Electrochemical Characteristics Of Graphene Composites

Lithium-ion batteries are widely used in mobile communications equipment,portable electronic devices, electric vehicles and other fields because of its highenergy, high voltage, long life, no memory effect, little self-discharge characteristicswhich recommends it as an important power source for modern and future. Graphene,a one-atom thick and two-dimensional closely packed honeycomb lattice, has usuallybeen employed as an important component of various composite materials because ofits extraordinary electronic transport properties, large surface area, and highelectrocatalytic activities. Tin oxide (SnO2)/graphene composite andZnO-SnO2/graphene are synthesized via different methods using different rawmaterials and characterized their properties through a variety of testing methods.Flower-like SnO2/graphene composite was synthesized through a hydrothermalmethod and graphene/SnO2composite was also synthesized through the same methodusing SnCl4·5H2O and graphene as raw materials. In the former the GO was reducedto graphene nanosheet (GNS) and flower-like SnO2nano-crystals with size about40nm were homogeneously distributed on the surface of GNS. In the latter, thesynthesized composite exhibits enhanced capacity retention at large current densities,which can be attributed to the highly uniform distribution of large amount of SnO2nanoparticles on the graphene nanosheet (GNS).Tin oxide (SnO2)/graphene composite is synthesized via a simple wet chemicalmethod through an oxidation-reduction reaction between graphene and SnCl2·2H2O.SnO2nanoparticles with dimension around5nm are uniformly distributed on thegraphene matrix. The SnO2/graphene composite exhibits outstanding electrochemicalperformance such as high reversible capacities and good cycling stability. The initialdischarge and charge capacities are1995.8mAh·g-1and1923.5mAh·g-1, respectively.After40cycles, the reversible discharge capacity is still maintained at1545.7mAh·g-1at the current density of1A·g-1.We have prepared SnO2/graphene composite as an anode material for lithium ionbatteries mainly through the precipitant effect of urea. The graphene of high reductiondegree can provide high conductivity, which makes a contribution to the good cyclingstability of the composite. The first discharge and charge capacities of the compositeare2751.4mAh·g-1and1254.6mAh·g-1at the density of100mA·g-1. After30cycles,the reversible discharge capacity is still remained at985.5mAh·g-1. A hydrothermal method has been developed to synthesize zinc oxide (ZnO)-tinoxide (SnO2)/graphene composite as anode materials for lithium ion batteries. TheZnO-SnO2/graphene composite exhibits outstanding electrochemical performancesuch as high reversible capacities and good cycling stability. The composite delivers ahigh initial discharge specific capacity of1287.6mAh·g-1with a reversible specificcapacity of1209.4mAh·g-1at the current density of1A·g-1. The charge capacity canremain about1075.3mAh·g-1after10cycles. And even after50cycles, the chargecapacity still remains at800.9mAh·g-1. Every component of the composite may makea contribution to the enhanced lithium storage capacity and cycling stability.