Activation of MnO 6 Units via an Interfacial Electric Field: Electron Injection into Mn t 2g for Rapid and Stable Sodium Ion Storage in CeO 2 /MnO x .

Manganese-based oxides (MnO x ) suffer from sluggish charge diffusion kinetics and poor cycling stability in sodium ion storage. Herein, an interfacial electric field (IEF) in CeO 2 /MnO x is constructed to obtain high electronic/ionic conductivity and structural stability of MnO x . The as-designed CeO 2 /MnO x exhibits a remarkable capacity of 397 F g -1 and favorable cyclic stability with 92.13% capacity retention after 10,000 cycles. Soft X-ray absorption spectroscopy and partial density of states results reveal that the electrons are substantially injected into the Mn t 2g orbitals driven by the formed IEF. Correspondingly, the MnO 6 units in MnO x are effectively activated, endowing the CeO 2 /MnO x with fast charge transfer kinetics and high sodium ion storage capacity. Moreover, In situRaman verifies a remarkably increased structural stability of CeO 2 /MnO x , which is attributed to the enhanced Mn─O bond strength and efficiently stabilized MnO 6 units. Mechanism studies show that the downshift of Mn 3d-band center dramatically increases the Mn 3d-O 2p orbitals overlap, thus inhibiting the Jahn-Teller (J-T) distortion of MnO x during sodium ion insertion/extraction. This work develops an advanced strategy to achieve both fast and sustainable sodium ion storage in metal oxides-based energy materials.