Free-Standing Selenium Impregnated Carbonized Leaf Cathodes for High-Performance Sodium-Selenium Batteries

A novel approach of carbonizing leaves by thermal pyrolysis with melt diffusion followed by selenium vapor deposition is developed to prepare the carbon-selenium composite cathodes for sodium-selenium batteries. The carbonized leaf possesses internal hierarchical porosity and high mass loading; therefore, the composite is applied as a binder- and current collector-free cathode, exhibiting an excellent rate capability and a high reversible specific capacity of 520 mA h g−1 at 100 mA g−1 after 120 cycles and 300 mA h g−1 even 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 facilitate Na+/e− transport to activate selenium which can guarantee a high utilization of the selenium during discharge/charge process, demonstrating a promising strategy to fabricate advanced electrodes toward the sodium-selenium batteries.