A new path for the design of safe and efficient, all-solid-state Li-ion batteries by spark plasma sintering (SPS) is considered. To reach a good electrochemical performance from such batteries, several parameters are investigated, such as the composite-electrode formulation (active material/electrolyte/carbon ratio) and the influence of the sintering parameters on their compactness. The formulation is optimized to ensure good ionic and electronic percolation through the composite electrode's volume. The compactness has to be sufficient to guarantee a good mechanical aspect, while the residual porosity in the composite electrode allows electrode-volume changes upon insertion and deinsertion, preserving the electrode/electrolyte interfaces, which are crucial in such technology. Based on these investigations, an all-solid-state battery with a surface capacity of 2.2 mA h cm−2 is assembled by SPS, displaying a promising electrochemical performance at 80 °C.