Fabrication and Characteristics of All-Solid-State Li-S Batteries for Spacecraft Power Source

The main power for spacecraft such as artificial satellites and space probes is supplied by solar cells. However, when solar cells cannot secure power in the shade, power is generally supplied by lithium-ion batteries, which are small, lightweight, and have high charge/discharge efficiency. Currently, in order to reduce the cost of launching artificial satellites and to increase the loading ratio of various mission equipment, further weight reduction of battery packs and solar cells, which account for a large weight, is required. To reduce the weight of battery packs, it is expected that next-generation batteries with high weight energy density, which can reduce the weight more than existing lithium-ion batteries, will be installed. As next-generation battery systems with high weight energy density, Li metal batteries using Li metal for the negative electrode and lithium-sulfur batteries using sulfur or sulfide-based positive electrode active materials for the positive electrode are considered promising. In addition, all-solid-state batteries that use solid electrolytes have a high possibility of increasing energy density by applying high-potential and high-capacity active materials, which have not been put to practical use in existing lithium-ion batteries. Furthermore, since they have a wider operating temperature range than existing lithium-ion batteries, they can be easily operated even in harsh temperature environments such as outer space, so they are considered as a very promising battery system. We have focused on argyrodite-type sulfide (Li 6 PS 5 Cl), which has high ionic conductivity, and have been developing an argyrodite-type sulfide-based positive electrode active material that imparts electronic conductivity and becomes an active material by combining an argyrodite-type sulfide-based solid electrolyte, an argyrodite-type sulfide, and a carbon-based conductive material. Specifically, we have worked on improving the chemical stability of the argyrodite-type sulfide and reducing its elastic modulus to ensure the interface with the positive and negative electrode active materials, and on elucidating the charge/discharge mechanism and controlling the composition to further increase the capacity of the argyrodite-type sulfide-based positive electrode active material. We have combined these materials to fabricate dry-pressed all-solid-state batteries, and have been able to demonstrate good battery performances, with calculations showing a high energy density of over 400Wh/kg in the battery element shape. In this presentation, we will investigate the fabrication of practical pouch-type all-solid-state batteries using these materials. First, we will create a coated electrode film and compare the battery performance with that of a dry-mixed cathode composite. We will report on issues related to current collectors and binders. Next, we will discuss the progress of the pouch-type battery composed of developed materials. Here, we will mention the effects of components and pressing conditions on battery characteristics, as well as the challenges faced when aiming for installation on spacecraft.