Crystal Structure and Electrochemical Properties of Ni-Substituted Li2CuO2 as a Positive Electrode

INTORDUCTION Positive electrodes with high energy density have been in demand for lithium-ion battery as a power source of the electrical vehicle. We have focused on copper oxides. They have some unique feature which is different from other popular positive electrodes. Firstly, copper has abundant resources and less toxicity compared to cobalt or nickel. Secondary, they adopt mutually similar structure which has the square planner CuO4 with the copper atom in the center and the oxygen atoms at the corners. Thus, this structure leads to characteristics of electronic structure that Cu 3d and O2p orbitals overlap dominantly. This overlapping is the important for high-Tc superconductivity. Hence, it is likely that not only copper but also oxygen in the Cu-containing oxides may take on the electrochemical reaction. However, investigations on Cu-containing oxides are very limited. Li2CuO2 was reported that a rechargeable capacity was 130 mAhg with an average voltage of 2.5 V although it has 490 mAhg of the theoretical capacity[1]. Recently, we have reported changes in electronic and crystal structure of Li2CuO2 during Li-deintercaltion process [2,3]. By combining experimental and calculated results, it was concluded that oxygen could participate in charging process during the oxidation of Li2CuO2. In addition, CuO formed by the oxidation reacted with Li reversibly, accompanied by the generation of O2 gas. The objective of this paper is to determine the crystal structure of Nisubstituted Li2CuO2 by using synchrotron X-ray and neutron diffraction and XAFS measurements, and then to investigate the effect of the substitution of Ni on the electrochemical properties of Li2CuO2.