Li4MeWO6 (Me=Ni, Mn, Co) As Positive Electrode Materials for Li-Ion Batteries

Wednesday, October 14, 2015: 14:30
105-A (Phoenix Convention Center)
S. Kumakura (Umicore Japan, Tokyo University of Science), S. Komaba (Tokyo University of Science, ESICB-Kyoto University), and K. Kubota (Tokyo University of Science, ESICB-Kyoto University)
Li-rich layered oxides, Li2MO3 (M = a variety of tetravalent metal(s), typically Mn), have been widely studied as next generation cathode materials for Li ion batteries. Recently, Li4NiTeO6 was reported as a cathode material with 1.5 Li reversible reaction.[1] It has honeycomb structure with ordered arrangement of Te and Ni similar to that of Mn and Li in Li2MO3. The hexavalent Te stabilizes divalent state of Ni ions in the structure. A reversible electrochemical performance based on the redox reaction of Ni2+/Ni4+ was observed. Here, we tried to replace Te for W in Li4NiTeO6. Tungsten is often used as a dopant for positive electrode materials to improve rate performance of Li ion batteries etc. but not popular as a main element building framework because of its heaviness, cost and electrochemical inactivity. In order to understand the influence on the structure and electrochemical properties, we synthesized mainly tungsten-containing materials, Li4MeWO6 (Me=Ni, Mn, Co) expecting hexavalent W6+ ions to stabilize the crystal structure with divalent ions and to improve the diffusion of Li ions during charge and discharge.

Li4MeWO6 was obtained by a conventional solid state reaction with heating and grinding several times. Me used was Ni, Mn, and Co to prepare Li4NiWO6, Li4MnWO6 and Li4Ni0.6Mn0.2Co0.2O6, respectively. XRD pattern of the Li4MeWO6 samples showed a single phase and clear diffraction peaks attributed to honeycomb ordering of Li, Me and W ions in the slab. The electrochemical properties for the Li4MeWO6 materials with different Me composition, were examined using coin-type lithium cells with electrolyte solution of 1M LiPF6/ EC:DMC (1:1).

Figure 1 shows charge/discharge curves of Li4NiWO6, measured with different voltage window at a constant current of 13 mA g-1. In the voltage range of 4.1 - 3.0 V, initial discharge capacity of 83 mAh g-1, corresponding to 1.1 Li extraction from Li4NiWO6 is delivered. Reversible discharge curve and good cycle stability with low polarization are observed in the voltage range, probably on the basis of Ni redox reaction. On the other hand, charging up to 4.9 V results in more than 250 mAh g-1 of charge capacity equal to 3.4 Li extraction suggesting more than 2 electron reaction of Ni2/4+couple. In addition, the polarization is getting increased by increasing upper cut-off charge voltage.

The detailed structural change during charge/discharge and the correlation between Me composition and the electrochemical performance of Li4MeWO6as positive electrode materials in Li cells will be presented.


[1] M. Sathiya, J. M. Tarascon et al., Chem. Commun, 49, 11376 (2013).