Li2La3Zr2O12 (LLZ) solid electrolytes with Zr site partially substituted by Ta and Nb elements were prepared via the conventional solid-state reaction. All the compositions could lead to the cubic garnet-type structure after sintering at 1150 degrees C. The use of gamma-Al2O3 as a sintering aid in the preparation of doped LLZ was studied. It was shown that Al could help to improve the micro-structure for Nb doping, but not necessary for Ta doping. The Ta and Nb doping enhanced the ionic conductivity at 25 degrees C to 4.09 x 10 (-4) S cm-(1) and 4.50 x 10(-4) S cm(-1), respectively. A conductivity as high as 1.23 x 10(-3) S cm(-1) was obtained when measured at 50 C in air for the Nb-doped LLZ. All-solid-state batteries with LLZTa and LLZNb solid electrolytes were assembled and tested. The cyclic voltammetry (CV) measurement indicated the successful working of the batteries. (c) 2014 Elsevier B.V. All rights reserved.