Graphene-based lithium ion batteries (LIBs) have been considered as one of the most promising strategies[1] to fulfill the requirements of efficient energy-storage devices. In this context, strong efforts have been dedicated on improving the performance of graphene-based LIBs.[1-4] However, so far the focus was on both oxidized and functionalized flakes that normally suffer from large irreversible capacity and rapid capacity fade,[2] while, on the contrary, only a few works have exploited the full potential of pristine graphene flakes.[3-6] Moreover, it is still unclear the role of the graphene flakes morphology, such as lateral size and thickness, on the Li+ ion storage mechanisms.[2-4]

In this work, we investigate the lithiation/de-lithiation processes occurring in few- (FLG) and multi- (MLG) layer graphene-based electrodes, linking their electrochemical performance to the morphology of the flakes. The FLG and MLG flakes are prepared by liquid phase exfoliation of pristine graphite, sorted by lateral size (from 380 to 75 nm) and thickness (from 40 to 2 nm) exploiting a sedimentation-based separation in centrifugal field and, finally, deposited onto Cu disks for the realization of four different FLG- and MLG-based electrodes. The electrochemical lithium storage properties of these electrodes are assessed in half-cell configuration by means of galvanostatic cycling and differential capacity analysis. The results suggest that decreasing lateral size and thickness is effective for achieving large specific capacity, up to 1267 mAh g-1. However, an increasing amount of irreversible capacity is also associated to the reduction of flakes’ size. Moreover, the preferential Li ions storage by adsorption rather than intercalation in small lateral size (<100nm) FLG flakes has an unfavorable effect on the average de-lithiation voltage, resulting on lower voltage efficiency of these anodes with respect to the ones based on the large lateral size (~400nm) MLGs. We believe that the results reported in this work, provide important guidelines for the practical exploitation of graphene-based electrodes.

Graphene-based lithium ion batteries (LIBs) have been considered as one of the most promising strategies[1] to fulfill the requirements of efficient energy-storage devices. In this context, strong efforts have been dedicated on improving the performance of graphene-based LIBs.[1-4] However, so far the focus was on both oxidized and functionalized flakes that normally suffer from large irreversible capacity and rapid capacity fade,[2] while, on the contrary, only a few works have exploited the full potential of pristine graphene flakes.[3-6] Moreover, it is still unclear the role of the graphene flakes morphology, such as lateral size and thickness, on the Li+ ion storage mechanisms.[2-4]

In this work, we investigate the lithiation/de-lithiation processes occurring in few- (FLG) and multi- (MLG) layer graphene-based electrodes, linking their electrochemical performance to the morphology of the flakes. The FLG and MLG flakes are prepared by liquid phase exfoliation of pristine graphite, sorted by lateral size (from 380 to 75 nm) and thickness (from 40 to 2 nm) exploiting a sedimentation-based separation in centrifugal field and, finally, deposited onto Cu disks for the realization of four different FLG- and MLG-based electrodes. The electrochemical lithium storage properties of these electrodes are assessed in half-cell configuration by means of galvanostatic cycling and differential capacity analysis. The results suggest that decreasing lateral size and thickness is effective for achieving large specific capacity, up to 1267 mAh g-1. However, an increasing amount of irreversible capacity is also associated to the reduction of flakes’ size. Moreover, the preferential Li ions storage by adsorption rather than intercalation in small lateral size (<100nm) FLG flakes has an unfavorable effect on the average de-lithiation voltage, resulting on lower voltage efficiency of these anodes with respect to the ones based on the large lateral size (~400nm) MLGs. We believe that the results reported in this work, provide important guidelines for the practical exploitation of graphene-based electrodes.