Abstract
Ionic liquid-based electrolytes proved to be effective in terms of alleviating the safety problems associated with lithium/sodium ion batteries, especially for large-scale applications, due to their superior thermal stability and nonflammability. The main disadvantage of ionic liquids is their relatively high viscosity. Adding a suitable amount of organic “thinning” solvents could be a potential solution for this problem: while the electrolyte viscosity is greatly reduced, the electrochemical properties and thermal stability remain almost as good as those of pure ionic liquid. In this study, electrolyte mixtures based on 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl) (EMI-TFSI) and carbonate solvents (EC-PC) were prepared. The electrochemical compatibility in half-cell configuration with respect to sodium metal anode of various electrode materials, including SnS/C, hard carbon (HC), and Na0.44MnO2, was evaluated. Moreover, the thermal stability, the flammability, and the conduction mechanism of such electrolyte mixtures were also explored and discussed.
Highlights
Li-ion batteries (LIBs) have been widely used in portable devices due to their high-voltage and high-energy density characteristics
Pure EMI-TFSI has low melting temperature of −18.5°C and excellent thermal stability. erefore, the introduction of EMI-TFSI as a cosolvent to ethylene carbonate (EC)-propylene carbonate (PC) (1 : 1) mixture are aimed to enhance the thermal stability and oxidation potential limit of carbonate-based electrolytes, and it should not impose any penalty on the ionic conductivity
At the highest EMI-TFSI concentration (50 wt.%), the highest evaporation temperature and the lowest weight loss were obtained (Figure 1(b)). e second step is in accordance with the decomposition of ionic liquid, which originates from the reduction in ionic interaction between cation and anion. at being said, EMI-TFSI-based electrolytes show almost no sign of the second weight loss up until 350°C. is confirms the high thermal stability of EMI-TFSI (Figure 1(a)). e presence of EC does not have a negative effect on the thermal stability of the pure ionic liquid phase
Summary
Li-ion batteries (LIBs) have been widely used in portable devices due to their high-voltage and high-energy density characteristics. The concern about lithium shortage for large-scale applications and the continuously increasing price of lithium carbonate have driven researchers to investigate alternative battery technologies for large-scale application (stationary storage or future electric vehicles). The chemical similarities between Na and Li allow the comprehensive knowledge about LIBs to be applied successfully to sodium cells, making Na-ion batteries (NIBs) competitive to Li-ion batteries in the cell market [8,9,10]. Eftekhari [11] mentioned that the target-specific energy/energy density of future commercial sodium-ion battery (NIB) is only 20% lower than that of LIBs
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