Study on Phase Transitions of Lithium-Nickel-Manganese Oxide Li1+XNi0.5Mn1.5O4.0 (0 < x < 1) As High-Voltage and High-Capacity Cathode Materials

Abstract

Rising demands for high-energy density Li-ion batteries require the development of new cathode active materials with enhanced specific capacity and energy, increased safety and reduced cost. Currently used high-cost metals, such as cobalt and nickel, need to be replaced with more abundant and less toxic elements. A Co-free cathode material with high-voltage and high-capacity has been developed in our labs. The lithium‐nickel‐manganese oxide with composition Li1+xNi0.5Mn1.5O4.0 (0<x<0.5) was tailored with respect to morphology, particle size and shape distribution. The particles consist of densely packed nano‐sized primary crystallites and the free‐flowing powder shows a tap‐density of 2.4 g cm-3. The cathode material shows a specific capacity of about 210 mA h g-1 in the potential window 2.4-4.9 V. The working mechanism involves two distinct voltage plateaus at 4.7 and 2.9 V vs. Li/Li+. Very good cycling stability is obtained for more than 200 cycles in half-cell. Compared to other high-capacity materials, such as lithium-manganese-rich layered oxides, their spinel integrated variants and the cation disordered materials [1-3], this material does not need an activation cycle; it shows good rate capability and low voltage hysteresis. In full-cell vs. graphite anode, a stable capacity of 160 mA h g-1 is reached. For full-cell application no electrochemical pre-treatment or structural activation has to be applied in order to achieve the full capacity; therefore, the material can be directly assembled vs. graphite anode. Cathode material features will be described, electrochemical performances in half- and full-cell will be presented and the influence of the operating voltage window will be shown. The effects of particle shape, grain architecture and structural features on the electrochemical behavior will be discussed. Phase transitions in the low-potential region have been studied by HRTEM, EELS and XRD and the involved mechanism will be discussed. Acknowledgements This work was supported by the German Federal Ministry of Education and Research (BMBF) in the project Li-EcoSafe (03X4636A).