Synthesis Of Carbon-coated Fe₃O₄ And Their Modification Research In Lithium-ion Battery Anodes

Fe₃O₄ has high theoretical capacity, environmental friendly, abound resources and high security as lithium ion battery anode material. It is a research hotspot in recent years. However, due to the lithium storage mechanism of Fe₃O₄ transformation, the Fe and Li2 O particles in 1-5 nm were generated during the charge discharge process. It leads to the powder agglomeration of electrode materials and the cycle performance of the battery is poor. Therefore, the researchers used to change the structure nanomaterials and the preparation of carbon-coated composite materials, to improve the electrochemical properties of materials.The porous spheres and small particles of Fe₃O₄ were prepared by solvent thermal method. Glucose as carbon source for carbon coated Fe₃O₄ particles. These four materials are used as the negative electrode to study the electrochemical performance of Fe₃O₄. These four materials were used as anode materials for lithium ion batteries. The electrochemical properties of Fe₃O₄ were studied. The initial specific capacity of P-Fe₃O₄ and N-Fe₃O₄ electrode materials were higher than the theoretical specific capacity. After 50 cycles, the retention rate of the P-Fe₃O₄/C and N-Fe₃O₄/C electrode material was 27.8 % and 34 %, which was higher than that of the Fe₃O₄ electrode materials. Its special morphology can provide additional space to alleviate the volume change, while the carbon-coated can alleviate the volume expansion of the stress and prevent the material powder agglomeration.The porous spherical P-Ni-Fe₃O₄ and small particles N-Ni-Fe₃O₄ nanocomposites were prepared by the method of solvent thermal doping. The initial capacity of the battery was improved. Carbon-coated doped particles were prepared by hydrothermal carbonization method, which improved the cycle performance of the battery.After 50 cycles, the P-Ni-Fe₃O₄ and N-Ni-Fe₃O₄ of electrode materials in coulombic efficiency are nearly 100%. The remaining capacity is higher than than of Ni-Fe₃O₄. The results show that the doping is beneficial to improve the electronic conductivity of the crystal, while the carbon layer as a protective layer can maintain the stability of the electrode material and reduce the attenuation of the capacity.In the same way, cobalt was used as the doping ion to prepare Co-Fe₃O₄ nanoparticles. The compound material of Co-Fe₃O₄/C nanometer was prepared by the method of the carbonization of glucose. After 50 cycles, the P-Co-Fe₃O₄/C and N-Co-Fe₃O₄/C of electrode materials in coulombic efficiency are nearly 100%.The residual capacity is higher than that of the Co-Fe₃O₄ electrode material.Graphene itself has a good performance of lithium storage and conductive properties. It can buffer the volume change of Fe₃O₄ particles during the lithium insertion. It maintains the reaction activity of the components in the composite. Electrode materials were prepared by one-step solvent thermal method. Materials include P-Ni-Fe₃O₄/GNs, N-Ni-Fe₃O₄/GNs, P-Co-Fe₃O₄/GNs and N-Co-Fe₃O₄/GNs. The specific capacity and cycle performance of the graphene composite electrode materials are much higher than that of the Ni-Fe₃O₄ and Co-Fe₃O₄ electrode materials. After 50 cycles, the charge discharge capacity is basically maintained at about 800 m Ah/g.The amount of attenuation is very small and coulombic efficiency can be as high as 98 %.