Impact of Electrolyte Salts on Na Storage Performance for High-Surface-Area Carbon Anodes

High-surface-area carbon (HSAC) has been regarded as one of the most promising anode materials for sodium-ion batteries. However, it generally suffers from low initial Coulombic efficiency (ICE), which is closely related to the formation process of a solid electrolyte interface (SEI). Herein, the impact of different electrolyte salts on the electrochemical performance and SEI formation of a commercial HSAC anode is studied. It is found that the use of NaCF3SO3 enables much higher ICE (69.28%) and reversible capacity (283 mA h g-1) of the HSAC anode compared with the NaPF6 electrolyte (59.65%, 243 mA h g-1). Through comprehensive characterizations, the improvement in electrochemical performance facilitated by NaCF3SO3 could be attributed to the reduced amount of NaxC and the thinner SEI formed on the surface of HSAC during the initial cycle, which not only provides extra active sites for Na+ storage but also contributes to the promoted ICE. This work not only provides a deeper understanding of the role of electrolyte salt in SEI formation in the HSAC anode but also proposes a new method to further promote the ICE of the HSAC anode in sodium-ion batteries.