화학공학소재연구정보센터
Solid State Ionics, Vol.148, No.3-4, 299-309, 2002
Nanocrystalline LiCo1-xNixO2 (0 <= x <= 0.3) for Li-ion batteries
Nanocrystalline LiCo1-xNixO2 (0less than or equal toxless than or equal to0.3)-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 fori-nation 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 (TEND confirm the formation of layered alpha-NaFeO2 structure at temperature as low as 330 degreesC. 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 degreesC is in the range of 10-15 nm. Substitution of nickel retards the crystal growth. Solid state Li-6-Magic Angle Spinning (MAS) NMR investigation reveals that the micro-structural short range ordering of nickel ions in LiCo1-xNixO2 (0less than or equal tox0.3) is minimum at lower processing temperatures. Li-6-MAS NMR studies show that considerable amount of short range ordering of nickel ions is observed when the calcination temperature is raised beyond 800 degreesC indicating that the upper limit for processing temperature is around 750 degreesC. 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.