  The development of sustainable transportation and communication systems
requires an increase in both energy density and capacity retention of
Li-batteries. Using substrates forming a solid solution with body centered
cubic Li enhances the cycle stability of anode-less batteries. However, it
remains unclear how the substrate microstructure affects the lithiation
behavior. Here, we deploy a correlative, near-atomic scale probing approach
through combined ion- and electron-microscopy to examine the distribution of Li
in Li-Ag diffusion couples as model system. We reveal that Li regions with over
93.8% at.% nucleate within Ag at random high angle grain boundaries, whereas
grain interiors are not lithiated. We evidence the role of kinetics and
mechanical constraint from the microstructure over equilibrium thermodynamics
in dictating the lithiation process. The findings suggest that grain size and
grain boundary character are critical to enhance the electrochemical
performance of interlayers/electrodes, particularly for improving lithiation
kinetics and hence reducing dendrite formation.
