Microstructural Investigations on Selectively Laser Treated Li6.6La3Zr1.6Ta0.4O12 Solid Electrolyte for Solid-State Batteries

Energy conversion and storage applications are the key technologies for e-mobility. Besides the development of suitable materials, alternative approaches for microstructural design [1] and suitable manufacturing technologies [2,3] are of great importance in order to meet the requirements regarding performance as well as safety and durability. In this context, additive manufacturing (AM) techniques have gained significant attention for fabricating complex components with specified microstructures and almost unlimited freedom of design [4]. In the field of energy storage, the future potential is currently attributed to solid-state batteries as they are safer and more stable high-energy storage systems [5]. However, the manufacturing of solid-state batteries still remains a major challenge. Therefore, in this study, we investigated the laser-powder interaction using the selective laser sintering AM methods to optimize the sintering process of solid separators for solid-state batteries. Li6.6La3Zr1.6Ta0.4O12 (LLZTO) was synthesized as an electrolyte powder by solid-state reaction then a single layer of LLZTO powder on Al2O3 substrates as well as pressed pellets of the electrolyte powder were treated with different lasers in near-infrared (NIR) and middle infrared (MIR) spectrum range by varying the process parameters such as laser power, scan speed, and track overlap. For comparison, a solid separator was also produced by the conventional sintering method. Phase analyses were carried on by using Seifert Sun X-ray diffractometer (XRD) 3003 by using Cu-Kα radiation (15 – 80° 2θ, the scan rate of 0,026°/min.). Electron microscopy investigations were performed in a Zeiss Sigma 300VP, equipped with EDAX energy dispersive X-ray (EDX) spectroscopy (without polishing, thermal or chemical etching). Additionally, absorption measurements were performed in the IR to UV range for LLZTO and NMC. NIR laser radiation shows insufficient absorption into the LLZTO (Fig. 1). However, the MIR laser technology is promising for sintering LLZTO (Fig. 2d), which is confirmed by large spectral-range FTIR measurements. Moreover, no reaction product between LLZTO and the Al2O3 substrate was observed in the XRD pattern of the laser-treated samples (Fig. 2a) [6]. SEM SE image of (a) a LLZTO pellet with NIR laser-treated regions. (b) Enlarged image of a NIR laser treated region marked with green rectangular in “a”. (a) XRD pattern on the LLZTO powder, pristine substrate and MIR laser treated region. (b) SEM BSE image of a MIR laser treated region. (Bright regions: the laser treated lines, dark regions: substrate and loosen powder) (c) Enlarged image of the MIR laser treated region marked in “b” (d) MIR laser sintered LLZTO region.