Understanding the electro-chemo-mechanics of Li plating in anode-free solid-state batteries with operando 3D microscopy

Anode-free solid-state batteries can enable high energy densities and the ability to manufacture high-quality interfaces. However, during in situ anode formation, dynamic mechanical stresses influence the initial Li metal plating morphology. This work utilizes operando 3D video microscopy to characterize electrode morphology during in situ anode formation on garnet Li7La3Zr2O12 (LLZO) solid electrolytes. The coupled morphological evolution and electrochemical signatures are identified and are attributed to changes in stress at the interface. We demonstrate the influence of stress on both thermodynamic and kinetic behaviors at the interface. A mechanistic framework provides insight into the importance of tuning the interfacial toughness, current collector properties, stack pressure, and cell geometry to optimize performance and control plating uniformity. Informed by these insights, the areal Li coverage after 2 mAh/cm2 of plating is increased from 50% to 95%. The understanding from this study informs future optimization of in situ anode formation in solid-state systems.