Alleviating the Jahn–Teller Distortion of P3-Type Manganese-Based Cathodes by Compositionally Graded Structure for Sodium-Ion Batteries

P3-type manganese-based cathodes with high specific capacity and low cost have attracted considerable attention. But the Mn3+ with unpaired, eg* electron gives rise to the Jahn-Teller distortion and disproportionation reaction, which further leads to the rapid capacity/voltage decay. In this work, we design a compositionally graded P3-type manganese-based oxide, in which the nickel content increases linearly while the manganese fraction decreases gradually from the interior to the surface of a single particle. At the surface, the nickel/manganese solid solution phase is formed when 1/3 of manganese ions are substituted by nickel, in which all manganese ions act as +4, suggesting the lowered Jahn-Teller distortion and thus induced structural evolutions. The preferable composition of this solid solution is also expected to reduce the disproportionation of Mn3+ ions. Consequently, the stability of the Mn3+/Mn4+ redox couple in the P3-type cathode is significantly improved by building a compositionally graded structure. The graded P3-type electrode shows superior cycling stability with a capacity retention of 72.9% even after 400 cycles at 1C. These findings offer new insight into mitigating the Jahn-Teller effect and thus improving the electrochemical properties of manganese-based cathodes for advanced sodium-ion batteries.