The Preparation And Electrochemical Performance Of Graphene Matrix Composites As Anode Materials For Lithium-ion Battery

With the wide application of lithium ion batteries in electric vehicles and various energy storage fields,the requirements of energy density and power density for commercial batteries are also increased gradually.It is important that the choices of anode materials for improving the electrochemical property of lithium ion batteries.Although oxides and sulfides are often used as anode materials for lithium-ion batteries,the materials themselves have some disadvantages that cannot be ignored.For example,the theoretical capacity of some materials are not very high,and the volume expansion that often occurs in the process of charging and discharging of materials also hinders their further development.As a new material,the graphene not only has excellent physical and chemical properties,but also has controllable preparation in terms of morphology,size and chemical composition for constructing the multi-dimensional composite materials to meet people’s needs.Based on this,graphene was compounded with metal oxides and metal sulfides for improving the electrochemical property as the anode composites for lithium ion batteries.The contents include:（1）Firstly,grapheme@titanium dioxide（rGO@TiO₂）composites were obtained by simple one-step hydrothermal method and vacuum filtration,and 3D graphene@titanium dioxide（3DrGO@TiO₂）composites were obtained by freeze-drying method.The electrochemical properties of TiO₂,rGO@TiO₂ and 3DrGO@TiO₂were tested.It shows that the discharge capacity of 3DrGO@TiO₂ composite material is about 350 mAh·g^-1 at the second cycle.After 200 cycles,the discharge capacity is about 270 mAh·g^-1,and the coulomb efficiency is close to 100%.（2）Secondly,compare to TiO₂,the Cu₂O with higher theoretical capacity was synthesized by one-step hydrothermal method,and the rGO@Cu₂O was also synthesized by the hydrothermal method.At the same time,3D graphene@Cu₂O（3DrGO@Cu₂O）composite was obtained by the freeze-drying.As the anode,the second discharge capacity is 280mAh·g^-11 at the current density of 100 mA·g^-1.After200 cycles,the specific capacity remains at 200 mAh·g^-1,and it shows relatively excellent electrochemical stability compare to the Cu₂O and rGO@Cu₂O electrode.（3）The copper sulfide（Cu₂S）with nanoflower morphology were prepared by one-step hydrothermal method.In the hydrothermal process,the formation process of Cu₂S nanoflower was explored by the different hydrothermal times.Then,base on the same method in the first two chapters,Cu₂S nanoflower particle with rGO and 3DrGO composite was also synthesized successfully.The electrochemical properties of different materials was tested.Compared with the other electrode materials（Cu₂S and Cu₂S@rGO）,it was found that Cu₂S@3DrGO composite showed the best electrochemical performance.Under the current density of 100 mAh·g^-1,the discharge capacity is 1180 mAh·g^-1 at the second cycle,and specific capacity is stable at 680mAh·g^-1 after 200 cycles.It also shows that the higher rate capability.