New material may help cut battery costs for electric cars, cellphones

Researchers at the University of Texas at Dallas and Seoul National University have designed a novel battery cathode material that offers a potentially lower-cost, more eco-friendly option to lithium-ion batteries. Their sodium-ion design, which retains the high energy density of a lithium-ion cathode, replaces the most of the lithium atoms (green) with sodium (yellow). The layered structure of the new material also incorporates manganese (purple) and oxygen (red). The research is published in the journal Advanced Materials. Credit: University of Texas at Dallas

In the battle of the batteries, lithium-ion technology is the reigning champion, powering that cellphone in your pocket as well as an increasing number of electric vehicles on the road.
   "Lithium is a more expensive, limited resource that must be mined from just a few areas on the globe," Cho said. "There are no mining issues with sodium—it can be extracted from seawater. Unfortunately, although sodium-ion batteries might be less expensive than those using lithium, sodium tends to provide 20 percent lower energy density than lithium."

The energy density, or energy storage capacity, of a battery determines the run time of a device.

"We used our previous experience and thought about these issues—how can we combine these ideas to come up with something new to solve the problem?" Cho said.

A battery consists of a positive electrode, or anode; a negative electrode, or cathode; and an electrolyte in between. In a standard lithium-ion battery, the cathode is made of lithium, cobalt, nickel and oxygen, while the anode is made of graphite, a type of carbon. When the battery charges, lithium ions move through the electrolyte to the anode and attach to the carbon. During discharge, the lithium ions move back to the cathode and provide electric energy to run devices.

"There was great hope several years ago in using manganese oxide in lithium-ion battery cathodes to increase capacity, but unfortunately, that combination becomes unstable," Cho said.

In the design developed by Cho and his colleagues, sodium replaces most of the lithium in the cathode, and manganese is used instead of the more expensive and rarer elements cobalt and nickel.

"Our sodium-ion material is more stable, but it still maintains the high energy capacity of lithium," Cho said. "And we believe this is scalable, which is the whole point of our research. We want to make the material in such a way that the process is compatible with commercial mass production."

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