Study On The Electrochemical Performance Of Quasi-solid Sodium-air/carbon Dioxide Battery

Na-air batteries have attracted wide attention due to their high energy density,low cost and charging voltage.However,for most sodium-air batteries,they operate under dry pure oxygen.When moisture is present,Na-air batteries exhibit poor safety and cycle life.In this paper,single-walled carbon nanotubes?SWNTs?are dispersed in an ionic liquid?[C₂C₁im][NTf₂]?by van der Waals force and“Cation-?”interaction force,a novel quasi-solid-state Na-battery is proposed.This battery uses NASICON(Na₃Zr₂Si₂PO₁₂)structure solid electrolyte and gel cathode for the first time.It not only protects the metal sodium anode,but also solves the problems of volatility,leakage and combustion of traditional liquid electrolyte,which significantly improves the battery's safety and cycle life.Compared to pure oxygen,Na-air batteries exhibit more excellent electrochemical performance based on a gel cathode in ambient air.With a current density of 0.1 m A cm^-2,it can stably cycle 125 times and the cycle time is 528 hours.At a higher current density of 0.5 m A cm^-2,the first discharge capacity is 2181 m Ah g^-1,and at 80°C,the discharge capacity is as high as 2856m Ah g^-1,exhibiting a wide operating temperature.In-situ X-ray diffraction?In-situ XRD?,ex-situ transmission electron microscopy?Ex-situ TEM?,and high resolution transmission electron microscopy?HRTEM?were used to further verify the reaction mechanism of Na-air battery.Similar to aqueous sodium-air batteries,during the discharge process,due to the strong hydrophobic nature of the gel,gaseous water in ambient air is deposited on the surface and converted into liquid water.It reacts with Na₂O₂ to generate Na OH,and then part of the generated Na OH is dissolved in water to form Na OH with high electrical conductivity;During the charging process,Na OH decomposes to generate free metal Na,which effectively reduces the overcharge potential of the charge.And it has been confirmed experimentally that when a certain amount of water is present,the discharge capacity also increases significantly with the increase of the water content.This work is of great significance for the development and promotion of practical applications of metal-air batteries.Based on the study of quasi-solid Na-air batteries,the above gel electrolyte was modified,and sodium salt?Na TFSI?was added,which significantly reduced the battery's overcharge potential.The zeolite imidazole framework?ZIF-67?was calcined in a mixed gas?Ar:H₂=9:1?to prepare a nitrogen-doped metal-organic framework?MOF-NCNTs?cathode catalyst.The synergistic effect between the porous cage structure and the cobalt nanoparticles in the hollow carbon nanotubes,and the nitrogen doped on the tube wall played a positive role in the adsorption and reduction of carbon dioxide.The constructed quasi-solid Na-CO₂ battery can stably cycle 145 times at a current density of 0.1 m A cm^-2,a cycle time of 585 h,and a first discharge capacity of 3153 m Ah g^-1.The reaction mechanism was analyzed by in situ raman spectroscopy,and the main discharge products were found to be metastable sodium oxalate?Na₂C₂O₄?and trace sodium carbonate?Na₂CO₃?,and proved its reversible formation and decomposition.This work provides new ideas for the efficient electrochemical conversion of carbon dioxide.