manganese-oxide compound in 2016. By replacing the traditional cobalt with less expensive manganese, the team developed a cheaper electrode with more than double the capacity. Unfortunately the battery performance degraded so significantly within the first two cycles that researchers did not consider it commercially viable. They also did not fully understand the chemical origin of the large capacity or the degradation.
After composing a detailed, atom-by-atom picture of the cathode, Wolverton’s team discovered that the high capacity comes from oxygen participating in the reaction process. By using oxygen — in addition to the transition metal — to store and release electrical energy, the battery has a higher capacity to store and use more lithium.
“Armed with the knowledge of the charging process, we used high-throughput computations to scan through the periodic table to find new ways to alloy this compound with other elements that could enhance the battery’s performance,” said Zhenpeng Yao, co-first author of the paper and a former Ph.D. student in Wolverton’s laboratory.
The computations pinpointed two elements: chromium and vanadium. The team predicts that mixing either element with lithium-manganese-oxide will produce stable compounds that maintain the cathode’s high capacity. Wolverton and his team now plan to make and test the compounds in the laboratory.
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