Lanthanum-doped LiCoO2 cathode with high rate capability

Lanthanum-doped LiCoO2 composite cathode materials, containing 0.1-10 mol% of La were synthesized by citric acid aided combustion technique. Thermal analyses showed that the sharp decomposition reaction for pristine LiCoO2 became sluggish upon addition of lanthanum. X-ray diffraction analyses of the composites revealed existence of minute quantities of lanthanum-rich perovskite phases-rhombohedral LaCoO3 (R (3) over bar) and tetragonal La2Li0.5Co0.5O4 (14/mmm), along with rhombohedral LiCoO2 (R (3) over barm). Electron microscopy showed a distinct grain growth with increasing La content. An increase of about two orders of magnitude in the electrical conductivity (1.09 x 10(-3) Scm(-1)) was observed for 1.0 mol% La-doped LiCoO2. An excellent cycling performance with capacity retention by a factor of similar to 10 in comparison to the pristine LiCoO2 was observed for the composite cathode containing 5.0 mol% La, when 2032 type coin cells were cycled at 5C rate. This has been ascribed to the structural stability induced by La doping and presence of the ion-conducting phase La2Li0.5Co0.5O4 which acts as a solid electrolyte for Li+ ions. A negligible growth of impedance upon repeated cycling has been observed. Cyclic voltammetry showed a remarkable improvement in reversibility and stability of the La-doped electrodes. These composite cathodes might be very useful for high rate power applications. (c) 2008 Elsevier Ltd. All rights reserved.