Posted May 21, 2014

Temple chemists develop a way to make lithium batteries safer, cheaper

Lithium ion batteries, central to powering most modern technology such as laptop computers, cell phones, hybrid vehicles and even solar-energy storage, are potentially dangerous—the liquid electrolytes used in the manufacturing of those batteries can be volatile.

Now, two Temple chemists have developed a way of creating a solid electrolyte that might reduce the battery’s volatility without decreasing its conductivity or increasing its costs.

Electrolytes in batteries serve as ionic conductors: A current is carried through the movement or flow of ions.

“There have been quite a few thrusts toward making lithium batteries safer, and one of them is to make everything in the battery a solid,” said Professor of Chemistry Stephanie Wunder, who is collaborating with Assistant Professor of Chemistry Michael Zdilla. “But in general, solids are less conductive.”

Zdilla’s lab has developed a new, solid electrolyte matrix by dissolving organic liquids with lithium salts—like table salt but with lithium instead of sodium ions. Both materials are similar to those currently used in lithium ion batteries. A non-polar solvent is then added.

“The non-polar solvent causes the organic liquid/lithium salt solution to crystallize into a solid,” Zdilla said. “One-dimensional channels are formed through the crystals by lithium and chlorine ions surrounded by an organic matrix, which allows the free flow of ions.

“There are no novel chemicals being used,” he noted. “They are the same materials that are going into lithium batteries right now. The chemicals are all very inexpensive.”

Zdilla said the current solid electrolytes most researchers are focusing on really grip the ions, hindering their flow and severely hampering conductivity. “The temperature-independent behavior of our solid suggests the free-flowing ions don’t even see the sides of the channel.”

Zdilla brought the new material—synthesized under his guidance by one of his undergraduate students, Rebecca Clymer, CST ’13—and the formation of its channels to the attention of Wunder. Wunder’s graduate student, Parameswara Rao Chinnam, later examined the new electrolytes and tested their temperature-dependent conductivity.

“What we found was that this new organic matrix seemed to have extremely good, low temperature conductivity,” Wunder said.

Though the matrix currently decomposes above room temperature, the researchers placed it in dry ice (-78 C). It held the same ability for conductivity as it did at room temperature.

“I’m not aware of any material, solid or liquid, that has ever behaved like that for ion conduction at low temperatures,” Zdilla said. “This technology could be valuable for battery performance in extremely cold temperatures like space, the deep sea, the Arctic or Antarctica. Even in some more temperate places, it still gets cold enough that regular batteries do not perform well.”

The researchers are confident that this technology has the potential for making lithium ion batteries better and safer, but stress that it is still only in a prototype stage.

“The lithium ion battery used in laptop computers took about 35 years to develop,” Wunder said. “We still need to work on stabilizing this material above room temperature before we begin assembling batteries.”