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

Abstract

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.