Methods for scalable production of solid-state batteries based on sulfide solid electrolytes

Summary:

The increasing demand of electrically powered vehicles requires new battery technologies with higher safety and better performance than common lithium ion batteries (LIB) can provide. Solid-state batteries (SSBs) with a solid electrolyte (SE) of high ionic conductivity instead of organic liquid electrolytes are the most promising candidates to reach both requirements at the same time. In particular, lithium thiophosphates with lithium ion conductivities up to 10^-2 S/cm [1] have gained increasing attention in literature. However, most publications on these sulfide based SSBs are related to pelletized powder cells [2,3], which is difficult to extend for large-scale production. Therefore, we established the whole process chain for a scalable production of sulfide SSBs under inert glovebox atmosphere. All processes are scalable and closely related to conventional LIB manufacturing steps, beginning from the synthesis of the sulfide solid electrolyte to the cell assembly and testing.
The SE can be synthesized by a mechano-chemical ball-milling process of the precursors in sealed containers. Subsequent milling may be used to decrease/adjust its particle size distribution to a certain extend which is necessary for a better intermixing and interconnection of the particles. For the production of SSB cathodes composed of cathode active material, sulfide SE, conductive additive and a polymeric binder, the dry components can by pre-mixed as powders and evenly distributed in a solvent by different dispersion techniques to get coatable slurries, e.g. by a dissolver or extrusion process in an argon glovebox. These slurries are coated by a doctor blade on aluminium foils as substrate and dried subsequently on the heatable film applicator. The same dispersion and coating methods can be used to produce separator sheets, e.g. by layer-on-layer coating directly on the composite cathode. These sheets are stable enough to be die-cut for further electrochemical or other analyses. A custom-built sealable sample holder is used to compact the electrode and separator sheets in a laboratory press and to perform electrochemical impedance spectroscopy or full cell cycling. Certain pressures up to 200 MPa can be applied on the cell by a metallic framework which is still necessary for low contact resistances of all SSB components.

[1] N. Kamaya et al., Nature Materials 10, 682-686 (2011).
[2] W. Zhang et al., ACS Appl. Mater. Interfaces 9, 35888-35896 (2017).
[3] Y. J. Nam et al., Journal of Power Sources 375, 93-101 (2018).