Crystal structures and electrochemical properties of Ni-substituted Li_2CuO_2 as a cathode material

摘要

A single orthorhombic phases of Li_2CuO_2-Li_2NiO_2 solid solutions were prepared in the range of x = 0 to 0.4 in Li_2Cu_(1-x)Ni_xO_2. 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 LiNiO_2 phases were not observed for fully charged Li_2Cu_(1-x)Ni_xO_2. 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 Li_2Cu_(0.6)Ni_(0.4)O_2 to LiCu_(0.6)Ni_(0.4)O_2 and then to lower energy by charging LiCu_(0.6)Ni_(0.4)O_2. An irreversible capacity was improved by the substitution of 10 or 20 mole % of divalent Ni for divalent Cu.