Fabrication of thin Li6PS5Cl separators for all-solid-state lithium-ion batteries

Thin Argyrodite Separators for All-Solid-State Lithium-Ion-Batteries

Thin sulfide separators (&lt“;“30µm) for all-solid-state lithium-ion batteries are crucial to obtain low internal battery-cell resistances, i.e. good battery-cell performances, and high energy densities. A two-dimensional sulfide separator sheet consists commonly of sulfide powder and a polymeric binder. The components are dispersed in a solvent and casted to a given sacrificial substrate.

Current challenges for thin separator fabrication include either (1) high costs for commercial sulfide material with very fine particle sizes (&lt“;“5 µm) or (2) very large particle size distributions (&lt“;“1 to 100 µm) for “lower-cost” commercial sulfide powders. Since the separator thickness is limited to the diameters of the largest particles, sulfide particles are preferred to be smaller than ~5 µm at an affordable price.

In this work, we have produced thin two-dimensional sulfide separator sheets with thicknesses of 20 µm from commercial “lower-cost” Li₆PS₅Cl material. The powder was wet-ball-milled and dried before it was subjected to paste fabrication and separator casting. Using x-ray diffraction and electrochemical impedance spectroscopy, it was proven that crystal structure and Li-ion conductivities of Li₆PS₅Cl were unhampered from the mechanical treatment. Secondary electron images of the separator cross-sections revealed ultra-fine particles and the strikingly low separator thickness of 20 µm.

The thin separators were transferred to NMC cathodes using uniaxial compression. The cathode/separator units were assembled into pouch bags, using indium foils as anodes. The cells showed stable voltages, indicating absence of short circuiting despite thin separator sheets. Currently, the cells are electrochemically investigated.

This work is part of the FestBatt Cluster in the Thiophosphate platform.