Methyl acetate–based solutions for dual–ion batteries

Abstract

Recently, methyl acetate (MA)–based electrolyte solutions have attracted afresh interests in the field of electrochemical energy storage devices at low temperature on account of their distinctive physical properties of low viscosity and melting point. In this work, LiPF6–MA based solutions are employed in Li/graphite dual–ion batteries (DIBs). The intercalation behavior of solvated PF6− in graphite positive electrode from 1 M LiPF6–MA during the initial charge process is quite different from those in the subsequent cycles of charge–discharge. They are diagnosed by conventional electrochemical tests and in situ X–ray diffraction (XRD) measurements. Ethyl methyl carbonate (EMC) is introduced to activate the anion storage in graphite electrode, and then the discharge capacity of graphite positive electrode increases remarkably even in the solution of 1 M LiPF6–MA. Moreover, for 1 M LiPF6–MA/EMC (5:5 by vol.) at the low working–temperature of −25 °C, the discharge capacity of 41 mA h g−1 delivered by graphite positive electrode is apparently higher than those in both 1 M LiPF6–MA and LiPF6–EMC. Therefore, the LiPF6 solutions based on MA/EMC binary solvent mixtures may be suitable for graphite positive electrode working at the low temperatures.