Research On Synthesis And Modifition Of Cathode Materials For Lithiun-ion Batteries

In terms of poor rate performances and poor cyclic stability for lithium-ion batteries,investigation on the electrochemical performances of cathode materials such as LiNi1/3Co1/3Mn1/3O2,and Li1.2Mn0.54Ni0.13Co0.13O2 and LiNio.5Mn1.5O4,with surface-modification was carried out.This paper consists of three work as follows,Firstly,layered LiNi1/3Co1/3Mn1/3O2 cathode material is prepared by a sol-gel method and subsequently coated with YF3 layer via a wet chemical process.The pristine and YF3-coated samples are characterized by X-ray diffraction(XRD),scanning electron microscopy(SEM)with Energy dispersive spectroscope(EDS).The effect of YF3-coating on the electrochemical performances of LiNi1/3Co1/3Mn1/3O2@YF3 cells is investigated systematically by the charge/discharge testing.In comparison,the YF3-coated LiNi1/3Co1/3Mn1/3O2 exhibits higher rate capability and better cyclic stability than that of the pristine one.Analysis from Cyclic voltammograms(CV)and electrochemical impedance spectroscopy(EIS)indicates that the improved performances of LiNi1/3Co1/3Mn1/3O2@YF3 is mainly attributed to the smaller charge-transfer resistances and more stable electrolyte/electrode interfacial structure due to the suppression of the electrolyte decomposition.Secondly,Li1.2Mn0.54Ni0.13Co0.13O2 cathode materials are successfully prepared by sol-gel method,followed by surface-modification with EuF3 layer.The effect of EuF3-coating on the electrochemical performances of Li1.2Mn0.54Ni0.13Co0.13O2 is systematically investigated by XRD,SEM,charge-discharge test and AC impedance.In comparison with Li1.2Mn0.54Ni0.13Co0.13O2,Li1.2Mn0.54Ni0.13Co0.13O2@EuF3 exhibits superior rate performances and cyclic stability.Analysis from the electrochemical measurements reveals the enhanced performances would result from the smaller charge-transfer resistances and faster lithium-ion diffusion.In addition,EuF3-layer on the Li1.2Mn0.54Ni0.13Co0.13O2 surface would protects the active materials from chemical attack by HF,which suppresses the dissolution of Ni or Mn from Li1.2Mn0.54Ni0.13Co0.13O2 in the LiPF6 based electrolyte.Thirdly,spinel cathode materials are prepared by sol-gel technique,followed by surface-modification with fluoride-doping.In comparison with pristine LiNi0.5Mn1.5O4,LiNi0.5Mn1.5O4/F exhibits better rate capability and superior cycling stability.The improved performances would be attributed to the metal-fluorine(M-F)bond partially replacing metal-oxygen(M-O)bond at the surface,enhancing the entire bond energy as well as the structure stability.In addition,fluoride-doping would reduce the charge-transfer resistances and facilitate lithium-ion diffusion in the electrode as well as the suppression of the electrolyte decomposition.