A super solid electrolyte of Ba-substituted Li10GeP2S12 is designed and fabricated to achieve high electrochemical stability. Among the Ba-substituted Li10GeP2S12 solid electrolytes, the composition of Li9.4Ba0.3GeP2S12 exhibits the highest ionic conductivity of 7.04 x 10(-4) S cm(-1) with an activation energy of 2827 kJ mol(-1) at 25 degrees C. The electrochemical window of Li9.4Ba0.3GeP2S12 is between 0 and 6 V (vs. Li), which is higher than the typical 5 V window of Li10GeP2S12. As compared with Li(10)GeP(2)S(12)z, Li9.4Ba0.3GeP2S12 demonstrates a significantly reduced polarization and a better cycle stability though its ionic conductivity is slightly lower than that of the former. The electrochemical stability of Ba-substituted Li10GeP2S12 can be attributed to the structural stability resulting from the stable interaction between Ba2+ and S2- in the structure. (C) 2017 Elsevier B.V. All rights reserved.