"This battery has reached the highest capacity ever achieved for a transition metal oxide electrode battery, more than twice the capacity of batteries in cell phones and tablets currently in use." Christopher Wolverton, a professor of materials science at Northwestern University's McCormick School of Engineering, who was responsible for the study, said, "A battery capacity this high is a big step forward for the goal of using lithium-ion batteries in electric vehicles."
The findings were published in ScienceAdvances on May 14.
Lithium-ion batteries work by moving lithium ions back and forth between the cathode and anode. The cathode consists of a compound containing lithium ions, a transition metal and oxygen. As the lithium ions move from the anode to the cathode, or back from the cathode to the anode, the transition metal (usually cobalt) effectively stores and releases electrical energy. The cathode capacity is what is limited by the electrons in the transition metal that can participate in the reaction.
A French research group first reported high-capacity lithium-manganese oxide compounds in 2016. By replacing conventional cobalt with cheaper manganese, the team developed cheaper but more than twice the capacity of conventional batteries with electrodes. But the study ran into challenges: the battery's performance dropped significantly after just two rounds of charging, preventing commercialization of the battery. And they didn't fully understand the nature of the battery's high capacity and declining capacity chemistry.
After studying a schematic of the cathode structure down to the atom, Wolverton's team discovered the reason behind the material's high capacity: it drives oxygen into the reaction. By using oxygen to store and release electricity in addition to the transition metal, the battery has the ability to store and use more lithium.
Next, the Northwestern team turned its attention to stabilizing the battery and preventing its storage capacity from rapidly declining.
"Based on the knowledge we had of charging and discharging, we used high-throughput calculations to traverse the periodic table of elements, looking for elements that were suitable for incorporation into the electrodes and thus improved battery performance." said ZhenpengYao, one of the paper's first authors and a former doctoral student in Wolverton's lab.
The calculation method identified two elements: chromium and vanadium. The team predicted that using either of them mixed with lithium-manganese oxide would result in compounds that maintain high cathode capacity. Next, Wolverton and his co-workers will test these theoretical compounds in the lab.
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