Trace Moisture Drives Lithium Volatility during Cathode Synthesis

Abstract

Synthesis of cathodes for lithium ion batteries is typically conducted via a reaction between a mixed metal hydroxide precipitate and a lithium source at elevated temperatures. While anecdotal evidence suggests that some portion of lithium may vaporize during thermal treatment, a thermodynamic analysis of lithium volatility has not been previously published. The formation of lithium vapor would be beneficial for overcoming mass transport limitations in otherwise solid–solid reactions but may also result in lithium loss and alteration of the intended stoichiometry of the final product. To rigorously quantify the extent to which lithium vaporization is thermodynamically feasible and the nature of the lithium species involved, high-level quantum chemical calculations have been performed on gaseous molecular lithium oxides and hydroxides and their extents of formation assessed from Gibbs Free Energy considerations. Results show that while the volatility of lithium oxide is negligible under dry conditions, ppm concentrations of water vapor are sufficient to dramatically enhance lithium vaporization via gaseous LiOH intermediates. Controlling the moisture level during synthesis is therefore of paramount importance in the production of high-quality lithium ion cathode materials.