Effect of lithia and substrate on the electrochemical performance of a lithia/cobalt oxide composite thin-film anode

Highly porous reticular Li2O/CoO composite thin films fabricated by electrostatic spray deposition were investigated by using X-ray diffraction, scanning electron microscopy, galvanostatic cell-cycling measurements, and AC impedance spectroscopy measurements. The results of the electrochemical tests indicate that the initial coulombic efficiency and capacity retention are dependent on Li2O content and the specific surface area of the deposited layer. Irrespective of the type of substrate, the electrode gave the best electrochemical performance when the molar ratio of Li to Co was controlled at 1:1. At the optimal composition, at 0.2 C the initial coulombic efficiency was as high as 81.9% and 83.6% for the film on Cu foil and on porous Ni, respectively. The Li2O/CoO (Li/Co = 1:1) films on Ni foam and Cu foil had sustained capacities of up to 790 and 715 mAh g(-1), respectively, at a rate of 1 degrees C over 100 cycles at 25 degrees C. Similar cycling experiments carried out at 70 degrees C showed that the capacity is temperature-sensitive, and it exhibited reversible capacities as high as 1018 (Cu foil) and 1269 mAh g(-1) (Ni foam) for up to 100 cycles. The thin-film electrodes on Ni foam always performed better than those on Cu foil. Cycling at elevated temperature (70 degrees C) also resulted in a significant increase in capacity.