Beyond the lithium-cobalt-oxide battery
Lithium-ion batteries work by shuttling lithium ions back and forth between the anode and the cathode. When the battery is charged, the ions move back to the anode, where they are stored. The cathode is made from a compound that comprises lithium ions, a transition metal, and oxygen. The transition metal, which is 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.
"In the conventional case, the transition metal is doing the reaction," Wolverton said. "Because there is only one lithium ion per one cobalt, that limits of how much charge can be stored. What's worse is that current batteries in your cell phone or laptop typically only use half of the lithium in the cathode."
The lithium-cobalt-oxide battery has been on the market for 20 years, but researchers have long searched for a less expensive, higher capacity replacement. Wolverton's team has improved upon the common lithium-cobalt-oxide battery by leveraging two strategies: replacing cobalt with iron, and forcing oxygen to participate in the reaction process.
If the oxygen could also store and release electrical energy, the battery would have the higher capacity to store and use more lithium. Although other research groups have attempted this strategy in the past, few have made it work.
"The problem previously was that often, if you tried to get oxygen to participate in the reaction, the compound would become unstable," Yao said. "Oxygen would be released from the battery, making the reaction irreversible."