Reversible hybrid sodium-CO2 batteries with low charging voltage and long-life

A reversible long-life hybrid Na-CO 2 battery is proposed by using Na 3 Zr 2 Si 2 PO 12 solid electrolyte as a separator, N-doped single-wall carbon nanohorns (N-SWCNH) as a catalyst and the saturated NaCl solution as an aqueous catholyte. The Na 3 Zr 2 Si 2 PO 12 ceramic not only has high Na + ion conductivity, but also prevents potential contamination from H 2 O and CO 2 to sodium anode, and avoids the internal short-circuit touch of Na dendrite with cathode, improving the safety of the battery. Benefiting from N dopants , unique internal and interstitial nanoporous structures, N-SWCNH have large surface area for discharge products accumulation, offer substantial structural defect sites for CO 2 adsorption and electron transfer , contributing to high catalytic activity and reversibility . Most importantly, the hybrid Na-CO 2 battery with aqueous electrolyte facilitates the dissolution of the insulated discharge product, which overwhelmingly improves the discharge and charge reactions kinetics. Na-CO 2 batteries exhibit a low charging voltage of 2.62 V and a small voltage gap of 0.49 V at a current density of 0.1 mA cm −2 , a superior discharge capacity of 2293 mAh·g −1  at a current density of 0.2 mA cm −2 , a high round trip efficiency of ~68.7% after 300 cycles. In-situ Raman and ex-suit XRD analyses convincingly show that NaHCO 3 and carbon are the main discharge products.