Induced Stress Evolution at Argyrodite Sulfide/Li-Metal Interface—Tension or Compression?

Argyrodite sulfide (Li₆PS₅Cl) has demonstrated great potential as a solid electrolyte (SE) for high-energy-density all-solid-state batteries (ASSB). However, Li dendrite penetration in Li₆PS₅Cl causes electrical short circuits, which has heavily limited the development of ASSBs using Li₆PS₅Cl. It is evident that Li₆PS₅Cl undergoes interfacial chemical reactions and decomposition when in contact with Li metal, forming a solid electrolyte interphase (SEI).<br/><br/>Currently, there is controversy over whether this chemical-reaction-induced SEI causes compressive or tensile stress at the interface, thereby mitigating or facilitating Li dendrite penetration Li₆PS₅Cl, respectively. To answer this question, a customized multiple-beam Optical Stress Sensor (MOSS) system was used to measure curvature changes that occur are induced by the Li₆PS₅Cl reaction with Li metal. These were evaluated with a finite element modeling to determine the stress. The composition of the SEI was also investigated with XPS and ToF SIMs and compared with predictions from atomistic modeling. The results show that the SEI formation generates tensile rather than compressive stress, which is expected to facilitate Li dendrite propagation. We believe this finding provides critical guidance for cycling ASSBs using Li₆PS₅Cl as a SE and for engineering the interface between Li₆PS₅Cl and Li metal.