Structural, magnetic, and electrochemical studies on lithium insertion materials LiNi1−xCoxO2 with 0≤x≤0.25

The structural, magnetic, and electrochemical properties of the LiNi1−xCoxO2 samples with x  = 0, 0.05, 0.1, and 0.25 have been investigated by powder X-ray diffraction analyses, magnetic susceptibility (χ)(χ) measurements, and electrochemical charge and discharge test in non-aqueous lithium cell. According to the structural analyses using a Rietveld method, the occupancy of the Ni ions in the Li layer was estimated to be below 0.01 for all the samples and was eventually independent of x. The temperature (T  ) dependence of χ−1χ−1 obtained with the magnetic field H=10 kOe indicated that all the samples are a Curie–Weiss paramagnet down to ∼100K. At low T, all the samples entered into a spin-glass-like phase below Tf. The magnitude of Tf was found to decrease almost linearly with x, as in the case for the x dependences of the lattice parameters of ah- and ch-axes, Weiss temperature, and effective magnetic moment. It is, therefore, found that the change of the magnetic properties with x is simply explained by a dilution effect due to the increase of the quantity of Co3+ ions. On the other hand, the electrochemical measurements demonstrated that the irreversible capacity at the initial cycle is drastically decreased by the small amount of Co ions. Furthermore, the discharge capacity (Qdis) for the x=0.05 and 0.1 samples are larger than that for the x=0 sample; namely, Qdis=180 mAh g−1 for x=0, Qdis=217 mAh g−1 for x=0.05, and Qdis=206 mAh g−1 for x=0.1. Comparing with the past results, the amount of Ni ions in the Li layer is found to play a significant role for determining the magnetic and electrochemical properties of LiNi1−xCoxO2.

Graphical AbstractThe inter-relationship between structural, magnetic, and electrochemical properties of the lithium insertion materials LiNi1−xCoxO2 with 0≤x≤0.250≤x≤0.25 were investigated by X-ray diffraction measurements, magnetic susceptibility measurements, and electrochemical charge and discharge test in non-aqueous lithium cell. The magnitude of spin-glass-like transition temperature Tf was found to decrease almost linearly with x, as well as the x dependences of effective magnetic moment, Weiss temperature, and lattice parameters. Figure optionsDownload full-size imageDownload as PowerPoint slide