In situ construction of uniform and robust cathode-electrolyte interface toward high-stable P2-Type sodium layered oxide cathodes

As a kind of potential cathode for sodium-ion batteries (SIBs), P2-type Na2/3Ni1/3Mn2/3O2 (P2-NNMO) suffers from the dissolution of transition metals and severe side reactions in conventional electrolytes, which greatly deteriorates its electrochemical performance. Herein, an artificial cathode-electrolyte interface (CEI) is in situ constructed on P2-NNMO cathode based on a spontaneous redox reaction between P2-NNMO material and organic solvent tetrahydrofuran (THF). The uniform and robust CEI layer on P2-NNMO cathode (named P2-NNMO-T) mainly comprises organic Na-based species (R-O-Na, R-CO-Na, and R-O2CO-Na), and converts from an initial thickness of 2 nm into 4.6 nm after cycling. It can serve as a versatile interlayer to facilitate Na+ transport, shield the attack of electrolyte solvents, and suppress the transition metal dissolution effectively, thus boosting the cycling stability and fast charging capability of P2-NNMO cathodes. More importantly, the concept of in situ CEI construction can be extended to other layered oxides beyond SIBs discussed herein.