Preparation And Performance Of Carbon-Selenium Composite Electrode For Sodium-Ion Battery

With the rapid growth of electronic devices,sustainably rechargeable batteries are urgently needed to give the urgent rise to exploit energy storage devices with high capacity and satisfactory rate performance.Lithium-sulfur（Li-S）batteries are greatly developed by the reasons of the low cost and high theoretical energy density of S.However,the insulated nature of S and the dissolution of polysulfide are major challenges,leading to sluggish electrochemical reaction and low utilization of S,which hinders their practical applications.Sodium-selenium（Na-Se）batteries are considered to be one of the promising alternative for the Li-S batteries due to that the earch-abundance of Na is cheaper than Li and the electric conductivity of Se is much higher than S.Therefore,researching the high performance electrode materials of the Na-Se batteries have drawn increasing interest in these years.In this research,the carbon bio-materials were used to prepare the free-standing carbon-selenium（C/Se）composite cathodes and the performance of Na-Se batteries were studied,moreover,the electrode was introduced with AZO to further improve the performance.1.A new type of the frees-standing carbonized-leaf was developed to keep the inartificial hierarchical leaf structure and greatly simplified the fabricated processes of Na-Se batteries,which was obtained by thermal pyrolysis of natural leaves in a facile way.When they were used as the sodium ion batteries（SIBs）cathode,they exhibited the reversible specific capacity of 100 mA h g^-1 at 50 mA g^-1 after 500 cycles.Therefore,the biomass hard carbon with the unique structure stability can prolong the cycle life of the SIBs.2.A novel approach of carbonizing leaves by thermal pyrolysis with melt diffusion followed by selenium vapor deposition was developed to prepare the freestanding C/Se composite cathodes for the SIBs.They exhibited the high reversible specific capacity of 520 mA h g^-1 at 100 mA g^-1 after 120 cycles and 300 mA h g^-1even at 2 A g^-1 after 500 cycles without any capacity loss.Moreover,the unique natural three-dimensional structure and moderate graphitization degree of leaf-based carbon facilitated Na⁺/e^-transport to activate selenium and it can guarantee a high utilization of selenium,demonstrating a promising strategy to fabricate advanced electrodes toward the Na-Se batteries.3.The aluminium-doped zinc oxide（AZO）and selenium were combined to improve the banana biochar as ferrstanding electrodes.When they were used as the Na-Se batteries cathodes,they exhibited the excellent reversible specific capacity of490 mA h g^-1 at 100 mA g^-1 after 500 cycles,which confirmed that the adsorption and catalytic polyselenides of AZO demonstrated a promising strategy to fabricate advanced electrodes toward the Na-Se batteries.