Crystal Structures and Electrochemical Properties of Ni-Substituted Li2CuO2 as a Cathode Material

Abstract

A single orthorhombic phases of Li2CuO2-Li2NiO2 solid solutions were prepared in the range of x = 0 to 0.4 in Li2Cu1-x Ni x O2. An improvement of specific capacity by the Ni-substitution was obtained as reported previously. Our present study clarified the phase relationship and changes in chemical oxidation states of Cu and Ni ions caused by Li-extracting. The XRD patterns using synchrotron radiations showed that CuO, NiO or LiNiO2 phases were not observed for fully charged Li2Cu1-x Ni x O2. It is likely that the substitution of Ni has an effect to depress the formation of these oxides during charging. X-ray absorption spectra for both Ni and Cu K-edges shifted to higher energy from Li2Cu0.6Ni0.4O2 to LiCu0.6Ni0.4O2 and then to lower energy by charging LiCu0.6Ni0.4O2. An irreversible capacity was improved by the substitution of 10 or 20 mole % of divalent Ni for divalent Cu.