An electrochemical investigation into the lithium insertion properties of LixNiO2 (0<=x<=1)

The thermodynamic and kinetic properties for the lithium insertion in LixNiO2 have been probed by electrochemical techniques. The preparative method used ensured the starting material was nominally stoichiometric with a low estimated level of Li and Ni inter-mixing. The step potential protocol of the electrochemical voltage spectroscopy method was adopted to reveal the nature of the lithium insertion and extraction reactions. The first cycle demonstrated a poor coulombic efficiency, which may be associated with the structural rearrangement caused by the initial hexagonal to monclinic phase transition. The efficiency improved during the second cycle and showed that a specific capacity around 180 mA h/g (Delta x = 0.65) could be cycled reversibly. Several sharp differential capacity peaks were detected, which appeared to correlate well with the structural phase transitions previously determined from in-situ XRD studies. The differential capacity profile indicated that the main extraction-insertion peaks were well-defined with only minor peak separation consistent with a reversible system demonstrating low overvoltage. The multiple phase transitions were demonstrated to have a profound efect on the nature of the ionic transport properties within the host lattice. Over most of the concentration range, the diffusion coefficients averaged around 10(-8) cm(2) s(-1), values which are comparable with similar measurements carried out on composite electrodes made from the alternative high voltage cathode materials LixMn2O4 and LixCoO2.