Regulation of Coordination Chemistry for Ultrastable Layered Oxide Cathode Materials of Sodium‐Ion Batteries

Abstract

AbstractLayered transition‐metal (TM) oxide cathodes have attracted growing attention in sodium‐ion batteries (SIBs). However, their practical implementation is plagued by Jahn–Teller distortion and irreversible cation migration, leading to severe voltage decay and structure instability. Herein, O3‐Na0.898K0.058Ni0.396Fe0.098Mn0.396Ti0.092O2 (KT‐NFM) is reported as an ultrastable cathode material via multisite substitution with rigid KO6 pillars and flexible TiO6 octahedra. The K pillars induce contracted TMO2 slabs and their strong Coulombic repulsion to inhibit Ni/Fe migration; and Ti incorporation reinforces the hybridization of Ni(3deg*)‐O(2p) to mitigate the undesired O3–O'3 phase transition. These enable the reversible redox of Ni2+↔Ni3.20+ and Fe3+↔Fe3.69+ for 138.6 mAh g−1 and ultrastable cycles with >90% capacity retention after 2000 cycles in a pouch cell of KT‐NFM||hard carbon. This will provide insights into the design of ultrastable layered cathode materials of sodium‐ion batteries and beyond.