Enhancement of LiCoO2 Electrode Reaction by Considerable Amounts of Powdery Alpha-LiAlO2

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Considerable amounts of powdery LiAlO2 (LAO) with a layered NaCl-type crystal structure increased a specific capacity of LiCoO2 (LCO) and decreased a polarization resistance. Though LAlO is an electronic insulator, both impedance measurements and low-temperature charge-discharge testing showed that LCO electrode reaction was activated by including the LAO powder with well-crystalized. Alpha-LAO was prepared via sol-gel method. Rietveld refinement showed that the crystal structure was the same as that of conventional LCO. The LCO electrodes including several tens of mass percent of LAO were obtained by mixing the LAO and LCO powders with vibrational milling at room temperature. The obtained electrodes were characterized by electrochemical testings. LiCoO2 powder (C-5H, Nippon Chemical Industrial Co. Ltd.) was used. The average particle size is around 6 to 7 μm. The working electrode was composed of LCO composite, acetylene black and binder. Li metal was used as a negative electrode and the electrolyte was 1 M LiPF6 in ethylene carbonate (EC):dimethyl carbonate (DMC) (3:7 v/v%). The charge-discharge testing were conducted galvanostatically at various current densities over the voltage range from 2.0 to 4.2 V at 25 °C. The XRD patterns of samples showed an overlapping of those of LCO and LAO, but no solid solutions were formed. The charge-discharge curves for various investigated LCO composites kept those of bare-LCO, but the specific capacity increased. STEM-EELS of fully-charged LCO composite indicated that the electronic states of LAO (Li K-and Al L-edges) were the same as those of as-prepared. In addition, DFT calculation suggests that it is unable to remove Li ions from LAO up to 4.2 V and LAO may undergo an oxidation reaction at voltages of 5 V or higher. Therefore, the LAO does not participate in the increased capacity, but LAO makes the LCO electrode reaction active kinetically. Accordingly, it enhances a rate-performance of LCO electrode as well as shown in Figure 1. The LCO-LAO composite electrode potentially could reduce the usage of rare metal cobalt and lead a cost cut as well while improving the battery performance. We will present and discuss an unique effect of powdery LiAlO2 on the LiCoO2 electrode reaction in details. Figure 1