| With the rapid progress of electron devices and IT industry, higher energy and power density lithium ion batteries are more required for the wide use in mobile telecommunication, digital processing machine and portable computer, especially for space techniques, national defense equipments and also the research and development of the electric vehicle (EV). Conventional organic electrolytes can not be satisfied with the demand of advanced lithium ion batteries due to their lower boiling point, lower flash point, flammability, volatility and bad heat dissipation effect. Recently, ionic liquids (ILs) showing excellent properties including chemical and thermal stability, wide liquid phase range, non-flammability, high ionic conductivity, and negligible vapor pressure, have attracted many researchers as new promising solvents in the electrolytes to improve the safety of lithium ion batteries.At present, their use in lithium ion batteries is an exploration stage. Most of their work focus on the design and synthesis of new kinds of ionic liquids, while few research are involved with the compatibility between the electrode materials and ionic liquid electrolytes. To realize the application of ionic liquids in lithium ion batteries, it is very important to investigate the compatibility of electrode materials and ionic liquid electrolytes. Aluminum (Al) current collector and copper (Cu) current collector are key components for the electrodes in lithium ion batteries. They play an important role in exchanging the electron between the electrode materials and the external circuit. However, their immersing in the electrolytes may be subject to the corrosion during the charge / discharge processes, which lead to degraded the performance and worsen the safety of lithium ion batteries. Once the ionic liquids serve as new electrolyte materials for lithium ion batteries, it is very required to investigate the compatibility between the current collectors and ionic liquids.In this research, the electrochemical behaviors of Al foil in 1-alkyl-3-methyl imdazolium tetrafluoroborate ionic liquids have been investigated, which showed that a passivate film formed on the Al foil surface after the cyclic voltammetry in EMI-BF4, PMI-BF4 and BMI-BF4. Comparatively, a better stable passivate film was obtained after the electrochemical measurement in BMI-BF4. In addition, the anodic polarization behavior of Al foil in BMI-BF4, PP14-BF4 and BMI-TFSI, which combined of the same cation BMI+ with the anions TFSI- and BF4-, and the same anion BF4- with the cations BMI+ and PP14+, were also tested. It was found that the passivate film formed on the Al foil surface after the anodic polarization in BMI-TFSI was not stable, resulting in its breakdown potential at about 10 V vs. Ag+ / Ag, while a better stable passivate film formed on Al foil surface after the anodic polarization in BMI-BF4 and PP14-BF4, which did not breakdown until the potential was up to 90 V vs. Ag+ / Ag. In addition, higher breakdown potential of Al foil was presented after the anodic polarization in BMI-BF4. These results indicated that the anodic polarization behavior of Al foil in ionic liquids is related to the anions of ionic liquids. Further research by EDX and XPS showed that the stable passivate film on Al foil surface after the anodic polarization in 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids composed mainly of the fluoride and oxide such as AlF3, Al2O3 and / or nonstoichiometric Al-O-F compounds, which contributed to their higher breakdown potential.The anodic behaviors of Al foil in a series of 1-alkyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl] imide ionic liquids (EMI-TFSI, PMI-TFSI and BMI-TFSI) and EC+DMC containing 1M LiTFSI were investigated. It was found that aluminum corrosion occurred in EC+DMC solutions, while not found in the IL electrolytes. These results indicated that EMI-TFSI, PMI-TFSI and BMI-TFSI could be used as candidates to inhabit the corrosion of aluminum current collector in the electrolytes. Further research by EDX and XPS showed that the passivate film composed mainly of Al-TFSI compounds after the anodic polarization in the electrolytes, which were soluble in EC+DMC solvents and resulted in the occurrence of aluminum corrosion, while it did not dissolve in the IL electrolytes which firmly attached on the surface to become a protective film and inhibited further aluminum corrosion. Moreover, the influence of ES, EC and VC into the BMI-TFSI electrolytes on the anodic behavior of aluminum was also studied. As a result, VC showed the best performance for stabilizing effect on aluminum current collector in the BMI-TFSI, which may further enhanced the practical use of BMI-TFSI in lithium ion battery. In addition, the influence of temperature on the surface passivate film was tested, only the erosion potential of Al foil shifted to more and more negative potential at elevated temperature, a passivate film still firmly formed on the aluminum surface which suppressed the further oxidation of aluminum current collector.The anodic behaviors of Al current collector were investigated in several kinds of the ILs i.e. BMI-TFSI, S114-TFSI and BMI-BF4, which combined of the same cation BMI+ with the anions TFSI- and BF4-, and the same anion TFSI- with the cations BMI+ and S114+, containing 1 M LiTFSI. A weaker anodic current of the Al foil in the IL electrolytes decreased during the cycle voltammetry measurement, which indicated that a better passivating film firmly formed on the Al foil surface. Moreover, the anodic current of the Al foil decreased in the IL electrolytes during the chronoamperometry process which indicated that the passivating film can resist the potential higher than 4.2 V vs. Li+/Li. After the chronoamperometry measurement in the IL electrolytes, it was found that no corrosion pits were obvious observed on the Al surface, which indicated that the passivate film on the Al foil was kinetic stable. Further research by EDX and XPS measurements showed that a passivating film composed mainly of Al-TFSI on the surface layer and Al2O3 / AlF3 compounds in the inner layer which firmly formed on aluminum foil surface after the anodic polarization in the BMI-TFSI and S114-TFSI electrolytes to inhibit the further aluminum corrosion, while a wholly passivate film composed mainly of AlF3 / Al2O3 on the Al foil surface during the anodic polarization in BMI-BF4, which surpassed the aluminum corrosion. These results suggested that the anodic behavior of Al foil was strongly related to the anions in the RTIL electrolytes.The electrochemical behaviors of Cu current collector in 1-alkyl-3-methyl imidazolium bis[(trifluoromethyl)sulfonyl] imide ionic liquids and EC+DMC solutions containing LiTFSI were investigated. It was found that the Cu foil displayed the oxidation-reduction properties at about 3.5 V vs. Li+/Li in the EC+DMC solutions while it was passivated in the IL electrolytes. Moreover, the reduction of the electrolytes was also study which showed that the reduction of the electrolytes provided a limit protection for the Cu foil after the electrochemical measurement in EC+DMC solutions and it was not stable to suppress the further oxidation of the Cu foil when the potential swept to high potential. In comparison, a better passivating film covered on the Cu foil surface in the IL electrolytes which protected the Cu foil from being oxidized even the potential up to 5.0 V vs. Li+/Li. Further research by XPS analysis showed that the solid products composed mainly of the reduction products of the electrolytes such as carbonate and carbonyl species on the Cu foil surface after the electrochemical measurement in the EC+DMC solutions, which was not stable at the potential up to 5.0 V vs. Li+/Li and thus the dissolution of the Cu foil appeared. Whereas a better passivating film, coming from the reduction products of (CF3SO2)2N- anion in the IL electrolytes, coated on the Cu foil surface wholly to markedly inhibit its further oxidation and provided a effective protection for the copper foil to resist higher voltage. These results indicated that a good film-coating behavior of the Cu foil associated with the IL electrolytes which were favor for the stability of copper current collector for advanced lithium ion batteries.Overall, the electrochemical behaviors of Al current collector and Cu current collector in 1-alkyl-3-methylimidazolium tetrafluoroborate ionic liquids and 1-alkyl -3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide ionic liquid electrolytes were investigated by the electrochemistry analysis and surface characterization methods. It hope that the present work may enrich the knowledge of the interface chemistry between the metal and the electrolytes, promote the application of ionic liquids in lithium ion batteries, and benefit for the design and development of high power density, long life and safety lithium ion batteries.
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