Rechargeable magnesium batteries with their low cost, high safety, and environment-friendly are considered a promising post-lithium battery. Develop suitable cathode material and an electrolyte are the greatest challenges facing their commercialization. Herein, a halogen-free electrolyte-based Mg(NO3)2 in co-solvent of acetonitrile and tetraethylene glycol dimethyl has been successfully synthesized for the first time. A solid polymer interface-based polyvinyl alcohol PVA, and Mg(O3SCF3)2 has been designed to protect the surface of the Mg anode from direct contact with the liquid electrolyte. The as-synthesized electrolytes with and without interface have been exhibited good Mg plating/stripping performance, high anodic stability up to >3 V (vs. Mg/Mg2+), and high ionic conductivity of 0.11, 0.0036 mS/cm, respectively. The Ba0.85Sm0.1TiO3 (BSTO) is designed and characterized. As a result, the Mg-BSTO battery was constructed with an initial discharge capacity up to 88 mAh/g and a charge capacity up to 20 mAh/g.