There are a few reasons Christopher Wolverton’s super lithium-rich battery shouldn’t work. The novel battery uses iron, an inexpensive metal that has previously failed in batteries. The battery also leverages oxygen to help drive the chemical reaction, which researchers thought would cause the battery to become unstable. But, despite these problems, the battery does work.
Wolverton teamed up with Argonne National Laboratory. Wolverton’s group at Northwestern University has developed rechargeable lithium-ion batteries that can cycle more lithium ions than the common lithium-cobalt-oxide counterpart.
The result is a higher capacity battery that could enable smartphones and battery-powered automobiles to last a lot longer. By using computation, they discovered the right balance of lithium, iron and oxygen ions to allow the oxygen and iron to simultaneously drive a reversible reaction without allowing oxygen gas to escape.
"Our computational prediction of this battery reaction is very exciting, but without experimental confirmation, there would be a lot of skeptics," said Wolverton, professor of materials science and engineering in Northwestern's McCormick School of Engineering. "The fact that it actually works is remarkable."
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 transitional metal and oxygen. The transitional metal, which is usually cobalt, effectively stores and releases electrical energy when lithium ions move from anode to 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 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. Researchers have been searching for a less expensive and higher capacity replacement. Wolverton’s team has improved upon the common lithium-cobalt-oxide battery by leveraging two strategies: replacing the 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. Other research groups have attempted it in the past but they have not been successful.
"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."
Through computational calculations, the team discovered a formulation that works reversibly. First, they replaced cobalt with iron, which is a huge advantage because it is the cheapest element on the periodic table. By using computation, they discovered that the right balance of lithium, iron and oxygen ions to allow the oxygen and iron to simultaneously, drive a reversible reaction without allowing oxygen gas to escape.
"Not only does the battery have an interesting chemistry because we're getting electrons from both the metal and oxygen, but we're using iron," Wolverton said. "That has the potential to make a better battery that is also cheap."
The fully rechargeable battery starts with four lithium ions instead of one. The current reaction can reversibly exploit one of the lithium ions, which significantly increased the capacity beyond today’s batteries. The potential to cycle all four back and forth by using iron and oxygen to drive the reaction is tantalizing.
"Four lithium ions for each metal -- that would change everything," Wolverton said. "That means that your phone could last eight times longer or your car could drive eight times farther. If battery-powered cars can compete with or exceed gasoline-powered cars in terms of range and cost that will change the world."
Wolverton has filed a provisional patent for the battery with Northwestern’s innovation and New Ventures Office. Next, the team plans to explore other compounds where the strategy could work.