Abstract
In this manuscript, a functionalized ionic liquid 1-cyanoethyl-2-methyl-3-allylimidazolium bis (trifluoromethanesulfonimide) salt (CEMAImTFSI) was synthesized and explored as an electrolyte component to improve the oxidation resistance of the electrolyte in high-voltage lithium-ion batteries. Based on the calculation by Gaussian 09, CEMAImTFSI has a higher highest occupied molecular orbital (HOMO) value than the organic solvents ethylene carbonate (EC) and dimethyl carbonate (DMC), suggesting that CEMAImTFSI is more susceptible to oxidation than EC and DMC. Moreover, a low Li+ binding energy value of –3.71 eV and the lower lowest unoccupied molecular orbital (LUMO) enable CEMAImTFSI to migrate easily to the surface of the LiNi0.5Mn1.5O4 cathode and participate in the formation of the SEI (solid electrolyte interphase) film, protecting the electrode materials. Electrochemical studies showed that the LiNi0.5Mn1.5O4/Li cell with 1.0 mol/L LiPF6-EC/DMC/10 vol% has the best cycling stability in the voltage range of 3–5 V. The initial discharge specific capacity of the cells was 131.03 mAh·g−1 at 0.2 C, and even after 50 cycles the discharge specific capacity value of 126.06 mAhg−1 was observed, with the cell showing a capacity retention as high as 96.2%. Even at the rate of 5 C, the average discharge specific capacity of the cell was still 109.30 mAh·g−1, which was 1.95 times higher than the cell without the CEMAImTFSI addition. The ionic liquid molecules adsorption on the cell electrode surface was confirmed by X-ray photoelectron spectroscopic (XPS) analysis after charge–discharge measurements.
Highlights
Lithium-ion batteries (LIBs) have become one of the main power batteries for electric vehicles due to posessing high energy density [1], low self-discharge, and long cycle life [2,3]
Whether an additive is suitable for cells can be predicted by comparing highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energy values between the functional additives and the electrolyte solvent
An ionic liquid CEMAImTFSI was synthesized as an electrolyte additive to improve the oxidation resistance of the electrolyte in high-voltage lithium-ion batteries
Summary
Lithium-ion batteries (LIBs) have become one of the main power batteries for electric vehicles due to posessing high energy density [1], low self-discharge, and long cycle life [2,3]. The use ionic liquids asand electrolyte additives is the the most economical application of LNMO is impeded by the limitation of the narrow electrochemical window of the and effective approach to improve the performance of LIBs [15,16,17,18,19,20]. Themanuscript, frontier film which is critical the enhancement of battery performance [35,36,37,38,39,40] In this based on orbital energy and Li+ binding affinity (Eb) are the main factors that affect the formation of the solid the theoretical calculation of Gaussian 09, a new ionic liquid 1-cyanoethyl-2-methyl-3-allylimidazolium electrolyte interphase (SEI) film which is critical for the enhancement of battery performance [35,36,37,38,39,40].
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