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Researchers have developed a new way of constructing lithium-ion batteries that might pave the way for stronger energy densities, performance, and battery safety, according to a report from Penn State.
The Solid-Electrolyte Interphase
Sitting between the lithium metal of the battery and its electrolytes is the solid-electrolyte interphase (SEI), and it has been a roadblock to developing better performing batteries for years.
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There is increasing demand for higher energy densities in rechargeable lithium-ion batteries as their use spreads to all sorts of electronic devices, from cell phones to electric vehicles, and so the SEI is naturally one of the places researchers are going to look to try to improve performance.
"This layer is very important and is naturally formed by the reaction between the lithium and the electrolyte in the battery," said Donghai Wang, Professor of Mechanical and Chemical Engineering at Penn State. "But it doesn't behave very well, which causes a lot of problems."
Creating a Better Solid-Electrolyte Interphase
The problems start when the SEI begins to degrades. Over time, this results in the formation of dendrites, needle-like growths on the lithium electrode of the battery which gradually inhibit their performance and safety.
"This is why lithium metal batteries don't last longer—the interphase grows and it's not stable," Wang said. "In this project, we used a polymer composite to create a much better SEI."
Led by Yue Gao, a chemistry doctoral student at Penn State, the engineers crafted a new SEI is a reactive polymer composite made up of polymeric lithium salt, lithium flouride nanoparticles, and graphene oxide sheets.
Evan Pugh University Professor of Chemistry Thomas E. Mallouk lent his assistance to the project to help create the thin layers of the materials.
"There is a lot of molecular-level control that is needed to achieve a stable lithium interface," Mallouk said. "The polymer that Yue and Donghai designed reacts to make a claw-like bond to the lithium metal surface. It gives the lithium surface what it wants in a passive way so that it doesn't react with the molecules in the electrolyte. The nanosheets in the composite act as a mechanical barrier to prevent dendrites from forming from the lithium metal."
This was accomplished by controlling the surface of the lithium at the level of individual atoms and molecules which enabled the project to be successful.
"When we engineer batteries, we don't necessarily think like chemists, all the way down to the molecular level, but that's what we needed to do here," said Mallouk.
"With a more stable SEI, it's possible to double the energy density of current batteries, while making them last longer and be safer," Wang said.
The research was published today in the journal Nature Materials.