Stereolithographic Additive Manufacturing of Solid Electrolyte Ceramic Sheets with Micro Emboss Pattern for All Solid Battery Application

Abstract

Additive manufacturing (AM) and 3 dimensional printing (3DP) technologies have been developed to create metal or ceramic components with complicated structures rapidly and exactly by computer aided design, manufacture and evaluation (CAD/CAM/CAE). In a stereolithographic AM technique, photo sensitive acrylic resin with nanoparticles of ceramics or metals spreading equally is used. The resins are spread on a glass substrate at certain thickness, and ultraviolet laser beams are scanned to form and laminate cross sectional layers through photo chemical reactions. Micro functional structures could be created through conventional dewaxing and sintering processes. The stereolithography had been customized to process ceramic components with functional structures of geometric patterns, for example, electromagnetic devices, biological implants and energy storage modules, which are centimeter order components including micrometer sized structures.In this investigation, micro emboss patterns composed of solid electrolyte Li7La3Zr2O12 (LLZ) for longer service life, higher efficiency and improved safety of all solid battery. In generic battery, fluid material is used as an electrolyte, and it is an obstacle to improve performance of the battery. Then, all solid battery is an innovative form of battery.The solid electrolyte LLZ particles of 1 μm in average diameter were dispersed into a photo sensitive acrylic resin at 25 volume %. The schematic illustrated stereolithography process was shown in Fig. 1. The obtained paste was spread with 10 μm layer thickness on a glass substrate by using a mechanical knife edge. A laser beam of 355 nm in wavelength was scanned to laminate cross sectional layers at 1200 mm/s in drawing speed. The laser power was changed from 8 to200 mW, and the beam diameter was changed from 10 to 50 μm.The micro emboss pattern of 10×10×0.2 mm in outer dimensions with angle holes of 240×240×100 μm in sizes on the upper surface was designed as shown in Fig. 2. Through the stereolithographic AM, solid cross sections of 10 μm in thickness were formed and laminated for 20 layers. The lower part of 20 layers was a simple plate, and the upper part had an emboss pattern. The laser lithographic conditions of scanning speed, irradiation power, spot size, raster pattern and offset are shown in Tab. 1. The meanings of these parameters were schematically illustrated in Fig. 3 and Fig. 4. The fabricated emboss patterns were observed by using a digital optical microscope to measure the part accuracy.In the lithography process, the laser beam should be scattered by the dispersed particles, the photo sensitive resin were over cured comparing with the laser beam diameter. To increase the dimensional accuracies in the cross sectional micro patterns, the scanning lines of the laser beam were adjusted about 10–15 μm in offset values according to the drawing conditions as shown in Table 1 and Fig. 3-(b). The scan pattern X/Y means a single laser scanning for X and Y-directions on odd and even numbered layers, respectively as shown in Fig. 4. The acryl micro emboss structures with LLZ particles dispersion are shown in Fig. 5 (a), (b) and (c) using lithographic conditions of A, B and C in Table 1, respectively.As shown in Fig. 5-(a), the anisotropic angle holes of 150×200 μm in edge lengths were obtained through the highest laser power drawing. Comparing with this, in the case of Fig. 5-(b), the isotropic angle holes of 260 μm in edge length were opened in the composite plate with the larger size toward the graphically designed model as shown in Fig. 2. Through the optimization of lithographic conditions, the laser power and edge offset were decided, and the micro emboss pattern with higher part accuracy could be obtained as shown in Fig. 5-(c). The size tolerance was less than 10 μm. Each layer could be joined strongly without cracking. Figure 6-(a) and (b) are the composite precursor and full ceramic component through the conventional dewaxing and sintering, respectively. The solid electrolyte particles of lithium-lanthanam-titanate (LLT: Li0.33La0.55TiO3) were dispersed into acrylic resin at 38 volume %. The micro emboss pattern could be obtained according to the design model.By using stereolithographic additive manufacturing, micro acryl components with solid electrolyte particles of Li7La3Zr2O12 (LLZ) could be fabricated. Micro emboss structures composed of fine angle holes were created to be applied for all solid battery through computer aided design, manufacture and evaluation. Part accuracies were improved successfully by optimization of laser lithographic conditions. Composite precursors could be dewaxed and sintered into full ceramic components.