Thursday, 23 June 2016
Riverside Center (Hyatt Regency)
Metal corrosion is a serious problem that has beset various electrochemical systems. For lithium-ion batteries, oxidative corrosion of an Al current collector has been a great challenge in designing new electrolyte materials, and only a few lithium salts (e.g., LiPF6) are in practical use. Lithium bis(fluorosulfonyl)amide (LiFSA, LiN(SO2F)2) has attracted increasing attention as a state-of-the-art Li salt due to its high thermal/chemical stability and highly dissociative nature, but LiFSA-based electrolytes are known to induce severe oxidative corrosion of the Al current collector, which limits its widespread applications in lithium-ion batteries. The present work shows effective suppression of Al corrosion up to 4.5 V vs Li+/Li by using highly concentrated LiFSA electrolytes.1-4 The corrosion prevention mechanism can be interpreted in relation to a remarkable change in solution structures; all solvent molecules coordinate to Li+ and free solvent molecules disappear over a certain threshold concentration, as is evident from both spectroscopic analyses and first-principle molecular dynamics simulations. The stabilization of the Al current collector through the control of electrolyte solution structures is advantageous over LiPF6-based electrolytes, because the present case does not depend on F-, which also has negative effects on battery performance. Using highly concentrated LiFSA/acetonitrile (AN) electrolytes without free solvent molecules (5.0 and 6.0 mol dm-3), we demonstrated highly reversible charge-discharge cycling of both LiMn2O4/Li cell (with an Al current collector)3 and graphite/Li cell,2 which cannot be achieved in less concentrated electrolytes (3.0 and 4.0 mol dm-3). Furthermore, the rate performance far exceeds that in a state-of-the-art commercial electrolyte. This finding of superior performance in superconcentrated electrolyte will be an important breakthrough in developing a new electrolyte design strategy for advanced high-rate lithium-ion batteries.
1. Yuki Yamada et al., Chem. Commun., 49, 11194 (2013).
2. Yuki Yamada et al., J. Am. Chem. Soc., 136, 5039 (2014).
3. Yuki Yamada et al., ChemElectroChem, 2, 1687 (2015).
4. Yuki Yamada et al., J. Electrochem. Soc., 162, A2406 (2015).