Rechargeable Na-CO₂ Batteries Starting from Cathode of Na₂CO₃ and Carbon Nanotubes

Na-CO₂ batteries have attracted significant attentions due to their high energy density and effective utilization of greenhouse gas CO₂. However, all reported Na-CO₂ batteries employ excessive preloaded metal Na, which will lead to safety issues such as dendrite formation and short circuit. In addition, the charging mechanism of reported Na-CO₂ batteries is not very clear. Here we report the Na-CO₂ batteries, starting from the cathode of cheap Na₂CO₃ and multiwalled carbon nanotubes (CNTs). Due to the effective electron transfer and high reactivity, the decomposition of Na₂CO₃ and CNTs could take place under 3.8 V. The charging mechanism of 2Na₂CO₃ + C → 4Na + 3CO₂ without any side reactions is revealed by in/ex situ techniques such as Raman, gas chromatograph, and optical microscope. Dendrite-free Na can quantitatively deposit on the Super P/Al anode because of large specific surface area and low nucleation barrier of the anode for Na plating. The batteries could deliver an energy density of 183 Wh kg^-1 (based on the whole mass of the pouch-type batteries, 4 g) with stable cycling performance. This work reveals that safe rechargeable Na-CO₂ batteries could be constructed by cheap Na₂CO₃ and multiwalled carbon nanotubes.