Host materials for Mg2+ intercalation

Abstract

As time goes by, need for energy storage system is increasing. Especially, with the development of electric vehicles and smart grid system, interest for energy storage system with high energy density and safety is getting increased. Until now, lithium ion batteries (LIBs) have been in charge of that energy storage system. However, LIBs have limitations in the view of high price and safety issues to be used as large scale energy storage system. So, needs for next generation battery systems are getting larger. Magnesium based battery systems are promising candidates to alternate lithium based systems. They provide lower price and better safety than lithium based system. However, they also have limitations. First, only a few high voltage cathodes have been introduced. Second, magnesium metal cannot be used with conventional polar aprotic solvent. So, in this study, I will introduce cathode material which can store Mg2+ ions and operates in high voltage region. In addition, I will introduce magnesium insertion anode which is expected to be used with conventional solvents. Na0.69Fe2(CN)6 and Fe2(CN)6 were tested as cathode material for magnesium based system. Na0.69Fe2(CN)6 showed reversible cycling with the capacity about 70 mA h g-1. However, Fe2(CN)6 did not show electrochemical activity with magnesium. Na0.69Fe2(CN)6 showed small and reversible structural change and stable cycle performance over 30 cycles. By comparing Na0.69Fe2(CN)6 and Fe2(CN)6, it seems that the existence of Na+ helps reversible intercalation/de-intercalation of magnesium. Natural graphite was tested as magnesium insertion anode. It showed reversible and stable cycling when cycled with the capacity of 180 mA h g-1. According to insertion/de-insertion of magnesium, it showed reversible structural change. The existence of magnesium in the natural graphite was observed with TEM. In this report, magnesium intercalation phenomena into Na0.69Fe2(CN)6 and natural graphite were reported. They showed possibility as cathode and anode for magnesium based energy storage system. Because these are first reports for magnesium based system, they are expected to introduce new way for magnesium system research.