  All solid state Li-ion batteries employing metallic lithium as an anode offer
higher energy densities while also being safer than conventional liquid
electrolyte based Li-ion batteries. However, the growth of tiny filaments of
lithium (dendrites) across the solid state electrolyte layer leads to premature
shorting of cells and limits their practical viability. The microscopic
mechanisms that lead to lithium dendrite growth in solid state cells are still
unclear. Using garnet based lithium ion conductor as a model solid state
electrolyte, we show that interfacial void growth during lithium dissolution
precedes dendrite nucleation and growth. Using a simple electrostatic model, we
show that current density at the edges of the voids could be amplified by as
much as four orders of magnitude making the cells highly susceptible to
dendrite growth after void formation. We propose the use of metallic
interlayers with low solubility and high nucleation overpotential for lithium
to delay void growth. These interlayers increase dendrite growth tolerance in
solid state electrolytes without the undue necessity for high stack pressures.
