Electrochemistry and redox characterization of rock-salt-type lithium metal oxides Li1+z/3Ni1/2-z/2Ti1/2+z/6O2 for Li-ion batteries

Abstract This work explores the compound Li 1+z/3 Ni 1/2-z/2 Ti 1/2+z/6 O 2 (z = 0, 0.1, 0.2, 0.3, 0.4, 0.5) and compares the electrochemical performance difference with z to the proposed percolation network. X-ray diffraction combined with Rietveld refinements show that rock-salt structure is obtained by the simple sol-gel process, and the lattice parameters are increased with the increasing level of Li-excess. Micromorphology observation reveals that particles are irregular and the size is distributed within 100 nm. In addition, a detailed reaction mechanism is examined by X-ray photoelectron spectroscopy and cyclic voltammetry, which exhibits the evolution of Ni, Ti and O in the initial charge-discharge process and confirms that they all make contributions to capacities. Electrochemical performance test shows that the discharge capacities increase with the amount of Li and Li 1.17 Ni 0.25 Ti 0.58 O 2 delivers the discharge capacities up to 223.9 mAh g −1 . At the current density of 400 mA g −1 , it still provides a large capacity of 120 mAh g −1 . Furthermore, Li 1.17 Ni 0.25 Ti 0.58 O 2 has the highest lithium ion diffusion coefficient among all samples.