Enabling high-voltage stability of P2-type layered oxide cathodes using ionic liquid electrolytes

Abstract

The high-voltage performance of sodium-ion batteries is strongly influenced by electrolyte chemistry, as parasitic reactions at the cathode interface can accelerate capacity loss. For layered oxide cathodes, the instability of the cathode-electrolyte interphase (CEI) becomes more severe at elevated voltages. Thus, optimizing the electrolyte is critical for maintaining interfacial stability and long-term cycling behavior. In this work, a NaFSI-containing ionic liquid electrolyte was introduced and compared with a conventional carbonate electrolyte using P2-type Na2/3Li1/4Sb1/12Mn2/3O2 as a model cathode. Within 1.5-4.5 V at 50 mA g−1, the IL-based cell retains 70.5% of its initial capacity after 200 cycles, while the carbonate-based cell retains only 25.3%. ToF-SIMS depth analysis together with 3D reconstruction indicates that the ionic-liquid electrolyte facilitates the formation of a spatially homogeneous CEI containing a relatively stable inorganic-rich domain. This interface is associated with reduced electrolyte decomposition and mitigated high-voltage interfacial degradation. The present results suggest that regulating interfacial chemistry through ionic-liquid electrolytes is beneficial for enhancing the durability of high-voltage sodium-ion batteries.