We hypothesized that pressure and temperature affect Li metal solid-state battery (LMSB) resistance and susceptibility to Li metal penetration during cycling. To validate this, the kinetics and stability of the Li-solid electrolyte interface was studied using the model polymer electrolyte system: Li/Polyethylene oxide-LiTFSI (PEO-LiTFSI). It was determined that the interface impedance decreased with increasing pressure and was invariant above 400 and 200 kPa at 60 and 80 degrees C, respectively. In tests to determine susceptibility to Li metal penetration as a function of current density, it was determined that the current density at which Li metal penetrates PEO-LiTFSI, was consistently 0.5 mA/cm(2) for all temperatures tested (60, 80, and 100 degrees C). To gain a mechanistic understanding of how Li metal penetrates a solid electrolyte at and above the current density for onset of Li metal penetration, an operando optical visual cell was used. A clear correlation between erratic DC polarization behavior and the onset and propagation of Li metal penetration was made. The empirical observations in this study could help better understand the factors that affect the kinetics and stability of the Li-solid electrolyte interface. We believe these findings could help to advance the maturity of LMSB. (C) 2018 The Electrochemical Society.