Preparation And Electrochemical Performance Of Cobalt Oxide/Carbon Composite As Anode Materials For Lithium Ion Battery

In this thesis,to improve the electrochemical performance of Co₃O₄ as anode material of Lithium ion battery,we use the method of combining carbon with Co₃O₄ to deal with the issue that Co₃O₄ has the problem of huge volume variation during cyclic process and poor cycling performance.The main contains are as follows:?1?A novel yolk-shell structured Co3O4/C composite was prepared by using ionic liquid as carbon source.Structure characterization result reveals that Co3O4 particles are well-distributed in carbon materials and the boundary of carbon and Co₃O₄ particles bind tightly.This benign yolk-shell structure improves electronic conductivity and structure stability of the composite.Compared with bare Co₃O₄,Co₃O₄-CoO/C electrodes has enhanced cycling performance.The Co₃O₄-CoO/C electrode show a high reversible capacity of 590 mAh·g^-1 after 50 charge/discharge cycles at a current rate of 89 mA·g^-1 which is far above that of bare Co₃O₄ electrode(200 mAh·g^-1).?2?Co₃O₄/CNOs composite was prepared by using ionic liquid as carbon source through a carbothermic reduction and low temperature oxidation method.Structure characterization result reveals that nano-Co₃O₄ particles evenly embedded in onion like carbon materials and partially exposed in the electrolyte.This unique structure has the following merits:?1?ensuring the contact of electrolyte and active materials effectively and improving the transmission efficiency of lithium ions,?2?onion like carbon is beneficial for reliving the volume variations of the composites during cycling,?3?onion like carbon is beneficial for transmission efficiency of electrons.The Co3O4/CNOs electrode shows enhanced electrochemical performance.The first discharge capacity is 1468 mAh·g^-1 and the first charge capacity is 1093 mAh·g^-1.The first Coulombic efficiency is 74.47%.After 200charge/discharge cycles at a current rate of 0.1C,the reversible capacity is 672mAh·g^-1,and the Coulombic efficiency is 99%,showing a favorable cycling performance.?3?Co3O4/C composite was prepared by using ionic liquid as carbon source through a carbothermic reduction and low temperature oxidation method.Structure characterization result reveals that well crystallized Co3O4 combined with carbon material humorously.This unique Co₃O₄/C has the following merits:?1?the close contact between Co₃O₄ and carbon ensures the homogeneity of the composite during cycling,and thus,improves the cycling performance,?2?carbon materials conduces to enhanced kinetic performance and improved electronic conductivity.Electrochemical performance of Co₃O₄/C electrode shows a reversible capacity of 868mAh·g^-1 at a current density of 0.1C after 200 cycles and a rate performance of 660 mAh·g^-1 at a current density of 2C.Co₃O₄/C electrode has an obvious decay after 100 cycles a current density of 0.1C,and then,tends to be stationary.EIS test shows that the charge transfer resistance of the composites has an abrupt raise at the cycle of100^th,and then,tends to be stationary.The EIS result indicates that Co₃O₄/C electrode has a structure breach,and lead to the reconstruction of the contact between electrode material and electrolyte,which further conduces to the electrochemical performance decay.