Achieving a long-life 165 Wh/kg sodium-ion pouch-cell via regulating intergrowth structure in layered oxide cathode with anionic redox

Abstract

The Na-O-Li configurations in P2-type sodium layered transition metal (TM) oxide cathode can trigger additional oxygen redox at high charging voltage (deep de-sodiation). However, the P-type to O-type phase transition and irreversible TM migration would be simultaneously aggravated at high state-of-charge, resulting in structural distortion. Herein, we demonstrate that excessive de-sodiation of Na0.67Li0.1Fe0.37Mn0.53O2 (NLFMO) induces Li removal from lattice and the formation of neighboring O-stacking faults with an OP4-O2 intergrowth structure, which is the chief culprit of structural distortion. Regulating Li migration from the pristine TM layer (LiTM) to the alkali-metal layer (LiAM) would sustain a repetitive P-stacking state (not evolve into a deteriorated neighboring O-stacking), and tune the reversible movement of TM ions during cycling. Accurately regulating the O/P-intergrowth structure (within the OP4 boundary phase) does not bring any obvious trade-off on capacity, but enhances the structural stability of NLFMO cathode, achieving a long-life 165 Wh/kg pouch-cell with cationic/anionic redox activities.