Synergetic Effect of Ethyl Methyl Carbonate and Trimethyl Phosphate on BF4– Intercalation into a Graphite Electrode

LiBF 4 –ethyl methyl carbonate (EMC)-based solutions have not been successfully employed in dual-ion batteries (DIBs) mainly on account of few solvated BF 4 – intercalations into graphite positive electrodes. In this article, trimethyl phosphate (TMP) is introduced into 1 M LiBF 4 –EMC solution as the electrolyte solution for DIBs, thus revealing a synergetic effect in which the discharge capacity for the anion storage using 1 M LiBF 4 –EMC/TMP (8:2 by vol) (ca. 26.7 mA h g –1 ) is far superior to that for the batteries using 1 M LiBF 4 –EMC (ca. 2.7 mA h g –1 ) or 1 M LiBF 4 –TMP (ca. 1.1 mA h g –1 ). In this case, the effects of TMP on LiBF 4 in 1 M LiBF 4 –EMC/TMP electrolyte solutions are explored by conventional electrochemical tests, ex situ X-ray diffraction, in situ Raman spectroscopy, and nuclear magnetic resonance.