The LiNi 0.8 Co 0.2 O 2 was synthesized by the coprecipitation method, and then measured using powder neutron diffractions of electrochemically cycled cathodes. Crystal and electronic structure analyses were conducted using the Rietveld and maximum entropy methods (MEM). Based on those results, we tried to reveal the charge and discharge mechanism of this material, and to clarify the influence of the crystal structure on the several charge or discharge depths. We analysed the crystal structures of the electrodes after second discharge process as well as the pristine electrode by the Rietveld analysis which used neutron diffraction and synchrotron X-ray diffraction data. As a result, it was demonstrated that the crystal structure analysis by ex-situ measurement could be successfully performed even for the electrode with a weight of about 10 mg. Furthermore, we examined the average structure of the electrode accompanying with charge depths. The electrodes were prepared about 2.50 V, 3.65 V, 3.85 V, and 4.30 V which corresponded to the plateau portions of a 10th charging curve. In the analysis of the electrode accompanying charge depths, it was suggested that there was almost no participation to cation mixing accompanying charge depth.
A facile and convenient synthesis of trisubstituted (E)-α,β-unsaturated esters was developed by improving our previously established method. The new method circumvented the separation of the intermediates, which have an activating group of the hydroxyl group in β-hydroxy esters, furnishing α,β-unsaturated esters in shorter steps than the previous method: an acetylation of β-hydroxy group and subsequent E1cB reaction proceeded in tandem. In addition, the new method can not only employ a diastereomeric mixture of the substrate for the E1cB reaction, it has a wide substrate scope as well, which would enable the synthesis of various trisubstituted (E)-α,β-unsaturated esters.
INTRODUCTION
Positive electrode material, Li(Ni,Co)O2 system, of Li-ion battery has been attractive because it has the advantage in low environmental load due to low Co content. There are many previous works about the Li(Ni,Co)O2 and the aluminum-substituted one because of high heat stability. However, detail structural changes during electrochemical processes are still ambiguous for site occupancy, local structures, and electronic structures even though these would play important roles on the battery characteristics. In this research, we used several quantum beam techniques to reveal the crystal structures, electronic and nuclear densities, and local structures of LiNi0.8Co0.2O2 during charge process.
EXPERIMENTAL
To synthesize the LiNi0.8Co0.2O2, the precursor was prepared by co-precipitation method. The co-precipitated material was annealed at 800 °C in air for 15 h. The product was identified by powder XRD and ICP-OES. To study change of crystal and electronic structure of this cathode material during electrochemical process, cathode materials were prepared by four charge depths, and were investigated using the synchrotron X-ray diffraction (BL02B2, SPring-8) and neutron diffraction (BL20, J-PARC). The data was analyzed with the Rietveld technique using Rietan-FP and Z-Rietveld, and by the MEM using the Dysnomia and Z-MEM programs. To examine the local structures, X-ray absorption spectroscopy (BL14B2, SPring-8) and X-ray total scattering (BL04B2, SPring-8) were measured.
RESULTS AND DISCUSSION
The neutron diffraction patterns were measured for the cathode after 2nd discharge process as well as the pristine electrode. It was demonstrated that the crystal structure analysis by ex-situ measurement could be successfully performed even for the electrode with an amount of about 10 mg. The values of 3b-6c bond length decreased and λ2, which expresses the distorted degree of the Li-O6 and M-O6 octahedra, were increased with increasing charge depth. Synchrotron-based experiments using high energy X-ray total scattering and pair distribution function (PDF) analysis (Fig. 1) indicated that the oxygens arranged to crystallographic a-b plane were disturbed in the charge state of 4.3 V after 2nd cycle (Fig. 2).
ACKNOWLEDGMENTS
This research was supported by the RISING-project of the New Energy and Industrial Technology Development Organization (NEDO), Japan.
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