Synthesis And Electrochemical Performance Of Co₃O₄/Graphene Composites

Lithium-ion batteries(LIBs)has been widely used in people's daily life due to their high energy density,environmentally friendly.The anode material is an important component of LIBs.At present,the anode material of commercial application is mainly graphite material,and its theoretical capacity is only 372 mAh/g.With the development of times,especially in the application of power battery,the demand for anode materials with high capacity will also be more urgent.Co3O4 is one of the most promising anode materials because of its high theoretical capacity(890 mAh/g),low cost,easy synthesis,environmental benignity and abundance.However,the conductivity of Co3O4 is poor,and during the processes of discharge/charge,the dramatic change in volume of Co3O4 can resulting in crushing the electrode material,and thus leading to a rapid decline of capacity these shortcomings will limit its commercial applications.Graphene has a large specific surface area and excellent conductivity.Therefore,we can improve the electrochemical properties of Co3O4 by prepareing the Co3O4/graphene composite materials.Firstly,the precursors of Co3O4/graphene composites were prepared by hydrothermal method,and then the precursors were treated under different annealing condition.The final products were characterized by XRD,TGA,TEM and XPS.The results show that Co3O4/graphene composites can be successfully prepared by annealing the precursor in argon at 350? for 3 h and then annealing in air at 200?for 0.5 h,and the largest amount of graphene is retained in the composites.Secondly,the Co3O4/graphene composites with different graphene contents were prepared by hydrothermal method.The graphene contents in composite material were 20.1wt%,33wt%and 38.8wt%respectively.Then the structure and morphology of samples were characterized and the electrochemical properties were investigated.The results show that the cycle and rate performances of Co3O4/graphene composites with different graphene contents are all better than pure Co3O4.The composites with the graphene content of 33wt%show the best cycle performance in three samples.At the current density of 0.1 A/g,the first discharge capacity is up to 1341 mAh/g,and the capacity during 50 cycles is very stable.The capacities during the 50 cycles are almost about 900 mAh/g,and the maximum capacity can be high to 988mAh/g,which is higher than 890mAh/g of the theoretical capacity of the pure Co3O4.And after 50 cycles,the discharge capacity of the composites with the graphene content of 33wt%still remain 951 mAh/g.Finally,Ni-doped Co3O4/graphene composites with different Ni content of were prepared by hydrothermal method.The content of Ni was 10wt%and 20wt%,respectively.The electrochemical performance of Ni-doped Co3O4/graphene composites was investigated.The experimental results show that Ni-doped Co3O4/graphene composites with 10%Ni show the best cycle performance and rate performance compared to the composites with 20%Ni and 0%Ni.Its first discharge capacity is up to 1341 mAh/g,and the discharge capacity after 50 cycles is still maintains at 972 mAh/g.The improved performance can be attributed to the synergistic effect between the active material and graphene,and the metal oxide particles of Ni-doped composites becomes smaller,which will lead to reduction of the charge transfer resistance of the material.