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Na–CO 2 battery is one of the most promising energy storage devices for the exploration of Mar. To fix the evaporation problem of liquid electrolytes in an open system, solid-state electrolyte Na 3 Zr 2 Si 2 PO 12 (NZSP) is used to fabricate a solid-state Na–CO 2 battery. In the battery, the interface between the Na-metal anode and NZSP plays a vital role in improving electrochemical performance. The interfacial parasitic reaction between NZSP and Na-metal results in a Na-rich kinetically stable interphase. (200) and (−111) planes are the preferentially etched crystal planes of NZSP, as SiO 4 and PO 4 tetrahedrons on the planes are easily broken by extra Na-ion injection. Aside from the interfacial reaction, the poor contact between Na-metal and NZSP is a more serious problem, which leads to large interfacial resistance and poor cycling stability. To fix this problem, carbon black is mixed with melted Na-metal to prepare a composite anode (Na@C). The Na@C composite anode easily wets NZSP, thus decreasing the interfacial resistance from 918 to 98 Ω cm2. Symmetrical cells stably cycled 1100 h at 0.1 mA cm−2, when using Na@C as the electrode. Furthermore, Na–CO 2 battery with Na@C composite anode also shows a prolonged cycling life. [Display omitted] ● (200) and (−111) planes are found as preferentially etched crystal planes of NZSP. ● Kinetically stable interphase between Na and NZSP has been found. ● Poor interfacial contact between Na and NZSP results in poor cycling stability. ● Na@C composite anode makes intimate contact with NZSP. ● The solid-state Na–CO 2 battery shows better performance by using Na@C. [ABSTRACT FROM AUTHOR]