Exploring key processing parameters for lithium metal anodes with sulfide solid electrolytes and nickel-rich NMC cathodes in solid-state batteries

The integration of lithium metal anodes (LMAs) into solid-state batteries (SSBs) offers a promising route toward significantly increased energy densities. However, the mechanical and electrochemical instability of the Li|solid electrolyte (SE) interface remains a major challenge for practical long-term cycling stability. This study systematically examines key parameters affecting the interface formation, including contact pressure, holding time, and the microstructure of the sulfide-based SE using electron microscopy and electrochemical impedance spectroscopy (EIS). To enable the use of thin electrolyte layers in larger cell formats, the SE is fabricated using a scalable slurry-based process with hydrogenated nitrile butadiene rubber (HNBR) binder. Long-term cycling over 300 cycles with a coulombic efficiency (CE) exceeding 99.5% is demonstrated in application-oriented pouch cells with a LMA and a nickel manganese cobalt oxide (NMC) cathode. The cells are assembled with a precompressed SE film with a thickness of 230 μm and a high-pressure compression step of 360 MPa. Applying the adapted pressurization method enables stable cycling performance with thin SE layers (90 μm thickness). The presented findings identify critical parameters for LMA-based SSB with thin sulfide SE layers and provide practical guidelines for the processing and assembly of lithium metal–based solid state prototype pouch cells.