Recently, many studies have been conducted on the materialization of spent batteries. In conventional cases, lithium is recovered from an acidic solution through the leaching and separation of valuable metals; however, it is difficult to remove impurities because lithium is recovered in the last step. Cathode active materials of lithium-ion batteries comprise oxides with lithium, such as LiNi_xCo_yMn_zO₂ and LiCoO₂. Thus, lithium should be converted into a compound that can be leached in deionized water for selective lithium leaching. Recent studies on the leaching and recovery of Li₂CO₃ through a carbon reduction reaction show low economic efficiency, due to the solubility of Li₂CO₃ at room temperature being as low as 13 g/L. This paper proposes a method of roasting after nitric acid deposition for selective lithium leaching and recovery to LiNO₃. Based on experiments involving the varying of the amount of nitric acid, roasting temperature, and solid–liquid ratio, optimal values were found to be dipping in 10 M HNO₃ 2 mL/g, roasting at 275 °C, and deionized water with a solid–liquid ratio of 10 mL/g, respectively. Over 80% Li leaching was possible under these conditions. IC analysis confirmed that the purity was 97% lithium nitrate.

In this study, a fabrication method of tapered microstructures with high aspect ratio was proposed by deep X-ray lithography. Tapered microstructures with several hundred micrometers and high aspect ratio are demanded owing to the high applicability in the fields of various microelectromechanical systems (MEMS) such as optical components and microfluidic channels. However, as the pattern and gap size were downsized to smaller micro-scale with higher aspect ratio over 5, microstructures were easily deformed or clustered together due to capillary force during the drying process. Here, we describe a novel manufacturing process of tapered microstructures with high aspect ratio. To selectively block the deep X-ray irradiation, an X-ray mask was prepared via conventional ultraviolet (UV) lithography. A double X-ray exposure process with and without X-ray mask was applied to impose a two-step dose distribution on a photoresist. For the clear removal of the exposed region, the product was developed in the downward direction, which encourages a gravity-induced pulling force as well as a convective transport of the developer. After a drying process with the surface additive, tapered microstructures were successfully fabricated with a pattern size of 130 μm, gap size of 40 μm, and aspect ratio over 7.

The use of lithium-ion batteries (LIBs) has increased in recent years. Thus, efficient recycling is important. In this study, the Taguchi method was used to find the optimal selective lithium leaching parameters for spent LIB recycling. Orthogonal array, signal-to-noise ratio, and analysis of variance were employed to investigate the optimization of selective lithium leaching. The experimental parameters were heat treatment and leaching conditions. The lithium leaching ratio was analyzed by inductively coupled plasma (ICP). The reaction temperature was analyzed by thermogravimetry differential scanning calorimetry (TG-DSC) using lithium cobalt oxide (LCO) and carbon powder, and X-ray diffraction (XRD) was performed after heat treatment at different temperatures. From the XRD analysis, a Li₂CO₃ peak was observed at 700 °C. After heat treatment at 850 °C, a peak of Li₂O was confirmed as Li₂CO₃ decomposed into Li₂O and CO₂ over 723 °C. The Li₂O reacts with Co₃O₄ at a high temperature to form LCO. The phase of lithium in the LIB changes according to the conditional heat treatment, affecting the lithium leaching rates. As heat treatment conditions, N₂ atmosphere combined with 700 °C heat treatment is suitable, and the solid–liquid ratio is important as a leaching factor for selective lithium leaching.

This study investigated the recovery behavior of valuable metals (Co, Ni, Cu and Mn) in spent lithium ion-batteries based on Al2O3-SiO2-CaO-Fe2O3 slag system via DC submerged arc smelting process. The valuable metals were recovered by 93.9% at the 1250℃ for 30 min on the 20Al2O3-40SiO2-20CaO-20Fe2O3 (mass%) slag system. From the analysis of the slag by Fourier-transform infrared spectroscopy, it was considered that Fe2O3 and Al2O3 acted as basic oxides to depolymerize SiO4 and AlO4 under the addition of critical 20 mass% Fe2O3 in 20Al2O3-40SiO2-CaO-Fe2O3 (CaO + Fe2O3 = 40 mass%). In addition, it was observed that the addition of Fe2O3 ranging between 20 and 30 mass% lowers the melting point of the slag system.

In this research, a Ni-Fe mold insert for the efficient replication of high aspect-ratio microstructure arrays was fabricated via hard X-ray lithography and an electroforming process. For the X-ray exposure on a photoresist, a gold-based X-ray mask was prepared with conventional UV photolithography. The gold thickness was designed to be over 15 μm to prevent development underneath the absorber and to enhance the adhesion strength between the photoresist and substrate. By using the X-ray mask, a positive-type photoresist was selectively exposed to X-ray under an exposure energy of 4 kJ/cm³. Thereafter, the exposed region was developed in a downward direction to effectively remove the residual photoresist from the substrate. During the evaporation process, deionized water mixed with a surface additive prevented the bending and clustering of the photoresist microstructure arrays by lowering the capillary force, resulting in a defect-free mother structure for electroforming. Lastly, the mother structure was uniformly Ni-Fe electroformed on a conductive substrate without the formation of any pores or detachment from the substrate. Based on the proposed microfabrication process, a Ni-Fe mold insert with a 183 μm pattern size, 68 μm gap size, 550 μm height, 2116 microcavities and a hardness of 585 Hv was precisely manufactured. It can be utilized for the mass production of high aspect ratio metal and ceramic microstructure arrays in micro molding technologies.