A new film-forming electrolyte additive in enhancing the interface of layered cathode and cycling life of sodium ion batteries

Sodium layered oxides have been widely investigated as cathodes for sodium-ion batteries (SIBs), and extensive research efforts have been made to enhance their performance through composition design and structural engineering. However, limited attention has been paid to developing the electrolyte system and stabilizing the electrolyte–cathode interface, which play important roles in determining the cycling life of SIBs. Herein, a new electrolyte additive, diglycolic anhydride (DGA), is investigated as a film-forming additive. A Na/Na0.67Li0.2Ni0.23Mn0.67O2 (NLNMO) cell with 2 wt% DGA in the electrolyte exhibits a capacity of 85 mAh g−1 at a rate of 1 C, with a retention of 92.59% after 1000 cycles. Soft X-ray absorption characterization, 18O2 isotopic labeling, titration mass spectrometry, and online electrochemical mass spectrometry measurements are performed. The results reveal that the robust interface formed by DGA inhibits side reactions between the electrolyte and (O2)n– species formed through the oxidation of lattice oxygen, thus resulting in the retention of the original NLNMO cathode structure and a prolonged lifespan in Na/NLNMO batteries. Furthermore, electrochemical impedance spectroscopy using a three-electrode cell system reveals the influence of DGA on the interface at the NLNMO cathode and Na metal anode.