Departmental Bulletin Paper リチウム二次電池正極材料 Li 5 SiN 3 の結晶作成と物性評価

竹内, 優作

The structure of Li 5 SiN 3 is closely related to the antifluorite type Li3AlN2. The structure of Li 3 AlN 2 is essentially attributed to the six ionic Li-N bonds in the sublattice. In Li 3 AlN 2, Li and Al cations occupy 3/4 and 1/4 of tetrahedral holes of the N sublattice. In Li5SiN3, 1/3 of the equivalent tetrahedral Al positions (16c) in Li 3 AlN 2 are substituted by Li and Si atoms, therefore occupy the remaining 2/3 of these positions. Li5SiN3 crystals are synthesized by direct reaction between Li3N and Si3N4 with the molar ratio Li3N:Si3N4 of 10:1. Reaction is performed at 1073 K for 1h under a nitrogen atmosphere of 700 Torr. The lattice constant is 4.718Å determined by the X-ray powder diffraction method. The band gap of Li5SiN3 was found to be direct gap of about 2.5 eV by optical absorption and photoacoustic spectroscopy methods. The 5×5mm2 sized lithium secondary battery of Li 5 SiN3 cathode / propylene carbonate + LiClO 4 electrolyte / Li anode structure shows a discharge capacity of 2.4μAh/cm2 for a discharge current of 1.0μA. Key Words : Li 5 SiN 3 , electro properties ,lithium secondary battery

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