Versatile Roles of Modifiers in Crystal Growth and Morphology Modification of Lithium Hydroxide Monohydrate

Lithium hydroxide monohydrate (LHM) is an important lithium salt, which was widely used as the lithium source of cathode materials of the lithium battery. With the increasing global demand for lithium batteries, the market for LHM has expanded remarkably in recent years. However, LHM crystals are mostly flakes or needles with rough surfaces, strong hygroscopicity, and easy agglomeration, which is not conducive to storage and causes great product loss. Herein, we investigated the effect of various types of modifiers on the crystal growth modification and morphology modulation of LHM using a combination of crystallization experiments and density functional theory (DFT) calculations. Bulk LHM crystals were from a supersaturated solution of LHM, and the crystal morphology was indexed by single-crystal X-ray diffraction. Four types of potent modifiers were selected (including anionic surfactants, oxygen-rich polymers, hydroxyl-rich polymers, and carboxyl-rich polymers). The impact of various modifiers on the growth rate perpendicular to the (011) and (01̅1) surfaces was examined and evaluated through single-crystal growth experiments. TW20 and poly(ethylene glycol) (PEG) are potent inhibitors, and SDS and SLS serve as growth promoters. The action mechanisms of modifiers were revealed by binding specificity and DFT calculations through analyses of the surface electrostatic potential and adsorption energy. It was found that the electronegativity of the crystal surface plays an important role in determining the promotion or inhibition effect of selected modifiers. Our finding highlights the importance of electrostatic interactions in the screening of modifiers for inorganic salt crystals.