Interface Engineering for High-performance Sodium Metal Batteries

The growing demands of human society on fossil fuels have caused serious problems of global warming and air pollution. Renewable energy resources such as solar, wind, and tide are considered promising candidates to relieve fossil-fuel dependence. Due to the intermittent nature of renewable energy resources, however, energy storage systems (ESSs) are required for continuous energy harvesting and steady energy output. Sodium-metal batteries (SMBs) operating with a similar mechanism to that of commercial lithium-ion batteries (LIBs) are considered affordable alternatives, as a result of the desirable performances with high energy density and high power density, as well as abundant resources of sodium. Nevertheless, the direct utilization of Na as anode material is accompanied by notorious problems, including unstable electrode interfaces, growing Na dendrites, internal short circuits, as well as fire and explosions. It is essential for the practical application of SMBs to stabilize the Na metal anodes and eliminate the side reactions. Host material design has been verified as a feasible approach to accommodate the Na metal in the porous host, which could relieve the volume changes to enhance the stability of the solid-electrolyte interfaces (SEI). While the reported host materials are generally porous metals that exhibit heavy material weight which would sacrifice the energy density of the Na metal anodes. Besides, simply improving the Na metal anodes with porous host materials is not enough, which could not inhibit the side reactions between Na metal and the electrolytes. On the other hand, the material price of SMBs should be further decreased to enhance the practical viability, especially, the utilization of expensive electrolyte salts has long been a tremendous burden for the material price of SMBs. Therefore, the research in this doctoral thesis has been focused on improving the cycling stability of Na metal anodes, as well as decreasing the material price of SMBs for practical applications.