Not quite how lithium ions move in batteries
- Author:Ella Cai
- Release on:2017-03-29
The theory explaining how lithium ions move in batteries is not quite right, according to the Institute for Basic Science (IBS) in Korea, which has been examining the process in femtosecond detail.
The model was, said IBS, that lithium ions (green dots) move surrounded by a shell of ethylene carbonate (EC, blue ovals) molecules, and that these entities (‘solvation shells’ or ‘solvation sheaths’) are assisted in their motion through the electrolyte by a mixture of dimethyl carbonate (DMC), and diethyl carbonate (DEC) – all three chemicals, in equal concentration, are in the battery’s electrolyte.
Institute for Basic Science Li-ion transport
10psHowever, by looking at bonding dynamics using fast two-dimensional infra-red spectroscopy, the team found lithium ions binding to the oxygen atoms of the DEC, with bonds making and breaking in 2-17ps, and the same is true for DMC.
It means that dimethyl carbonate and diethyl carbonate are not simply lubricants for the lithium/ethylene carbonate solvation shells, but part of the solvation shells and, according to IBS, may play an active role in transporting lithium ions to the battery’s pole.
“It was believed that EC makes a rigid shell around lithium ions during the migration between electrodes,” said Professor Cho Minhaeng. “However, this study shows that the solvent shell is not that rigid, it is constantly restructured during the ion transport. For this reason, revising the existing lithium ion diffusion theory is inevitable.”
The research team is working on a follow-up study to refine the theory of lithium ion diffusion, and it is building a high-speed laser spectroscope that can record the chemical reaction on top of the cell electrodes.
The model was, said IBS, that lithium ions (green dots) move surrounded by a shell of ethylene carbonate (EC, blue ovals) molecules, and that these entities (‘solvation shells’ or ‘solvation sheaths’) are assisted in their motion through the electrolyte by a mixture of dimethyl carbonate (DMC), and diethyl carbonate (DEC) – all three chemicals, in equal concentration, are in the battery’s electrolyte.
Institute for Basic Science Li-ion transport
10psHowever, by looking at bonding dynamics using fast two-dimensional infra-red spectroscopy, the team found lithium ions binding to the oxygen atoms of the DEC, with bonds making and breaking in 2-17ps, and the same is true for DMC.
It means that dimethyl carbonate and diethyl carbonate are not simply lubricants for the lithium/ethylene carbonate solvation shells, but part of the solvation shells and, according to IBS, may play an active role in transporting lithium ions to the battery’s pole.
“It was believed that EC makes a rigid shell around lithium ions during the migration between electrodes,” said Professor Cho Minhaeng. “However, this study shows that the solvent shell is not that rigid, it is constantly restructured during the ion transport. For this reason, revising the existing lithium ion diffusion theory is inevitable.”
The research team is working on a follow-up study to refine the theory of lithium ion diffusion, and it is building a high-speed laser spectroscope that can record the chemical reaction on top of the cell electrodes.
