Nanocrystalline LiCo1−xNixO2 (0≤x≤0.3) for Li-ion batteries

Nanocrystalline LiCo1−xNixO2 (0≤x≤0.3)—a promising cathode material for rechargeable lithium batteries has been successfully prepared by a novel soft chemical route. Both the formation of the metal–glycine complex and subsequent decomposition of the same at low temperatures under carefully controlled oxygen flow play a critical role in the formation of nanocrystalline material. The thermal history of the as-prepared gel is established by differential thermal analysis (DTA) and thermogravimetric analysis (TGA). Powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) confirm the formation of layered α-NaFeO2 structure at temperature as low as 330 °C. The exothermic combustion reaction of the organic precursors, which generates high temperature, should be avoided as it results in the spontaneous growth of large crystals. High-resolution transmission electron microscopy (HRTEM) investigation reveals that the particle size of LiCo0.7Ni0.3O2 heated at 400 °C is in the range of 10–15 nm. Substitution of nickel retards the crystal growth. Solid state 6Li-Magic Angle Spinning (MAS) NMR investigation reveals that the micro-structural short range ordering of nickel ions in LiCo1−xNixO2 (0≤x≤0.3) is minimum at lower processing temperatures. 6Li-MAS NMR studies show that considerable amount of short range ordering of nickel ions is observed when the calcination temperature is raised beyond 800 °C indicating that the upper limit for processing temperature is around 750 °C. These materials were fabricated into thin electrodes using polyvinylidene fluoride (PVDF) as polymer binder and the electrochemical properties such as charge/discharge and impedance were evaluated. The electrodes cycled well with a coulombic efficiency of close to one.