The growth rate of LiCl solid electrolyte layers on Li was studied in neutral and acid LiAlCl 4SOCl 2 solutions over periods of years. For SO 2-containing acid solutions, a small anodic load resulting from the coupling of lithium to stainless steel proved to be more important than the acidity. The ionic and electronic conductivities of the layers were derived from impedance measurements and passivation rates, respectively. In neutral solutions, the Li + conductivity decreased with increase in the layer thickness; this effect was not observed in acid SO 2-containing solutions. Factors influencing the growth rate of the LiCl layer are briefly analysed. It is concluded that increasing the ratio of ionic to electronic conductivity would be the most efficient way of improving the performance of the solid electrolyte.