Structure and electron density analysis of electrochemically and chemically delithiated LiCoO(2) single crystals

Single crystals of Li(0.68)CoO(2), Li(0.48)CoO(2) and Li(0.35)CoO(2) were successfully synthesized for the first time by means of electrochemical and chemical delithiation processes using LiCoO(2) single crystals as a parent compound. A single-crystal X-ray diffraction study confirmed the trigonal R (3) over barm space group and the hexagonal lattice parameters a = 2.8107(5) angstrom, c = 14.2235(6) angstrom, and c/a = 5.060 for Li(0.68)CoO(2); a = 2.8090(15) angstrom, c = 14.3890(17) angstrom, and c/a = 5.122 for Li(0.49)CoO(2); and a = 2.8070(12) angstrom, c = 14.4359(14) angstrom, and c/a 5.143 for Li(0.35)CoO(2). The crystal structures were refined to the conventional values R = 1.99% and wR = 1.88% for Li(0.68)CoO(2); R = 2.40% and wR = 2.58% for Li(0.48)CoO(2); and R = 2.63% and wR = 2.56% for Li(0.35)CoO(2). The oxygen-oxygen contact distance in the CoO(6) octahedron was determined to be shortened by the delithiation from 2.6180(9) angstrom in LiCoO(2) to 2.5385(15) angstrom in Li(0.35)CoO(2)). The electron density distributions of these Li(x)CoO(2) 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. (c) 2006 Elsevier Inc. All rights reserved.