All-solid-state half-cell of Li/a-Si film using guest Li+ conductor 15NaI∙LiBH4 as a solid electrolyte

In the present study, an all-solid-state half-cell Li/ amorphous Si (a-Si) was fabricated using the guest Li+ ion conductor (15NaI∙LiBH4) as a solid electrolyte. Continuous lithiation/delithiation of the a-Si film was confirmed. At room temperature, the charge-discharge cycles were stable over 80 cycles with the high Coulombic efficiency of 99%. On the other hand, the poor rate performances are the problem; the capacities remained at approximately 1300 mAh/g at 12.7 μA/cm2. Heating the cell at 60 °C resulted in the improvement of the rate performance, which can be due to the improvement of the Li+ conductivity of 15NaI∙LiBH4. In order to understand the correlation between the microstructure and Li+ conductivity of 15NaI∙LiBH4, the as-milled sample was post-annealed and the variation in the microstructure was observed by transmission electron microscopy (TEM). It was indicated that the lattice defects, such as dislocation and lattice distortion, have a significant contribution for the Li+ ion conductivity of the 15NaI∙LiBH4.