For realizing sustainable world, Lithium-ion batteries are required to have higher energy density. Aluminum metal have been dominantly used as a current collector of positive electrode. A mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) containing 1 mol dm^-3 Lithium hexafluorophosphate (LiPF₆) has been used as an electrolyte solution, however, aluminum corrosion may occur due to this electrolyte solution under high voltage condition. On the other hand, super-concentrated electrolyte solution (SCES), which consists of only two or three times as much solvent as lithium salt, has been attracting attention as a new electrolyte solution of Lithium-ion battery. Motsumoto et al. proposed that aluminum corrosion was remarkably suppressed in lithium bis(trifluoromethanesulfonyl)imide (LiTFSI)-based SCES. However, the electrolyte solution containing fluorine has the problem which is the dissolution of the active material due to the decomposition product of the electrolyte solution．In the present work, we investigated aluminum corrosion in the lithium perchlorate (LiClO₄)-based SCES as a fluorine-free solution.

The LiClO₄ based SCES was prepared by dissolving LiClO₄ into DMC as the molar ratio of 1 : 2. For comparison, DMC solution containing 1 mol dm^-3 LiClO₄ was also prepared. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) were measured. X-ray photospectroscopy (XPS) was performed to evaluate the decomposition product on the aluminum electrode. Anodic current of the dilute electrolyte solution is observed at 3.9 V vs. Li/Li⁺. By contrast, in the LiClO₄ based SCES, the anodic current is less than 100 µA cm^-2 when polarized to 6 V vs. Li/Li⁺. In the dilute electrolyte solution, the ClO₄^- anion is decomposed to form Cl^-, which promotes aluminum corrosion. By contrast, the SCES has high oxidative stability, suggesting that the liquid structure of the SCES differ from that of the dilute electrolyte solution. two intense peaks appear at 196 and 198 eV in in XPS spectra of Cl 2p for the aluminum surface after LSV measurement in the dilute electrolyte solution. On the other hand, a weak peak is observed at approximately 199 eV in XPS spectra of Cl 2p for the aluminum surface after LSV measurement in the SCES. This result suggests that the ClO₄^- anion is not decomposed in the SCES.

References

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[2] J. Wang, Y. Yamada, K. Sodeyama, C. Chiang, Y. Tateyama, and A. Yamada, Nat. Commun., 7, 1-9, (2016).