Optimization of graphene dose for improved electrochemical performance of silicon-graphene negative electrodes in lithium batteries

Different percentages of nanoparticles graphene (G) were mixed with nano-micron sized silicon (Si) particles as follows: 10, 20, 30 and 40 wt% graphene to silicon ratios. The crystal structure of pure Si powder pattern has cubic phase SEM, TEM/SAED and XPS equipments were implemented to study the surface properties of the prepared G@Si composites. Cyclic voltammetry (CV) measurement for the G@Si cell revealed two broad cathodic peaks, related to the deposition of Li2O thin layer on Si particles and the lithiation process of Si to form lithium silicide. Meanwhile, the oxidation of LixSi into Si and Li ionis confirmed by the anodic strong peak at 0.56 V. Electrochemical impedance spectroscopy (EIS) measurements revealed high interfacial resistance similar to 1825 omega for pure Si anode in comparison with that of G@Si composite anode. It is concluded that graphene acts as a conductive shielding pathway to inhibit the large volume change and minimize the capacity fading during successive galvanostatic cycling of G@Si composite anode materials versus Li/Li+. Accordingly, the specific discharge capacity of 30%G@Si cell delivered about 1240 and 900 mAhg(-1) for 1st and 100th charge-discharge cycles, respectively.