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Bulletin of the Korean Chemical Society (BKCS)

ISSN 0253-2964(Print)
ISSN 1229-5949(Online)
Volume 21, Number 11
BKCSDE 21(11)
November 20, 2000 

Effect of pH on the Synthesis of LiCoO2 with Malonic Acid and Its Charge/Discharge Behavior for a Lithium Secondary Battery
Do-Hoon Kim, Euh-Duck Jeong, Sang-Pil Kim, Yoon-Bo Shim
The pH effect of the precursor solution on the preparation of LiCoO₂ by a solution phase reaction containing malonic acid was carried out. Layered LiCoO₂ powders were obtained with the precursors prepared at the different pHs (4, 7, and 9) and heat-treated at 700℃ (LiCoO₂-700) or 850℃ (LiCoO₂-850) in air. pHs of the media for precursor synthesis affects the charge/discharge and electrochemical properties of the LiCoO₂electrodes. Upon irrespective of pH of the precursor media, X-ray diffraction spectra recorded for LiCoO₂-850 powder showed higher peak intensity ratio of I(003)/I(104) than that of LiCoO₂-700, since the better crystallization of the former crystallized better. However, LiCoO₂ synthesized at pH 4 displayed an abnormal higher intensity ratio of I(003)/I(104) than those synthesized at pH 7 and 9. The surface morphology of the LiCoO₂-850 powders was rougher and more irregular than that of LiCoO₂-700 made from the precursor synthesized at pH 7 and 9. The LiCoO₂electrodes prepared with the precursors synthesized at pH 7 and 9 showed a better electrochemical and charge/discharge characteristics. From the AC impedance spectroscopic experiments for the electrode made from the precursor prepared in pH 7, the chemical diffusivity of Li ions (DLi+) in Li0.58CoO₂determined was 2.7 ×10-8 cm²s-1 . A cell composed of the LiCoO₂-700 cathode prepared in pH 7 with Lithium metal anode reveals an initial discharge specific capacity of 119.8 mAhg-1 at a current density of 10.0 mAg-1 between 3.5 V and 4.3 V. The full-cell composed with LiCoO₂-700 cathode prepared in pH 7 and the Mesocarbon Pitch-based Carbon Fiber (MPCF) anode separated by a Cellgard 2400 membrane showed a good cycleability. In addition, it was operated over 100 charge/discharge cycles and displayed an average reversible capacity of nearly 130 mAhg-1 .
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