Intercalation/De-Intercalation Behavior of Li-Ion Encapsulated By 12-Crown-4-Ether into Graphite Electrode

Abstract

From the viewpoint of abundance of Mg and advantage originated from divalent ion, Mg-ion batteries have much attention as a next-generation energy device. The development of electrolytes which can achieve reversible Mg-deposition/dissolution is still a challenge. Since Mg ion is a stronger Lewis acid than monovalent ion such as Li ion and Na ion when using carbonate-based solvent employed in commercially available Li-ion batteries (LIBs), Mg ion is more stabilized by solvation molecules. Consequently, in regard to graphite as a host material, carbonate-based electrolyte with high dielectric constant blocks intercalation (charge transfer) reaction involved in desolvation. Meanwhile, one of cyclic ether, crown ether with repeating unit being ethyleneoxy (−CH2CH2O−) has high affinity and selectivity to alkali metal ion and alkaline-earth metal ion and encapsulates in itself to form complex. As a strategy for storage of Mg ion in graphite interlayer, we considered a reversible battery reaction based on the intercalation of the solvated ions without desolvation. The electrochemical co-intercalation of solvated Li ion is mainly limited to the use of oligoether (glyme) regardless of carrier ion to the best of authors knowledge. As a preliminary stage to a study of an electrochemical behavior of graphite electrode in the presence of encapsulated Mg ion by crown ether, we investigated intercalation/de-intercalation properties of Li ion coordinated by 12-crown-4-ether having a suitable cyclic size for encapsulation. In the present study, solvation structure of Li ion and the influence of encapsulation on formation for electrochemical graphite intercalation is discussed. Electrochemical intercalation/de-intercalation behavior of Li ion encapsulated by 12-crown-4-ether into/from graphite electrode was studied and compared with a commercially available Li-ion battery electrolyte (1 mol kg-1 LiOTf/EC:DEC). In electrolyte solution in which Li ion is coordinated by 12-crown-4-ether, the interlayer of graphite expanded from 0.335 nm to 1.137 nm at charged state of 0.1 V, which is three times larger than that (0.371 nm) in the commercial electrolyte. Charge transfer reaction without desolvation process using Li ion encapsulated by 12-crown-4-ether was successfully progressed even at the high rate of 2C. The insight obtained in this study extend the diversity of carrier ion. Figure 1