In this study we report an experimental study of the substitution series Li3YBrxCl6-x (x = [0, 6] steps of 1.5) and investigate the influence of the halogen composition on the crystal structure, ionic conductivity and the electrochemical stability window. It is found that the composition Li3YBrxCl6-x x=1.5 is a good compromise, with increased ionic conductivity compared to Li3YCl6 while maintaining the higher oxidative stability of Li3YCl6.