Synthesis Of Nickel Based Gradient Cathode Materials Li[Ni_0.85Co_0.15-xMnx]_O2for Secondary Lithium-ion Batteries

With the development of new energy vehicles and the demand for new energy storage sources such as solar energy and wind energy, recent researches on lithium ion batteries have focused on the cathode materials with high energy density. Ni-rich cathode material has become one of the ideal materials because of its high capacity of more than200mAh-g"1. Two different types of nickel-based cathode materials for high capacity lithium ion batteries were synthesized in this thesis:the gradient coating composite material Li[Ni0.85Co0.1Mn0.05]O2and a series of full gradient composite materials Li[Ni0.85Co0.15-xMnx]O2.X-ray diffractometry(XRD), Energy dispersive X-ray spectroscopy(EDX), Scanning electronic microscopy(SEM), Tap density test, Particle size test, Inductively coupled plasma test(ICP), Galvanostatic charge/discharge measurement and Electrochemical Impedance Spectrum(EIS) were employed to study the lattice parameter, particle morphology, elements content and the electrochemical performance of the materials.A new core-shell structure material Li[Ni0.85Co0.1Mn0.05]O2was synthesized with the core of LiNi0.9Co0.1O2and the gradient concentration of Ni-Co-Mn shell, where the nickle decreases while cobalt and manganese increase from the center to the outer layer. Li[Ni0.85Co0.1Mn0.05]O2has a layered hexagonal α-NaFeO2structure and a spherical morphology. The line scan test of elements on the cross section area of coating shell show that the main elements of the materials change gradiently. The initial discharge capacity is195.0mAh·g-1at1C rate between2.8and4.3V, it retains95.5%after100cycles at25℃. When cycled at55℃, the initial discharge capacity is216.3mAh·g-1and retains87.9%after100cycles, indicating good electrochemical capacity and cycling stability.The full gradient material Li[Ni0.85Co0.15-xMnx]O2was synthesized with continual change of Ni-Co-Mn full gradient from the center to the outer surface. Li[Nio.85Co0.15-xMnx]O2has a layered hexagonal α-NaFeO2structure and a spherical morphology. The line scan test of elements on the cross section area show that the main elements of the best material Li[Ni0.85Co0.08Mn0.07]O2change gradiently. The initial discharge capacity is192.3mA·g-1at1C rate between2.8and4.3V and retains90.1%after100cycles.When cycled at55℉, the initial discharge capacity is at1C rate is207.2mAh·g-1and retains82.5%after100cycles, indicating good electrochemical capacity and cycling stability.