Analysis of Surface Deposit Formed on the Natural Graphite Negative Electrode in N, N-Diethyl-N-Methyl-N-(2-methoxyethyl) Ammonium Bis (trifluoromethylsulfonyl) Amide Containing Lithium Ion

Abstract

We investigated the charge-discharge characteristics of the natural graphite negative electrode in N, N-diethyl-N-methyl-N-(2-methoxyethyl) ammonium bis (trifluoromethylsulfonyl) amide (DEME-TFSA) containing lithium ion as the electrolyte for non-flammable lithium-ion batteries. The charge-discharge tests showed that the discharge capacity was stably maintained at ca. 300 mAh g-1 until the initial 10th cycle and the charge-discharge efficiencies reached ca. 100% after the initial cycles. The FE-SEM / EDX mapping results showed that the surface deposit (O, F, and S) deriving from DEME-TFSA was formed during the 1st charge. The XPS analysis results indicated that the surface deposit would compose of LiF, O, and S. It was found that the LiF-based compound containing O and S as a surface deposit was formed on the natural graphite electrode due to the cathodic decomposition of the TFSA- anion as a side reaction during the 1st charge.