Critical review on cathode electrolyte interphase towards stabilization for sodium-ion batteries

The electrode/electrolyte interface, as an essential part, considerably influences the cycle lifespan, rate capability, and safety of batteries. However, researches on interfacial chemistries of the cathode and associated cathode electrolyte interphase (CEI) are still rare, which was hindered by the low operating potentials of most cathodes studied in recent years not exceeding the thermodynamic stability window of the electrolyte. Moreover, complicated (electro)chemistry reactions at cathode/electrolyte interface involving various side reactions and chemically unstable components at high potential, brings great challenges for the CEI's stability of high-voltage cathodes, which requires further attention for dense-energy batteries. In this review, a comprehensive analysis of CEI in sodium-ion batteries (SIBs), including formation and failure mechanisms, is provided. The characteristics of interfacial reactions and generated interphases on typical cathode materials are systematically discussed. Based on this, reasonable interphase stabilization strategies are outlined, from the regulation of the electrode and electrolyte to the construction of artificial interphase layers. Finally, the promising directions and potential solutions for interphase research are identified to stimulate revolutionary design of dense-energy and high-lifespan SIBs.