Electrochemical investigation of ion-beam sputter-deposited carbon thin films for Li-ion batteries

Abstract

The C-rate capability of 230 nm- and 16 nm-thin ion-beam sputter-deposited amorphous carbon films, an interesting class of carbonaceous material for lithium-ion batteries, was investigated up to Li-platting. Stepwise ascending and descending constant Li+ currents after each fifth cycle, followed by hundreds of cycles with the highest current were applied. The carbon films show similar cycling with irreversible losses during the first five cycles, followed by reversible cycling with a capacity close to that of graphite. The capacity is significantly lower at high currents; however, it is restored for subsequent cycling again at low currents. Differential charge and differential capacity curves reveal three Li+ uptake and three Li+ release peaks located between 0 and 3 V. Irreversible as well as reversible Li bonding can be associated with all these peaks. Irreversibly bonded Li can be found at the surface (solid electrolyte interphase) and in the bulk of the carbon films (Li trapping). Reversible Li bonding might be possible inside the carbon films in graphite-like nano-domains and at defects. The thinner film reveals a more pseudo-capacitive cycling behavior, pointing to enhanced Li kinetics.Graphical abstract