Strategies for Sodium Metal Batteries with Long Lifespan and High Safety

Sodium metal as anode material applied to SMBs has gained considerable attention in recent years, owing to its high theoretical capacity (1166 mAh g-1), low cost and earth abundance when compared with Li metal. However, there is still a long way to go before realizing the practical application of SMBs. Sodium metal anode (SMA) suffers from challenging issues, such as unstable SEI, Na dendrites growth, and infinite volume change during cycling, etc, leading to rapid capacity decay, shortened lifespan and even safety concerns. So far, a variety of strategies have been put forward to addressing the above problems and developing high-performance SMBs, including in interfacial engineering, improving electrolyte recipes advanced Na electrode engineering, which are reviewed in this dissertation. My doctoral work mainly focuses on enhancing the stability and safety of Na electrode to improve the performance of SMBs, including in in situ build an ASEI on Na metal electrode, exploring functional additive and non-flammable electrolyte. In addition, the performance of full cells applying Na electrode as anode paired with conventional cathodes (PB, NVP) has also been studied. In the first case, we reported that a sodium benzenedithiolate (PhS2Na2)-rich protection layer synthesized in situ on sodium by a facile methodology effectively prevents dendrite growth in the carbonate electrolyte, leading to a stabilized sodium metal electrodeposition for 400 cycles (800 h) of repeated plating/stripping at a current density of 1 mA cm-2. The organic salt, PhS2Na2, is found to be a critical component in the protection layer, and is different from traditional inorganic salts. Furthermore, the mechanism of the role of functional group of Ph-S-Na was studied by DFT calculations. This finding opens up a new and promising avenue, based on organic sodium slats, to stabilize sodium metals with a protection layer.