Preparation And Electrochemical Properties Of Carbon-based Anode Materials For Sodium Ion Battery

Sodium ion battery is a battery system which works like lithium-ion battery.Both lithium and sodium belong to the same group,with the similar physical and chemical properties.Sodium is abundant and low cost.Therefore,sodium ion battery has a good prospect in the large-scale energy storage.The anode material is the one of key elements which determines the performance of sodium ion batteries,and it has been a hot research topic in sodium ion batteries.The components,structures,electrochemical performances and mechanisms of graphite,pyrocarbon and composite materials have been systematically studied.It is desirable to provide a theoretical basis for the design and production of high-capacity sodium ion battery anode materials.Natural graphite was modified by high energy ball milling or oxidation reduction.The results indicate that the storage capacities are all about 20 mAh/g for the unmodified graphite with different particle sizes.But after modified by milling or oxidation reduction,the storage capacities increase to 128.4 mAh/g and 181.6 mAh/g,respectively.However,the first coulombic efficiencies are all very low only about 31.6%and 24.8%,respectively.The increase of sodium storage capacity is due to the increase of the modified layer spacing and active sites.The increasing specific surface area results in a low initial coulombic efficiency.Using the method of high temperature oil treatment and carbonization treatment,the composite(RGO/C800)has been prepared.It indicates that RGO/C800 has good electrochemical property with a high initial discharge capacity of 268.4 mAh/g,high initial coulombic efficiency of 79.2%and a good cycle performance with the capacity retention rate of 88.7%after 50 cycles.Graphite oxide presents no expansion during the preparation process of the composite materials.Layer spacing and specific surface area are 0.372 nm and 3.00 m2/g,respectively.These will provide a theoretical basis for the preparation of materials with a larger layer spacing and lower specific surface area.Using graphite oxide and SnCl2·2H2O as raw materials,metal oxides SnO2 and RGO composite materials(SnO2/RGO)were prepared by hydrothermal method.The results show that the initial reversible capacity and coulombic efficiency are 425.1 mAh/g and 43.9%,respectively.The capacity retention rate is 88.8%after 20 cycles.The material has higher capacity and better cycle stability,which are attributed to nano size of SnO2 particles(about 5 nm)and uniform dispersion in the RGO.Using the method of carbonization treatment after high temperature oil treatment,the composite(C/Sn/RGO)of RGO,Sn and pitch carbon has been prepared.The results show that the initial reversible capacity and coulombic efficiency are 476.2 mAh/g and 70.3%for C/Sn/RGO,respectively.Compared with the SnO2/RGO,the higher initial coulombic efficiency for C/Sn/RGO is because SnO2 reduced to metallic Sn.The pitch carbon effectively prevented aggregation and growth of Sn particles with the size of less than 200 nm.Using glucose and petroleum pitch as raw materials,the pyrocarbon of pitch and glucose were prepared by pyrolysis method.The results show that the initial reversible capacities of pitch and glucose pyrocarbon are 171.9 mAh/g and 79.2 mAh/g,respectively.The initial coulombic efficiencies are 47.2%and 33.9%,respectively.Compared with pitch pyrocarbon,the glucose pyrocarbon has a higher degree of amorphous,larger layer spacing and more nano holes,which are the reasons for the good electrochemical performance of glucose pyrocarbon.Using glucose and SnCl2·2H2O as raw materials,the composite of metal oxides SnO2 and glucose pyrocarbon(SnO2/C)was prepared by hydrothermal method.The results show that the initial reversible capacity and coulombic efficiency are 294.5 mAh/g and 52.3%,respectively.Compared with glucose pyrocarbon,SnO2/C has hihger capacity,which is because of the composite with SnO2.Using SnO2/C and pitch as raw materials,the composite of pitch pyrocarbon,metal Sn and glucose pyrocarbon(C/Sn/C)was prepared by pyrolysis method.The results show that the initial reversible capacity and coulombic efficiency are 356.8 mAh/g and 65.4%,respectively,but after 20 cycles the retention rate of capacity is only 41.1%.Compared with SnO2/C,the cycle performance of C/Sn/C is poor,which is mainly caused by the excessive growth of Sn in the process of reduction.