All-solid-state Li-ion batteries (ASSB) are one of the most attractive next generation batteries for large scale application due to improved safety and higher energy density. However, the high temperature process required for densification of the solid-state electrolytes and for co-sintering of the multilayered ASSB is still a major challenge for large scale fabrication. In this study, a low temperature process, named cold sintering process, is applied to co-sinter all the layers in the ASSB at a low temperature. The cold sintered ASSB, a full-cell of Li4Ti5O12/Li7La3Zr2O12/LiFePO4 has densified microstructures and exhibits impressive electrochemical performance. The ASSB delivers high capacity of 140 mAh g−1 at 0.1 C, rate capability of up to 2 C with 85 mAh g−1, and 90% capacity retention over 100 cycles at room temperature under a current density of 0.2 C.