Selection of Sodium Salt Electrolyte Compatible with Na0.67Ni0.15Fe0.2Mn0.65O2 Cathode for Sodium‐Ion Batteries

The construction of an optimized electrolyte system compatible with layered transition metal (TM) oxides is of great importance to advanced sodium‐ion batteries (SIBs). Herein, a low‐cost iron‐containing manganese‐based layered cathode material of Na 0.67 Ni 0.15 Fe 0.2 Mn 0.65 O 2 (N‐NFM) is prepared through an improved coprecipitation method. Then, the chemical properties of interfaces between the N‐NFM cathode and organic liquid electrolytes based on NaClO 4 and NaPF 6 are investigated, respectively. Results show that the cathode electrolyte interphase (CEI) film formed in the NaPF 6 ‐based electrolyte is dense and uniform, which inhibits the dissolution of TM ions effectively and provides a low energy barrier for the transport of Na + . Apart from that the CEI film formed in the NaClO 4 ‐based electrolyte contains more organic but less inorganic compounds, resulting in an increase in impedance. In addition, it is believed that the stability of the CEI film is susceptible to the perchlorate with strong oxidizing property. In this role, a small part of the CEI film falls from the cathode surface, accelerating the dissolution of TM ions and leading to the reactivation of electrolyte decomposition.