Charge Tuning and Anchor Effect Achieving Stable High-Voltage Layered Metal Oxides for Sodium-Ion Battery

Layered metal oxides (LMOs) that can stably operate at high voltage are vital to developing high-energy sodium-ion batteries (SIBs). However, the irreversible oxygen redox reaction of LMOs at the high voltage region (i.e., >4.0 V vs. Na⁺/Na) will cause serious oxygen evolution and structural instability, and therefore sharp capacity fading. Herein, we report the charge tuning and anchor effect of La doping to enhance the cycling stability of layered NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM) under extreme conditions (e.g., high voltage and temperature). The La doping introduces additional negative charges to the oxygen ligands of transition metals (TM) and facilitates charge transfer, thereby reducing oxygen evolution at 4.1 V and enhancing the kinetics of the redox process. Moreover, the as-formed LaO₆ octahedra serve as stable anchors for the TM layers, preventing the formation of lattice nanocracks. As a result, the La-modified NFM exhibits a high capacity of 173.4 mAh g^-1 at 0.1C (1C = 150 mA g^-1) and capacity retention of 71.21% at 2.0-4.2 V after 500 cycles at 1C, which are higher than those of NFM. Additionally, the full cell achieves a high energy density of 438.78 Wh kg^-1 (based on cathode mass), with a retention of 70.2% over 400 cycles, implying the great application potential of this concept.