X-ray absorption spectroscopic study of LiAl_yCo_1-yO₂ cathode for Li rechargeable batteries

LiAl_yCo_1-yO₂ powders were synthesized by the sol-gel process using acrylic acid as a chelating agent. The X-ray diffraction pattern for LiAl_0.25Co_0.75O₂ powders calcined at 600°C or above shows that these materials have a well-developed layered HT-LiCoO₂ structure. The capacity fading of the gel-derived LiAl_0.25Co_0.75O₂ samples greatly decreased at lower temperatures. Galvanostatic cycling for the gel-derived LiAl_0.25CO_0.75O₂ samples calcined at various temperatures indicates that electrodes calcined at 600°C show enhancement in capacity and cyclability. The variations in the local structures with Li deintercalation and cycling process of LiAl_0.25Co_0.75O₂ were investigated as a function of calcination temperature using X-ray absorption spectroscopic technique. X-ray absorption near-edge structure and extended X-ray absorption fine structure results for LiAl_0.25Co_0.75O₂ synthesized at 600 and 800°C during the charging and cycling process revealed that the large capacity fading of LiAl_0.25Co_0.75O₂ synthesized at a higher temperature is strongly related to the remaining Co⁴⁺ ions and the local structure distortion.