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 LiMn₂O ₄ from cubic to tetragonal. Such an interface in the LiMn ₂O₄/Au/Al₂O₃ system facilitates high-quality epitaxial film growth to thicknesses of a couple hundred nanometers.