The flammability of organic electrolyte solutions has a safety risk during the large-scale application of energy storage devices. Therefore, it is essential to suppress the flammability of organic electrolyte solutions. In this article, the flame-retardant electrolyte solution of 3 M LiPF 6 -ethyl methyl carbonate (EMC)/trimethyl phosphate (TMP) (7:3 by vol) has been applied in a Li/graphite dual-ion battery. Both the initial-cycle discharge capacity (almost 100 mAh g −1 ) and capacity retention rate (92.3% after 450 cycles) surpass those for the battery using 1 M LiPF 6 -EMC. Besides, the burning times of the above electrolyte solutions are 6 and 66 s, respectively. Conventional electrochemical tests, ex situ X-ray diffraction, and nuclear magnetic resonance have been carried out to explore the influences of TMP on PF 6 − in EMC/TMP mixed solvents.

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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. −