Mechanisms of enhanced lithium intercalation into thin film V2O5 in ionic liquids investigated by X-ray photoelectron spectroscopy and time-of-flight secondary ion mass spectrometry.

Room temperature ionic liquids (RTILs) attract much attention as a new type of environmentally benign electrolytes for Li-ion batteries due to their numerous interesting physicochemical properties. Here, in this paper, Li intercalation/deintercalation in presence of the N -butyl- N -methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (PYR 14 TFSI) and N -methyl- N -propylpyrrolidinium bis(fluorosulfonyl)imide (PYR 13 FSI) containing 0.3 M LiTFSI, was evaluated in a thin 100 nm layer of V 2 O 5 deposited on Al substrate by atomic layer deposition. Potentiodynamic tests performed in LiTFSI/Pyr 14 TFSI show a quasi-reversible Li intercalation during 10 cycles (between 2.4 and 5 V) with an average coulombic efficiency of 99%. The capacity, calculated from the 1st cycle, is found to be 182 mAh g −1 , about 19% (±2%) higher than the theoretical capacity reported for V 2 O 5 (147 mAh g −1 ). X-ray photoelectron spectroscopy analysis confirms that the intercalation of more than 1 mol of Li + per V 2 O 5 is achieved as also the possible presence of a solid permeable interface (SPI) layer on the V 2 O 5 surface. Likewise, the Li + in-depth distribution on the V 2 O 5 layer after intercalation in RTILs measured by time-of-flight secondary ion mass spectrometry ion depth profiles, show small irreversible electrode modifications with the presence of lithium through the entire V 2 O 5 layer with significant lithium trapping at the V 2 O 5 layer/Al substrate interface. [ABSTRACT FROM AUTHOR]