Lanthanum-doped LiCoO 2 cathode with high rate capability

Abstract

Lanthanum-doped LiCoO 2 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 LiCoO 2 became sluggish upon addition of lanthanum. X-ray diffraction analyses of the composites revealed existence of minute quantities of lanthanum-rich perovskite phases—rhombohedral LaCoO 3 ( R 3 ¯ ) and tetragonal La 2Li 0.5Co 0.5O 4 (14/ mmm), along with rhombohedral LiCoO 2 ( R 3 ¯ m ) . 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 × 10 −3 S cm −1) was observed for 1.0 mol% La-doped LiCoO 2. An excellent cycling performance with capacity retention by a factor of ∼10 in comparison to the pristine LiCoO 2 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 La 2Li 0.5Co 0.5O 4 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.