Origin of the lithium metal anode instability in solid-state batteries during discharge

Summary

Enabling the lithium metal anode (LMA) in solid-state batteries (SSBs) would increase energy density and specific energy compared with lithium-ion batteries. However, pore formation in LMAs with irregular morphology, even at low current density, during discharge results in an unstable, high-impedance interface. Understanding and addressing this inherent anode instability is essential for increasing the power densities in SSBs. Herein, we suggest that the morphology of the stripped electrode is related to dislocations in the LMA. To investigate the influence of dislocations, symmetric cells, LiǀLi_6.25Al_0.25La₃Zr₂O₁₂(LLZO)ǀX-Li, are studied, where X-Li represents the microstructurally controlled LMA obtained via suitable thermomechanical processing. Operando impedance measurements are corroborated with SEM, confocal microscopy, and AFM data. Based on the experimental observations, a mechanism for pore formation is proposed. We show that the stack pressure required to maintain a stable interface is governed by the lithium microstructure and its thermomechanical processing history.