Understanding the Electrochemical Compatibility and Reaction Mechanism on Na Metal and Hard Carbon Anodes of PC-Based Electrolytes for Sodium-Ion Batteries.

Electrolytes as an important part of sodium-ion batteries have a pivotal role for capacity, rate, and durability of electrode materials. On account of the high reduction activity of sodium metal with organic solvents, it is very important to optimize the electrolyte component to realize high stability on Na metal and hard carbon anodes. Herein, chemical and electrochemical stability of propylene carbonate (PC)-based electrolytes on sodium metal and hard carbon anodes is investigated systematically. The results demonstrate that whether using NaClO4 or NaPF6, the PC-based electrolytes are not stable on Na metal, but adding of FEC can immensely enhance the stability of the electrolyte because of the compact solid electrolyte interphase film formed. The electrolytes containing FEC also exhibit high electrochemical compatibility on hard carbon anodes, showing high reversible capacity and excellent cycling performance. A reaction mechanism based on the Na+ induction effect is proposed by spectrum and electrochemical measurements. This study can provide a new insight to optimize and develop stable PC-based electrolytes and be helpful for understanding the other electrolyte systems.