Effect of La-doping on the structural, morphological and electrochemical properties of LiCoO₂ nanoparticles using Sol-Gel technique

Sol-Gel auto combustion technique was used to synthesis La³⁺substituted LiCoO₂ lithium-rich cathode materials to improve the cycling performance and rate capability. Samples with different concentration of La containing LiCo_1−xLa_xO₂ (with 0 ≤ x ≤ 0.20) were chemically prepared and calcined the obtained powders at 850 °C for 6 h. Various techniques for the investigation of lanthanum behaviour in LiCoO₂ have been utilised, such as x-ray diffraction (XRD), Field emission scanning electron microscope (FESEM), Attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), Near Edge x-ray absorption spectroscopy (NEXAS), Galvanostatic charge-discharge tests and cyclic voltammetry (CV). The formation of a hexagonal lattice of the α-NaFeO₂ structure of LiCoO₂, having space group R-3m is confirmed by x-ray diffraction analysis. FESEM results reveal that by increasing La contents the grain growth becomes distinct, well defined and smaller grains obtained. ATR-FTIR confirms the functional bonding in the prepared samples, as well XANES spectra reveals the electronic configuration valence state, chemical bonding character and local coordination of a specific atom. Maximum discharging capacities were observed in the La-doped material which is 182.38 mAhg⁻¹ and 56.2 mAhg⁻¹ at 0.1C and 5 C respectively and on average, this is more than 5% higher as compared to the pure LiCoO₂. After 5C, the discharge capacity of the doped material at 0.1C can again reach 163.83 mAhg⁻¹, about 89% of the discharge capacity obtained in the first cycle. When 2032 type coin cells were cycled at a constant rate, an excellent cycling performance with capacity retention by a factor of ∼2 in comparison to the pristine LiCoO₂ was observed for the composite cathode containing 4.0 mol% La. This reveals the structural stability induced by La doping. Remarkable improvement in reversibility and stability of the La-doped electrodes shown by cyclic voltammetry (CV). These composite cathodes might be very useful for high rate power applications. (paper)