This paper proposes a strategy to stabilize the garnet/Li interface by introducing Li3PO4 as an additive in garnet-type Li6.5La3Zr1.5Ta0.5O12. The Li3PO4-added Li6.5La3Zr1.5Ta0.5O12 electrolyte exhibits a room temperature Li-ion conductivity of 1.4 x 10(-4) S cm(-1), which is less than that of the Li3PO4-free counterparts (4.6 x 10(-4) S cm(-1)). However, the presence of Li3PO4 improves the interfacial compatibility and suppresses Li-dendrite formation during Li-metal plating/stripping. The symmetric Li/garnet/Li cells with Li3PO4-added Li6.3La3Zr1.5Ta0.5O12 have been successfully cycled at a current density of 0.1 mA cm(-2) at 60 degrees C for 60 h; on contrast, the control cells with Li3PO4-free Li6.5La3Zr1.5Ta0.5O12 display noisy potential with large voltage polarization and get short-circuited completely after 33-h cycling under the same operating condition. The outstanding interface stability can be attributed to the in situ reaction of the Li flux with Li3PO4 to form a self-limiting and ion-conducting interphase, Li3P, which is confirmed experimentally. (C) 2017 Elsevier B.V. All rights reserved.