A team of researchers from Shinshu University in Nagano, Japan is now closer to a thin, high-capacity lithium-ion battery that could open the gates to better energy storage systems for electric vehicles.
"Lithium-ion batteries are very promising energy storage systems for electric vehicles that require relatively high energy densities," said the study's author Nobuyuki Zettsu, a professor in the CEES and in the Department of Materials Chemistry at Shinshu University. "However, their high operating voltages commonly result in the oxidative decomposition of the electrode surface, which subsequently promotes various side reactions."
Lithium-ion batteries store a lot of energy, but the force it takes to make the battery disperse the energy is too much -- so much, in fact, that the resulting damage makes the battery lose storage capacity.
To combat this issue, Zettsu and colleagues examined the electric and electrochemical properties of the high-voltage (>4.8 V, vs Li+/Li) cathode, where the electrons enter the battery cell.
Zettsu may have turned the tide on surface modifiers through the use of a self-assembled monolayer. His team applied an ultra-thin coating of fluoroalkylisilane to the surface of the cathodes. Fluoroalkylisilane, a type of silicone, organizes itself into the most efficient arrangement to conduct lithium ions and insulate electrons while remaining only one atom thick.
"We discovered... that coating the surface of the active material with a self-assembled monolayer... promoted efficient transportation within the electrodes, while also suppressing the side reactions occurring at the electrode and electrolyte interface," Zettsu said. "This coating provided improvement in both the power density and the cyclability in high-voltage lithium-ion batteries."
The researchers saw that the direct contact between the cathode and the electrolyte entering the battery was minimized, and that the capacity of the battery did not degrade even after it was cycled one hundred times.
"Due to the world's environmental regulations, the push towards electric and hybrid automobiles is proceeding at a steady momentum. The performance level required for lithium ion batteries is very high," Zettsu said. "Currently, we are working on manufacturing real battery cells for plug-in hybrid vehicles and battery electric vehicles using the coating process and experiments in automatic driving modes."
This work was supported by Japan Science and Technology Agency and the Japan Society for the Promotion of Science.
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