Growth of Individual, Highly Oriented LiFePO4 Crystals on a SUS Substrate Using NaCl–KCl Flux Coating

Olivine-type LiFePO4 has been an interesting material in the development of catalysts and lithium-ion rechargeable batteries. In this study, we propose a new method for growing thin films of LiFePO4 crystals directly on SUS substrates using flux coating. Molten NaCl–KCl flux promoted the formation of individual LiFePO4 crystals with well-defined facets surrounded by {100}, {110}, and {201} faces and highly oriented along the [100] direction. The LiFePO4 crystals attached tightly to the SUS substrate, implying that crystal growth began directly at the SUS surface via heterogeneous nucleation, driven by supersaturation in the NaCl–KCl flux. We further demonstrated the formation of LiFePO4 crystal films using an infrared light–heating furnace system, which reduced the fabrication time from several hours to less than 30 min. Rapid heating and cooling effectively suppressed the corrosion of the SUS substrate caused by the NaCl–KCl flux.