Abstract
Monophase Li1-x(NiyCo1-y)1+xO2 oxides (0 ≤ y ≤ 0.4 and 0.8 ≤ y ≤ 0.9) with a layered structure (R3̄m space group) have been prepared by interaction of (NiyCo1-y)3O4 (0 ≤ y ≤ 0.4) and NiyCo1-yO (0.8 ≤ y ≤ 0.9) with LiOH at low temperature (450°c). As in the case of high-temperature analogues, cobalt substitution for nickel stabilizes the Ni3+ ions and improves the two-dimensionality of the crystal lattice. Acid treatment of LT and HT oxides leads to a partial dissolution of the solid and to removal of lithium and "impurity" cobalt and/or nickel from LiO2 layers of the trigonal framework. For cobalt-rich oxides, the ion extraction is accompanied by partial Li+/H+ exchange, especially for LT samples. Acid-delithiated oxides are studied as cathode materials in lithium batteries. The resulting cells show a high value of the initial voltage (4 V), which allows a direct discharge of the cell without previous charge. For LT samples, the discharge and charge processes occur at lower voltage (especially for Co-rich oxides) and the reversibility of the cell is lower as compared to that of HT analogues. The better reversibility of the cell in the 4.0-3.2 V range is found for HT Ni-rich oxide. The composition of the acid-treated oxides can be recovered without an enhancement polarization of the cell. XRD analysis and IR spectroscopy show good reversibility of lithium insertion and extraction reactions by chemical and electrochemical procedures.
Published Version
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