| To develop lithium-ion batteries (LIBs) with high performance, it requires higherenergy density, higher power density, longer cycle life and lower cost. Anode materialis one of the most decisive factors to improving battery performance. This work ismainly focus on graphene and its composite materials with graphite and CuO.Graphene oxide was synthesized from expanded graphite powder by a simpleone-step oxidation method. Graphene sheet, which remained a small amount of oxygenfunctional groups, was synthesized using a microwave-assisted hydrothermal reductionmethod. The discharge capacity of graphene sheet was1500mAh/g in the first cyclewith initial coulombic efficiency of40.7%and58.4%retention of the reversiblecapacity after50cycles. Oxygen functional groups of graphene sheet could be almostremoved after heat treatment, which may cause a decline of initial reversible capacityand coulombic efficiency, however, cycle stability and charge transfer resistance got asignificant increase and decrease, respectively.Graphite/graphene composite is synthesized to improve the properties of graphiteanode electrode. Graphene could decrease the irreversible capacity of graphite andimprove cycle stability. In contrast, a3D conducting network was formed whichreduced electrode’s resistance drastically.CuO, act as spacers, prevent effectively the agglomeration of graphene sheets inthe CuO/graphene composite. At the same time, graphene formed a3D conductingnetwork favorable for fast electron transfer, as well as buffered spaces to accommodatethe volume expansion/contraction of CuO during discharge/charge process. TheCuO/graphene composite exhibited the enhanced electrochemical performances withimproved initial coulombic efficiency of67.3%and reversible capacity of816mAh/gwith86.3%retention of the reversible capacity after50cycles. The results also showedthe initial coulombic efficiency of the CuO/graphene composite could get highlyimproved by mixing graphene oxide two times during the synthesis process. |
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