Study of the Crystal Structure and Thermochemical Properties of Lithium Carbonate

Lithium carbonate is of enormous interest to researchers because of its widespread use as a reagent and its formation as a component of the solid electrolyte during the operation of lithium batteries. This article presents an X-ray diffraction study of the crystal structure of chemically pure monoclinic lithium carbonate. The X-ray diffraction pattern of lithium carbonate was recorded using synchrotron radiation with a wavelength of 0.688199 Å in Debye–Scherrer geometry over a 2θ angular range from 2° to 70° and analyzed by full-profile Rietveld refinement, including refinement of the unit-cell parameters and ion positions. After refinement of the crystal structure, the ion positions in the unit cell were relaxed within the density functional theory framework using the Broyden–Fletcher–Goldfarb–Shanno algorithm implemented in Quantum ESPRESSO, where the atoms were modeled using pseudopotentials. The refined and optimized crystal structures were formally compared by determining the maximum difference between equivalent positions of identical ions, the arithmetic mean of the differences between the coordinates of equivalent positions, and the similarity measure. The thermochemical properties were studied experimentally over the temperature range from 25 to 900°C in a flowing air–argon mixture using a simultaneous thermal analyzer in thermogravimetric analysis–differential scanning calorimetry mode. The resulting data were used to determine the melting point of lithium carbonate and to discuss its mass loss, decomposition mechanism, and possible interaction with the crucible material over the specified temperature range.