Same-size lithium ion battery, 10 times the storage

Northwestern University and Argonne National Laboratory this week published advances on research that takes on lithium ion batteries’ weak spot: the electrodes that hold electric charge. Both efforts reflect the quest among researchers to improve batteries by improving the anode and cathode material used in today’s lithium ion batteries.

With a better anode, a cell phone could be charged in 15 minutes and have 10 times the energy storage capacity of current lithium ion batteries, according to Northwestern University researchers, who predict the technology could be available in three to five years.

Argonne’s battery researchers, meanwhile, say that replacing the traditional graphite anode with titanium oxide could lead to cell phones that can get half their full charge in less than 30 seconds.

In consumer electronics’ batteries, lithium ions (atoms with a positive charge) move between the anode and cathode end of a battery, drawn by electrical charge. During discharge, the ions move in one direction and then the other during charging, traveling through a gel-like electrolyte.

Northwestern University professor of chemical and biological engineering Harold Kung tried to address the speed with which those ions can move by creating a new anode material. Instead of using very thin sheets of carbon graphite, he and his collaborators put clusters of silicon between the sheets.

This approach allows more lithium atoms to attach to the sheets since silicon can hold more lithium ions than carbon. By sandwiching the silicon between the carbon sheets and creating tiny holes on the sheets for the ions to move through, the silicon can maintain its integrity. It hasn’t been used before because it tends to expand and fragment during charging and discharging, according to Northwestern.

"We have much higher energy density because of the silicon, and the sandwiching reduces the capacity loss caused by the silicon expanding and contracting. Even if the silicon clusters break up, the silicon won’t be lost," Kung said in a statement. "Even after 150 charges, which would be one year or more of operation, the battery is still five times more effective than lithium-ion batteries on the market today."

Lithium ion batteries have become the preferred battery chemistry for consumer electronics and plug-in electric vehicles because lithium is the lightest metal and produces ample power for electric car applications. But researchers are trying to boost the amount of energy lithium ion batteries can hold per volume and extend their life.

Researchers at Argonne National Laboratory are also working to replace graphite as the anode material but instead are using titanium oxide. The material was considered a poor candidate for anode materials since it its not a crystalline structure with well-understood electrical properties. But in the course of charging and discharging the battery, researchers said that the titanium oxide molecules began to line up in a way that could lead to much better performing batteries.

"We’re seeing some nanoscale phase transitions that are very interesting from a scientific standpoint, and it is the deeper understanding of these materials’ behaviors that will unlock mysteries of materials that are used in electrical energy storage systems," said Argonne scientist Jeff Chamberlain, in a statement.