2002 Volume 70 Issue 2 Pages 117-121
Complex oxides LiMO2 (M = transition metal) have been used as cathode materials for lithium ion secondary batteries. To improve the performance of these materials, we should control the composition without non-stoichiometric phases that are inactive on the lithium intercalation. Therefore, it is very important that the ratio of lithium to transition metals in the complex oxide have to be controlled accurately. Spectroscopic methods such as ICP-AES (induced coupled plasma atomic emission spectroscopy) and AAS (atomic absorption spectroscopy) are generally used for the quantitative analysis of metal cations. Fatal interference between cations included in composite oxides, however, often produces erroneous data in some cases. On the other hand, IC (ion chromatography) is very useful technique for cation analytical method that equipped with a carboxylate-type separation column designed for alkali and alkaline earth metal cations. It can separate simultaneously both alkali metal ions and transition metals ions by using the mixed eluent of nitric acid and oxalic acid. In this study, we investigated the composition analysis of cathode materials using the IC technique. The data by IC had sufficient reliability and reproducibility compared with those by ICP-AES. The relationship between the heat treatment temperature and the ratio of lithium to transition metals in lithium nickel oxides showed that the fluctuation of the composition increased with increasing temperature and was larger in air atmosphere than that in oxygen. Such findings agreed well with the previous report.