Structural and electrochemical characterizations of surface-modified LiCoO2 cathode materials for Li-ion batteries

Commercial LiCoO2 has been coated with metal oxides including MgO, Al2O3 and SnO2. The morphology and structure of the coating layer have been characterized with scanning electron microscope (SEM) and high-revolution transmission electron microscope (HRTEM). It is found that the coating layer is amorphous and rather compact. LiCoO2 coated with different metal oxides demonstrate different electrochemical performances. MgO-coated LiCoO2 cathode shows very good electrochemical stability up to a charge cutoff voltage of 4.7 V while Al2O3-coated LiCoO2 is electrochemically stable up to 4.5 V. However, SnO2-modified LiCoO2 is stable only at low-charge cutoff voltages. Cyclic voltammetry (CV) and charge–discharge cycling show that surface modification does not influence the phase transitions below 4.5 V but the phase transition at about 4.58 V is drastically suppressed. These improvements are attributed to the modifications to the surface property of the particles by coating and to the lattice structure of LiCoO2 during cycling.