凯发

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

In this work, weinvestigate the lithiation/de-lithiation processes occurring in few- (FLG) andmulti- (MLG) layer graphene-based electrodes, linking their electrochemicalperformance to the morphology of the flakes. The FLG and MLG flakes areprepared by liquid phase exfoliation of pristine graphite, sorted by lateralsize (from 380 to 75 nm) and thickness (from 40 to 2 nm) exploiting asedimentation-based separation in centrifugal field and, finally, depositedonto Cu disks for the realization of four different FLG- and MLG-basedelectrodes. The electrochemical lithium storage properties of these electrodesare assessed in half-cell configuration by means of galvanostatic cycling anddifferential capacity analysis. The results suggest that decreasing lateralsize and thickness is effective for achieving large specific capacity, up to1267 mAh g-1. However, an increasing amount of irreversible capacityis also associated to the reduction of flakes’ size. Moreover, the preferentialLi ions storage by adsorption rather than intercalation in small lateral size(<100nm) FLG flakes has an unfavorable effect on the average de-lithiationvoltage, resulting on lower voltage efficiency of these anodes with respect tothe ones based on the large lateral size (~400nm) MLGs. We believe that theresults reported in this work, provide important guidelines for the practicalexploitation of graphene-based electrodes.