Using In Situ Analysis to Design Ex Situ Solid State Syntheses of Spinel Nanowire Targets for Battery Cathodes (RPA Pilot / Seed Project)

Solid state synthesis provides a simple route to build complex functional materials with a multitude of phases, yet the dynamics of the solid-state mechanism, as bonds break and form, particles change shape and sinter, and transient phases fleetingly emerge and are consumed, are often shrouded by a figurative synthetic “black box” within which knowledge of the key mechanistic factors are lost. Solid-state reactions form the basis for most new material discovery, especially bulk powder phases. For new inorganic nanomaterials, however, they have been underexploited, largely due to difficulties in understanding and controlling mechanistic details over the multiple length scales necessary to create homogeneity within a particle, yet particles themselves which have finite size and anisotropic morphologies. The use of solid-state “shake and bake” approaches for the creation of ternary nanomaterials (containing three or more elements) holds great appeal, however. The ideal starting materials for solid state reactions are those with known stoichiometry, phase purity, and high reactivity – precisely the characteristics of high-quality nanoparticles. Equally, unlike the more commonly utilized approaches for nanoparticle growth such as solvothermal syntheses and vapor-liquid-solid growth, composition in the solid-state may be controlled without loss of elements to liquid or vapor phases or to a discarded solvent fraction. Further, anisotropic morphologies such as nanowires may be trapped kinetically in the solid-state by utilizing anisotropic starting materials. Here we propose using in situ TEM to open the figurative black box, and determine the mechanistic details in the solid-state syntheses of LiMn2O4 and MgMn2O4 nanowires for battery cathodes.