Effects of sodium salts on compatibility between Na2Ti3O7@C anode and electrolyte for sodium-ion batteries

A non-carbonaceous titanium-based materials of Na2Ti3O7 have been considered as an attractive anode material for sodium ion battery (SIBs), due to its low charge potential and high energy density. However, the selection of preferred sodium salts in liquid electrolyte is still a challenge to improve battery performance. Herein, the compatibility of Na2Ti3O7 @C anode material with sodium perchlorate (NaClO4)-based and sodium trifluoromethyl sulfonate (NaCF3SO3)-based electrolytes are studied, respectively. The results show that solid electrolyte interphase (SEI) film formed by NaCF3SO3-based electrolyte is thin, compact and uniform, which can effectively reduce the transmission energy barrier of Na+. Different from that, the SEI film derived in NaClO4-based electrolyte contains more Na2CO3 and NaF, caused by the continuous decomposition of NaClO4 salt in carbonate solvent. It makes the SEI film thicker and the interface impedance larger, which results in the decline of battery cycle performance. In addition, more sulfur-containing compounds with good sodium conductivity and stability are generated due to the decomposed of NaCF3SO3 salt in carbonate solvent, which improves interfacial transport performance of materials, and inhibits the increase of the SEI film thickness and thus improves the cycling and rate performance of batteries. This study provides a reference method for designing advanced SIBs.