Sodium secondary batteries have gained much attention as alternative power sources to replace lithium secondary batteries. However, some technical issues must be solved to ensure their success. Here, a highly safe and cost-effective Na-based dual-ion battery system employing self-formulated CuCl cathode material starting from a mixture of Cu and NaCl in conjunction with a nonflammable NaAlCl4 ·2SO2 inorganic liquid electrolyte is demonstrated. It is found that CuCl is spontaneously formed by redox coupling of Cu/Cu(I) and SO2 /SO2 - anion radical. In the proposed battery, Na+ and Cl- are employed as energy carriers for the anode and cathode, respectively, and it is further demonstrated that the Na-metal-free battery configuration is possible using a hard carbon anode. Owing to the use of cheap electrode materials and a highly conductive and safe electrolyte, the proposed batteries deserve to be regarded as a promising approach for next-generation Na rechargeable batteries.