Preparation of thin solid electrolyte by hot-pressing and diamond wire slicing

The thickness of a solid electrolyte influences the performance of all-solid-state batteries due to increased impedance with a thick electrolyte. Thin solid electrolytes are favourable to improve the performance of all-solid-state batteries due to the short Li ion diffusion path and small volume of the solid electrolytes. Therefore, the preparation of thin solid electrolyte is one of the key process techniques for development of all-solid-state batteries. In this study, thin Li_1.5Ge_1.5Al_0.5(PO₄)₃ solid electrolyte with a Na super ion conductor structure is prepared by diamond wire slicing. The Li_1.5Ge_1.5Al_0.5(PO₄)₃ solid electrolyte is prepared by melt-quenching followed by crystallization at 800 °C for 8 h, after which the crystallized Li_1.5Ge_1.5Al_0.5(PO₄)₃ rod is subjected to wire slicing. Thin Li_1.5Ge_1.5Al_0.5(PO₄)₃ with a thickness of 200 μm is obtained. The crystal structure and cross-sectional morphology are not affected by the slicing. The total Li conductivity of the thin Li_1.5Ge_1.5Al_0.5(PO₄)₃ and activation energy are 3.3 × 10^-4 S cm^-1 and 0.32 eV, respectively. The thickness and total conductivity are comparable to those of Li_1.5Ge_1.5Al_0.5(PO₄)₃ prepared by the tape-casting method which needs several steps to prepare Li_1.5Ge_1.5Al_0.5(PO₄)₃ tape-sheet and high temperature and a long sintering process. The ionic transference number of the thin Li_1.5Ge_1.5Al_0.5(PO₄)₃ is 0.999. The diamond wire slicing is a useful method to prepare thin solid electrolytes.