Atomistic insights into role of urea additive in lithium nanoparticles formation

• Fine-sized lithium agglomerates with uniform structure by urea additive. • Changed reaction paths of lithium precursor with urea additive. • Intensified microexplosion due to increased gas release and weakened lithium bonds. • Role of urea progressively diminishes as further elevated ambient temperature. Recently, urea additive has been demonstrated to benefit the formation of cathode nanomaterials through spray flame synthesis with improved homogeneity in lithium atoms distribution. Nevertheless, its intrinsic mechanism has not been well understood. In this study, reactive molecular dynamic simulations are performed to gain atomistic insights into the pyrolysis and oxidation mechanisms of a lithium precursor droplet with or without urea additive. A series of comparisons involving the reaction kinetics and pathways of lithium clusters, along with the gas release, energy profiles and morphological characteristics of droplets, is conducted to elucidate the role of urea additive at 1500 K and 0.1 MPa. Urea additive is observed to exert a homogenising impact on the distribution of lithium atoms within the synthesized nanoparticles, as evidenced by the decreased number of large-sized lithium agglomerates and less concentrated lithium element. This can be ascribed to changed reaction pathways of lithium clusters due to urea additive, where the lithium clusters are prone to decompose into fine nanoparticles through initial bonding with urea atoms, followed by bond-breaking to generate gases. The increased amount of gas released from the decomposition of precursor with urea additive leads to a more violent droplet microexplosion, which in turn results in droplet breakup and thus fine droplets. As the ambient temperature is elevated, the presence of urea additive facilitates the formation of fine-sized nanoparticles with enhanced homogeneity of lithium atoms.