This thesis focuses on the development of novel solid electrolyte suitable for Li and post-lithium batteries. Novel hydroborates are proposed as potential candidate for this role. The understanding of their structures, characterized by X-ray diffraction, was necessary to understand the ionic mobility and to make possible the developments of strategies to stabilize conducting phases at room temperature. The best results were obtained within the closoborates, by means of anion mixing, where the ionic conductivity exceeds 1 mS/cm already at room temperature (a very competitive value compared to the conventional liquid electrolytes). The best performing ionic conductors where hence characterized in electrochemical cells to understand possible kinetic and compatibility limitations with respect to different electrodes: sodium, tin and indium were selected as anode materials, showing in the best cases (In) a reversible Na-shuttling for more than 2000 hours.