X-Ray Absorption Spectroscopic Study of LiAl[sub y]Co[sub 1−y]O[sub 2] Cathode for Li Rechargeable Batteries

LiAl y Co 1 − y O 2 powders were synthesized by the sol-gel process using acrylic acid as a chelating agent. The X-ray diffraction pattern for LiAl 0.25 Co 0.75 O 2 powders calcined at 600°C or above shows that these materials have a well-developed layered HT ­ LiCoO 2 structure. The capacity fading of the gel-derived LiAl 0.25 Co 0.75 O 2 samples greatly decreased at lower temperatures. Galvanostatic cycling for the gel-derived LiAl 0.25 Co 0.75 O 2 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 0.25 Co 0.75 O 2 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 0.25 Co 0.75 O 2 synthesized at 600 and 800°C during the charging and cycling process revealed that the large capacity fading of LiAl 0.25 Co 0.75 O 2 synthesized at a higher temperature is strongly related to the remaining Co 4 + ions and the local structure distortion.