(Invited) Electrochemical Properties of Graphite Electrode in Propylene Carbonate-Based Electrolyte Solution Containing Mg Salt

It is well-known that charge-discharge reactions of graphite electrode cannot take place in propylene carbonate (PC) based electrolyte solutions. Since the melting point of PC is much lower than that of ethylene carbonate (EC), PC-based electrolyte solutions are preferable when lithium-ion batteries are operated in the lower temperature regions. Vast work has been done on graphite electrodes in PC-based electrolyte solutions. One of our colleagues, Jeong found that concentrated salt PC solutions enabled charge-discharge reactions at graphite electrodes [1]. This was the first approach for use of concentrated salt electrolyte solutions. The concept of the concentrated electrolyte solutions was the change of the solvation states of lithium-ion. We also found that the addition of divalent cations such as calcium ion and magnesium ion in the PC-based electrolyte solutions also made graphite electrode active for the intercalation/de-intercalation of lithium-ion [2,3]. Since the Lewis acidities of Mg 2+ and Ca 2+ are higher than that of Li + , PC should preferentially solvate with the divalent cations. This will result in the change of solvation states of lithium-ion. Then, charge-discharge reactions could take place at graphite electrode. Further, we used “ in situ ” atomic force microscopy (AFM) for the understanding of the formation of solid electrolyte interface (SEI) on graphite electrode in PC-based electrolyte solutions containing Mg 2+ . As a result, we found the co-intercalation of lithium-ion and solvent was suppressed by the addition of Mg 2+ . The detail will be reported in the conference. References [1] S. K. Jeong, Electrochem. Solid State Lett. 6, A13 (2003) [2] S. Takeuchi et al., Electrochim. Acta , 56 (2011) 10450. [3] S. Takeuchi et al., submitted. Acknowledgement This work was partially supported by CREST, JST and JSPS KAKENHI Grant Number 16H04216.