Laser-Micro-Annealing of Microcrystalline Ni-Rich NCM Oxide: Towards Micro-Cathodes Integrated on Polyethylene Terephthalate Flexible Substrates

Here in this work, we report on micro-Raman spectroscopy investigations performed on freestanding Ni-rich NCM (Li_xNi_0.83Co_0.11Mn_0.06O₂) microcrystals transferred to flexible polyethylene terephthalate (PET) host substrates. This technological procedure introduces a first building block for future on-chip-integrated micro-accumulators for applications in flexible optoelectronics, sensors, microbiology, and human medicine. An after-synthesis thermal treatment was used to help improve the material homogeneity and perfection of the cathode material. To this end, a local laser micro-annealing process was applied to the freestanding Ni-rich NCM microcrystals. The thermally initialized structural processes in the singular micro-cathode units were characterized and determined by micro-Raman spectroscopy. Micro-Raman mapping images revealed the evolution of a recrystallization process after the local annealing procedure. Furthermore, laser micro-annealing led to the suppression of the pristine "polycrystalline morphology" of the investigated micro-cathode regions. Besides the dominant characteristic Raman mode at ~1085 cm^-1, most likely ascribed to lithium carbonate, metal oxides with Raman modes around ~550 cm^-1 were identified. This highly efficient transfer and integration technology represents a basic building block towards micrometer-sized accumulators for a large range of emerging applications.