Preparation And Modification Study Of Novel Cathode Materials For Lithium Ion Batteries

Due to the excellent performance, Lithium-ion batteries have been concerned byresearchers. The cathode materials play a key role to improve the performance of Lithium-ionbatteries. Here, several cathode materials were researched. By the wet method, wesynthesized the Ti⁴⁺doped Li₉V_3-xTi_x（P₂O₇）₃（PO₄）₂/C series of compounds and reserched theeffect of doping on the electrochemical performance; we synthesized the LiCoBO₃compoundand studied their electrochemical performance for the first time; in addition, theelectrochemical performance of the LiV₃O₈surface coated LiCoO₂was researched.A series of Ti⁴⁺-doped Li₉V_3-xTi_x（P₂O₇）₃（PO₄）₂/C compounds have been prepared by wetmethod. X-ray-diffraction measurement shows that the single phase region can be expressedas x0.10. The effects of substitution of Ti for V on the electrochemical properties ofLi9V3-xTix（P2O7）3（PO4）2compounds have been researched. Our investigations results showthat Ti-doping can improve the electrochemical performance. TheLi₉V₂.95Ti₀.05（P₂O₇）₃（PO₄）₂/C exhibits the best cycle performance and the highest firstdischarge capacity of120.7mAh g^-1at0.2C. The electrochemical impedance spectroscopy（EIS） indicates that, with the increase of the Ti⁴⁺content, the charge transfer resistancedecreases initially and then increases monotonically when x>0.05.Lithium cobalt borate, LiCoBO₃, was synthesized at the temperature higher than600℃with carbon black in the starting materials by carbonthermal reduction method. The crystalstructure of the compound was determined, and we reported the electrochemical performanceof this material for the first time. The initial specific discharge capacity of103.4mAh/g forthe cathode material was obtained within a window of1.5-4.7V at current density of10mA/g.Even at the current density of20mA/g, a specific discharge capacity of61.8mAh/g wasobtained at the range of1.5-4.8V. the cycle performance shows that LiCoBO₃exhibits goodcycle stability. An increase of capacity is expected to be reached by reduce kineticpolarization.The amorphous LiV₃O₈coated LiCoO₂materials were synthesized by the wet method forthe first time, and its electrochemical performance has been studied. The crystal structural andmorphological properties were characterized by XRD and SEM. Compared with un-coated LiCoO₂, the first charge-discharge curves shows that appropriate amount of LiV₃O₈coated onthe LiCoO₂surface can raise the voltage platform and increase the first charge-dischargecapacity, where the initial discharge capacity of LiCoO₂with5wt%coating amount is169.8mAh g^-1and the increasing ratio is about15.8%. After50cycles for un-coated LiCoO₂, thedischarge capacity is97.4mAh g^-1at the current rate of0.5C under2.7-4.4V; The dischargecapacity of144.2mAh g^-1,120.6mAh g^-1and122mAh g^-1can be obtain for the materialswith the coating amount of5wt%,7wt%and10wt%, respectively. Based on theexperimental results, it can be concluded that the material with the coating amount of about5wt%gives the best electrochemical performance.