Low-purity natural graphite, which is used as an anode active material for lithium-ion batteries, contains various impurities. To investigate the effects of these impurities on the lithium ion battery system, various metal oxides such as Fe2O3, Al2O3, and SiO2 were mixed with high-purity natural graphite using a glycine nitrate process (GNP) or hydrothermal method. While there are no significant changes in the physical or chemical structure due to the addition of metal oxide impurities, the electrochemical performance was considerably improved. Both Fe2O3- and SiO2-natural graphite composites showed a larger first charge capacity and better capacity retention compared to the high-purity natural graphite (NG-R) due to the conversion reaction and formation of the solid electrolyte interface (SEI) film, respectively. Specifically, the 05-Fe sample showed a charge capacity of 421.8 mAh/g at the first cycle, but a high irreversible capacity of 50.4 mAh/g due to the irreversible conversion reaction. Nevertheless, the 05-Fe sample exhibited a significantly higher capacity retention (95.9%) than NG-R (84.9%).

Keywords: lithium-ion batteries, natural graphite, impurity, low-purity, anode materials.