Effect of CO 2 on layered Li 1+ zNi 1− x− yCo xM yO 2 (M = Al, Mn) cathode materials for lithium ion batteries

Abstract

We investigated the effect of CO 2 on layered Li 1+ z Ni 1− x− y Co x M y O 2 (M = Al, Mn) cathode materials for lithium ion batteries which were prepared by solid-state reactions. Li 1+ z Ni (1− x)/2 Co x Mn (1− x)/2 O 2 (Ni/Mn mole ratio = 1) singularly exhibited high storage stability. On the other hand, Li 1+ z Ni 0.80Co 0.15Al 0.05O 2 samples were very unstable due to CO 2 absorption. XPS and XRD measurements showed the reduction of Ni 3+ to Ni 2+ and the formation of Li 2CO 3 for Li 1+ z Ni 0.80Co 0.15Al 0.05O 2 samples after CO 2 exposure. SEM images also indicated that the surfaces of CO 2-treated samples were covered with passivation films, which may contain Li 2CO 3. The relationship between CO 2-exposure time and CO 3 2− content suggests that there are two steps in the carbonation reactions; the first step occurs with the excess Li components, Li 2O for example, and the second with LiNi 0.80Co 0.15Al 0.05O 2 itself. It is well consistent with the fact that the discharge capacity was not decreased and the capacity retention was improved until the excess lithium is consumed and then fast deterioration occurred.