An ionic liquid, [C4mpyr][Tf2N] (N-methyl-N-butyl-pyrrolidinium bis(trifluoromethanesulfonyl)amide), was selected as a model electrolyte-base, which has high stability at the very cathodic potential such as lithium redox potential2. The electrolyte was prepared by adding 10 wt.% of Li[Tf2N] to [C4mpyr][Tf2N] in dried air. The cell was fabricated using Ni foil as working electrode and Li foil as counter electrode, in an Air-filled glove box. Lithium electrodeposition was conducted with current density of 200 μA cm-2 for charge amount of 0.1 C cm-2 at the temperature ranged from 25 to 55 °C. The Ni working electrode was observed by SEM after dismantling the cell and washing the electrode with dimethylether.
The number of the deposits on the working electrode tends to decrease with increase in holding temperature6. The number of the deposits per unit area, in other words, nuclear density is thought to be affected by overpotential of working electrode. The overpotential is thought to be proportional to charge-transfer resistance. To confirm this hypothesis the charge-transfer resistance was obtained though impedance spectroscopy measurement at each temperature and the result imply the hypothesis is to be the case. At the meeting site, the growth behavior of electrodeposited lithium and lithium ion diffusion coefficient at each temperature will be also presented, and the ideal electrochemical properties for dendrite suppression will be discussed.
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