Modification And Electrochemical Properties Of NiFe₂O₄ As Anode Materials

Nowadays, the application of lithium-ion battery become more widely in electric vehicles and large-scale energy storage, due to the increasing social demand for clear energy, and the electrochemical property of energy densitiy need to further improvement at the same time. So far, the hotspot of research around Li-ion battery is mainly focused on the exploration of anode materials with higher specific capacity、better cycling performance and better safety. NiFe2O4 are considered to be promising anode materials among transition metal oxides due to its high theoretical capacity(915 mAhg-1), natural abundance, low cost and eco-friendliness. However, NiFe2O4 shows poor cycling stability and unsatisfied electrochemical performance arising from their low electrical conductivity and large volume change during charge/discharge cycling. In this paper, based on the excellent conductivity and lithium storage properties of graphene and composite technology, NiFe2O4/graphene anode composite materials was prepared by in situ synthesis. Meanwhile, the NiFe2O4/graphene/C materials was synthesized by carbon-coated to improve the electrochemical properties of the material, and the effects of structures and morphologies on the electrochemical performance of composites were systematically studied. The main results obtained from this paper are as follows:(1) The NiFe2O4 spherical nanoparticles anode material with uniform size and higher degree of crystallinity were prepared by hydrothermal. The preparation process has been studied and found: the hydrothermal time was 24 h and the heat treatment temperature was 400 ℃,NiFe2O4 material shows good electrochemical performance and the first discharge capacity was 1361 mAhg-1 at the current density of 100 mAg-1.(2) Composite materials were prepared by one-step in situ synthesis and the NiFe2O4 nanoparticles uniform dispersed on the surface of graphene. Composite grapehen can be benefits the dispersion of NiFe2O4 and used as a stress buffer matix and improve its electronic conductivity. NiFe2O4/graphene showed the best electrochemical when the hydrothermal temperature at 180 ℃ and the amount of graphene is 10%, its discharge capacity for the first time was 1068 mAg-1 and the reversible capacity retention rate was 70.8% after 20 cycles. The impedance and cyclic voltammetry measurements indicated the NiFe2O4/graphene composite internal resistance was smaller and exhibits better reversibility.(3) NiFe2O4/graphene/C composite materials was synthesized by carbon-coated, and the results show that the materials has the excellent electrochemical when the amount of sucrose or ascorbate is 20%. Galvanostatic charge/discharge tests shows that Sucrose-coated and Ascorbate-coated composites discharge specific capacity for the first time were separately 1031、1362 mAhg-1 at current density of 100 mAg-1, and the reversible capacity retention rate were separately 72.2%、71.6% after 20 cycles, the results show that NiFe2O4/graphene/C composite materials which cycle performance is more superior than that uncoated materials. Sucrose or Ascorbate carbon-coated can improve the electronic conductivity and results in better electrochemical performance.