Insights into layered–tunnel dynamic structural evolution based on local coordination chemistry regulation for high‐energy‐density and long‐cycle‐life sodium‐ion oxide cathodes

Abstract The pursuit of high energy density while achieving long cycle life remains a challenge in developing transition metal (TM) oxide cathode materials for sodium‐ion batteries (SIBs). Here, we present a concept of precisely manipulating structural evolution via local coordination chemistry regulation to design high‐performance composite cathode materials. The controllable structural evolution process is realized by tuning magnesium content in Na 0.6 Mn 1− x Mg x O 2 , which is elucidated by a combination of experimental analysis and theoretical calculations. The substitution of Mg into Mn sites not only induces a unique structural evolution from layered–tunnel structure to layered structure but also mitigates the Jahn–Teller distortion of Mn 3+ . Meanwhile, benefiting from the strong ionic interaction between Mg 2+ and O 2− , local environments around O 2− coordinated with electrochemically inactive Mg 2+ are anchored in the TM layer, providing a pinning effect to stabilize crystal structure and smooth electrochemical profile. The layered–tunnel Na 0.6 Mn 0.95 Mg 0.05 O 2 cathode material delivers 188.9 mAh g −1 of specific capacity, equivalent to 508.0 Wh kg −1 of energy density at 0.5C, and exhibits 71.3% of capacity retention after 1000 cycles at 5C as well as excellent compatibility with hard carbon anode. This work may provide new insights of manipulating structural evolution in composite cathode materials via local coordination chemistry regulation and inspire more novel design of high‐performance SIB cathode materials. image