Na@C composite anode for a stable Na|NZSP interface in solid-state Na–CO₂ battery

Na–CO₂ 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 Na₃Zr₂Si₂PO₁₂ (NZSP) is used to fabricate a solid-state Na–CO₂ 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 SiO₄ and PO₄ 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–CO₂ battery with Na@C composite anode also shows a prolonged cycling life.