Epitaxial Growth of LiMn2O4 Thin Films by Chemical Solution Deposition for Multilayer Lithium-Ion Batteries

Cathodic LiMn2O4 films on various single-crystal substrates for use in thin-film Li-ion batteries prepared using a chemical solution deposition method are reported. Transmission electron microscopy is utilized to characterize the microstructures of the films. The results show that the film/substrate lattice misfit can affect significantly the quality of epitaxially grown grains of LiMn2O4. Using state-of-the-art high-angle annular dark-field imaging, the degree of coherency and lattice distortion at interfaces between LiMn2O4 and Au-coated and uncoated Al2O3 (0001) single-crystal substrates are examined at the atomic scale. When the lattice misfit is sufficiently small, fully coherent LiMn2O4/Au heterointerfaces form, although lattice strain to a distance of up to around 10 nm from the interface changes the symmetry of spinel LiMn2O4 from cubic to tetragonal. Such an interface in the LiMn2O4/Au/Al2O3 system facilitates high-quality epitaxial film growth to thicknesses of a couple hundred nanometers.