  All-solid-state batteries are expected to enable batteries with high energy
density with the use of lithium metal anodes. Although solid electrolytes are
believed to be mechanically strong enough to prevent lithium dendrites from
propagating, various reports today still show cell failure due to lithium
dendritic growth at room temperature. While cell parameters such as current
density, electrolyte porosity and interfacial properties have been
investigated, mechanical properties of lithium metal and the role of applied
stack pressure on the shorting behavior is still poorly understood. Here, we
investigated failure mechanisms of lithium metal in all-solid-state batteries
as a function of stack pressure, and conducted in situ characterization of the
interfacial and morphological properties of the buried lithium in solid
electrolytes. We found that a low stack pressure of 5 MPa allows reliable
plating and stripping in a lithium symmetric cell for more than 1000 hours, and
a Li | Li6PS5Cl | LiNi0.80Co0.15Al0.05O2 full cell, plating more than 4 um of
lithium per charge, is able to cycle over 200 cycles at room temperature. These
results suggest the possibility of enabling the lithium metal anode in
all-solid-state batteries at reasonable stack pressures.
