Preparation Of Ionic Liquid Electrolytesand Research In The Li-ion Battery

Lithium ion batteries have broad application prospects in electric vehicles due to the advantages of high work potential, huge specific energy, environment friendly. However, the flammable organic solvents are the main lithium ion battery electrolytes, which cause safety problems easily because of their exothermic reactions. Compared to the organic solvents, the ionic liquids（ILs） have attracted a lot of attention because of their unusual chemical and physical characteristics such as chemical and electrochemical stability, negligible vapor pressure (no flammability) and wide liquid range. In this work, we synthetized1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (AMIMTFSI) and studied the electrochemical properties of ionic liquid electrolytes and the compatibility with electrode.based on1-allyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (AMIMTFSI) and1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (PMIMTFSI)(Scheme1) and propylene carbonate (PC) and their comparison with the pure components.The results showed that AMIMTFSI was obtained with high disposition tempreture (370℃)、high conductivity (7.8mS/cm，25℃) and a wider electrochemical window (4.7V) than that of PMIMTFSI(4.1V) and LiPF6-EC-DMC (4.3V). Raman and FTIR observations revealed AMIMTFSI-based electrolytes achieved higher degree of [Li(TFSI)2] anionic clusters and less free ions with the increase of LiTFSI concentration,which caused the conductivity decreased.Nine sorts of ionic liquid electrolytes were prepared including: Mixtures of LiTFSI with AMIMTFSI、LiTFSI-AMIMTFSI electrolytes containing addictives (PC、VC、LiCl) and IL-organic electrolyte (LiPF6-EC-DMC、LiTFSI-EC-DMC) mixtures and their comparison with1-propyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (PMIMTFSI). The compatibilites of ionic liquid electrolytes with LiFePO4, LiMn2O4and sulfur material were also evaluated. The results reveal that LiTFSI-AMIMTFSI electrolyte could form a protective layer on the electrode surface due to the polymerization of AMIMTFSI. The layer can prevent further decomposition of electrolytes. However, LiTFSI-AMIMTFSI electrolyte showed some poor medium and high rate cycling performance. Adding LiCl in the LiTFSI-AMIMTFSI, the discharge capacity of LiFePO4remained165mAh/g after eight months cycles. The Li/LiFePO4cell showed interfacial stability and stable discharge capacities with a retention of97.4%(151mAh/g) after100cycles at0.1C rate when LiTFSI-AMIMTFSI electrolyte containing PC. We also investigated AMIMTFSI as additives in organic electrolyte LiTFSI-EC-DMC. The electrolyte maked the still placed performance of Li/LiFePO4and the cycling property of Li/LiMn2O4improved, but the charge-discharge performance of Li/S have not effectively improved.