Preparation And Electrochemical Performance Of Electrode Materials For Power Lithium-ion Batteries

Lithium-ion batteries are promising power sources for hybrid electric vehiclesand electric vehicles due to their high voltage, high energy density and power density,long cycle life, environmental friendliness and so on. In this work, Li4Ti5O12,LiNi0.5Mn1.5O4and Li3V2(PO4)3have been synthesized and researched. Additionally,LiFePO4/Li4Ti5O12,LiNi0.5Mn1.5O4/Li4Ti5O12coin-type full cells,18650and26650LiMn2O4/Li4Ti5O12cylindrical batteries, and liquid state soft pack LiMn2O4/Li4Ti5O12battery with the capacity of10Ah have been fabricated. The work has significanttheoretical and practical value.Li4Ti5O12, LiNi0.5Mn1.5O4and Li3V2(PO4)3electrode materials have beensystematically researched via X-ray diffraction (XRD), scanning electron microscope(SEM), transmission electron microscope (TEM), galvanostatic charge and discharge,cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and so on.Additionally, LiFePO4/Li4Ti5O12, LiNi0.5Mn1.5O4/Li4Ti5O12coin-type full cells,18650and26650LiMn2O4/Li4Ti5O12cylindrical batteries, and liquid state soft packLiMn2O4/Li4Ti5O12battery with the capacity of10Ah have been systematicallyresearched via various electrochemical methods. Glycine as single chelating reagent,glycine and beta-cyclodextrin as composite chelating reagents have been firstlyintroduced into the Li3V2(PO4)3system and can significantly improve theelectrochemical performance of Li3V2(PO4)3/C prepared by sol-gel route. It is a newand effective way of improving the rate capability for Li3V2(PO4)3/C by coating theLi3V2(PO4)3/C by Li4Ti5O12with high lithium ion diffusion coefficient. It is a new andsimple way of enhancing the electrochemical performance of Li3V2(PO4)3/C throughmodifying the fabrication of the electrode.The resuls show that the Li4Ti5O12synthesized at800℃for16h has the bestelectrochemical performance. The LiFePO4/Li4Ti5O12system with the P/N value of30%has the best cyclic and rate performance. The LiNi0.5Mn1.5O4synthesized at900℃for12h with the pH value of6.0has the best electrochemical performance.The LiNi0.5Mn1.5O4/Li4Ti5O12system with the P/N value of40%has the best cyclicand rate performance. The Li3V2(PO4)3/C has the best electrochemical performance prepared via glycine-asisted sol-gel method at800℃for8h with the molar ratio ofglycine to metal ions of0.8. Compared with the Li3V2(PO4)3/C prepared byglycine-asisted sol-gel method, the Li3V2(PO4)3/C prepared via sol-gel method basedon composite chelating reagents of glycine and beta-cyclodextrin has betterelectrochemical performance. The electrochemical performance can be largelyimproved by coating Li3V2(PO4)3/C with Li4Ti5O12and using LiCoO2as slurryadditive.In conclusion, compared with the LiFePO4/Li4Ti5O12system, theLiNi0.5Mn1.5O4/Li4Ti5O12system has better electrochemical performance. SpinelLiNi0.5Mn1.5O4has higher voltage plateaus aroud4.7V (vs. Li/Li+) than those ofmonoclinic Li3V2(PO4)3. LiNi0.5Mn1.5O4is a more promising cathde material forpower lithium-ion batteries.