Structure and electron density analysis of electrochemically and chemically delithiated LiCoO2 single crystals |
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Authors: | Yasuhiko Takahashi Kaoru Dokko Matsuhiko Nishizawa Junji Akimoto |
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Institution: | a National Institute of Advanced Industrial Science and Technology (AIST), 1-1-1 Higashi, Tsukuba 305-8565, Japan b Graduate School of Engineering, Tohoku University, Aramaki-Aoba, Aoba-ku, Sendai 980-8579, Japan |
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Abstract: | Single crystals of Li0.68CoO2, Li0.48CoO2, and Li0.35CoO2 were successfully synthesized for the first time by means of electrochemical and chemical delithiation processes using LiCoO2 single crystals as a parent compound. A single-crystal X-ray diffraction study confirmed the trigonal R3¯m space group and the hexagonal lattice parameters a=2.8107(5) Å, c=14.2235(6) Å, and c/a=5.060 for Li0.68CoO2; a=2.8090(15) Å, c=14.3890(17) Å, and c/a=5.122 for Li0.48CoO2; and a=2.8070(12) Å, c=14.4359(14) Å, and c/a=5.143 for Li0.35CoO2. The crystal structures were refined to the conventional values R=1.99% and wR=1.88% for Li0.68CoO2; R=2.40% and wR=2.58% for Li0.48CoO2; and R=2.63% and wR=2.56% for Li0.35CoO2. The oxygen-oxygen contact distance in the CoO6 octahedron was determined to be shortened by the delithiation from 2.6180(9) Å in LiCoO2 to 2.5385(15) Å in Li0.35CoO2. The electron density distributions of these LixCoO2 crystals were analyzed by the maximum entropy method (MEM) using the present single-crystal X-ray diffraction data at 300 K. From the results of the single-crystal MEM, strong covalent bonding was clearly visible between the Co and O atoms, while no bonding was found around the Li atoms in these compounds. The gradual decrease in the electron density at the Li site upon delithiation could be precisely analyzed. |
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Keywords: | Crystal structure LiCoO2 LixCoO2 Single-crystal X-ray diffraction Electron density analysis MEM |
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