Optical floating-zone growth of single crystals of Li-ion battery material LiCoO2

Abstract

Large, high quality single crystals of Li-ion battery cathode material LiCoO2 have been grown using the optical floating zone technique employing a four-mirror furnace. Several growth experiments reveal that the calcination temperature, quantity of excess Li in the starting feed rod, the atmosphere in the growth chamber, and the growth speed are crucial parameters that govern the stability of the molten zone and in turn the phase purity, stoichiometry and crystallinity of the grown crystal. It is observed that high-quality, phase pure single crystals can only be grown in an Ar-atmosphere of 9 bar and using slow growth speeds of 1–2 mm/h, using feed rods containing 15% excess Li content. The structural refinement of the powder x-ray diffraction data along with the Laue diffraction patterns confirms a rhombohedral crystal structure (space group R3¯m) and the presence of a single grain along the length (~2.5 cm) of the grown crystal. Atomic emission spectrometry (ICP-AES) ascertained the uniformity in stoichiometry along the length of the grown crystals. The x-ray rocking curve of the crystal has a resolution limited full-width at half-maximum (FWHM) of 0.22°, confirming the high single crystalline quality of the sample.